DIB Removal Research Articles

Administration of Beta-Nerve Growth Factor during the Preovulatory Stage Improves Endocrine and Luteal Function in Dairy Heifers

The neurotrophin beta-nerve growth factor (NGF), which is present in the semen of different mammals, elicits potent ovulatory and luteotrophic actions in llamas following systemic administration. Here, we determine if purified NGF given intramuscularly (IM) during the preovulatory stage affects the corpus luteum (CL), hormone production, endometrial gene expression, and pregnancy rate of dairy heifers. Holstein-Friesian heifers were estrus-synchronized using estradiol benzoate (EB) plus an intravaginal progesterone (P4) device (DIB). After eight days, the device was removed and cloprostenol was given IM; the next day (day 9), heifers received EB IM plus one of the following: (i) 1 mg of NGF (NGF D9 group), (ii) 1 mg of NGF 32 h after EB (NGF D10 group), or (iii) phosphate buffer saline (control group). To measure pregnancy rates, heifers were treated similarly, then artificially inseminated with sexed semen 48-52 h after DIB removal, then an ultrasound was conducted 30 days after insemination. The females given NGF along with EB (NGF D9) showed significantly higher luteinizing hormone (LH) concentrations, larger CL vascular areas, and higher plasma P4 concentrations than the NGF D10 and control animals. Downregulation of the P4 receptor (PGR), and upregulation of both lipoprotein lipase (LPL) and Solute Carrier Family 6 member 14 (SLC6A14) endometrial genes, were detected in NGF D9 heifers. Furthermore, these heifers had a 10% higher pregnancy rate than the control group. We conclude that the higher P4 output, in response to the early NGF administration, led to the enhanced gene expression of transcripts related to uterine receptivity that may result in enhanced pregnancy rates.

Heterologous beta-nerve growth factor (β-NGF) given at the LH surge enhances luteal function in dairy heifers

Genetic selection for high yield milk production has led to a decline in dairy cattle's reproductive performance over the last 40 years. Low progesterone (P4) plasma content following ovulation is associated with suboptimal fertility in dairy cattle. Several pieces of evidence indicate that the protein beta-nerve growth factor (β-NGF) that is present in the male seminal plasma exerts potent ovulatory and luteotrophic effects following systemic administration in camelids but also in other species. In this study, we determine whether systemic administration of purified llama β-NGF given at the induced preovulatory luteinizing hormone (LH) peak improves corpus luteum (CL) function in dairy heifers subjected to an estradiol (E2) / P4 estrus-synchronization protocol. To achieve this, we first determined plasma E2 and LH hormone profiles to establish the timing of the estradiol benzoate (EB)-induced LH peak in estrus-synchronized heifers. Then, we tested whether the administration of β-NGF given at the end of this peak affects the CL and its function by analyzing diameter, vascular area, and P4 output. Our results show that, with the estrus-synchronization protocol applied, plasma LH concentrations peaked (P < 0.01) 40-h and 16-h after removal of the bovine intravaginal device (DIB; containing 1.0 g of P4) plus cloprostenol injection and subsequent EB administration, respectively; after peaking, plasma LH concentrations remained stable for the next 8-h to then return to basal levels. Heifers synchronized with this protocol and receiving a dose of 1 mg of β-NGF at the end of the LH peak (ie, 48-h after DIB removal) did not show significant differences in CL diameter, but these exhibited a greater CL vascular area (P = 0.01) than the observed in vehicle-injected heifers. Furthermore, plasma P4 concentration in β-NGF-treated heifers was higher (P = 0.001) than those quantified in vehicle-injected heifers. These results support the use of β-NGF in estrus-synchronization protocols to improve the early luteal function in dairy heifers.

Pregnancy rate to FTAI in Braford heifers submitted to J-Synch protocol

The objective of the present work was to evaluate the effect of J-Synch protocol on pregnancy rate (PR) of heifers artificially inseminated after detected estrus (DEAI) or at fixed-time (FTAI). Two hundred ninety-three Braford heifers were used. On day 0, all animals received 2.0 mg of estradiol benzoate administered intramuscularly (IM) and an intravaginal progesterone-releasing device (DIB, 0.5 g). Heifers were assigned to the following group: 1) J-Synch: on day 6, DIB devices were removed and 500 µg of d-Cloprostenol sodium (d-CS) was administered IM and paint was applied on tail base (tail-paint). On day 9 (60 h after DIB removal), heifers with ? 40% of the tail-paint rubbed off were inseminated. Those not showing estrus by 72 h after DIB removal received 100 µg of GnRH at that time and were FTAI. 2) Conventional: on day 7, DIB devices were removed, and 500 µg of d-CS and 0.5 mg of estradiol cypionate were administered IM and tail-paint. Forty-eight hours after DIB removal, heifers with the tail-paint rubbed off were DEAI. Those not showing estrus by 54 h after DIB removal were FTAI. Pregnancy rate was diagnosed by ultrasonography 30 days after FTAI in all heifers and did not differ between protocols (44.28% and 42.48%, P = 0.673). In both protocols, higher PR was observed in DEAI heifers (P = 0.047). In conclusion, the use of the J-Synch protocol generated similar PR to the Conventional protocol, allowing its use with the same efficiency. Furthermore, the DEAI generated better PR than the FTAI, regardless of the protocol used.

7 Pregnancy rates in suckled beef cows synchronized with a shortened progesterone/oestradiol-based protocol (J-synch) and inseminated with conventional or sexed-sorted semen

An experiment was designed to evaluate pregnancy rates (P/AI) in suckled beef cows synchronized with a progesterone (P4)/oestradiol-based protocol (J-Synch) and inseminated (AI) with sexed or nonsexed (conventional) semen. Angus or Angus crossbred cows (n=877), 60 to 90 days postpartum, with a body condition score of 2.5 to 3.5 (scale of 1 to 5) and a corpus luteum or a follicle &amp;gt;8mm in diameter detected by ultrasonography, were randomly allocated to be AI with sexed-sorted or nonsexed (conventional) semen. The experiment was performed in 4 farms, and the sexed-sorted (SexedUltra™ 4M, with 4 million sperm; ST Genetics, Navasota, TX, USA) and conventional (25 million sperm) semen were from split ejaculates from 5 Angus bulls. All cows received a P4 device (DIB 0.5, Zoetis, Villa Adelina, Argentina) and 2mg of oestradiol benzoate (Gonadiol, Zoetis) on Day 0. On Day 6, cows received 400IU of eCG (Novormon 5000, Zoetis) and 500µg of cloprostenol (Ciclase DL, Zoetis) and DIB was removed. All cows were also tail painted and observed for signs of oestrus (i.e. &amp;gt;30% of the tail paint rubbed off) at 60, 72, and 84h after DIB removal. Cows with the tail paint rubbed off by 60 or 72h after DIB removal were artificially inseminated at 72h with either sexed or conventional semen. Those not showing oestrus by 72h received 100µg of gonadorelin acetate (Gonasyn GDR, Zoetis) at that time and were artificially inseminated with either sexed-sorted or conventional semen 12h later (i.e. 84h). Pregnancy was diagnosed by ultrasonography 30 days after AI. Data were analysed by general linear model for binary data with a logit link. Overall, 76.4% (678/877) of cows showed oestrus 60 to 84h after DIB removal, and there were differences in P/AI between sexed-sorted and conventional semen (P&amp;lt;0.01; Table 1); however, there was no farm effect (range: 52-59%) and no interactions. Fertility differed (P&amp;lt;0.05) among bulls and ranged from 25.8 to 55.3% for sexed-sorted semen and from 53.1 to 73.9% for conventional semen. In cows artificially inseminated with sexed-sorted semen, P/AI was the highest in cows showing oestrus and AI at 84 h; however, no differences were detected among cows artificially inseminated with conventional semen (Table 1). Although P/AI was lower for sexed-sorted than conventional semen, tail painting for oestrus detection can be successfully applied to AI beef cows with sexed-sorted semen synchronized with a shortened P4/oestradiol-based protocol. Table 1.Effect of semen type (sexed-sorted or conventional) and time of oestrus and AI on P/AI in suckled beef cows synchronized with a shortened P4/oestradiol-based protocol Research was supported by Fondo Nacional de Ciencia y Tecnología (FONCYT PICT 2017-4550) and UNVM.

7 INFLUENCE OF ESTRUS EXPRESSION AND TREATMENT WITH GnRH ON PREGNANCY RATES IN BEEF CATTLE SYNCHRONIZED WITH PROGESTERONE DEVICES AND ESTRADIOL AND INSEMINATED AT A FIXED-TIME

We have previously shown that expression of oestrus significantly influences the time of ovulation and pregnancy rates to timed-AI (P/TAI) in beef cattle synchronized with progesterone devices and oestradiol (Bó et al. 2016 Theriogenology 86, 388–396). Furthermore, delaying TAI from 48 h to 54–58 h after device removal improved P/TAI of those animals not showing oestrus by 48 h. The objective of the present study was to determine whether the administration of GnRH to those animals not showing oestrus by 48 h after device removal had an impact on P/TAI. Non-lactating and suckled beef cows and heifers (Bonsmara, Brangus, and Braford; n = 868), with a corpus luteum (CL) or a follicle ≥8 mm in diameter detected by ultrasonography (Mindray DP 30 Vet, 7.5 MHz, China) and body condition score 2 to 4 (1 to 5 scale) were synchronized in 3 replicates. On Day 0, animals received a progesterone device (DIB 0.5 g, Zoetis, Argentina) and 2 mg of oestradiol benzoate (Von Franken, Argentina). On Day 8, DIB were removed and cows received 0.150 mg of D+cloprostenol (Río de Janeiro, Argentina) plus 0.5 mg oestradiol cypionate (Cipiosyn, Zoetis). In addition, all cows were tail-painted on the sacrococcygeal area (CeloTest, Biotay, Argentina) at DIB removal and were observed to determine the expression of oestrus, according to the percentage of paint loss (PL) 48 h later. The animals that showed oestrus (PL &gt; 30%) were recorded and TAI at that time while those with PL ≤ 30% (not in oestrus) were randomly allocated to receive 100 μg of gonadorelin (GnRH; Gonasyn, Zoetis) or no treatment and TAI between 54 to 58 h after DIB removal. Pregnancy was diagnosed by ultrasonography at 45 days after TAI, and data were analysed by logistic regression. There were no significant differences among replicates, inseminators, semen source or animal class (dry cows, suckled cows or heifers; P &gt; 0.11). However, animals showing oestrus by 48 h after DIB removal had higher P/TAI (371/666; 55.7; P &lt; 0.04) than those that did not show oestrus (96/202; 47.5%). Within animals not showing oestrus at 48 h, those that were in oestrus by the TAI at 54 to 58 h had higher P/TAI (71/124, 57.3%; P &lt; 0.01) than those that did not show oestrus within that period (27/78; 34.6%). In addition, P/TAI was higher (P &lt; 0.01) in animals that received GnRH (66/113; 58.4%) than in those that did not receive GnRH (30/89; 33.7%). In conclusion, the expression of oestrus significantly affected P/TAI in beef cattle synchronized with progesterone devices and oestradiol. Furthermore, treatment of animals not showing oestrus by 48 h after DIB removal with GnRH resulted in improved P/TAI performed 6 to 10 h later.

103 INFLUENCE OF ESTRUS EXPRESSION AND TREATMENT WITH GONADOTROPIN-RELEASING HORMONE ON PREGNANCY RATES IN RECIPIENTS SYNCHRONIZED WITH PROGESTERONE DEVICES AND ESTRADIOL AND TRANSFERRED AT A FIXED TIME

An experiment was designed to evaluate whether expression of oestrus in recipients synchronized with progesterone devices and oestradiol affects pregnancy rates to a fixed-time embryo transfer (FTET). A secondary objective was to determine whether administration of gonadotropin-releasing hormone (GnRH) to those recipients not showing oestrus by 48 h after device removal had an effect on pregnancy rates. Mature, non-lactating beef recipients (Bonsmara, Brangus, and Braford; n = 729), with a corpus luteum (CL) or a follicle ≥8 mm in diameter detected by ultrasonography (Mindray DP 30, Shenzhen, China) and body condition score 2 to 4 (1 to 5 scale) were synchronized in 7 replicates. On Day 0, recipients received a progesterone device (DIB 0.5 g, Zoetis, Buenos Aires, Argentina) and 2 mg of oestradiol benzoate (Gonadiol, Zoetis). On Day 8, DIB were removed and recipients received 400 IU eCG (Novormon 5000, Zoetis) plus 0.5 mg of oestradiol cypionate (Cipiosyn, Zoetis) and 500 μg of cloprostenol (Cyclase, Zoetis). In addition, all cows were tail-painted on the sacrococcygeal area (CeloTest, Biotay, Buenos Aires, Argentina) at DIB removal and were observed to determine the expression of oestrus, according to the percentage of paint loss 48 h later. The animals that showed oestrus (paint loss &gt;30%) were recorded, and those with paint loss ≤30% (not in oestrus) were randomly allocated to receive 100 μg of gonadorelin (GnRH; Gonasyn, Zoetis) or no treatment. On Day 17, all recipients were examined by ultrasonography and those with a CL ≥18 mm (G1), ≥16 and &lt;18 mm (G2), or ≥14 and &lt;16 mm (G3) in diameter received in vivo-produced frozen-thawed embryos by direct transfer or fresh in vitro-produced embryos. Pregnancy was diagnosed by ultrasonography at 23 days after FTET, and data were analysed by logistic regression. There were no differences between replicates, in vivo- and in vitro-produced embryos, or operators (P &gt; 0.2). However, the proportion of recipients transferred and pregnant (P/FTET) was higher (P &lt; 0.05) for those that showed oestrus at 48 h after DIB removal (422/454, 93.0% and 227/471, 48.2%) than those that did not show oestrus (109/211, 51.7% and 45/120, 37.5%). Within the recipients not showing oestrus, P/FTET was significantly higher (P &lt; 0.05) in those that received GnRH (34/74, 45.9%) than in those that did not receive GnRH (12/46, 26.1%). There was a significant interaction (P &lt; 0.05) between CL diameter and expression of oestrus. When recipients had CL ≥18 mm in diameter (G1), P/FTET did not differ (oestrus: 164/338, 48.5% v. no oestrus 30/65, 46.2%); however, when CL diameter was &lt;18 mm and ≥14 mm (G2 and G3), P/FTET was higher (P &lt; 0.05) in those that showed oestrus (37/85, 43.5%) than in those that did not show oestrus (11/43, 25.6%). Finally, P/FTET was higher (P &lt; 0.05) in recipients with a CL (268/573, 46.8%) on Day 0 than in those with follicles &gt;8 mm in diameter (4/18, 22.2%). In conclusion, the expression of oestrus significantly affected the percentage of recipients selected for embryo transfer and P/FTET. Furthermore, treatment of recipients not showing oestrus by 48 h after DIB removal with GnRH at that time increased P/FTET.

7 PREGNANCY RATES IN BEEF HEIFERS SYNCHRONIZED WITH A SHORTENED OESTRADIOL-BASED TREATMENT THAT PROVIDES FOR A PROLONGED PROESTRUS

An oestradiol-based protocol (named J-Synch) has been developed recently with the aim of providing for a longer proestrus, enhancing the development of the dominant follicle before ovulation, and increasing pregnancy rates following fixed-time AI (FTAI) in heifers (de la Matta and Bo 2012 Taurus 55, 17–23). Two experiments were performed in Uruguay with 1953 Angus × Hereford crossbred heifers to compare pregnancy rates obtained with the J-Synch protocol with the conventional 7-day oestradiol-based protocol. A secondary objective was to determine the effects of the time of FTAI and the addition of eCG at the time progestin device removal on pregnancy rates. In Experiment 1, 966 heifers received a DIB device (0.5 g of progesterone, Syntex, Buenos Aires, Argentina) plus 2 mg of oestradiol benzoate IM (Syntex) on Day 0. Heifers in the conventional treatment group (n = 485) received cloprostenol (500 μg, Ciclase DL, Syntex) and oestradiol cypionate (0.5 mg, Cipiosyn, Syntex) IM and had their DIB removed on Day 7 a.m. Heifers in this group were then subdivided to be FTAI on Day 9 a.m. or p.m. (i.e. 48 or 56 h after DIB removal). Heifers in the J-Synch treatment group (n = 481) received cloprostenol IM and DIB removal on Day 6 p.m. and received gonadotropin-releasing hormone (100 μg gonadorelin acetate, Gonasyn Gdr, Syntex) on Day 9 a.m.; heifers were then FTAI on Day 9 a.m. or p.m. (i.e. 60 or 72 h after DIB removal). All heifers in this experiment were also treated with 300 IU of eCG (Novormon, Syntex) at DIB removal. In Experiment 2, 987 heifers were treated with the J-Synch protocol as described in Experiment 1. At device removal (Day 6 p.m.), heifers were divided to receive (n = 488) or not (n = 499) 300 IU of eCG IM at that time and were further subdivided to receive gonadotropin-releasing hormone and FTAI on Day 9 a.m. or p.m. (i.e. 60 or 72 h after DIB removal). Pregnancy rates were determined by ultrasonography 30 days after FTAI. Data were analysed using logistic regression, and results are shown in Table 1. J-Synch-treated heifers tended (P &lt; 0.1) to have higher pregnancy rates following FTAI, whereas time of FTAI only affected pregnancy rates following the conventional 7-day treatment (P &lt; 0.05). However, removal of eCG from the J-Synch protocol in Experiment 2 resulted in reduced pregnancy rates when inseminations were done on Day 9 p.m. (P &lt; 0.05). In summary, the addition of eCG to the J-Synch protocol provided for a wider window of insemination times facilitating FTAI in large groups of beef heifers. Table 1.Effect of length of progestin insertion, time of insemination and eCG treatment on pregnancy rates in beef heifers

8 COMBINATION OF OESTRUS DETECTION AND FIXED-TIME ARTIFICIAL INSEMINATION IN BEEF HEIFERS FOLLOWING A SHORTENED OESTRADIOL-BASED PROTOCOL THAT PROVIDES FOR A LENGTHENED PROESTRUS

Studies have shown that gonadotropin-releasing hormone-based protocols that reduce the period of progestin insertion and prolong the period from progestin removal to gonadotropin-releasing hormone and fixed-time AI (FTAI; named 5-day Co-Synch) results in similar or higher pregnancy rates than the conventional 7-day Co-Synch protocol in beef cows and heifers (Bridges et al. 2008 Theriogenology 69, 843–851). Similar findings have been reported following the use of an oestradiol-based protocol that also provides for a longer period of proestrus (named J-Synch; de la Mata and Bó 2012 Taurus 55, 17–23). An experiment was designed to compare the J-Synch protocol for synchronization of ovulation that allows for a prolonged proestrus with a conventional 7-day oestradiol-based protocol for FTAI in heifers. Cycling 18-month old Angus and Hereford heifers (n = 208) with a body condition score of 6 to 7 (scale of 1 to 9) were randomly allocated to 1 of 2 treatment groups. Heifers in the 7-day EB group (n = 105) received a progesterone (P4) device (DIB 0.5 g of P4, Syntex SA, Buenos Aires, Argentina) and 2 mg of oestradiol benzoate (EB, Syntex SA) on Day 0 and 500 μg of cloprostenol (PGF; Ciclase DL, Syntex SA) and 0.5 mg oestradiol cypionate (Cipiosyn, Syntex SA) on the day of DIB removal (Day 7). Heifers were also tail painted at the time of DIB removal and observed for signs of oestrus (i.e. tail paint rubbed off). Those with the tail paint rubbed off by 36 h after DIB removal were inseminated 12 h later, whereas those not showing oestrus by 36 h were FTAI at 54 h. Heifers in the J-Synch group (n = 103) received DIB and 2 mg of EB on Day 0 and PGF on the day of DIB removal (Day 6). Heifers in this group were also tail painted at DIB removal, and those with their tail paint rubbed off by 48 h were inseminated 12 h later; those not showing oestrus by 60 h received 100 μg of gonadorelin acetate (gonadotropin-releasing hormone, Gonasyn gdr, Syntex SA) and were FTAI at 72 h after DIB removal. Pregnancy was diagnosed by ultrasonography at 55 days after FTAI (Honda 101V, 5.0-MHz transducer). Data were analysed by logistic regression. Oestrus detection rate and pregnancy rate to FTAI did not differ (P &gt; 0.1) between groups (38.8%, 40/103 and 60.3%, 38/ 63 for heifers in the J-Synch group v. 28.5%, 30/105 and 45.3%, 34/75 for those in the 7-day EB group). However, pregnancy rates to observed oestrus tended (P &lt; 0.09) to be higher and the overall pregnancy rate was significantly higher (P &lt; 0.01) in heifers in the J-Synch group (80.0%, 32/40 and 67.9%, 70 /103) compared with those in 7-day EB group (50%, 15/30 and 46.6%, 49/105). Furthermore, heifers within the J-Synch group that had their tail paint rubbed off by 48 h after DIB removal and were AI 12 h later (i.e. 60 h) had higher (P &lt; 0.05) pregnancy rate than those in the same group that were FTAI. In conclusion, reducing the time of progestin device insertion and lengthening the proestrus period, as in the J-Synch protocol, results in higher pregnancy rates than with the conventional oestradiol-based protocol. Furthermore, the combination of oestrus detection and FTAI would appear to improve the pregnancy outcome even more.

14 IS THE LOW NUMBER OF OVARIAN ANTRAL FOLLICLES ≥3mm IN DIAMETER ASSOCIATED WITH LOW FERTILITY IN LACTATING NELORE COWS?

The follicular growth in cattle occurs in a wave pattern of 2 to 3 waves per oestrous cycle and is characterised by synchronous growth of a cohort of antral follicles, where usually only one of these will become dominant. The amount of recruited follicles per wave is variable between animals and breeds but is highly repeatable among individuals. Some studies report that in Bos indicus the amount of follicles recruited by wave is higher when compared with Bos taurus. The variation in the size of the ovarian follicular population can affect fertility by influencing oocyte competence (Ireland et al. 2007). We aimed to identify Nelore (Bos indicus) cows with high and low numbers of antral follicles recruited by follicular wave and to compare their pregnancy rates. We used 268 multiparous Nelore cows between 40 and 70 days postpartum and body condition score between 3.5 to 4.5 (5-point scale). The cows were sorted in ascending order according to the average number of follicles at all examinations (≥3 mm in diameter). Hence, 33% of animals with the greater follicular population were enrolled in the high population group (HG, n = 89, ≥38 follicles), whereas the intermediate animals (33%) were placed in the intermediate group (IG, n = 88, between 28 and 38 follicles), and animals (33%) with lower follicular population were included in the low population group (LG, n = 91, ≤28 follicles). The animals underwent 3 ultrasound examinations (days D–10, D0, and D28). In D0, at random day of the oestrous cycle, all cows received an intravaginal device containing progesterone (1.0 g, DIB®) and oestradiol benzoate (EB, 2.0 mg, IM, Estrogin®). Eight days later (D8) we administered 75 μg of d-cloprostenol (Croniben®), and the intravaginal device was removed. Twenty-four hours after DIB removal, the cows were treated with EB (1.0 mg, IM), and after 30 to 36 h animals were AI at a fixed time. Data were analysed using PROC GENMOD SAS System 9.1 for Windows (2002–2003). The mean (±SD) of antral follicles in both ovaries was 32.7 ± 17.8. There was no difference (P = 0.144) in pregnancy rates between the HG, LG, and IG animals (32.6, 46.6, and 42.9%, respectively). Thus, we conclude that there was no difference in pregnancy rates between Nelore cows either with high or low population of ovarian antral follicles after AI at a fixed time.Research was supported by grants #2013/02201-3 (VGP), #2011/50259-5 (RLE), #2012/23409-9 (EMR), #2012/50533-2 (MFGN), São Paulo Research Foundation (FAPESP).

8 SYNCHRONIZATION OF OVULATION IN DAIRY HEIFERS USING A SHORTENED ESTRADIOL-BASED PROTOCOL THAT PROVIDES FOR A LENGTHENED PROESTRUS

Several studies, performed mainly in North America, have shown that the 5-day co-synch timed-AI (TAI) protocol results in similar or higher pregnancy rates than conventional 7-day co-synch protocols in beef cows and beef and dairy heifers. It is hypothesised that the 5-day co-synch protocol reduces the incidence of persistent follicles and provides for a longer proestrus, with increasing oestradiol concentrations due to continuous gonadotropin support for the dominant follicle (Bridges et al. 2008 Theriogenology 69, 843–851). Similar findings have been reported recently following the use of a shortened oestradiol-based protocol that also provides for a longer proestrus (named J-synch; de la Matta and Bo 2012 Taurus 55, 17–23). A study was designed to compare these 2 treatment protocols for synchronization of ovulation that allow for a prolonged proestrus with the conventional oestradiol-based protocol currently used for TAI in South America for heifers. Cycling Holstein heifers that were, on average, 17 months of age, weighting 350 to 380 kg, and with a body condition score of 2.5 to 3.5 (scale of 1 to 5), were randomly allocated to 1 of 3 treatment groups. Heifers in the 7-day estradiol benzoate (EB) group received a progesterone device (DIB 1 g of progesterone; Syntex SA, Buenos Aires, Argentina) and 2 mg EB (oestradiol benzoate, Syntex SA) on Day 0, 500 μg of cloprostenol (prostaglandin F2α; Sincronil, Proagro SA, Argentina) and DIB removal on Day 7, 1 mg of EB on Day 8, and TAI 30 h later (54 h after DIB removal). Heifers in the J-synch group received a DIB and 2 mg of EB on Day 0, PGF and DIB removal on Day 6, and 10 μg of buserelin acetate [gonadotropin-releasing hormone (GnRH); Receptal, Intervet, Millsboro, MD, USA] and TAI on Day 8 (72 h later). Heifers in the 5-day co-synch group received a DIB and GnRH on Day 0, DIB removal and prostaglandin F2α (twice, 12 h apart) on Day 5, and GnRH along with TAI on Day 8 (72 h later). Treatments were coordinated so that DIB were removed in all groups at the same time to decrease a possible time effect of follicle parameters and pregnancy rates. Two experiments were conducted; the first evaluated follicular dynamics and ovulation rates by twice daily ultrasonography (Honda 101 V, 5.0 MHz) in 20 heifers per group and the second determined pregnancy rates to TAI in 172 heifers. The mean (± standard error of the mean) interval from DIB removal to ovulation was shorter in the 7-day EB group (82.7 ± 3.1 h) than in the J-synch (103.8 ± 3.3 h) and 5-day co-synch (96.8 ± 3.3 h) groups (P = 0.01). However, the mean diameter of the dominant preovulatory follicle was smaller (P = 0.01) in the 7-day EB (12.8 ± 0.5 mm) and the J-synch (13.1 ± 0.6 mm) groups than in the 5-day co-synch group (14.9 ± 0.6 mm). Although pregnancy rates in the second experiment were numerically lower in the 7-day EB group (31/58; 53.4%) and 5-day co-synch group (30/55; 54.5%) than in the J-synch group (37/59; 62.7%), differences were not significant (P &gt; 0.3). Preliminary results indicate that the 3 protocols evaluated result in comparable pregnancy rates to TAI in dairy heifers.

116 PREGNANCY RATES AFTER ADMINISTRATION OF EQUINE CHORIONIC GONADOTROPIN (eCG) AT PROGESTERONE INTRAVAGINAL DEVICE REMOVAL AND 14 DAYS AFTER FIXED-TIME AI IN BEEF CATTLE

An important proportion of embryonic deaths in cattle occur during the critical period of embryo development and maternal recognition of pregnancy. High serum progesterone concentrations during this period are associated to higher embryo survival, and the use of eCG could enhance luteal activity. Two experiments were carried out to evaluate the effect of administering eCG at the time of removal of a progesterone-releasing device and 14 days after fixed-time artificial insemination (FTAI) in beef cattle. Multiparous suckled cows between 60 and 90 days postpartum (n = 297; Exp. 1), and two-year old prepuberal heifers (n = 689; Exp. 2) with a body condition score (BCS) between 3.5 and 5 (1 to 8 scale) were used. At the beginning of the experiments, none of females used had a corpus luteum detected by ultrasonography. Females received an intravaginal device containing 0.5 g progesterone (DIB 0.5, Syntex, Buenos Aires, Argentina) and 2 mg oestradiol benzoate i.m. (Benzoato de Oestradiol, Syntex). Eight days later, 500 μg of cloprostenol (Ciclase DL, Syntex) and 0.5 mg oestradiol cypionate (Cipiosyn, Syntex) were given i.m. and devices were removed; FTAI was performed 52 to 56 h after DIB removal. At the time of device removal, the animals were randomly allocated to 4 groups, to receive 400 IU of eCG i.m. (Novormon, Syntex) or placebo at device removal and/or 14 days after FTAI, in a 2 × 2 factorial design. Control group did not receive eCG. In Exp. 1, nose plates were placed on calves on the day of DIB insertion and left for 10 days in order to prevent suckling. Pregnancy diagnosis was performed by ultrasonography at 30 and 60 days after FTAI. Data were analysed by logistic regression. Pregnancy rate at 30 days after FTAI was affected by treatment (P &lt; 0.05; Table 1). Late embryonic/fetal loss rates (non-pregnant females at 60 days after FTAI over those pregnant at 30 days) were 1.6% (3/182) for cows in Exp. 1 and 4.8% (14/292) for heifers in Exp. 2; no differences were detected among groups. In conclusion, administration of 400 IU of eCG at device removal increases pregnancy rate, both in anestrus cows and heifers. However, the administration of a second dose of eCG 14 days after FTAI suggests a possible effect on embryo survival within the first 30 days of pregnancy in cows but not in heifers. Further studies are required to confirm these results. Table 1.Pregnancy rates after administration of eCG at time of progesterone device removal and/or 14 days after insemination in beef cattle Supported by Syntex.

20 PREGNANCY RATES IN SUCKLED BEEF COWS SYNCHRONIZED WITH PROGESTERONE INTRAVAGINAL DEVICES AND RECEIVING eCG FOURTEEN DAYS AFTER BREEDING

An experiment was designed to test the following hypotheses: (1) the administration of 400IU of eCG (Novormón, Syntex SA, Buenos Aires, Argentina) 14 days after fixed-time artificial insemination (FTAI) increases pregnancy rates in cross-breed Zebu × Bonsmara suckled cows synchronized with progesterone releasing devices (DIB 0.5, 0.5 g of progesterone, Syntex SA); and (2) pregnancy rates in cows treated with estradiol or GnRH, combined with a DIB device, are not different. Primiparous suckled cows (n = 260), between 60 and 120 days postpartum (DPP) and with a body condition score between 2.0 and 2.5 (1 to 5 scale) were used. At the beginning of the experiment (Day 0), all cows were examined by rectal palpation (only 11% had a CL), received a DIB device, and were randomly allocated to 1 of 3 treatment groups. Cows in the E2 group received 2 mg of estradiol benzoate (EB) intramuscularly (i.m.) at DIB insertion and those in the two GnRH groups received 100 μg of gonadorelin (GDR Gonasyn, Syntex SA) at the same time. On Day 7, DIB devices were removed and all cows received 500 μg of cloprostenol (Ciclase DL, Syntex SA) plus 400 IU of eCG (i.m.). Cows in the E2 group received 0.5 mg of estradiol cypionate (ECP, Cipiosyn, Syntex SA) and underwent FTAI administered by one technician, using semen from 1 of 2 bulls between 52 and 56 h later. Cows in the GnRH groups received a dose of 100 μg of gonadorelin (full GnRH group) or 50 μg of gonadorelin (1/2 GnRH group) at the time of the FTAI (52 to 56 h after DIB removal). Fourteen days after FTAI cows in the 3 groups were further subdivided (3 × 2 factorial) to receive or not 400 IU of eCG i.m. Pregnancy was determined 30 days after FTAI using real-time ultrasonography. Data were analyzed by logistic regression, taking into account the effect of the synchronization treatment, eCG or noteCG, 14 days after FTAI and sire used. No differences in pregnancy rates were found (P = 0.16) among treatment groups (E2: 39/87, 43.7%, full GnRH: 38/92, 41.3%, and 1/2 GnRH: 25/81, 30.9%). However, there was a significant (P = 0.02) effect of eCG treatment 14 days after FTAI (eCG: 60/127, 47.2% v. no eCG: 41/133, 30.8%). Furthermore, bull A (77/155, 47.1%) resulted in higher pregnancy rate (P = 0.009) than bull B (28/107, 26.2%), but there were no significant interactions between bull and synchronization treatment or eCG administration 14 days after FTAI (P &gt; 0.1). We conclude that the application of 400 IU of eCG 14 days after FTAI increases pregnancy rates in suckled Bos taurus × Bos indicus primiparous cows with fair to poor body condition score synchronized with progesterone releasing devices. Furthermore, the use of estradiol ester or GnRH at DIB insertion and removal did not affect pregnancy rates.

39 EFFECT OF TIME OF FIXED-TIME AI ON PREGNANCY RATES IN ZEBU CROSS-BRED BEEF HEIFERS TREATED WITH PROGESTERONE RELEASING DEVICES AND ESTRADIOL CYPIONATE

Two experiments were designed to evaluate the effect of the timing of fixed-time AI (FTAI) in relation to the removal of an intravaginal progesterone-releasing device (1 g of progesterone, DIB, Syntex SA, Buenos Aires, Argentina) on pregnancy rates in Bos indicus × Bos taurus cross-bred heifers. In experiment 1, 285 Bonsmara × zebu cross-bred heifers, between 18 and 24 months of age and with a body condition score (BCS) between 3.0 and 3.5 (1-5 scale) were used. On the day of initiation of treatment (Day 0), the heifers’ ovaries were palpated (92% of them had a CL) and they received a new DIB plus 2 mg of estradiol benzoate (EB; Syntex SA) and 250 μg of cloprostenol (Ciclase DL, Syntex SA). On Day 8, DIB devices were removed and all heifers received 250 μg of Ciclase plus 0.5 mg of estradiol cypionate (ECP; Cipiosyn, Syntex SA). At that time the heifers were randomly divided to receive FTAI between 48 to 49 h, 53 to 54 h, or 58 to 59 h after DIB removal. The heifers underwent FTAI with semen from 4 bulls by 2 inseminators. In experiment 2, 260 heifers from the same group as those used in experiment 1 (87% with a CL) were treated exactly as those in experiment 1, except that previously used DIB was inserted on Day 0. Pregnancy diagnosis was performed 30 days post-fixed-time AI by ultrasonography. The data were analyzed by logistic regression, taking into account the effect of time of FTAI, semen, and inseminator on pregnancy rates. In experiment 1, pregnancy rates were lower (P = 0.04) in the heifers undergoing FTAI between 48 and 49 h after DIB removal (46/95, 48.4%) than those undergoing FTAI 53 to 54 h (61/99, 61.6%) or 58 to 60 h (57/91, 62.6%) after DIB removal. However, no differences in pregnancy rates were found (P = 0.72) in experiment 2 between the 3 treatment groups, with 39/91 (42.9%) for the 48 to 49 h group, 45/89 (50.6%) for the 53 to 54 h group, and 35/89 (43.8%) for the 58 to 59 h group. There was no effect of the semen or inseminator (P &gt; 0.2) in either experiment. We conclude that when Bos indicus × Bos taurus beef heifers are synchronized with new DIB devices and ECP, higher pregnancy rates are obtained in heifers undergoing FTAI late (between 53 to 60 h after DIB removal) than in those undergoing FTAI early (48 to 49 h after DIB removal). However, time of insemination does not apparently affect pregnancy rates when Bos indicus × Bos taurus beef heifers are synchronized with previously used DIB devices and ECP.

145 FACTORS AFFECTING PREGNANCY RATE FOLLOWING TIMED EMBRYO TRANSFER PROGRAM IN CATTLE UNDER FIELD CONDITIONS

Hormonal estrus synchronization followed by heat detection of recipient animals is a widely used technique in embryo transfer (ET) programs around the world. However, the successful outcomes of ET rely heavily on appropriate heat detection of recipient animals. Additionally, limited availability of personnel and time to detect heat makes ET impractical at times. Therefore, pregnancy rates (PR) following a timed embryo transfer (TET) program were evaluated taking into account different variables of recipient cows, donor embryos, and season of transfer under field conditions in Argentina. Recipient cows were synchronized utilizing a progesterone (P4) intravaginal device (DIB, Syntex, Argentina) for 7 days. On Day 0 (day of DIB insertion) 2 mg of estradiol benzoate (EB) i.m. was administered and immediately after DIB removal on Day 7, 500 μg of D(+) Cloprostenol i.m. (PG, Ciclase, Syntex), 400 IU of eCG i.m. (Novormon, Syntex) plus 1 mg of cypionate estradiol i.m. (ECP; König, Agentina) were administered to all recipient cows. Fresh (n = 1746) and frozen (n = 2047) beef bovine embryos were nonsurgically transferred into recipient cows on Day 9 after PG. The effects of body condition score (1–9, BCS I: ≤5, n = 804 and BCS II: ≥6, n = 2989), corpus luteum (CL) score (CL1: prominent papilla, n = 932, CL2: small papilla, n = 2028, and CL3: asymmetric, n = 833), location of embryo placement in uterine horn (upper, n = 3566, and lower, n = 227), and type of recipient such as heifer (n = 487), lactating (n = 1010), or dry cows (n = 2296) on PR were evaluated. Additionally, stage of embryo development (4–7), quality (1–3), and season of transfer (spring, summer, fall, and winter) were included in the analysis. Pregnancy rate was confirmed by rectal palpation 60 days after ET. Data were first screened by chi square and then analyzed by Proc Logistic of SAS (SAS Institute Inc., Cary, NC). Overall PR was 54.7%. body condition score, CL, type of recipients, stage of embryo development, and year were not significantly (P &gt; 0.05) associated with PR. As expected, cows that received direct fresh embryos had 1.49 times greater odds of conceiving (odds ratio, OR = 1.49, 95% CI: 1.22 to 1.82) than those receiving frozen embryos. Additionally, cows receiving embryos graded as quality 1 had greater probability to conceive (OR = 1.62, 95% CI: 1.34 to 1.95, or OR = 1.64, 95% CI: 1.25 to 2.21) compared to quality 2 or 3 respectively. Moreover, embryos placed into the upper portion of uterine horn were more likely (OR = 1.48) to conceive than those placed in the lower uterine portion. Regardless of embryos and recipient cow variables analyzed, there was a greater probability for cows to conceive during winter (OR = 1.41, 95% CI: 1.13 to 1.95) as compared with summer. In conclusion, synchronized recipient animals for a TET program resulted in acceptable PR for both fresh and frozen embryos. Results suggested that the quality and location of embryos (upper portion) in uterine horn were the most important variables associated with PR in recipient cows. Therefore, TET is a viable and practical option allowing a successful outcome for many beef operations where availability of personnel is limited.

Use of different doses of rBST associated to a protocol for multiple ovulation and embryo transfer in buffalo (Bubalus bubalis)

The efficiency of different doses of rBST in a MOET protocol was verified in buffaloes. The animals received an intravaginal progesterone device (DIB) plus 2.0 mg of estradiol benzoate (Ric-BE, i.m.) and 0 mg, 250 mg or 500 mg of rBST. Ovarian follicular growth was stimulated by treatment with 200 mg of FSH in decreasing amount (12/12hs). Buffaloes received injections of PGF2α on D6 and on D7. The DIB was removed on D7. On D8, 24 hours after DIB removal, ovulation was induced with GnRH. The follicular emergence and the response to FSH treatment were evaluated by ultrasound on D4 and D8. The artificial insemination (AI) was performed 12 and 24 hours after the GnRH administration. The embryonic structures were collected 5.5 days after the first AI. Data were analyzed by ANOVA. No statistical differences were found between groups. The results indicated that rBST, associated to a MOET protocol at the different dosages used, does not to improve the efficiency of the technique in buffalo.

22 PREGNANCY RATES IN DAIRY COWS TREATED WITH PROGESTERONE-RELEASING DEVICES AND DIFFERENT GONADOTROPIN-RELEASING HORMONE OR ESTRADIOL PLUS EQUINE CHORIONIC GONADOTROPIN FIXED-TIME ARTIFICIAL INSEMINATION PROTOCOLS

We have previously shown that the addition of eCG improved pregnancy rates following fixed-time artificial insemination (FTAI) in lactating dairy cows treated with estradiol benzoate (EB) and progesterone releasing devices (Veneranda et al. 2006 Reprod. Fertil. Dev. 18, 118). An experiment was designed to compare pregnancy rates in lactating dairy cows treated with progesterone-releasing devices and EB plus eCG with different gonadotropin-releasing hormone (GnRH)-based protocols. Five-hundred lactating dairy cows between 30 and 51 days postpartum (when prostaglandin F (PGF) treatments were given in the Pre-Synch groups), with a milk yield of 29.5 � 7.0 kg per day (range 13.0 to 46.0 kg) and a body condition score (BCS) between 2.5 to 3.5 out of 5 were used. Cows were blocked by days postpartum and randomly assigned to five treatment groups. Cows in the Pre-Synch group received PGF 28 and 14 days prior to the insertion of a DIB device (1 g progesterone, Syntex SA, Buenos Aires, Argentina) and the administration of 50 µg of Lecirelin (GnRH, Ovusin, Syntex SA) IM (Day 0). On Day 7, DIB were removed and cows received PGF (0.5 mg cloprostenol, Ciclase, Syntex SA). On Day 9, cows received a second GnRH treatment and were FTAI 16 h later (60 h after device removal). Cows in the Modified Pre-Synch group were treated similarly except that they received a DIB for 7 days prior to the second PGF injection and no DIB at the time of the first GnRH. Cows in the P4-Synch group were treated as those in the Pre-synch group but did not receive the two doses of PGF 28 and 14 days earlier. Cows in the P4 + EB + eCG groups received a DIB for 8 days, 2 mg of EB at DIB insertion (Day 0), and PGF and 400 IU eCG (Novormon, Syntex SA) IM at DIB removal (Day 8); they were subdivided to receive 1 mg of EB on Day 9 (P4 + EB + eCG + EB group) or GnRH on Day 10 (P4 + EB + eCG + GnRH group). Cows in these latter two groups were also FTAI 60 h after device removal. Pregnancy was determined by rectal palpation 50 days after FTAI and data were analyzed by logistic regression. Pregnancy rates were not affected by BCS, days postpartum, or milk yield (P &gt; 0.5). However, there was a significant group effect due to a higher (P &lt; 0.05) pregnancy rate in the P4 + EB + eCG + EB (49%) and P4 + EB + eCG + GnRH (44%) treatment groups than in those in the Modified Pre-Synch group (30%). Pregnancy rate in the P4-Synch group (39%) was lower (P &lt; 0.05) than those in the P4 + EB + eCG + EB group but not different from the others. Finally, pregnancy rate in Pre-Synch group (41%) was intermediate and not different from the other treatment groups. Results of these experiments suggest that treatments with progesterone-releasing devices, EB, and eCG result in pregnancy rates that are comparable to or better than those obtained in GnRH-based protocols in lactating dairy cows. Further studies are needed to investigate whether eCG could increase pregnancy rates in cows treated with GnRH and progesterone-releasing devices. The authors thank Syntex SA for providing the hormones used in the study.

383 EFFECT OF TIME OF OVULATION INDUCTION BY GONADOTROPIN-RELEASING HORMONE OR PITUITARY LUTEINIZING HORMONE ON OVA/EMBRYO PRODUCTION IN SUPERSTIMULATED BEEF COWS INSEMINATED AT A FIXED TIME

It has been shown than it is possible to AI embryo donors at a fixed time (FTAI) by removing the progestin-releasing device at the time of the last FSH treatment and inducing ovulation with gonadotropin-releasing hormone (GnRH) or porcine luteinizing hormone (pLH) at either 12 h (dairy cows: Bos indicus) or 24 h (beef cows: Bos taurus) after device removal (Bo et al. 2006 Theriogenology 65, 89–101). An experiment was designed to determine the best interval from device removal to GnRH or pLH treatment in Angus (beef cow) donors. Red Angus donors (43 cows and 56 heifers) were blocked by parity and randomly assigned to 1 of 4 treatment groups in a 2 × 2 factorial design. On Day 0, all donors received a DIB vaginal device (Syntex, Buenos Aires, Argentina) plus 2.5 mg estradiol-17β and 50 mg progesterone (P4; Laboratorio Rio de Janeiro, Argentina) IM. Superstimulatory treatments were initiated on Day 4, with a total dose of 320 mg (cows) or 200 mg (heifers) NIH-FSH-P1 of Folltropin-V (Bioniche Animal Health Inc., Belleville, Ontario, Canada) in twice daily IM injections over 4 days. All cows received prostaglandin-F treatment (150 µg d-cloprostenol; Bioprost; Biotay, Buenos Aires, Argentina) on Day 6 (AM and PM); DIB devices were removed with the last Folltropin-V treatment on Day 7 PM. Donors received 0.050 mg GnRH (Lecirelina; Gonasyn; Syntex, Buenos Aires, Argentina) or 25 mg Armour pLH (Lutropin-V; Bioniche) 12 h (Day 8 AM) or 24 h (Day 8 PM) later and were FTAI 12 and 24 h after GnRH or pLH. Ova/embryos were collected nonsurgically and classified according to IETS recommendations on Day 15 AM for donors receiving GnRH or pLH on Day 8 AM and on Day 15 PM for those receiving GnRH or pLH on Day 8 PM. Data were analyzed by two-way ANOVA. Although there was no effect of induction agent (GnRH vs. pLH; P &amp;gt; 0.2) and/or interaction between the induction agent and the time of treatment (P &amp;gt; 0.13) on ova/embryo production, treatment with GnRH or pLH on Day 8 AM (i.e. 12 h after DIB removal) resulted in a significantly lower (P &amp;lt; 0.05) number of fertilized ova and Grades 1 and 2 embryos than treatment on Day 8 PM (i.e. 24 h after DIB removal; Table 1). It was concluded that GnRH and pLH were equally efficacious for inducing ovulation in superstimulated donors that were fixed-time AI. Furthermore, a 24-h interval from progestin device removal to GnRH or pLH administration was preferable for Bos taurus beef donors. Table 1. Ova/embryo production in Angus donors treated with GnRH or pLH 12 or 24 h after removal of a progestin-releasing device and FTAI 12 and 24 h later

214 EFFECT OF TIMING OF PGF, eCG, AND ESTRADIOL BENZOATE IN RECIPIENTS SYNCHRONIZED WITH A PROGESTIN-BASED PROTOCOL FOR FIXED-TIME EMBRYO TRANSFER

An experiment was designed to evaluate alternative treatment protocols for fixed-time embryo transfer (FTET) in recipients in order to reduce cattle handling. Non-lactating, cycling Bos taurus � Bos indicus beef cows (n = 918), with a body condition score (BCS) of 2.5 to 3.5 out of 5, received a progesterone-releasing device (DIB; Syntex, Buenos Aires, Argentina) and 2 mg estradiol benzoate (EB; Syntex) IM on random days of the cycle (Day 0); DIB were removed on Day 8. Cows were placed randomly into 6 treatment groups in a 3 � 2 factorial design. The factors evaluated were time of administration of PGF and eCG [control treatment: PGF Day 5 and eCG Day 5 (Bo et al. 2002 Theriogenology 57, 53–72); PGF Days 0 and 8 and eCG Day 5; PGF Days 0 and 8 and eCG Day 8] and the time of administration of the second injection of EB (at DIB removal or 24 h later). Therefore, cows in the control treatment received 150 �g of d-Cloprostenol (PGF, Ciclase; Syntex) and 400 IU eCG (Novormon; Syntex) on Day 5, whereas cows in the other 2 treatments received 75 �g of PGF on Days 0 and 8 and 400 IU eCG on either Day 5 or Day 8. Each treatment group was further subdivided to receive 1 mg EB IM on either Day 8 (EB Day 8) or Day 9 (EB Day 9). All recipients, whether observed in estrus or not and with more than one CL with luteal area (total CL area minus cavity area) &amp;gt;76 mm2 on the day before embryo transfer, received frozen-thawed embryos (IETS Grade 1) on Day 16 (EB Day 8) or Day 17 (EB Day 9) by direct transfer. Pregnancy was determined by ultrasonography 30 days after FTET. Continuous data were analyzed by ANOVA and pregnancy rates were analyzed by logistic regression. No effects of body condition score or technician were detected (P &amp;gt; 0.1). Although there were no differences in conception rates between recipients treated with EB on Day 8 or Day 9 (168/321, 52.3% vs. 203/350, 58.0%, respectively; P &amp;gt; 0.1), treatment with EB on Day 8 resulted in fewer recipients selected/treated (321/460, 69.7% vs. 350/458, 76.4%; P &amp;lt; 0.05) and pregnant/treated (168/460, 36.5% vs. 203/458, 44.3%; P &amp;lt; 0.05) than 24 h later (EB Day 9), respectively. The mean interval from DIB removal to estrus was shorter (P &amp;lt; 0.05) for recipients in the EB Day 8 (28.1 � 7.2 h) than in the EB Day 9 (43.5 � 9.4 h) group, and the mean (� SEM) CL area was also less in the EB Day 8 group than in the EB Day 9 group (261.7 � 96.7 vs. 293.1 � 114. mm2; P &amp;lt; 0.05). The number of recipients selected/treated was higher in the group receiving PGF on Days 0 and 8 and eCG on Day 8 (243/305, 79.6%) than in the group receiving PGF on Days 0 and 8 and eCG on Day 5 (208/301, 69.1%) or the control group (220/312, 70.5%). Although the luteal area was greater (P &amp;lt; 0.05) in the PGF on Days 0 and 8 and eCG on Day 5 group (304.4 � 127.1 mm2) than in the groups receiving PGF and eCG on Day 5 (274.6 � 98.6 mm2) or PGF on Days 0 and 8 and eCG Day 8 (258.4 � 90.2 mm2), pregnancy rates did not differ between PGF and eCG treatment groups (P &amp;gt; 0.05). It was concluded that it may be possible to reduce animal handling by treating recipients with a half dose of PGF at the time of DIB insertion and removal, when eCG is also administered, without compromising pregnancy rates.

12 THE EFFECT OF PROGESTERONE CONTENT IN A VAGINAL INSERT ON PREGNANCY RATES IN BEEF AND DAIRY CATTLE INSEMINATED AT FIXED TIME

Three experiments were conducted to compare pregnancy rates in cows and heifers treated with intravaginal progesterone (P4)-releasing devices impregnated with either 0.5 or 1.0 g of P4 and inseminated at a fixed time (FTAI). In Experiment 1, 102 postpartum beef cows (Hereford and Angus crossbred with Tuli, 60 to 90 d postpartum) with a body condition score (BCS) of 2.5 to 3.0 (1 to 5 scale) were used. On Day 0, all cows received 2 mg of estradiol benzoate (EB; Syntex, Argentina) i.m. and were randomly assigned to receive an intravaginal progesterone-releasing device with 0.5 g of P4 (DIB 0.5 g; Syntex) or 1.0 g of P4 (DIB 1.0 g; Syntex). On Day 7, DIB devices were removed and all cows received 150 µg D(+)cloprostenol (Ciclase; Syntex) i.m. On Day 8, all cows received 1 mg EB and were FTAI 52 to 56 h after DIB removal. In Experiment 2, 93 Holstein cows that were 90 to 110 days in milk (DIM), producing on average 5000 kg of milk per lactation and with a BCS of 2.5 to 3.0 received the same treatments as those in Experiment 1. In Experiment 3, 100 Holstein heifers, 20 to 22 months old, with a BCS of 2.5 to 3.0, also received the same treatments as those in Experiment 1. Pregnancy rates in all experiments were determined by ultrasonography 35 days after FTAI and compared by chi-square test. No differences in pregnancy rates were detected between lactating beef cows, dairy cows, or dairy heifers treated with DIB devices impregnated with 0.5 or 1.0 g of P4 (Table 1). It was concluded that vaginal P4 releasing devices impregnated with 0.5 g or 1.0 g of P4 results in comparable pregnancy rates in FTAI protocols in beef and dairy cattle. Table 1. Pregnancy rates in postpartum beef cows, Holstein cows, and Holstein heifers treated with DIB devices impregnated with 0.5 or 1.0 g of P4 and subjected to FTAI

362 EFFECT OF TIME OF REMOVAL OF A PROGESTERONE RELEASING DEVICE AND GnRH TREATMENT ON THE INTERVAL TO AND DISTRIBUTION OF OVULATIONS IN SUPERSTIMULATED BEEF COWS

An experiment was designed to evaluate the effect of the time of removal of an intravaginal progesterone (P4) releasing device and GnRH treatment on the interval to and the distribution of ovulations in beef cows superstimulated with Folltropin-V (Bioniche Animal Health, Belleville, Ontario, Canada). Red Angus donors (22 cows and 12 heifers) with a body condition score between 2.5 to 3.5 out of 5 were blocked by parity and randomly assigned to one of four treatment groups in a 2 × 2 factorial design. On Day 0, all donors received an i.m. DIB vaginal device (Syntex, Argentina) plus 2.5 mg estradiol-17β and 50 mg P4 (Laboritorio Rio de Janeiro, Argentina). Superstimulatory treatments were initiated on Day 4, with a total dose of 320 mg (cows) or 200 mg (heifers) NIH-FSH-P1 (Folltropin-V; Bioniche Animal Health, Inc., Belleville, Ontario, Canada) in twice daily i.m. injections over 4 days. All cows received PGF treatment (150 μD(+)cloprostenol: Ciclase; Syntex) in the morning and afternoon of Day 6 and were randomly divided to have DIB devices removed at the time of the second PGF treatment (Day 6.5) or 12 h later (Day 7). On Day 8, donors were further subdivided to receive GnRH (0.050 mg Lecirelina, Gonasyn; Syntex) or no further treatment, and all cows were fixed-time AI either 60 and 72 h after the first PGF injection (0 h). All cows and heifers were examined by ultrasonography every 8 h for a period of 120 h commencing at the time of DIB removal, to determine the time and distribution of ovulations. For each cow, mean time of ovulation was used for the statistical analysis. The distributions of ovulations were compared among groups by Levene's test, and then by ANOVA (equal variances) or Friedman two-way non-parametric ANOVA (unequal variances). No significant differences were detected between cows and heifers (P &gt; 0.13) for the parameters evaluated, and data were combined. There was no effect (P &gt; 0.22) of treatment on the number of ovulations (GnRH: 12.6 ± 1.6 vs. no GnRH: 15.1 ± 1.1 and Day 6.5: 13.7 ± 1.3 vs. Day 7: 14.3 ± 1.5), or numbers of transferable embryos (GnRH: 5.1 ± 1.1 vs. no GnRH: 3.1 ± 0.8 and Day 6.5: 3.5 ± 0.8 vs. Day 7: 4.81 ± 0.1). However, there was a significant effect of GnRH treatment and a GnRH-by-time-of-DIB-removal interaction on the distribution of ovulations (P &lt; 0.05; Table 1). The administration of GnRH in a superstimulatory protocol using P4 releasing devices results in earlier and more synchronous ovulations than when GnRH is not used. Table 1. Distribution of ovulations (hours after the first PGF) in superstimulated Red Angus donors treated with progesterone-releasing devices (DIB) for 6.5 or 7 days with and without GnRH treatment on Day 8