Percentage Of Heifers Research Articles

Optimizing ReBreed21 I: Evaluation of endocrine and ovarian dynamics in non-bred Bos indicus heifers

The present study evaluated follicular and endocrine dynamics during ReBreed21, a reproductive strategy that allows resynchronization of ovulation every 21 days in Bos indicus (Nelore) heifers. A synchronized estrous cycle was induced using a standard timed ovulation protocol (d −10: P4 implant inserted + 2 mg estradiol benzoate; d −2: P4 removed+ 0.5 mg cloprostenol + 0.6 mg estradiol cypionate + 200 IU equine chorionic gonadotropin (eCG); d0: 8.4 μg buserelin) without AI to ensure nonpregnancy in heifers. Day of GnRH was designated d0 of estrous cycle. On d12, heifers (n = 80) were randomized into three experimental groups: (1) ReBreed21 (n = 28) d12 P4 device inserted, d19 P4 device withdrawal plus 200 IU eCG, and d21 8.4 μg buserelin (GnRH); (2) ReBreed21+G (n = 26) same as ReBreed21 plus GnRH (16.8 μg) treatment on d12; and (3) Control (n = 26) no treatment. ReBreed21+G increased two-fold (62.9%; 18/26) percentage of heifers with synchronized follicular wave emergence compared to Control (34.6%; 9/26) whereas ReBreed21 (53.6%; 15/28) was intermediate. The ReBreeed21 groups (eCG on d19) increased (P < 0.01) follicular growth between d19 and d21 in ReBreed21 (2.3 ± 0.2 mm) and ReBreed21+G (3.4 ± 0.2 mm) compared with Control (1.2 ± 0.3 mm), resulting in greater (P < 0.01) follicle diameter on d21 for ReBreed21 (10.7 ± 0.4 mm) and ReBreed21+G (10.8 ± 0.4 mm) compared with Control (9.1 ± 0.5 mm). Structural luteolysis was similar among groups (P = 0.51), although the average day when P4 was <1 ng/mL was later (P < 0.01) for ReBreed21 (20.5 ± 0.2) and ReBreed21+G (20.7 ± 0.2) compared to Control (19.2 ± 0.4). Overall ovulation at the end of the estrous cycle was increased (P = 0.03) for ReBreed21 groups (83.3%; 45/54) compared with Control (57.7%; 15/26). Synchronized ovulation on day 22–23 was greater (P < 0.01) for ReBreed21 (78.6%; 22/28) and ReBreed21+G (76.9%; 20/26) compared with Control (30.8%; 8/26). Thus, the ReBreed21 resynchronization program produced acceptable endocrine and follicular dynamics, including synchronized ovulation at the end of the protocol in nonpregnant heifers providing good rationale for testing the fertility and practical implementation of this protocol under field conditions.

Influência da estação de nascimento de bezerras girolando no desenvolvimento na fase de cria e desempenho reprodutivo e produtivo

Abstract Raising heifers is one of the most important activities in dairy farming because heifers eventually replace the herd. This study was performed to evaluate how the calf’s birth season affects its early development and its reproductive and productive performance. The experiment was conducted at the Glória Experimental Farm of the Federal University of Uberlândia, Minas Gerais, Brazil. In total, 74 female calves born from January 2018 to March 2020 were evaluated from the first day of life to the end of their first lactation. The animals were classified according to their season of birth: spring/summer (October–March) or fall/winter (April–September). During the initial phase of life, the animals’ weights were assessed on days 0, 30, and 60 after birth and at weaning. The rectal temperature, fecal score, feed intake, and animal behavior were recorded daily. In the mature phase of life, the dates of conception and calving were evaluated, and milk production during the first lactation was monitored. The following variables were analyzed according to season of birth: weight gain and occurrence of diseases during the initial phase, percentage of heifers that calved, age at first calving, and average milk production during the first lactation. Continuous variables were analyzed by analysis of variance, and binomial variables were analyzed by logistic regression using the Minitab software program. Calves born in fall/winter had a higher weight at 30 days; however, this difference was compensated for during the initial phase and did not interfere with reproductive and productive performance.

Effect of Ovarian Status on Reproductive Performance in Dairy Heifers Inseminated with Sexed Semen

Background: The intensive reproductive management in the dairy farms requires inclusion of a large group of replacement heifers in the breeding program for a shorter period. In this aspect, a creation of effective estrus synchronization protocols with timed artificial insemination (TAI) by sexed semen and optimization of the current ones have a crucial role for obtaining high pregnancy rate. These protocols are beneficial, because they led to reduced interval to first AI, lack of need for estrus detection, and allow obtaining a large group of female calves for on time. Because of limited fertilizing potential of sexed spermatozoa this type of semen is applied mainly for heifers, as fertility is higher compared to lactating cows. The main objective of the present study was to investigate the effect of ovarian status on the reproductive performance in dairy heifers subjected to estrus synchronization and timed artificial insemination with sexed semen. Materials, Methods &amp; Results: Forty-eight Holstein healthy heifers separated in 2 groups were subjected to PGF2α-GnRH pre-treatment and Ovsynch or PRID-5-day estrus synchronization protocol and timed artificial insemination (TAI) with sex-sorted semen, staring 6 days after end of the hormonal pre-treatment. The ovarian status (presence of follicles with or not a corpus luteum) of the heifers at the begin of the treatment, on day of TAI and pregnancy rate in different groups were determined and compared. Additionally, the ovarian status at the begin of the treatment, ovarian status and size of preovulatory follicle (PF) on day of TAI and total values for both groups according to reproductive performance (pregnant or non-pregnant) were also analyzed. On day of TAI the animals with PF and a lack of corpus luteum (CL) in both groups were more that those with PF and CL (39.3% and 30% vs. 60.7 % and 70%), with significant (P &lt; 0.05) difference in PRID-5-day group. The pregnancy rate tended to be higher in PRID-5 day than Ovsynch treatment (65% vs. 35.7%). A higher percentage (100% and 67.9%) of the pregnant animals in both treatments had not CL on day of TAI, and the size of the PF (1.58 ± 0.12 cm and 1.64 ± 0.13 cm) was increased (P &lt; 0.05). Similar effects of the ovarian status on reproductive performance were obtained after a comparison of the total values between pregnant and non-pregnant animals. The percentage of heifers with observed PF without CL on day of TAI was significantly greater (P &lt; 0.05) in pregnant compared to non-pregnant group (91.3% vs. 40%). The opposite dependence was determined for the parameter presence of follicles and corpus luteum (8.7% vs. 60%; P &lt; 0.05). Furthermore, the size of the PF measured immediately before TAI was increased in animals became pregnant (1.60 ± 0.12 cm vs. 1.34 ± 0.17 cm; P &lt; 0.05). Discussion: The analysis of the obtained results showed that the ovarian status on day of TAI affects the reproductive performance in dairy heifers subjected to estrus synchronization and timed artificial insemination with sexed semen. Hormonal pre-treatment with onset of PRID-5-day protocol 6 days later and TAI with sex-sorted semen ensure acceptable pregnancy rate. The greater preovulatory follicle and a lack of corpus luteum before insemination provide significantly (P &lt; 0.05) more pregnant animals, compared to the cases when CL is presented. Ultrasound determination of the ovarian function before insemination can be used in selection of heifers for TAI with sex-sorted semen. Keywords: heifers; estrus synchronization; sexed semen, pregnancy.

233 Estrus Response and Pregnancy Rates of Beef Replacement Heifers Enrolled in Two Fixed-time Artificial Insemination Protocols, with or Without Pre-synchronization

Abstract Pre-synchronization strategies with prolonged exposure to exogenous progesterone have the potential to alter estrus expression and improve fertility in replacement beef heifers. The objective of this study was to evaluate the estrus response and pregnancy rate of beef heifers enrolled in two fixed-time artificial insemination (TAI) protocols. A total of 306 heifers (14 ± 2 months of age; 372 ± 24 kg body weight [BW]) at three locations were enrolled in the study. Within location, heifers were stratified by age and BW and randomly assigned to one of two treatments: 1) PG-CIDR54 (n = 152), heifers were administered prostaglandin F2α (PGF; 25 mg) and a controlled internal drug releasing (CIDR) insert (Day -14), an injection of GnRH [100 μg (Day -7)], PGF injection and CIDR removal (Day 0), and a second injection of GnRH concurrently with TAI 54 ± 2 h later (Day 2); 2) 7-day CO-Synch+CIDR (CTRL; n = 154), heifers were administered GnRH (100 μg) and a CIDR insert (Day -7), PGF (25 mg) injection and CIDR removal (Day 0), and a second injection of GnRH concurrently with TAI 54 ± 2 h later (Day 2). All heifers received an estrus alert patch on Day 0 and were evaluated for patch activation at TAI on Day 2. Pregnancy was diagnosed by transrectal ultrasonography between 35 and 55 days after TAI. The percentage of heifers exhibiting estrus between Day 0 and 2 was greater (P &amp;lt; 0.01) in PG-CIDR54 compared with CTRL (77.0 and 39.6%, respectively). In addition, pregnancy rate to TAI tended (P = 0.08) to be greater for PG-CIDR54 compared with CTRL (48.0 and 38.3%, respectively). We conclude that beef heifers enrolled in the PG-CIDR54 protocol had increased estrus expression and tended to have greater pregnancy rate when compared with heifers enrolled in the 7-day CO-Synch+CIDR protocol.

Effect of PGF2α treatments during early corpus luteum development on circulating progesterone concentrations and ovulation in breeding-age Holstein heifers

The objective of this study was to test the effect of low circulating concentrations of progesterone (P4) on pre-ovulatory follicle development in heifers as part of an overarching objective to develop a model to understand this phenomenon in dairy cattle without the confounding factors of lactation. Holstein heifers between 12 and 13 mo of age were pre-synchronized to ensure all heifers were on d 6 of the estrous cycle at the start of the Ovsynch program. Only heifers with CL regression and ovulation to the following pre-treatment strategy were used in the study: 0.5 mg cloprostenol (PGF2α), 2 d later, 0.1 mg GnRH, 6 d later, GnRH (G1; 1st GnRH of Ovsynch). Heifers (n = 159) responding to pre-treatment were randomly assigned to 4 groups and completed the Ovsynch program: high P4 control (HPC), low P4 control (LPC; PGF2α 24 h after G1), PG2 (PGF2α 24 and 48 h after G1) and PG3 (PGF2α 24, 48, and 96 h after G1). Only heifers that had ovulation to G1 remained in the study. Blood samples were collected in all heifers on d 7 (n = 157) and in a subset of heifers on d 1, 2, 3, 4 (n = 82) after G1 to measure serum P4. Pre-ovulatory follicle size at G1 (13.0 ± 0.1 mm; P = 0.53) and mean serum P4 24 h after G1 (d 1; 3.62 ± 0.11 ng/mL; P = 0.46) did not differ among treatments. HPC heifers had greater (P < 0.001) mean serum P4 compared to LPC, PG2 and PG3 on d 2, 3, 4, and 7. On d 2, 3 and 4, mean serum P4 of LPC, PG2 and PG3 heifers did not differ (P > 0.10). On d 7, LPC heifers had greater (P < 0.001) serum P4 compared to PG2 and PG3 heifers. Mean ± SEM serum P4 on d 7 after G1 was 8.43 ± 0.39, 2.55 ± 0.36, 1.58 ± 0.20, and 1.21 ± 0.15 ng/mL for HPC, LPC, PG2, and PG3, respectively. Percentage of heifers with P4 < 0.50 ng/mL on d 7 was greater (P < 0.05) for LPC, PG2 and PG3 (27, 32 and 26%, respectively) compared to HPC (0%). A greater (P < 0.05) proportion of heifers ovulated before G2 in the LPC, PG2 and PG3 than in the HPC. For heifers that ovulated after G2, low serum concentrations of P4 in LPC, PG2 and PG3 induced double ovulations in 6/97 heifers after the final GnRH of Ovsynch compared to 0/33 in HPC. In summary, PGF2α treatments during early CL development reduced circulating P4 concentrations 7 d after G1 compared with both HPC and LPC. However, it did not effectively control CL and follicle function to be utilized as a model to test high vs. low serum P4 on fertility parameters in Holstein heifers.

Evaluation of the herd reproduction program with sexed seed in a large agricultural enterprise

For diary herding, milk production is one of the determining factors of effective actions. That is why it’s very important to get a high percentage of heifers into a processing of herd reproducing, which became possible after introduction of sexed seed – sperm, which cells are divided concerning the sex. Using of sexed seed allows us to repair the herd more quickly, and also to increase the realization volume of heifers by breed enterprises, which very good influence on their profitability. Provided of researching analyses showed us, that using the seed divided by sex into a large agricultural enterprise, the fertility rate is lower on 5-8%, than we will use the traditional seed, and female calves are much higher.

PSIV-10 Effects of stair-step vs. constant supplementation amount on growth, reproduction, and intravaginal temperature in Bos indicus-influenced beef heifers

Abstract This study investigated growth and reproductive performance of Bos indicus-influenced beef heifers provided a concentrate supplement at either a constant or stair-step supplementation. Sixty-four Brangus heifers were stratified by initial BW and age (255 ± 20 kg; 270 ± 22 d) and assigned to 1 of 16 bahiagrass pastures (4 heifers/pasture). Treatments were randomly assigned to pastures (8 pastures/treatment) and consisted of concentrate DM supplementation at: (1) 1.50% of BW from d 0 to 100 (CON) and (2) 1.05% of BW from d 0 to 49 and 1.95% of BW from d 50 to 100 (STP). Supplementation started on d 0 and continued until start of estrous synchronization on d 100. Intravaginal temperatures (16 heifers/treatment) were collected every 30 minutes from d 25 to 31 (September) and d 85 to 91 (November). All heifers were provided supplement at 1.50% of BW from d 101 to 211. Heifers were bred by AI from d 113 to 115 and Brangus bulls were placed with heifers from d 121 to 211. Data were analyzed using the MIXED procedure of SAS with treatment, time, and interaction as fixed effects. From d 0 to 49, ADG did not differ (P = 0.87); however, STP heifers had greater (P = 0.01; 0.73 vs. 0.56 kg/d) ADG from d 50 to 100 compared to CON heifers. Percentage of pubertal heifers, percentage of heifers in estrus, or reproductive tract scores did not differ between treatments (P ≥ 0.40). Intravaginal temperatures were greater (P &amp;lt; 0.0001) for CON vs. STP heifers from d 25 to 31 but did not differ (P = 0.74) from d 85 to 91. Using a stair-step vs. constant supplementation amount (1.05 to 1.95% vs. 1.50% of BW) before the breeding season reduced intravaginal temperatures and increased overall ADG in Bos indicus-influenced beef heifers.

PSIV-12 Evaluation of reproductive performance and herd longevity when heifers grazing native range are vaccinated with a lifetime regimen of a killed viral or modified live viral vaccine

Abstract Fifty-eight Angus × Hereford cross heifers born in the spring of 2015 were randomly assigned to treatments of receiving a modified-live viral (MLV) or killed viral (KV) vaccination against bovine viral diarrhea virus (BVDV) at 60-d of age to determine the effects of vaccination on fertility and herd longevity. Heifers received vaccine treatments again at weaning (205d) at re-vaccination, and a yearly booster for the duration of their time in the herd. Blood samples were collected every two weeks prior to breeding to assess puberty attainment and were subsequently subjected to ovarian ultrasonography to measure antral follicle counts (AFC) and reproductive tract score (RTS). Heifers were synchronized utilizing the 7-d CIDR-PG protocol with AI following estrus detection. Heifer AFC, uterine horn diameter, RTS, and proportion of females attaining puberty before the breeding season were similar among treatments (P ≥ 0.38). Artificial insemination pregnancy rates, final pregnancy rates, and percentage of heifers that calved in the first 21 days were similar between vaccination treatment groups (P ≥ 0.19). Body condition score through the third parity at calving and weaning were not different between vaccination types (P ≥ 0.59). Females receiving a MLV vaccination remain in the herd in a similar proportion to those receiving a KV vaccination (P = 0.86). These results indicate that different vaccination strategies can be successfully used in beef cattle grazing native range without impacting fertility, or herd longevity.

Presynchronization with CIDR, with or without GnRH, prior to CO-Synch in beef heifers

Objectives were to compare ovarian responses and pregnancy per AI (P/AI) in Angus-cross beef heifers (n = 521; 4 locations) synchronized with CIDR–CO–Synch (CCOS) versus CIDR-GnRH–CO–Synch (CGCOS) protocols. Heifers were assigned a reproductive tract score (RTS: 1, immature, acyclic; 5, mature, cyclic), body condition score (BCS: 1, emaciated; 9, obese) and temperament score (0, calm, 1, excitable). Heifers in the CCOS (n = 261) group received a CIDR on Day −20 (removed on Day −13), 100 μg GnRH on Day −10, 25 mg PGF2α on Day −3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Heifers in the CGCOS (n = 260) group received a CIDR on Day −26 (removed on Day −19), 100 μg of GnRH on days −16 and −10, 25 mg of PGF2α on Day −3 and were timed inseminated 60 h later, with concomitant GnRH (Day 0). Ovarian ultrasonography was done in a subset of heifers (n = 60; 30 in each group) to determine number and size of ovarian follicles and presence of corpus luteum (CL). There was increased (P < 0.05) percentage of heifers with CL in CGCOS group compared to heifers in CCOS group on Day −10 (82.3 vs 68.2%) and on Day −3 (88.3 vs 75.1%). Average size of the largest ovarian follicle on Day 0 was greater for heifers in CGCOS group compared to CCOS group (P < 0.05). However, P/AI did not differ between CCOS and CGCOS groups, 55.0% (143/260) and 59.8% (156/261), respectively (P > 0.1). In conclusion, CIDR presynchronization with or without GnRH (CCOS and CGCOS protocols) in beef heifers resulted in similar P/AI. Adding GnRH to presynchronization with CIDR resulted in more heifers with a CL at PGF2α and increased preovulatory follicle diameter at AI. Future studies are needed with bigger sample size and CIDR + CO-Synch treatment as control to determine economic benefit.

105 Optimization of a five-day fixed-time embryo transfer program in dairy heifers: Use of gonadotrophin-releasing hormone at initiation of the protocol

Optimized fixed-time embryo transfer (FTET) protocols for synchronization of recipients have the potential to improve the overall efficiency and profitability of embryo transfer (ET) programs. The objective of the present study was to evaluate the effect of dose of gonadotrophin-releasing hormone (GnRH) at initiation of a 5-day synchronization protocol for FTET. Holstein heifers (n=2689) at two locations were synchronized using a 5-day CO-Synch protocol as follows: Day 0: CIDR inserted, Day 5: CIDR removed, prostaglandin (PG)F2α treatment (500μg cloprostenol), Day 6: PGF2α treatment, Day 8: GnRH (100μg of gonadorelin). On Day 0, at the time of CIDR insertion, heifers were assigned in a completely randomised design to the following groups: Single (a single dose of GnRH; 100μg of gonadorelin), Double (200μg of gonadorelin) or No GnRH (control). All heifers received an Estrotect patch placed on Day 5 and evaluated for signs of oestrus on Day 8. At location A, heifers were evaluated by ultrasonography 5 days after GnRH to determine presence and size of corpus luteum (CL), whereas at location B presence and location of CL were determined by transrectal palpation at the time of transfer. Heifers with a CL received an embryo 7±1 days after GnRH administration, and pregnancy was determined by ultrasonography 41 and 63 days after GnRH. Data were analysed by generalized linear mixed models. Oestrus expression was greater in heifers that received Single and Double GnRH than in the No GnRH group (P=0.001). Similarly, utilisation rate (number transferred per number treated) was greater for heifers in the Single and Double GnRH group than for those in the No GnRH group (P=0.02). Pregnancy data were analysed for a subset of recipients using data from Day 41 (n=2267) and Day 63 (n=2042). The analysis of fertility outcomes included as covariates the type of embryo (invitro fresh or frozen and invivo fresh or frozen), embryo stage, embryo quality, interval from GnRH to transfer, and oestrus expression. Pregnancies per embryo transfer (P/ET) at Days 41 and 63 were not different between treatment groups (P=0.86), and there was no interaction between type of embryo and treatment (P&amp;gt;0.15). Pregnancy loss between Days 41 and 63 was not different (P=0.49) between treatments groups. In conclusion, the removal of the initial GnRH from a 5-day FTET protocol resulted in a slight but significant reduction in the utilisation rate and the percentage of heifers showing oestrus. However, there was no detrimental effect on fertility. As a result, the overall cost of the FTET program can be reduced by eliminating the need for the initial GnRH treatment without compromising fertility. Table 1.Reproductive performance in recipients receiving different doses of gonadotrophin-releasing hormone (GnRH) at initiation of the synchronization protocol Treatment Oestrus (n) Utilisation rate (n) P/ET1 D41 (n) P/ET D63 (n) Pregnancy loss (n) No GnRH 69.2%B (621/898) 85.0%B (763/898) 41.6% (308/740) 39.9% (268/672) 4.3% (12/280) Single GnRH 76.1%A (685/900) 88.8%A (799/900) 42.7% (329/770) 39.5% (272/689) 6.5% (19/291) Double GnRH 75.3%A (671/891) 88.7%A (790/891) 41.5% (314/757) 38.9% (265/681) 5.4% (15/280) A,BValues with different superscripts within a column differ (P&amp;lt;0.05). 1P/ET=pregnancies per embryo transfer.

Artificial insemination in beef cow practice

Even after a severe drought and a few very challenging years, there is still close to 30 million beef cows in the United States. It is estimated that less than 5% of producers are utilizing an AI program in their herds. Accordingly, there are about 4.1 million replacement heifers in the US with around 15% utilizing AI. The percentage of heifers being bred using AI is on the rise, and will continue to rise as we begin to rebuild the nation’s beef herd. With only 3 to 5% of herds utilizing AI across the United States, there is tremendous room for growth of these services.&#x0D; We’ve seen the price of bulls go up exponentially over the past few years. The price of an AI program hasn’t changed that much. Semen prices and synchronization drugs have increased by less than 5%. It’s a lot easier to talk to producers about an AI program now than it has ever been in the past. I believe the veterinarian is the person best suited to offer the most complete services. From genetics consultation to synchronization programs to arm service to all the associated services, artificial insemination has the potential to be a profit driver for any bovine-associated veterinary practice.

Comparación de dos protocolos para sincronizar ovulación e implementar inseminación artificial en vaquillonas

Se efectuaron dos experimentos (EI y EII) en vaquillonas Bos taurus de 20-24 meses de edad y 3-3,5 de condición corporal (escala 1 a 5). El objetivo fue comparar dos protocolos de sincronización de la ovulación (PSO), utilizando dispositivos intravaginales con progesterona (DISP) combinados con cipionato de estradiol (CPE) administrado al momento de retirar el DISP o benzoato de estradiol (BE) 24 h más tarde. En el día 0, las vaquillonas (EI, n=16; EII, n=173) recibieron un DISP (1 g de progesterona) más 2 mg BE; en el día 8 se retiró el DISP, se administraron 0,150 mg de D-Cloprostenol y se aplicó, a sendos PSO, una inyección de 1 mg de CPE en dicho momento o 1 mg de BE 24 h más tarde. En EI, se efectuaron ecografías (días 0, 8 y 9 y desde este último momento cada 12 h hasta el día 11) y muestreos sanguíneos para determinar progesterona plasmática (P4; días 8, 9, 10, 11 y 21); se determinó porcentaje de vaquillonas con cuerpo lúteo (días 0 y 8), los diámetros de los folículos dominante (FD, día 8) y ovulatorio. En EII, se realizó IATF (día 10) y se determinó preñez (día 35). Los análisis estadísticos se realizaron por SAS. Los diámetros del FD (13,1±2,4 mm) y ovulatorio (15,4±2,2 mm) y el intervalo retiro DISP-ovulación (65,3±5,3 h) no difirieron entre PSO (p&gt;0,05); se observó un efecto del día sobre el nivel de P4 (p&lt;0,05), no así del PSO o interacción PSO x día (p&gt;0,05), el nivel de P4 al día 8 (4,6±4,4 ng/ml) disminuyó a valores &lt;1ng/ml post retiro del DISP. La preñez fue similar entre PSO (60,7%; p&gt;0,05). Se concluye que en vaquillonas Bos taurus, ambos PSO generan similares cambios ováricos, variaciones en el nivel de P4 y porcentajes de preñez.

Synchronization of ovulation in cattle with an aromatase inhibitor–based protocol

A study was designed to determine the effect of stage of the estrous cycle on the proportion of animals that ovulated and the synchrony of ovulation of heifers treated with an aromatase inhibitor–based protocol. Forty-eight heifers were treated intramuscularly with 500 μg of cloprostenol (PGF) followed by 100 μg of GnRH 24 hours later to serve as control data for comparison of the ovulatory response to a subsequent aromatase inhibitor protocol. Daily ultrasound examinations were done to determine the incidence of and interval to ovulation. At the time of ovulation (Day 0), heifers were assigned randomly to five day-groups (n = 8-11/group) and given an intravaginal device containing 3 g of letrozole for 4 days starting on Day 0, 4, 8, 12, or 16. At the time of device removal, heifers were given PGF followed by GnRH 24 hours later. Ultrasound examinations were done daily from 2 days before device insertion to 9 days after the posttreatment ovulation. The preovulatory follicle diameter after letrozole treatment was larger in the Day 4 group compared to the Day 0 and 16 groups and intermediate in the Day 8 and 12 groups (P < 0.001). Compared to control data, the percentage of heifers that ovulated after letrozole treatment was greater (87.1% vs. 69.4%, respectively; P < 0.05) as was the synchrony of ovulation (residuals: 0.24 ± 0.07 vs. 0.68 ± 0.13; P < 0.01). The day on which letrozole treatment was initiated did not affect the proportion of heifers that ovulated or the interval to ovulation. Plasma estradiol concentrations at the time of removal of the letrozole device in the Day 0 and 4 groups was lower (P < 0.05) than in the corresponding controls. Estradiol concentrations in the Day 8 and 12 groups did not differ from already low concentrations in the respective controls. Corpus luteum diameter profiles and progesterone production were not affected by day-group although reduced luteal lifespan after letrozole treatment was observed and requires further investigation. In summary, a protocol involving a letrozole-impregnated intravaginal device for 4 days, PGF treatment at device removal, and GnRH 24 later resulted in a greater ovulation rate and greater synchrony of ovulation than in heifers not given letrozole. Results suggest that the protocol may be initiated effectively at random stages of the estrous cycle and may provide impetus for further studies to assess the efficacy of a letrozole-based synchronization protocol for fixed-time insemination.

Evaluation of treatment with a 5-day versus 7-day controlled internal drug-release insert on reproductive outcomes of beef heifers using a modified timed–artificial insemination protocol

The objective of this experiment was to determine the effect of reducing the duration of controlled internal drug-release insert (CIDR) exposure in a CIDR-based, fixed-time-AI protocol on pregnancy per AI (P/AI) and pregnancy rates in beef heifers. The experiment was conducted in 4 consecutive years. British crossbred heifers (yr 1, n = 82; yr 2, n = 68; yr 3, n = 86; yr 4, n = 53) were stratified by BW and age and were assigned randomly to 1 of 2 treatments: (1) CIDR7 heifers (n = 145) received a CIDR insert for 7 d; and (2) CIDR5 heifers (n = 144) received a CIDR insert for 5 d. Heifers in CIDR7 and CIDR5 were given prostaglandin F2α (25 mg) upon CIDR removal followed by gonadotropin-releasing hormone (75 μg) and fixed-time AI 56 to 59 h after CIDR removal. Estrual behavior was monitored following CIDR removal. In all 4 yr, heifers received AI by a single inseminator. Fourteen days after AI, heifers were exposed to bulls for 40 d. Blood samples were collected on the day of CIDR insertion. Pregnancy status was determined by ultrasonography at d 35 and d 67 to 82 after AI. Data were analyzed by logistic regression and ANOVA. Percentage of heifers detected in estrus was different (P 0.2) between treatments. At CIDR insertion, mean serum progesterone concentrations were similar between CIDR7 and CIDR5, and there was no effect of treatment-by-year interaction on progesterone concentrations (P > 0.2). There was a treatmentby-year interaction effect on P/AI (P < 0.05). For CIDR7 and CIDR5, in yr 1, P/AI was 39 and 65.8% (P < 0.05), respectively; in yr 2, P/AI was 64.7and 41.1% (P < 0.05), in yr 3, P/AI was 59 and 73.8% (P = 0.09), and in yr 4, P/AI was 50 and 70.4% (P = 0.25). Overall, P/AI tended (P = 0.07) to be greater for CIDR5 compared with CIDR7 (63.8 vs. 53%). Regardless of treatment, heifers detected in estrus had a greater (P < 0.01) P/AI compared with those not detected in estrus (65.9 vs 47.9%). The final pregnancy rates of heifers were unaffected by the treatment protocols or year (92 and 95.5% for CIDR7 and CIDR5, respectively). The P/AI results from this study suggest that reducing the duration of CIDR treatment from 7 to 5 d in a CIDR-based and single-prostaglandin-injection, fixed-time-AI protocol may improve P/AI in beef heifers.

Effect of gonadotropin-releasing hormone in long-term controlled internal drug-release protocols on pregnancy rates in beef heifers artificially inseminated after observed estrus or fixed time

<h2>ABSTRACT</h2> Beef heifers at 4 ranches were assigned to 1 of 2 estrus synchronization protocols: CIDR Select heifers received a controlled internal drug-release device (CIDR) on d 0, which was removed on d 14, gonadotropin-releasing hormone (GnRH) on d 23, and prostaglandin (PG) F_2α on d 30; and CIDR-PG heifers received CIDR on d 0, which was removed on d 14, and PG on d 30. At 3 ranches (n = 264, Exp. 1), heifers were observed for estrus and AI 12h after exhibition of estrus (EAI) or were fixed-time AI (TAI) with GnRH at 72h. Heifers at the fourth ranch (n = 320, Exp. 2) were fitted with estrus-detection patches at PG administration, which were scored 72h later at TAI. In Exp. 1, the percentage of heifers observed in estrus, the interval to observed estrus, variance for the interval to estrus, and the distribution of observed estrus did not differ (P > 0.52) between treatments. Pregnancy rate to EAI did not differ (P = 0.18) between treatments (71% for CIDR Select and 59% for CIDR-PG). There was a treatment × ranch interaction (P = 0.01) for TAI pregnancy rate. Pregnancy rate to EAI was greater (P = 0.003) than pregnancy rate to TAI (64 vs. 45%). In Exp. 2, estrus-detection patches on heifers synchronized with CIDR Select tended (P = 0.08) to have less wear than patches on heifers synchronized with CIDR-PG. Fixed-time AI pregnancy rate in Exp. 2 did not differ (P > 0.67) between treatments, averaging 50%. Timed-AI pregnancy rate was greater (P = 0.05) for heifers with estrus-detection patches that were 50 or 100% color change than for heifers with patches that had no color change. Inclusion of GnRH in long-term CIDR protocols did not improve synchrony of estrus or AI pregnancy rates.

Follicular populations and luteal function in dairy heifers treated with a controlled internal drug release insert for 14 days as a method to synchronize the estrous cycle before prostaglandin F2α treatment and artificial insemination

Progesterone-containing controlled internal drug release (CIDR) inserts are used to synchronize the estrous cycle before PGF2α is administered for timed AI (14dCIDR-PGF2α program). The program, initially designed for beef cattle, was recently shown to be efficacious in dairy heifers. We hypothesized that the 14-d CIDR treatment would synchronize the estrous cycle in dairy heifers and result in a uniformly sized corpus luteum (CL) and largest follicle (LF) at the time of PGF2α treatment. Holstein (n=110) or Holstein × Guernsey (n=4) dairy heifers were assigned to 2 treatments: (1) 14dCIDR-PGF2α [CIDR in for 14d, CIDR out for 16d, PGF2α and AI after observed estrus (n=57)] or (2) control [PGF2α and AI after observed estrus (n=57)]. Regardless of treatment, additional PGF2α injections were administered at 14-d intervals to heifers that were not seen in estrus. Ovarian ultrasonography and blood sampling were done on d 0 (CIDR administered), 14 (day CIDR removed), 19 (5d after CIDR removed), 30 (PGF2α administered), and 44 (second PGF2α dose administered to heifers that were not detected in estrus after the first PGF2α). Compared with control (untreated), more CIDR-treated heifers were categorized as having a small CL (≤9.9mm) and large LF (15.0–19.9mm) on d 14 (CIDR removal) and, as expected, a greater percentage of CIDR-treated heifers were in estrus during the 5d after the CIDR removal compared with control heifers (75.4 vs. 22.8%, respectively). On d 19, the CIDR-treated heifers had apparently ovulated based on disappearance of LF and appearance of small CL. On d 30 (PGF2α administration), 89% of 14dCIDR-PGF2α heifers had CL that were ≥20mm in diameter compared with 55% for control. Presence of larger CL on d 30 was associated with greater concentrations of plasma progesterone in 14dCIDR-PGF2α compared with control (10.5±0.5 vs. 5.0±0.6ng/mL, respectively). The percentages of heifers with LF in the smallest category (≤9.9mm) tended to be less (5.3 vs. 16.6%) and the percentage of heifers with LF in the medium-size category (10.0 to 14.9mm) tended to be greater (84.2 vs. 69.1%) for 14dCIDR-PGF2α versus control, respectively, on d 30. More heifers were detected in estrus within 5d after the first PGF2α (86.0 vs. 56.1%) and conception rate to AI using sexed semen tended to be greater (61.2% vs. 40.6%) for 14dCIDR-PGF2α compared with control (respectively). Treating dairy heifers with a CIDR for 14d was an effective method to synchronize an estrous cycle before PGF2α was administered.

Evaluation of reproductive and economic outcomes of dairy heifers inseminated at induced estrus or at fixed time after a 5-day or 7-day progesterone insert-based ovulation synchronization protocol

The objectives of the current experiment were to evaluate the reproductive performance and economic outcome of 3 synchronization strategies for first artificial insemination (AI) of dairy heifers. Holstein heifers from 2 herds (site A, California, n=415; site B, Idaho, n=425) were assigned to 1 of 3 treatments. Heifers assigned to the AI on estrus (AIE) treatment received an injection of 25mg of PGF2α at enrollment (d 0) and every 11 d thereafter until AI occurred. Heifers assigned to the CIDR5 treatment received a controlled internal drug release insert (CIDR) containing 1.38g of progesterone, which was removed 5 d later concomitantly with an injection of 25mg of PGF2α, and received fixed-time AI (TAI) concomitantly with an injection of 100μg of GnRH 53 to 60 h later. Heifers assigned to the CIDR7 treatment received a CIDR insert, which was removed 7 d later concomitantly with an injection of 25mg of PGF2α, and received TAI concomitantly with an injection of 100μg of GnRH 53 to 60 h later. Heifers were observed for estrus and inseminated up to 98 and 73 d after enrollment in sites A and B, respectively. Thereafter, heifers were moved to pens with bulls and considered failure to conceive to AI if still not pregnant at the end of the observation period. Economic outcomes were based on cost of synchronization protocol (CIDR treatment=$11, PGF2α or GnRH treatments=$2.5/treatment, estrous detection=$0.80/heifer per day), rearing cost ($2.75/heifer per day), and economic loss if a heifer did not conceive to first AI ($150). Input cost of the reproductive programs=synchronization protocol cost + semen cost + rearing cost + replacement cost. Pregnancy per AI (P/AI) 38±3 d after first AI was greatest for AIE heifers (61.1%) followed by CIDR5 (44.8%) and CIDR7 (35.7%) heifers. Furthermore, P/AI 73±7 d after first AI was greatest for AIE (58.8%) and tended to be greater for CIDR5 (42%) than for CIDR7 (34.1%) heifers. The percentage of heifers that had spontaneous luteolysis from CIDR insertion to CIDR removal was reduced for CIDR5 compared with CIDR7 (13.8 vs 31.8%). Pregnancy rate was greatest for AIE heifers but did not differ between CIDR5 [adjusted hazard ratio (95% confidence interval)=0.75 (0.63, 0.90)] and CIDR7 [adjusted hazard ratio (95% confidence interval)=0.65 (0.54, 0.77)] heifers. Consequently, rearing cost and input cost of AIE heifers ($67.1±4.4 and −$107.1±7.0, respectively) were reduced compared with CIDR5 ($86.9±5.1 and −$143.4±8.1, respectively) and CIDR7 ($98.3±5.1 and −$156.5±8.2, respectively) heifers, but no differences were observed between CIDR5 and CIDR7 heifers.

Association of recombinant bovine somatotropin (rBST) with equine chorionic gonadotropin (eCG) on antral follicle count and oocyte production in Holstein and Tabapuã heifers

The objective of this study was to investigate whether the use of rbST and eCG prior to ultrasound-guided follicular aspiration (OPU) improves oocyte yield and quality in Tabapua and Holstein heifers. The study was conducted in two phases, 20 days apart, in a change-over design. The dominant follicle was ablated two days (D-2) before two treatments: stimulation (6 Holstein and 8 Tabapua), 500 mg of rbST (Boostin®) on D0 and 500 IU of eCG (Folligon) on D2; and control (6 Holstein and 8 Tabapua), in which heifers received injections of the excipient. Heifers were aspirated on D4. Oocytes were subjected to a well established commercial in vitro embryo production protocol (Vitrogen®) and embryos were evaluated seven days after fertilization. There was an effect from the interaction of treatment and breed, so that hormonal stimulation increased antral follicle count (2-8 mm) in Tabapua (29.9±2.6 to 41.4±2.6), but not in Holstein heifers (14.4±2.6 to 15.5±2.6). Tabapua heifers had higher mean antral follicle count than Holsteins (35.6±1.8 vs. 15.0±2.1). The number of viable oocytes was not increased by stimulation in Tabapua (from 4.7±1.0 to 5.2±1.1 in control and simulation, respectively) or in Holstein heifers (1.3±1.9 to 2.0±1.6 in control and simulation, respectively). There was no difference in the percentage of heifers with more than five viable oocytes in the group treated (33 vs 27%). The number of blastocysts was not affected by treatment (1.75 vs. 1.00 in hormonal stimulation and control, respectively). The increase in antral follicle count in the stimulated Tabapua heifers did not reflect upon oocyte yield. The differential breed response to the hormonal treatment underscores the need for additional tests, especially for the Holstein breed, in order to enhance OPU efficiency.

Prostaglandin F2α promotes ovulation in prepubertal heifers

The objective was to determine the effects of exogenous prostaglandin F2α (PGF), with or without progesterone treatment, on first ovulation in prepubertal heifers. We tested the hypothesis that PGF has a luteolysis-independent ovulatory effect in cattle. Crossbred Angus heifers (12 to 14 mo old, 250 kg body weight, and an average body condition score of 3 out of 5) were examined by transrectal ultrasonography on two occasions, 11 days apart. Heifers in which a CL was not detected at either examination were considered prepubertal. Heifers were assigned randomly to three experimental groups: (1) PG group (N = 14); heifers were treated with a PGF analog (500 μg cloprostenol im) 5 days after the emergence of a spontaneous (i.e., naturally occurring, noninduced) follicular wave; (2) PPG group (N = 12); heifers were given an intravaginal progesterone-releasing insert (CIDR; Pfizer Animal Health, Montreal, QC, Canada), and a follicular wave was induced with 50 mg of progesterone + 2 mg of estradiol benzoate im, and a PGF analog was given at the time of CIDR removal, on Day 5 of the follicular wave (on average, 8.6 ± 0.5 days after CIDR insertion); and (3) control group heifers were given no treatment (N = 14). Heifers were examined daily by transrectal ultrasonography from the start of the experiment to confirmation that ovulation had occurred, or to 5 days after PGF injection (PG and PPG groups) or until dominant follicles of the next follicular wave reached 8 mm (control group). The percentage of heifers that ovulated within 10 days after wave emergence was higher in PPG (10/12; 83.3%) and PG (11/14; 78.5%) groups than in control (1/14; 7.1%; P < 0.0001). Ovulations occurred 69.6 ± 6 h and 93.8 ± 5 h after PGF treatment in PPG and in PG groups, respectively, whereas only one heifer in the control group ovulated 96 h after Day 5 of follicular wave (P = 0.13). In summary, PGF treatment was associated with ovulation in prepubertal heifers whether or not exogenous progesterone was used as a pretreatment. The hypothesis that PGF will induce ovulation by a luteolysis-independent mechanism was supported.

A structural equation model to evaluate direct and indirect factors associated with a latent measure of mastitis in Belgian dairy herds

In dairy cattle, many farming practices have been associated with occurrence of mastitis but it is often difficult to disentangle the causal threads. Structural equation models may reduce the complexity of such situations. Here, we applied the method to examine the links between mastitis (subclinical and clinical) and risk factors such as herd demographics, housing conditions, feeding procedures, milking practices, and strategies of mastitis prevention and treatment in 345 dairy herds from the Walloon region of Belgium. During the period January 2006 to October 2007, up to 110 different herd management variables were recorded by two surveyors using a questionnaire for the farm managers and during a farm visit. Monthly somatic cell counts of all lactating cows were collected by the local dairy herd improvement association. Structural equation models were created to obtain a latent measure of mastitis and to reduce the complexity of the relationships between farming practices, between indicators of herd mastitis and between both. Robust maximum likelihood estimates were obtained for the effects of the herd management variables on the latent measure of herd mastitis. Variables associated directly (p<0.05) with the latent measure of herd mastitis were the addition of urea in the rations; the practices of machine stripping, of pre-and post-milking teat disinfection; the presence of cows with hyperkeratotic teats, of cubicles for housing and of dirty liners before milking; the treatment of subclinical cases of mastitis; and the age of the herd (latent variable for average age and parity of cows, and percentage of heifers in the herd). Treatment of subclinical mastitis was also an intermediate in the association between herd mastitis and post-milking teat disinfection. The study illustrates how structural equation model provides information regarding the linear relationships between risk factors and a latent measure of mastitis, distinguishes between direct relationships and relationships mediated through intermediate risk factors, allows the construction of latent variables and tests the directional hypotheses proposed in the model.