Bos Indicus Beef Research Articles

Understanding the Ovarian Interrelationship with Low Antral Follicle Counts (AFC) in the In Vivo Bos indicus Cow Model: Unilateral and Bilateral Main AFC as Possible Biomarkers of Ovarian Response to Hormonal Synchronisation.

Simple SummaryThe number of growing antral follicles visualised by ultrasound generates an antral follicle count (AFC), which can predict the number of female gametes remaining in an animal’s ovary. However, important information on ovarian biology with regard to the ovarian interrelationship with the main number of antral follicle populations (mAFC) is scarce; therefore, it is important to uncover additional information on ovarian biology that can be helpful in predicting the ovarian response after hormonal stimulation in mono-ovulatory animal species. Thus, mono-ovulatory Bos indicus beef cows with low numbers of AFC were induced using a hormonal programme in an effort to increase the understanding of the interrelationship with unilateral mAFC (main number of antral follicle populations appearing on only one side of the ovary). Based on the odds ratio, our results emphasise that the likelihood of an ovarian response was higher in cows with unilateral mAFC relationships on the day of exogenous hormonal stimulation.The antral follicle count (AFC) is a test in which the number of oocyte-containing follicles that are developing in both ovaries are visually counted. The count of these follicles strongly relates to the population of the growing follicle reserve on the ovaries. However, the importance of the main number of antral follicle populations (mAFC) in mono-ovulatory animal species has yet to be completely elucidated. Moreover, the investigation of the ovarian interrelationship with unilateral mAFC (main number of antral follicle populations appearing on only one side of the ovary) and bilateral mAFC (main number of antral follicle populations appearing in equivalent numbers on both sides of the ovary) and how understanding this interrelationship can offer possible indicators of ovarian response to hormonal induction have not yet been investigated in mono-ovulatory Bos indicus beef cows. The aim of this study is to investigate the different ovarian interrelationships of mAFC (unilateral and bilateral mAFC) at the time of exogenous hormonal stimulation on the total number of AFC (left and right ovaries) at the beginning of the hormonal protocol for ovarian stimulation and ovarian response at the completion of exogenous hormonal stimulation as well as their usefulness as possible biomarkers of successful hormonal stimulation in Bos indicus beef cattle. Beef cows (n = 104) with low total numbers of AFC (4.7 ± 2.4 follicles) were stimulated with a gonadotropin-releasing hormone-progesterone-prostaglandin F2α-based protocol. At the beginning of the hormonal protocol, ovarian ultrasound scans were performed to evaluate AFC from both ovaries of cows. Beef cows were divided into two groups, unilateral (n = 74) and bilateral mAFC (n = 30), according to the ovarian interrelationship. At the completion of the hormonal stimulation, ovarian ultrasound scans were performed to evaluate the dominant follicle (DF) and cows with DF > 8.5 mm in diameter emerging on their ovaries were defined as having experienced a response to hormonal stimuli. There was a difference of 19.1% between Bos indicus cows bearing unilateral mAFC that produced an increase in ovarian response (odds ratio = 2.717, p < 0.05) compared to the responsive rate of cows displaying bilateral mAFC (82.4% vs. 63.3%). In unilateral mAFC, cows bearing mAFC ipsilateral to the ovary of dominant follicle (DF) had a higher responsive rate than cows bearing mAFC contralateral to the DF ovary (50.0% vs. 32.4%, p < 0.05). In mAFC ipsilateral to the DF ovary, pregnancy rates were greatest in cows bearing mAFC and DF on the right ovary compared with cows bearing mAFC and DF on the left ovary (25.0% vs. 9.1%, p < 0.05). In primiparous and multiparous cows, unilateral mAFC occurs with a greater (p < 0.05) frequency than bilateral mAFC (69.0% and 72.0% vs. 31.0% and 28.0%, respectively). In unilateral mAFC, primiparous cows bearing mAFC ipsilateral to the DF ovary had a greater responsive rate than primiparous cows bearing mAFC contralateral to the DF ovary (55.0% vs. 20.0%, p < 0.05). In mAFC ipsilateral to the DF ovary, responsive and pregnancy rates were greatest (p < 0.05) in multiparous cows bearing mAFC and DF on the right ovary compared with multiparous cows bearing mAFC and DF on the left ovary (58.1% and 22.6% vs. 25.8% and 3.2%, respectively). Furthermore, there was a positive correlation between the mean diameter of AFC at the time of the exogenous hormonal trigger and the mean diameter of DF at the completion of hormonal synchronisation (p < 0.05). Our findings emphasise that the ovarian interrelationship with unilateral mAFC at the time of the hormonal trigger might be a promising biomarker for predicting success in ovarian response to hormonal stimulation of mono-ovulatory Bos indicus beef cows with low AFCs.

The effect of subclinical endometritis on reproductive performance in postpartum Bos indicus multiparous beef cows

The objective was to investigate the prevalence of subclinical endometritis (SE) in postpartum Bos indicus multiparous beef cows using different polymorphonuclear cells (PMN) threshold ratios, and to evaluate the impacts of SE on their reproductive performance. A total of 689 postpartum Nellore cows (45.2 ± 7.8 days postpartum) were submitted to an estrus synchronization protocol + timed-artificial insemination (TAI). Endometrial cytology samples were collected by cytobrush before the beginning of the protocol. Cows were considered positive for SE if: (PMN) ≥ 3% (PMN3), PMN ≥ 5% (PMN5) and PMN ≥ 7% (PMN7). Pregnancy diagnosis was performed at 30 and 100 d after TAI. The prevalence of cows categorized as positive for SE increased (P < 0.05) as the threshold was lowered (PMN7 = 3.9%; PMN5 = 5.5%; PMN3 = 9.1%). Positive SE cows had similar (P > 0.41) BCS, days postpartum, and expression of estrus at TAI compared with negative SE cows. Positive SE cows had decreased (P = 0.04) pregnancy rates compared to negative SE cows in the PMN5 threshold (26.3 ± 8.7% vs 44.5 ± 4.1%); however, no difference (P > 0.45) was observed between positive and negative SE cows in the PMN3 and PMN7 thresholds. Embryonic mortality between days 30 and 100 was not affected by SE (P > 0.16). In conclusion, the prevalence of SE varies based on the PMN threshold used, whereas SE at the beginning of the TAI protocol decreased the pregnancy rates in postpartum Bos indicus beef cows when the PMN5 was used.

Impacts of body condition score at beginning of fixed-timed AI protocol and subsequent energy balance on ovarian structures, estrus expression, pregnancy rate and embryo size of Bos indicus beef cows

These two studies evaluated the effects of body condition score (BCS) at beginning of fixed-timed artificial insemination (FTAI) protocol and subsequent BCS change on ovarian structures, estrus expression, pregnancy rate and embryo size of multiparous Nellore beef cows. In Experiment 1, 240 cows, distributed over four years (n = 40, 20, 82 and 98 cows, for years 1, 2, 3 and 4, respectively) were assigned to FTAI protocol from d -11 to 0. Cow BCS (d -11 and 40), body weight (BW; d -11 and 40), dominant follicle (d 0) and corpus luteum (CL; d 7 and 14) size, plasma progesterone (d 7 and 14), pregnancy rate (d 40) and embryo size (d 40) were evaluated. In Experiment 2, 2443 cows (single year) were assigned to FTAI protocol from d -11 to 0. Cow BCS (d -11 and 30), BW (d -11 and 30), estrus expression (d 0), and pregnancy rate (d 30) were evaluated. BCS scale used ranged from 1 (extremely thin) to 9 (extremely fat) and the cows were categorized in groups (BCS ≥ 5 and < 5 and in lost, maintained and gained BCS). Experiment 1, cows with BCS ≥ 5 at beginning FTAI protocol tended (P ≤ 0.10) to have greater CL diameter (d 7), CL volume (d 7 and 14) and had greater (P ≤ 0.05) plasma concentration of progesterone (d 14) and embryo size (d 40), compared to cows with BCS < 5. Further, cows that gained BCS from d -11 to 40 tended (P = 0.10) to have greater dominant follicle size and cows that gained and maintained BCS had greater (P = 0.02) plasma concentration of progesterone (d 14), compared to cows that lost BCS. The embryo size was greater (P < 0.01) for cows that gained, intermediary to cows that maintained and lower to cows that lost BCS. In Experiment 2, cows with BCS ≥ 5 had greater (P = 0.02) estrus expression, compared to cows with BCS < 5, and the pregnancy rate increased linearly with BCS (P < 0.01; 20.0 to 69.1% for BCS 2 and 9, respectively). Further, cows that gained had greater (P < 0.01) estrus expression compared to cows that maintained and lost BCS, and cows that gained and maintained BCS had greater pregnancy rate compared to cows that lost BCS (P < 0.01; 62.2, 59.7 and 49.3 ± 10.3%, respectively). Thus, cows with greater BCS at beginning of FTAI protocol or that gained or maintained BCS during synchronization and after AI had greater ovarian structures development, estrus expression, pregnancy rate and embryo size.

Performance of Bos indicus beef cattle supplemented with mineral or with concentrates in tropical Urochloa decumbens pastures: A meta-regression approach

Models are useful to predict responses of beef cattle to supplementation and its interactions with pasture quality. Therefore, this study was conducted to quantitatively understand variables that influence the performance of cattle under grazing, with or without supplementation, in the tropics by using a meta-analytical approach. The database was composed of individual data of 577 heifers and 194 young bulls from 18 experiments. Information collected included: sex (male or female), total dry matter intake, supplement dry matter intake, forage crude protein (CPforage), forage indigestible neutral detergent fiber (iNDFforage), forage neutral detergent fiber, neutral detergent insoluble protein, crude protein intake from supplement (CPIsupp), metabolizable energy intake from supplement (MEIsupp), initial body weight (BW), final BW and average daily gain (ADG). Additionally, the intakes of rumen degradable protein (RDP), rumen undegradable protein (RUP), and metabolizable protein (MP) from the supplement of each study were calculated. To model animal performance, values within each experiment were divided into two components: ADG-pasture (ADG of non-supplemented animals) and ADG-supplement (differential ADG in relation to non-supplemented animals). Data were evaluated using a meta-analysis approach to estimate fixed and random effects of experiment using linear and nonlinear mixed models. There was no correlation between ADG-pasture and initial BW or final BW. The CPforage was positively correlated, and iNDFforage was negatively correlated with ADG-pasture. Therefore, two equations were developed to predict ADG-pasture, as follows: ADG-pasturemales (kg/day) = 0.007434 × CPforage – 0.001044 × iNDFforage; ADG-pasturefemales (kg/day) = 0.01445 × CPforage – 0.0000642 × CPforage2 – 0.001598 × iNDFforage. There was no correlation between ADG-supplement and total dry matter intake, initial BW, or final BW. The ADG-supplement was positively correlated with CPIsupp and MEIsupp. An exponential model was chosen to fit ADG-supplement. Equations to predict ADG-supplement were composed of three exponential compartments based on ADG-pasture, CPIsupp (or RDP, RUP or MP intakes from supplement), and MEIsupp. The replacement of CPIsupp by RDP, RUP or MP intakes from supplement demonstrated that all protein components could be used to predict the performance of grazing animals. Still, the best fit was observed when RUP intake from supplement was used. The validation process through cross-validation analyses demonstrated that all equations had high accuracy and moderate precision. In conclusion, our results indicate that ADG-pasture can be estimated from CPforage, iNDFforage. The ADG-supplement can be estimated from ADG-pasture, MEIsupp, and protein components intake in grazing heifers and young bulls.

Antral follicle count, oocyte production and embryonic developmental competence of senescent Nellore (Bos indicus) cows

Information on the follicular population and oocyte quality of cows in the final period of reproductive life is scarce. The present study aimed to compare the antral follicle count (AFC), oocyte production and embryonic developmental competence of young versus long-lived and senescent Bos indicus beef cows. Nellore cows (Bos indicus) were classified into three groups according to age: young (4–9 years, n = 10), long-lived (14–17 years, n = 10) and senescent (17–23 years, n = 10). At a random time in the estrus cycle, the cows received cloprostenol sodium salt (0.5 mg, IM), estradiol benzoate (1 mg, IM) and an intravaginal P4 device (1.4 g). Five days later, the P4 devise was removed and oocyte collection (OPU1) was performed. A second OPU (OPU2) was performed 5 days after the first in order to aspirate only growing follicles. During each OPU, AFC and the number and quality of cumulus–oocyte complexes (COCs) were evaluated. Then, the COCs were placed in standard maturation medium (IVM), fertilized and incubated for 9 days. The data were subjected to ANOVA and Multinomial Logistic Regression. The AFC was smaller in long-lived and senescent cows in both OPU1 and OPU2 when compared to younger cows. There was no difference in AFC between OPU1 (19.9 ± 1.8) and OPU2 (17.6 ± 1.9) in young cows, however, more follicles were punctured in long-lived and senescent cows in OPU1 (12.0 ± 2.6 and 19.3 ± 4.6) than in OPU2 (9.2 ± 1.9 and 10.3 ± 2.3), respectively (P < 0.01). The numbers of COCs recovered from young cows (OPU1 = 14.2 ± 1.8; OPU2 = 8.4 ± 0.9) were higher than those obtained from long-lived cows (OPU1 = 5.9 ± 2.3; OPU2 = 4.3 ± 1.0) and senescent cows (OPU1 = 7.2 ± 3.0; OPU2 = 4.1 ± 1.7), respectively (P < 0.05). The cleavage rate did not differ between groups. However, the rate of blastocyst formation was higher for young (64.8%) and long-lived (65.0%) compared to senescent (16.5%) cows (P < 0.01). In conclusion our results indicate that the AFC is lower in long-lived and senescent cows compared with young cows. However, unlike in senescent cows, the embryonic development of long-lived cows is similar to that of young cows. This suggests that Nellore cows aged >17 years begin to have reduced embryonic development capacity due to ovarian aging.

Relationship among serum metabolic hormones with pregnancy rates to fixed-time artificial insemination in Bos indicus beef females

Two experiments compared body parameters and serum concentrations of GH, IGF-I, and leptin in Bos indicus females based on their pregnancy status to fixed-time artificial insemination (FTAI). In Exp. 1, 226 nulliparous heifers were assigned to a puberty induction protocol (d -35 to d -23), followed by an estrus synchronization and FTAI protocol (d -11 to 0). Heifers received a controlled internal progesterone releasing insert (CIDR) previously used three times on d -35, followed by 0.6 mg of estradiol cypionate and CIDR removal on d -23. Heifers received 2 mg of estradiol benzoate and a CIDR previously used twice on d -11, 12.5 mg of dinoprost tromethamine in addition to CIDR removal, 0.6 mg of estradiol cypionate and a 200 IU of eCG on d -2, followed by FTAI on d 0. Heifer BW and BCS were recorded on d -35, -11, and 30, whereas blood samples were collected on d -35, -23, -11, 0, and 30. In Exp. 2, 821 multiparous lactating Nelore beef cows were assigned to the estrus synchronization and FTAI protocol described in Exp. 1, but received 300 IU of eCG on d -2. Cow BW and BCS were recorded on d -11 and 30, and blood samples were collected on d -11, 0, and 30. In both experiments, pregnancy status was verified via transrectal ultrasonography on d 30. In Exp. 1, heifers that became pregnant had greater (P = 0.03) IGF-I concentrations on d 0 and less (P = 0.05) IGF-I concentrations on d 30 compared to heifers that did not become pregnant (pregnancy status × day; P < 0.01). No differences in BW, BCS, GH and leptin were detected (P ≥ 0.23) according to heifer pregnancy status. In Exp. 2, cows that became pregnant had less (P = 0.03) leptin concentrations on d -11, and less (P = 0.01) IGF-I concentrations on d 30 compared to cows that did not become pregnant (pregnancy status × day; P ≤ 0.05). No differences in BW, BCS, and GH were detected (P ≥ 0.15) according to cow pregnancy status. In summary, serum leptin at the beginning of estrus synchronization was negatively associated with pregnancy rates to FTAI in multiparous cows. A negative relationship was also observed between serum IGF-I during early gestation with pregnancy rates to FTAI across parities. These results provide novel insights on the relationships among metabolic hormones with reproductive performance of B. indicus females.

117 Effect of length of insertion of a progesterone device on follicular diameter, time of ovulation, and pregnancy rates in Bos indicus cows treated with an oestradiol/progesterone-based protocol with a prolonged proestrus

Three experiments were designed to evaluate the effect of the length of insertion of a intravaginal progesterone (P4) device on follicular and corpus luteum (CL) diameter, time of ovulation, and pregnancy rates following fixed-time AI (P/FTAI) in Bos indicus cows treated with an oestradiol/P4-based treatment with a lengthened proestrus, named J-Synch. Multiparous suckled Bos indicus beef cows that were 35 to 60 days postpartum were used in Experiments 1 and 2, whereas non-lactating cows were used in Experiment 3. All cows had a CL or a follicle of at least 8mm in diameter and a body condition score between 2.5 and 4 (1 to 5 scale) at the time of treatment. On Day 0, all cows received 2mg of oestradiol benzoate (EB; Sincrodiol, Ourofino, Brazil) and a previously used intravaginal device (1g of P4; Sincrogest, Ourofino). The P4 device was removed on Day 6 in the J-Synch 6-day group and on Day 7 in the J-Synch 7-day and Control groups. All cows received 500µg of cloprostenol (Sincrocio, Ourofino) and 400IU of equine chorionic gonadotrophin (SincroeCG, Ourofino) at the time of P4 device removal, and cows in the Control group also received 0.5mg of oestradiol cypionate (ECP, SincroCP, Ourofino) at the same time. In Experiment 1, cows (n=20 per group) were examined every 12h, from P4 device removal to determine the time of ovulation and 7 days after ovulation to measure the CL. In Experiment 2, all cows (n=200 per group) were tail-painted for oestrous detection. Cows with=50% of the tail-paint rubbed-off by 72h (J-Synch groups) or 48h (Control group) after P4 device removal, were FTAI at that time. Cows not designated as showing oestrus at that time received 10µg Buserelin (GnRH, Sincroforte, Ourofino) and were FTAI 8h later. In Experiment 3, P/FTAI was compared in cows that received the J-Synch 7-day treatment (n=265) or the 7-day Control treatment (n=250). Data were analysed using the GLM mixed procedure (InfoStat). In Experiment 1, the diameter of the ovulatory follicle was larger (P&amp;lt;0.05) and the interval to ovulation was longer (P&amp;lt;0.05) in the J-Synch groups (J-Synch 7 d: 16.4±0.2mm and 86.0±3.0 h; J-Synch 6 d:15.5±0.3mm and 83.0±4.0h) than in the Control group (13.8±0.2mm and 64.0±3.0h). Furthermore, CL diameter was greater (P&amp;lt;0.05) in the J-Synch 7-day group (21.9±0.8mm) than in the J-Synch 6-day (18.7±0.8mm) and Control (16.8±0.9mm) groups. In Experiment 2, P/FTAI was higher (P&amp;lt;0.05) in the J-Synch 7-day group (116/200; 58.0%) than in the J-Synch 6-day (93/200; 46.5%) and Control (98/200; 49.0%) groups. In Experiment 3, P/FTAI was higher (P&amp;lt;0.05) in the J-Synch 7-day group (161/265; 60.7%) than in the Control group (124/250; 49.6%). In conclusion, delaying the removal of the P4 device by 1 day (i.e. Day 7 vs. Day 6) in the J-Synch protocol and lengthening the proestrous period (i.e. J-Synch 7-day vs. 7-day Control) resulted in higher P/FTAI in Bos indicus cows.

Comparison of three doses of estradiol benzoate for synchronization of follicular wave emergence in suckled Bos indicus beef cows.

We aimed to compare the effect of three estradiol benzoate (EB) doses on follicular wave emergence (FWE) and dominant follicle growth of suckled Nelore cows submitted to TAI (D0). On a random day of estrous cycle (D−10), multiparous (MULT; n=36) and primiparous (PRIM; n=20) suckled Nelore cows received an intravaginal progesterone (P4) device and were assigned in three groups. Cows in the EB-1 (n=20), EB-1.5 (n=15) or EB-2 (n=21) groups received, respectively, an im treatment with 1, 1.5 or 2 mg EB. A subgroup (n=10-13 cows/group) were subject to daily ovarian evaluations from D−10 to D0. On D−2, P4 devices were removed, and all cows received the same treatment: 1 mg estradiol cypionate, 0.53 mg sodium cloprostenol, and 300 IU eCG. Statistical analyses were performed considering only the main effects of treatment group and parity order. The proportion of cows with a synchronized FWE and the moment of the FWE did not differ (p>0.05) among the treatment groups (overall: 80% [28/35] and 4.1 ± 0.4 days); however, the FWE occurred earlier (p=0.007) in MULT (3.8 ± 0.2 days) than PRIM (5.1 ± 0.4) cows. The proportion of animals detected in estrus was greater (86% [31/36] vs. 70% [14/20]; p=0.02) and the dominant follicle was larger on D−2 (9.7 ± 0.3 mm vs. 7.8 ± 0.7 mm; p=0.006) and D0 (11.9 ± 0.4 mm vs. 10 ± 0.5 mm; p=0.008) in MULT than PRIM cows. In conclusion, the three EB doses presented similar efficiency to synchronize the FWE in suckled Nelore cows. Moreover, a delayed FWE and smaller dominant follicle is observed in PRIM cows, contributing to the reduced reproductive performance in this parity category when using similar TAI protocols of MULT cows.

Effects of pre- and postpartum supplementation on lactational and reproductive performance of grazing Nellore beef cows

Context Few studies have evaluated the effects of providing concentrate pre- or postpartum, or during both of these intervals, to beef cows grazing tropical pastures, even though this information is important for planning breeder herd management. Aims A study was undertaken to examine the effects of supplementation with concentrates before calving (prepartum), after calving (postpartum) or during both these intervals on production and reproductive efficiency in Bos indicus beef cows grazing Urochloa decumbens pasture. Methods Nellore cows, initially 6 months pregnant (mean ± s.e.), weighing 516 ± 1.3 kg and body condition score 4.7 ± 0.15 (1–9 scale), were used in an experiment with four treatments in a 2 × 2 factorial design with 20 animals per treatment. The treatments comprised no supplementation or provision of a supplement (1 kg/cow.day containing 28% crude protein) for 90 days prepartum only, 90 days postpartum only or during the pre- and postpartum intervals. Key results Responses could be described in terms of the main effects of providing the supplement pre- or post-calving; the interactions were not significant (P > 0.05). Prepartum supplements increased the cow bodyweight at calving by 29 kg, and calf birthweight by 3.7 kg (P 4 did not change the response to postpartum supplementation. Implications Prepartum supplementation may increase cow performance and calf weight at birth, whereas postpartum supplementation may improve the reproductive efficiency.

Administering an additional prostaglandin F2α injection to Bos indicus beef cows during a treatment regimen for fixed-time artificial insemination

Two experiments were conducted to evaluate if an additional prostaglandin F2α (PG) injection during an estradiol-based estrous synchronization treatment regimen affects pregnancy rates resulting from fixed-time artificial insemination (FTAI) in Nelore cows. In Experiment 1, 1039 cows were administered estradiol benzoate and an intravaginal progesterone releasing device (CIDR) on d -11, an injection of PG on d -4, with CIDR removal and administration of estradiol cypionate and eCG occurring on d -2, and FTAI on d 0. Cows were administered an additional injection of PG (PG2) or saline (PG1) on d -2. Percentage pregnancy per FTAI on d 30 was greater (P = 0.01) in cows of the PG2 than PG1 group (54.5 % and 46.6 %, respectively). In Experiment 2, there was use of the same treatment regimen for estrous synchronization of 934 cows as that for Experiment 1 followed by FTAI, with there being diagnosis of whether cows had or did not have a corpus luteum on d -4. Response to estrous synchronization, largest follicle diameter at FTAI, and pregnancy per FTAI were greater (P ≤ 0.05) in cows of the PG2 than PG1 group with a body condition score (BCS) < 5.0 at FTAI (81.2 % and 72.6 %, 11.9 and 11.2 mm, 55.5 and 45.6 %; respectively). These treatment responses did not differ (P ≥ 0.18) in cows with BCS ≥ 5.0. Collectively, results indicate that treatment with PG2 increased pregnancy per FTAI in B. indicus cows deficient in body energy reserves, by enhancing follicle development and estrous synchronization response.

The effect of clitoral stimulation post artificial insemination on pregnancy rates of multiparous Bos indicus beef cows submitted to estradiol/progesterone-based estrus synchronization protocol.

Clitoral stimulation after artificial insemination (AI) in beef cattle is a common practice utilized by AI technicians; however, the effect of clitoral stimulation during fixed-time AI (TAI) is still unknown. The objective of the present experiment was to evaluate the effect of clitoral stimulation on temperament responses and pregnancy rates to TAI in Bos indicus beef cows. A total of 1,186 multiparous Nellore cows across three different locations were assigned to an estradiol/progesterone-based estrus synchronization + TAI protocol (day -11 to 0). Cows were randomly assigned to receive either 3 s of clitoral stimulation (n = 602) or no clitoral stimulation (n = 584) immediately after TAI (day 0). Cow body condition score (BCS) was recorded on day -11. Estrus expression was evaluated based on estrus detection visual aid patch activation on day 0 (estrus, ≥50% activated; no estrus, <50% activated). Temperament was assessed by individual chute score based on a 5-point scale before TAI, and individual exit velocity was measured after clitoral stimulation. Pregnancy diagnosis was performed 30 d after TAI via transrectal ultrasonography. Pregnancy rate to TAI was positively affected by BCS (P < 0.01) and estrus expression (P = 0.03). Pregnancy rates of cows receiving clitoral stimulation did not differ (P = 0.39) from cows non-stimulated (47.5 ± 4.6% vs. 44.3 ± 4.6%, respectively). No interaction of clitoral stimulation and estrus expression was observed (P = 0.26). Chute score was positively correlated to exit velocity (P < 0.01; r = 0.29); however, clitoral stimulation did not affect exit velocity (P = 0.86). In summary, pregnancy rates to TAI are influenced by various factors and multiple strategies have the potential to increase the fertility of beef cows submitted to TAI; however, clitoral stimulation of Bos indicus beef cows did not improve TAI pregnancy rate.

Feed efficiency and maternal productivity of Bos indicus beefcows.

This study evaluated 53 primiparous cows (36.8±1.23 months old and 484±40.9 kg of body weight) performance tested (GrowSafe® System) from 22±5 to 190±13 days of lactation in order to obtain daily dry matter intake (DMI). The animals received a high-forage diet (forage-to-concentrate ratio of 90:10). Milk production of the cows was evaluated three times by mechanical milking and the energy-corrected milk yield (ECMY) was calculated. Energy status (through the indicators glucose, cholesterol, triglycerides, and β-hydroxybutyrate), protein status (indicators albumin, urea, and creatinine), mineral status (indicators calcium, phosphorus, and magnesium), and hormonal status (indicators insulin and cortisol) were estimated four times throughout lactation. The residual feed intake (RFI) of cows was calculated considering DMI, average daily gain (ADG) and mid-test metabolic weight (BW0.75) obtained in early lactation (from 22±5 to 102±7 days), and the animals were classified as negative (most efficient) or positive RFI (least efficient). The RFI model explained 53% of the variation in DMI. The mean DMI, ADG, ECMY, and calf weight as a percentage of cow weight were 12.47±2.70 kg DM/day, 0.632±0.323 kg/day, 10.47±3.23 kg/day, and 36.6±5.39%, respectively. Negative RFI cows consumed 11.5% less DM than positive RFI cows, with performance and metabolic profile being similar to those of positive RFI cows, except for a lower milk protein content and higher blood cholesterol concentration. In conclusion, negative (most efficient) and positive RFI (least efficient) Nellore cows, fed an ad libitum high-forage diet, produced similar amounts of milk, fat and lactose and had similar subcutaneous fat thickness, weight, calf weight as a percentage of cow weight, and blood metabolite concentrations (except for cholesterol). Therefore, there are economic benefits to utilizing RFI in a cow herd since cattle had decreased DMI with similar overall performance, making them more profitable due to lower input costs.

Progesterone-based timed AI protocols for Bos indicus cattle II: Reproductive outcomes of either EB or GnRH-type protocol, using or not GnRH at AI

The aim of these experiments was to study ovarian dynamics and fertility of Bos indicus beef cattle submitted to 7-d progesterone (P4)-based fixed-time AI (FTAI) protocols using different hormonal treatments. In Exp. 1, 2 yr old Nelore heifers (n = 973) were randomly assigned to one of four treatments: EB-0 (estradiol benzoate, EB on D0 and no GnRH at AI), EB-G (EB on D0 and GnRH at AI), G-0 (GnRH on D0 and no GnRH at AI), or G-G (GnRH on D0 and at AI). On D0, heifers received an intravaginal P4 implant (0.5 g) for 7 d and EB (1.5 mg) or GnRH (16.8 μg). On D7, the P4 implant was withdrawn and heifers received cloprostenol (PGF; 0.5 mg) and estradiol cypionate (EC, 0.5 mg). Heifers in G groups also received PGF and eCG (200 IU) on D6, whereas EB heifers received eCG on D7. At FTAI on D9, only EB-G and G-G groups received GnRH (8.4 μg). In Exp. 2, Nelore cows (n = 804) received the same treatments (EB-0, EB-G, G-0, or G-G) using a 1.0 g P4 implant, 2.0 mg EB, and 300 IU eCG. Effects were considered significant when P ≤ 0.05. After treatment on D0, G had more ovulations than EB in heifers (60.3 [287/476] vs. 12.7% [63/497]) and cows (73.7 [83/112] vs. 24.4% [28/113]). Luteolysis after D0 was greater in EB than G in heifers (39.2 [159/406] vs. 20.0% [77/385]) and cows (25.5 [14/55] vs. 1.6% [1/64]). Heifers in G had larger follicles (mm) than EB on D7 (10.3 ± 0.2 vs. 9.2 ± 0.2) and at AI (11.9 ± 0.2 vs. 11.3 ± 0.2). Cows had larger follicles in G than EB on D7 (11.0 ± 0.3 vs. 9.9 ± 0.3) but not at AI. More estrus was observed in G than EB for heifers (80.3 [382/476] vs. 69.6% [346/497]) and cows (67.6 [270/400] vs. 56.2% [227/404]). There was no interaction between D0 and D9 treatments on pregnancy per AI (P/AI) in heifers (EB-0: 56.7 [139/245], EB-G: 53.6 [135/252], G-0: 52.6 [127/241], and G-G: 57.5% [135/235]). However, cows from EB-G had greater P/AI than EB-0 (69.5 [142/204] vs. 60.2% [120/200]), whereas P/AI for G-0 (62.7% [127/203]) was similar to G-G (60.9% [120/197]). In heifers, there was no interaction of GnRH at AI with estrus, however, cows that did not display estrus had greater P/AI if they received GnRH at AI (GnRH = 59.1 [91/154] vs. No GnRH = 48.2% [78/162]). Thus, protocols initiated with EB or GnRH for Bos indicus heifers and cows had differing ovarian dynamics but similar overall fertility, enabling their use in reproductive management programs. Treatment with GnRH at time of AI increased fertility in some instances in Bos indicus cows but not in heifers.

The effect of false mount on quality of frozen-thawed semen in Bos indicus beef bulls.

This study evaluated the effect of false mounts (FM) on quality of frozen-thawed semen in beef bulls. Five mature Brahman bulls at the Standard Semen Production Center in Thailand were subjected to semen collection. Overall, 60 ejaculates were collected over a 12-week period of which 30 were collected without, and another 30 were collected using FM. A range of quality parameters of fresh, pre-frozen, and frozen-thawed semen were evaluated. Use of FM resulted in significant improvement of most parameters of fresh semen except progressive motility and sperm viability. The quality parameters of pre-frozen and frozen-thawed semen also significantly improved with FM. Use of FM significantly improved the viability of frozen-thawed semen, possibly indicating the protective effect of seminal plasma proteins.

PSII-38 The effect of clitoral stimulation post fixed-time insemination in Bos indicus beef cattle

Abstract The objective of this experiment was to evaluate the effect of clitoral stimulation post-insemination on pregnancy rates in Bos indicus beef cattle. A total of 1186 multiparous Nelore cows were assigned to an estradiol-based estrus synchronization + timed-AI protocol (FTAI, d 0), and randomly assigned to receive either 2 to 5 seconds of clitoral stimulation or no clitoral stimulation after artificial insemination. Estrus expression prior to AI was evaluated based on patch activation (estrus, ≥ 50% activated; no estrus, &amp;lt; 50% activated) using Estrotect Heat Detector and chute exit velocity after AI was evaluated. Individual exit score was calculated within each group by dividing exit velocity into quintiles and assigning cows with a score from 1 to 5 (1 = slowest; 5 = fastest). Artificial insemination was performed by 7 different technicians. Pregnancy diagnosis was performed 30 days after FTAI via transrectal ultrasonography. Overall pregnancy rate at day 30 was 46.0% (545/1186). Clitoral stimulation had no beneficial effect (P = 0.42) on pregnancy rate of multiparous cows when compared to those not stimulated (47.5% ± 4.6 vs. 44.3% ± 4.6). Cows that expressed heat at d 0 (n = 602) had a greater (P &amp;lt; 0.01) pregnancy rate compared to no heat expression (37.6% ± 4.7 vs. 60.6% ± 4.6), but no effect of the clitoral stimulation was observed on pregnancy rate in cows that did or did not express heat (P &amp;gt; 0.05). Furthermore, clitoral stimulation did not affect exit score (P = 0.67) of cows after FTAI. No effect of the technician was observed on pregnancy rate when clitoral stimulation was applied or not (P = 0.21). In summary, clitoral stimulation was not a useful managerial tool to improve pregnancy rate in multiparous Bos indicus cows submitted to FTAI using estradiol-based protocols.

172 Effect of period of insertion of a progesterone-releasing device and pro-oestrus length on follicular and luteal characteristics and pregnancy rates to fixed-time AI in Bos indicus heifers

An experiment was designed to evaluate the effect of the length of insertion of a progesterone (P4)-releasing device and the length of pro-oestrus on follicular and luteal characteristics and pregnancy rates to AI (P/AI) in Bos indicus heifers treated with oestradiol/P4-based treatments. Bos indicus beef heifers (n=374), 22-26 months of age, with a corpus luteum (CL) or at least one follicle ≥8mm in diameter and with a body condition score between 2.5 and 3.5 (1-to-5 scale) were synchronised using three treatments for fixed-time AI (FTAI). On Day 0, all heifers received 2mg of oestradiol benzoate (Sincrodiol, Ourofino) and an intravaginal device with 1g of P4 (Sincrogest, Ourofino). The P4 device was removed on Day 6 in heifers in the J-Synch 6 group (n=120) and on Day 7 in heifers in the J-Synch 7 group (n=105) and conventional group (n=165). All heifers received 500μg of cloprostenol (Sincrocio, Ourofino) and 300IU of equine chorionic gonadotrophin (SincroeCG 6000UI, Ourofino) at the time of P4 device removal. Furthermore, heifers in the conventional treatment group received 0.5mg of oestradiol cypionate (SincroCP, Ourofino) at the same time. In addition, all heifers were tail-painted for oestrus detection (CeloTest, Biotay). Heifers that had lost ≥50% of the tail paint by 70-74h (J-Synch groups) or 48-52h (conventional group) after device removal were FTAI at that time. Heifers not showing oestrus by 70-74h (J-Synch groups) or 48-52h (conventional group) received 10μg of gonadotrophin-releasing hormone (Sincroforte, Ourofino) at the same time and were FTAI 8h later. All heifers were also examined using ultrasonography (Mindray DP50 Vet) every 12h from the time of device removal to determine the time of ovulation, 6 days after ovulation to determine the diameter of the CL, and 28 days after FTAI for P/AI determination. Data were analysed using the MLGM procedure (InfoStat) for normal data families (follicular dynamics) and binary data family (P/AI). The results are shown in Table 1. The diameter of the dominant preovulatory follicle and the CL did not differ among groups (P&amp;gt;0.12). However, the interval from device removal to ovulation was longer in heifers in the J-Synch groups than in heifers in the conventional group (P&amp;lt;0.05). Furthermore, P/AI was not different among groups. In conclusion, although the J-Synch protocols delayed the interval from P4 device removal to ovulation, the three protocols evaluated in the present study were equally effective in Bos indicus heifers. Table 1.Mean (±s.e.m.) diameter of the preovulatory follicle (P/Foll) and corpus luteum (CL), interval from progesterone (P4) device removal to ovulation, and pregnancy rates to AI (P/AI) in Bos indicus heifers Treatment P/Foll, mm Interval to ovulation, h CL diameter, mm P/AI,% (n) J-Synch 6 10.5±0.7 101.4±2.3a 18.6±1.0 52.0 (62/120) J-Synch 7 10.6±0.7 96.0±2.2a 16.5±0.9 39.0 (41/105) Conventional 9.4±0.7 73.0±1.9b 16.8±0.9 45.0 (74/165) a,bDifferent superscripts denote differences between groups in the interval from P4 device removal to ovulation.

170 Embryonic loss and pregnancy rate in response to resynchronisation using oestradiol benzoate or injectable progesterone at 14 days after timed AI in Bos taurus×Bos indicus beef heifers

The effect of the exposure of pregnant cattle to oestradiol benzoate (EB) or injectable long-acting progesterone (iP4), as well as their use for early resynchronisation of non-pregnant (NP) females within the second week after timed AI (TAI), is yet to be assessed. This study aimed to assess the pregnancy rate and embryonic loss of cross-bred Bos taurus×Bos indicus beef heifers in response to an EB- or iP4-based resynchronisation strategy implemented 14 days after the first TAI. A total of 677 cyclic heifers (Braford and Brangus; 24 months old) were subjected to an EB/P4 synchronisation protocol for the first TAI (Day 0=TAI). On Day 14, all heifers received a new P4 intravaginal device (1g, Sincrogest, Ourofino Saúde Animal) and were randomly assigned to two groups: EB (1mg intramuscularly, Sincrodiol; n=339) or iP4 (75 mg intramuscularly, Sincrogest Injetável; n=338). On Day 22, P4 devices were removed and heifers underwent colour Doppler ultrasonography evaluation. Non-pregnant females were identified by the assessment of structural regression of the corpus luteum, as previously reported by our group. On Day 22, NP heifers received 1mg of oestradiol cipionate (SincroCP), 250µg of sodium cloprostenol (Sincrocio), and 200IU of equine chorionic gonadotrophin (SincroeCG), and they were inseminated on Day 24. On Day 22, the diameter of the preovulatory follicle (POF) was also recorded. Pregnancy was diagnosed via B-mode ultrasonography on Days 35-40 and 54. Statistical analyses were performed using SAS software (ver. 9.2, SAS Institute Inc.). The MIXED procedure was used to evaluate the POF diameter, and the GLIMMIX procedure was used to develop a multivariate model including treatment, breed, age, farm (1-7), and possible interactions of treatment with farm, breed, and age to evaluate the binomial data (pregnancy rates and embryonic loss). In NP heifers, the diameter of the POF on Day 22 did not differ (P&amp;gt;0.05) between the EB (9.77±0.25mm) and iP4 (9.92±0.22 mm) groups. Exposure to EB or iP4 on Day 14 post-TAI did not influence pregnancy rates as assessed on Day 22 (56.3% (191/339) vs. 60.1% (203/338)) and on Days 35-40 (49.6% (168/339) vs. 53.3% (180/338)). In addition, embryonic loss between Days 22 and 35-40 was not different between the EB (12%, 23/191) and iP4 (11.3%, 23/203) groups. On the other hand, pregnancy rates in heifers submitted to the second TAI were greater (P=0.01) in the EB group (45.95%, 68/148) than in the iP4 group (31.85%, 43/135). In conclusion, improved pregnancy rates can be achieved using 1mg of EB associated with a P4 intravaginal device on Day 14 of the resynchronisation protocol without affecting the first TAI pregnancy rates and embryonic loss. However, further investigation is warranted to assess the lower pregnancy rates obtained in response to the association of iP4 and P4 device. This research was supported by FAPESP (2015/10606-9; 2019/15514-6), Graduate Studies Support Program (PAPG-UNIPAMPA), and Ourofino Saúde Animal.

Effects of monensin source on in vitro rumen fermentation characteristics and performance of Bos indicus beef bulls offered a high-concentrate diet.

In Exp. 1, Brachiaria ruziziensis (11.1 % CP) was inoculated or not with two sources of monensin, resulting in three treatments: 1) no monensin inoculation (CONT), 2) 20 mg of monensin sodium-A/kg of DM (Elanco Animal Health; MON-A), and 3) 20 mg of monensin sodium-B/kg of DM (Shandong Qilu King-Phar Pharmaceutical Co. Ltd.; MON-B). Three rumen-fistulated Jersey steers were offered a cool-season forage-based diet and were used as the rumen inoculum donors. Volatile fatty acids concentrations were evaluated at 0, 6, 12, 24, 30, and 48 h after treatment inoculation. Overall, acetate and butyrate concentrations were reduced in MON-A vs. CONT (P ≤ 0.02), whereas both monensin products reduced Ac:Pr ratio vs. CONT (P ≤ 0.01); however, MON-A also (P = 0.05) reduced the Ac:Pr ratio vs. MON-B. A treatment × hour interaction was detected for rumen propionate concentration (P = 0.01), primarily because MON-A resulted in greater propionate than CONT and MON-B at 24 and 48 h (P ≤ 0.03), but no differences were observed between CONT vs. MON-B (P ≥ 0.27). In Exp. 2, 240 Nellore bulls (initial BW = 363.2 ± 40.9 kg) were ranked and blocked according to initial BW, and within blocks animals were allotted into pens (n = 10 pens/treatment). Pens were randomly assigned into one of three treatments: 1) corn-based diet with no monensin (CONT), 2) CONT plus 28 mg of MON-A/kg of DM, and 3) CONT plus 28 mg of MON-B/kg of DM. The CONT diet was composed of sugarcane bagasse, ground corn, DDGS, urea, and a mineral-vitamin mix. The experimental period lasted 106 d and was divided into a 21-d adaptation period and an 85-d finishing phase. During the adaptation phase, both monensin sources increased (P ≤ 0.01) BW change, ADG, and F:G, as well as reduced DMI variation (P = 0.02). When the entire experimental period was evaluated, no treatment effects were detected for final BW, DMI, and ADG (P ≥ 0.26). Nonetheless, DMI variation was reduced as monensin was included (P = 0.01) and only MON-A improved the efficiency by reducing F:G vs. CONT (P = 0.05) and biological efficiency vs. MON-B (P = 0.05). Additionally, carcass ADG tended (P = 0.10) to be greater for MON-A vs. MON-B, whereas no other differences in the carcass characteristics were observed (P ≥ 0.53). In summary, the source of monensin inoculated in vitro and offered to Nellore bulls during the feedlot phase significantly affected the energetic efficiency and the performance of the animals.

Relationships between antral follicle count, body condition, and pregnancy rates after timed-AI in Bos indicus cattle

An experiment was performed to evaluate the association between the antral follicle count (AFC) plus body condition score (BCS) and the pregnancy rate in Bos indicus undergoing timed artificial insemination (TAI). A total of 736 Nelore cows with BCSs ranging from 2 to 4 received a conventional protocol for TAI. On a random day of the estrous cycle (Day 0), all cows received an intravaginal P4 device and an intramuscular (i.m.) injection of 2.0 mg estradiol benzoate. On Day 8, the P4 device was removed, and 150 μg sodium D-cloprostenol, 300 IU equine chorionic gonadotrophin and 1.0 mg estradiol cypionate were administered by i.m. injection. TAI was performed 48 h after P4 device removal, and pregnancy diagnosis was performed by ultrasonography after 30 days. On Day 0, all cows were examined by ultrasonography to determine the AFC by counting the number of follicles >3 mm in diameter that were present in both ovaries and to evaluate the BCS (scale of 1–5). The cows were then classified based on their AFCs as those with low (≤10 follicles), intermediate (11–29 follicles) and high AFC (≥30 follicles). Furthermore, cows were classified as having low (≥2.0 to ≤ 2.9) and high (≥3.0 to ≤ 4.0) BCSs. The AFCs and BCSs were analyzed using the generalized linear model, and the pregnancy rate was assessed with the binary logistic regression model (P ≤ 0.05). The pregnancy rate was influenced (P < 0.05) by AFC and BCS classification and by interactions (P = 0.034) between these factors. Cows with a low AFC exhibited higher a pregnancy rate than did cows with a high or an intermediate AFC (57.7% a, 47.9% b and 49.7% b, P = 0.008). Low BCS resulted in a higher pregnancy rate than did high BCS (55.2% vs. 50.4%, P = 0.008). Cows with a high BCS and a low AFC had a higher pregnancy rate (P < 0.05) than did those with a high BCS and an intermediate or a high AFC (59.8%a, 48.0%b, and 38.0%b, respectively). An interaction (P < 0.05) was observed between the AFC and BCS, and the pregnancy rate decreased significantly in cows with an AFC > 30 and a BCS between 3 and 4. In conclusion, AFC and BCS classifications influence the pregnancy rate of Bos indicus beef cattle subjected to TAI. In addition, an important interaction between these factors was observed, namely, the lowest pregnancy rates were found in cows with high BCSs and high AFCs.

Effects of dietary roughage neutral detergent fiber levels and flint corn processing method on growth performance, carcass characteristics, feeding behavior, and rumen morphometrics of Bos indicus cattle1

Flint corn processing method [coarse ground corn (CGC; 3.2 mm average particle size) or steam-flaked corn (SFC; 0.360 kg/L flake density)] was evaluated in conjunction with 4 levels of NDF from sugarcane bagasse (SCB) as roughage source (RNDF; 4%, 7%, 10%, and 13%; DM basis) to determine impact on growth performance, carcass characteristics, starch utilization, feeding behavior, and rumen morphometrics of Bos indicus beef cattle. Two hundred and forty Nellore bulls were blocked by initial BW (350 ± 37 kg), assigned to 32 feedlot pens and pens within weight block were randomly assigned, in a 2 × 4 factorial arrangement (2 corn processing and 4 levels of RNDF) to treatments. Effects of corn grain processing × RNDF level were not detected (P ≥ 0.14) for growth performance, dietary net energy concentration, carcass traits, rumen morphometrics, and feeding behavior, except for time spent ruminating and time spent resting (P ≤ 0.04), and a tendency for papillae width (P ≤ 0.09). Bulls fed SFC-based diets consumed 7% less (P = 0.001), had 10.6% greater carcass-adjusted ADG (P < 0.001) and 19% greater carcass-adjusted feed efficiency (P < 0.001) compared with bulls fed CGC-based diets. Observed net energy for maintenance and gain values were 14.9% and 19.4% greater (P < 0.001), respectively, for SFC than for CGC-based diets. Fecal starch concentration was less (P < 0.001) for bulls fed SFC compared with those fed CGC. No grain processing effects were detected (P = 0.51) for rumenitis score; however, cattle fed SFC presented smaller ruminal absorptive surface area (P = 0.03). Dry matter intake increased linearly (P = 0.02) and carcass-adjusted feed efficiency tended (P = 0.06) to decrease linearly as RNDF increased. Dietary RNDF concentration did not affect carcass characteristics (P ≥ 0.19), except for dressing percentage, which tended to decrease linearly (P = 0.06) as RNDF in finishing diets increased. Increasing RNDF in finishing diets had no effect (P = 0.26) on time spent eating, but time spent ruminating and resting increased linearly (min/d; P < 0.001) with increased dietary RNDF. Steam flaking markedly increased flint corn energy value, net energy of diets, and animal growth performance, and led to improvements on feed efficiency when compared with grinding, regardless of RNDF content of diets. Increasing dietary RNDF compromised feedlot cattle feed efficiency and carcass dressing.