R. W. Rorie

Endocrine factors and ovarian follicles are influenced by body condition and somatotropin in postpartum beef cows.

Multiparous beef (1/4 to 3/8 Bos indicus; n = 99) cows were managed to achieve low (BCS = 4.3 +/- 0.1; n = 50) or moderate (BCS = 6.1 +/- 0.1; n = 49) body condition (BC) to determine the influence of bovine (b) ST on the number of follicles, diameter of largest follicle, and serum concentrations of IGF-I, triiodothy-ronine (T3), thyroxine (T4), and prolactin. Beginning 32 d postpartum, cows within each BC were assigned randomly to treatment with or without bST. Non-bST-treated cows received no treatment, and treated cows were administered bST (Posilac, 500 mg, s.c.) on d 32, 46, and 60 postpartum. On d 60, all cows received a controlled internal drug-releasing (CIDR) device for 7 d and PGF(2alpha) at CIDR removal (CIDR-PGF(2alpha)). Blood samples (7 mL) were collected at each bST treatment and d 39 and 67 postpartum. Ultrasound was performed 1 d after CIDR-PGF(2alpha) to determine the number of small (2 to 9 mm) and large (>/=10 mm) follicles and the diameter of largest follicle. Cows treated with bST in low BC had increased (P < 0.05) IGF-I vs. low-BC non-bST-treated cows on d 39, 46, 60, and 67 postpartum. Prolactin and T3 were greater (P < 0.05) in moderate-BC than in low-BC cows on all sample dates. Thyroxine was greater (P < 0.001) in moderate-BC cows on d 46, 60, and 67 compared with low-BC cows. On d 67, bST-treated cows had greater (P < 0.05) T4 compared with non-bST-treated cows. Diameter of the largest follicle 1 d after CIDR-PGF(2alpha) was greater (P < 0.01) in anestrous cows treated with bST than for non-bST-treated anestrous cows. Diameter of the largest follicle was correlated with concentrations of IGF-I (r >/= 0.18; P </= 0.08), T3 (r >/= 0.17; P </= 0.10), and prolactin (r >/= 0.20; P </= 0.06). Treatment with bST increased IGF-I in low-BC cows, and IGF-I was correlated with the diameter of the largest follicle 1 d after CIDR-PGF(2alpha). Undernutrition of cattle may be communicated to the hypothalamic-pituitary-ovarian axis via metabolic hormones including IGF-I, thyroid hormones, or prolactin.

8 ANTI-MLLERIAN HORMONE AT WEANING AND BREEDING AS A PREDICTOR OF BEEF HEIFER FERTILITY

This study examined the relationship between serum anti-Müllerian hormone (AMH) concentration at weaning and breeding to determine if either or both measures could predict subsequent fertility of beef heifers. Blood was collected from 71 Angus based heifers at ~7 and 14 months of age and serum stored frozen (-20°C) until analysis for AMH, using bovine AMH ELISA kits (AL115; Ansh Laboratories, Webster, TX, USA). Before breeding, transrectal ultrasonography was used to determine cyclic status of heifers. Heifers received 25mg of prostaglandin F2α (PGF) and those detected in oestrus were AI ~12h after detected oestrus. Heifers not detected in oestrus after 7 days received a second PGF injection and oestrus detection and AI continued for 4 days. Ten days later, the heifers were exposed to fertile bulls for a 45-days breeding season. At 50 to 60 days after insemination, transrectal ultrasonography was used to identify pregnant heifers and to confirm conception date based on fetal size. At 60 days after bull removal, ultrasonography was performed to determine pregnancy in heifers conceiving during the breeding season and confirm continuing pregnancy in heifers previously identified as pregnant. Based on fetal size at ultrasonography, the oestrous cycle after initiation of breeding when conception occurred was estimated. For comparison, AI pregnancies were considered cycle 1, and pregnancies initiated during subsequent 21-day intervals of the breeding season were classified as cycles 2, 3, and 4, respectively. For analysis, frequency distribution was used to assign serum AMH concentration measured at weaning, breeding, and the change from weaning to breeding, into quartiles. Comparisons were then made via Chi-squared analysis for heifers in each quartile that were cyclic at synchronization, detected in oestrus, conceived after AI, pregnant at the end of the breeding season, and the estimated cycle that conception occurred. Comparison of heifers based on serum AMH quartiles at weaning failed (P ≥ 0.35) to detect any effect of AMH on subsequent heifer cyclicity at breeding, oestrous response after synchronization, AI conceptions, overall pregnancy rate, or estimated oestrous cycle of the breeding season when conception occurred. Based on AMH concentration at breeding, heifers in the lowest quartile (Q1) had a lower (10%; P=0.02) AI conception rate than heifers in other quartiles (43 to 73%), and conceived at a later oestrous cycle (P=0.03) in the breeding season. Comparison of heifers based on the change in AMH concentrations from weaning to breeding revealed that none of the heifers in the lowest quartile (Q1) conceived after AI, compared with 80% in the highest quartile (Q4; P<0.001). Heifers in the lowest quartile also conceived at a later oestrous cycle in the breeding season than heifers in the other quartiles (P=0.01). Results indicate that either AMH concentration at breeding or the change in AMH from weaning to breeding can identify beef heifers more likely to conceive to AI and to conceive early in the breeding season.

21 EVALUATION OF SEMEN EXTENDERS FOR SHORT-TERM STORAGE OF RAM SEMEN AT 4°C

Preliminary studies found that progressive motility of ram sperm declined ~75% when stored at 4°C for 24h, and continued to decline over time when using extenders supplemented with 5% egg yolk. The current study evaluated the effects of different combinations of extenders, ethylene glycol (EG), egg yolk, and penicillamine, hypotaurine, and epinephrine on ram sperm progressive motility during storage. Semen collected from 3 Katahdin and 2 Suffolk rams by electroejaculation was distributed across treatment combinations consisting of either TRIS citrate or milk extender supplemented with 5 or 20% (v/v) egg yolk,±1% ethylene glycol (EG) and±20µM penicillamine, 10µM hypotaurine and 2µM epinephrine (PHE). For each semen collection, TRIS citrate extender was prepared from a 4× solution so that the TRIS, citric acid and fructose concentration were constant at 300, 94.7, 27.8mM, respectively, regardless of semen dilution factor. A 4× milk extender was also used so that the extender contained 10% (w/v) milk powder, regardless of semen dilution factor. Both extenders were supplemented with 50µgmL-1 of gentamicin. Semen was diluted in extender to a final concentration of 300 million sperm/mL in 1.5-mL tubes, and cooled to 4°C over a 2- to 3-h period. Semen was evaluated initially and daily for 3 days, using computer-assisted sperm analysis. Repeated-measures data were analysed using the mixed model (JMP 12.0 software; SAS Institute Inc., Cary, NC, USA) for main effects of extender, supplements, and their interactions. Nonsignificant interactions were removed from the model before reanalysis. Data are presented as LSMeans±standard errors. Initially, sperm progressive motility averaged 41±6.2% across treatments. After an initial decline, overall progressive motility did not change (P>0.05) significantly (mean of 22.3±1.6 and 23.05±1.3% at 48 and 72h, respectively). Over time and across treatment combinations, mean progressive motility was maintained to a greater extent (P<0.01) by milk than TRIS-based extender (28.2±1.1v. 18.9±1.1%, respectively). Across extenders, progressive motility of sperm was similar (P=0.50) for 5 and 20% egg yolk (22.2±1.4v. 24.4±1.4). Addition of 1% EG increased (P<0.01) progressive motility (25.8±1.05v. 21.3±1.05). Addition of PHE also increased (P<0.01) progressive motility from 20.9±1.04 to 26.3±1.04%. There was an interaction between EG and% egg yolk, primarily due to an effect on sperm stored in TRIS citrate extender. Addition of 1% EG to extender containing 5% egg yolk improved (P<0.01) progressive motility from 18.5±1.5 to 26.9±1.5%). Addition of 1% EG to TRIS citrate extender also increased (P<0.05) progressive motility, from 14.6±1.5 to 23.2±1.5%. Results indicate that milk extender supplemented with 1% EG, PHE, and either 5 or 20% egg yolk is capable of maintaining progressive motility of ram semen at ~60% of its initial value when stored at 4°C for up to 72h. Additional studies are needed to evaluate pregnancy rate after insemination of ewes with stored semen.

331 DIRECT EFFECTS OF ERGOT ALKALOIDS ON BOVINE SPERM MOTILITY IN VITRO

Ergot alkaloids have been associated with decreased livestock reproductive rates. Concentration of alkaloids in the reproductive tract after consumption of toxic forage is unknown. In addition, the direct effects of alkaloids on bovine spermatozoa have not been determined. We investigated the direct and interactive effects of 3 ergot alkaloids (ergotamine, dihydroergotamine, and ergonovine) on motility of frozen–thawed bovine spermatozoa. Thawed spermatozoa from 3 bulls were pooled and washed using a Percoll density gradient. Sperm motility was visually estimated by counting at least 100 spermatozoa in each triplicate well (> 300 per treatment per replicate). The cell counting was conducted using phase contrast (400×) on an inverted bright field microscope. Spermatozoa were considered motile if they exhibited free progressive forward or other movement and were not attached to the well surface. Motile spermatozoa were exposed to alkaloids ranging in concentration from 0 to 100 µM. Assays were conducted in modified sperm-TL (mSPTL) medium at 39°C in moist air without CO2 for 6 to 12 h. The results showed that both ergotamine (ET) and dihydroergotamine (DHET) inhibited (P < 0.05) sperm motility at concentrations greater than 50 µM and 33.3 µM, respectively. Ergonovine (EN) did not inhibit sperm motility at the test concentrations. Inhibitory effects of alkaloids on sperm motility were concentration-dependent for ET and DHET incubations and time-dependent for DHET incubations. Sperm motility also was inhibited by an interaction (P < 0.05) between ET and DHET at concentrations of 16.7 µM or above. The medium pH affected the toxic effects of both ET and DHET, whereas the medium osmolarity affected only the toxic effect of ET on relative sperm motility (P < 0.05). Medium osmolarity of 358 mOsm and/or pH higher than 7.1 exacerbated the toxic effects of the alkaloids. These results demonstrate that ergot alkaloids can directly interact with spermatozoa and impair sperm motility. Herbivores consuming toxic tall fescue are exposed to a cocktail of ergot alkaloids. Alkaloid interactive effects coupled with altered cell chemistry, due to increased respiration rates and frequent urination, on spermatozoa may indicate the mechanism by which reproduction is impaired in animals consuming toxic forage.

Timed Insemination in Beef Heifers After Synchronization of Estrus with Controlled Intravaginal Drug Releasing Device and Melengestrol Acetate1

Two progestin estrous synchronization programs with timed AI (TAI) were used to compare effects on conception to TAI and overall pregnancy rates in beef heifers. Angus-cross heifers in two herds were sorted by age of heifers, body condition score (BCS), and BW then randomly assigned to a treatment. Treatments were 1) MPGG [melengestrol acetate (MGA®; Pfizer Animal Health, New York, NY) at 0.5 mg per head for 14 d followed by prostaglandin F2α (PGF2α) 17d after MGA® withdrawal and a gonadotropin-releasing hormone (GnRH) injection 48 h after PGF2α or 2) CIDR [a new controlled intravaginal drug-releasing (CIDR®) device inserted for 6 d with GnRH at CIDR insertion, PGF2α: at CIDR removal, and a second GnRH injection 48 h later. All heifers in both treatments were bred 18 h after the second GnRH injection.] Bulls were placed with heifers 10 d following TAI for approximately 50 d. Age of heifers, BCS, and BW in Herd 1, Herd 2, or the combined herds were not different (P≥0.25) between treatments. Across treatments, there was a difference between herds in BCS and BW (P<0.0001), but no difference in age of heifers (P=0.51). Conception rates (CR) and overall pregnancy rates (OP) were not different between herds, or between treatments in Herd 1, Herd 2, or in the combined groups (P≥0.40). The results in this study demonstrate similarities between MPGG and CIDR estrous synchronization protocols on conception rates to TAI and overall pregnancy rates in beef heifers.

Variation in the Percentage of Female Births over Time in Five Breeds of Registered Beef Cattle1

Breed and sire effects on the percentage of female births over time in five breeds of registered beef cattle were studied. Breed groups were managed separately, and matings were performed by artificial insemination and natural service. The percentage of female births was included in the study for sires that were used for at least 2 yr and sired at least seven progeny. Progeny of 48 Angus, 7 Charolais, 19 Horned Hereford, 17 Polled Hereford, and five Red Poll sires were used in the study. The numbers of birth years by breed were 33, 21, 31, 31, and 15 for Angus, Charolais, Horned Hereford, Polled Hereford and Red Poll, respectively. Variances for breed and sire were partitioned for percentage female births using a nested random effects analysis of variance. Breed effects for percentage of female births were 0.46% of total variance. Sire effects accounted for 0.27% of total variance. Means for percentage female births by breed were 50 ± 1% for Angus, 47 ± 3% for Charolais, 48 ± 2% for Horned Hereford, 52 ± 2% for Polled Hereford, and 49 ± 5% for Red Poll. Although sire variance was minimal, there were some sires that consistently produced a greater or lesser number of females over time. These results suggest that more research is needed to determine the factors that influence sex ratio in cattle due to its economic importance to the industry.

Growth, Luteal Activity, and Pregnancy Rates of Three Breed Types of Dairy Heifers in a Forage-Based Development Program

Growth, luteal activity, and pregnancy rates were evaluated in 89 dairy heifers raised as contemporaries. Breed types were Holstein (H, n = 35), Jersey x H (JH, n = 30), and Brown Swiss x H (BSH, n = 24); they ranged in age from 129 to 205 d at the beginning of the trial. Heifers grazed pasture and received grain supplementation to ensure 0.9 kg of daily BW gain. Hip height, chest depth, and BW were obtained monthly; BCS was recorded at ca. 14 mo of age. At ca. 12 mo of age, two blood samples for each heifer were collected (10 d apart) by jugular vein puncture for progesterone assay. Heifers were considered cycling if progesterone concentrations were > 1 ng/ mL in either of the two serum samples. Heifers were bred artificially (AI) on a synchronized estrus starting at 14 mo of age, and pregnancy status was determined ultrasonically 60 d after breeding. The BSH and H had similar (P>0.05) weights and hip heights; whereas JH were lighter and shorter (P 0.05) occurred for depth of chest and mean BCS. Estrus occurrence by 12 mo of age was greater (P<0.05) for JH (90%) than for BSH (75%) and lowest (P<0.05) for H (47%). Pregnancy rates did not differ (BSH = 96%, JH = 87%, H = 77%). These data suggest that genetic effects of crossbreeding influence early growth and cyclicity at 12 mo of age for replacement dairy heifers. Forage-based development of dairy heifers may be a suitable option to concentrate feeding for dairy producers in Arkansas and the Southern Region.