Breeding soundness evaluations of 3,648 yearling beef bulls using the 1993 Society for Theriogenology guidelines.

Our objective was to perform a retrospective analysis of breeding soundness evaluations (BSEs) as classified by the 1993 Society for Theriogenology (SFT) guidelines [Chenoweth et al., Guidelines for using the bull breeding soundness evaluation form, in: Theriogenology Handbook, 1993, pp. B-10]. Data included BSE information obtained from five performance-testing stations in South Carolina (SC1, SC2, SC3) and Tennessee (TN1, TN2) from 1986 through 1999 on 3648 Angus, Brangus, Charolais, Chianina, Gelbvieh, Limousin, Polled Hereford, Santa Gertrudis, Simbrah, and Simmental bulls. Analyses were simplified by classifying all bulls as either satisfactory or unsatisfactory potential breeders. Of the 3648 bulls evaluated, 76.2% were classified as satisfactory potential breeders. Of all bulls evaluated, 4.0% were unsatisfactory due to inadequate spermatozoal motility, 7.0% due to inadequate spermatozoal morphology and 2.6% due to a combination of inadequate motility and morphology. Unsatisfactory classifications due to non-spermatozoal parameters out of all bulls were 10.2%, with 7.1% for inadequate scrotal circumference and 3.1% for physical abnormalities. For satisfactory and unsatisfactory bulls, respectively, means and standard deviations were 35.8 +/- 2.7 and 33.0 +/- 4.1 cm (P < 0.001) for scrotal circumference, 63 +/- 18 and 35 +/- 24% (P < 0.001) for percent motility, and 86 +/- 7 and 63 +/- 21% (P < 0.001) for percent normal morphology.

Weight necessary to change body condition scores in Angus cow.

Weights and body condition scores (BCS) were measured and assessed on Angus females (n = 367) over 14 yr (1981 to 1994) to allow calculation of weight adjustments for different BCS. Data were collected at five time periods: prepartum, postpartum, prebreeding, postbreeding, and midgestation. Individual cows with multiple records were included in the analysis as repeated measures to yield 3,912 total observations. Body condition score was assigned on a scale of 1 = emaciated to 9 = obese. Only BCS 2 through 8 were analyzed, as there were zero recorded observations of BCS 1 or 9. The final model included age and the time period by BCS interaction as fixed effects. Year by animal within age interaction and a residual error term were treated as random effects. Animal was included to correct for repeated measures across time periods and years for individual animals. All these effects were significant (P < 0.0001). Weight adjustments for BCS were calculated for each time period. Cow weight and weight adjustments for BCS were not consistent for each time period. Overall weight adjustments to adjust cows to BCS of 5 were (kg +/- SEM) BCS = 2 (68 +/- 12), BCS = 3 (50 +/- 4), BCS = 4 (21 +/- 1), BCS = 5 (0), BCS = 6(-24 +/- 2), BCS = 7(-51 +/- 3), and BCS = 8 (-73 +/- 7).

Streptozocin-induced pancreatic islet destruction in beef cows.

Streptozocin (STZ) induces diabetes mellitus in sheep and pigs. To test the effect of STZ in cattle, cows were given 75-150 mg STZ per kilogram of body weight. Cows receiving 150 mg/kg required euthanasia within 24 hours after infusion because of the severe systemic effects of STZ. Seven cows receiving doses of < or = 100 mg/kg had mild to marked decrease in islet immunoreactivity for insulin and in pancreatic islet density and mild to severe tubulointerstitial nephritis. Two cows receiving 75 and 85 mg/kg STZ regained their ability to produce insulin and return blood glucose to basal levels. One cow given 100 mg/kg STZ developed insulin insufficiency consistent with type I diabetes mellitus. These findings demonstrate the susceptibility of the bovine pancreas to STZ: however, severe systemic complications were encountered. Alternative dosages and methodologies should be considered in future attempts to induce diabetes in cattle using STZ.

Estrus and pregnancy after synchrony with lutalyse in conjunction with Syncro-Mate-B.

Estrous response and pregnancy rates are decreased for cows given Syncro-Mate-B (SMB) during metestrus (Day 1 to 5 of an estrous cycle). Data indicate these decreases are due, in part, to retention of a functional corpus luteum (CL). Our objective was to determine whether PGF2alpha administered in conjunction with SMB would improve estrous response and pregnancy rates in metestrous cows with no detrimental effects to cows in other stages of the estrous cycle. Three hundred seventy-three suckled beef cows were observed for estrus for 21 d before SMB administration to determine stage of an estrous cycle. Blood samples were collected 14 and 7 d before treatment and at SMB administration. Serum was assayed for concentration of progesterone to verify stage of estrous cycle or noncyclicity. All cows received the standard SMB regime and were allotted by age and stage of cycle to one of two groups. Cows denoted SMB + L received 25 mg of PGF2alpha 8 d after implantation, whereas cows denoted SMB served as controls. On Day 10, SMB implants were removed and females were observed for subsequent estrus. At this time, calves were removed from their dams for 48 h. Artificial insemination was performed 12 hr after observation of a standing estrus. Timed insemination was performed at 48 hr after implant removal for cows not inseminated at 24 or 36 hr after implant removal. Interval to synchronized estrus (within 5 d of implant removal) was lengthened for metestrous cows compared to cows in other stages of the cycle irrespective of treatment (P < 0.001). Cows receiving PGF2alpha had a greater pregnancy rate at 5 d compared to controls (P = .0672). Interval to estrus, estrous response, and pregnancy rate to A1 at d 28 or end of breeding season were not affected by administration of PGF2alpha in conjunction with SMB when compared to the standard SMB protocol.

Outcomes of breeding soundness evaluation of 2898 yearling bulls subjected to different classification systems.

This study is a retrospective analysis comparing data on yearling bull breeding soundness evaluation (BSE) subjected to 3 different classification systems: the Society for Theriogenology (SFT) 1983 and 1993 systems, and the Western Canadian Association of Bovine Practitioners (WC) 1993 system. Data were collected at 5 performance bull-test stations located in South Carolina and Tennessee from 1986 through 1996. Yearling bulls (n=2898) that were 10 to 20 mo of age were used in the analysis. To simplify analysis, bulls were determined to be either satisfactory or unsatisfactory potential breeders (including those classified as questionable, deferred or unsatisfactory). Data were analyzed 1) within location where a location was treated as an individual experiment, 2) with breeds and locations collapsed, and 3) within age-group where each age-group was treated as an individual experiment. An ANOVA was performed using GLM procedures of SAS, and this model was used to generate least square means for the proportion of bulls classified as satisfactory and the 5 possible unsatisfactory outcomes due to inadequacies in scrotal circumference, spermatozoal morphology, spermatozoal motility, a combination of inadequate spermatozoal morphology and motility, or physical abnormalities. Inadequate scrotal circumference or physical abnormality did not affect differences for BSE outcomes among systems. Using the SFT93 system, bulls failed at a higher rate due to inadequate spermatozoal morphology (P < 0.05) than when subjected to the SFT83 system. In the WC93 system, a higher percentage of bulls failed due to inadequate spermatozoal motility and to a combination of inadequate spermatozoal morphology and motility than in the other 2 systems (P < 0.05). The proportion of bulls in this data failing under the WC93 system appears to be the result of overestimation.

Retention of a functional corpus luteum and peripheral concentrations of 13,14-dihydro-15-keto-prostaglandin F2alpha following metestrus administration of Syncro-Mate-B.

This study was conducted to examine the effects of metestrus administration of SyncroMate-B (SMB) on PGF2alpha secretion and corpus luteum (CL) development. In a study replicated over 2 yr, cows were observed for spontaneous estrus in yr 1, and cows received an injection of 25 mg of PGF2alpha and were observed for subsequent estrus in yr 2. At standing estrus (estrus = d 1), cows were randomly allotted to receive either the standard SMB regimen (n = 40) on d 3 of the estrous cycle or no treatment (n = 8). Fifty percent (n = 20) of SMB-treated cows were administered PGF2alpha on d 10 of the estrous cycle 48 h prior to implant removal. Twice-daily blood samples were collected in the morning (AM) and evening (PM) from d 2 AM through d 14 AM of the treated estrous cycle and subsequently analyzed for progesterone (P4) and PGF2alpha metabolite (PGFM). Prior to statistical analysis, SMB- and SMB/PGF2alpha-treated cows were sorted according to P4 concentration at d 10 of the treated estrous cycle to either a CL functional group (P4 > or = 1 ng/mL; n = 20) or a CL nonfunctional group (P4 < 1 ng/mL; n = 17). Following d 10 AM administration of PGF2alpha, functional and nonfunctional groups were further subdivided based on treatment. The groups were as follows: untreated control cows (n = 8); SMB-treated cows retaining a functional CL (SMB-F; n = 8); SMB-treated cows with a nonfunctional CL (SMB-N; n = 11); SMB/PGF2alpha-treated cows retaining a functional CL (SMB/PG-F; n = 12); and SMB/PGF2alpha-treated cows with a nonfunctional CL (SMB/PG-N; n = 6). Of all SMB-treated cows, 54% retained a functional CL through d 10 AM of the treated estrous cycle. Mean serum P4 concentrations increased for cows in all groups until d 7, after which P4 concentrations increased for cows in SMB/PG-F, SMB-F, and control groups and decreased for cows in SMB/PG-N and SMB-N groups. Following PGF2alpha administration on d 10, mean serum P4 concentrations remained < 1 ng/mL for cows in SMB/PG-N and SMB-N groups, decreased to < 1 ng/mL for cows in the SMB/ PG-F group, and remained > 1 ng/mL for cows in SMB-F and control groups. Mean serum PGFM concentrations tended (P = .06) to increase in cows with nonfunctional CL compared with control cows on d 8 AM and were greater (P < .05) in cows with functional CL on d 8 PM through d 9 PM. These results indicate that retention of a functional rather than a nonfunctional CL following metestrus administration of SMB is dependent on a premature release of uterine PGF2alpha.

Influence of prepartum body condition score change on reproduction in multiparous beef cows calving in moderate body condition.

Multiparous, spring-calving beef cows (n = 250) were used to determine whether large changes in body energy reserves during mid- to late gestation influenced subsequent reproductive performance of cows calving in moderate body condition. In three states, cows were blocked by BW and body condition score (BCS; 1 = emaciated to 9 = obese) then allotted to receive either a high or low plane of nutrition from late summer to early winter over a 3-yr period. This generated an array of BCS by the beginning of the last trimester of pregnancy when cows were grouped by BCS as follows: Group 1, BCS < or = 4; Group 2, BCS of 5 or 6; and Group 3, BCS > or = 7. Each group was managed so that individual cows would calve with a BCS of 5 to 6. At the time of group assignment, mean BW and BCS differed (P < .01) among groups and were 480 kg and 3.6, 541 kg and 5.5, and 594 kg and 7.1 for Groups 1 to 3, respectively. Within 28 d before calving, BW and BCS were similar (P > .20) among groups averaging 555 kg and 5.1. Prepartum BCS changes averaged 1.4, -.4, and -2.0 units for Groups 1 to 3, respectively (P < .01). Cows were managed as a single group after calving in each state. Location effect was significant for the prepartum and postpartum BW and BCS changes but not for postpartum reproductive performance. Significant location x BCS group interactions were found for the 90-d prepartum BW, BCS at calving, and prepartum changes in BW, but were caused by differences in magnitude among locations. The percentage of cows with luteal activity at the start of a subsequent breeding season was not affected (P > .20) by either location or BCS group, and averaged 66%. Mean pregnancy rates at 20, 40, and 60 d of a subsequent breeding season were 55, 76, and 89% for Group 1; 51, 67, and 82% for Group 2; and 64, 79, and 89% for Group 3 (P > .30). Mean days to conception were 89, 87, and 85 for Groups 1 to 3, respectively (P = .70). Neither calf birth weight (x = 38.6 kg) nor adjusted 205-d weight (x = 223.6 kg) were affected by prepartum BW and BCS changes. We conclude that reproductive performance of cows calving in moderate body condition is not influenced by large changes in body energy reserves during the last trimester of pregnancy.

Body condition at parturition and postpartum weight gain influence luteal activity and concentrations of glucose, insulin, and nonesterified fatty acids in plasma of primiparous beef cows.

Effects of body condition score (BCS) at parturition and postpartum weight gain on luteal activity and concentrations of glucose, insulin, and NEFA in plasma were evaluated during the breeding season in 242 primiparous beef cows over 3 yr (Y) at three locations (L). At approximately 90 d prepartum, cows were blocked by breed, expected calving date, and BCS and randomly assigned to diets so that cows would calve in BCS of 4, 5, or 6. At calving, cows were blocked by breed, calving date, and BCS and randomly allotted to gain .45 (M) or .90 (H) kg/d, from parturition to the start of breeding (postpartum nutrition; PPN). During the 60-d breeding season, weekly blood samples were obtained from cows, and progesterone, insulin, glucose, and NEFA were quantified. Progesterone concentrations greater than 1 ng/mL for more than 1 wk indicated luteal activity. To determine the possible value of blood constituents as predictors of luteal activity, categorical data analyses were performed. Cows with greater BCS at parturition had greater concentrations of glucose during breeding (P < .07). Similarly, PPN influenced glucose at the beginning of breeding, but the differences were minimal after d 28 (PPN x day; P <.001). Cows with greater BCS at parturition and M-PPN had greater concentrations of insulin during the breeding season (BCS x PPN; P < .02). Cows with a BCS of 6 at parturition had the lowest concentrations of NEFA; however, cows on H-PPN had greater concentrations of NEFA (BCS x PPN; P < .03). Location, BCS, PPN, and day affected luteal activity (P < .002). Location differences in luteal activity were associated with the interval from calving to the start of breeding. In general, a greater percentage of cows with BCS of 5 or 6 at calving had luteal activity by the end of the breeding season. Concentrations of metabolites in blood during breeding were not predictive of luteal activity. We conclude that BCS at parturition and postpartum nutrition influence concentrations of glucose, insulin, and NEFA in blood and the onset of luteal activity in primiparous beef cows.

A retrospective analysis of factors contributing to calf mortality and dystocia in beef cattle.

Records of 2191 calvings from the Clemson University Beef Physiology Unit between 1981 and 1993 were analyzed to determine factors affecting malpresentation, mortality and dystocia. Only 20 (0.91%) parturitions involved malpresentation: posterior presentation (n = 14), leg deviations (n = 3), head deviations (n = 2) and breech birth (n = 1). Dystocia affected calf mortality within 24 h of birth (P < 0.05), with mortality increasing as the severity of dystocia increased. There was an overall 4.5% death loss within 24 h of birth, with 4 and 7% mortality rates for calves from multiparous and primiparous dams, respectively (P < 0.05). Mortality was higher for bull vs heifer calves (P < 0.05). Ninety-four percent of calvings were unassisted, while 6% were assisted births. Dystocia was greater (P < 0.01) in primiparous (17%) than in multiparous dams (4%). In births involving dystocia, 28.1% required mild traction, 69.3% required heavy traction and 2.6% required Cesarean section. Birth weights associated with normal births and mild traction (36 and 36 kg) were lighter than those associated with heavy traction and Cesarean section (40 and 42 kg, respectively; P < 0.05). In conclusion, malpresentations were too few to be of significance, and dystocia influenced mortality within 24 h of birth. Calf birth weight and parity of dam explained most of the observed variations in dystocia.

Serum testosterone concentration, efficiency of estrus detection and libido expression in androgenized beef cows.

Twenty multiparous, cyclic, nonlactating beef cows were blocked by dominance rank and randomly and equally allotted to 1 of 4 treatment groups: an untreated control group, a synovex-treated group which received 8 Synovex-H implants with no additional hormones, a testosterone-treated group which received 500 mg, i.m. and 1500 mg, s.c. testosterone enanthate on Day 1 with additional 1000 mg, s.c. doses of testosterone enanthate every 14 d, and a synovex + testosterone-treated group which received 8 Synovex-H implants with 500 mg, i.m. and 1500 mg, s.c. testosterone enanthate on Day 1 only. Blood samples were collected via jugular venipuncture once a week beginning 3 wk prior to start of treatment. In addition, samples were collected just prior to treatment; once a day for 1 wk after initiation of treatment; and then twice a week until 225 d after treatment. Efficiency of estrus detection was assessed 22 d prior to start of treatment and every 14 d thereafter for 98 d, using estrus detection trials with synchronized females or modified libido tests. Scores for estrus detection trials included total mounts in 1 h and the percentage of estrous cows detected. Libido was scored on a scale of 0 through 6. All testosterone treatments raised plasma testosterone concentrations above control and pretreatment levels (testosterone and synovex + testosterone > synovex > control; all P < 0.05). Synovex-, testosterone- and synovex + testosterone-treated females performed more mounts in 1 h than the controls (18, 9, 6 and 1, respectively; all P < 0.05). All testosterone-treated cows mounted a higher number of estrous females than the controls (P < 0.05). Only synovex + testosterone- and testosterone-treated cows received libido scores above pretreatment and control values. However, libido of testosterone-treated cows decreased over time, while that of synovex + testosterone-treated females remained high until Day 98. Libido scores correlated positively with the number of mounts in 1 h and the percentage of estrous females detected (0.70 and 0.44, respectively), and the correlation coefficient for these two factors was 0.63. In conclusion, the synovex + testosterone treatment was most effective for producing estrus detector females and libido testing was useful for evaluating sexual activity in androgenized females.

Comparative effects of early weaning or once-daily suckling on occurrence of postpartum estrus in primiparous beef cows.

We concurrently evaluated early weaning and once-daily suckling as options for shortening postpartum interval to estrus in primiparous cows calving in good body condition. Over 2 consecutive years, a total of 77 primiparous cows were assigned to 1 of 3 treatments: control (ad libitum suckling); once-daily suckling (for 30 d prior to start of breeding); or early weaning (calves weaned 30 d prior to start of breeding). All cows had a body condition score (BCS) of > or = 5 at parturition and were maintained in good condition throughout the breeding season. Cows were observed for estrus twice daily and blood samples for subsequent measurement of progesterone were collected at 48-h intervals. For data analysis, cows were divided into early- (> or = 85 d post partum) and late-calving (< 85 d post partum) groups at the onset of the breeding season. All calves were weighed at birth, at the onset of treatment, at weekly intervals until the start of the breeding season, and within 45 d of 205 d of age. Early weaning or once-daily suckling shortened the postpartum interval to first estrus of late-calving primiparous cows by 17 (P < 0.01) and 12 d (P < 0.08), respectively, compared with control group cows. However, among early-calving cows, neither early weaning nor once-daily suckling influenced the postpartum interval. Postpartum intervals of once-daily suckled cows and early-weaned cows were similar (P > 0.10).

The new Society for Theriogenology breeding soundness evaluation system.

In 1993, The Society for Theriogenology published revised standards for breeding soundness evaluation of bulls. These revised standards replaced the old semen score format with minimum acceptable scores for scrotal circumference (varies with age), motility (30% or fair), and morphology (70%).

Breeding soundness evaluation of yearling bulls.

Breeding Soundness Evaluations (BSEs) are a useful tool to improve reproductive performance and profitability in beef herds. Veterinarians providing this service must be thorough in their evaluation, especially in yearling bulls. The 1993 Society for Theriogenology guidelines for BSE provide appropriate standards for classifying yearling bulls; veterinarians are advised to adhere to these standards as minimums for classification of the satisfactory potential breeder.

Effect of dietary energy restriction on follicular development and luteal function in nonlactating beef cows.

Twenty nonlactating beef cows were used to determine the effects of dietary energy restriction on ovarian follicular and corpus luteum (CL) development. Cows were fed to either gain (controls) or lose (restricted; RES) body weight. Observations continued until RES cows developed a subfunctional CL (progesterone [P4] < 1.5 ng/mL on d 10 of a cycle; n = 4) or had functional CL (P4 > or = 1.5 ng/mL on d 10 of a cycle; n = 6) followed by anestrus, at which time observations were discontinued on individual controls. Estrous cycles were then standardized for all cows. For RES cows developing subfunctional CL, cycle A was the cycle before development of the subfunctional CL, and cycle B was the 11-d period during development of a subfunctional CL. For RES cows with a functional CL, cycle A was the next to last cycle before anestrus, and cycle B was the 11-d period during formation of a functional CL. Daily P4 concentrations did not differ (P > .10) between controls or RES cows developing functional CL during cycle B but were lower (P < .05) in RES cows developing subfunctional CL. Ovulatory follicles and CL were smaller (P < .05) in RES cows during cycles A and B compared with controls. Daily IGF-l concentrations were higher on d 2 through 4 of both cycles in RES cows developing functional CL compared with RES cows developing subfunctional CL (P < .05). Feeding diets limited in energy resulted in two types of CL. These differences may have been due to IGF-I concentrations.

Methodology for adjusting scrotal circumference to 365 or 452 days of age and correlations of scrotal circumference with growth traits in beef bulls.

A retrospective analysis was conducted on data collected from 1983 through 1991, where weight and hip height were measured at start of test and every 28 d on 604 bulls completing a 224-d forage-based gain test. Scrotal circumference (SC) was measured at start of test, and at either end of test or end of the weigh period after individual bulls reached 365 d of age. Over 3 yr of this study, SC was additionally measured every 28 d. Bulls were representatives of 5 breed groups: Angus, Santa Gertrudis, Simmental, Continental (predominantly Charolais), and Zebu (predominantly Simbrah). Adjusted 365-d SC and adjusted 452-d SC were calculated by regression analysis and from formulas based on SC growth of individuals to 140 and 224 d on test, respectively. Breed group differences were observed for age of dam, birth weight, hip height, weight per day of age, average daily gain and SC at start of test, 140 d, and end of test (224 d). Scrotal circumference was positively correlated with all growth traits. Scrotal circumference was related to breed group, age, weight, hip height, average daily gain, weight per day of age, age by year, and age-by-breed group (P<0.05), as determined by regression analysis. However, omitting weight, hip height, average daily gain, and weight per day of age from the regression model did not significantly affect R2 value. Scrotal circumference growth was linear to 140 d on test; however, SC growth to 224 d on test was curvilinear. The 365-d SC predicted from the formula and from regression analysis differed for Simmental and Zebu by 0.3 and 0.4 cm, respectively (P<0.05). The 452-d SC differed for Santa Gertrudis and Zebu by 0.5 and 0.6 cm, respectively (P<0.05). Formulas based on SC growth of individuals are reasonably accurate predictors of SC at 365 and 452 d of age, when compared with more complex regression analysis. Basing SC adjustments on individual growth appears to account for variables known to affect yearling SC.

Reproductive responses and calf birth and weaning weights as affected by body condition at parturition and postpartum weight gain in primiparous beef cows.

Effects of body condition score (BCS) at parturition and postpartum weight gain on reproduction and production responses were evaluated using 240 primiparous (21 to 28 mo) beef cows calving in 60-d periods in three states over 3 yr. Cows were randomly allotted 90 d before parturition and fed to achieve BCS of 4, 5, or 6 (1 = emaciated, 9 = obese) at parturition. After parturition, one-half of these cows (within state) were group-fed to gain .45 kg/d (moderate) or .90 kg/d (high) until the start of a 60-d breeding season. Cows calving in BCS of 4, 5, or 6, respectively, had calves with progressively heavier (P < .05) birth weights, but dystocia score was not influenced by BCS at calving. Parturient BCS of cows had no effect on actual or 205-d adjusted weaning weights of calves. Birth weights, dystocia score, and actual and 205-d adjusted weaning weights were affected by location (P < .05). Cows with greater weight gains postpartum had calves with heavier (P < .05) actual and 205-d adjusted weaning weights than did cows with moderate weight gains. No significant interactions among location, BCS, or postpartum nutrition-group were observed for any of the production variables described above. Greater BCS at calving resulted in more (P < .05) cows in estrus and more (P < .05) cows pregnant by 40 and 60 d of a breeding season. Luteal activity by start of breeding, as well as estrus responses and pregnancy rates at 20, 40, or 60 d of a breeding season, were affected by location (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of dietary lipid supplementation on progesterone concentration and reproductive performance in suckled beef cows.

Using whole cottonseed as a lipid source, silage-based diets that were isocaloric and isonitrogenous yet varied in lipid level were fed to multiparous cows. In Experiment 1, 48 cows (n = 12 per treatment) were allotted to 1 of 4 treatments where diets were formulated to supply 3.9, 4.3, 5.3 and 6.3% of total lipid. In Experiment 2, 66 cows (n = 22 per treatment) were allotted to 1 of 3 treatments where diets were formulated to supply 3.1, 5.5 and 8.3% of total lipid. Length of the first ovarian cycle, length of the first normal estrous cycle, postpartum intervals to onset of ovarian luteal activity and to first estrus were not affected by diet (P>0.10) in either experiment. Mean progesterone (P(4)) concentrations for first normal estrous cycles were not different (P>0.10) in either experiment. Anestrous periods were divided into 3 phases for analyses: Phase I) parturition to onset of ovarian luteal activity, Phase II) first ovarian luteal activity and Phase III) first normal estrous cycle. No differences were observed in P(4) concentrations during any phase of the postpartum period. In conclusion, isocaloric and isonitrogenous diets with increasing levels of lipid had no effect on reproductive performance in suckled beef in these experiments.

Inhibition of estrus and corpora lutea function with Norgestomet.

Forty-five nonpregnant, nonlactating, Angus and Brangus cows were utilized to determine how long a Norgestomet ear implant would inhibit estrus when administered at various stages of an estrous cycle. All cows completed a nontreated estrous cycle to ensure normal cyclicity. At the second observed estrus (estrus = Day 1), cows were randomly allotted to be treated at metestrus (Day 3 or Day 4, n = 15); at diestrus (Day 9 or Day 10, n = 14); or at proestrus (Day 15 or Day 16, n = 16). All cows received a 2-ml intramuscular injection of 3 mg of Norgestomet accompanied by a 6-mg Norgestomet ear implant, which remained in situ for 21 days, or until individual cows were observed in estrus. Estrus was inhibited for a mean (+/- SEM) of 18.7 +/- 0.7, 19.9 +/- 0.8, and 17.0 +/- 0.8 days, respectively, when cows were treated at metestrus, diestrus, and proestrus (metestrus and diestrus vs proestrus; P < 0.05). Estrus was inhibited for an entire 21-day implantation period in 27, 50, and 38% of cows treated at metestrus, diestrus, and proestrus, respectively (P > 0.10). Norgestomet inhibited estrus in all cows for 11, 17, and 11 days after implantation when treatment was initiated at metestrus, diestrus, and proestrus, respectively (P > 0.10). These data indicate that a 6-mg Norgestomet ear implant effectively inhibits estrus in all cows for a maximum of 11 days, with some cows exhibiting estrus by Day 12 with the Norgestomet implant in situ.

Effects of metestrous administration of a norgestomet implant and injection of norgestomet and estradiol valerate on luteinizing hormone release and development and function of corpora lutea in suckled beef cows.

Sixteen suckled beef cows were used to determine effects of Syncro-Mate-B (SMB) on the development and function of corpora lutea (CL) and LH release. Twelve cows were treated 2 d after estrus with the standard SMB treatment regimen, a 6-mg Norgestomet ear implant (in situ 9 d) and a 2-mL i.m. injection of 3 mg of Norgestomet and 5 mg of estradiol valerate at time of implant insertion. Four cows served as untreated controls. In cows treated with SMB with subsequently nonfunctional CL (n = 5), mean concentrations of progesterone (P4) were lower on d 9, 12 (implant removal), and 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL (n = 7), mean concentrations of P4 were lower only on d 12 of the treated cycle than those in control cows (P < .01). In cows treated with SMB with subsequently nonfunctional CL, CL were smaller from d 9 through 14 of the treated cycle than in control cows or in those cows treated with SMB that developed functional CL (P < .01). In cows treated with SMB that developed functional CL, CL were smaller on d 9 and 11 of the treated cycle than in control cows (P < .01). Regardless of subsequent CL function, mean concentrations of LH and numbers of LH pulses were lower in cows treated with SMB than in control cows on d 3 and 4 of the treated cycle (P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Maintenance of pregnancy in postpartum beef cows that have short-lived corpora lutea.

The first two experiments examined the role of the uterus in low pregnancy rates of beef cows induced to ovulate by early weaning. At 20 to 25 d postpartum, one-half of the cows in Exp. 1 and 2 received a s.c. implant containing 6 mg of norgestomet (NOR) for 9 d (NOR-pretreated) and the remaining cows were untreated controls (CON). Lengths of first postpartum luteal phase after weaning of calves at d 7 after implant insertion were expected to be normal in NOR-pretreated and short in CON cows. In Exp. 1, cows of both groups received an implant containing 3 mg of NOR at d 4 after first estrus and a silastic implant with 15 or 25 mg of NOR at d 7 after first estrus. At 7 d after first estrus, two embryos were transferred into the uterus of each cow and pregnancy was diagnosed by ultrasonography at d 35. Blood samples were collected daily from onset of treatment to d 8 after estrus and then every other day to d 24. Only 4 of 22 cows were pregnant at d 35, concentrations of estradiol (E2) were elevated after luteolysis, and large follicles were present at d 35. In Exp. 2, all cows were injected with 100 mg of progesterone (P4) twice daily from d 4 to 35 after first estrus. Embryos were transferred, pregnancy was diagnosed, and blood samples were collected as in Exp. 1, except blood sampling was continued to d 34.(ABSTRACT TRUNCATED AT 250 WORDS)