J.H. Britt

Effect of retinol palmitate on ovulation rate and embryo quality in superovulated cattle

Abstract We evaluated the influence of administration of retinol palmitate (Vitamin A) on ovulation rate and embryo quality in 48 beef cows superovulated with 2 different doses of FSH. Synchronization of estrus was accomplished by giving 2 injections of prostaglandin F 2α (PGF) 11 d apart. Multiple ovulation was induced by giving a total of either 32.5 mg or 27 mg of FSH over 4 d beginning on the 8th to 10th d post estrus. Within FSH dose, cows received either 1 million IU of Vitamin A (im) in corn oil or an equivalent volume of corn oil alone on the 1st d of FSH injections. Embryos were recovered nonsurgically and evaluated 7 d post estrus. Ovulation rate was estimated on the day of embryo recovery by use of transrectal ultrasonography and actual counts of corpora lutea were made on ovaries taken at slaughter following embryo recovery. The FSH response rate (percentage of cows with multiple ovulations) for all cows was 65.9% and was not affected by FSH dose or Vitamin A. Cows with less than 20 ovulations had a higher percentage of total embryos recovered (59.6 vs 35.8%; P = 0.002), and more of those embryos were transferable (36.2 vs 14.3%; P = 0.005) compared to cows with more than 20 ovulations. The dose of FSH did not affect embryo quality or the total number of embryos recovered, but the lower dosage resulted in more ovulations per cow (26.7 vs 18.0; P = 0.03). Vitamin A did not affect ovulation rate or total embryos recovered, but it increased the mean number of high quality (Grades 1 and 2; 4.25 vs 1.86; P = 0.01) and total transferable embryos (Grades 1, 2 and 3; 5.87 vs 3.13; P = 0.04). The mean number of blastocysts was greater for Vitamin A-treated cows (2.25 vs .73; P = 0.02). Means for nontransferable embryos were not different between FSH dose or Vitamin A treatment groups. These findings suggest that 1) ovulation rates above 20 per cow do not yield gains in total or transferable embryos, and 2) Vitamin A may improve embryo quality without affecting ovulation rate in superovulated cattle.

Agreement among evaluators of bovine embryos produced in vivo or in vitro

Six experienced individuals evaluated 40 embryos on videotape for stage of development and quality grade. These 40 observations comprised 15 embryos produced in vivo, 15 embryos produced in vitro, and 10 embryos that were repeated throughout the videotape. Embryos produced in vivo were recovered from uterine flushings of superovulated heifers 7 d after estrus, and embryos produced in vitro were harvested 7 d after insemination of in vitro-matured oocytes. Embryos of various stages (morulae, blastocysts, or degenerated) and quality grades (1 = excellent, 2 = good, 3 = fair, 4 = degenerated) were recorded on videotape for evaluation. After video microscopy, the embryos were stained and the number of nuclei per embryo was counted. Six evaluators reviewed the videotape and the percentage of agreement and kappa (k; agreement beyond chance) among evaluators were determined for classifications of stage and grade. Consistency of each evaluators responses was estimated using the 10 repeated embryos. Agreement within evaluators was higher for stage of embryo development (89.2%) than quality grade (68.5%). Agreement among evaluators for stage was slightly higher with embryos produced in vivo (85.0%, k = 0.74) than in vitro (72.3%, k = 0.48). Agreement among evaluators for grade was similar with embryos from in vivo (61.0%, k = 0.46) and in vitro (57.7%, k = 0.42) production. For both sources of embryos, agreement was substantially better for Grades 1 and 4 than for Grades 2 and 3. The results of this study suggest that good to excellent agreement exists for classifying Day 7 bovine embryos by stage and by extremes of quality grade (Grades 1 and 4) but not by degree of abnormal morphology (Grades 2 and 3). Simple grading criteria of Grade 1 (highest quality), Grade 2 (morphologic defects), and Grade 3 (degenerated) maximized agreement among evaluators.

Characterization of summer infertility of sows in large confinement units.

Data were from 3119 farrowings in three large swine confinement units in eastern North Carolina. Litters were weaned during April through October. Interval to first estrus after weaning was greater during June through September than during other months. The two-way interactions among farm unit, parity and month weaned all affected weaning-to-estrus interval. Conception rate at first estrus was lower for primiparous than for multiparous sows and declined from April through July. Conception rate at first estrus was affected by farm by parity interaction. Weaning-to-conception interval was longer for primiparous than multiparous sows and was longer during June through October. Weaning-to-conception interval was affected by interactions of unit with parity and unit with month weaned. Total pigs farrowed at the subsequent farrowing was affected by unit, parity, length of the previous lactation and the unit x parity interaction. Overall, reproductive performance varied among farm units, was lower in primiparous than in multiparous sows and was reduced during June through October.

Influence of season on estrous and luteinizing hormone responses to estradiol benzoate in ovariectomized sows.

The objective of this experiment was to determine whether seasonal differences existed in estrous and LH responses to estradiol benzoate (EB) in ovariectomized sows. Sows were ovariectomized after weaning their first litter, and treatment was begun 120 d after ovariectomy. Sows were given 400 mug EB intramuscularly (i.m.) on July 24, 1982 (summer), October 24, 1984 (fall), January 29, 1985 (winter), and March 27, 1985 (spring). Beginning 24 h after EB, sows were checked for estrus four times daily. Proportion in estrus was affected by season, with all sows exhibiting estrus within 5 d after EB in summer, winter, and spring. Only three of five sows exhibited estrus within 5 d after EB in fall. Interval (h) to estrus was delayed in fall (80 h) compared to other seasons (62.6 h; SEM = 4.5). Concentrations of LH were suppressed within 6 h after EB in all seasons but rebounded to pre-injection levels more slowly in fall and spring than in winter and summer. Frequency of LH peaks (3.2 +/- .4 4 h ) was not affected by season, but amplitude (1.9 vs 0.9 ng/ml) and baseline (2.7 vs 1.6 ng/ml) were greater (P < 0.05) for summer than for the other seasons combined. At 6 h after injection, concentrations of estradiol-17beta (pg/ml) were greater in summer (58.3) than in fall (19.0), winter (32.4), or spring (16.6; SEM = 10.4). We conclude that environmental factors associated with season alter responsiveness of the brain to estradiol, thereby controlling sexual behavior and LH secretion.

Fertility of dairy cattle treated with human chorionic gonadotropin (hCG) to stimulate progesterone secretion

Two experiments were conducted to determine if progesterone secretion and fertility would be affected by administration of human chorionic gonadotropin (hCG) before or after the first insemination. In Experiment 1, 48 Holstein heifers received 1000 IU of hCG or 1 ml of saline on Days 2, 3, and 4 of an estrous cycle. They were inseminated at the subsequent estrus. In Experiment 2, 110 Jersey and 105 Holstein cows received a single injection of 5000 IU of hCG or 5 ml of saline on Day 3 after estrus. These cows were first inseminated either at the estrus immediately preceding treatment or at the subsequent estrus. In both experiments, blood samples for determination of progesterone were collected thrice weekly for 3 to 4 wk following treatment. In Experiment 1, progesterone concentrations during mid-cycle were higher in hCG-treated heifers than in saline-treated controls. Treatment with hCG resulted in an 11% increase in the first service conception rate (P < 0.48). In Experiment 2, hCG-treated cows displayed higher progesterone secretion during mid-cycle than saline-treated herdmates. The conception rate of cows inseminated prior to hCG-treatment was not affected by treatment, but cows inseminated after treatment had a marginally lower fertility rate. The conception rate of cows receiving a repeat insemination following hCG treatment was higher than for the controls. We conclude that treatment with hCG did not improve the conception rate at the first insemination, but it may be beneficial for cows that require a repeat service.

Estimates of pregnancy outcomes based on selection of bovine embryos produced in vivo or in vitro

The objective of this study was to estimate the degree of variation among experienced evaluators selecting in vivo- or in vitro-produced embryos for transfer and to determine how this affects both the proportion of recipients becoming pregnant after transfer, and the number of embryo transfers required per pregnancy. Data from 6 experienced evaluators who graded Day 7 embryos produced either in vivo (n = 15) or in vitro (n = 15) were used to estimate these effects. The evaluators viewed video recorded images of the embryos and classified each embryo for stage of development and quality grade (1 = excellent, 2 = good, 3 = fair, 4 = degenerated and nontransferable). The statistical model considered transfer of embryos of the following individual or combined grades: Grade 1 only, Grade 2 only, Grade 3 only, Grades 1 and 2, Grades 2 and 3, and Grades 1, 2 and 3. Probabilities of pregnancy after embryo transfer were based on pregnancy rates of recipients at the facility of 1 of the 6 evaluators where the percentages of heifers pregnant after the transfer of Grade 1, 2 and 3 embryos, by embryo source, were 76, 65 and 54% (in vivo), and 59, 45 and 30% (in vitro). Within most grades, the proportion of embryos selected for transfer differed (P < 0.05) among the 6 evaluators. Although no significant differences (P > 0.10) were found among evaluators in the proportion of recipients pregnant after transfer within any embryo grade, there was substantial variation among evaluators in the proportion of recipients becoming pregnant, especially for embryos produced in vitro. Estimated percentages of heifers becoming pregnant for embryos classified as Grade 1, 2 or 3 were 66 to 76, 62 to 69, and 54 to 60%, respectively, for in vivo-produced embryos; and, 39 to 59, 15 to 45, and 24 to 32%, respectively, for in vitro-produced embryos. Approximately twice as many transfers were needed per pregnancy for embryos produced in vitro as for those produced in vivo regardless of the grade.

Absence of a nocturnal rise in either norepinephrine, N-acetyltransferase, hydroxyindole-O-methyltransferase or melatonin in the pineal gland of the domestic pig kept under natural environment photoperiods

Castrated male and intact female pigs were kept under natural photoperiodic and temperature conditions and were killed over a 24 h period in either May (under long days) or in December (under short days). Neither the pineal norepinephrine (NE) concentration nor the melatonin content rose at night; likewise, neither the activities of N-acetyltransferase (NAT) nor hydroxyindole-O-methyltransferase (HIOMT) increased during darkness. In May pineal melatonin content actually decreased (P less than 0.05) at night while in December NAT activity fell (P less than 0.05) at night. Daytime levels of each of these variables were equivalent to those measured in other species. The absence of a nocturnal increase in pineal melatonin production in either May or December raises the possibility that pineal melatonin may be involved in regulating seasonal breeding in the pig in a manner different from other mammals. Alternatively, pineal melatonin production may be unrelated to seasonal reproduction in the pig.

Luteinizing hormone, total estrogens and progesterone secretion during lactation and after weaning in sows

Abstract Two experiments were conducted to determine changes in serum concentrations of LH, total free estrogens and progesterone before and after weaning in sows. Blood was collected either via indwelling anterior vena cava cannula or by venipuncture and serum hormones were measured by radioimmunoassay. In Exp. I, blood was collected at 15-min intervals for 4 hr on day 7 and day 21 postpartum from three sows on each day. In addition, individual samples were collected from 10 sows on days 4 and 14 postpartum and from 11 sows on days 1, 3 and 5 after weaning (day 23 postpartum). Serum LH ranged from .2 to .8 ng/ml during lactation and averaged 1.1 ± .7, 1.1 ± .7 and 2.7 ± .7 on days 1, 3 and 5 after weaning, respectively. Progesterone was low ( In Exp. II, blood was collected from seven sows at 12 to 24 hr intervals from 2 days before until 5 days after weaning (day 26 postpartum). Mean serum LH was .7 ± .1 ng/ml during 48 hr before weaning and remained unchanged after weaning until day 3 when LH increased to 6.1 ± .8 ng/ml. Serum LH concentrations then declined to 1.3 ± .8 and .9 ± .8 ng/ml on days 4 and 5 after weaning. Total estrogens averaged 31 ± 4 pg/ml during 48 hr prior to weaning and 32 ± 4, 43 ± 17, 28 ± 1, 30 ± 2, 16 ± 2 and 18 ± 2 on days 0 to 5 after weaning. Progesterone increased from 1.0 ± .3 ng/ml 24 hr before weaning to 3.0 ± .3 at weaning and then remained low ( Results from these two experiments indicate that in sows: (1) LH is suppressed during early lactation (day 7), gradually increases during late lactation (day 21) and then reaches peak concentrations after weaning near the onset of estrus, (2) estrogens increase between weaning and estrus and decline thereafter, and (3) progesterone rises transiently at weaning and then increases after estrus and ovulation.

Associations among progesterone, estradiol-17β, oxytocin and prostaglandin in cattle treated with hCG during diestrus to extend corpus luteum function

Treatment of cattle during the middle of the luteal phase with appropriate doses of human chorionic gonadotropin (hCG) causes a 5 d extension of the estrous cycle. Three experiments were conducted to determine how treatment with hCG affected the pattern of secretion of prostaglandin F2 alpha, as indicated by blood levels of 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM). In experiment 1, Holstein cows were given saline (Sal) or hCG (10,000 IU, im) on d 10 of the estrous cycle and blood samples were collected over a 6 h period on d 14 and 18 during which oxytocin (10 and 100 IU, iv) was given at 2 and 4 h. Concentrations of PGFM before and after oxytocin were similar between Sal and hCG-cycles, but PGFM was higher on d 18 than d 14 (P less than 0.05). In experiment 2, episodic PGFM was measured from d 16 to 20 in cows given Sal or hCG on d 10. There was tendency for hCG to reduce PGFM baseline and pulse amplitude (P = 0.22). In experiments 1 and 2, estradiol increased during d 16 to 20 of Sal-cycles, but did not change during this period of hCG-cycles. Therefore, in experiment 3, Holstein heifers were given Sal or hCG (5000 IU, im) on d 10, followed by corn oil (Oil) or estradiol benzoate (EB; 200 micrograms, im, 2X/day) on d 15 to 18. No difference in progesterone secretion was observed between Sal-Oil and Sal-EB heifers; however, EB hastened luteolysis in hCG-treated heifers (P less than 0.05), without causing an increase in PGFM. Although subtle differences were seen in pulsatile PGFM, we conclude that hCG altered the pattern of estrogen secretion, and this led to delayed luteolysis.

Alteration of Activation, Growth, and Atresia of Bovine Preantral Follicles by Long-Term Treatment of Cows with Estradiol and Recombinant Bovine Somatotropin

Abstract The hypothesis was that long-term treatment of cattle with estradiol (E2) and bovine somatotropin (bST) would alter the earliest stages of folliculogenesis. Nonlactating Holstein cows (n = 26) were treated in a 2 × 2 arrangement with E2 (2 × 24 mg implants, 67.1 ± 1.4 days) and bST (Posilac, 63.6 ± 1.5 days). At Day 67 ± 1.3, one ovary was removed for morphometric and immunohistochemical analysis. For each ovary, 388 ± 38 microscopic fields (2 × 2 mm) were examined and follicles within each field were classified by histological stage. Fields that contained no follicles were classified as empty. Empty fields (n = 100 per ovary) were further classified as containing no evidence of follicles or containing atretic remnants of follicles. Approximately 30 4-μm sections per ovary were stained for proliferating cell nuclear antigen (PCNA), and 150 fields per ovary were evaluated. Additional sections (n = 10 per ovary) were assessed immunohistochemically for apoptosis, and fluorescence intensity was determined for each follicle. Treatment with bST significantly decreased percentage of empty fields containing atretic remnants. Treatment with E2 induced activation of follicles as shown by a decrease in percentage of primordial follicles and an increase in percentage of primary follicles as determined by PCNA staining. At the primary follicle stage the combination of bST + E2 decreased apoptosis as shown by decreased fluorescence intensity. Thus, E2 induced activation of follicles, bST enhanced survival, and the combination lowered atresia.