The aim of the present study was to test the hypothesis that elevated concentrations of progesterone (P4) resulting from the induction of an accessory corpus luteum (CL) by human chorionic gonadotrophin (hCG) administration on day 5 after oestrus would lead to advanced conceptus elongation on day 14 following embryo transfer on day 7. The oestrous cycles of cross-bred beef heifers were synchronised and animals were randomly assigned to receive either of two treatments: (1) intramuscular injection of 3000 IU hCG on day 5 after oestrus (n=14); or (2) intramuscular injection of saline on day 5 after oestrus (n=13). Ovaries were scanned daily by transrectal ultrasonography to assess CL development. Serum concentrations of P4 were determined from daily blood samples collected from the jugular vein. In vitro-produced bovine blastocysts were transferred to synchronised recipients on day 7 after oestrus (n=15 blastocysts per recipient). Heifers were killed on day 14 after oestrus and the uterus was flushed to recover the embryos. Injection of hCG on day 5 induced ovulation of the dominant follicle in all treated heifers and increased the total area of luteal tissue on the ovary, which was associated with a significant increase (P<0.001) in serum concentrations of P4 from day 7 to day 14. Positive associations were detected between circulating P4 with CL area (within-day correlations ranging from r=0.45 to r=0.67) and total area of luteal tissue (within-day correlations ranging from r=0.65 to r=0.86) Administration of hCG did not affect the proportion of day 14 conceptuses recovered. However, compared with the control group, hCG-treated heifers had increased conceptus length (3.91±1.23 vs. 5.57±1.02 mm, respectively; P=0.06), width (1.00±0.06 vs. 1.45±0.05 mm, respectively; P=0.002) and area (5.71±0.97 vs. 8.31±0.83, respectively; P=0.02). Although numerically greater, mean interferon-τ (IFNT) production in vitro did not differ significantly (P=0.54) between embryos recovered from hCG-treated and control heifers. In contrast, there was a strong positive correlation between individual embryo length (r=0.76; P<0.001) and individual embryo area (r=0.72; P<0.001) and IFNT production. In conclusion, administration of hCG on day 5 after oestrus resulted in the formation of an accessory CL and hypertrophy of the original CL, the result of which was an increase in P4 concentrations from day 7 onwards. These elevated P4 concentrations were associated with an increased conceptus area. Furthermore, conceptus size was highly correlated with IFNT secretion in vitro.

The aim of this study was to determine the relationship between observed estrous-related behavior, activity clusters (AC; detected by automatic activity monitor), endocrine profiles, and ovulation time. Twenty-one cows in estrus (after 2 cloprostenol treatments, 11 d apart) and 12 nonsynchronized cows, to establish Heatime (SCR Engineers Ltd., Netanya, Israel) herd baseline activity, were enrolled. Cows had Heatime monitors applied 3 wk before the trial to establish their own baseline activity level. Cows in standing estrus had ultrasonography and phlebotomy carried out every 4 h to determine dominant follicle size, endocrine profiles, and ovulation time. After ovulation, these procedures were repeated once on d 3 to 6. Heatime alerted estrus in 90% of cows, and incorrectly alerted 17% of AC. The mean±SEM duration for standing estrus was 9±1 and 13±1 h for estrous-related behavior. Estrous-related behavior began after the start of the proestrous estradiol-17β (E2) increase (59±6.5 h). Cows with longer durations of raised proestrous E2 had longer intervals from its onset to the start of standing estrus and AC. The AC duration increased with longer durations of estrous-related behavior. Higher peak E2 occurred with longer standing estrus and estrous-related behavior. As E2 concentration decreased after the peak, 90% of cows still had estrous-related behavior. Duration of estrous-related behavior increased with higher average E2 concentration during the last 8 h before the start of the LH surge. During this surge 90% of cows had all of their standing estrus. As yields increased, so did the magnitude of the preovulatory FSH surges. Higher surges occurred with shorter standing estrus and estrous-related behavior. Cows with shorter LH surges had longer standing estrus. Peak LH preceded the AC peak (6.6±0.8 h). Duration of overlap between the AC start and the LH surge end ranged between 0 and 14 h; 1 cow had none. No association was found between the AC characteristics with the E2, LH, or FSH profiles. In conclusion, the relationship between the timing of the E2 increase and estrous activity may be mediated by other factors (GnRH surge). Estrous-related behavior, but not endocrine profiles, was related to AC duration. Timing of standing estrus during the LH surge ensures that mating allows sperm maturation before ovulation. Based on the interval from the start of an AC to ovulation (27±1 h), the optimum time to artificial insemination is, on average, between 9 and 15 h after the AC start.

No abstract

This study investigated the factors affecting circulating progesterone (P4) concentrations in cows with similar genetic merit for milk production traits, but with extremes of good (Fert+) or poor (Fert-) genetic merit for fertility traits. Study 1: 28 cows were enrolled in an ovulation synchronization protocol at 61±13 (±standard deviation) days postpartum, and data are presented for 13 Fert+ and 9 Fert- cows that remained in the study. Progesterone concentrations were determined from d 0 to 9 (d 0=estrus) and on d 7, corpus luteum (CL) volume and blood flow area (BFA) were measured by B-mode and Doppler ultrasonography, respectively. Cows were administered PGF2α on d 7 in the p.m. and d 8 in the a.m. to regress the CL, and 2 controlled internal drug release devices were inserted per vaginum on d 8 in the a.m. Liver biopsies were collected on d 9 and hepatic mRNA abundance of genes involved in P4 catabolism was determined. On d 10, the controlled internal drug release inserts were removed and frequent blood samples were collected to measure the rate of decline in circulating P4. The Fert+ cows tended to have greater dry matter intake compared with Fert- cows (+0.79kg of dry matter/d), but similar milk production (29.82kg/d). After synchronized ovulation, the rate of increase in circulating P4 concentrations was greater in Fert+ cows compared with Fert- cows. No effect of genotype on CL volume was detected, but BFA was 42% greater in Fert+ cows compared with Fert- cows. The Fert- cows had greater mRNA abundance of cytochrome P450, family 3, subfamily A (CYP3A) compared with Fert+ cows, but the mRNA abundance of aldo-keto reductase family 1, member C1 (AKR1C1), AKR1C3, AKR1C4, and cytochrome P450, family 2, subfamily C (CYP2C) were similar. The half-life and metabolic clearance rate of P4 were similar in Fert+ cows and Fert- cows. Study 2: 23 cows were enrolled in an ovulation synchronization protocol at 55±7 (±standard deviation) d postpartum, and data are presented for 13 Fert+ and 8 Fert- cows that remained in the study. On d 4, 7, 10, and 13 (d 0=estrus), CL volume and BFA were measured as in study 1. Progesterone concentrations were measured from d 1 to 13. Corpus luteum volume was 41% greater in Fert+ cows compared with Fert- cows but no effect of genotype on BFA was detected. Mean circulating P4 concentrations were 79% greater in Fert+ cows compared with Fert- cows. Milk yield was similar in both genotypes. The results indicate that greater circulating P4 concentrations were primarily due to greater CL P4 synthetic capacity rather than differences in P4 clearance in this lactating cow genetic model of fertility.

The aim was to assess the ability of corpus luteum (CL) and uterine ultrasound characteristics on d 18 to 21 to predict pregnancy status in lactating dairy cows. Ultrasound examinations were carried out on cows (n = 164) on d 18 to 21 following artificial insemination (AI). Images of the uterus and CL were captured using a Voluson i ultrasound device (General Electric Healthcare Systems, Vienna, Austria) equipped with a 12-MHz, multi frequency, linear array probe. Serum concentrations of progesterone were determined from blood samples collected at each ultrasound examination. Images of the CL were captured and stored for calculation of CL tissue area and echotexture. Images of the CL and associated blood flow area were captured and stored for analysis of luteal blood flow ratio. Longitudinal B-mode images of the uterine horns were stored for analysis of echotexture. Diagnosis of pregnancy was made at each ultrasound examination based on CL blood flow, CL size, and uterine echotexture. Pregnancy was confirmed by ultrasonography on d 30 after AI. The relationship between ultrasound measures and pregnancy outcome, as well as the accuracy of the pregnancy diagnosis made at each ultrasound examination was assessed. Progesterone concentrations and CL tissue area were greater in pregnant compared with nonpregnant cows on all days. The CL blood flow ratio was higher in pregnant compared with nonpregnant cows on d 20 and 21 after AI. Echotexture measures of the CL and uterus were not different between pregnant and nonpregnant cows on any day of examination. The best logistic regression model to predict pregnancy included scores for CL blood flow, CL size, and uterine echotexture on d 21 following AI. Accuracy of pregnancy diagnosis was highest on d 21, with sensitivity and specificity being 97.6 and 97.5%, respectively. Uterine echotexture scores were similar for pregnant and nonpregnant cows from d 18 to 20. On d 21, pregnant cows had higher uterine echotexture scores compared with nonpregnant cows. The logistic regression equation most likely to provide a correct pregnancy diagnosis in lactating dairy cows included the visual score for CL blood flow, CL size, and uterine echotexture on d 21 after AI. In support of this finding, the diagnostic accuracy for visual scores of CL blood flow, CL size, and uterine echotexture were also highest on d 21.