J.J. Dufour

Synchronization of estrus and fertility in beef cattle with two injections of buserelin and prostaglandin.

Postpartum beef cows and heifers in Group 1 received 8 mug of buserelin on Day 0 (the beginning of the experiment) and 500 microg of cloprostenol (PGF) on Day 6 (GnRH I, n=54). In Group 2 (GnRH II, n=54), the females were injected with buserelin on Day 0 (8 microg) and Day 3 (4 microg), and PGF on Day 6 and Day 9 for females not detected in estrus previously. Animals were bred by AI 12 hours after the onset of estrus. Blood samples were collected on Day -11 and Day 0 to assess cyclicity and on Day 3 and Days 6 to 12 to examine luteal activity. Progesterone levels did not differ between the 2 groups between Days 0 to 9. In both groups, the proportion of spontaneous estruses from Days 0 to 6 was reduced. Precision of estrus was higher (P<0.005) in the GnRH II group than in the GnRH I group of cows that were detected in estrus between Days 6 and 9. The synchronization rate, interval to estrus, pregnancy and conception rates were similar in GnRH I and GnRH II groups. The conception rate and interval to estrus were similar in cyclic and acyclic cows. Increasing the number of buserelin injections enhanced the precision of estrus, but not the conception rate, without any detrimental effect on luteal activity and induced more estruses in postpartum acyclic beef cattle.

Ovarian follicular dynamics and relationship between ovarian types and serum concentrations of sex steroids and gonadotrophin in prepubertal gilts

This study was designed to determine (1) the ovarian follicular dynamics in 12 Yorkshire × Landrace crossbred gilts by using as measures the type of ovaries (grape ‘G’, honeycomb ‘H’ and intermediate ‘I’ types) and their amplitude of change at different periods before puberty; (2) the relationship between ovarian types and serum concentrations of sex steroid (oestradiol-17b, E2; testosterone, T; androstenedione, A) and luteinizing hormone (LH). Five successive laparoscopies at 5-day intervals between 160 and 180 days of age were performed on each gilt to determine the ovarian type and the distribution of follicles present on the ovarian surface. Blood sampling for RIA analyses of hormones was at 15-min intervals for 6 h in eight of the 12 gilts, 1 or 2 h before each laparoscopy. Within a gilt, no ovary maintained the same ovarian type over the five successive laparoscopies. The H type was found to be stable for three successive laparoscopies, whereas the G and I types were generally maintained for only two successive laparoscopies. When an ovary switched from the G type to the H or I type, the number of large follicles (> 6 mm in diameter) decreased (P < 0.01) by seven follicles or less while that of the small follicles (1–3 mm in diameter) increased (P < 0.01) by 15 follicles or more. When an ovary switched from the H type to the G or I type, the inverse phenomenon was observed; the number of large follicles increased (P < 0.01) by six follicles or less while that of the small follicles decreased (P < 0.01) by 16 follicles or more. Moreover, the concentrations of E2, T, A and LH in serum were not influenced by ovarian types. However, when H gilts became I gilts, the concentration of A increased by 1 ng ml−1. When 1 gilts became H gilts, the inverse phenomenon occurred; the concentration of A decreased by 0.68 ng ml−1. The results of the present study demonstrate that between 160 and 180 days of age (1) all ovaries undergo morphological change at least once; (2) the time during which the three types of ovaries remain stable rarely exceeds 10 days for the H type, and 5 days for the G and I types; (3) the change of ovarian morphology is associated with a change in follicular population; (4) no relationship exists between ovarian types and serum E2, T, A and LH concentrations. However, the concentration of A increases or decreases depending on whether H gilts change to I gilts or I gilts change to H gilts. Thus, during the prepubertal period in gilts, ovarian morphology is not static but undergoes continuous changes suggestive of follicular waves.

Effects of gonadotropin treatment on ovarian follicle growth, oocyte quality and in vitro fertilization of oocytes in prepubertal gilts.

This study was undertaken to compare the effects of FSH-pituitary (FSH-P), eCG, and a combination of gonadotropins containing 400 IU eCG and 200 IU hCG (PG 600) on the growth of large follicles, oocyte quality and in vitro fertilization (IVF) rate of in vitro matured (IVM) oocytes in prepubertal gilts. The ovaries were removed via midventral laparotomy 48 h (Experiment 1) or 72 h (Experiment 2) after the first injection. In Experiment 1, 30 gilts received 1 of 5 treatments: 1) saline (3 ml i.m., once, n = 6); 2) FSH-P8 (8 mg i.m., twice, with a 24-h interval, n = 6); 3) FSH-P16 (16 mg i.m., twice, with a 24-h interval, n = 6; 4) eCG (1000 IU i.m., once, n = 6); or 5) PG 600 (5 ml i.m., once, n = 6). Compared with saline, treatment with PG 600 or eCG induced significant (P < 0.05) growth of large follicles (> or = 6 mm). In Experiment 2, 16 gilts received 1 of 5 treatments: 1) saline (n = 4); 2) FSH-P8 (n = 4); 3) FSH-P16 (n = 4); 4) eCG (n = 4), or 5) PG 600 (n = 4). The same injection protocol as in Experiment 1 was used. Compared with treatment with FSH-P8 or FSH-P16, eCG increased (P<0.05) the number of large follicles. The proportion of good oocytes was increased (P<0.05) with FSH-P8 or FSH-P16 compared with treatment with eCG or PG 600. Moreover, oocytes from eCG-treated gilts had a greater (P<0.05) rate of male and female pronuclei than FSH-P or saline-treated gilts. In conclusion, treatment with FSH-P resulted in a higher proportion of oocytes with multilayer cumulus cells, whereas treatment with eCG resulted in higher pronuclear rates following in vitro fertilization in prepubertal gilts.

Buserelin overcomes the effect of the corpus luteum on ovarian follicular development in postpartum cycling cows

Abstract Follicular development after treatment with a gonadotropin-releasing hormone agonist (buserelin) was compared in ovaries of postpartum cows bearing (CLO) or not bearing (NCLO) a corpus luteum (CL). In the first experiment, 16 cows on day 7 of the estrous cycle (day 0 of treatment) were treated either with saline or 8 μg of buserelin. Both ovaries were collected on day 3 or day 6 ( n = 4 per group per day) and follicles over 1.57 mm in diameter were observed histologically. Compared with day 3 in the saline group, there was a greater decrease in the percentage of Class I total (1.57–3.67 mm; P P P P P P P > 0.1) between CLO and NCLO within 3 days after treatment. In the second experiment, follicular responses in CLO and NCLO were compared by daily ultrasonography in cows that had ( n = 6) or did not have ( n = 4) a buserelin-induced ovulation. After buserelin treatment, the numbers of medium (5–10 mm) and large (over 10 mm) follicles were not different ( P > 0.1) between the CLO and the NCLO whether ovulation occurred or not. Results indicate that treatment with buserelin overcame most of the local effects of the CL on the growth and atresia of ovarian follicles in postpartum cycling cows within a 6 day period and this occurred whether ovulation was induced or not.

Estrus synchronization efficiency of PGF2α injection in Shorthorn-Hereford and crossbred Charolais cattle not having exhibited estrus at 4 or 7 days prior to treatment

The objective of this study was to compare the estrus synchronization efficiency of PGF2alpha in cattle (n = 470) not having shown estrus for 4 (D4 treatment) or 7 d (D7 treatment) after onset of the breeding season. The physiological status of crossbred Charolais cows was studied, and their reproductive performance was compared to that of Shorthorn-Hereford cows. The percentage of cows in estrus during the 7 d prior to PGF2alpha treatment was superior (P < 0.01) to that observed during the 4 d preceding PGF2alpha. The daily rates of estrus were similar during the 2 periods. For both the Shorthorn-Hereford (87.8 vs 74.7%; P < 0.03) and crossbred Charolais (87.8 vs 66.3%; P < 0.005) females, the estrus synchronization rate during the 5 d post PGF2alpha was higher in treatment D7 than in the D4 treatment. Therefore, for both Shorthorn-Hereford (92.8 vs 81.4%) and crossbred Charolais (93.1 vs 75.0%) the D7 program permitted insemination in 12 d (before and after PGF2alpha) of a higher percentage (P < 0.01) of females than the D4 program did in 9 d. The intervals PGF2alpha to estrus and their variances were similar for both treatments. The conception rate of Shorthorn-Hereford was the same whether they were inseminated after spontaneous (73.4%) or PGF2alpha-induced estrus (D4 treatment: 78.5%; D7 treatment: 72.2%). However, crossbred Charolais cows inseminated after a PGF2alpha-induced estrus in the D4 treatment had a fertility rate (50.9%) slightly inferior (P < 0.07) to that of cows inseminated after spontaneous estrus (70.1%) or after PGF2alpha-induced estrus in the D7 treatment (67.4%). The reproductive performances of multiparous Shorthorn-Hereford and crossbred Charolais were similar in treatment D7; however, in the D4 treatment, the conception rate of Shorthorn-Hereford was higher than that of crossbred Charolais (81.0 vs 42.9%; P < 0.002). Primiparous crossbred Charolais in the D4 treatment had a slightly lower (P < 0.10) synchronization rate (48%) than nulliparous (71%) and multiparous crossbred Charolais (78%). In contrast, the reproductive performances of nulliparous, primiparous and multiparous crossbred Charolais were similar in the D7 treatment. These results indicate that the efficiency of PGF2alpha to synchronize estrus is greater when the estrus detection period increases from 4 to 7 d before PGF2alpha. Only in the D7 treatment was the fertility rate of crossbred Charolais similar to that of Shorthorn-Hereford.