We compared pregnancy rates of beef cows subjected to the traditional Syncro-Mate-B protocol or the new Ovsynch protocol and timed insemination. Multiparous Angus cows (n = 436) were stratified by age, postpartum interval, and AI sire and were randomly divided into two treatment groups for synchronization of estrus/ovulation. Approximately half of the cows (n = 216) received the traditional Syncro-Mate-B protocol with 48-h calf removal from the time of implant removal until breeding. The remaining cows (n = 220) received the Ovsynch protocol, which consists of an injection of GnRH (100 microg) on d -10, an injection of PGF2alpha (25 mg) and 48-h calf removal on d -3, another injection of GnRH and calf return on d -1, and timed insemination 24 h later (d 0). Blood samples were collected from all cows before treatment to identify anestrous and cyclic females. Pregnancy rates were higher (P < .025) for Ovsynch-treated cows (54%) than for Syncro-Mate-B-treated cows (42%). Pregnancy rates of cyclic Ovsynch-treated cows (59%) were higher (P < .005) than pregnancy rates of cyclic Syncro-Mate-B-treated cows (38%). Pregnancy rates of anestrous cows also tended to favor synchronization with the Ovsynch protocol. From these data, we conclude that the Ovsynch protocol is capable of inducing a fertile ovulation in cyclic and anestrous beef cows and that pregnancy rates to a timed insemination are higher than those obtained with synchronization of estrus using Syncro-Mate-B.
In order to assess the optimal time of artificial insemination (AI) in relation to ovulation, lactating dairy cows (n = 732) from herds with rolling herd averages of 9980 to 11,800 kg from three milkings per day were randomly assigned to five groups by stage of lactation and parity. Ovulation was synchronized by administration of GnRH followed 7 d later with PGF2 alpha followed 2 d later with a second treatment with GnRH. Cows were inseminated at 0, 8, 16, 24, or 32 h after the second injection of GnRH (ovulation occurs between 24 and 32 h after GnRH). Pregnancy diagnoses were performed by ultrasound at 25 to 35 d post-AI. Pregnancy rates per AI were similar for the groups inseminated at 0, 8, 16, and 24 h and lower for the group inseminated at 32 h. A significant quadratic effect of treatment suggests that the middle time periods (8, 16, and 24 h) may produce the greatest pregnancy rate per AI. However, the group inseminated at 0 h had lowest pregnancy loss, and the group inseminated at 32 h tended to have the greatest pregnancy loss compared with that of the other groups. The calving rate was similar between the groups inseminated at 0, 8, 16, and 24 h and lower in the group inseminated at 32 h. The time of AI also appeared to affect gender of calf: cows bred at 0 and 32 h having a higher percentage of female offspring. In conclusion, there appears to be substantial flexibility in the time of AI after the second injection of GnRH, and lower reproductive rates were observed only when AI was after the time of ovulation.
The ability of zeranol and trenbolone acetate (trenbolone) to alter testis function, weight gain and carcass traits of young bulls was studied. In Exp. 1, the effects of age at initial zeranol implantation was determined. After a 235-d experimental period, sequential implantation (56-d intervals) beginning at 100 or 150 d of age had reduced testis growth (P less than .01), sperm production (P less than .01) and serum testosterone concentration in response to gonadotropin releasing hormone (GnRH; P less than .01). The 200-d age group was partially suppressed, while the 250-d age group was not affected. Body weights were similar to controls in all groups. In Exp. 2, bulls previously implanted with zeranol at 175 and 231 d of age received single implants of zeranol, trenbolone or trenbolone plus zeranol at approximately 300 d of age. At slaughter (135 d later), body weight and carcass characteristics in all treatments were similar to controls. However, trenbolone reduced sperm production (P less than .05), zeranol reduced sperm production and testes weight (P less than .05), but trenbolone plus zeranol was similar to controls. Mean testosterone response to GnRH was suppressed in all implant groups on d 65 (P less than .01), but only in trenbolone or trenbolone plus zeranol groups on d 112 (P less than .05). Results indicate that zeranol suppresses spermatogenesis and testosterone production if implanted before approximately 200 d of age. Reduction of endogenous testosterone without alteration of weight gain or carcass characteristics may be of benefit if behavioral or masculinity traits of bulls are altered. Also, it appears that no benefit is derived from implanting bulls with both trenbolone and zeranol.
The objective of this study was to characterize endometrial secretion (in vitro) of prostaglandin F (PGF), 15-keto-13,14-dihydro-prostaglandin F2 alpha (PGFM), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) on Day 5 following the first postpartum estrus of cows anticipated to have a short compared to a normal estrous cycle. Twenty-seven beef cows were randomly assigned into four groups. The Short Cycle (n = 6; control) and Short Cycle/Explant (n = 8; endometrial explants) groups had their calves weaned at 30-32 days postpartum. The Normal Cycle (n = 5, control) and Normal Cycle/Explant (n = 8; endometrial explants) groups received norgestomet (progestin) implants for 9 days beginning 21-23 days postpartum, and calves were weaned at implant insertion. Estrous cycle length (mean +/- SE; p less than 0.01) for the Short Cycle group was 11.5 +/- 1.9 days compared to 18.8 +/- 0.6 days for the Normal Cycle group. On Day 5 following the first postpartum estrus, cows in the Short Cycle/Explant and Normal Cycle/Explant groups were hysterectomized, and endometrial explants were incubated in Earle's Balanced Salt solution/Medium 199 for 90 min with or without arachidonic acid (AA) in the presence of three levels of oxytocin. Mean concentrations of PGF and PGFM were combined to obtain a value for total PGF. Concentrations of total PGF, PGE2 (from explants without AA treatment), and 6-keto-PGF1 alpha in medium of the Short Cycle/Explant group were higher (p less than 0.01) than in medium of the Normal Cycle/Explant group.(ABSTRACT TRUNCATED AT 250 WORDS)
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