Gonadotropin-releasing hormone increased pregnancy risk in suckled beef cows not detected in estrus and subjected to a split-time artificial insemination program12

Abstract

We hypothesized that GnRH would increase pregnancy risk (PR) in a split-time AI program for cows in which estrus was not detected. A total of 1,236 suckled beef cows at 12 locations in 3 states (Colorado, Kansas, and North Dakota) were enrolled. Before applying the fixed-time AI program, BCS was assessed. Cows were treated on d −7 with a progesterone insert concurrent with 100 μg GnRH and on d 0 with 25 mg PGF 2α plus removal of the insert. Estrus-detection patches were affixed to cows at insert removal. Estrus was defined to have occurred when an estrus-detection patch was >50% colored (activated). Cows in estrus by 65 h (n = 758; 61.3% of all cows) were randomly allocated to 2 treatments: 1) 100 μg GnRH and early + GnRH (E+G; n = 373) or 2) AI only at 65 h (early -no GnRH [E-G]; n = 385). The remaining cows were randomly allocated to 2 treatments: 1) 5(L+G; n = 252) or 2) AI only at 84 h (late no GnRH [L-G]; n = 226). Pregnancy was determined 35 d after AI via transrectal ultrasound. Pregnancy risk did not differ (P = 0.68) between E+G and E-G cows (61.9 vs. 60.4%, respectively). Conversely, for cows inseminated at 84 h, PR was greater (P = 0.01) in cows that received GnRH (L+G) compared with their herd mates not receiving GnRH (L-G; 41.7 vs. 30.8%, respectively). Of those cows not detected in estrus by 65 h, 42.1% were detected by 84 h, for a total expression of estrus by all cows of 77.6%. Administration of GnRH increased (P < 0.01) PR in cows not detected in estrus by 84 h (+GnRH = 33.4% [n = 146] vs. no GnRH = 15.0% [n = 128]) but had no effect in cows expressing estrus by 84 h (+GnRH = 65.3% [n = 103] vs. no GnRH = 61.7% [n = 97]). Neither estrus expression by 65 or 84 h nor PR was influenced by BCS, parity, or days postpartum at AI. Cows had greater PR when they had been detected in estrus before AI, and PR was improved by administration of GnRH at 65 h after insert removal in cows that were not detected in estrus and inseminated at 84 h.

Transition dairy cow health is associated with first postpartum ovulation risk, metabolic status, milk production, rumination, and physical activity

“…Blood samples were collected weekly beginning on d 21 ± 3 until d 63 ± 3 to determine the onset of luteal function and before ovulation synchronization injections of GnRH and PGF 2α for later assessment of progesterone concentration (Figure 1). Concentrations of progesterone in blood serum were measured by direct quantitative (nonextracted) RIA using Im-muChem Double Antibody progesterone 125 I kits (MP Biomedicals LLC, Solon, OH) previously validated for bovine serum (Hill et al, 2016). Intra-and interassay coefficients of variation for a low (0.26 ± 0.01 ng/mL) were 5.2 and 16.6% and for a luteal marginal (1.22 ± 0.1 ng/mL) concentration pool were 6.4 and 16.1%, respectively.…”

Hormonal adjustments for fixed-time artificial insemination and physiologic variables influence in the reproductive performance of >i<Bos indicus>/i< heifers

“…On the other hand, Prata et al described the no effect of the GnRH treatment at the AI time of the 2 years old heifer's category (With GnRH: 47.3% vs. without GnRH: 47.2%) [5], as was not different for the P/AI in this research, rejecting the second hypothesis of the present study, having no difference between the two experimental groups (With or without GnRH at the TAI), as well as there was no influence even for those heifers without expression of estrus, different from the reported benefits in reproductive performance of cows with no expression of estrus prior the TAI (Without estrus -without GnRH: 15.0% vs. without estrus -with GnRH: 33.4%) [52]. However, despite of the non-relevant results for the P/AI, the GnRH administration increase the pregnancy loss between 30 and 60 days of gestation, results that could be supported on the GnRH effect on the induction of ovulation of a small follicle, leading to a reduction on the steroidogenic capacity of those follicles submitted to the GnRH treatment, which decreases the influence of the endogenous estradiol on the uterine environment which have been described as positive for the pregnancy maintenance in dairy cattle [53], probably explaining the negative effect of the GnRH treatment described above on the pregnancy loss, different of what was reported by our laboratory, describing in an anterior study the no association of the GnRH treatment at the AI moment with the pregnancy loss in Nelore cows [54].…”

Increasing estrus expression in the lactating dairy cow

“…Samples were stored on ice and transported to the laboratory for storage at 5°C until serum was harvested by centrifugation (1,200 × g at 5°C for 15 min). Sera samples were stored at −15°C until assayed for progesterone concentration by RIA (Hill et al, 2016) using ImmuChem Double Antibody progesterone 125 I kits (catalog #07-170105, MP Biomedicals LLC, Orangeburg, NY); inter-and intraassay coefficients of variation were 8.0 and 4.8% for a low concentration pool, and 6.2 and 4.4% for a high concentration pool, respectively.…”