Factors influencing hormonal patterns during postpartum anestrus in beef cattle

Abstract

Studies were performed to evaluate postpartum (PP) hormonal profiles in beef cattle. One study examined the effect of aspirin (A) feeding on PP endocrine profiles and reproductive function. The second study evaluated the effect of breed, day PP and endogenous opioid peptides (EOP) on hormone secretion in beef cows. Primiparous cows (P) had higher plasma salicylate concentrations after A administration than pluriparous cows (M). Aspirin-treated P had longer PP intervals than either control P or M or A-treated M. Cows receiving A had a lower pregnancy rate, an increased incidence of abnormal estrous cycles and a decline in the presence of corpora lutea after estrus (CL). Progesterone (P4) concentrations were higher in P than in M on day 7 PP. Cows that formed a CL and had received A had higher P4 release between days 6 and 14 after estrus. Cows that did not form CL and had received A had lower P4 release between days 9 and 14 after estrus. This could reflect a detrimental action of the treatment on ovarian follicular growth. Plasma 13,14-dihydro-15-keto-prostaglandin F2α (PGFM) concentrations were high after parturition, decreasing rapidly until day 6 PP and declined slowly afterwards and were lower in P that had female calves. Aspirin treatment decreased plasma PGFM concentrations in M, but increased them in P. These results add support to the concept that PP physiology in differs with stage of maturity. Naloxone treatment induced an increase in luteinizing hormone (LH) release in Brahman (BI) and Angus (BT) cows, demonstrating the presence of EOP inhibition of LH secretion in PP cows of both breed types. Mean, basal and pulse height concentrations of LH increased from day 17 to day 34 PP in BI and BT cows. Higher mean and basal LH concentrations, higher LH pulse frequency and a greater LH release after the GnRH challenge was found in BI than in BT cows. Serum cortisol (C) concentrations were higher on day 14 than on day 34 PP in both breeds. Breed differences were not detected in C release after an adrenocorticotropin challenge. Naloxone administration did not increase C release. Plasma PGFM concentrations were higher in 17-day PP BI cows than either 34-day PP BI cows or BT cows on either day PP.