Contribution of the Adrenal Glands to Postpartum Anestrus in Suckled Cows

Suckling prolongs the postpartum anestrous (PPA) period in postpartum cows while inducing hypersecretion of adrenocorticoids. Hyperadrenocorticism affects reproductive function in cattle as well as in many species. To evaluate the role of adrenal glands in suckling-induced PPA in cattle two experiments were conducted. Exp. 1: Effects on luteinizing hormone (LH) secretion of 3 levels of exogenous corticosteroids; T$\sb1$ = no corticoids, T$\sb2$ = 75 mg of cortisone acetate (CA) + 20 mg of deoxycorticosterone acetate (DOCA) daily and T$\sb3$ = 75 mg CA + 20 mg DOCA daily + 8 mg of dexamethasone every other day were tested on 6 intact ovariectomized (I-OVX) cows and 6 adrenalectomized (ADX-OVX) cows. T$\sb3$ caused suppression (p $<$ 0.05) of LH secretion in both groups while T$\sb2$ did not. Exp. 2: Ten pluriparous cows at parturition were randomly assigned either to intact-suckled (IS) or to ADX-suckled (ADXS) groups at the day of calving and all cows were suckled by two calves. On day 3 postpartum, adrenalectomy in ADXS cows or sham-adrenalectomy in IS cows was performed. ADXS cows received corticoid replacement (T$\sb2$). Commencing from day 10 postpartum at weekly intervals, sequential blood samples (12 min intervals) were collected for 24 hours until estrus or day 70 postpartum, whichever came first. On day 70 anestrous cows were weaned and 48-hours post-weaning sequential blood samples for 24 hours were collected. The weaned anestrous cows remained in the experiment until they resumed estrous cyclicity. Plasma was assayed for LH and cortisol. Adrenalectomy in postpartum suckled cows did not shorten the postpartum interval or facilitate LH secretion or affect weaning to estrus length or affect weaning-induced increase in LH. On the other hand, the frequency of LH pulses was negatively correlated with mean corticosteroid concentrations in both groups. These results suggest that suckling does not extend PPA period primarily by a mechanism involving adrenocorticoids. Nevertheless, the increased adrenocorticoids present in the suckled cow may facilitate the expression of the predominant mechanism(s) responsible for PPA.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Veterinary Medical Science

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2014

Author dc:creator

• Abeygunawardena, Harischandra

Contributors dc:contributor

• Hixon, James E.

• Biology, Veterinary Science

Identifier

(UMI)AAI8802972

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/71346