Nursing enhances the negative effect of estrogen on LH release in the cow.
Twenty-three crossbred beef cows between 4 and 5 yr of age were assigned at random to one of six treatments: (1) ovariectomized 4 d postpartum (OVX) with early weaning of calves 21 d postpartum (OVX-EW; n = 4), (2) OVX-EW and 17 beta-estradiol implants (OVX-E2-EW; n = 4), (3) OVX and normal nursing by calves throughout the experiment (OVX-NN; n = 3), (4) OVX-NN and 17 beta-estradiol implants (OVX-E2-NN; n = 4), (5) intact cows and early weaning of calves 21 d postpartum (EW), (6) intact cows and normal nursed (NN). Blood was collected at 15-min intervals over a 4-h period once weekly during the 12-wk postpartum period in the OVX cows. Early weaned intact cows exhibited estrus 23 d sooner (P less than .05) than normally nursed cows. A hormone level for each cow at each week was determined from the mean of the 17 samples collected over the 4 h period each week. There were no significant changes due to E2 treatment, for concentrations of LH, FSH or number of pulses during wk 1 through 3. However, during wk 4 through 12 the linear and quadratic contrasts of wk X estrogen X nursing were significant for serum LH, indicating there was no difference between the treatments for EW and NN without E2 but there was a large difference in the presence of E2. During nursing E2 suppressed serum LH below that of nonestrogen-treated cows while after weaning E2 stimulated LH release above that of nonestrogen-treated cows.(ABSTRACT TRUNCATED AT 250 WORDS)
D000828:Animal Population Groups; D000818:Animals; D000833:Animals, Suckling; D002369:Castration / Q000662:veterinary; D002417:Cattle / Q000502:physiology*; D003864:Depression, Chemical; D004343:Drug Implants; D004958:Estradiol / Q000494:pharmacology*; D004971:Estrus; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood*; D007774:Lactation; D007986:Luteinizing Hormone / Q000097:blood*; D011247:Pregnancy; D011863:Radioimmunoassay
D004343:Drug Implants; D004958:Estradiol; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone