Journal of Animal Science, Vol 73, Issue 11 3230-3234, Copyright © 1995 by American Society of Animal Science

JOURNAL ARTICLE

Effect of norgestomet treatment after insemination on the calving rate of postpartum suckled beef cows

R. J. Favero, D. B. Faulkner, T. G. Nash and D. J. Kesler
Department of Animal Sciences, University of Illinois, Urbana 61801, USA.

Two experiments were conducted on postpartum suckled beef cows synchronized with Syncro-Mate B and artificially inseminated approximately 48 h after implant removal. In Exp. 1, cows (> or = 42 d postpartum at the timed AI) were randomly assigned to treated (n = 101) and control (n = 85) groups on d 12 after the timed AI. Treated cows received norgestomet/silicone implants that were left in situ for 9 d. Norgestomet treatment had no effect (P > .25) on the calving rates from the initial timed AI or from the return estrus. Nonpregnant norgestomet-treated cows returned to estrus in a more (P < .05) synchronized manner than the nonpregnant control cows. In Exp. 2, early postpartum cows (< 42 d postpartum at the first AI; n = 30) were included and all 118 cows (88 cows were > or = 42 d postpartum) received norgestomet/silicone implants as in Exp. 1. Of the 30 early postpartum cows, eight (19 to 41 d postpartum at the time of the first AI; mean = 29.3 d) calved to the first AI and nine calved to the second synchronized estrus. The calving dates at the next calving season for these 17 cows (57% of the cows in this group) was advanced an average of 46 d (319-d calving interval). The calving rates for the two timed insemination periods were similar (P > .25) for early and later (> or = 42 d postpartum) postpartum cows. Treatment with norgestomet implants on d 12 through 21 had no detrimental effects on established or subsequent pregnancy, synchronized the return estrus of nonpregnant cows, and was efficacious in establishing pregnancy early postpartum.