|Roberts, Andrew - Andy|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Abstract only
Publication Acceptance Date: 4/1/2007
Publication Date: 6/20/2007
Citation: Roberts, A.J., Grings, E.E., Macneil, M.D., Waterman, R.C., Alexander, L.J., Geary, T.W. 2007. Reproductive Performance Of Heifers Offered Ad Libitum Or Restricted Access To Feed For A 140-D Period After Weaning. Proceedings Western Section of Animal Science 58:255-258. Interpretive Summary:
Technical Abstract: Reproductive performance was evaluated in heifers born in 4 years that were randomly assigned to either control (fed to appetite; n = 268) or restricted (fed at 80 % of that consumed by controls adjusted to a common BW basis; n = 263) feeding during a 140-d postweaning trial, beginning about 2 mo after weaning at 6 mo of age. Heifers were fed a diet of 64 % corn silage, 23 % alfalfa and 13 % of a protein-mineral supplement (DM basis). Restricted fed heifers consumed 26 % less feed over the 140-d trial and had lower ADG (0.48 vs. 0.66 kg/d; P < 0.001) than control heifers. After the trial, heifers were combined and subjected to an estrous synchronization protocol. Heifers were artificially inseminated at about 14 mo of age and then were exposed to bulls for the remainder of a 51-d breeding season. Differences in BW of restricted and control fed heifers persisted (P < 0.01) throughout the prebreeding period (316 vs. 338 kg at approximately 13.5 mo of age) and subsequent grazing season (404 vs. 414 kg at about 19.5 mo of age), but ADG from the end of the 140-d trial to 19.5 mo of age was greater (P < 0.01) in restricted heifers than control heifers (0.49 vs. 0.42 kg/d). The proportion of heifers attaining puberty by 14 mo of age was less (P < 0.01) in restricted (58 %) than control fed heifers (69 %). Means of age at puberty were adjusted to reduce bias from differences in proportions of animals that attained puberty, assuming age of puberty to be normally distributed. Adjusted age at puberty was greater in restricted heifers than control heifers (418 vs. 398 d; P < 0.05). Mean BW at puberty, predicted from regression of BW on age, was less (P < 0.01) in restricted (317 kg) than control (337 kg) heifers. Pregnancy rate from AI did not differ (P = 0.3; overall mean = 50 %) due to feed level. Final pregnancy rate averaged 87 and 91 % for restricted and control heifers, respectively (P = 0.15). Accounting for differences in pregnancy rate, amount of harvested feed provided per pregnant heifer was reduced 22 % with the level of restriction implemented in this study.