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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #210166
Title: Reproductive Performance Of Heifers Offered Ad Libitum Or Restricted Access To Feed For A 140-D Period After Weaning

Author
item Roberts, Andrew
item Grings, Elaine
item Macneil, Michael
item Waterman, Richard
item Alexander, Leeson
item Geary, Thomas

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/15/2007
Publication Date: 6/15/2007
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. Western Section of Animal Science Proceedings. WSASAS Proceedings 58:255-259.

Interpretive Summary: Reproductive performance was evaluated in heifers born in 4 years that were developed on 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) levels of 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 (1.0 vs. 1.5 lb/d) 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 exposed to bulls for the remainder of a 51-d breeding season. Prior to breeding, heifers that were developed on the restricted level of feeding weighed 695 lb, whereas control fed heifers weighed 744 lb. The proportion of heifers attaining puberty by 14 mo of age was less in restricted (58 %) than control fed heifers (69 %). The level of restriction imposed in this study was predicted to result in a 20-d delay in puberty and pregnancy rate was reduced in restricted fed heifers that failed to reach puberty prior to breeding, which resulted in a 4 % reduction in overall pregnancy rate. After accounting for differences in pregnancy rate, a 22 % reduction in harvested feed provided per pregnant heifer was obtained with the level of restriction implemented in this study. In addition, ADG from May to Dec, while grazing native range, was 16 % higher in heifers that had been restricted than control fed heifers. Differences in market values of heifer calves and open heifers will impact potential economic advantages of restricted feeding.

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 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.