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Carcass Composition and Mammary Development Responses to Photoperiod and Plane of Nutrition in Holstein Heifers¹

Michigan State University³, East Lansing 48824

Abstract

Twenty prepubertal heifers (averaging 155 kg body weight) were assigned to one of four treatment groups in an experiment of 2 x 2 factorial design. The main effects were photo-periods of 8 h light:16 h dark (8L.16D) vs 16L:8D, and LOW vs HIGH plane of nutrition. Heifers on the LOW plane of nutrition were fed to achieve a growth rate of approximately .7 kg/d; daily feed intake was restricted with no orts and was identical in both groups of heifers subjected to either 8 or 16 h of light daily. Heifers on the HIGH plane of nutrition were fed ad libitum to achieve a growth rate > 1 kg/d. All heifers were slaughtered during the luteal phase of an estrous cycle at an average body weight of 337, 334, 360 and 349 kg for 8L:16D-LOW plane, 16L:8D-LOW plane, 8L:16D-HIGH plane and 16L:8D-HIGH plane groups, respectively. Average time on treatment was 233, 236, 206 and 181 d and average estimated carcass weight gain was .39, .40, .55 and .61 kg/d, respectively. Within LOW or HIGH planes of nutrition, photoperiod did not affect live body weight gains. A photoperiod of 16L:8D, compared with 8L:16D, increased protein content in the 9–10–1lth rib section of heifers on HIGH nutrition (16.2 vs 14.6%), but not in heifers fed the LOW plane of nutrition (15.5 vs 16.1%). However, within 8L:16D groups, HIGH plane reduced rib section protein content as compared with LOW plane of nutrition (14.6 vs 16.1%); there was no difference observed within 16L:8D groups. Fat content in the rib section was greater for heifers on HIGH plane than for heifers on LOW plane of nutrition (25.2 vs 20.3%). Photoperiod did not influence measures of mammary development. But, HIGH plane of nutrition reduced DNA concentration (1.77 vs 1.92 mg/g) and total amounts of DNA (170.2 vs 227.4 mg/100 kg body weight) in mammary parenchymal tissue in comparison with low plane of nutrition. In conclusion, level of protein and fat accretion in the carcass can be manipulated by photoperiod and level of nutrition. However, only level of nutrition influenced development and composition of mammary parenchymal tissue.

¹ Michigan Agr. Exp. Sta. Journal Article No. 10782. This research was supported in part by USDA Grant 901-15-2 and 59-2261-0-2-012-0.

² On leave from Lennoxville Research Station, Agriculture Canada, Lennoxville, Quebec.

³ Dept. of Anim. Sci.

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