title: Carcass composition and mammary development responses to photoperiod and plane of nutrition in Holstein heifers.
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 photoperiods 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 greater than 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 9-10-11th 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.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001823:Body Composition; D001835:Body Weight; D002417:Cattle / Q000254:growth & development / Q000502:physiology*; D004247:DNA / Q000378:metabolism; D002149:Energy Intake; D005260:Female; D008027:Light; D008321:Mammary Glands, Animal / Q000254:growth & development* / Q000378:metabolism; D012741:Sexual Maturation
chemical_list: D004247:DNA