title: Body growth, growth hormone, prolactin and puberty response to photoperiod and plane of nutrition in Holstein heifers.
abstract: Effects of photoperiod and plane of nutrition on growth, serum concentrations of prolactin (PRL) and growth hormone (GH) and puberty were assessed in Holstein heifers. Sixty pre-pubertal heifers were assigned to one of four treatment groups arranged in a 2 X 2 factorial. The two main effects were photoperiods of 8 h light: 16 h dark (8L:16D) vs 16L:8D, and a low vs high plane of nutrition. Heifers on the low plane of nutrition were fed a diet formulated to achieve a body growth rate of approximately .7 kg/d. Daily feed intake was restricted and similar in both groups of low plane 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. Body weight was recorded every month for 5 mo. The PRL and GH concentrations were measured at d 9, 53 and 132 in serum collected every 30 min for 6 h from five heifers in each treatment group. Progesterone was monitored biweekly in all heifers as an index of puberty (greater than 1 ng/ml). Heifers subjected to 8L:16D-low plane, 16L: 8D-low plane, 8L:16D-high plane or 16L:8D-high plane gained .61, .72, .98 and 1.08 kg/d, respectively. In the same treatment order, averaging across all bleedings, concentrations of PRL were 32, 37, 38 and 46 ng/ml serum, and GH averaged 10.9, 9.3, 9.8 and 9.0 ng/ml serum. Similarly, body weight at puberty averaged 268, 257, 278 and 268 kg, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000818:Animals; D001835:Body Weight; D002417:Cattle / Q000502:physiology*; D004032:Diet; D005260:Female; D013006:Growth Hormone / Q000097:blood*; D008029:Lighting; D011388:Prolactin / Q000097:blood*; D012621:Seasons; D012741:Sexual Maturation
chemical_list: D011388:Prolactin; D013006:Growth Hormone