Effect of energy balance and somatotropin on insulin-like growth factor I in serum and on weight and progesterone of corpus luteum in heifers.
Holstein heifers (approximately 1 yr old) were fed to be in negative energy balance (n = 14; NEB) or positive energy balance (n = 15; PEB) during four estrous cycles. Each heifer was given PGF2 alpha to control the timing of fourth estrus. From 1 d after PGF2 alpha injection until 10 d after estrus, half of the heifers were injected daily with 14 mg of somatotropin (bST), and the corpus luteum (CL) was collected on d 10. Heifers in NEB had less IGF-I in serum (P < .01), smaller CL (P < .01), and less progesterone in CL (P < .01) than heifers in PEB. Exogenous bST increased (P < .01) IGF-I in serum, but this increase was greater in heifers in PEB than those in NEB (P < .01 for interaction of energy balance and bST). Nonetheless, bST did not alter weight or progesterone content of the CL in either energy balance group. In addition, serum IGF-I during the first 10 d after estrus was not correlated to luteal weight and only weakly correlated (r = .3) with luteal progesterone content. We conclude that exogenous bST given during luteal development does not alter growth or progesterone content of the CL in heifers. Reduced concentration of IGF-I in serum during luteal development does not account for suppressed luteal growth and progesterone synthesis of heifers in NEB.
Yung
M C
MC
Department of Animal Science, Michigan State University, East Lansing 48824, USA.
VandeHaar
M J
MJ
Fogwell
R L
RL
Sharma
B K
BK
D000818:Animals; D001835:Body Weight / Q000502:physiology; D002417:Cattle / Q000378:metabolism* / Q000502:physiology*; D003338:Corpus Luteum / Q000033:anatomy & histology* / Q000737:chemistry / Q000378:metabolism*; D004734:Energy Metabolism / Q000502:physiology*; D004971:Estrus / Q000502:physiology; D005260:Female; D013006:Growth Hormone / Q000097:blood / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D009929:Organ Size; D011374:Progesterone / Q000032:analysis / Q000378:metabolism*
D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone