Circulating Insulin-Like Growth Factor I, Insulin-Like Growth Factor Binding Proteins, Growth Hormone, and Resumption of Estrus in Postpartum Cows Subjected to Dietary Energy Restriction1

The objective of this study was to determine whether serum concentrations of growth hormone ( GH) , IGF-I, IGF binding proteins (IGFBP), and glucose at wk 2 and 10 postpartum were associated with the ability of postpartum beef cows to resume cycling when maintained on a limited nutrient environment. Cows (n = 29) were individually fed either 130 or 170 kcal ME × BW−.75 × d−1 during nonlactation and 170 or 210 kcal ME × BW−.75 × d−1 during lactation for an average of 4.1 yr before sample collection. The proportion of cows that resumed estrus within 20 wk after parturition was less ( P < .05) at the lower feeding rate (5 of 14) than at the higher feeding rate (11 of 15). Concentrations of IGF-I increased from wk 2 to 10 in cows that resumed cycling but not in cows that remained anestrous and were less ( P < .05) at wk 2 and 10 in cows that remained anestrous compared to cows that resumed cycling. Circulating amounts of IGFBP-2 at wk 2 were greater ( P < .05) and IGFBP-3 concentrations were lower ( P < .05) in cows that remained anestrous compared to cows that resumed cycling. Cows on the lower feeding rate that did not cycle had lower body condition scores and greater concentrations of GH compared ( P < .05) to other cows. At the higher feeding rate, body condition score and concentrations of GH did not differ between cows that did or did not resume cycling. Circulating concentrations of IGF-I and IGFBP-2 and -3 at wk 2 postpartum were indicators of the capacity of energy-restricted cattle to resume cycling after parturition.