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 RESTRICTION

The objective of this study was to determine whether serum concentrati ons of growth hormone (GH), IGF-I, IGF binding proteins (IGFBP), and g lucose at wk 2 and 10 postpartum were associated with the ability of p ostpartum beef cows to resume cycling when maintained on a limited nut rient environment. Cows (n = 29) were individually fed either 130 or 1 70 kcal ME x BW-.75 x d(-1) during nonlactation and 170 or 210 kcal ME x BW-.75 x d(-1) during lactation for an average of 4.1 yr before sam ple collection. The proportion of cows that resumed estrus within 20 w k 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 c ows that remained anestrous and were less (P < .05) at wk 2 and 10 in cows that remained anestrous compared to cows that resumed cycling. Ci rculating amounts of IGFBP-8 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 concent rations of GH compared (P < .05) to other cows. At the higher feeding rate, body condition score and concentrations of GH did not differ bet ween cows that did or did not resume cycling. Circulating concentratio ns of IGF-I and IGFBP-8 and -3 at wk 2 postpartum were indicators of t he capacity of energy-restricted cattle to resume cycling after partur ition.