Title: 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
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 1997
Publication Date: N/A
Interpretive Summary: Failure of cows to exhibit estrous in an appropriate period of time after calving substantially reduces the economic return to an operation. Limited dietary intake can prolong the period of time between calving and resumption of estrous activity, yet excessive feeding can be cost prohibitive. Studies were conducted to determine if concentrations of metabolic hormones in the blood of cows would be reflective of their ability to exhibit estrous during the 20-wk period after calving. Cows were fed either a low (n = 14) or a moderate (n = 15) level of feed intake. The proportion of cows that resumed cycling within 20 wk after calving was less at the low feeding level (5/14) than the moderate level (11/15), indicating that level of feed intake influenced the ability of cows to resume cycling; but the effect was not absolute (i.e., not all cows responded the same way). Body condition scores were lower in cows on the low feeding level that failed to cycle but did not differ between moderately fed cows that did or did not cycle. Thus, body condition score was not useful for predicting nutritional status of moderately fed cows. Concentrations of insulin-like growth factor-I (IGF-I) were less at wk 2 and 10 after calving in cows that failed to cycle compared to cows that did resume cycling, regardless of feeding level. The amounts of two other proteins (IGF binding proteins 2 and 3) also differed among cows that did or did not subsequently resume cycling. Results indicate that circulating concentrations of IGF-I and IGF binding proteins 2 and 3 may be indicative of the ability of cows to resume cycling during the post-calving period. These metabolic factors may provide a method to identify females that are more effective at converting limited feed resources into marketable product.
Serum concentrations of growth hormone (GH), IGF-I, IGF binding proteins (IGFBPs), and glucose were measured at wk 2 and 10 postpartum to determine if these variables differed between beef cows that did or did not resume cycling by wk 20 postpartum. Cows were individually fed either 130 or 170 kcal ME per kg metabolic weight during nonlactation and 170 or 210 kcal ME per kg metabolic weight during lactation for an average of 4.1 years prior to sample collection. The proportion of cows that resumed estrus within 20 wk after parturition was less (P < .05) at the lower daily feeding rate (5/14) than the higher feeding rate (11/15). Concentrations of IGF-I were less (P < .05) at both wk 2 and wk 10 in cows that failed to resume cycling compared to cows that resumed cycling. Concentrations of IGF-I increased from wk 2 to wk 10 in cows that resumed cycling but not in cows that remained anestrus. 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 in the study. At the higher feeding rate, body condition score and circulating concentrations of GH did not differ between cows that did or did not resume cycling. Circulating concentrations of IGF-I, IGFBP-2 and -3, determined at wk 2 postparturition, were demonstrated to be useful indicators of the capacity of energy restricted cattle to resume cycling during the postpartum period.