|Roberts, Andrew - Andy|
Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2003
Publication Date: 6/1/2003
Citation: ROBERTS, A.J., JENKINS, T.G. ASSOCIATIONS AMONG CIRCULATING CONCENTRATIONS OF IGF-1 AND GH DURING THE POSTPARTUM PERIOD WITH RESUMPTION OF ESTRUS, CALF WEIGHTS, AND MILK PRODUCTION IN MATURE CROSSBRED COWS FED VARYING LEVELS OF ENERGY INTAKE. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2003. v. 54. p. 288-290. Interpretive Summary: Biological variation within and across different breeds or breed types provides an opportunity to select cows best suited for particular nutrient and management production systems. The present research provides evidence that circulating concentrations of IGF-1 and GH determined at different times during the postpartum period may be indicative of energy balance, and therefore useful in identifying animals best suited for production under limited nutrient environments. However, application of this methodology will require development of adjustment factors for use across different breeds, and application may not be informative under ad libitum fed situations.
Technical Abstract: Circulating concentrations of IGF-1 and GH fluctuate in response to nutritional status. Objectives of this study were to evaluate usefulness of circulating profiles of IGF-1 and GH during the postpartum period as predictors of capacity to resume estrus and level of production (milk and calf growth). Mature crossbred cows produced from Angus, Hereford, Shorthorn, Galloway, Longhorn, Nellore, or Salers sire breeds were fed at 132 or 189 kcal ME/kg metabolic BW or ad libitum (6 to 8 cows/sire breed/feed level). Concentrations of progesterone in weekly blood samples collected 2 through 14 wk post-calving were used to estimate length of anestrus. Concentrations of IGF-1 and GH were determined in serum samples collected at wk 2, 4, 8, and 14 postpartum. Within cow regressions were used to obtain estimates (i.e., slopes) of changes in IGF-1 and GH concentrations over time. Analyses of covariance were used to evaluate linear effects of concentration at wk 2 and slope of IGF-1 or GH, fixed effects of sire breed, and interactions among linear and fixed effects on length of anestrus, peak week and level of milk production, and adjusted weaning weight (WW) of calf. Breed of sire accounted for variation (P < 0.02) in all variables except peak week of milk production. Length of anestrus was influenced (P < 0.03) by interactions between IGF-1 covariate terms with breed of sire. Peak level of milk production was associated negatively (P < 0.01) with IGF-1 at wk 2. Time of peak milk production was influenced (P < 0.1) by the interaction of GH at wk 2 with breed of sire. Adjusted WW of calf was associated negatively with both GH covariate terms (P < 0.01). Within breed, initial concentrations (wk 2) and pattern of change in IGF-1 and(or) GH concentration during the postpartum period are predictive of capacity to resume cycling and potential for productivity (milk and calf wt).