Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: May 1, 2002
Publication Date: June 22, 2002
Citation: Roberts, A.J., Jenkins, T.G. 2002. Effects of varying energy intake and sire breed on duration of postpartum anestrus, IGF-1 and GH in mature crossbred cows. Western Section of Animal Science Proceedings. 53:454-456. Interpretive Summary: Effective use of cattle breeds requires that cow/calf producers match the genetic potential for production with available feed resources. Information characterizing the production performance of breeds or breed crosses to variations in feed energy should assist producers in improving production efficiency. Extended post partum intervals decrease the opportunity of cows to rebreed during restricted breeding seasons. Information from this study documented an interaction in postpartum interval among mature cows sired by bulls of diverse breeds of cattle and concentration of circulating IGF-1. These results indicated producers could identify breed crosses to fit within the nutritional parameters that limit the effect of nutrition on post partum interval in mature cows.
Technical Abstract: Objectives of this study were to evaluate effects of sire breed (BREED; Angus, Hereford, Shorthorn, Galloway, Longhorn, Nellore or Salers) and level of daily metabolizable energy intake (DMEI; 132 or 189 kcal ME/kg metabolic BW or ad libitum) on postpartum anestrus and nutritional status in F1 cows out of Angus or Hereford dams (6 to 8 cows/BREED/DMEI). Circulating concentrations of progesterone in weekly blood samples collected 2 to 14 wk after calving were used to predict length of postpartum anestrus. Concentrations of IGF-1 and GH were determined at wk 2, 4, 8, and 14 to evaluate changes in nutritional status (i.e., high GH and low IGF-1 indicates negative energy balance). Within cow linear regressions were used to estimate intercepts and slopes for IGF-1 and GH. Analyses of variance were used to evaluate fixed effects of BREED, DMEI, and interaction of BREED and DMEI on length of anestrus, and slopes and intercepts of IGF-1 and GH. Length of anestrus was affected by DMEI in Galloway, Longhorn, and Nellore sired cows, but not other breeds (P < 0.02 for interaction of BREED and DMEI). Intercept for IGF-1 was affected by BREED (P < 0.001) and DMEI (P < 0.01). Intercept for IGF-1 was largest for Nellore (19.5), intermediate for Longhorn (16; P < 0.05 vs others), and smallest (12 to 13), but not different among remaining sire breeds. Intercept for IGF-1 was larger in ad libitum fed cows (16) than 189 kcal (13.7) or 132 kcal (12.7) fed cows. Slope of IGF-1 changed from a negative value (i.e., decreasing concentrations over time, indicating negative energy balance) towards a positive value as DMEI increased, but magnitude of change between levels of DMEI varied by BREED (P < 0.12 interaction of BREED and DMEI). Concentrations of GH increased at a greater rate over time in cows fed 132 kcal than cows fed 189 or ad libitum DMEI (P < 0.01 for DMEI effect on slope). Breed of sire influenced length of postpartum anestrus and energy balance (as predicted by IGF-1) in crossbred cows fed restricted levels of DMEI.