Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 8, 2002
Publication Date: June 2, 2002
Citation: ROBERTS, A.J., JENKINS, T.G. 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. 2002. 53:454-456. Interpretive Summary: Previous research has demonstrated that different breeds or biological types of cattle respond differently to limited nutrient environments. In this study, we evaluated how sire breed (Angus, Hereford, Shorthorn, Galloway, Longhorn, Nellore or Salers) influenced length of postpartum anestrus in F1 cows out of Angus or Hereford dams, when cows were fed at one of 3 levels of daily metabolizable energy intake (132 or 189 kcal ME/kg metabolic BW or ad libitum). Concentrations of two metabolic hormones, IGF-1 and GH, were also measured in the blood as indicators of nutritional status (i.e., high GH and low IGF-1 indicate negative energy balance). Length of anestrus was affected by level of energy fed in Galloway, Longhorn, and Nellore sired cows, but not other breeds. Level of energy fed affected concentrations of IGF-1 and GH, and the patterns of changes in these hormones during the postpartum period. As we have observed previously, restricted availability of energy intake resulted in decreasing concentrations of IGF-1 and increasing concentrations of GH over time after calving. These changes indicate that animals in the restricted feeding groups were in a negative energy balance, which corresponds to increased levels of milk productions that occur during the first 2 to 3 months postpartum. However, magnitude of change in IGF-1 observed between the different feeding levels varied by sire breed. Cows sired by Nellore and Longhorn bulls had higher levels of IGF-1 than cows from other sire breeds, yet these cows actually exhibited longer periods of anestrus than cows from other breeds. These results indicate that caution needs to be taken when using levels of IGF-1 as an indicator of nutritional status across different breed types. The present study demonstrates that choice of sire breed to produce crossbred cows influences reproductive performance of cows as measured by length of postpartum anestrus, and through energy balance (as predicted by IGF-1) as levels of energy availability vary.
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 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. Intercept for IGF-1 was largest for Nellore (19.5), intermediate for Longhorn (16), and smallest (12 to 13) for remaining sire breeds. Intercept for IGF-1 was larger in ad libitum fed cows (16) than 189 kcal (13.7) or 138 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. Concentrations of GH increased at a greater rate over time in cows fed 132 kcal than cows fed 189 or ad libitum DMEI. Breed of sire influenced length of postpartum anestrus and energy balance (as predicted by IGF-1) in crossbred cows fed restricted levels of DMEI.