|Roberts, Andrew - Andy|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/19/2005
Publication Date: 7/1/2005
Citation: Roberts, A.J., Klindt, J.M., Jenkins, T.G. 2005. Effects of varying energy intake and sire breed on duration of postpartum anestrus, insulin like growth factor-1, and growth hormone in mature crossbred cows. Journal of Animal Science 83(7):1705-1714. 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 (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 body condition score, length of postpartum anestrus and nutritional status in F1 cows out of Angus or Hereford dams (6 to 8 cows/sire 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. Length of anestrus was affected by level of DMEI in Galloway, Longhorn, and Nellore sired cows, but not other breeds (P < 0.02 for interaction of sire breed and DMEI). Sire breed and level of DMEI affected (P < 0.01) body condition score was. Concentrations of IGF-1 and GH were determined at wk 2, 4, 8, and 14 to provide insight into changes in nutritional status (i.e., high GH and low IGF-1 indicates negative energy balance). Concentrations of IGF-1 (P < 0.03) were influenced by the 3-way interaction among sire breed, level of DMEI and wk postpartum. Concentrations of GH varied (P < 0.001) due to the interaction of DMEI and wk postpartum. To provide interpretation of these interactions, within cow linear regressions were used to estimate initial postpartum concentrations (intercepts) and change over time (slopes) for IGF-1 and GH. Intercept and wk 2 IGF-1 varied due to sire breed (P < 0.001), being greatest for Nellore, intermediate for Longhorn, and lowest, but not different among other sire breeds. Intercepts and slopes for IGF-1 and GH varied due to level of DMEI (P < 0.02). Slope of IGF-1 changed from a negative value (i.e., decreasing concentrations over time, indicating negative energy balance) to a positive value as DMEI increased, but magnitude of change between levels of DMEI tended to vary by sire breed (P < 0.09). 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). When examined across all sire breeds (simple correlation), length of anestrus was associated (r = .16; P < 0.06) with slope of GH. When effects of sire breed were accounted for (residual correlation), length of anestrus was inversely associated (r = -.23; P < 0.01) with intercept and wk 2 IGF-1 concentrations. Breed of sire influenced length of postpartum anestrus and energy balance, as predicted by IGF-1, in crossbred cows fed restricted levels of DMEI.