Gomez, Robynne 1977- (2010-09). Characterization of Feed Efficiency Traits and Relationships with Temperament, Serum Hormones and Serum Metabolites in Growing Brangus Heifers. Master's Thesis.
Thesis
Physiological traits that are biologically associated with feed efficiency may be useful indicator traits residual feed intake (RFI). The objective of this study was to examine the relationships between RFI, temperament, serum hormones and serum metabolites in growing heifers. A 4 yr study (n = 114-119 heifers/yr) was conducted with Brangus heifers (Initial BW = 271 +- 26 kg) that were weaned for 25.5 +- 8.6 d prior to high roughage diet adaptation (ME = 2.0 Mcal/kg DM). Individual dry matter intakes (DMI) were measured using Calan gate feeders and BW measured at 7-d intervals during the 70-d studies. RFI was calculated as the residual from the linear regression of DMI on mid-test BW0.75 and average daily gain (ADG). Temperament scores and exit velocity (EV) were taken at 0-d. Temperament index (TI) was calculated as the average of EV and chute score. On 0-d, blood samples were collected and assayed for partial blood counts (WBC, RBC, hemoglobin, HB), metabolites (total protein, TP; glucose; creatinine; blood urea nitrogen, BUN; ?-hydroxybutyrate, BHB) and hormones (cortisol; insulin-like growth hormone I, IGF-I). Across all heifers, RFI was positively correlated with DMI (0.70) and feed:gain (0.59). Heifers with low RFI (< 0.5 SD from mean RFI 0.00 +- 0.71 kg/d) consumed 16 percent less DMI and had 16 percent lower feed:gain than heifers with high RFI (> 0.50 SD from mean RFI). RFI was weakly correlated (P < 0.05) with WBC (0.15), HB (-0.11), total protein (-0.10), BUN (0.10), creatinine (-0.11) and BHB (0.13). Hemoglobin and BHB were weakly correlated with all feed efficiency traits except feed conversion ratio (FCR). No phenotypic correlation was found between cortisol and IGF-I with RFI. Temperament was not correlated with RFI. Cortisol, creatinine and glucose were moderately correlated with all temperament traits. Low TI heifers (calm) had significantly higher Final BW, ADG and DMI than high TI heifers. Calm animals had significantly lower cortisol, HB, creatinine and glucose and higher BHB. These results suggest that the temperament and serum metabolites evaluated in this study have limited utility as indicator traits for RFI in growing heifers.
