Abstract
This study aimed to evaluate the performance in feedlot and temperament of Nellore bulls classified by residual feed intake. The residual feed intake was calculated as the difference between the observed and predicted dry matter intake. Bulls classified as low residual feed intake had lower dry matter intake (kg day-1) and dry matter intake (g kg-1 d-1) of body weight, and were more efficient in feed conversion ratio than those classified as medium and high. The average daily gain didn't differ among residual feed intake classes and was 1.69 kg day-1, 1.82 kg day-1 and 1.71 kg day-1 for bulls classified as low, medium, or high, respectively. The residual feed intake was positively associated with dry matter intake, feed conversion ratio and subcutaneous fat thickness. The subcutaneous fat thickness was lower in bulls classified as low residual feed intake than in those with medium and high. No differences were observed in flight speed and reactivity score among residual feed intake classes. Overall, we concluded that bulls classified as low residual feed intake consumed less dry matter than high, with no differences in average daily gain, temperamentand had better feed efficiency, albeit their subcutaneous fat thickness was lower.
Highlights
The improvement of feed efficiency in the beef cattle production system is economically important because of the high cost of feed
The present study aimed to evaluate the growth performance, subcutaneous fat thickness, rump fat thickness, loin-eye area, temperament, and body morphometric measurements of Nellore bulls classified by residual feed intake (RFI)
The dry matter intake (DMI), kg day−1 and DMI (g kg−1 d−1) of body weight was significantly lower (P < 0.05) in bulls classified as low RFI than in those classified as medium and high RFI
Summary
The improvement of feed efficiency in the beef cattle production system is economically important because of the high cost of feed. Feed conversion ratio is one of the variables used to measure feed efficiency in beef cattle. This measurement is related to body size and growth rate, and selection may result in heavier animals (Herd & Bishop 2000) and, increased maintenance requirements. Selection based on residual feed intake (RFI; Koch et al 1963) has been recently used as a measure of feed efficiency as it is not related to body weight (BW; Herd & Bishop 2000).
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