Abstract
The objective of this work was to evaluate performance, efficiency parameters and phenotypic correlations among measurements of energy efficiency of Nellore cattle selected for post weaning weight and classified according to residual feed intake, calculated by the difference between observed and predicted intake, based on average metabolic body weight and average daily gain. Thus, animals were classified within three groups: high (> mean + 0.5 standard deviation, less efficient); medium (±0.5 standard deviation of the mean); and low (< mean - 0.5 standard deviation, more efficient) residual feed intake. No differences were observed at initial and final body weights, average daily gain and dry matter intake among groups. Animals with low residual feed intake also had greater feed efficiency, feed conversion and partial efficiency of growth and did not differ from the other animals regarding to relative growth rate and Kleiber ratio. Residual feed intake was significantly correlated to feed efficiency (-0.25), feed conversion (0.25), partial efficiency of growth (-0.37) and dry matter intake (0.16) but it did not present significant correlation with body weight (0.04), average daily gain (-0.02), relative growth rate (-0.03) and Kleiber ratio (-0.05). Significant correlations were found between feed conversion and initial body weight (0.34) and average daily gain (-0.46). Partial efficiency of growth presented significant correlation with all other efficiency parameters analyzed. Residual feed intake has high potential in productive efficiency, when compared to the other energy efficiency measurements, being independent of growth and size of the animals.
Highlights
Feed efficiency improvement is a major concern in animal production, technological advances have been generated to quantify feed intake by an easy and low cost manner (Basarab et al, 2003)
Another definition is the selection toll not dependent on growth traits as conversion or feed efficiency (Koch et al, 1963). This fact has been demonstrated in studies performed with feedlot animals (Arthur et al, 2001), proving that there are no genetic correlations between residual feed intake and metabolic body weight and average daily gain (-0.06 and -0.04, respectively)
After five years of diverging selection, Australian scientists confirmed that the selection of animals for efficiency resulted in a progeny of lower intake and slightly thinner, but the performance was similar to the animals selected for high residual feed intake (Arthur et al, 2008)
Summary
Feed efficiency improvement is a major concern in animal production, technological advances have been generated to quantify feed intake by an easy and low cost manner (Basarab et al, 2003). Residual feed intake is the difference between the expected intake of the animal and what it consumes, based on its metabolic weight and average daily gain Another definition is the selection toll not dependent on growth traits as conversion or feed efficiency (Koch et al, 1963). This fact has been demonstrated in studies performed with feedlot animals (Arthur et al, 2001), proving that there are no genetic correlations between residual feed intake and metabolic body weight and average daily gain (-0.06 and -0.04, respectively). Average daily gain tended for a negative association with residual feed intake
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