Net Feed Intake of Growing Bulls and Relationships with Performance, Fertility and Ultrasound Composition Traits

Net feed intake (NFI) is a moderately heritable feed efficiency trait that has been shown to be genetically independent of ADG and BW in beef cattle. Objectives of this study were to characterize NFI in growing bulls, and to examine phenotypic correlations between NFI and performance, body composition, and fertility traits. Net feed intake was positively correlated phenotypically with feed conversion ratio (FCR), but was phenotypically independent of BW and ADG. Bulls with low NFI (< 0.5 SD below mean) consumed 20% less feed than bulls with high NFI (> 0.5 SD above mean), even though both groups of bulls gained the same and had similar BW. Net feed intake was not correlated with longissimus muscle area, but tended to be positively correlated with subcutaneous fat thickness at the 12 rib and percent intramuscular fat of the longissimus muscle. Scrotal circumference and sperm motility traits measured in this study were not correlated with NFI, although scrotal circumference was positively correlated with FCR. These results suggest that NFI may be a useful trait to improve feed efficiency in cattle, independent of growth traits. NFI was not related to bull fertility traits in this study, but additional studies are warranted to confirm these results and to further examine the relationships between NFI and body composition and meat quality traits.