Finding new ways to be efficient in the beef industry is an important goal, but we need to be aware of interactions between characteristics that may have unintended consequences.
Residual feed intake (RFI) is a measure of feed efficiency that is currently undergoing a great deal of research to determine its value in selection of beef cattle. RFI relates feed intake to a measure of body weight representing energy demand. Cattle with high positive values for RFI require more feed than predicted for their weight and are considered less-efficient, whereas cattle with negative values for RFI are more-efficient. When considering a specific trait for selection, it is important to consider the relationship of that trait to other significant traits.
Some research has suggested that heifers with low (more-efficient) RFI may reach puberty at a later age, but there has been little research on the relationship between RFI ranking and fertility in bulls. A paper in the November 2012 issue of the Journal of Animal Science presented the results of a study evaluating the relationship between RFI and several reproductive measures in beef bulls.
Researchers in Texas conducted several experiments using Angus, Bonsmara, and Santa Gertrudis bulls. After weaning, feed intake and weight gain was measured over 70 days to calculate RFI. Carcass composition was determined by ultrasound. Bulls were given breeding soundness exams after the feeding period to determine sperm quality. Bulls were between 365 to 444 days-old at the time of these exams.
Neither sperm motility nor scrotal circumference was related to RFI ranking in these cattle. However, sperm morphology was slightly poorer in the lower (more-efficient) RFI bulls. Low-RFI bulls were leaner than the high-RFI bulls, and the researchers suggested that this might be the cause of the slightly lowered percentage of normal sperm in the low-RFI bulls. Previous work has shown that bulls that are either too fat or too thin can have lowered sperm production and quality.
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