High feed costs in recent years have driven growing interest in feed efficiency in cattle and the potential for genetic selection to improve efficiency. At the same time, advancements in technology have allowed more accurate measurement of individual feed intake, providing a means for comparing feed efficiency among groups of cattle.
However, while these systems collect individual intake data on cattle in confinement, measures of intake and efficiency in pasture cattle remain elusive. Current tests typically rely on systems such as Grow Safe bunks, which use radio-frequency readers on feedbunks to capture the identification of each animal as it feeds, linked with scales under each bunk to record the actual amount of feed each animal consumes. Combined with regular measurements of animal weights, this provides data for calculating measures of feed efficiency such as feed-to-gain ratio, residual feed intake (RFI) or residual gain.
During the Beef Improvement Federation (BIF) Conference last week, University of Illinois animal scientist Dan Shike, PhD, explained that feed efficiency is relatively easy to measure in cattle that are gaining weight, such as young bulls, heifers or feedlot steers. In mature cows though, most intake energy goes to maintenance and other functions such as gestation and lactation, rather than weight gain. Feed efficiency still varies though, with some cows requiring more or less feed intake, relative to mature weight, to function and maintain body condition, than other cows. More efficient cows can better maintain body condition and fertility, particularly in limited-feed range environments, compared with cows with higher maintenance requirements.
So, while researchers have measured intake and efficiency in growing heifers, and found considerable variability, questions remain as to how efficiency at that stage translates to efficiency as mature cows.
To pursue that question, Shike and his team conducted a five-year trial, beginning with 511 Angus and Simmental-Angus crossbred heifers. They initially measured individual intake in the heifers using a Grow Safe system, and identified low-, medium- and high-efficiency groups based on RFI. The selected 366 replacement heifers from the original group and put them into a typical cow-calf production system. Following calving, they brought the two-year-old females back into the Grow Safe system for 14-day tests at 60 days and 240 days post-partum, feeding them a ration that mimicked forage in a grazing setting.
They found the animals that were in the low-intake group as heifers continued to have lower intake compared to the medium and high groups as two-year-olds. At the same time, they also found no significant differences in breed-back rates or calf weaning weights. Calf birth weights were slightly lower in the low-intake females, as was the average age of the heifer at calving. The researchers concluded that in this trial, feed efficiency in heifers translated to feed efficiency in mature cows, and had little effect on reproductive efficiency. This work, Shike says, could help researchers incorporate more accurate EPDs for feed efficiency into selection indices.