Heritability of feed efficiency benefits producer’s bottom line
Feed accounts for around 70 percent of total costs on a cow/calf operation and its importance is well known. Improving feed efficiency within any or all sectors of an operation can reduce costs and increase performance. This can be achieved through genetic selection, as it is a moderately heritable trait.
“Beef cattle producers may derive economic benefits from selection for improved feed conversion if selection pressure is applied against excessive accumulation of subcutaneous fat,” explains a Journal of Animal Science (JAS) article that covers postweaning feed conversion in Angus cattle.
The article covered a study that found a realized heritability estimate for unadjusted feed conversion (feed/gain) of 0.26 and for adjusted feed conversion of 0.46, which means the trait is moderately heritable.
Another JAS article says researchers performed a similar study to determine the genetic and phenotypic relationship between feed intake and growth efficiency, and carcass merit. In addition to the heritability of feed conversion, it also looked at dry matter intake (DMI), average daily gain (ADG) and other feed-related traits of importance.
Data was collected on several hundred steers grown under feedlot conditions and was repeated for three years. Initially steers were fed a backgrounding ration consisting of 40 percent smooth bromegrass hay, 40 percent oats, and 20 percent corn or barley and were also given mineral supplementation. The ration was designed to promote growth at 2.2 pounds per day. The backgrounding period was followed by a 30-day adjustment period prior to starting the test. During this time grain levels were increased until they reached between 65 and 80 percent of the total ration.
“Feed intake was measured for each animal using the GrowSafe automated feeding system. Daily feed intake for each animal was recorded by the GrowSafe system,” states the article.
Body weights of all animals were recorded weekly the first year and bi-weekly the second and third years of the trial. Ultrasound was used to measure rib fat and marbling scores were conducted every 28 days. Animals were on full feed and water prior to any weights or measurements.
Animals were shipped to a commercial packing plant after final weights had been recorded. They were slaughtered the day after being shipped and carcass data was collected after carcasses had chilled at negative four degrees Celsius for 24 hours.
Carcass information was recorded on 381 animals. Results found that DMI had strong genetic correlations with ADG and metabolic body weight, and with ultrasound and carcass traits.
“The high genetic correlations of DMI with ADG and metabolic body weight imply that 76 percent of the genetic variation in intake is associated with genetic differences in maintenance and growth, and the remainder represents only a small proportion of the total genetic variance,” states the JAS article.
Producers should be aware that only selecting for faster growth and increased feed intake could easily result in larger framed animals that will eat more. If a steer is eating more and growing to a larger final weight, feed costs will increase and efficiency hasn’t always been enhanced. But, maintaining a moderate frame score while increasing feed intake and daily gain will reduce days on feed and thus lower feed costs, as the second study found.
Carcass grade was only moderately correlated with residual feed intake, which is the difference between an animal’s actual intake and its expected intake based on body weight and growth rate over a period of time. Low residual feed intake animals were found to have greater lean yield and higher quality yield grades compared with high residual feed intake animals.
“Evidence from this and other studies generally points toward a potential for small reductions in carcass fat and rate of gain in subcutaneous fat coupled with a slight improvement in carcass lean meat yield and yield grade following selection against residual feed intake. Selection against residual feed intake should be preferred over other measures of efficiency,” states the JAS article.
Neither study included the effects increased feed efficiency has on females, especially those kept as replacements. Heifer replacements should be genetically similar to their male siblings. By selecting for more efficient females and breeding them to feed efficiency bulls, ranchers can increase the degree to which feed efficiency traits are expressed throughout their herd.
As a herd’s overall efficiency increases, research shows cows are likely to maintain condition on less feed and calves can be expected to perform better on fewer pounds. But, as with any trait, research indicates balance is the key. According to the JAS, adding emphasis on feed efficiency can provide benefits to an operation, but it says producers should be careful not let other traits of importance slip as a result.
Compiled from Journal of Animal Science articles. Heather Hamilton is editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org