Cattle breeders are often cautioned to avoid selecting too heavily for a single trait. Avoiding extremes is the obvious reason; selecting for small frame size in the 1950s accidentally resulted in a dwarfism problem in a few breeds. Another reason is that a lot of traits are genetically correlated, meaning that selecting for one trait can have effects on other seemingly unrelated traits, such as how selecting for increased growth rate or leanness eventually results in later puberty in heifers and larger mature cows. No matter what trait you’re selecting for, there will always be unintended consequences on other genetic traits. Breeding your way into a corner can happen quite quickly, but breeding your way out can take a lot longer.
Feed efficiency has received a lot of attention in recent years because of its economic importance in every stage of cattle production. Feed:gain ratio is the economically relevant measure of feed efficiency in commercial feedlot cattle. But researchers don’t like feed:gain because it is influenced too much by differences in animal weight, growth rate and fatness. Researchers and geneticists prefer to measure residual feed intake (RFI) instead. RFI is feed intake that has been adjusted for growth rate, size and fatness. A low RFI identifies efficient animals that need less feed to grow and fatten at the same rate as animals with a high RFI. Some Canadian breed associations include RFI in their genetic evaluations, while others are considering adding it.
But before getting too carried away with selecting for RFI, it’s important to make sure that it won’t have undesirable consequences on other traits. Beef tenderness is one potential concern. The reasoning goes like this: muscle is very metabolically active, requiring energy as it constantly grows, breaks down, and replaces itself. Perhaps low-RFI cattle are more efficient because they may grow more muscle, more quickly and maintain more of it than inefficient (high-RFI) cattle. What if low-RFI animals grow and maintain more muscle because they have a slower rate of muscle breakdown? Does that mean they also won’t respond as well to post-slaughter electrical stimulation or aging? Could selecting for low RFI accidentally result in tougher beef that will reduce consumer satisfaction?
In an upcoming Canadian Journal of Animal Science paper, Dr. Heather Bruce and collaborators from the University of Alberta and Agriculture and Agri-Food Canada Lacombe investigate “Meat and sensory quality of major muscles from Angus, Charolais, and Angus crossbred steers with high and low residual feed intake” (doi.org/10.1139/CJAS-2019-0012).
What they did: Angus, Angus-cross and Charolais steers born in April or May 2014 were weaned at six months of age, backgrounded to 11 months and finished on a barley-based diet. Feed intake was measured for eight to nine weeks during the finishing period and RFI was calculated. The steers were slaughtered at 15 to 17 months of age. Growth performance, carcass measurements and a series of lab-based beef quality assessments and trained taste panels were carried out using cross-rib, inside (top) round, sirloin, and striploin steaks that had been aged for three versus 13 days and cooked to medium/medium-well done. Results were compared between steers with the lowest RFI (12 Charolais, 12 Angus and 12 Angus-cross steer calves) and steers with the highest RFI (12 Charolais, 12 Angus and 12 Angus-cross steer calves).
What they learned: Breed group differences reflected common industry perceptions and are unlikely to surprise any producers, have an impact on any breed promotion material or revolutionize any long-standing retail or food-service beef marketing programs.
Aging, as expected, improved tenderness. Aging for 13 days reduced shear force scores by 14 per cent (inside round), 18 per cent (sirloin), 24 per cent (cross-rib) and 35 per cent (striploin).
RFI group only affected one laboratory measurement and two taste panel measurements and only in the cross-rib steak. The pH of the cross-rib steaks from low-RFI steers was slightly higher than those from high-RFI steers. But the difference in pH was so small (5.57 vs. 5.55) and well below the point where dark cutting starts (at pH 5.8 to 6.0) that the commercial relevance is questionable. Cross-rib steaks from low-RFI steers had slightly lower scores for beef flavour intensity and sustained juiciness scores than those from high-RFI steers. Again, the differences were very small, and since cross-rib steaks are (or should be) marinated, it’s likely that the differences observed in these controlled lab conditions would not be noticeable in most home-cooking situations.
What it means: These results suggest that beef from cattle that differ in RFI does not necessarily differ in eating quality. This is encouraging, but it is important to note that these were simply baseline measurements. These steers just represent the variation naturally present in unselected populations, because these Angus, Angus-cross and Charolais herds had not been genetically selected for high and low RFI. But selection for RFI has begun in these herds, so the benefits or drawbacks of selecting for feed efficiency on the production traits that are important to cow-calf producers (e.g. fertility), cattle feeders (growth rate and feed:gain) and packers (quality grade and tenderness) will start to become clearer.
The Beef Research Cluster is funded by the Canadian Beef Cattle Check-Off and Agriculture and Agri-Food Canada with additional contributions from provincial beef industry groups and governments to advance research and technology transfer supporting the Canadian beef industry’s vision to be recognized as a preferred supplier of healthy, high-quality beef, cattle and genetics.