– Cunningham-Hollinger , Z. Gray, K. Christensen, W. Means, S. Lake, S. Paisley, K. Cammack and A. Meyer
Canadian Journal of Animal Science, Vol 102(4), December 2022 (https://cdnsciencepub.com/doi/pdf/10.1139/cjas-2022-0015)
Meat production is projected to increase by 48,000 kg by the year 2027, and beef production specifically is projected to be 21% greater in developing countries and 9% greater in developed countries in 2027. To allow for this increase in production, improvements in feed efficiency will be required to maintain or reduce input costs while increasing productivity. Residual feed intake (RFI) has been used as a measure of feed efficiency in both research and production fields, as it allows for selection of improved animal feed efficiency without increasing mature body weight.
Hereford-Angus crossbred steers (year 1: 59 steers); year 2: 75 steers) from a single contemporary group in each year (birth to slaughter) were used in a 2-year study.
The presence of small intestinal mass differences only in year 1, when the lower fiber diet was used, is interesting and suggests that diet type may influence the role of the small intestine in feed efficiency. Additionally, greater large intestinal mass in high efficiency steers in year 2 suggests that more hindgut capacity improves efficiency with greater fiber content of the diet. Often the reported differences in previous studies are confounded with dry matter intake differences between concentrate and forage-based diets, even if energy or protein intake is similar among or between diet types. Dry matter intake was not affected by year but was affected by Residual feed intake class in the current study, indicating that Residual feed intake class differences are likely more related to dry matter intake whereas year differences may be due to fiber content.
In summary, small intestinal, stomach complex, liver, and kidney visceral organ masses relative to body weight and hot carcass weight in this study were less in high efficiency than low efficiency finishing steers from a single contemporary group per year from birth to slaughter. This occurred even when steers of divergent Residual feed intake classification had similar body weight, hot carcass weight, and average daily gain, as well as minimal carcass differences. Less gastrointestinal and visceral organ mass could lead to decreased energy expenditure for the maintenance of tissues in high efficiency steers.