Thoughts on the energetic efficiency of grazing cattle

Authors: Gunter, Stacey; Moffet, Corey

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 10/10/2018
Publication Date: 7/29/2019
Citation: Gunter, S.A., Moffet, C. 2019. Thoughts on the energetic efficiency of grazing cattle. Journal of Animal Science. 97(E Supplement 1):69. https://doi.org/10.1093/jas/skz053.156.
DOI: https://doi.org/10.1093/jas/skz053.156

Interpretive Summary:

Technical Abstract: Energetic efficiency of cattle is a significant issue to the beef industry. Ruminant nutritionists have made strides in improving the efficiency of production, but we still see significant variation among individuals. A popular method for evaluating the efficiency of cattle is selection based on residual feed intake. This method has some limitations because of mounting evidence that it has a genotype x environmental interaction and individuals that are deemed most efficient when fed in confinement are found to not differ once grazing. Hence, cattle efficiencies need to be evaluated in appropriate environments. Because it is impossible to directly measure dry matter intake (DMI) by grazing cattle, we need to develop proxies to assess the animal’s efficiency. Experimental methods such as breath cloud analysis can provide us with individual estimates of total heat of production. By using known constants for retained energy in body weight (BW) gain, we can calculate ME energy intake. However, we still lack an ability to measure DMI unless the true digestibility of a grazed diet is known. The basal metabolism of cattle is their greatest energetic expense and if we are to decrease it, we will need to examine their body composition and differences in protein-turnover rates. The rates of protein and fat deposition in the carcass affects an animal’s efficiency and average daily gain (ADG) chiefly because of the higher energy density of fat but with greater percentages of carcass protein there also is a higher ME requirement for its maintenance. Energy expensed for protein turnover is approximately 23% of the total energy intake by cattle. Management that decreases carcass protein degradation probably would result in a decreased basal metabolism. The research needed to truly improve the energetic efficiency of grazing cattle will be time consuming and expensive, but for progress to be made it will be required.