39 Thoughts on the energetic efficiency of grazing cattle

Energetic efficiency of cattle is a significant issue in the beef industry. Ruminant nutritionists have made strides in improving production efficiency, but we still see significant variation among individuals. A popular method for evaluating the cattle efficiency is selection based on residual feed intake. This method has some limitations because of mounting evidence that it has a genotype x environment interaction. Individuals deemed most efficient being fed in confinement are not most efficient when their environment is grazing. Hence, cattle efficiencies need to be evaluated in appropriate environments. Because it is impossible to directly measure DMI by grazing cattle, we need to develop proxies to assess the animal’s efficiency. By using experimental methods such as breath cloud analysis to provide individual estimates of total heat of production and known constants for retained energy in BW gain, we can calculate ME energy intake. However, we still lack the ability to measure DMI without the true digestibility of the grazed diet. The greatest energy expenditure is basal metabolism and if we are to decrease it, we will need to examine their body composition and protein-turnover rates. The rates of protein and fat deposition in the carcass affects an animal’s efficiency and ADG chiefly because of the higher energy density of fat. However, with great protein deposition, there also is a higher ME requirement for its maintenance because of the high protein turn-over rate. Energy expensed for protein turnover is approximately 23% of the total energy intake by average cattle. Management that decreases body protein turn-over rate 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.