Empty body weight gain, retained energy differ in pre-weaned, post-weaned calves
By Caleb Hildebrand
Accuracy and precision are important in formulating diets to achieve production goals. Nutritionists use models and equations published by the National Research Council to accomplish this.
Specifically, this study looked at an equation used to predict empty body weight gain from the energy gained in muscle and fat. This equation works well for calves after weaning and has application in stocker, backgrounding and finishing operations. However, previous studies suggest that the equation may not work well for calves before weaning, but a comprehensive analysis has not been performed.
The discrepancy in the predictive ability of the equation between pre-weaning and post-weaning calves could be due to differences in the proportion of protein and fat in the gain. Older, more physiologically mature cattle deposit greater quantities of fat, which is an extremely energy dense tissue.
Oppositely, young calves tend to deposit mass in the form of protein as muscle fiber which tends to be composed primarily of water and has a lower energy content. Thus, the relationship between weight gain and energy gain (also known as retained energy) is likely quite different between pre-weaned and post-weaned calves.
A recent study at the Beef Cattle Institute at Kansas State University investigated the differences in the relationships of empty body weight gain (EBG) with empty body protein gain (EBPG) and empty body fat gain (EBFG) and retained energy (RE) in calves pre-weaning and post-weaning. It was hypothesized that discrepancies in the predictive ability of the nutritional equation used to predict empty body gain in calves pre-weaning and post-weaning could be due to differences in proportion of protein and fat in the gain.
A literature search was conducted to identify studies focusing on calves before weaning with EBG, EBPG and EBFG data available. Keywords and phrases such as calves, empty body, protein gain and fat gain were used in the search. This data set was combined with a previously compiled data set that focused on the same data for calves after weaning. The final combined data set was comprised of 177 observations from 42 studies.
A nonlinear regression model was chosen to evaluate the relationship between EBG and RE after computing correlations between EBG and the three variables of interest: EBPG, EBFG and RE. The effects of breed type and age were also evaluated.
Results from the correlation analysis indicated that EBPG and RE were more strongly correlated with EBG in calves before weaning than in calves after weaning. This is shown in the bar graph where EBG is on the y-intercept and the three variables of interest are on the x-axis.
Additionally, there was a greater difference between the correlation of EBG with EBPG and EBG with EBFG in pre-weaned calves than there was in post-weaned calves.
Interpretation of this data suggests that in pre-weaned calves protein or muscle gain has a greater effect on weight gain. This makes sense based on what is known about growth curves and physiological maturity.
The scatterplot shows the nonlinear regression EBG and RE for each of the calves in our data set. Visual observation of this data suggests that RE has a different relationship with EBG in preweaning calves (i.e., it has a greater slope) and visually, the relationship of EBG and RE is less variable in pre-weaned calves than the variability in post-weaned calves.
To summarize the results of this study, the relationship between empty body weight gain and retained energy differs between the two groups of calves. This suggests that a more robust equation or group of equations should be used in nutrition models. A new equation would better estimate the nutrient requirements of calves before they are weaned to maximize health and performance.
Additionally, cow herd simulation models could be improved. These models evaluate genetics and management practices to determine optimum production systems to maximize profitability. Lastly, producers could use the equation to predict the weaning weights of calves. This would allow them to market calves more effectively.
Hildebrand is a student intern with the Beef Cattle Institute, Kansas State University.
