|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2010
Publication Date: 6/1/2010
Publication URL: http://hdl.handle.net/10113/42988
Citation: Cooper, A.J., Ferrell, C.L., Cundiff, L.V., Van Vleck, L.D. 2010. Prediction of Genetic Values for Feed Intake from Individual Body Weight Gain and Total Feed Intake of the Pen. Journal of Animal Science. 88(6):1967-1972. Interpretive Summary: Gain and feed intake are economically important to beef producers. Individual gain is relatively easy to obtain. Individual feed intake is difficult and expensive to measure. Total pen feed intake is relatively easy to obtain. Gain is highly, but not favorably, correlated with feed intake. The goal of this study was to examine the possibility of estimating genetic value of an animal for feed intake without measuring its feed intake. The idea is to use total feed intake of the pen of the animal and the animal’s gain to estimate its genetic value for feed intake. Records of individual feed intake and gain were available for 289 steers that had been randomly assigned to 39 pens of 6-9 per pen. Appropriate individual feed intakes were summed to obtain total pen feed intake for this study. Genetic evaluations (estimated breeding values, EBV) for feed intake were compared for five methods using: 1) the animal’s feed intake and gain, 2) the animal’s feed intake, 3) the animal’s gain making use of the high genetic correlation with feed intake, 4) the animal’s gain and total feed intake of its pen, and 5) total feed intake of its pen. Methods 1 and 2 require each animal to have feed intake measured. EBV from Methods 1 and 2 were nearly the same: rank correlation of 99%. A rank correlation of 100% means animals are ranked exactly the same by both methods. The same animals would be selected for their breeding values. The rank correlations of EBV from Method 1 with EBV from Methods 3, 4 and 5 were 53%, 32%, and 15%. Methods using total feed intake of the pen of the animal were not as good as using EBV for feed intake using only gain of the animal (Method 3). Some of the same records were then assigned to 36 ‘artificially constructed’ pens of five paternal half sibs (same sire) to determine whether having relatives in the same pen would improve the methods using total feed intake of the pen of the animal. The rank correlations of EBV from Method 1 with EBV from Methods 3, 4, and 5 were 47%, 64%, and 62%. Responses from selection of the best 10% for Methods 3, 4, and 5 were 60%, 80%, and 77% of that for Method 1. This pilot study shows that a relatively inexpensive way to estimate breeding value for feed intake of an animal might be to use the animal’s gain and total feed intake of the pen of the animal without the expense of measuring feed intake of each animal when paternal half sibs are in the same pen. This method requires that pen effects are not large. If pen effects are large, confounding of pen effect and total pen feed intake of paternal half sibs would bias estimates of breeding values for feed intake. Further study with more animals of the use of total feed intake of the pen of the animal to obtain EBV for feed intake seems warranted.
Technical Abstract: Records of individual feed intake (FI) and gain (G) were obtained from the Germ Plasm Evaluation (GPE) program at US Meat Animal Research Center (USMARC). Animals were randomly assigned to pens. Only pens with 6 to 9 steers were used for this study (Data Set 1,289 steers). Variance components and genetic parameters were estimated using Data Set 1. Estimated breeding values (EBV) for FI were calculated using: 1) individual FI and G, 2) individual FI alone, 3) two-trait with individual G but with FI missing, 4) individual G and pen total FI, and 5) pen total FI. The analyses were repeated but with some of the same records assigned artificially to 36 pens of 5 and 4 paternal half sibs per pen (Data Sets 2 and 3). Models included year as a fixed factor and birth and weaning weights, age on test, and days fed as covariates. Estimates of heritability were 0.42 ± 0.16 and 0.34 ± 0.17 for FI and G. The estimate of the genetic correlation was 0.57 ± 0.23. Empirical responses to selection were calculated as the average EBV for the top and bottom 10% based on rank for each method but with EBV from Method 1 substituted for the EBV on which ranking was based. With Data Set 1, rank correlations between EBV from Method 1 (assumed best) and EBV from Methods 2, 3, 4, and 5 were 0.99, 0.53, 0.32, and 0.15, respectively. Empirical responses relative to Method 1 agreed with the rank correlations. Accuracy of EBV for Method 4 (0.44) was greater than for Method 3 (0.35) and for Method 5 (0.29). Accuracies for Methods 4 and 5 were greater than indicated by empirical responses and correlations with EBV from Method 1. Comparisons of the five methods were similar for Data Sets 2 and 3. With Data Set 2, rank correlations between EBV from Method 1 and EBV from Methods 3, 4, and 5 were 0.47, 0.64, and 0.62. Average accuracies of 56, 75, and 75% relative to Method 1 (0.67) generally agreed with the empirical responses to selection. As was found, accuracy using pen total FI and gain to obtain EBV for FI should be greater than using gain alone. Empirical responses and correlations with EBV from Method 1, however, were considerably less than expected from the accuracies with steers randomly assigned to pens. With assignment of five paternal half sibs to artificial pens, using pen total FI and individual gain was about 81% as effective for selection as using individual FI and gain to obtain EBV for FI and was substantially more effective than use of gain alone.