|Elzo, M - UNIVERSITY OF FLORIDA|
|Hansen, G - N. CAROLINA STATE UNIV.|
|Johnson, D - UNIVERSITY OF FLORIDA|
|Myer, R - N. FL. RES. AND EDU. CEN.|
|Wasdin, J - UNIVERSITY OF FLORIDA|
|Driver, J - UNIVERSITY OF FLORIDA|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2009
Publication Date: December 11, 2009
Citation: Elzo, M.A., Riley, D.G., Hansen, G.R., Johnson, D.D., Myer, R.O., Coleman, S.W., Chase, C.C., Wasdin, J.G., Driver, J.D. 2009. Effect of breed composition on phenotypic residual feed intake and growth in Angus, Brahman, and Angus x Brahman crossbred cattle. Journal of Animal Science. 87:3877-3886. Interpretive Summary: Feed efficiency in cattle is an important economic trait that has been shown to be moderately heritable. Brahman influenced cattle are very important to the southern US and are often targeted for price discounts based on perceived inefficiency in the feedlot. We evaluated temperament and feed efficiency of Angus(A), Brahman(B) and various combinations of Angus and Brahman breeding in a series feeding trials. Feed efficiency was recorded both as feed required for each increment of live gain (FCR) and as the residual of actual feed intake and that expected for the weight and rate of gain for an individual animal (RFI). This study found significant B breed effects for RFI, depending on the sex of the calf (negative and non-significant for bulls, negative and significant for heifers, and positive and non-significant for steers). Still, results here indicated that B cattle tended to be more efficient by RFI than A cattle for postweaning growth (PWG) under Florida subtropical conditions. As the fraction B of calves increased they tended to consume less feed but, the amount of feed needed per kg of weight gain (FCR)increased, making calves with greater B fraction less efficient than calves with greater A fractions. Lastly, B estimates for PWG were all negative indicating a decrease in PWG as the fraction of B in calves increased. As indicated above, results for FCR contradicted results for RFI. This is another aspect that would need to be reevaluated as new data are collected in Florida. Crossbreds were not different from BB for RFI, FCR, or rate of gain, but it increased feed intake. Temperament was not an important factor for any of the traits, with the exception of feed intake, where animals that consumed more feed exited the chute more slowly. This may be an indication of better temperament, or it may simply suggest that animals that ate more were more sluggish out of the chute. Due to prior exposure to being worked through chutes, perhaps calves became accustomed to this level of management, and consequently behavioral differences among calves decreased, and so did the potential impact of temperament on feed efficiency and weight gain traits. Heritabilities for all traits, except for FCR were reasonable. Similarly, estimates of genetic and phenotypic correlations seemed reasonable considering the size and complexity of the multibreed dataset used here. Estimates of genetic parameters here confirm that genetic variability existed and that selection for RFI would be feasible in the Florida Angus-Brahman multibreed population.
Technical Abstract: The influence of additive and nonadditive genetic effects and temperament on 4 postweaning feed intake and growth traits was evaluated in a group of 578 bull, heifer, and steer calves born in 3 Florida herds in 2006 and 2007. Calves had breed compositions ranging from 100% Angus (A) to 100% Brahman (B). They were randomly allocated to 24 pens each year by herd (Brooksville, Gainesville, Marianna), sire group (A, ¾ A ¼ B, Brangus, ½ A ½ B, ¼ A ¾ B, and B), and sex (bull, heifer, and steer) in a GrowSafe automated feeding facility at Marianna, FL. Calves were fed a concentrate diet during the 21-d adjustment and the 70-d trial periods. Individual daily feed intakes were recorded daily, and weights, chute scores, and exit velocities every 2 weeks. Phenotypic daily residual feed intake (RFI) was computed as the difference between actual and expected feed intakes. Calves were assigned to 3 RFI groups: high (RFI > mean + 0.5 SD), low (RFI < mean - 0.5 SD), and medium (RFI between mean ± 0.5 SD; SD = 1.8 kg). Traits were analyzed using mixed linear models. Fixed effects were contemporary group (herd-year-pen), RFI group (except when trait was RFI), age of dam, sex of calf, age of calf, B fraction of calf, heterozygosity of calf, mean chute score (CS), and mean exit velocity (EV). Brahman fraction and heterozygosity of calf were nested within sex of calf for RFI, and within RFI group for DFI, FCR, and PWG. Random effects were sire and residual. Feed efficiency tended to increase (lower RFI) as B fraction increased. However, calves required larger amounts of feed per kg gain (larger FCR) as B fraction increased. Postweaning gain tended to decrease as B fraction increased. Temperament traits were unimportant for all traits, except exit velocity for DFI, suggesting perhaps a lack of variation for temperament traits in this herd, or that calves got accustomed to the level of handling pre and postweaning, thus decreasing behavioral differences among them.