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Title: Associations among heat shock protein 70 genotype, forage system, and horn fly infestation of beef cattle

item TURNER, CHRISTINA - University Of Arkansas
item BROWN, HAYDEN - University Of Arkansas
item BROWN, MICHAEL - Retired ARS Employee
item STEELMAN, DAYTON - University Of Arkansas
item ROSENKRANS, CHARLES - University Of Arkansas

Submitted to: Professional Animal Scientist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/21/2013
Publication Date: 6/1/2013
Citation: Turner, C.M., Brown, H., Brown, M.A., Steelman, D., Rosenkrans, C. 2013. Associations among heat shock protein 70 genotype, forage system, and horn fly infestation of beef cattle. Professional Animal Scientist. 29(2013):237-241.

Interpretive Summary: Beef cattle response to the stress caused by horn flies has been reported to cause annual production losses near $876 million. One economically important trait affected by horn flies is milk production in beef cows which, in turn, affects preweaning growth and weaning weights of their calves. Control of horn flies has historically been accomplished by the use of insecticides. However, considerable insecticide resistance has developed in horn flies and more specific information on effects of horn flies on production traits is needed in order to develop effective strategies to mitigate losses. Research was conducted by the USDA-ARS, Grazinglands Research Laboratory and the University of Arkansas, Department of Animal Science to estimate losses in milk yield in beef cows as horn fly numbers increased. Monthly horn fly populations and milk yield and quality were measured each month on a herd of 53 cows from May to October. Cows were sired by Bonsmara (BONS), Brangus (BRAN), Charolais (CHAR), Gelbvieh (GELV), Hereford (HERF), and Romosinuano (ROMO) bred to Brangus dams. Results from this research showed that the milk yield of BONS and GELV-sired cows was affected by horn fly numbers to a greater extent that other sire breeds and the milk yield of HERF and ROMO-sired cows was affected to a lesser extent than other sire breeds. Results also demonstrated that the effects of horn flies on milk yield were greater during early lactation (May, June, July) compared to August, September, and October. Since BONS and GELV-sired cows were greater in milk yield than other sire breeds and HERF and ROMO-sired cows lesser in milk yield than other sire breeds, it appears that the effects of horn fly infestation on milk yield in beef cows in associated with level of milk production. Similarly, milk yield of all cows was greater in May, June, and July, supporting the hypothesis that horn fly infestation does more harm when milk yields are higher. Since beef cows are under higher metabolic stress at higher levels of milk yields, it seems reasonable to hypothesize that the additional stress of horn fly infestation exacerbates this stress, resulting in greater impacts on milk yield. These results suggest that horn fly control is particularly critical in early lactation and in breeds with higher genetic potential for milk yield. They also suggest that potential for significant horn fly infestation is a factor in determining the appropriate genetic potential for milk yield in beef cattle.

Technical Abstract: Horn fly infestations negatively impact economic traits of beef cattle. The impact of horn flies on beef cattle milk yield and quality was evaluated in cows sired by Bonsmara (BONS; n = 7), Brangus (BRAN; n = 13), Charolais (CHAR; n = 8), Gelbvieh (GELV; n = 5), Hereford (HERF; n = 12), and Romosinuano (ROMO; n = 8) from Brangus dams (n = 53). Horn fly counts and estimates of milk yield and quality were recorded monthly from May-October on individual cows. Horn fly counts were transformed to natural log horn fly count prior to analysis. Data for milk yield and quality, and horn fly count were analyzed by mixed model least squares using a linear model including sire breed, cow in sire breed, month, and month x sire breed. Effects of horn fly count on milk yield and quality were estimated by analysis of covariance using log horn fly count and log horn fly count x sire breed. Horn fly counts varied by month (P < 0.0001), with lowest population recorded in May (99 flies) and peaking in August (520 flies). Bonsmara and GELV sired cows had greater milk yield compared to HERF sired cows (8.75 and 8.62 vs. 6.02 kg/d; respectively; P < 0.05), with CHAR, ROMO and BRAN sired cows intermediate (7.28, 7.00, and 7.06 kg/d; respectively). The regression of milk yield on fly count differed among sire breeds (P < 0.05). Milk yield was reduced by 0.99 and 0.64 kg/d per unit increase in log horn fly count in GELV and BONS sired cows (P < 0.05). The regression coefficient for milk yield on log horn fly count was reduced in GELV sired cows versus BRAN, CHAR, HERF, and ROMO sired cows (P < 0.01), and reduced in BONS sired cows versus BRAN sired cows (P < 0.05). Increases in log fly count were associated with decreases in milk fat (P < 0.05), SNF (P < 0.05) and milk urea nitrogen (P < 0.02). Milk yield was reduced by increased fly numbers (P < 0.05) depending upon month of lactation and interaction with log horn fly count. In May, June and July milk yield was reduced 0.72, 0.68, and 0.71 kg/d per unit increase in log horn fly count. Our results indicate horn fly infestations reduce milk yield and quality of beef cows depending on sire breed and month of lactation in spring calving cows. Development of sustainable beef production systems may include selecting breed types whose milk yield and quality is less influenced by horn flies, allowing for better expression of genetic potential for milk yield in nutritionally challenging environments.