Milk production traits of beef cows as affected by horn fly numbers and breed type

Authors: BROWN, MIKE - Retired ARS Employee; MAYS, A - University Of Arkansas; CLIFTON, S - Redlands Community College; ROSENKRANS JR., C - University Of Arkansas

Submitted to: American Society of Animal Science Southern Section Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/1/2012
Publication Date: 2/5/2013
Citation: Brown, M.A., Mays, A.R., Clifton, S.M., Rosenkrans Jr., C.F. 2013. Milk production traits of beef cows as affected by horn fly numbers and breed type. American Society of Animal Science Southern Section Meeting. https://asas.org/docs/southern-section/2013southern_abstracts_web.pdf

Interpretive Summary: Abstract Only

Technical Abstract: Pesticide resistance in horn flies indicates the need for more sustainable production systems. 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 were used to determine breed differences in horn fly count (HFC) and effect of HFC on milk yield and quality. Total HFC and milk yield estimates were collected every 28 d from May to October. Milk weight was adjusted to 24-h milk yield. Horn fly counts were transformed to natural log fly count (LFC) prior to analysis. Data for milk yield and quality and HFC were analyzed by mixed model least squares using a linear model including breed group, cow in breed group (random), month (repeated), month x breed and a linear covariate for calf birth date. Effects of HFC on milk yield and quality were estimated by including linear covariate of LFC and LFC x breed group. Horn fly counts varied over time (P<0.0001), with lowest population recorded in May (94±42 flies) and peaking in August (503±41 flies). Bonsmara and GELV had greater milk yield compared to HERF (8.74±0.73 and 8.64±0.86 vs. 5.99±0.57 kg/d, respectively, P<0.05), with CHAR, ROMO and BRAN intermediate (7.28±0.65, 7.01±0.65, 6.91±0.56 kg/d, respectively). An interaction of breed type and LFC affected (P<0.05) milk yield. Milk yield was reduced by 0.99 and 0.64 kg/d per unit increase in LFC in GELV and BONS (P<0.05). There was less evidence of HFC effects on milk yield in other breeds (P>0.25), but the regression coefficients were negative, with the exception of BRAN. The regression coefficient for milk yield on LFC was lesser in GELV than BRAN, CHAR, HER, and ROMO (P<0.05) and lesser in BONS than BRAN (P<0.05), where lesser indicates greater reductions in milk yield. For every one unit increase in LFC milk fat decreased by 0.15% (P<0.05), solids not fat decreased by 0.10% (P<0.05) and milk urea nitrogen decreased by 0.62 mg/dL (P<0.02). Our results indicate horn fly infestation negatively impacts milk production and quality of beef cows. Future multi-trait selection for sustainable cattle production may include parasite resistance.