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Productive Longevity of First-Cross Cows Produced in a Five-Breed Diallel: II. Heterosis and General Combining Ability¹

Texas Agricultural Experiment Station, College Station 77843

Abstract

Records of 498 females from five purebred and 10 crossbred (reciprocals pooled) breed types were analyzed to determine the effects of crossbreeding on productive longevity and reason for removal and to estimate general and specific combining abilities. The breeds were Angus (An), Brahman (Br), Hereford (He), Holstein (Ho) and Jersey (Je). Average heterosis for productive longevity was 829 d (P < .001); most estimates of heterosis for particular crosses were significant. Estimates of heterosis ranged from 468 d (BrHe) to 1,189 d (BrHo). Crossbred cows had fewer deaths due to disease (19.5 vs 30.2%) and calving difficulty (1.8 vs 6.5%) and lower overall mortality rate (24.6 vs 39.7%) than purebred cows. Crossbred cows also had a lower incidence of removal due to infertility (13.1 vs 17.2%); however, crossbred cows were more structurally unsound (26.7 vs 23.7%) and had more severe vaginal or uterine prolapses (3.6 vs 1.8%) than purebreds. A higher frequency of purebred cows were removed for general illnesses, cancer eye and deaths due to unknown causes. Overall, more crossbred cows were in production at 14 yr of age than purebred cows (22.2 vs 5.9%). Breed effects and average heterosis were significant sources of variation; estimates of general combining ability (GCA) ranged from –383.1 d for Je to 241.4 d for Br. The GCA for An, Br and He were greater than for Je. Specific combining ability was not a significant source of variation. Crossbreeding can increase the longevity of beef cows and decrease mortality rates if breeds are chosen correctly. Crossbreeding to Brahman would increase longevity of cows for beef producers in the South.

¹ Dept. of Anim. Sci.

² Present address: Texas A&M Univ. Agric. Res. Ext. Center, Overton 75684.