MILK-PRODUCTION IN ANGUS, BRAHMAN, AND RECIPROCAL-CROSS COWS GRAZING COMMON BERMUDAGRASS OR ENDOPHYTE-INFECTED TALL FESCUE

Milk yield and quality were measured on 139 Angus, Brahman, and recipr ocal-cross cows grazing common bermudagrass or endophyte-infected tall fescue for 4 yr to evaluate interactions of direct and maternal breed effects and heterosis for these traits with forage environment. Milk yield was estimated by method of milking machine, and milk fat, protei n, and somatic cell counts were evaluated in a commercial dairy labora tory, Monthly estimates were made beginning on an average d 61 of lact ation and continued monthly for six estimates in 3 yr and five estimat es in 1 yr. Data were averaged over month within year, and the model i ncluded sire breed, sire in sire breed, dam breed, forage, and age ave rages. Somatic cell counts were transformed using natural logarithms p rior to analyses. Forage effects for milk yield mere dissimilar among sire breed x dam breed subclasses (P < .10), resulting in higher level s of heterosis on common bermudagrass than on tall fescue. Maternal br eed effects for milk yield favored Angus on bermudagrass (P < .05) but not on tall fescue, whereas direct breed effects were similar on both forages and favored Brahman. Milk fat was reduced on tall fescue comp ared to bermudagrass by an average of .6% (P < .01), and direct breed effects were similar across forages and averaged 1.04% (P < .01) in fa vor of Brahman. Heterosis and maternal breed effects for milk fat were not important. There was little evidence of direct and maternal breed effects or heterosis for milk protein or somatic cell counts. These d ata suggest that heterosis for milk yield is larger on common bermudag rass than on tall fescue and that-grazing endophyte-infected tall fesc ue is detrimental to milk fat.