Relationships of milk yield and quality from six breed groups of beef cows to preweaning average daily gain of their calves.

ABSTRACT

Milk yield and quality influence calf preweaning growth and ultimately the sale value of the calf at weaning. This study was conducted to evaluate the relationships of milk production and quality of beef cows to calf preweaning ADG in beef cows sired by Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano and from Brangus dams to determine whether the relationships were homogeneous across cow breed group. Approximately 50 cows/yr were milked monthly for 6 mo in each of the 7 yr of this study. Milk traits were included in models as linear and quadratic covariates along with interactions of the covariates with sire breed. Tests for curvilinearity and homogeneity of regression coefficients indicated the relationship of calf preweaning ADG to milk yield and quality was quadratic and homogeneous across Charolais and Gelbvieh; linear and homogeneous across Bonsmara, Brangus, and Romosinuano; and linear and different from other sire breeds in Herefords (P < 0.05). Exceptions to this were in the regression of calf preweaning ADG on the natural logarithm of somatic cell count (SCC) and milk urea nitrogen (MUN). The relationship of calf preweaning ADG to SCC was quadratic in Brangus (P < 0.05) and linear in Gelbvieh (P < 0.05) with little evidence (P > 0.05) of a relationship in Bonsmara, Charolais, Hereford, or Romosinuano. There was little evidence (P > 0.05) of a relationship of calf preweaning ADG to MUN in any of the sire breed groups. Results from this study confirmed the importance of the influence of milk yield and quality on calf preweaning growth but indicated this influence can depend on the breed composition of the cow. Furthermore, results suggest that breed origin or adaptation may have influenced the relationships of calf preweaning ADG to cow milk yield and quality.