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

Author
item LIU, TING - Gansu Agricultural Uiversity
item MAYS, ANGELA - University Of Arkansas
item Turner, Kenneth
item WU, JIANPING - Gansu Agricultural Uiversity
item BROWN, MICHAEL - Retired ARS Employee

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/12/2015
Publication Date: 5/1/2015
Citation: Liu, T., Mays, A.R., Turner, K.E., Wu, J., Brown, M.A. 2015. Relationships of milk yield and quality of six breed groups of beef cows to preweaning average daily gain of their calves. Journal of Animal Science. 93:1859-1864.

Interpretive Summary: Milk yield and quality in beef cows are known to influence preweaning gain in their calves and considerable emphasis has been placed on genetic improvement of milk yields in beef cows. However, the relationships of calf preweaning gains to dam milk yield and quality may not be the same for all breeds of beef cattle. We determined calf preweaning gains based on milk yield and quality in cows sired by Bonsmara, Brangus, Charolais, Gelbvieh, Hereford, and Romosinuano breed groups, and from Brangus dams. Using regression models, results indicated that these regression equations differed across cow breed groups. Equations were similar for Charolais- and Gelbvieh-sired cows (European breeds) and similar among Bonsmara-, Brangus-, and Romosinuano-sired cows (tropically adapted breeds), but Hereford-sired cows differed from the other breed groups. Our research suggested that improvements in milk traits beyond a maximum effective level in European breed types, such as Charolais and Gelbvieh, may not result in improvements in calf performance. Improving milk traits in tropically-adapted breed types and Herefords has the potential to increase calf preweaning performance, within the range of the data of this study. This information is useful to scientist, extension agents, and producers refining beef cattle production programs to increase resilience to environmental factors.

Technical 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 to calf preweaning average daily gain (ADG) of 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 per 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 natural log 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. Further, results suggest that breed origin or adaptation may have influenced the relationships of calf preweaning ADG to cow milk yield and quality.