Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/1999
Publication Date: N/A
Interpretive Summary: For a cattle firm, these results extend the concept of matching the breed resources to the production environment. The calf's genetic potential for growth becomes a consideration in identifying the breeds or breed crosses to be used and this must be considered in conjunction with the marketing endpoint. Management of cow/calf enterprises, where revenue is primarily generated from weaning calf sales, using genetic resources to enhance growth performance of the calves requires consideration of the genetic potential for lactation of the cows. With constraints in cow feed resources that result in a cow herd with lower milk production, the enhanced growth potential in the calf crop may not be realized. Likewise, if high growth potential calves are produced by low milk potential cows, the growth is not realized by the cow/calf enterprise. If the cattle firm extends ownership beyond weaning or is paid a price premium sufficient to offset any additional cost incurred, this management consideration of calf growth and cow lactation becomes of lesser importance. In the former, benefits of higher genetic growth potential are realized in the post weaning enterprises. In the latter, the cow/calf producer offsets higher costs with increased revenues generated by marketing increased weights. The need to ensure a premium is necessitated by two factors. First, the curvilinear relationship between increasing levels of DMEI and weaning weight resulting in a diminishing rate of return in the conversion of cow ME to calf weight and; secondly, risks associated with future reproductive performance associated with higher milk production potentials.
Technical Abstract: The objective of the study was to evaluate differences in lactation traits and calf weights produced under varying daily metabolizable energy availability of F1 cows. Measures of milk yields and calf weight traits were recorded on mature F1 cows produced from matings of Angus or Hereford dams with sires representing Angus/Hereford, Shorthorn, Galloway, Longhorn, ,Nellore, and Salers breeds. Individual daily intakes of a diet composed o a corn silage or alfalfa silage plus corn silage diet were recorded from approximately 2 wk post partum until the calves were weaned at an average age of 170 d. Sources of variation considered included sire breed of the cow (SBC) and the covariates weaning age of the calf and daily metabolizable energy intake (DMEI) of the cow for lactation and calf weights. The interaction between SBC and DMEI (linear) was significant for total yield, persistency, and weaning weight. Sire breed of cow differences (P < .05) were observed for milk yield at time of peak yield and preweaning ADG. Increasing DMEI linearly increased peak yield and total yield (P < .05). The linear effect of DMEI was heterogeneous across SBC for total yield, persistency, and weaning weight. The pooled quadratic effect of DMEI was significant for all traits except birth weight. DMEI (Mcal ME/d) at which maximum weaning weight would be predicted were 26.7, 39.9, 26.5, 25.8, 28.0, and 24.9 for Angus/Hereford, Shorthorn, Galloway, Longhorn, Nellore, and Saler sired cows. Feed efficiency ratios (gm calf weight/Mcal DMEI) for the test period were 29, 29, 27, 30, 33, and 33 for Angus/Hereford, Shorthorn, Galloway, Longhorn, Nellore, and Saler sired cows, respectively, at the DMEI level from which diminished rate of increase in weaning weight per unit of DMEI increased occurred.