Lactation and calf weight traits of mature crossbred cows fed varying daily levels of metabolizable energy

Our objective was to evaluate differences in lactation traits and calf weig hts produced by Fl cows under varying daily metabolizable energy availabili ty. Measures of milk yields and calf weight traits were recorded on mature F-1 cows. The cows were produced from matings of Angus or Hereford dams wit h sires representing Angus/Hereford, Shorthorn, Galloway, Longhorn, Nellore , and Salers breeds. The cows' daily DM intakes of a diet composed of a cor n silage or alfalfa silage plus corn silage were recorded from approximatel y 2 wk postpartum until the calves were weaned at an average age of 170 d. Milk yield measurements were recorded when the calves were approximately 14 , 28, 56, 84, 112, 140, and 168 d of age. Sources of variation considered f or the traits of interest included sire breed of the cow (SBC) and the cova riates weaning age of the calf and daily metabolizable energy intake (DMEI) of the cow for lactation and calf weights. The linear and quadratic effect s were evaluated for DMEI. The SEC x DMEI (linear) interaction was signific ant for total milk yield. Sire breed of cow differences (P < .05) were obse rved for milk yield at time of peak yield, persistency, preweaning ADG, and weaning weight. Salers- and Shorthorn-sired cows had greater (P < .05) pea k yield than Galloway, Longhorn, or Nellore crossbred cows but were not sig nificantly different from the Hereford/Angus. Increasing DMEI linearly incr eased peak yield and total yield (P < .05). Preweaning ADG of calves from N ellore-sired cows was greater (P < .05) than all SEC. Preweaning ADG of cal ves from Galloway-sired cows was less than all SEC (P < .05). The linear ef fect of DMEI was heterogeneous across SEC for total yield. The pooled quadr atic effect of DMEI was significant for all traits except birth weight. The DMEI for expression of maximum weaning weight was estimated to be 29 Mcal. Feed efficiency ratios for the test period were 28, 27, 30, 25, 28, 32, an d 30 g calf weight:Mcal DMEI for reference and 1980s Angus/Hereford-, Short horn-, Galloway-, Longhorn-, Nellore-, and Salers-sired cows, respectively, at the DMEI level of 29 Meal.