Effects of Cow Mature Size on Intake Calf Weight and Milk Yield in a Spring-calving Commercial Cow/Calf Operation

Abstract

Two experiments were conducted to evaluate the effects of mature BW and cow efficiency on DMI, milk yield, and calf weaning BW on spring calving Angus sired commercial cows. Cows one SD above and one SD below the mean were selected to high (HBW) and low (LBW) BW treatment groups, respectively. Cows were individually fed ad libitum low quality prairie hay. Cows were adapted to pens and diets for 5 days followed by a 5 day collection period. Dry matter intake tended to be higher (P = 0.15) at 10.26 kg/d for HBW cows compared with LBW 9.86 kg/d during late gestation. Intakes only tended to be different (P = 0.06) during early lactation between HBW and LBW, consuming 13.33 and 12.54 kg/d, respectively. Heavy cows consumed more than LBW during late lactation (11.49 vs. 10.26; P = 0.01). No difference in calf weaning BW was found. Annual DMI was 267 kg lower (P = 0.01) for LBW as compared with HBW. Efficiency index was calculated by annual intake divided by adjusted calf weaning BW. No difference was seen in efficiency index between HBW and LBW. Using the efficiency index, 9 cows from experiment 1 were selected; one SD above the mean for low efficiency (LE) treatment group and 9 cows one SD below the mean for a high efficiency (HE) cow treatment group. High efficiency cows had lower DMI than low efficiency cows (8.25 vs. 9.04 kg/d; P = 0.01) during late gestation. During late lactation, HE cows consumed 14.6 % less forage (P = 0.02) than LE. Dry matter intake was 3997 kg/yr for HE as compared with LE cows at 4354 kg/ yr (P = 0.01). Weaning BW was higher (P < 0.01) for HE than LE (222 vs. 178 kg). Heavy BW cows consumed more forage and weaned the same size calf as LBW, while at the same time having similar efficiency index numbers. High efficiency cows consume less forage and wean more calf.