Nutrient requirements to maintain weight of mature, nonlactating, nonpregnant cows of four diverse breed types.

Four breed types with 12 cows/breed-type (Hereford x Angus, AHx; Charolais and Angus and Charolais x Hereford, Cx; Jersey x Angus, Jersey x Hereford, Jx and Simmental x Angus, Simmental x Hereford, Sx) were used to estimate nutrient requirements for zero daily weight change. Four nonpregnant, nonlactating cows of each breed type were assigned to one of three feeding levels [90 kcal metabolizable energy (ME).kg body wt (kg)-.75 . d-1, 150 kcal ME.kg-.75.d-1 and ad libitum] for a 140 d feeding period. The feeding trial was: Period 1 (d 0 to 70) and Period 2 (d 70 to 140). Effect of breed type, feeding level and the two-way interaction upon weight, weight change and feed intake data were initially analyzed. Two-factor interactions tended not to be significant for weight and weight change. The main effects of breed type and feeding level tended to be significant for weight and weight change in each of the periods. On d 0, the Sx (570 +/- 13 kg) and Cx (578 +/- 14 kg) were heavier (P less than .05) than the AHx (527 +/- 13 kg) all of which were heavier than the Jx (458 +/- 14 kg). Under the two restricted diets, the breed type ranking for dry matter intake corresponded to the ranking for initial body weight. However, at the ad libitum feeding level, the Cx tended to consume less dry matter than the other breed types. Measures of weight change were evaluated to test the effect of breed type and dry matter intake. The effect of breed type was significant only for daily weight change (kg/d) during Period 2. The linear and(or) quadratic effects of dry matter intake (2.53 Mcal ME/kg dry matter) on measures of weight change were significant in all periods. During Period 1, the pooled dry matter intake estimate for zero daily weight change and zero metabolic weight change were 8.1 kg/d and 75.3 g.kg-.75.d-1, respectively. For AHx, Cx, Jx and Sx during Period 2, daily dry matter intake for zero weight gain was 4.2, 5.3, 4.2 and 5.5 kg/d, respectively. A pooled estimate of 43.9 g . kg-.75 . d-1 was obtained for dry matter intake relative to metabolic size in Period 2.