A study was conducted to evaluate the effect of sire growth potential, steer age, and cow size on intake, growth, and production efficiency in grazing cattle. Data were collected on 24 cow-calf pairs during each of four summers (1989 to 1992) and on 12, 7-mo-old and 12 yearling steers during three summers (1990 to 1992). Suckling calves and older steers were sired by either high- (Charolais with high EPD for yearling weight) or moderate-growth-potential (Line 1 Hereford with average yearling weight ratios) bulls. Cow size was defined by principal component scores developed from cow weights, condition scores, and hip heights. Forage, but not milk, OM intake by suckling calves was influenced (P < .05) by sire growth potential. Yearling high-growth-potential steers tended to consume more OM than yearling moderate growth potential steers (P < .10) when expressed as kilograms/day but not when expressed as grams/kilogram BW (P > .10). Seven-month-old steers ate less (P < .01) forage (4.3 kg/d) than yearlings (5.6 kg/d) when expressed as kilograms/day but more (P < .01) when expressed as grams/kilogram BW (7-mo-old, 15.9 vs yearling, 14.4 g/kg BW). Cow OM intake was affected by cow size and milk production but not calf growth potential. Milk production but not cow size was a significant covariate for cow efficiency (grams of calf BW gain/kilogram of forage OM intake by cow-calf pair). Calf sire growth potential did not affect cow efficiency. We conclude that growth potential of sire for suckling calves and steers and cow size for cows affected intake of rangeland forage in summer but did not affect efficiency of production from Northern Great Plains rangelands.
