Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/3/1996
Publication Date: N/A
Citation: Interpretive Summary: Genetic selection and breed choice are two means used by the beef cattle industry to alter growth rate in cattle. The impact that increased growth rate may have on efficiency of production depends upon the growth stage of the animal and the environment under which efficiency is measured. Cattle grazing on rangeland are subjected to a fluctuating environment with changes in nutrient quantity and quality throughout the year. This potentially limiting environment may affect the animal's ability to express genetic differences in growth potential and may, in turn, affect efficiency of production. A four year study was conducted to evaluate the effect of sire growth potential, steer age, and cow size on growth, intake and production efficiency (expressed as kilograms of calf weaned per kilogram of forage intake by the cow-calf pair) in cattle grazing rangelands in the Northern Great Plains. Growth potential of calf sire did not influence efficiency of production to weaning, even though weaning weight was greater for the high growth potential calves. High growth potential calves consumed more forage to meet the nutritional demands for extra growth. Calf sire growth potential did not affect milk production or cow intake so that there were no extra nutritional demands placed on the cow rearing a high growth potential calf. Efficiency of production increased with increasing milk production. Sire growth potential did not influence growth rate of older steers even though they tended to consume slightly more OM, indicating that rangeland may not supply the nutrients required for growing cattle to express genetic differences.
Technical Abstract: A study was conducted to evaluate the effect of sire growth potential, 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 (1989-1992) and on twelve 7-mo-old and 12 yearling steers during three summers (1990-1992). 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. Forage, but not milk, OMI by suckling calves was influenced (P<.05) by sire growth potential. Milk OM intake decreased from 1029 g/d (10.1 g/kg BW) in June to 696 g/d (3.3 g/ kg BW) in September, while forage OM intake increased from 394 g/d (4.2 g/kg BW) in June to 2311 g/d (10.3 g/kg BW) in September. Older, high growth potential steers tended to consume more OM than moderate growth potential steers (P<.10) when expressed as kg/d but not when expressed as g/kg BW (P>.10). Seven-mo-old steers ate less (P<.01) forage (4.3 kg/d) than yearlings (5.6 kg/d) when expressed as kg/d, but more (P<.01) when expressed as g/kg 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 (g calf BW gain/kg forage OMI 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. The greatest influence on efficiency of cow-calf production was milk production by the cow.