Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 8, 2005
Publication Date: November 1, 2005
Repository URL: http://ars.usda.gov/SP2UserFiles/Place/54340000/Publications/calvingsystem.pdf
Citation: Grings, E.E., Short, R., Klement, K.D., Geary, T.W., MacNeil, M.D., Haferkamp, M.R., and Heitschmidt, R.K. 2005. Calving system and weaning age effects on cow and preweaning calf performance in the Northern Great Plains. Journal of Animal Science 83:2671-2683. Interpretive Summary: Rangeland forage quality in the Northern Great Plains is very dynamic exhibiting a narrow period of high quality forage in May and June when temperature and precipitation conditions are optimal for growth of native cool-season forages. In late summer, forage quality declines rapidly and generally stays low into autumn and winter, creating a long period when nutritional quality may be limiting to maximal beef production. The adequacy of Northern Great Plains forage quality for meeting beef cow nutrient requirements is dependent on the season of calving. Optimal calving times may vary depending on the particular goals of an individual operator. A three-year study evaluated late winter, early spring, and late spring calving systems with varied weaning strategies on beef cow and calf performance from Northern Great Plains rangelands. Study results show that choice of calving season can have large impacts on outputs from rangeland-based beef operations in the Northern Great Plains. Careful consideration of all goals is required in choosing the optimal calving time for a specific enterprise. Weaning weights are affected by both time of calving and age at weaning. While calf weights are greater in Feb and Apr calving systems compared to Jun, feed inputs may also be increased. Feed costs need to be weighed against calf prices and marketing strategies to determine optimum calving time. The impacts of trading harvested feed for grazing of native forge need to be considered in determining the appropriate herd size for a fixed forage base for each calving season strategy.
Technical Abstract: A 3-yr (1999-2001) study evaluated late winter (Feb), early spring (Apr), and late spring (Jun) calving systems (SC) in conjunction with varied weaning strategies on beef cow and calf performance from Northern Great Plains rangelands. Crossbred cows were randomly assigned to one of three calving seasons (avg n . SC-1 . year-1 = 168) and one of two weaning times (Wean 1, 2) within each calving season. Feb and Apr calves were weaned at 190- and 240-d of age; Jun calves were weaned at 140- and 190-d of age. Breeding by natural service occurred in a 32-d period that included estrous synchronization. Cows were managed through the year as appropriate for their calving season. Quantity and quality of hay and supplements were provided based upon forage and weather conditions, physiological state of the cows, and available harvested feed resources within a year. After weaning, two-thirds of the early weaned steers were fed in confinement in Montana and one-third shipped to Oklahoma and either grazed or fed forage, whereas half of the early weaned heifers grazed seeded pastures and half were fed in confinement. Early weaned calves were weighed on approximately the same day as late weaning. Birth weight (P = 0.14) and overall rate of gain from birth to weaning (P = 0.23) did not differ for calves from the three calving seasons but timing of gain did, with slowest rates of gain for Feb calves occurring from birth to 69-days of age and for Jun calves from 69- to 190-days of age. Calf weaning weight differed by weaning age within calving season (P = 0.001), and calves from the Jun calving season and weaned at 190-d of age tended (P = 0.06) to be lighter than the same age calves from the Feb or Apr calving seasons. Cow weight change and body condition score dynamics were affected by calving season, but the proportion of cows pregnant in the fall was not (P > 0.10). Cows suckled until later dates gained less or lost more weight between weaning times than cows weaned earlier. Previous year's weaning assignment did not impact production in the following year. Estimated harvested feed inputs were much less for the Jun cows compared to Feb and Apr cows. We conclude that season of calving and weaning age have significant impacts on outputs from rangeland-based beef cattle operations.