Calving system and weaning age effects on cow and preweaning calf performance in the Northern Great Plains1,2

Abstract

A 3-yr study evaluated late winter (Feb), early spring (Apr), and late spring (Jun) calving systems 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 systems (on average n= 168.calving system(-1).yr(-1)) and one of two weaning times (Wean 1, 2) within each calving system. The Feb and Apr calves were weaned at 190 and 240 d of age, whereas 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 throughout the year as appropriate for their calving season. Quantity and quality of hay and supplements were provided based on 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 were shipped to Oklahoma and were grazed or fed forage. One-half of the early weaned heifers grazed seeded pastures, and the other half was fed in confinement. Early weaned calves were weighed on approximately the same day as late-weaned calves. Birth weight and overall rate of gain from birth to weaning did not differ for calves from the three calving systems. Calf weaning weight differed by weaning age within calving system (P = 0.001), and calves from the Jun calving system that were weaned at 190 d of age tended (P = 0.06) to be lighter than calves of the same age from the Feb or Apr calving systems. Cow BW change and BCS dynamics were affected by calving system, but the proportion of cows pregnant in the fall was not. Cows suckled until later dates gained less or lost more BW during the 50 d between the first and second weaning than dry cows during this period. The previous year's weaning assignment did not affect production in the following year. Estimated harvested feed inputs were less for the Jun cows than for the Feb and Apr cows. We conclude that season of calving and weaning age affect outputs from rangeland-based beef cattle operations.

Calving date and wintering system effects on cow and calf performance I: A systems approach to beef production in the Nebraska Sandhills

“…The nutrient content of native range declines precipitously as range plants mature and enter dormancy. Grings et al (2005) found BCS differences between spring and summer calving cows similar to those observed in the present study. They reported summer calving cows had greater change in BCS throughout the production year compared with spring-calving cows.…”

“…Average daily gain of calves in the present study were similar to results reported by Grings et al (2005) where calves born in the spring were heavier at weaning than calves born in the summer at a constant weaning age. Forage quality dynamics explain the difference in weaning weight.…”

Economics of early weaning in northern great plains beef cattle production system

“…The long-term average precipitation is 343 mm with about 65% occurring during the mid-April through mid-September growing season. The average annual forage standing crop at the study site is 870 ± 14 kg/ha [10].…”

Effects of reduced in utero and post-weaning nutrition on milk yield and composition in primiparous beef cows

“…Predominant grasses at this site include grama (Bouteloua), needlegrass (Hesperostipa) and wheatgrass (Pascopyrum; Küchler, 1964). Average standing crop of forage produced annually at the study site is 870 ± 14 kg/ha (Grings et al, 2005). Stocking rate was 1.27 ha/animal unit month and the quantity of forage available in the 53.8 ha pasture during 128 days that primiparous cows were on trial was in excess of cattle needs.…”