Long-Term Effects of Winter Supplement on the Productivity of Range Cows

Abstract

For 10 consecutive winters, beginning at the age of 8 months, 120 Hereford females were fed Low, Moderate, High and Very High levels of supplement to determine the long-term effects of level of winter supplement on the productivity of beef cows. In addition, one half of the Very High level cows were switched to the Moderate level after three winters. In the first four calf crops high levels of supplement resulted in earlier (P<.025) calving dates. Increasing supplement from the Low to High levels resulted in larger birth weights in calf crops one (P<.001), two (P<.025), three P<.025) and nine (P<.025). Birth weights of calves from Very High level cows that were switched to the Moderate level tended to parallel birth weights of calves from cows on the Moderate level, whereas birth weights of calves from cows remaining on the Very High level were lower until the sixth calf crop. Calving percentages declined in the calf crops two and three, but all treatment groups had similar values in calf crop four and succeeding calf crops. Very High level females weaned only 66.3% of their calves in calf crop one, the other 33% were stillborn. After the first calf crop, High level females weaned more kilograms of calf per cow exposed than any other group. Differences among the Low, Moderate and High groups decreased rapidly through the third calf crop, and values for these groups remained similar for calf crops four through nine. Weighted average calving percent data through nine calf crops indicated that the Low (91.4%) and Very High (92%) groups ranked lower than the Moderate (95.5%), High (95.1%) and Very High Moderate (97.5%) groups. The weighted average weaning percentages were slightly lower for the Very High groups than for the other four groups. The treatment rank of kilograms of calf weaned per cow exposed was High (197), Moderate (187), Very High-Moderate (184), Very High (177) and Low (176).