PROTEIN SUPPLEMENTATION TO ENHANCE THE PERFORMANCE OF PREGNANT COWS ON ROUGH FESCUE GRASSLANDS IN WINTER

Rough fescue grasslands are readily damaged with heavy grazing pressur e in the summer but tolerate grazing in winter. In addition, these gra sslands have physical and nutritive properties that make them favourab le for winter grazing by cattle, which reduces the cost of winter feed ing while preserving the integrity of the grasslands. This study was c onducted on the rough fescue grassland to determine the impact of prot ein supplementation on pregnant Hereford cows and the effect of supple mentation on forage intake. A secondary objective was to determine the winter quality of forage from this grassland as measured by crude pro tein (CP), phosphorus (P), and acid detergent fibre (ADF) of selected species. The study site was in the rough fescue grasslands at the Agri culture and Agri-Food Canada Range Research Substation west of Stavely , AB. A canola based supplement (32% CP) with added minerals was fed t o pregnant Hereford cows at four levels [0, 0.4, 0.8, and 1.2 kg d(-1) per animal] from 1 November to 31 January over 3 yr. Two animals were used in each of 12 paddocks (1.67 ha each) arranged in a randomized c omplete block design with three blocks. Cow weight and backfat were re corded before and after each feeding period. Forage biomass and feed i ntake were estimated by harvesting plots before and after grazing, and with the use of a non-destructive method based on measurements of ind ividual plants that allowed estimates for each forage species. Cow wei ghts were affected (P = 0.002) by supplementation. Cows receiving 0.4 kg d(-1) supplement lost the most weight while cows receiving 0.8 or 1 .2 kg d(-1) lost the least. Backfat was not responsive to supplementat ion (P > 0.05). Rough fescue grasslands must be in good condition to b e able to support winter grazing because rough fescue provides most of the forage utilized by cattle in winter.