Protein supplementation to enhance the performance of pregnant cows on rough fescue grasslands in winter

Abstract

Rough fescue grasslands are readily damaged with heavy grazing pressure in the summer but tolerate grazing in winter. In addition, these grasslands have physical and nutritive properties that make them favourable for winter grazing by cattle, which reduces the cost of winter feeding while preserving the integrity of the grasslands. This study was conducted on the rough fescue grassland to determine the impact of protein supplementation on pregnant Hereford cows and the effect of supplementation on forage intake. A secondary objective was to determine the winter quality of forage from this grassland as measured by crude protein (CP), phosphorus (P), and acid detergent fibre (ADF) of selected species. The study site was in the rough fescue grasslands at the Agriculture and Agri-Food Canada Range Research Substation west of Stavely, AB. A canola based supplement (32% CP) with added minerals was fed to 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 complete block design with three blocks. Cow weight and backfat were recorded before and after each feeding period. Forage biomass and feed intake were estimated by harvesting plots before and after grazing, and with the use of a non-destructive method based on measurements of individual plants that allowed estimates for each forage species. Cow weights 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 supplementation (P > 0.05). Rough fescue grasslands must be in good condition to be able to support winter grazing because rough fescue provides most of the forage utilized by cattle in winter. Key words: Winter grazing, Festuca campestris, rough fescue, weight loss, backfat, digestibility, beef cattle