Effect of pasture allowance and cows’ lactation stage on perennial ryegrass sward quality, pasture dry matter intake and milk performance of Holstein-Friesian cows

Abstract

Efficient exploitation of grass for cattle requires the application of appropriated grassland management strategies to maximize pasture dry matter intake (PDMI) while maintaining high sward quality by allocating cows to an adequate pasture allowance (PA). The aim of this study was to investigate the effect of two PA, low (L) vs. high (H), on sward quality, PDMI and milk performance of Holstein-Friesian cows (n=72) at two lactation stages (LS), early (E) vs. middle (M). Cows were randomly assigned to four groups (LE, LM, HE and HM) in a 2×2 factorial design. The low PA treatments completed 5 rotations, with more grazing days (+13), lower pre- (14.3) and post-grazing (5.3) sward heights (cm) and higher herbage utilization (81.7%). The low PA had higher stocking rate than the high PA treatments (4.8 vs. 3.9 cows ha-1)and lower PDMI (13.4 kg vs. 14.4 DM cow-1 day-1) with higher (p<0.05) (g kg-1 DM) protein (149.1), carbohydrates (166.7) and digestibility (746.8) while lower (p<0.05) DM (18.4%), acid (283.5) and neutral detergent (508.6) fibers (g kg-1 DM). Sward quality is deteriorated (p<0.05) from rotation 1 to 5, lower decrease was found on low PA treatments. Milk yield (MY) was higher (p<0.05) in cows at early LS (24.8 kg cow-1 day-1), with the lowest (p<0.05) protein (28.9) and fat (36.9) content (g kg-1). No differences were found on MY between PA treatments, but higher protein and fat content were observed on low PA. Decreasing PA resulted in higher sward and milk quality without penalizing MY.