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

摘要

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 over the grazing season by applying an adequate stocking rate (SR). The aim of this study was to investigate the effect of two SR (cows ha -1 ), low (L, 3.9) and high (H, 4.8), on swards chemical composition, PDMI and milk performance of Holstein-Friesian cows (n=72) at two stages of lactation (SL), spring (S) and autumn (A) calving. Animals were randomly assigned to four groups (LS, LA, HS and HA) in a 2x2 factorial design. The high SR groups completed 5 rotations, with more grazing days (+13), lower pre- (14.3) and post-grazing (5.3) heights (cm) and higher herbage utilization (81.7%). The herbage allowance and PDMI (kg DM cow -1 day -1 ) were lower (p<0.05) with high SR (16.4 and 13.4) but higher (p<0.05) (g kg -1 DM) protein (149.1), carbohydrates (166.7) and digestibility (746.8) and lower (p<0.05) DM (18.4%), acid (283.5) and neutral detergent (508.6) fibre (g kg -1 DM) were found. Sward quality is deteriorated (p<0.05) from rotation 1 to 5, lower decrease occurred with high SR. Milk yield (MY) was higher (p<0.05) in spring calving cows (24.8 kg cow -1 day -1 ), with the lowest (p<0.05) milk protein (28.9) and fat (36.9) (g kg -1 DM). No differences were found on MY between treatments for SR, but higher protein and fat were reached using high SR. Increasing SR is achieved lower PDMI, but higher sward quality without penalizing MY and quality. 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. 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