Pasture mass and pasture allowance influence on sward quality, pasture intake and milk performance

Abstract

Sixty-four Holstein-Friesian cows were randomly assigned to one of four treatments (M15, M20, H15 and H20) in a 2x2 factorial design, by considering: two pre-grazing pasture mass levels (PM, kg DM/ha): medium (M-1,600) vs. high (H-2,400); and two pasture allowance levels (PA, kg DM/cow/day): low (15) vs. high (20). Two periods (PI vs. PII) were studied. Sward density and pre-grazing sward height were higher in high compared to medium pre-grazing PM swards in PI (P<0.001, 255 vs. 235 kg DM/cm/ha and P<0.001, 14.8 vs. 10.9 cm, respectively) and PII (P<0.001, 216 vs. 196 kg DM/cm/ha and P<0.001, 14.3 vs. 13.0 cm, respectively). Lower post-grazing sward height and higher pasture utilization were obtained in low compared to high PA swards in PI (P<0.001, 4.1 vs. 4.9 cm and P<0.001, 98.8 vs. 89.9 %, respectively) and PII (P<0.001, 4.3 vs. 5.0 cm and P<0.001, 97.1 vs. 89.9 %, respectively). Pasture crude protein content and pasture organic matter digestibility were higher in medium compared to high pre-grazing PM swards in PI (P<0.001, 210 vs. 176 g/kg DM and P<0.05, 846 vs. 836 g/kg DM, respectively) and PII (P<0.05, 212 vs. 192 g/kg DM and P<0.05, 828 vs. 821 g/kg DM, respectively). This was due to higher leaf and lower dead proportions in medium than in high pre-grazing PM swards. Pasture dry matter intake (PDMI) (P<0.001, 16.5 vs. 14.7 kg DM/cow/day), milk yield (MY) (P<0.01, 23.8 vs. 22.7 kg/day) and milk solids yield (MSY) (P<0.05, 1.69 vs. 1.61 kg/cow) were higher in high compared to low PA swards in PI. Higher PDMI (P<0.001, 15.7 vs. 14.1 kg DM/cow/day), MY (P<0.001, 15.4 vs. 13.6 kg/day) and MSY (P<0.01, 1.19 vs. 1.08 kg/cow) were also found in high than in low PA swards in PII. The highest (P<0.001) milk output per ha (16,983 kg/ha) and milk solids per ha (1,268 kg/ha) were found in the group of dairy cows grazing in the M20 swards.