Effect of herbage mass and allowance on sward characteristics, milk production, intake and rumen volatile fatty acid concentration

The objective of this study was to examine the effect of herbage mass and daily herbage allowance (DHA) on sward characteristics and animal performance, dry-matter intake, rumen pH and volatile fatty acid production of unsupplemented spring-calving dairy cows throughout the main grazing season. Sixty-eight Holstein-Friesian dairy cows were randomly assigned across four treatments (n = 17) in a 2 × 2 factorial design. Two swards were created with different levels of pre-grazing herbage mass [allocated above 4 cm (>4 cm); 1700 kg DM ha^-1 (medium; M) or 2200 kg DM ha^-1 (high; H)] and two levels of DHA (>4 cm; 16 or 20 kg DM per cow d^-1). An additional eight lactating ruminally cannulated Holstein-Friesian dairy cows were randomly assigned to each treatment in a replicated 4 × 4 Latin square design. Sward and animal measurements were collected across four periods each of 1 week duration in April and May (PI) and July and August (PII). Maintaining the medium-mass sward across the season improved the nutritive value of the sward in the latter part of the grazing season compared with high-mass swards, thus resulting in increased animal intakes and milk production throughout PII. The higher organic matter digestibility of the medium-compared with high-masses during PII indicates that grazing severity and herbage mass in the spring to mid-summer period will determine sward quality parameters in the late summer period.