Effect of herbage mass and allowance on sward characteristics, milk production, intake and rumen volatile fatty acid concentration
2010
McEvoy, M. | Delaby, Luc | Murphy, J. P. | Boland, T. M. | O'Donovan, M.
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 x 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 x 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.
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