Effect of increasing pasture allowance and grass silage on animal performance, grazing behaviour and rumen fermentation parameters of dairy cows in early lactation during autumn

The aim of the present study was to determine the effect of daily pasture allowance and grass silage supplementation on milk production performance, grazing behaviour, rumen function, and blood and urinary metabolites in early lactation of dairy cows grazing on low herbage mass pastures. The study was conducted with 32 Holstein-Friesian cows over a time period of 63 days. Prior to experimental treatment, milk production, body weight, and days in milk averaged 23.8±0.70 kg/day, 537±9.6 kg, and 37.1±1.02, respectively. Four dietary treatments resulted from the combination of two pasture allowances above ground level (low 17 vs. high 25 kg of dry matter (DM)/cow/day) and grass silage supplementation offered at levels of 4.5 and 9.0 kg DM/cow/day. All of the cows received 2.6 kg DM of concentrate supplementation. Total DM intake was determined using the controlled-release chromium capsules method and milk composition was analysed weekly using infrared spectroscopy (Foss 4300 Milko-scan). Pasture allowance and grass silage supplementation had no significant effect on milk production (average 23.4 kg/day) or on milk composition. Grazing time and ruminating time were not significantly affected by pasture allowance. The rate of intake was significantly reduced (P<0.001) from 32.0 to 19.1 g DM/min by increasing grass silage supplementation. Increasing pasture allowance increased (P<0.001) daily live weight change (−0.061 and 0.553 kg/day for low and high, respectively). High pasture allowance decreased plasma β-hydroxybutyrate (P<0.05) and increased plasma urea-N (P<0.05) (3.95 and 4.10 mmol/L for low and high, respectively). Supplementation with grass silage had no significant effect on blood and urinary metabolites. Rumen ammonia and total volatile fatty acid concentrations were not significantly affected by increasing pasture allowance or increasing grass silage supplementation. This value, the lowest measured, is below the range recommended for optimal microbial growth. Rumen microbial nitrogen efficiency did not appear to be affected by pasture allowance or grass silage supplementation in that the purine derivative/creatinine ratio was similar for the four dietary treatments.