The impact of grain-based concentrate allocation and pasture state on ryegrass pasture on in vitro digestibility

This study investigated the impact of 4 pasture states, 3 grain-based concentrate (GBC) allocations and 3 pasture fractions on the in vitro dry matter (DM) digestibility (IVDMD) of ryegrass (Lolium multiflorum ) pasture. Thirty six dairy cows in mid-lactation that grazed ryegrass were divided into 3 groups having 12 cows in each group. Cows in each group were offered 2.7 (low), 5.4 (medium) or 8.1 (high) kg DM GBC/cow/day, provided in two equal allocations in the milking bail. Each group of 12 cows in each GBC was further divided into 4 groups as they accessed 4 pasture states. These were fresh-fresh (FF), fresh-depleted (FD), depletedfresh (DF) and depleted-depleted (DD) ryegrass accessed by the cows in AM-PM, respectively. Rumen fluid was collected from 3 cows per treatment after the morning GBC feeding and milking on days 1 and 7 of the experimental period using a stomach tube. Rumen fluid from each cow were pooled by treatment (3 rumen fluid samples combined) before the commencement of two incubations on day 1 and 7. Pasture samples were harvested 5 cm above ground level on day 1 of the experimental period from three different locations within a paddock of the day 2 pasture allocation and cut vertically from the bottom to top into 5 to 10 (BF), 10 to 15 (MF) and >15 (TF) cm fractions with a scissor. The IVDMD of these pasture fractions was determined by in vitro batch culture incubations in rumen fluid collected from treatments above. Rumen fluid from cows that accessed fresh pasture in their last allocation (FF and DF) before GBC feeding did not improve IVDMD with medium compared to low GBC, but IVDMD increased when incubated in rumen fluid of cows offered with high GBC. However, IVDMD was increased in rumen fluid from cows that accessed depleted pasture in their last allocation (DD and FD) before GBC feeding and offered with medium-high GBC