Implementing press cake from biorefined grass as a roughage in the diet of Holstein-Friesian dairy cows

A feeding trial was conducted with 60 mid-lactation cows that were, on average, 116 DIM, parity 3.5, and with a fat- and protein-corrected milk (FPCM) yield of 34 kg/d. Cows were blocked based on cow traits and milk performance. Cows in each block were randomly allocated to 1 of 3 treatments that differed by replacement of half of the dietary grass silage component (involving an exchange of 20% of dietary DM). Treatments were a regular high-quality grass silage (positive control; GS-POS), an ensiled press cake obtained from grass biorefinery (GS-PC), or a lower-quality grass silage (negative control; GS-NEG). After 2 pretreatment weeks with 10% ensiled press cake in dietary DM for all cows, cows received their treatment for 10 measurement weeks in which cow performance and gaseous emissions were measured with the GreenFeed system. Digestibility was measured with TiO2 as a marker in the eighth measurement week for half of the cows (i.e., 10 cows per treatment). Cows on GS-POS and GS-PC appeared to perform equally, whereas on GS-NEG, feed intake and FPCM yield were 6.5% and 6.6% lower, respectively. After an initial decline in milk protein content for GS-PC and GS-NEG compared with GS-POS, values increased again toward levels achieved for GS-POS after 6 wk of treatment. Milk protein yield on GS-NEG was 6.4% lower compared with GS-PC (mainly due to lower milk yield) and 8.8% lower compared with GS-POS (GS-POS and GS-PC did not significantly differ). Digestibility of DM and crude fat was higher for GS-PC compared with GS-POS (and numerically for all other nutrients) corresponding to in vivo trial with wethers that was conducted to determine in vivo the NEL value of press cake according to standard protocol for energy evaluation. Methane yields (g/kg DMI) of GS-POS and GS-PC did not differ, but were 4.5% lower than GS-NEG; likewise, carbon dioxide yield and hydrogen yield were 3.7% and 17.1% lower than for GS-NEG. It is concluded that a 20% dietary DM exchange of a high-quality grass silage with ensiled press cake that contained 39% more NDF and 29% less CP did not reduce cow performance or increase enteric methane, in contrast to exchange with a low-quality grass silage that contained 21% more NDF and 34% less CP. This outcome seems to be due to the higher digestibility of ensiled press cake compared with grass silage.