Biorefined press cake silage as feed source for dairy cows: effect on milk production and composition, rumen fermentation, nitrogen and phosphorus excretion and in vitro methane production

The objective of this study is to investigate the effect of replacing grass silage with biorefined grass silage (press cake silage) on dry matter intake (DMI), milk production and composition, rumen fermentation parameters, nitrogen and phosphorus excretion of early lactation Holstein Friesian dairy cows. An in vitro experiment using the rumen simulation technique (RUSITEC) also investigated the in vitro dry matter disappearance and methane (CH4) production of these feedstuffs. In this study, press cake silage was made from perennial ryegrass (Lolium perenne) using a novel biorefining process. Thirty early-lactation cows (Bos taurus strain Holstein Friesian) were used in a randomized complete block design experiment (n = 15) and offered two dietary treatments for a 56 d period: Grass silage (GS): 14 kg dry matter (DM) grass silage + 7.2 kg DM of concentrate + 0.44 kg DM of soyabean meal; Press cake (PC): 5 kg DM grass silage + 9 kg DM press cake silage + 7.2 kg DM concentrate + 0.44 kg DM soyabean meal. The dietary treatments were also incubated in vitro for a period of 18 days using the RUSITEC. In the in vivo study, DMI was lower for PC compared to GS. No difference was observed between the treatments for milk yield and milk quality; however, milk fat yield was lower and milk solids yield tended to be lower in PC compared to GS. Cows offered PC had higher N use efficiency (NUE, milk N/N intake), lower total N excretion and lower N excretion in feces and urine compared to cows offered GS. Total and fecal P excretion was lower in cows fed PC compared to cows fed GS. Ruminal NH3-N concentration was lower when PC was offered. In vitro rumen fermentation parameters such as pH, volatile fatty acids and CH4 output were not affected by treatment. In vitro dry matter disappearance and NH3-N concentration were lower for PC compared to GS. This study suggests that press cake silage can partially replace grass silage in the diet of dairy cows with beneficial effects on the environment and without compromising animal productivity.