The effect of dried apple pomace as a replacer for maize in the concentrate for Jersey cows grazing ryegrass pasture on production and rumen metabolism

Ryegrass pasture is characterised as having a high crude protein content (214-298 g/kg DM) but a low fibre content (390-550 g NDF/kg DM). Additional supplementation of energy based concentrates is provided to ensure profitable milk production. The high starch content in these supplements could negatively impact the rumen environment; lowering rumen pH and inhibiting pasture degradability. Dried apple pomace (DAP) is a possible alternative energy source to maize for dairy cows grazing pasture; however, little information is available on the effectiveness of this high fibre by-product for milk production from pastures. The aim of this study was to determine the potential use of DAP as an energy source for Jersey cows grazing ryegrass pasture. Seventy six lactating Jersey cows were blocked according to milk yield, days in milk and lactation number. Cows within blocks were randomly allocated to one of four treatments. Treatments were: NDAP-0% dried apple pomace and 75% maize; LDAP-25% dried apple pomace and 50% maize; MDAP-50% dried apple pomace and 25% maize; HDAP-75% dried apple pomace and 0% maize. Cows received 6 kg as is of the allocated concentrate in the milking parlour daily. Cows of all four treatments strip grazed perennial ryegrass pasture over an area of 8.6 ha. Additionally, four ruminally cannulated cows were used to monitor treatment effect on rumen activity and health. Each cow was randomly allocated to one of four treatments and subjected to a four period crossover. The 4% fat corrected milk yield was lower for cows in treatment HDAP than for cows in treatments NDAP and LDAP, differences ranging between 1.7 and 2.3 kg/day. The milk protein content was lowest for cows in treatments NDAP and MDAP, showing a cubic trend (P = 0.005), with milk fat content increasing as the level of maize substituted by DAP increased. Treatment had no effect on rumen metabolism parameters. Replacing maize with DAP is a viable option for cows grazing ryegrass pasture; however, the decrease in 4% fat corrected milk yield and the potential economic impact should not be overlooked.