Animal and Grazing Model, DMI and Enteric Methane Emissions Estimates

Briefly, a total of 40 spring calving late lactation dairy cows, balanced by breed (Holstein Friesian, Norwegian Red and Norwegian Red × Holstein Friesian) were selected in April 2011 from the main herd at the Dairygold Research Farm (Teagasc, Animal and Grassland Research and Innovation Centre, Moorepark, Fermoy, Co. Cork, Ireland). Cows were randomly assigned to two herds and rotationally grazed swards containing either perennial ryegrass (Lolium perenne) only (PRG; n = 20) or perennial ryegrass and white clover (Trifolium repens) (WCPRG; n = 20). A postgrazing sward height (PostGSH) of 4 cm above ground height was targeted to allow individual animals a daily herbage allowance (HA) of 16 kg of DM. Additionally, cows were allocated a supplementation of 1 kg of concentrate/cow per day (CP = 154.1, NDF = 40.9, and ash = 102.8 g/kg of DM). Concentrate supplementation was withdrawn three days prior to the measurement of dry matter intake (DMI), followed by an increase in HA to 17 kg of DM/cow per day.

The PRG swards contained a 50:50 mixture of tetraploid (AstonEnergy) and diploid (Tyrella) PRG varieties sown at 37 kg/ha. The WCPRG sward included the same relative PRG combination utilised in the PRG sward (37 kg/ha) in addition to a medium leaf white clover mixture of 50:50 (Chieftain and Crusader) sown at a rate of 5 kg/ha.