MAIZE SILAGE FOR THE PASTURE-FED DAIRY-COW .5. A COMPARISON WITH WHEAT WHILE GRAZING LOW-QUALITY PERENNIAL PASTURES IN THE SUMMER

Dairy cows in mid lactation grazed paspalum-dominant perennial pasture s and were offered either crushed wheat or maize silage at 0, 25, 50, or 75 MJ metabolisable energy/cow.day. Another herd was offered maize silage ad libitum. Milk yield and composition, liveweight and body con dition, and pasture intakes were monitored over 8 weeks during summer. Cow performance was recorded for another 3 weeks when all cows were s upplemented with the same feedlot ration. Samples of pastures before a nd after grazing, supplement, rumen fluid, and faeces were collected f or chemical analyses. Linear regressions were used to calculate mean m ilk responses and rates of pasture substitution for the 2 supplement t ypes. Yields of milk and milk solids increased with level of supplemen t fed (with 1 exception) and were higher in cows fed wheat at the same level of supplemental energy. However, cows fed maize silage achieved higher body condition scores. On average, cows supplemented with whea t and maize silage, respectively, produced 0.72 and 0.38 kg extra milk /kg supplement (DM), and they substituted pasture at the rate of 0. 87 and 1.01 kg pasture DM/kg supplement DM. Low pasture quality (117 g c rude protein/kg DM and 59.5% in vitro digestibility) was considered th e main cause of high levels of pasture substitution and poor milk resp onses to maize silage feeding. Cows fed 6.8 kg DM/cow.day of maize sil age had very low rumen ammonia-N and faecal N concentrations. It was c oncluded that additional N should be included with maize silage when f ed to cows grazing low quality perennial pastures, even with feeding l evels as low as 2 or 3 kg DM/cow.day.