Maize silage for the pasture-fed dairy cow. 5. A comparison with wheat while grazing low quality perennial pastures in the summer

摘要

Dairy cows in mid lactation grazed paspalum-dominant perennial pastures 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 condition, and pasture intakes were monitored over 8 weeks during summer. Cow performance was recorded for another 3 weeks when all cows were supplemented with the same feedlot ration. Samples of pastures before and after grazing, supplement, rumen fluid, and faeces were collected for chemical analyses. Linear regressions were used to calculate mean milk responses and rates of pasture substitution for the 2 supplement types. Yields of milk and milk solids increased with level of supplement 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 wheat 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 .O1 kg pasture DM/kg supplement DM. Low pasture quality (117 g crude protein/kg DM and 59.5% in vitro digestibility) was considered the main cause of high levels of pasture substitution and poor milk responses to maize silage feeding. Cows fed 6.8 kg DM/cow.day of maize silage had very low rumen ammonia-N and faecal N concentrations. It was concluded that additional N should be included with maize silage when fed to cows grazing low quality perennial pastures, even with feeding levels as low as 2 or 3 kg DM/cow.day.