Farmers needed to compare the cost benefit with alternatives such as using summer crops to prevent overgrazing and planting trees for reduced heat stress on their cows. They also needed to look at pasture substitution and the stocking rate effects of reduced supplement wastage.
He told an investing in off-paddock facilities workshop run by DairyNZ in Morrinsville in November that feed wastage was reduced when cow housing was used compared with paddock feeding, but there was little formal verification.
“It’s very difficult to measure,” he said.
A Dairy Australia study in 2009 compared six different feed-out methods on 50 dairy farms, all under dry conditions. The average feed wastage was 9% for paddock feeding compared with 2% for a system using permanent feeding facilities designed for minimal wastage and maximum control of feeding. The worst examples of wastage for each of the systems were 22% and 6% respectively.
DairyNZ’s published estimate of feed wastage for palm kernel was 30% in the paddock and for maize silage 25%. If those could be improved to 10% and 5% by through feeding via feedpads or a variation then 200kg drymatter (DM) more was eaten per tonne DM offered.
But Glassey said if there was less than 10% wastage on an uncovered pad that would probably not be reduced by covering it.
At Fonterra’s then forecast of $5.30/kg milksolids (MS), value was created by turning the feed into milksolids. There was the opportunity to create an extra $80 income per tonne of drymatter fed, by reducing feed wastage by 20%, using an 80g/kg DM response for 200kg DM. That equalled 16kg MS, which he priced at $5/kg MS.
“Alternatively it’s less future feed you have to buy to do the same production,” he said.
When it came to the effects of heat stress on cows, he said air temperatures of more than 21C and relative humidity of more than 75% reduced feed intake and lowered milk production in Friesian cows. The threshold for this breed as measured by a temperature humidity index (THI) was 68. Glassey said a THI calculator was available online with research showing that increasing the THI above the threshold by 10 meant a drop in milk production of 0.1kg MS/day.
Jerseys didn’t stop dropping milk production until the THI reached 75 and continued to stay more than 0.5kg MS/ day higher than Friesians up to THI levels of 85.
Avearge THI data showed there were small areas of Hawke’s Bay, King Country, Bay of Plenty and Northland which had THI levels of more than 68 for 20 days a year. But in one year in 10 this area extended to cover large parts of Waikato.
Glassey said farmers should assume the THI was more than 68 for 20% of the days every year which meant a 3.7kg MS loss/ cow equalling $20/cow/year.
“Reducing heat stress for a 500-cow Holstein Friesian herd has potential benefits of $10,000/year currently based on a $5/kg MS payout,” he said.
But other considerations needed to be looked at such as whether off-paddock facilities reduced THI impacts.
“Some farmers have recorded benefits and cows often seek shelter,” he said.
But there had been no New Zealand studies of the cooling effect of different shelters available so the expected benefits were yet to be verified. However barn design should consider summer cooling effects for many North Island regions.
Glassey said cows in centrally located facilities for 24 hours a day expended less energy walking to and from milking compared with those which were grazing. It was estimated they used two megajoules of metabolisable energy (MJ ME)/km on flat land and 6 MJ ME/km on hills so walking 3km/day over a 270-day lactation meant they used 1620 MJ ME on flat land and 4860 MJ ME on hills. Saving this energy could produce 2kg MS/cow on flat farms and 63kg MS/cow on hills.
Glassey said farmers claimed that walking their herd to an off-paddock facility at a cooler time of day reduced heat stress.
“Assume that preventing heat stress is worth about 50c/cow/day when conditions create heat stress,” he said.
When it came to shelters decreasing the risk of summer overgrazing, he said recent droughts had moved farmers to protect their pastures with cows off the paddocks for part of the day feeding on supplement, reducing grazing time. There was also a question as to whether there could be potential benefits from improved pasture persistence.
Looking at summer overgrazing he went back to 1950s research by Dr Ray Brougham which showed the annual yield for pastures grazed to 2.5cm in summer was 35% less than pastures grazed to 7.5cm. There was also a carryover effect into the next winter and spring with a 20% reduction in yield.
“Summer grazing management for persistency of annual yield is important,” he said.
The current recommendation was to prevent cows grazing below 3.5-4cm during summer with the same height recommended for other seasons apart from winter.
“Modern grazing management is consistent with Brougham’s conclusion,” he said.
Overgrazing to less than 3cm on a regular basis was estimated to reduce operating profit by $300-$600/ha.
“Farmers preventing cows from grazing below 4cm in summer adds to the returns from off-paddock facilities, but it’s not essential to have off-paddock facilities to get that,” he said.
On the flip side, under-grazing also had associated costs as if it happened repeatedly it reduced pasture growth rates and quality along with operating profit/ha.
Pastures grazed at a greater residual height had higher leaf death rates, lower average net growth rates and lower annual yields. Missing the target range for optimum residuals of 11 clicks on the rapid platemeter compared with seven to nine was estimated to cost $74/ha/grazing in lost feed supply.
Recent research quantifying the interactions between grazing interval, grazing intensity and nitrogen on the yield and growth of dryland and irrigated perennial ryegrass showed a mean yield over two years of 16,550kg DM/ha for pasture cut 8cm above ground level.
At a 5.5cm height the yield was 17,005kg DM/ha and at 3cm 17,450kg DM/ha. Working out the MS value of the extra 0.9t DM/ha between the highest and lowest rates it could be seen that 75kg MS at $5/kg MS equalled $375/ha if the extra feed grown was converted to MS.
