Better rations lift fertility
Better rations lift fertility
By Richard Allison
INCREASING starch and reducing protein levels of rations for high yielding cows can reduce negative energy and boost dairy cow fertility, according to researchers.
There is a chance for producers to feed their herd out of the decline in fertility, says CEDAR director David Beever. "Do not rule out breeding as a solution, but fertility can be quickly improved with better rationing.
"This has been demonstrated in a three-year MDC-funded project at the centre in conjunction with the Royal Vet College, which has investigated nutritional strategies for minimising negative energy in high genetic merit cows."
First, the energy balance of cows with a 305-day average yield of 10,500 litres were compared with those yielding 8000 litres, says project leader, Andy Hattan. "Higher yielding cows took longer to reach positive energy balance after calving. Some were taking more than 12 weeks."
These differences were reflected in lower yielding cows losing less body condition, but liveweight proved a poor indicator of negative energy. High genetic merit cows started to gain liveweight after week five despite still being in negative energy balance.
Mr Hattan believes this discrepancy is due to increase in gut, liver and kidney size during early lactation, as well as gut contents. This means some producers are trying to breed cows while they are still deficient in energy.
"But negative energy cannot be totally avoided, some cows have a 60-80MJ energy deficit in the first week of lactation, equivalent to more than 5kg feed dry matter. Ways are needed to manage the ration to minimise this energy shortage."
Many producers are advised to feed high undegradable protein (UDP) compound to stimulate grass silage intakes and boost milk output. But decreasing protein content of maize-based rations from 19% to 16% was found to reduce body condition loss and cows reached positive energy four weeks earlier.
This confirmed Mr Hattans previous experience when managing a 200-cow herd in south west Scotland. "The problem with high yielding herds is that consultants and nutritionists offer conflicting advice on how to feed them, often based more on costs than cow biology."
But reducing dietary protein does have a small milk yield penalty. Less milk has to be weighed up against the savings with improved fertility and better calving intervals. It seems such a waste to cull cows only after three lactations due to infertility, he says.
"Increasing starch levels from 24% to 27% was also found to reduce body condition loss. It works by increasing blood insulin levels, which partitions more nutrients towards body condition," says Mr Hattan.
He also investigated the common practice of steaming up dry cows before calving to build up body reserves for lactation. Autumn calving cows were either offered the milking ration with dry cow minerals and straw or simply grazing with mineral supplements before calving.
Cows fed the milking ration for two weeks before calving had a flatter lactation curve with milk yields at 40kg a day for nearly seven weeks. But there was no difference between the groups in total energy balance despite steamed up cows producing 700kg extra milk during the first 17 weeks of lactation, says Mr Hattan.
"This was unexpected as it was thought that the flatter lactation curve for steamed up cows would lead to a smaller negative energy balance."
During the project, Mr Hattan also became the technical herd manager for the CEDAR herd of 400 cows. Changing ration starch and protein levels in addition to steaming up, was part of a range of measures to improve fertility.
"The CEDAR herds conception rates to first service have increased by 10% to 69% and calving interval has improved by 40 days to 380 days. First service now occurs at day 60 onwards, as there is little point serving cows in negative energy."
Achieving high dry matter intakes after calving is also essential. Feed presentation and offering good smelling ingredients will help encourage intakes, but rations can still be kept simple, he adds. *