Feed supplement aids fertility levels
ADEQUATE supplementary feeding at grass is vital to maintain fertility levels in high genetic merit dairy cows, otherwise producers should select sires with a lower genetic merit.
As cows become better at partitioning nutrients towards milk production at the expense of body condition, feeding diets of low dry matter or energy density – such as grass – will impair fertility, says Bridget Drew, ex-director of ADAS Bridgets Research Centre.
"The challenge of forage-based systems for high genetic merit dairy cows is, therefore, to increase feed intake and quality to prevent excessive body weight loss."
To achieve this, she suggested feeding 8-10kg of concentrates in early lactation until pregnancy is established. This will help restrict body condition loss to no more than one condition score.
"Adopting a leader/follower system where lactating cows receive the best grass will help." Buffer feeding is also a useful option when grass is short or dry matter content is low, she adds. "In studies at ADAS Bridgets, although highest milk yields were obtained by feeding fixed rate concentrates to grazing cows, maize offered best value for money."
Even when steps are taken to maximise fertility, it will often be worse when cows are grazing than when housed, she explains.
"Expect heat detection rates to be lower in spring and early summer calved cows – 60% compared with 80% for other calving times. This is nothing to do with grass, but reflects difficulty with late night heat detection outside."
During mid-summer, pregnancy rates of 50-60% should be achievable when body condition is maintained. But pregnancy rate will fall to 30-40% when body condition is allowed to deteriorate, she warns. *