PLUGGING THE SUPER-COW ENERGY GAP
THE welfare of high-performance dairy cows is to be studied in a three-year Scottish Office-funded research programme.
"Super-cows of the future may run into metabolic stress as the gap between milk production and feed energy widens," says the SACs Dr Oldham (see diagram).
He explains high yielding cows cannot match energy output from feed during peak lactation and mobilise body fat to bridge the gap.
"It is a gap which widens with genetic merit, and it looks as if we are selecting for animals which can, increasingly, milk off their backs," says the SACs Dr Roel Veerkamp who, with Dr Geoff Simm, has been evaluating the consequences of genetic selection for yield at Langhill.
"The super-cow of today with a predicted transmitting ability (PTA) of +35kg combined fat and protein is able to mobilise at least an extra 65kg of body fat over the first six months of lactation, which is equivalent to an extra 700kg of milk," says Dr Oldham. "In the future, a doubling of PTA to +70 could mean expecting those cows to mobilise 135kg of body fat. That is a huge challenge and is probably unreasonable.
"We must, therefore, look at ways of sustaining the super-cow adequately, with nutrition to prevent too great a loss of body condition and to avoid health and welfare problems," he says.
His colleague, Dr Veerkamp, adds that the choice of selection goals could also be refined so that the knowledge which we now have about intake and output responses to genetic selection can be combined to sustain fit cows.
He feels the energy gap may not affect yields but cause health and fertility trouble. This could be especially true for high merit cows in low input systems.
"Up to now, no obvious problems of selection for yield have been seen at Langhill even in a reduced input system," said Dr Veerkamp. "But a thorough assessment of continuing genetic progress is needed now to make sure that our current selection goals are sustainable."
The SACs Dr Alistair Lawrence will study how metabolic stress may affect the behaviour of cows in the milking parlour – such as milk let down and milking speed. Vet Dr David Logue is involved in the study, monitoring leg problems and mastitis and, at the colleges Acrehead unit at Dumfries, there will be a comparison between high and low input herds to see if high index cows in the low input herd are subject to greater metabolic stress.
Three other Scottish research centres, the Moredun, Hannah and Roslin, are co-operating in the programme. Roslin scientists will focus on the effects of metabolic stress on reproduction.