25 December 1998

Choose a cow to suit your input regime?

COW genetics have improved rapidly, and this will have huge implications on future management, SAC Crichton Royal Farm researcher John Bax told the seminar.

High genetic merit cows are more difficult to manage, but when a lower input system is chosen a different type of cow may be needed.

"Heifer yields have increased by 3.73% a year for the past five years; 2% of that is estimated to be due to genetics, with the rest from improved management," said Mr Bax.

Cow yields range from 7640 litres for the top 20% yielding cows to 5240 litres for the lowest yielding 20%. Some producers aim for lower yields from lower inputs, so it is likely that range will increase as producers choose between high and low inputs.

Studies involving Crichton Royal Farms Acrehead herds show cow yields can be increased quickly within two years without a big impact on cows, providing they have sufficient genetic merit. "They do not appear to operate closer to their metabolic capacity and reproduction is only slightly affected by input level."

Genetic progress can pay: Selected £61 PIN cows fed 1.4t of concentrate outyield lower merit £6 PIN cows fed 2.8t of concentrate in studies at SAC Langhill. That showed the benefit of higher genetic merit, said Mr Bax.

"But the Acrehead study suggests low-input systems are less appropriate for high genetic merit cows, especially when they calve in spring. They can be managed on lower inputs but when things go wrong such as grass shortages the consequences for cows are severe.

"We should consider whether we are using the right breeds. Cross-breeding or different breeds could have more to offer in low input systems, possibly helping cut replacement rates and improving fertility."

Higher yielding cows need more care. Spring-calving cows on the high-input system at Acrehead yield 1400 litres less each year than high-input autumn calvers averaging 10,000 litres, despite having the same genetic potential at £35 PIN. That showed that it was more difficult to feed high yielders grass than silage, said Mr Bax.

Cows fed higher inputs also suffered more lameness, he added. When they began lifting cows feet to identify lameness they found incidence was double that seen otherwise.

"Higher output cows had three times the number of lameness cases because they were housed for longer. Cows grazing even in muddy, wet conditions had clean feet," said Mr Bax. There were no differences in somatic cell count.

GENETICSELECTION

&#8226 Different cows needed depending on inputs.

&#8226 Yield range will increase.

&#8226 Consider cross-breeding.