CONDITION A BETTER GUIDE THAN WEIGHT
BODY condition scores of higher yielding cows continue to decline into mid lactation, but condition loss of average yielders stops sooner.
Andy Hattan of CEDAR, Reading University, told delegates that his studies comparing weight loss and condition score show actual weight change is of little value.
Up to six weeks after calving cows lost 0.7kg a day. Then they started to gain weight at about 0.25kg a day, but this is likely to have been water or liver tissue because condition score continued to fall, he said.
"Weight gain commences soon after calving, but body tissue mobilisation continues into mid lactation. Body condition score, therefore, gives a better indication of cows energy status than weight."
However, milk yield was compromised in high yielding cows because they had an energy deficit of 22MJ a day six weeks after calving, said Mr Hattan.
CEDARs David Beever added that high yielding cows, peaking at 50kg, still had an energy deficit 12 weeks after calving. This deficit was about 8MJ a day – equivalent to two litres of milk.
But improved feeding meant that by week 14 these cows had moved into a positive energy balance faster than had been achieved in previous studies.
Prof Beever believes that they have managed to narrow the energy gap by feeding high yielders four forages and increasing the diet energy density. But its not practical to increase the energy density further in order to reduce this energy gap more, he says.
"We are now looking at starch feeding, transition cow management and opening up the physical structure of the diet to get cows to eat more – possibly using feeds such as lucerne."
Opening up the diet structure could reduce the energy gap in high yielding cows.