Danes in challenge to accepted wisdom
IT IS natural for animals to reduce feed intake and mobilise body reserves in the period around calving and too much emphasis has been placed on feeding to counter negative energy balance in dairy cows.
That challenge to accepted wisdom came at the BSAS metabolic stress conference in Edinburgh from the Danish Institute of Agricultural Sciences Klaus Ingvartsen.
"The assumption that there is scope for increasing intake and hence production, efficiency, and gross margin, has been, and still is, a major motivation for most studies on feed intake and prediction," he said.
"The dip in intake, which starts in late pregnancy and continues into early lactation, has traditionally been interpreted as a depression in intake due to physical constraints. But the role of physical constraints on intake have been over-emphasised, particularly in early lactation.
"There is mounting evidence that presence and mobilisation of body reserves in early lactation play an important role in intake regulation at this time," said Dr Ingvartsen.
When the cow was not compromised, changes in body reserves and the dip in intake represented the norm and provided the real basis against which to assess true depressions in intake when the cow was compromised by nutrition or environment.
It was generally accepted that changes in intake, yield, and body reserves in early lactation meant that the cow could not meet her milk production requirements due to inadequate intake.
"If that were true, we would expect cows with limited body reserves at calving to produce less milk than those with substantial reserves. However, there are a number of studies to show that this is not the case."
A trial of his own had shown no difference in early lactation yield between fat, medium, and thin heifers. "There are sufficient studies to cast doubt on standard interpretation. It should be abandoned if our understanding of intake regulation in early lactation is to progress," he said.
It was important to realise that, where she was not compromised, the cow had a desire to mobilise reserves and that desire had a higher priority than maintaining intake. "Understanding the normal changes in body reserves in early lactation should help us towards better detection of situations in which the cow is compromised," said Dr Ingvartsen.