Replenish reserves before lactation
BODY condition loss during early lactation is not a major problem when cows are managed to replenish body reserves before the next lactation.
Speaking at the Intermol and farmers weekly conference, University of Reading researcher David Beever told producers that modern high yielding cows typically mobilise up to 60kg of body fat during early lactation.
"But only 40% of this was replenished by day 210 when the study ended, which means 35kg must be gained by drying off. This is because high genetic merit cows are still in negative energy balance at week 20 of lactation, losing about 1kg of body fat/day."
This extended loss of body condition is reflected in a lower conception to first service rate of 39%, compared with 50% for average cows. In addition, high genetic merit cows have greater early embryo losses, he said.
"On closer inspection, more than 59% of high genetic merit cows had abnormal progesterone cycles compared with one-quarter of average merit cows."
The most common problem was cows showing oestrus at day 21-25 and then going into anoestrus. This resulted in high merit cows taking five inseminations to become pregnant with a calving to conception interval of 160 days, explained Prof Beever.
"But its not all bad news, as one recent study at the university showed that adjusting ration starch and protein levels during the transition period can reduce body condition loss during early lactation. Cows returned to positive energy balance six weeks earlier than controls."
This gives producers a chance to avoid declining fertility through feeding. "There is nothing wrong with body condition loss when we know its happening and cows are managed to replenish their reserves." *
More than 69% of high genetic merit cows had abnormal progesterone cycles in the study, said David Beever.
Maintaining energy supply is crucial for higher yielding cows producing up to 6kg a day of milk solids.
• Impact on fertility.
• Should be minimised.
• Starch and protein balance.