For decades, a 12-month calving interval has been economically considered the most cost-effective breeding pattern to use on a dairy. However, the remarkable increase in milk yield per cow over the years has also been accompanied by a decrease in reproductive efficiency, making a 12-month calving interval difficult to achieve.
A recent study published in the January issue of the Journal of Dairy Science examined the effects of extending the lactation period on various reproductive measurements of high-yielding cows.
Placed into three groups, cows were given a voluntary waiting period (VWP) of either 40, 120 or 180 days before being bred. Cows in both the extended lactation groups experienced greater overall first service conception rates along with a lower number of services per pregnant cow compared to animals who had a VWP of 40 days.
Scientists suggest that an increase of the VWP in high-producing cows corresponds to a higher health status. By extending the VWP, the negative energy balance commonly experienced during early lactation, which has detrimental effects on fertility, is lowered. Additionally, drying off a pregnant animal during high milk production is avoided. The authors also reported that the replacement of many short lactations with fewer, longer ones could improve the overall longevity of the herd.
In conclusion, extending the lactation period of high-yielding cows can improve main reproductive measurements, such as fertility. It was determined that this criterion could be used to adjust breeding strategies on the farm to generate higher conception rates while also reducing the expenditures budgeted towards breeding.
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