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 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.
One scenario the study did not examine was breeding animals at the common 60-day mark. According to multi-state university research, as many as 20% to 30% of cows are anestrous at 60 days in milk, meaning that they are not expressing signs of heat at the end of the “typical” VWP.
This especially holds true for any animal that has experienced reproductive or metabolic illnesses after calving, as they require more time to recover. These animals typically return to a normal estrus about one cycle later than their herd mates who calved without difficulties, according to Roy Ax, a University of Arizona extension dairy specialist.
The research suggests 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 scientists also reported that the replacement of many short lactations with fewer, longer ones could improve the overall longevity of the herd.
Money Saving Benefits
While a 12-month calving interval has long been assumed to be the most cost-effective breeding program, using a 15- or even 18-month system could offer additional economic benefits.
According to university research, extending the calving interval for higher producing cows may save you from breeding a cow during peak milk, a high energy demand period that could corollate to a lesser probability of conception. An economic betterment could also be experienced in primiparous animals because of the high persistency of their milk production and the increase in fat and protein contents as lactation progresses.
Additionally, extending the VWP by 30 or 60 days may help cut back on premature culling due to fertility problems as well as reduce the number of replacement animals needed in the future.
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.