The level of milk production is the most important selection criteria for dairy farmers to postpone the insemination moment and let cows consciously make longer lactations. This is evident from the first three partial reports of the "Lactatie op Maat" project that are now available.
In these reports, the researchers describe the results of interviews with livestock farmers about their motivation and strategy for consciously extending lactation, so-called endurance milking. Insemination and milk control data from the same dairy farmers were also analyzed. In addition, the researchers conducted a model study based on, among other things, data from Danish dairy farms that work with extended lactation to estimate the consequences for the economic result and the environment.
Fewer calving moments
The main reasons for the 13 Dutch dairy farmers in the 'Sustainable Milking' network to consciously extend the lactation of their cows were fewer calving times, fewer calves, drying at lower milk production, better fertilization percentages and savings in labor around drying and calving. The selection criteria of cows for extended lactation differed per farmer and usually based on milk production during the peak of the lactation curve, the decrease in milk production or the number of days in lactation.
Fertility equal with deliberately prolonged lactation
On the network farms, the percentage of pregnant animals after the first insemination was not higher in later first insemination. In that sense, fertility remained the same. However, the effect of insemination moment on fertility was intertwined with milk production level. The highly productive cows were selected for an extended lactation. In addition to selecting the high-yielding cows for an extended calving interval, poor pregnancy of high-yielding cows in early lactation, or less negative effect of pregnancy on the lactation curve may be reasons for a higher peak and higher 305-day production at a longer calving interval. Despite the highest 305-day production, the milk production per day between calving times was usually not highest with the longest calving interval. More research is needed to see if the reduction in milk money can be offset by reduced labor, feed or health costs, or an improvement in longevity.
Results in continuous milking depending on consequences for persistence and longevity
In Danish dairy farms where Holstein-Friesian cows deliberately extended lactation, the effects of extending the calving interval by 2 or 4 months on the total milk production are small. If only the heifers extended lactation, there was no difference in milk production per farm per year at all, but there were fewer calving moments and fewer days per year. For the emission of greenhouse gases per unit of milk, when extending lactation is accompanied by an extended lifespan of dairy cattle, this greatly reduces the greenhouse gas emissions per unit of milk. So only milking heifers in this study did not yield a reduction in milk money, the question remains whether reduced labor, health costs or a better lifespan can compensate for reduction in milk money during endurance milking of full flock.
Practical test Dairy Campus
Parallel to the 'Sustainable Milking' network, a trial is being conducted on the Dairy Campus with 150 cows and three different insemination times: from 50, 125 or 200 days in lactation. The last cows will leave this trial at the end of January 2020, the results of this trial will become available in the course of 2020.