For some time now, extended calving intervals have been a topic that is frequently mentioned in relation to the productive lifespan of cows, animal welfare and low calf prices. But what does this actually mean, and how does it benefit my farm?

With an extended calving interval, also known as extended lactation, the first insemination after calving is delayed longer than usual. The farm decides for itself how long a voluntary waiting period to allow the cow. A waiting period of 80 days or more can be described as an extended calving interval. But let’s start at the beginning. What is the calving interval or the voluntary waiting period? This is illustrated in Figure 1.

From a physiological point of view, a cow’s first oestrus occurs approximately 9 to 12 days after calving. The oestrus cycle lasts an average of 21 days and occurs regularly throughout the year. From the 40th day after calving, many cows show clear signs of oestrus.

As milk yield increases, these limits should be reconsidered, as the higher the average yield, the more days the cow should be allowed as a voluntary waiting period in order to capitalise on economic benefits and to improve animal health and welfare. Figure 2 shows the trend over the years based on the calving interval and average yield.

Whether extending the intercalving period is suitable for your own farm and cows depends on several factors. The extent to which the intercalving period is extended is a decision that must be made on an individual animal basis. The basic prerequisite is that the cow is healthy and in good physical condition. The housing environment must also be optimal for the extension to be successfully implemented.

Sufficient milk yield and good persistence are important. This means that a cow’s daily milk yield declines only slowly after the peak lactation period and that the cow consequently maintains a consistently good milk yield beyond the standard lactation length, enabling her to enter an extension period. Furthermore, good oestrus monitoring with a high pregnancy rate is important, which necessitates more intensive animal observation. The decision regarding the duration of the voluntary waiting period for each individual animal is therefore based on milk yield, the day of lactation and the lactation number. In addition, the best possible feed, tailored to the animal’s performance, must be ensured, particularly in late lactation.

If milk yields are too low or persistence is poor, the extension should be avoided. Fertility problems are also a criterion for exclusion. If there is a high demand for offspring, e.g. for the sale of breeding stock, extending the intercalving period makes no sense, as fewer calves will be born.

This means that cows with higher milk yields can be granted a voluntary waiting period of more than 100 days. Table 1 illustrates the latest possible insemination date depending on the day of lactation and the annual milk yield (kg).

However, the decision on the timing of insemination cannot be based solely on milk yield. The current body condition, as well as the fat-protein ratio (FPR), may be relevant for decisions specific to individual animals. The FPR should be below 1.4 at the time of insemination to ensure that the cows have sufficient energy for a new pregnancy and that ketosis is not present.

In addition to a longer productive life and higher lifetime milk yield, significantly fewer calves are born. This has the advantage of reducing the workload on both the cows and the calves. As fewer cows are culled, fewer heifers need to be made available for replacement, which reduces the costs of the expensive rearing of young stock.

Extending the calving interval also influences the persistence of dairy cows. Lactation persistence can increase as a result of delayed insemination. Studies by Rudolphi (2012) found that cows with a longer calving interval exhibit better persistence.

Overall, it can be said that extending the calving interval can bring benefits for animal health, the environment and the farmer.

Despite its many advantages, extending the calving interval also has disadvantages that must be taken into account. An extended calving interval is not suitable for every animal. The decision for or against it must be made on an individual animal basis, which involves greater effort.

In order to successfully implement an extended calving interval, heat detection and insemination success on the farm must generally be good. If these are inadequate, the risk of losses due to infertility may increase. In such cases, insemination must take place at least one cycle earlier.

By skipping the oestrus, the proportion of oestrous cows in the herd increases, the risk of injury from mutual mounting rises, and restlessness in the barn caused by bellowing cows may also increase.

If the lactation period is extended, particular care must be taken with feeding, especially in late lactation, as there is an increased risk of the cows becoming overweight. This can only be remedied through sensible feeding management. The higher the herd performance and the performance of the individual animals, the lower the risk.

What can be a major advantage can also be a disadvantage. The absence of calves for sale results in economic losses. This can be particularly significant in the Fleckvieh and Braunvieh breeds. Crossbred calves can be sold on the market at good prices, but this proportion decreases with a prolonged calving interval. Fewer calves born also leads to a slowdown in breeding progress.

A comparison of calving intervals of 400 days with those of 500 days in a project “OptiLak – Evaluations of the optimal lactation duration for differentiated milk yields” showed that, when revenues and costs are considered together, the contribution margin of dairy farms with calving intervals of 500 days increases, provided that the reproduction rate is deliberately reduced.

From the perspective of feed economy, too, the extended calving interval can be recommended. Hufe et al. (2021) expressed a similar view in their study. Although they calculated that the IOFC (Income over feed costs) per feed day is €33.00 higher per year for a 350-day calving interval compared to a 471-day interval, the IOFC per kg of ECM remains stable.

The benefits of allowing young cows a longer intercalving period have already been mentioned. However, it also has a positive impact on profitability. The reduced number of calves also offers an economic advantage. Fewer calf pens and housing spaces are required. This saves money and working time. However, one should not cut back on the intensity of handling the remaining calves. In Fleckvieh and Braunvieh herds, economic losses may arise if fewer calves are born, as these breeds command higher prices for calves and cow carcasses.

Direct breeding for extended ZKZ is complicated by the fact that ZKZ depends on management decisions specific to individual farms and individual animals. A persistence breeding value, designed to specifically breed for a slower decline in the lactation curve, is available in Germany for Fleckvieh and Braunvieh, and since April 2023 also for the Holstein breed. The ‘RZPersistence’ describes the ability of cows to maintain milk yield for as long as possible throughout lactation. It is derived from the fat and protein content and enables selection for higher milk yield in extended lactations (more than 305 days).