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Extended lactation: Which cows are suitable?

Intentional delay of the cow’s first insemination after calving results in an extended lactation. However, not all cows manage an extended lactation equally well. A new research project at Aarhus University examines the possibility of selecting suitable and unsuitable cows in advance.

When the farmer delays the first insemination after calving, it gives the opportunity to prolong the cow’s lactation. A previous AU project (Reprolac) has shown that an extended lactation may result in opportunities of improving the herd efficiency and the business economy as well as reducing the greenhouse gas emission per cow. However, the project also showed that we need more knowledge about the variation among cows regarding the ability to maintain a high yield during the extended lactation.

Therefore, a new research project at Aarhus University aims to support farmers in choosing suitable cows for an extended lactation and determine the optimum length of lactation for each cow in a given herd.

High peak yield and high persistence

The lactation curve shows the cow’s milk yield from calving to drying off. Typically, the yield increases after calving and peaks around 50-100 days after calving after which it decreases until drying off. A high persistence is equivalent to the cow being able to maintain a high milk yield over a long period of time, and this ability varies from cow to cow.

In a previous study in four herds, we divided the cows with extended lactation into three equally sized groups, depending on how much milk they had produced on average per day between calvings. The cows yielding the most milk had the highest top yield and the highest persistence while it was just the opposite for the cows yielding the least milk. If we could predict in advance whether a cow would have both a high top yield and a high persistence, then this cow could be interesting in relation to extended lactation. Contrarily, cows with both a low top yield and a low persistence would have to be inseminated as early as possible or be culled.

New experiment with extended lactation

We do not know why some cows can maintain a high milk yield through an extended lactation while others cannot. Therefore, we start up a new experiment in the autumn of 2020.

In the experiment, we follow 20 experimental and 20 control cows in 40 Holstein herds and 10 Jersey herds from calving to 150 days in the following lactation. We know that for some cows with an extended lactation there is a risk that they grow too fat, which may result in health problems during the next lactation. Therefore, it is important that the cows do well in the current but also in the following lactation.

The purpose of the new project is thus to obtain knowledge and develop a method that can help the farmer to select the best and the least suitable cows for an extended lactation based on the objective parameters estimated from data in the cattle database. In the end, this should contribute to a more climate effective and profitable milk production, which is also expected to support a longer life cycle in cows.

About the experiment


The project is funded by The Danish Milk Levy Foundation and runs during the period 2020-2023.


Department of Agroecology, AU; Department of Animal Science, AU; SEGES      

More information

  Link for project website: Forlænget laktation: Optimal strategi for laktationslængde på ko- og besætningsniveau (in Danish)  

The article is an abstract from an article published in the journal Bovilogisk in September 2020.


Jesper O. Lehmann, Department of Agroecology, Aarhus University

E-mail: JesperO.Lehmann@agro.au.dk