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Selko | Health and Fertility


Breeding dairy cows that are resistant to heat stress

Watch the entire presentation of Mr. Joost Klein Herenbrink presentating how cows can be made more resistant to heat stress through special breeding programmes.

Which genetic traits can be used to breed cows that can deal with heat stress?

The phenotypic performance of a cow is a combination of a lot of different factors, like environment, housing, feed, but also their genetic level. Genetics are responsible for 10 – 20% of the performance of a cow. Nowadays, there are many different traits to select and improve. Therefor it is very important that farmers know which traits are most relevant for them and when breeding, farmers should always look at their long-term goals. Heat stress is a temporarily disturbance, which could have a huge effect on the health of an animal. Animals with health problems do not only create more work for farmers, they are also less efficient.

Focus on health and lifetime production of dairy cows

When a farmer wants to breed more heat resistant cows, it is important to focus on traits that help improving the health of an animal and on treats that increase the lifetime production of a cow. Heat stress occurs when an animal's heat load exceeds its ability to lose heat. Heat stress in cattle results in less feed intake, a lower production, more health issues (particularly udder health and hoof health) and poor fertility. These health and fertility issues are also the 3 main health reasons for involuntary culling of cows. Animals under stress put a strain on their immune system and will have health issues surface quicker than those not under stress. Breeding cows with less health issues therefore will also breed cows naturally handling heat stress better than their herd mates. Besides the 3 aforementioned health traits, improving longevity will also lead to more heat resistant cows. High longevity animals have an improved ability to cope with any stressor, including heat stress.

Focus on improving persistency of milk production and on the level of milk solids

An important production trait to look at is persistency. Persistency is the ability of the cow to maintain milk yield (milk, fat and protein) after achieving peak production after calving. Highly persistent cows have a lower peak fluid production early in their lactation but they maintain their production at a higher level throughout the whole lactation. That means they balance production stress levels better throughout their whole lactation. Last but not least breeding for high milk solid levels instead of high volumes of milk produced will lead to cows that will handle heat stress better. Improving these traits will not only lead to more heat resistant cows, animals in the herd will also be easier to manage and more efficient throughout the whole year.

A mating programme for dairy cows is essential to make maximum progress

Once the most important traits have been determined, it is good to know what the level of your herd is for these traits. The genetic level can be determined based on pedigree and the own performance of a cow. Farmers can also have the DNA levels of their calves checked shortly after they have been born. When using this genomic information, the amount of information about the genetic value of a 14 day old calf is comparable to the information about the breeding value of a third calving cow. This means on a very young age, a farmer can make better selection decisions. Another big benefit is that the mating results will be better. So, using genomic information will lead to a faster genetic progress. To make the best matings and to maximise genetic progress, farmers should use a mating program to help them. A mating program should be objective and to maximize progress, it should enable adding as many bulls as possible from any supplier. This will guarantee the maximum genetic gain for a farmer on those traits he wants to improve within his herd.

Questions asked during the webinar...

Question Answer
What would be the critical heat stress temperature for heat adapted cows that reside in hot climates such as South Africa? If cows are in hot climates, they adapt to heat more easily. Critical heats stress temperatures would therefore be about 26 °C.
How much does the heat stress contribute to the reduction of milk production in terms of cow milk? As you have seen in the slides by Dr. Chamberlain the average production of heifers will drop by a THI between 62-72 with approx. 2 L/day, with a THI -79 you will loose 2-4 L/day and over 79 THI over 4 L/day.
Is there a difference in het tolerance of different breeds / animals reared in different conditions? and how to deal / with these differences with regard to recommendations? There are indeed breed differences, especially the Zebu and Girolando (Gir x Holstein cross) cope more easily with warmer conditions. Of course, these varieties do have production differences with, for example, Holstein, which also plays a role in the extent to which the varieties can tolerate heat.
Is it good to wash the cow to reduce heat stress? Cows cool down as a result of washing, as long as it does not result in an increase of te relative humidity. Thus, cows should be outdoors or in a well ventialted barn if they are being washed.
A very exciting presentation. In for example natural grazing systems what could be those critical interventions that can reduce heat stress? In a grazing system it's crucial to have enough shadow places, direct sunlight is the biggest risk factor. Provide shade, aim 4 – 6 m2 shade per cow. Maximize eating time / opportunities in evening. ‘Siesta’ management, give best grazing in evenings and offer enough clean and cool water options near grazing areas.
What do you suggest on a nutritional point of view to reduce heat stress? With more feeding moments, fresh and cool feed, cows will tolerate the heat more easily. For rumen health, sodium bicarbonate is a buffer and probiotics to support stressed rumen.

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Breeding cows with resistance to heat stress

Presentation by Joost Klein Herenbrink (CRV) during the CRV/Selko Webinar July 28, 2021.
Mr. Joost Klein Herenbrink discussed in his presentation how cows can be made more resistant to heat stress through special breeding programmes.

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