In practice we treat calves with diarrhea or lung problems every day. In order to take preventive measures, it is important to increase the calf’s immunity. Insight and knowledge of the structure of the immune system is essential for this. How does a calf’s immune system build up from the moment of fertilization until weaning?
The initial development of the immune system begins in the yolk sac. In the first stages after fertilization, all mammals develop an embryo that receives nutrition from this yolk sac. Thanks to these nutrients, the embryo grows. This happens until the placenta is formed.
But the immune cells of the liver also originate in the yolk sac. The liver functions as the ‘first immune organ’ during the first 90 days of the fetus. The immune cells then move to other organs, such as the thymus, spinal cord and lymph nodes.
The liver as an immune organ
The liver never ‘forgets’ its previous role as an immune organ. For example, the liver plays an important role in the initial response to inflammation, as part of the innate immune system. In acute inflammation, the liver responds with the production of acute phase proteins. This reaction can also occur when animals experience stress.
The functions that the liver has, on the one hand as an important organ in metabolism, on the other hand with an essential role in good resistance, remain clearly visible even in adult animals. For example, severe inflammation will have a negative effect on liver function and result in a reduction in feed intake, average growth and loss of milk production.
A disruption of liver function (for example due to fatty liver disease, chronic milk fever, copper poisoning) can also lead to a disruption in the build-up of immunity, a reduced immune system with increased susceptibility to diseases and reduced build-up of immunity after vaccination.
Factors that improve immunity building of the newborn calf
Due to the structure of the placenta, no antibodies are transferred from the cow to the calf in the uterus. So there are no antibodies circulating in the newborn calf. Immediately after birth, the calf must therefore ingest colostrum as soon as possible. Colostrum has a very high nutritional value and also contains a large amount of immune-modulating substances. It is not without reason that it is called liquid gold!
When the calf is just born, large molecules (such as antibodies) and immune cells can pass through the intestinal wall. During the first 4 hours of life, absorption is maximum and gradually decreases after 6 hours until absorption is no longer possible after 24 hours. During this short time there is the possibility of absorption of, among other things, IgG1 antibodies from colostrum. These are essential to provide the calf with the necessary protection for at least the first 2 to 4 weeks of life.
Colostrum is more than just antibodies!
The antibodies absorbed from the colostrum play an essential role in increasing passive immunity and therefore preventing disease in the young calf. But there are several bioactive components in colostrum such as growth factors, cytokines and antimicrobial factors (lactoferrin and oligosaccharides) that contribute to the formation and development of the active immunity of the newborn calf.
Colostrum also contains bacteria and large numbers of cells, including cow epithelial cells and white blood cells. The white blood cells play a very important role in the development and accelerated activation of the calf’s immune system. After passing through the blood tissue barrier in the intestines, the white blood cells colonize the calf’s body. They spread through the blood to peripheral tissues (mesenteric lymph nodes, spleen, liver and lungs). In the days after birth, these white blood cells will slowly be replaced by white blood cells from the calf itself.
All essential parts of the immune system are present in the newborn calf, but they are not yet fully fledged and functional until the calf is 2-4 weeks old. The colonization of microbiome in the intestines, absorption of colostrum, milk and solid feed stimulate the development of the calf’s immune system, which slowly replaces the passively absorbed immunity. The amount of antibodies absorbed from colostrum gradually decreases, during which there is a period of increased vulnerability of the calf to infections. This period of increased vulnerability is also called the “immunity gap”. The better the calf’s colostrum supply, the shorter the period during which the calf is vulnerable.
Immunity around weaning
The calf’s microbiome is influenced by age, nutrition, stress and environmental factors. The first colonization of bacteria takes place by ingesting the colostrum. As the calf grows older, several types of bacteria succeed each other in colonization. A ‘microbial community’ of benign bacteria is created. In the body there is an interaction between the immune system and the bacteria in the rumen, intestines and respiratory tract. This balance determines the health and integrity of the mucous membranes of the digestive and respiratory tract, but also of the immune cells located in the underlying tissues.
Sudden feed transitions, reduced feed intake, lack of milk, but also moving animals to another stable, transport and mixing of animals from different farms causes a major change in the population of the bacteria that form the microbiome. The result is a shift within the microbiome, resulting in dysbiosis. The consequence of dysbiosis can be that the mucous membranes of the respiratory tract and intestines become damaged and malignant germs have an easier time of entry. The immune cells grouped in the tissues under the mucous membranes of the digestive system and respiratory tract then work overtime. The risk of disease is very high with dysbiosis. In practice we see that calves are sick more often in the days after sudden weaning or feed changes, but also after a long transport or grouping of calves in large numbers from various origins via collection centers. Preventing diseases in young calves by optimizing the immune system will always remain a challenge!
Would you like to know more about building immunity in calves? Please contact one of our veterinarians Jessica Hartjes, 06-3800 8533 (Netherlands), Anne-Lynn Geertshuis (North-East Netherlands) 06-2046 9304, Annemiek Timmermans (Central Netherlands) 06-13702817, Sabine Hoogeveen (North- West Netherlands) 06-8279 0165 or Niels Groot Nibbelink (South Netherlands) 06-8100 2036
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2023-10-27 05:15:25
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