GUT HEALTH AND PULMONARY PROBLEMS: an interconnected problem
Intestinal and respiratory problems are considered as major threats because they are responsible for the main part of calves’ mortality and morbidity. In addition, a healthy and proper functioning rumen is crucial for calf growth and later production. In order to produce healthy, well producing and long living cattle, the focus should be on these topics right from the start.
threat nr. 1: CALF SCOURS
Calf scours is the main cause of mortality and morbidity during the first 5 weeks of life and may have several causes. The most important one is a bad colostrum management, incorrect (milk) feeding practices and the use of poor-quality milk replacer and calf starter.
threat nr. 2: Respiratory diseases
Respiratory problems mainly occur from 5 to 25 weeks of age. Bovine Respiratory Disease (BRD) causes high mortality and morbidity in the calf rearing phase, resulting in less growth and ultimately leading to less performance later on in life. BRD causes long lasting negative effects by irreversible damage to the lungs.
It seems like these two threats do not have much in common. However, nothing is less true. It has become increasingly evident that not only intestinal disorders can have pulmonary manifestations but also vice versa. This is because these two compartments are interconnected via the so-called “gut-lung axis” (fig.1).
The gastrointestinal tract and lungs communicate with each other on certain levels. If an intestinal disorder causes damage to the gut barrier for example, this results in bacteria, endotoxins and inflammatory cytokines entering the blood circulation. Via this route, these detrimental molecules can reach the lungs, and eventually cause some damage there.
Many studies suggest an important role of the gut-lung axis and highlight the need for intestinal barrier integrity or gut health. Calves suffering from intestinal problems in their early life will be more susceptible to pulmonary infections later on. Therefore, it is extremely important to focus on gut health, which is largely determined by the quality of feed given to calves.
Milk feeding: focus on protein digestibility
The focus of a good calf milk replacer (CMR) should be on protein quality. Premium quality protein is digested more easily by the calves and thus gives less risk for digestive disorders. In general dairy protein sources are highly digestible, so high quantities can be used in calf milk replacers. This is contrary to vegetal protein sources. So limiting less digestible vegetal protein sources like soybean flour in calf milk replacers is very important.
Solid feed: focus on rumen development
To develop a healthy rumen, good quality concentrates, fibers and water are required. First, the quality of the starter will determine the age at which the calf starts consuming solid feed. In this case, the earlier the better. More intake simply means more growth. The pre-weaned calf mostly relies on nutrients in milk. A higher milk intake results in higher growth rates before weaning, but implies a lower concentrate intake. So it’s crucial to find the good balance between milk and solid feed intake.
The amount and the composition of the calf starter eaten before weaning affects digestion of solid feed after weaning. Quigley et al. 2018 stated that the calf’s digestive system develops together with non-fiber carbohydrate (NFC) intake, and that about 15 kg of cumulative NFC intake is needed for the digestive system to be fully adapted to solid feed. As a consequence, everything that reduces total NFC intake, reduces solid feed digestion. This results in less energy and protein availability, consequently reducing growth rate.
NFC intake might be limited due to high fiber feeds, forage feeding or high milk intake. It’s possible to reach an optimal rumen development at 6 weeks of age, with a very palatable starter with good NFC content. From then on calves can be gradually weaned by reducing milk supply stepwise, avoiding any problems, stress or reduction in growth rate.
Finally, protein nutrition also has a huge impact on the calf’s development, especially when focusing on gut health and diarrhoea prevention. This is because too much (undigested) protein will result in bacterial protein fermentation and pathogen overgrowth. Remember that “bad” bacteria like E. Coli, Clostridium, etc. are known as dominant protein fermenters. By limiting total protein intake and choosing easily digestible protein sources, the amount of undigested protein in the gut can be restricted. Limiting protein content in calf starter enables you to incorporate more NFC. A protein content of 160 g/kg calf starter seems enough to ensure proper rumen development and fast growth after weaning. Another advantage of such a feed is that it can be provided ad libitum without any risk until the age of 6 months, resulting in a very fast growth.
Conclusion: Good nutrition goes beyond gut health and can benefit the overall (immune)-system, helping the animal to deal with numerous diseases.