One of the keys to minimising the risk of respiratory disease developing in calves is to ensure that their immune system develops as quickly as possible. A calf with a well-developed immune system will be better able to fight off unwanted viruses and bacteria by producing antibodies to these organisms.
When calves are very young, their immune system is not able to produce antibodies effectively; instead, these calves rely on antibodies supplied in colostrum. Providing calves with sufficient good-quality colostrum in the first hours after birth will help to ensure they are capable of fighting off disease. Ideally, calves should take 10% of their body weight in colostrum within the first 12 hours.
The living conditions of calves also influence their susceptibility to disease. Damp conditions in the shed provide an ideal habitat for fungi, viruses and bacteria to flourish. These can be transmitted on dust particles. If one calf becomes infected, it will not take long for the disease to spread, and the rate of spread will be more rapid if calves are crowded into pens. To reduce the effects of overcrowding, allow 1.5 m2 per calf, and have no more than 10-12 calves per pen. A pen with solid sides can also help to reduce the transmission of disease. A dry, well-insulated surface, such as wood shavings or straw, will also increase stock comfort and boost their health.
The air around the calves also needs to be considered. Calves need draught-free conditions, but the area must also be well-ventilated to prevent the build-up of harmful gases such as ammonia. Ammonia arises from the breakdown of urine in the bedding, and if it’s allowed to build up, it will irritate the calves’ respiratory system, predisposing it to infection. Aim to have the area around the calves free from draughts, but the area above them well ventilated, to allow gases and dust to escape. If you can smell ammonia in the shed, then it’s likely that the ventilation is not adequate.
Calves also need good nutrition – provide plenty of fresh, clean water, plus roughage in the form of hay or straw. To prevent the transmission of disease, keep the food and water up off the floor of the pen. Make sure there is sufficient feed for each animal in the pen – if they have insufficient feed they will become physically stressed and more vulnerable to disease. Having to compete for feed will also increase the animal’s stress.
Other stressors that can reduce a calf’s resistance to disease include transportation, changes to their feed, dehorning, castration and mixing groups of animals. All of these should be managed to minimise the amount of stress they cause.