Dr. Robert Tremblay
Calf pneumonia is one of the most common diseases of young dairy calves. We know that it has both short-term and long- term impacts on calves that get sick. It also costs farmers and the dairy industry in a variety of ways — cost of drugs to treat calves, treatment labour costs. There are also costs from calves that die from the pneumonia but even calves that survive may not do as well in the herd. Over the past few years, it has become increasingly obvious that having pneumonia as a calf impacts even first lactation milk production. Sickness, especially preventable sickness, could also be seen as a welfare issue for calves too.
Recently, veterinary researchers reviewed the research on impacts of calf pneumonia. They looked at research published in English up until February 2020. To be included, the research needed to be on calves during their first year of life. They ended up finding 27 studies that fit their criteria; 20 were from Canada or the United States and 7 were from Europe.
The review looked at as much evidence as possible on pneumonia having an impact on death losses or on removal from the herd before first calving. Removal could be because animals either died, were culled or were sold. The researchers also wanted to look at the evidence of pneumonia impact on growth or on milk production in a heifer’s first lactation.
It was no surprise that calves that got pneumonia were more likely to die from any cause. There are good treatments available for calf pneumonia but none of them is perfect. Calf pneumonia involves several different groups of microbes — bacteria, viruses and mycoplasmas. There are specific treatments only for bacteria and some mycoplasmas. There is no practical way to treat viruses. Even the best treatment tools will work best if calves are treated when they are just starting to get sick. It may not be easy to see when calves are just starting to get sick.
The research showed that heifers with pneumonia were more likely to be removed from the herd at any time before their first lactation compared to heifers that did not get pneumonia. That means that they are more likely to be culled or sold. Death losses and culling both in- crease the overall cost of raising replacements. Sales may also lead to an increase in replacement costs if sale prices do not match or exceed the actual investment in rearing heifers.
Pneumonia has some lasting impacts too. This was clear if you compared the growth rates of calves with pneumonia to calves that didn’t get pneumonia. The average difference over 10 research studies was 0.067 kg/day. Different studies followed calves for different periods of time. Reduced growth was the same whether calves were followed up to 3 months of age or up to 6 months of age. Pneumonia had a consistent and lasting impact on growth.
Another lasting impact is on milk production in the first lactation. Across five studies, the average difference in milk production between heifers that had pneumonia as calves and those that didn’t was 121 kg of milk in a 305-day lactation. The range of the impact on milk production was quite broad. The biggest difference was 525 kg of milk and the smallest was 70 kg. Four of the five studies found at least a 100 kg difference.
Other long-term effects that research studies have identified are that calves with pneumonia are older at first calving and that they are more likely to be culled during the first lactation. When the researchers looked at those outcomes, there was no way to pool the information.
This study pooled the results from several studies, not just one study, and strengthens our confidence that pneumonia does indeed have big impacts on dairy heifers. There is no doubt that pneumonia has serious and long-lasting effects. These are good reasons to focus on things we can do to prevent pneumonia rather than focus on treating it once it occurs.
Dr. Robert Tremblay is a veterinarian for Boehringer-Ingelheim and lives near Guelph.