Calf respiratory disease, housing systems

When I entered practice in 1981, local dairy farms were just finishing the transition from housing wet calves in barns to hutches. We still had a few farms that raised calves in pens and a couple that had those small, mechanically ventilated barns with calf crates inside, but it was not long until everyone got away from group housing. 

About 20 or 25 years later, automatic calf feeding systems were introduced to our area. Four of our clients installed them around the same time. Veterinarians were shocked at the prevalence of bovine respiratory disease in the first 60 days of life in those barns. It was often close to 100%. I did a non-scientific study that looked at the impact on milk production, using 305-day mature equivalent milk production, for these four farms. There was a remarkably consistent drop of about 1,400 pounds of milk for lactation one once all the group had been raised in the new barns when compared to previous times when calves were raised in hutches. All four farms discontinued use of the barns not long after. 

Fast forward another 10-15 years, and we began to see automatic feeder systems come back into the area. This time, producers were only putting about 25 calves in a pen, compared to 30-35 in the past, barns were naturally ventilated and well designed, and all had positive pressure tubes as described by the Dairyland Institute. We saw much lower mortality rates in these barns, but BRD rates were still very high, often 50% to 80%. In subsequent years, some producers tried several ways to mechanically ventilate automatic feeder barns. Around the same time, we began to see group housing systems using lockups and bottle holders that typically had nine calves per pen. During the last 10-15 years, lung ultrasound was described as a diagnostic tool in wet dairy calves, and its use to diagnose respiratory disease in calves became common a few years later. Lung ultrasound is a more sensitive diagnostic tool for BRD than physical exams, so one would expect greater rates of disease using ultrasound.

Throughout this whole period, the only constant has been that the prevalence of respiratory disease in group-housed calves is much greater than calves housed in hutches. Surprisingly, there is still little published data on the relative risk of disease by housing system. There have been some scientific publications that try to quantitate the cost of respiratory disease in wet calves, though. For example, according to Dunn (2018), the presence of one 3 centimeter, consolidated lung lesion any time before weaning results, on average, in 1,155 pounds less milk in the first lactation. Ollivet (2023) speculates that much of the negative effect on production is due to reduced growth rates before 60 days of life, but we do not know that for sure. Other studies have shown calves with lung consolidation were slower to get pregnant (Teixeira, 2017), were less likely to survive to first lactation (Adams, 2016) and grew more slowly (Cramer, 2019). There are also many studies showing negative effects of clinical pneumonia in young calves.

There are a few things we do know. For one, adequate mechanical ventilation of wet calf barns is difficult in cold climates. For example, according to the Dairyland Initiative website, “Natural ventilation is the preferred method of ventilation. … Mechanically ventilated facilities are not recommended for calves in climates similar to Wisconsin’s.” Visit the website for reasons, but, in short, at a minimal ventilation rate of four exchanges per hour, the inlets are so small that it is almost impossible to get good air flow and air quality throughout the barn. We also know, from the Dairyland Initiative website, that naturally ventilated barns do not achieve enough thermal buoyancy to properly exchange air because small calves do not generate enough heat. This is the main reason positive pressure tubes were developed for these facilities. 

We also know that smaller groups are better. Several studies have shown increased disease incidence, mortality, nasal or respiratory scores (Godden, 2021) for groups of seven, eight or nine calves or less, when compared to larger groups. The differences in risk range from 40% to 100% higher in the larger groups. We do not know if nine calves housed in a lock-up and bottle-feeder style barn have different rates of BRD than nine calves housed in an automatic-feeder barn, however. We also do not have much published data using lung ultrasound scores for different sized groups and feeding systems in calf barns.

After all these years, it is remarkable that we do not know more because lung consolidation is so common in group housing and because it is so expensive. The total cost to the U.S. dairy industry per year must be enormous. It is also remarkable how much risk dairy producers are willing to take on when building group housing facilities because the cost of high rates of respiratory disease could easily be more than the cost of the building in just a few years. However, building group-housing buildings may be understandable, considering the difficulty finding adequate labor to manage calves in individual housing. It is also remarkable that nearly every popular press article about group housing of wet calves says nothing about increased rates of consolidation or clinical respiratory disease.      

Without much data, what we know about group calf housing and BRD is as follows: 1. Natural ventilation is by far the best, but in winter, calves will need clean coats and lots of deep, dry and clean bedding. Positive pressure tubes are a must. 2. Trying to keep these barns warm is a losing battle, usually resulting in remarkably high rates of consolidation and clinical respiratory disease. 3. Nine or fewer calves in a pen is best. 4. The shared nipple in auto-feeder barns may be another significant risk factor.  5. With sensitive diagnostic tools, expect the prevalence of lung consolidation in well-managed automatic-feeder barns to be more than 50% on an annual basis.   

So, if you are planning to build a barn with group housing, be diligent and prepared. Determine your current rates of respiratory disease and/or lung consolidation and then project rates in the new facility. Is the cost of increased respiratory disease worth the gain? You may decide that it is, but if that is the case, make sure the design is right and the best it can be with current knowledge. 

Bennett is one of four dairy veterinarians at Northern Valley Dairy Production Medicine Center in Plainview, Minnesota. He also consults on dairy farms in other states. He and his wife, Pam, have four children. Jim can be reached at [email protected] with comments or questions.