Calf barn ventilation problems leading to pneumonia and respiratory disease are an issue, especially in cold winter weather. "The persons responsible for air quality tend to close up the barns in order to prevent ‘chilly drafts" on the calves, even in well-designed barns," says calf expert Sam Leadley, PhD, Attica Veterinary Associates, Attica, N.Y. "I often can measure differences in relative humidity of 15% and 20% between inside and outside the barn which is not good."
Unfortunately some barns are not designed to allow significant air exchange without direct drafts on young, preweaned calves (e.g., greenhouse barns with sides that roll up from the bottom). Short of tunnel ventilation nothing will save some of these barns.
The ideal housing situation for a calf, Leadley says, is clean, dry and with enough fresh air without being drafty, whether calves are in hutch housing or barn housing. Given that young calves lie down over 90% of the time, it is important that in cold housing the bedding base minimizes heat loss both by convection and conduction so the calf is losing minimal heat down through the bedding. And, she is nesting which lowers her convection heat losses.
In calf barns with individual pens, Leadley has seen a variety of types of bedding including pea gravel, sand, modified crushed stone, sawdust, wood shavings, coarse wood chips, straw from small grains, soybean "straw", chopped corn stalks. "In cold weather a regular supply of any bedding that will absorb moisture (= suck up the urine) and act as a physical barrier between soiled bedding and the calf seems to work well," he says.
Problem conditions for calves
In hutch housing when the bedding is wet and dirty in cold winter weather, calves are in a bind. If they lie down inside they lose a lot of body heat down through the wet bedding. There is no nesting effect so convection body heat losses are excessively high. And, it stinks in there ammonia levels are well above what is healthy. They can go outside to lie down if the weather is sunny and dry, but snowy nights are something else. Where can they go to rest? The most common mistakes, therefore, are:
1. Not adding enough good quality bedding to maintain a clean and dry resting base. Leadley says "good quality" is the key because he occasionally sees in Midwestern states producers trying to use soybean waste or chopped corn stalks as calf bedding. "The former has a low absorption capacity. The latter is usually too high in moisture to act effectively as insulation."
2. Failing to move the oldest calves out of hutches promptly. Leadley says the bedding area in a hutch is too small for 170–200 lb. calves. "They eat, pee and poop a lot so it is almost impossible to keep them clean and dry, but many farms often get overloaded in the first group pens and animals back up in the hutch housing."
In barn housing when the bedding is wet and dirty in cold weather the calves are in the same bind as in hutches loss of body heat down and out. And, they may be stuck with poor air quality issues worse than hutch calves because not only is their own bedding generating noxious gas but they may be forced to breathe "barn air" that contains excessively high levels of airborne pathogens. Leadley says the most common mistakes made for wintertime ventilation in barns are:
1. Too little air exchange (humidity is too high, pathogen concentration is too high, noxious gas load is too high).
2. Not adding enough good quality bedding to maintain a clean and dry resting base.
3. Failing to move the oldest calves out of individual pens promptly.
4. Housing transition calves in the same air space as the preweaned calves.
Rooting out pneumonia causes
Pneumonia problems in calves can be instigated by a variety of factors from pathogens, poor immune status and ventilation issues. When Leadley visits a farm that has identified a "pneumonia" problem he starts by collecting two kinds of information. "The first is the recent treatments for pneumonia," he says. "The second are the respiratory risk symptoms among preweaned calves, using Dr. Sheila McGuirk's scoring method from the University of Wisconsin."
From a clinical viewpoint, the treatment history gives him an idea of the age distribution of owner-identified respiratory problems in the barn. "There might be treatment spikes at certain ages. By walking the current calf population I can get a somewhat quantitative assessment of symptoms e.g., nasal and ocular discharge, spontaneous coughing, elevated respiration rates, shallow breath-ing, depressed attitude and body condition especially of two to three week-old calves. I also check for diarhea."
If treatment rates are excessively high and respiratory risk levels are elevated, Leadley digs deeper. "Does the farm check for BVD-PI status of calves? If there is a poor body condition on young calves we need to review the feeding program. Excessively high scours rates need to check out blood serum total protein levels, find bacteria culture results for ‘as-fed" colostrum and milk/milk replacer." Leadley digs out the Matheson toxic gas detector and checks ammonia levels as well as measures and compares the relative humidity and temperature inside and outside the barn."
Leadley notes that ventilation issues may be in a puzzling place. At one barn that had chimney vents at the roof peak and two positive-ventilation tubes and no ammonia smell, he measured 10 ppm ammonia in a nice clean calf pen as well as in one that was fairly wet and dirty. "I discovered the positive-ventilation tubes were not connected directly to the outside. Fans in the walls blew air into them with about a one-foot gap between the fan and the opening of the tubes. The positive-ventilation tubes were doing a good job recirculating inside air. Additional investigation revealed that the chimney vents were not working due to maintenance issues."
Leadley says the errors he made in his initial investigation were that he forgot about the gradual loss of sensitivity of his smelling senses to strong odors. "By the time I had been in the barn for an hour I had become accustomed to the barn odors and they became ‘normal." Second, I let my pre-conceived ideas tell me where I would find ammonia odors."
Why air quality matters
Poor air quality contributes to high levels of pathogen exposure and depressed immune defenses. Ammonia gas exposure, specifically, has the potential to depress the tracheal defense mechanisms designed to lower the number of pathogens getting into the lungs, Leadley explains. But, ventilation is only one part of a larger puzzle.
Feces and urine in contact with each other release ammonia. Feces supply the urease that comes from rumen microbes and urine supplies urea. "In some calf barns with individual pens the back part is bedded and the front part is concrete," Leadley notes. "This mix of waste products if not cleaned regularly generates a lot of ammonia. The same is true for feed alleys in group housing the feces/urine mix has to be removed regularly and frequently in order to control ammonia release."
A certain amount of ammonia is going to be generated where you have calves. However, if bedding practices establish conditions favorable to ammonia production, just increasing the rate of air exchange will not lower the concentration low enough for good respiratory health. Leadley has measured ammonia levels in individual pens and adjacent work alleys only a few feet away. "Six inches above the bedding I can find concentrations of 10ppm to 15ppm and six feet away in the alley the ammonia level can be only 1ppm to 3ppm. This is not to say that improving air exchange rates will not benefit the calves. Rather I am saying that air exchange alone cannot overcome poor bedding practices."
Leadley believes in having "hard" numbers when talking with clients about air quality. "I crawled into the front of some heifer stalls in England last March. The heifers in this barn had a high and persistent treatment rate for pneumonia. The building was open on one side to the rear of the stalls for feeding. Air out by the manger was fine. I picked up 10ppm or 12ppm ammonia at the front of the free stalls. That number was enough to convince the owner to add a positive ventilation tube at the front of the free stalls and revise the bedding protocol. The nice thing about the hard numbers is that we get beyond individual perception of how much ammonia gas is in the air."
The problem with using the "smell test" for ammonia is that we aren't where the ammonia is. Lead-ley says standing in the wrong place in the alley won't give you an indication of ammonia levels. "None of the calves live there. And, you shouldn't do it standing up on the bedded pack. None of calves breathe in at 60 inches above the pack." Leadley says you must get down to the level of the pack if you're going to smell the ammonia. He recommends a value under 5 ppm for good respiratory health.
Leadley explains that the effect of ammonia exposure is a function of both time and concentration. "It is because in most barns calves are restricted in making choices where to rest that they often have almost continuous exposure to whatever ammonia is in their individual pen. With group-housed calves in pens with 30 or more square feet of resting space calves often have a choice of where to rest dry vs. wet, next to another calf vs. off by herself, next to a wall vs. out in the middle of the pen. In a few cases in group housing I have found poorly maintained bedding, far too little resting space per calf, high ammonia levels everywhere in the pen leading to not only intense exposure to the gas but continuous exposure as well this combination is deadly."
Good controlled experimental studies that show the causal connection at given levels of ammonia gas concentrations between the ammonia and tracheal impairment are lacking for dairy calves. Right now Leadley uses swine data that shows values above 5ppm at "snout" level in feeder pig housing lead to elevated treatment rates for pneumonia. "Nevertheless, in practice I see big increases in treatment rates when concentrations get to 10ppm and above. At 20ppm and above I see 100% treatment rates in spite of constant use of AS700 with transition heifers."
Treat or prevent?
The calf barn is often an afterthought by the producer when the veterinarian visits. Often he or she will go to look at a couple of "sick" calves which are very likely chronic respiratory cases that have been treated more than once for pneumonia. "The owner's implied request is for a silver bullet that will ‘cure" the calves," Leadley states.
The veterinarian is faced with making a decision about whether or not to attack the larger question of what conditions generated these chronically ill calves. "Given that this is a cooperative client with a genuine concern about preweaned calf health, the veterinarian can schedule a time to come back and focus on respiratory health among preweaned calves. In that context it is essential that air quality be included in the set of factors leading to excessively high treatment rates and/or ineffective treatment protocols. Barn maintenance is always an issue fans don't work, curtains won't go either up or down. The same is true of the human side the farm may or may not have good protocols for operating the barn to insure good air quality but we know how protocol drift can erode the effectiveness of the best protocols."