Recommendations To Optimise Calf Health

Calf pneumonia is a common problem in calves housed in individual pens in modern ventilated calf barns. A study by Kenneth Nordlund, DVM at the University of Wisconsin-Madison, has identifed the key housing factors associated with reduced prevalence of respiratory disease in these calf barns during the winter months.
calendar icon 24 November 2009
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Enzootic pneumonia of calves is often associated with poorly ventilated housing conditions. Mr Nordlund and his team, conducted a trial in 13 different calf barns. The prevalence of respiratory disease was determined using a respiratory scoring system wherein points were assigned for temperature, cough, nasal and eye discharge and ear droop. The physical environments were evaluated in terms of space, temperature, humidity, bedding, ventilation rate and other characteristics. Air hygeine in the pens and alleys was assessed using airborne bacterial counts. The findings of the study has allowed, Mr Nordlund and his team to make the following recommendations to improve calf health through modification of pens, bedding practices and ventilation.

The study found that the concentrations of airborne bacteria measured in the pens and alleys were a risk factor for respiratory disease. Where the airborne bacterial counts in the alleys were considered excellent, the pen counts were highly variable. Ventilation is highly associated with alley bacterial concentration but not specifically with bacteria concentration in the pens. In the study, the average claf barn had an estimated air exchange rate of 18 changes per hour (range 0-94), which was well above the recommended minimal four changes per hour during winter during winter conditions. The quality of air in the pens of many of the "over-ventilated" barns was poor, which likely meant unhygenic air within the pens. However, a well-ventilated barn does not ensure hygenic air.

Key Housing Factors Associated with Calf Respiratory Health

Solid panel between calves

The difference in prevalence of respiratory disease in pens with a wire mesh or a solid panel between each pen was substantial. A solid panel between each calf is a traditional recommendation from veterinarians and engineers and perhaps helps to limit movement of pathogens from one calf to another. However, increasing the number of solid sides was associated with higher airborne bacterial counts, a factor adverse to respiratory health. Pens should be separated by a solid panel to avoid facial contact and control drafts, but the ends and top of the pens should be as open as possible.

Sufficient for the calf to 'nest'

Calves are vulnerable to cold stress in winter. The thermoneutral zone of a newborn calf is between 10 and 26°C and between 0 and 23°C for a 1-month old calf. The field trial was conducted on Wisconsin dairies during the months of January through March. The average temperature in the barns for a 2-hour period near noon was 3.9°C and ranged from -6.7 to 12.2°C. Overnight temperatures would be lower. Clearly, the young calves were exposed to temperatures below their thermoneutral zone during many days and nights through the period in which the trial was conducted.

Bedding provides a potentially effective mechanism for calves to reduce heat loss. If the bedding is sufficiently deep, the calf can “nest” and trap a boundary layer of warm air around itself, which reduces the lower critical temperature of the calf. Several aspects of bedding were evaluated, including type and dry matter, and the factor that emerged as having a significant association with the prevalence of calves with respiratory disease was “nesting” score. Nesting score 1 was assigned when the calf appeared to lie on top of the bedding with legs exposed. Score 2 was assigned where calves would nestle slightly into the bedding, but part of the legs were visible above the bedding. Score 3 was used when the calf appeared to nestle deeply into the bedding material, and its legs were not visible. Because all of the calves were not observed while lying down, a nesting score was assigned to each barn based upon the most frequently observed score.

Lower total airborne bacterial counts within pens

Lower total airborne bacterial counts were associated with reduced prevalence of respiratory disease in the barns. The total airborne bacteria recovered on the plates are a mixed population, usually dominated by various Staphylococci, Streptococci, Bacillus, and E. coli, not considered to be respiratory pathogens. The team also measured airborne coliform concentrations as counted on eosin-methylene blue differential media but found no significant association with prevalence of respiratory disease.

The total airborne bacterial counts should not be viewed as the cause of respiratory disease but rather as a marker of poorly ventilated spaces. Older studies point out that most airborne bacteria are non-pathogenic, but even dead airborne bacteria can be a burden to respiratory tract defenses. The actual disease stimulus could include any of many components of bacterial or fungal cellular components including endotoxin, enzymes, glucans, and others. Because calves spend 100 per cent of their time in the pens, the exposure to the air within the microenvironment is continuous and chronic. Air that is highly contaminated with noninfectious microorganisms in the work environments of people is recognized as a risk factor for respiratory disease and, although specific exposure limits have not been established, air with bacterial concentrations an order of magnitude greater than found outdoors or in “uncontaminated” areas (usually less than 104 cfu/m3) is considered to be “contaminated”.

Upon hearing the points discussed above, many people will inquire about ammonia levels in the pen. Ammonia was measured and averaged 2.2 ppm across all barns, ranging from 0-4 ppm, all considered to be low levels and not associated with any respiratory problems in these barns.

Techniques to Reduce Airborne Bacterial Counts in Pens

Increase the area within the pen

Stocking density is considered to be the primary determinant of airborne bacterial concentrations. Mean area of individual pens in all barns was 3 m2 (32.3 ft2) with a range from 2.3 to 4.1 m2. Data from the study suggested that increasing area from 2.3 to 4.1 m2 reduces the total airborne bacterial count to approximately half.

Reduce the number of solid panels surrounding the pen

The number of solid panels around the stall should be limited to two sides. Our ideal pen would have two solid sides and a short solid panel limited to about 20 inches high at the rear of the pen. Further enclosure of the pens increases airborne bacterial counts dramatically. If there are multiple rows of stalls within a barn, each row should be separated with an alley several feet wide. If they must be adjoined, a third solid side should separate the calves, and additional methods should be employed to reduce bacterial concentrations.

The practice of covering the pen with a “hover” or enclosing the pen with a solid front with a small feeding access hole should be discontinued. It has become clear from this field study that it is strongly preferable to control for thermal stress by providing ample bedding rather than through enclosure.

Supplemental mechanical ventilation

Because total airborne bacterial counts are associated with the prevalence of respiratory disease in young calves, a number of techniques have been tried in our clinical services in problem barns. The most successful intervention has been the installation of supplemental positive-pressure ventilation systems. Fresh, outside air is forced into a positive pressure duct system and directed downward into the pen microenvironment. Mr Nordlund and his team usually recommend fabric or polyethylene vent tubing, over metal ductwork, because of cost savings.

The supplemental installations have been designed so that fresh air is delivered to each pen at an approximate volume of 15 cfm per calf. This volume of air is consistent with traditional ventilation recommendations for mechanical systems. The fans are mounted in exterior walls, and the tubes are fixed directly to the fans, preventing any recirculation of interior air. The air distribution tubes are attached to suspended cables stretched between support walls.

The custom-punched holes are sized so that air is expected to exit the holes at a speed of approximately 800 fpm. The tube suppliers usually offer a range of hole diameters ranging from 1/2 to 3 inches. The larger the hole, the greater the “throw” distance. It was found that a combination of number and diameter of holes so that there is at least one hole per pen allowed the targeted exit air speed to be reached.

The holes are punched at various clock locations. The higher above the pens, the more vertical the hole location. If the bottom of the tube is located 8 to 12 feet above the floor, holes are usually punched at 4 and 8 o’clock positions. If higher than 12 feet, the locations of the holes are usually 5 and 7 o’clock.

The goal is to introduce small volumes of fresh air into the microenvironment without creating a draft. Drafts are described as air speeds of 0.3 and 0.5 m/s. More work is needed to define the combination of hole diameter, exiting air speed, and distance from the calf so the air does reach the pen but at a speed of less than 0.3 m/s.

The positive-pressure tubes can provide supplemental ventilation to microenvironments in both natural and negative-pressure systems. One complication has been identified using the tubes within wind-tunnel calf barns. Clinical investigations have shown high airborne bacterial counts within solid-sided pens in wind-tunnel barns where air traveling across the tops of the pens exceeds 250 feet per minute. Efforts to direct small volumes of air from a distribution duct have failed in these situations, presumably because the air coming from the positive-pressure duct gets caught in the wind-tunnel air stream and never reaches the microenvironment within the pen. In these situations, the exhaust capacity of the negative-pressure wind-tunnel system must be reduced substantially for the supplemental system to work.


Individual calf pens should be viewed as microenvironments within the calf barn, and ventilating the barn does not ensure adequate pen ventilation. In cold weather when the young calf is frequently exposed to temperatures below its thermoneutral zone, three key housing factors associated with respiratory health are a solid panel separating each calf, deep straw bedding allowing the calf to “nest,” and low airborne bacterial concentrations in the air in the pen. Practical approaches to reducing the concentrations of total airborne bacteria in the pens include making the pens larger, reducing the number of sides and eliminating covers from the pen, and. through the use of supplemental positive-pressure ventilation systems, directing small volumes of fresh air into the pens. Clinical experiences show these approaches are typically successful in achieving significant reductions of endemic calf pneumonia frequently found in modern naturally ventilated calf barns.

November 2009
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