The authors are with the Nurture Research Center, Provimi North America.

If you hear the title statement from your parents, you safely assume they want you to close a door. However, if you were a baby calf, it should have a completely different connotation.
Dairy calves are usually born either in a barn or on pasture. Either way, we change their environment very soon after birth to assist us in managing and rearing them. Because of differing management styles, physical facilities, and personal preferences, there are many options available for housing the newborn calf.

Recently, we evaluated different housing and bedding options in southwestern Ohio throughout the year. Average temperatures during the trials ranged from 46° to 70°F. Minimum temperatures dropped to 1°F, while maximums approached 94°F.

During the trials, calves were housed in either outdoor poly hutches without additional shade or indoors in wire mesh pens located in a curtain-sided nursery barn. All calves in the trials were from a single farm and between 2 and 5 days of age when the trial started. All calves on trials were fed a single milk replacer (26 percent crude protein, 17 percent fat) at 1.5 pounds of powder daily per manufacturer's recommendations along with free-choice access to starter (18 percent crude protein textured feed) and water.

The first trial compared housing in hutches with the nursery pens, when all calves were bedded with straw. Calves housed in the nursery had a 7 percent advantage in average daily gain (ADG) over those housed in hutches. In addition, nursery calves consumed the same amounts of milk replacer and starter feed, resulting in a 3.8 percent improvement in feed efficiency. The calf housing did not influence days scouring, body condition, or frame size of these calves.

The second trial compared housing all calves in the nursery barn bedded with either straw or sand to those in hutches bedded with sand. Again, calves housed in the nursery on straw had ADG 10 percent greater than those in the nursery on sand and 16 percent better than those in the hutches on sand. In addition, there was a slight reduction in severity and incidence of scouring for calves housed in the nursery on straw as compared to the other two bedding choices.

Calf nursery layout

The third trial compared calves in the nursery barn bedded with straw during summer months but provided with supplemental air movement through the use of fans. Calves in summer with fans providing supplemental air movement had a 24 percent edge in ADG and a 15 percent greater feed efficiency than calves simply housed in a curtain sidewall nursery.

During these trials, calves bedded in straw were observed to have a more "natural" resting posture than those bedded on other surfaces. It is possible that this helped the calves cope with the different environments, resulting in less energy expenditure by the calf in modifying their microenvironment. However, since calves in both the nursery pens and the hutches in trial one were bedded with straw, there must be other factors influencing the growth rates.

Air quality's effects
We also observed apparent differences in respiration rates of calves during the different studies. We wondered if air quality (and hence potential pathogen load) could be influencing the growth rate of calves in these studies. To evaluate this, we monitored air quality in our nursery barn, hutches, and group housing (postweaned calves). We measured airborne bacteria counts at 5, 40, 75, and 110 days of age. At all ages, the counts were greater than in the airspace from outside the barn or nursery. In addition, as calves aged, the counts of airborne bacteria rose.

Airborne bacteria concentrations

For both ages of calves housed in hutches, the bacterial counts were high and typically more than our equipment would measure. We interpret this to mean that air quality inside the hutches was poor as compared to the nursery pens. In addition, we noted that the younger calves tended to be more nestled in the bedding than the older calves and interpret this to say that the older calves tended to stir dust from their bedding. Still, the bacteria counts in the nursery pens were lower than those in the hutches.

Because our measures of air quality in the hutches were at the maximum our equipment would allow, we assumed that air exchange within the hutches was less than optimal. We then evaluated different practices which could allow for improved air quality in the hutches. First, we evaluated air quality at 0, 5, 10, and 15 feet away from the hutch opening. As we moved away from the hutch, bacteria counts dropped. We further attempted to promote airflow inside the hutch by elevating the rear with a 2x4 block of wood. Bacteria counts inside the hutch fell off as a result. In both of these cases, we assume that airflow accrued which allowed for intensified dispersion of bacteria that would have been contained in the calves' environment.

We have previously reported that calves bedded with straw in winter months had greater ADG than those bedded with wood shavings. In that work, we postulated that the calf was able to create a microenvironment around itself in the straw to provide insulation from the cold. This current work corroborates that idea and further extends it to indicate the possibility of a microenvironment insulating in warm weather also since these trials were conducted in all months of the year.

Other evidence
Other research groups have evaluated the impact of air quality on calf growth and health. Hillman and co-workers from Cornell University reported that providing filtered forced air to calf nurseries removed many airborne particles and bacteria, resulting in lowered incidence of respiratory disease. Later, work by researchers from the University of Wisconsin found deep bedding (similar to our straw) resulted in lowered bacterial counts inside individual calf pens.

We believe that these data support the idea that a microenvironment around the calves directly influences its growth rate. Calves in the nursery barn that were bedded with straw nested in the bedding and insulated themselves from temperature extremes. Further, because of the open pen walls, there was greater air exchange and lower bacteria loads in their environment.

We recognize that many individuals will regard our calf rearing facilities as above average in providing a quality environment to calves. However, if small improvements can be observed in our facilities, we anticipate that the results should be translatable to field observations. By making small changes to housing and bedding practices, we can provide situations that improve the microenvironment around the calf and, thus, have a positive impact on its early growth.

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