|Dozens of 55" fans driven by 2-hp three-phase motors power ventilation at the 3,000-cow Helmer Dairy near Garretson, S.D.
OK, it might be a stretch to call these newfangled cross-ventilated homes for cows the Goldilocks of barns.
Yet the principle of cross-vent barns are the same as in the children's fairy tale: Cows don't like it too hot or too cold. The closer that the environment you provide is to cows' thermal neutral zone, the happier they'll be. Not unlike Goldilocks.
"The thermal neutral zone of a dairy cow is 41¢ªF to 68¢ªF, and if the cow had her choice, she'd probably set the temperature at 50¢ª,” says John Smith, a dairy Extension specialist with Kansas State University. Smith is the guy who roughed out the first design of a cross-vent barn on a, um, bar napkin back in 2003.
Since then, cross-vents—housing from several hundred cows to more than 6,000 cows per barn—have been popping up from Texas to North Dakota. The idea of providing cows a consistent environment—temperature, air quality, light and daily routine—has been the driving force in all of them.
"These facilities allow producers to have control over a cow's environment during all seasons of the year,” Smith says. "Low-profile, cross-ventilated facilities allow for buildings to be placed closer to the parlor, thus reducing the time cows are away from feed and water.”
Heat stress is particularly cruel to a cow's physiology. When heat stress occurs, cows reduce their dry matter intake, increase sweating and panting and shift their energy from milk production to body maintenance.
Maintenance feed requirements can increase by 35% if heat stress is not managed. Milk production also suffers, with many herds losing 10 lb./cow/day. And those effects don't include the reproductive havoc that occurs at high temperatures: loss of sex drive, decreased fertility and increased embryonic loss.
Total economic losses, based on $18 milk and 12¢/lb. feed costs, can approach $40/cow/year, say Mike Overton, a reproductive specialist with the University of Georgia, and Barry Bradford, a Kansas State animal scientist. For a 500-cow herd, that can quickly total a $20,000 loss in income over feed costs.
While the industry has focused on heat stress, cold stress can also take a toll. Cows eat more as the temperature drops. They also produce more manure and feed efficiency suffers. "The decrease in diet digestibility results in an 8% decrease in income over feed costs as temperatures drop to –10¢ªF,” Bradford says. "Likewise, if ambient temperature is 5¢ª and the temperature inside the [cross-vent] barn is 15¢ª, income over feed cost is expected to increase by $1.15 per cow per day.”
A primary benefit of cross-vent barns is their ability to stabilize the cow's core body temperature, says Smith. In July 2006, he and other researchers conducted a cow heat-stress audit of a North Dakota cross-vent barn with evaporative cooling pads and a naturally ventilated barn equipped with feedline soakers and fans.
Vaginal temperatures from eight cows were recorded in each facility at five-minute intervals for three days. Ambient temperatures those days did not exceed 90¢ªF.
"Vaginal temperatures were acceptable in both groups of cows, but the temperatures of cows housed in the cross-ventilated facility were more consistent,” Smith says.
"Feedline soakers in naturally ventilated buildings are effective in cooling cows, but they require the cows to walk to the feedline to be soaked.”
The cross-vent's ability to cool cows is dependent on relative humidity. Cross-vents rely on cooling pads to provide the "air conditioning,” so to speak. Cooling pads, made of permeable material that water passes through, are placed at the air-inlet side of the building. Water then trickles down through the pads. As air is pulled through the pads, water is evaporated, dropping air temperature and increasing the relative humidity in the barn. The net result is that the temperature-humidity index is lower in the barn than it is outside.
However, if the outside air is already laden with moisture, it can't absorb much more and the cooling effect is reduced, says Joe Harner, a Kansas State ag engineer. For example, if relative humidity is 30% and air temperature is 100¢ªF, evaporative cooling can reduce air temperature by 25¢ª. But if the relative humidity is 60%, evaporative cooling can reduce that 100¢ª temperature to only 87¢ª.
Controlled lighting is another advantage for fully enclosed, cross-vent barns. Lactating cows exposed to 16 hours of continuous light each day will increase milk production about 8%. Feed intake also will increase about 6%, but the increased milk production will more than pay for it, according to University of Illinois research.
Uniformly lit barns also provide better cow movement, observation and care, as well as a better work environment for herdsmen, breeders, vets and farm labor.
But as Goldilocks found, not everything is peaches and cream. Cross-vent barns are just as expensive to build as naturally ventilated barns, if not more so.
The Kansas State experts say insulation of ceilings is usually warranted, particularly in Northern climates where wintertime condensation can be a problem. Insulation must also be properly done, since gaps can allow moisture to settle on any unprotected metal and eventually cause corrosion.
Cross-vent barns are tied to mechanical ventilation 24 hours a day, seven days a week, 52 weeks a year. Electrical costs from running fans will be a large line item on operating budgets. And emergency backup power is required to run a minimum number of fans.
Cross-vents also require emergency evacuation plans for humans and cattle. If backup power fails, manure gases can build up in the enclosed facilities, threatening worker safety.
|Steel baffles force air down over freestalls, which increases air speed and the barn's cooling effect.
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