Economics and Energy Considerations when Managing the Dairy Enterprise
by David B. Fischer
TAKE HOME MESSAGE
- Compare energy costs to cow performance benefits.
- Protect cows from heat stress with shade, natural ventilation and plenty of drinking water.
- Provide additional cooling methods including sprinklers and fans.
- Recognize that heat stress can occur below 80 degrees Fahrenheit.
The ability to make a profit in the dairy enterprise has been nearly impossible during 1995. Reasons include lower milk prices, poor quality forages, extreme summer heat stress, low cull prices, and higher feed costs. The margin between total costs and total returns grows tighter as production costs continue to climb. It is essential that every dairy producer has a record system in place to analyze the financial situation of the dairy. Profit-conscious dairy managers know what it costs to produce a hundred pounds of milk. Usually it is feed, labor, and capital investment related costs that concern producers the most. This is logical as these make up from 70 to 80 percent of the cost of producing milk. However, energy costs also deserve close attention as the dairy producer attempts to produce milk at the least cost possible and widen the profit margin. The summer of 1995 emphasized the importance of energy needs and costs as producers struggled to keep cows cool.
CONSIDERATIONS WITH HEAT STRESS
Many dairy producers can still feel the heat wave of last summer; certainly not the physical warmth, but the loss of milk production, reproduction, and cows along with increased energy bills. A major factor in maintaining optimum milk production and animal health during the summer is to reduce heat stress. Heat stress occurs when a cow's heat load is higher than her ability to lose the heat. Mild heat stress can begin when temperatures reach the mid 70 degree Fahrenheit range and the humidity is in the mid 70's or higher. The temperature and humidity generate a great deal of environmental heat that, when added to the cow's own body heat, creates a heat over load. In order to get rid of the excess environmental heat, a cow must have access to shade, air movement, and fresh drinking water. Unfortunately, even these three basic needs were not enough to completely combat last summer's longest string of hot weather days ever seen throughout Illinois.
In order to decrease body heat production, the animal will also reduce feed intake. A reduction in dry matter feed intake begins when daily temperatures exceed 75 degrees Fahrenheit. University of Missouri research trials showed a dry matter intake drop of 18 percent when temperatures change from 69 to 85 degrees Fahrenheit. This past summer, it was not uncommon to see a 30 percent feed intake depression. The 1995 severe heat stress not only caused reduced feed consumption and milk production but also was responsible for lack of heat detection, decreased fertility, early embryonic death, lower calf weights and dead cows.
The practice of providing shade should be routine, and the first step to relieving heat stress for the dairy herd. Trees are the most effective shade because the air underneath is cooler due to the transpiration of moisture from the trees and the reduction of radiation. Unfortunately for many producers, it is not practical to provide enough trees for all cows. In addition, tree shaded areas must have access to drinking water and feed in order to get cows to achieve maximum dry matter intake.
The more practical way to provide shade comfort for cows, especially larger herds, is to create artificial shade. Freestall barns need to be designed as a shade in the summer and a windbreak in the winter. This requires curtain sidewalls and ridge ventilation that will allow for adequate air movement. Barns need to have at least 2 inches of open ridge for every 10 feet of structure width. An eave height of 12 feet minimum is needed to provide air movement inside the barn by means of natural ventilation. This not only has a cooling effect, but also provides for needed air exchanges without the use of costly mechanical ventilation. The freestall barn has many advantages for serving as a permanent shade structure. However, there are a number of these older "cold barn" facilities that are closed up too tightly and create added heat stress to the cows. When this situation occurs, the use of fan power in the barn or portable shades is recommended. Portable shades may provide a lower cost of cooling as compared to forced air fans. However, portable shades must be managed to avoid mud and manure ladden resting areas resulting in mastitis problems. Providing 40 to 45 square feet of shade for a mature cow is adequate to reduce solar radiation.
Shade over feed bunks and holding pen areas will also help reduce heat stress and encourage feed intake. Properly designed shades will provide cows shelter from the solar heat. Metal roof structures will provide more protection from solar radiation and have increased longevity compared to shade cloth. However, shade cloth is less expensive than solid roofing material. Shade cloth is available in patterns providing 30 to 90 percent shade with the most common being polypropylene fabric providing 80 percent shade. It is necessary to maintain tension on the cloth to achieve the full life of the shade.
AIR MOVEMENT AND SPRINKLERS
Air movement is the second basic need for relieving heat stress. Natural air movement can be enhanced by proper building design and location. The most important factor for adequate air movement or ventilation is open-sided construction to maximize the air currents caused by wind. Wind or natural air movement will help hold down energy costs, but other cooling options must also be available. Fans will provide the cooling effect by moving air over the cows only if the air temperature is lower than the animal's body temperature. Fans can cause a substantial increase in electrical energy usage, especially when box fans or open-blade fans are used continuously in the housing or feeding area. However, air movement from fans and water from sprinklers can provide a powerful cooling combination.
Sprinklers in the feeding area, holding pen, or other areas will greatly increase the cooling power of the fans and further reduce the effects of heat stress on the cow. This cooling is coming from water evaporating from the haircoat and skin of the cow. Sprinkling with large water droplets is required to penetrate the haircoat. Sprinkling systems that are regulated by a timer and thermostat will provide adequate wetting without over-wetting the cow, udder, or footing area. A cycle of one minute water spray and off 5 to 10 minutes will provide an adequate job of conserving water usage while sufficiently wetting the animal. There are a number of nozzle types that can work, depending on how close to the cows the sprinkler is mounted. Generally, 180 degree low pressure (10 pounds per square inch) spray nozzles are capable of delivering the equivalent of about .5 to 1 gallon per minute. The nozzles should be spaced 5 feet apart to get an overlapping coverage over the cows.
Fans will need to run continuously and should be capable of handling air flow rates of 11,000 cubic feet per minute at a velocity of 400-600 feet per minute. Fans can be hung above the sprinklers and tilted downward at 20 to 30 degree angles to direct the air flow on the cows. A rule of thumb for placing horizontal-axis fans is to mount 36 inch fans to move air 30 feet and 48 inch fans to travel air 40 feet.
Another method of using water for cooling is through a fogger or mister system. High pressure foggers do not wet the cow. This system dispenses a very fine water droplet that will evaporate and cool the surrounding air. The fog nozzles can be placed from the rafters or built into the side of a fan. The fan air evaporates the water droplets and directs that cooled air onto the cows. This system must be used in barns or holding pens with open sides and ridges to allow moisture ladden air to escape. Respiratory problems can occur from the fog and mist systems if the area is not properly ventilated.
Other types of air movement used to relieve heat stress in stall barns include tunnel ventilation and air conditioning. Cow comfort, during the peak of summer heat, can be greatly improved by increasing the exchange rate and air movement by using tunnel ventilation. The tunnel system can produce a wind breeze of 2 to 5 miles per hour through the stall barn.
This air movement also displaces air exhaled by the cows which may improve the efficiency of the cow's cooling system. The basic design consists of placing the fans at one end of the barn which draws air from an inlet at the opposite end. Tunnel ventilation could be more energy efficient than using side wall fans to achieve the same air exchange rate and air movement. By using larger fans with high efficiency motors the power requirements are often less with a tunnel ventilation system. An extra may be less fly problems in the stall barn since flies tend to avoid breezy areas. Air conditioning is yet another way to eliminate heat stress from cows in stall barns. Studies conducted back in the late 60's and mid 70's demonstrated significant increases in milk production and reproductive efficiency with refrigerated air. This method seemed to be too costly to run and maintain. However, with new technology in the air conditioning area and greatly improved cow comfort, this may be a workable and profitable alternative for some dairy producers.
FRESH WATER AND FEED
Fresh drinking water is the most important nutrient for dairy cows during the summer heat stress. Cows will need to drink more water during the summer months because much of their body water is used to dissipate heat. If water intake is restricted to the cow she will have less water available for milk synthesis thus decreasing milk production. Water and feed should be placed close to the shaded or cooled areas where cattle will congregate. Other successful nutritional tips to beat the heat stress include feeding smaller meals more times a day, offering fresh feed in the cooler hours of the night, and increasing the nutrient density of the diet due to decreased dry matter intake.
Funds for this presentation were provided by a 1996 Illinois Department of Commerce and Community Affairs grant.