Peruse practical information for the dairy producer on essential topics including management, A.I. and breeding, new technology, and feed and nutrition.


Recent interest in animal welfare stems often from concerns related to intensive farming techniques.

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Water is one of the most basic, yet important things we can supply for our cows. Despite the central role that water plays in mammalian physiology, we tend to take it for granted.

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At recent dairy production workshops sponsored by the University of Minnesota and the Minnesota Milk Producers Association, Dr. Joe Harner, Kansas State University, offered Minnesota dairy producers a look at how high- producing cows spend their time.

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Dairy operators face a number of management problems during the production season. One of these problems is the control of insect pests.

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We have been hammering away at relieving heat stress on dairy cows for a long time, including how to design, build, modify and manage facilities. Heat stress occurs when the heat generated by the cow and heat received by her from the environment exceeds the amount of heat she can successfully release to her environment. SAAWW is a convenient tool for remembering the critical steps to cut heat stress.

• Shade for dairy cattle (any age) reduces the heat load on the animals from direct solar radiation.

• Air exchange is necessary when cows are inside a shelter to remove hot, stale, humid air and replace it with fresh outside air. A minimum 1000 cfm air exchange per cow is recommended.

• Air moving over cows at a high speed (220 to 440 feet per minute or 2.5 to 5 miles per hour) helps the cow increase the amount of heat she can lose from her body by convective cooling.

• Water is essential for a cow’s bodily functions. During heat stress conditions she needs extra water to enhance her cooling by evaporating it from her respiratory tract and the surface of her body. Plenty of clean fresh water to drink is the first step in any cow heat stress relief process.

• Water can also be applied to a cow’s skin and evaporation encouraged (sprinkling with a breeze) to remove more heat from her body. Passing air through a wet evaporative cooling pad or a fine water mist from a high- pressure misting nozzle will reduce the air temperature (and increase the humidity).

A mild day and a barn with inadequate air exchange (curtains closed or inadequate fans operating) can quickly increase the temperature humidity index (THI) and put a cow under heat stress conditions.

The upper temperature of a cow’s thermal comfort zone is usually expressed as about 77ºF. However, the impact of air humidity on the evaporation rate from the cow decreases cooling as humidity increases. This humidity can be a result of a hot, humid summer day or a hot, humid barn due to warm outside temperatures and inadequate air exchange. Cows can and do experience heat stress every month of the year due to poor or nonexistent ventilation systems.

A heat stress chart (Figure 1*) illustrates the relationship of air temperature and humidity and their impact on the cow’s stress level. A cow can begin to feel mild heat stress between 70 and 85ºF depending on the humidity in the air. At 80ºF and 80 percent relative humidity (RH) a cow in an under-ventilated, humid barn will feel a similar level of stress as a cow at 100ºF and 15 percent RH under a sunshade in the desert.

A dairy that does not respond to warm outside conditions with an appropriate increase in ventilation and drinking water could stress cows any month of the year. Does this happen at your dairy?

Use the chart in Figure 1* to learn the combined effect of temperature and relative humidity on heat stress. Humid, warm nights or barns with insufficient air exchange can be as harmful as higher temperatures when the relative humidity is low. PD

—Excerpts from Penn State Dairy Digest, April 2007

Robert E. Graves, Agricultural Biological Engineering Extension, Penn State University

Spring – time to plant corn, first cutting of hay and spread manure. But before you climb on the tractor seat, think about adjusting your barn ventilation in anticipation of warmer weather. That may be as simple as rolling up sidewall curtains or it may entail the removal of plastic tarps or plywood that protected structures from those brisk winter breezes. Regardless of what it takes, make sure to open up your barns before the hot weather.

The “comfort” zone for dairy cattle is 41 to 77ºF. Temperatures inside poorly ventilated barns could exceed that during the middle of the day even in early spring. Above 77ºF, cows are heat-stressed and dry matter intake suffers leading to a list of problems including reduced milk production, reduced reproductive efficiency and increased occurrence of metabolic disorders.

The effects of heat stress can haunt you for the rest of the year – recall that 1 pound of peak milk translates into 225 to 240 pounds per lactation. For example, 4.5 pounds decrease in peak milk can lower the lactation yield by 1,000 pounds. So make sure you have the capability to cool early lactation cows. Ration adjustments may be needed to compensate for reduced dry matter intake.

A great place to start addressing heat stress is the holding pen and the feed bunk. These two areas of higher cow traffic are prone to heat stress. Look for ways to provide fans and possibly sprinklers on cows at these locations. Below is a list of items to consider as the temperature rises:

• Open up barns (remove sides, roll up curtains) to maximize natural ventilation.

• Clean dust and residue off of fan cages as it can cause drag, which compromises the air-moving ability of the fan. (You would be amazed at how much better a clean fan can function relative to a dirty fan.)

• Ask yourself if any structures around cow housing can be removed or modified to allow for better air flow. Do you really need that ivy-covered corn crib you haven’t used in 10 years?

• Consider installation of a cow sprinkler system. (Your local dairy extension agent should be able to assist you in the design of these systems.)

• Is your feed bunk and holding pen adequately shaded? Is this true at different times of the day as the position of the sun changes? PD

—From Virginia Tech Dairy Pipeline, May 2007

M. Chase Scott, Extension Agent, Virginia Tech