This spring’s inclement New Jersey (NJ) weather has brought large amounts of precipitation in the form of rain, and concern about crop and forage losses. Rainfall, particularly during forage harvest season, can result in the production of low-quality hay and forages. This can result in lower forage intake by animals, decreased forage digestibility, and reduced animal performance. Table 1 describes crop progress this year. Rain has postponed some hay harvesting, however, according to USDA-NASS, NJ crop progress is similar to last year, but significantly less than a five-year average.
Table 1. Crop Progress as of June 16, 2019 (in percent)
| Item | This Week | Last Week | Last Year | 5 Year Avg. |
| Alfalfa Hay: First Cutting | 63 | 38 | 66 | 82 |
| Other Hay: First Cutting | 56 | 32 | 61 | 70 |
USDA-National Agricultural Statistics Service, NJ
It is important to remember that the amount of rain New Jersey has had this spring is no guarantee that there will not be a drought that lasts into the fall.
When summer temperatures rise as they often do in New Jersey, the first sign of heat stress may be declining feed intake followed by declining milk production, decreases in weight gain, and decreased overall performance. All livestock producers may observe decreased rates of gain and feed efficiency in growing animals, declining reproductive efficiency and performance, and possibly health and disease related problems.
Anyone who has entered a dairy barn on a cold winter day knows how much heat cows can produce. In the summer, though, this extra heat, which comes from digesting feed and producing milk, causes a cow’s heat load to increase. When a cow can’t get rid of excess heat, she will stop eating and milk production will decline. Table 2 lists the typical thermoneutral zones for several domestic livestock species. Below these temperature values (Lower Critical Temperature), an animal will have to expend extra energy to maintain body temperature.
Providing extra feed or shelter or other protection from the elements are good ways to help animals stay warm. Above these temperatures (Upper Critical Temperature) animals will have to get rid of extra heat. An animal’s first response when atmospheric temperatures are elevated may be to stop eating. This will lower the heat load, but growth, reproduction, and milk production will all be affected. Please remember that the values in Table 2 are not adjusted for the effects of humidity, wind or wind chill, or inclement weather. These will also vary by species, breed (beef vs. dairy), length of hair coat, shorn vs. unshorn, etc.
Table 2. Typical Thermoneutral Zones (Upper and Lower Critical Temperatures in Fahrenheit)
| Species | Temperature o F |
| Cattle | 32-61 |
| Calves | 54-75 |
| Sow | 32-59 |
| Hen | 64-82 |
| Sheep | 27-67 |
NRC. 1981. Effect of environment on nutrient requirements of domestic animals. National Research Council. Washington, D.C.: National Academy Press.
Since animal production is a farmer’s livelihood, what are some strategies to keep animals cool? First, it is important to remember that most domestic livestock animals, excluding horses, have few sweat glands. This means that they will not lose heat by evaporative heat losses through sweating. The first strategy should be to provide abundant supplies of cool water for drinking. Water will help to cool animals and help maintain feed intake. This is especially important in the case of lactating dairy cows that may need 30-40 gallons of water a day to maintain milk production. Second, shade from shelters or trees in pastures will reduce the effects of radiant heat from the direct rays of the sun. Keeping animals sheltered in the day and turning them out on pasture at night will limit the effects of radiant heat and allow animals to cool. Third, water sprinklers or misters will help cool animals and relieve some of the effects of heat. Animals, particularly cows or pigs, will seek out water if available for cooling. It is common in certain parts of the country for cows to stand in ponds or streams. This is not recommended because of concerns about contamination of water supplies, and in the case of lactating cows there are concerns about mastitis disease infections. In modern confinement systems, pigs are often housed in climate-controlled barns. Pigs will wallow in mud if given the opportunity; this can be a good means for cooling if no other options are available and provided environmental concerns are adjusted for. In addition to protecting from the heat of the sun, shade will also protect pigs from direct rays of the sun that can cause sunburn for a light skinned pig. Fourth, fans are also useful for cooling; air currents over an animal’s body will disperse excess body heat. Fans, when used along with shade, and sprinklers or misters, will promote evaporative cooling, an excellent means of reducing an animal’s heat load.
There are some feeding strategies that may help to manage heat stress. First, consider increasing the energy density of the diet. This can be accomplished by decreasing forage and fiber levels (consult a nutritionist before dietary forage or fiber levels are reduced for ruminant animals) or by adding an energy source such as extra grain, or fat, or perhaps oilseed products in the diet. Since much of an animal’s heat production comes from digestive heat, increasing energy density will increase energy relative to digestive heat production; this is particularly true when feeding ruminants. For dairy cows fine-tuning the diet through the addition of bypass proteins, yeast or minerals may also be helpful. Before making any dietary changes in response to concerns about heat stress, consult with your feed company’s nutritionist.
There are effective means of dealing with heat stress during the summer. Provision of abundant supplies of cool water, the use of shades, fans, sprinklers or misters, and properly managed diet modifications can all be effective approaches for dealing with summer heat stress.
This article was written by Michael L. Westendorf, Ph.D. Rutgers University School of Environmental and Biological Sciences Department of Animal Science. It appeared previously in the June 15 issue of the New Jersey Farmer.
