April 12, 2012 - According to Dr. Todd Bilby, associate professor and Texas AgriLife Extension Service dairy specialist at Stephenville, annually the dairy industry, across the US, loses about $1 billion due to the effects of heat stress, mainly on the loss of milk production and reproduction.
Given the warm winter and 80-plus degree spring temperatures, dairy cows may already be suffering from heat stress, and it is only going to get hotter.
"(Heat stress) is a combination of two things: temperature and humidity," Bilby explained. "So the higher the humidity, the lower the temperature can be.... I would say in our area, in Central and East Texas, around the 70- to 75-degree mark, these cows are just beginning to experience mild heat stress.
"So, it occurs a lot earlier than people think," he continued. "Because a dairy cows neutral zone is about 40 to 50 degrees Fahrenheit, where we are more like 70 degrees Fahrenheit. So, a cow is much more comfortable in colder weather than we are."
It is not only the severity of the heat stress, but the amount of time the dairy cow is in temperatures ranging from 70 to 100 degrees and above, but also the length of time they are exposed.
"Heat stress can occur over a two-day period or a whole three-month period," Bilby said. "There are heat waves in the Midwest that can have detrimental effects for example. Definitely, all the time that the cow is above 70, it is going to acquire heat stress."
Bilby has been a part of a USDA sponsored Dairy Heat Stress Road Show that is part of a five-year grant through the USDA, enabling Bilby and his associates to travel to four states and Puerto Rico to educate dairymen on heat stress affects and ways to prevent it.
Other Road Show experts include, from the University of Florida distinguished professor Dr. Pete Hansen and associate professors Dr. Jose Santos and Dr. Albert DeVries.
"We have been hearing different research over the past, this is a five-year grant, we are on year four right now, so what we wanted to do was take this road show out to different locations and display some of the past research and new research coming out on strategies producers can employ that might help them during the summer months," Bilby explained.
As heat stress is a major concern for dairymen, especially in the warmer states including Texas, finding ways to diminish the effects of this problem is essential to the dairy industry as a whole.
"We know that we lose anywhere from 10 to 15 percent on our milk production during the summer, and reproduction, we will lose 50 percent of our reproduction," Bilby said. "So our reproduction really tanks."
Some of this comes from the selection process. Dairy cattle have been bred to produce the largest quantities of milk possible, rather than to have strong reproductive systems, making it harder to get a successful breeding.
"When we select a cow to produce a lot of milk, so with that she focuses on producing milk, and not taking care of reproduction," Bilby said. "So, the whole point of this grant is to look at ways to improve fertility during the summer months."
While a dairy cows reproductive system can be complicated it is both a challenge to get a dairy cow bred and maintain that pregnancy in the summer. Fertility is a problem when it comes to heat stress as well for both the cow and the bull.
"A lot of times we can't get the cow to ovulate a good egg," Bilby explained. "So, there is no chance that it is going to get fertilized and make a good embryo, because heat stress will damage a follicle and the egg inside the follicle before she ever ovulates and it usually takes her almost two months to restore that fertility.
"That is why a lot of times, you don't see our pregnancy rates come back until late into the fall in November, first of December, because we are still ovulating heat-stressed eggs and it takes two months for the small follicle to come up and become a large follicle and the egg to ovulate."
So, not only is it is hard to get them pregnant, but at the same time, the embryo loss is very high. Factor in heat stress in the summer months, and it is even further decreased.
That is why it is important to make adjustments to the dairy cow's environment that include adequate cooling and shelter. There are all kinds of cooling systems from dairy barn fans and foggers, to portable cooling systems. Bilby suggests looking into management strategies as well by choosing to complete tasks like feeding and working cattle in the cooler parts of the day.
Other strategies to help improve not only milk production, but fertility, include utilizing herd synchronization, timed artificial insemination (A.I.), embryo transfers and heat detection.
"If we run them through a synchronization program, we are more apt to get them pregnant," Bilby said. "Another way is to reduce the amount of bull breeding. Bulls get heat stress too, so if you can take the bull out of the picture, and just use A.I., that is a way you can improve some fertility in the summer, and at the same time get increased genetic gain."
Implementing these strategies will help to reduce heat stress, thus keep fertility and milk production on a higher plain across the board, resulting in more money in the dairyman's bank account.
