[August 23, 2016]

How Heat Stress Reduces Reproduction Rates in Dairy and Beef Cows

Heat stress and higher than normal core body temperatures reduce reproductive performance of dairy and beef cows according to three new reports from TechMix Global. The first two reports measure the impact of core body temperatures and reproduction rates completed by the University of Puerto Rico and at two different dairy field trials in Spain. The third is a multi-page summary report that contains details on the impact of heat stress on reproduction rates from 14 different research papers completed by 39 different bovine health experts from leading agricultural research institutions in North America, Europe and the Middle East.

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"Reproductive performance for both beef and dairy cows declines during heat stress in three ways," says Dr. Rodrigo Garcia, DVM PhD, TechMix International. "First, estrus intensity lessens during heat stress. Second fertility is reduced. Last, the survival of early embryos can be compromised. Blood flow is redirected from the core to the periphery for cooling. This can lead to cellular nutrient loss which may hinder fetal development."

Puerto Rican and Spanish Studies Summary

The Puerto Rico study was conducted by the Department of Animal Science at the University of Puerto Rico, Mayaguez. Thirty-eight cows were assigned to two groups - a control group and a second group which was fed Bovine BlueLite® Pellets. A sub-sample of the cows (n=10) were inserted with vaginal thermometers to measure vaginal temperatures. A significant difference in vaginal temperatures was observed during times of high temperatures and humidity when the Temperature Humidity Index (THI) was greater than 80%.

The Spanish study was completed at two different dairy farms in Spain. The first dairy included a contrl group of 119 cows and a BlueLite® "treated" group of 122 cows which had historically showed the greatest negative response to heat stress. During the 60-day period the maximum and average THI values were 91 and 79.1, respectively. The pregnancy rate for the treated group was 15.8% vs. 12.7% for the control group. Average days to pregnancy for the treated group was 132.9 days vs. 140.8 days for the control group. The second dairy included a control group of 99 cows and a BlueLite "treated" group of 98 cows. During the 60-day period, the maximum and average THI values were 100 and 88.4, respectively. The pregnancy rate for the treated group was 11.3% vs. 8.5% for the control group. Average days to pregnancy for the treated group was 176.2 vs. 186.4 for the control group.

Reproductivity Research Summary

Lactating dairy cows are especially prone to metabolic heat increases due to diet, feed intake and increased metabolic activity required for digestion and milk production. Dr. Peter J. Hansen (University of Florida) documented how these factors led to excessive core body temperature during heat stress periods and how they lowered seasonal conception rates between 10-20%.

Elevated core body temperatures resulting from heat stress are also detrimental to the development of reproductive oocyte cells during the first 5-6 days of development. Heat stress that coincides with ovulation and oocyte development can result in embryos that are more likely to develop slowly and abnormally as documented by Dr. D. James Putney (University of Florida) and his colleagues in Animal Reproduction Science. Heat stress is also detrimental to the follicle that encloses the oocyte cell. There is a close correlation between follicle alterations and reduced concentrations of estradiol - a powerful ovarian and placental estrogen that prepares the uterus for implantation of fertilized ovum as discussed in research by Dr. Frank Gwazdauskas (Virginia Tech) and Dr. David Wolfenson (Hebrew University) and their respective colleagues.

High air temperatures 10 days before estrus were shown to be associated with low fertility as demonstrated by Y.M. Al-Katanani and associates. In studies completed by Dr. Irina Garcia-Ispierto and her associates found that about 10% of dairy cattle pregnancies at Day 40-50 result in fetal loss. When viewed with the temperature and humidity index, there is a clear correlation reduced probability of conception and fetal survival.

"We felt it was important to summarize into a single source the most important research studies from around the world about the impact of heat stress on reproductive health of dairy and beef cattle," says Garcia. "The bulletin emphasizes the importance managing heat stress and core body temperature to maximize production and profits."

About TechMix Global: Since 1983, TechMix has been manufacturing and marketing BlueLite®, the most recognized brand in animal hydration. It is often recognized as the Gatorade for animals but we believe it's so much more. At TechMix, we are constantly innovating with our customers, veterinarians, nutritionists and universities around the world to provide the best hydration products to protect animals and the producer's investment. Our product line, including key brands - BlueLite®, Blue2®, YMCP®, Liquitein® and Restart products help customers manage the stress events from birth to transport, by providing the right hydration at the right time - when your animals need it most. Bottom line, we are TechMix, redefining hydration to keep animals drinking, eating and producing.

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