By: Jeremy Howard, Simplot Animal Sciences
Rising temperatures, humidity and solar radiation during the summer months are responsible for heat stress. Researchers have developed a temperature-humidity index (THI) to gauge the level of heat stress an animal experiences. The index is calculated
using ambient temperature and relative humidity readings. Research indicates that a lactating dairy cow begins to experience heat stress when the THI meets or exceeds 70. A THI of 70 would correspond with 70°F at 100% humidity.
How does heat stress affect your herd?
Heat stress causes a reduction in fertility associated with oocyte quality. Impacts on oocyte quality can be observed for the next two to three heat cycles, which is why it takes a couple of months following the end of heat stress for reproductive
rates to rebound. The oocytes are less fertile because of the exposure to heightened temperatures while they grow and reach maturity.
Additionally, heat stress can impact reproductive rates by increasing early embryonic death. It has been shown that an embryo is highly susceptible to early embryonic death when heat stress occurs immediately following conception, thus reducing conception
and pregnancy rates.
decrease heat stress effects
To overcome the effects of heat stress, researchers have used assisted reproductive technologies such as superovulation and in-vitro fertilization (IVF).
These technologies allow for the transfer of an embryo that is seven days of age. It has been found that at this point in development, the embryo is resistant to many of the effects of heat stress. Additionally, these technologies allow for the possibility of collecting embryos when there is no heat stress and preserving them for use in times of heat stress. Early research using embryo transfer indicated that embryos transferred during summer months were quite successful and resulted in pregnancies.
Additional studies using either fresh superovulated embryos or IVF-produced embryos during times of heat stress have shown increased pregnancy rates when compared to A.I. Studies comparing cryopreserved and fresh embryos to A.I. are limited
but have shown tremendous promise.
In 2011, researchers at the University of Florida and Texas A&M University published a study comparing A.I. to fresh and vitrified IVF embryos. They found that fresh and vitrified embryos had higher pregnancy rates than those of A.I.
- Animals receiving a fresh embryo achieved a pregnancy rate double that of A.I. (42.1% vs. 18.3%).
- Animals receiving a vitrified embryo achieved a
higher pregnancy rate compared to A.I. (29.3% vs. 18.3%).
Investigating embryo opportunities
During the summer of 2019, Minnesota/Select Sires Cooperative, Inc. conducted the initial trials with SimVitro HerdFlex embryos to determine if full-beef embryos could be a profitable diversification option for dairy operations.
The trial herd showed a boost in reproductive rates for the HerdFlex beef embryo group over the conventional beef semen group. During
the summer heat stress period, the HerdFlex beef embryos exhibited more than 5% higher conception rates than conventional beef semen
(See Table 1).
Traditionally, conventional embryo flushing and IVF have been used to increase the number of offspring from genetically superior animals, and the cost associated has been too high to implement in commercial dairies. However, more recently, IVF
technology has been adapted, making embryos less expensive and more available to dairies.
For herds honing in on their reproductive performance during hot seasons, HerdFlex beef embryos can be a profitable solution. In addition to fertility performance, full-beef embryos can lead to greater opportunities in the beef market. As with any decision, a cost-benefit analysis should be performed to determine if this technology is right
for your operation. Contact your local Select Sires representative today to review your goals and decide if HerdFlex can bring more value to