Researchers have developed many management protocols and technologies that can be used to increase efficiencies of production on the dairy. One of these tools is advanced reproductive technologies.
Traditionally, assisted reproductive technologies such as embryo transfer and in vitro fertilization (IVF) have been used to increase the number of offspring from genetically superior animals.
Recently, there has been an increase in the research examining the transfer of embryos in lactating dairy cattle to increase reproductive rates. These studies have identified at least two instances where there is a benefit to using embryos over A.I.
This benefit is because the transfer of an embryo has the ability to bypass certain causes of infertility.
The repeat breeder
A cow that has not conceived after three or more services is defined as a repeat breeder. These cows can be frustrating when managing the reproduction in a herd. Generally, these cows are open later in lactation and may only have a few more opportunities to get bred before they are put on the “do not breed” list.
The reason for the reduction in fertility can be due to many factors such as uterine infections, early embryonic death, improper A.I. technique/timing and defects of the reproductive tract. Several studies have examined the fertility of this population of animals – and have found that they are fertile.
These studies have shown that the uterus of a repeat breeder cow is able to maintain a pregnancy. One such study observed pregnancy rates as high as 70 percent when a traditionally produced embryo was transferred into a repeat breeder cow.
Another study looked at the effect transferring IVF-produced frozen-thawed embryos into a repeat breeder cow or heifer would have on reproductive rates. This study used 532 Holstein dairy cows and heifers with at least three previous breedings.
The IVF-produced embryos were transferred on either day seven or eight after estrus into one of two groups of animals. One group of animals had been inseminated with semen in the same estrus cycle, and the second group had received no A.I. Greater pregnancy rates were observed in both heifers (49.2 versus 29.5 percent) and cows (41.5 versus 20.4 percent) in the embryo transfer and A.I. treatment group than in the embryo transfer-only treatment group, respectively.
These results indicate that IVF embryos can be used to improve pregnancy rates in repeat breeder dairy cattle.
Heat stress
During times of heat stress, reproductive rates can fall as much as 50 percent. Increases in temperature, humidity and solar radiation during summer months are responsible for heat stress. Because of the negative correlation between heat stress and reproduction, researchers have looked at what initiates this reduction in fertility and how it can be managed to lessen its effects.
Heat stress reduces fertility associated with oocyte quality. Impacts on oocyte quality can be observed for the next two to three estrus cycles, which is why it may take months after heat stress for reproductive rates to rebound. Oocytes are less fertile because of exposure to increased temperatures while they grow and reach maturity.
In addition, heat stress also impacts reproductive rates by increasing early embryonic death. Embryos are highly susceptible to early embryonic death when heat stress is experienced immediately after conception, thus reducing subsequent pregnancy survival.
The majority of transferred embryos are day seven blastocysts. At this point in development, the embryo is more resistant to many of the effects of heat stress. Collecting embryos during non-heat stress periods and preserving them for transfer during times of heat stress can improve efficiencies.
Early research using embryo transfer indicated that embryos transferred during summer months were quite successful and resulted in pregnancies.
Additional studies using either fresh, traditionally produced embryos or IVF-produced embryos during times of heat stress have produced increased pregnancy rates when compared with cows subject to insemination. Studies comparing cryopreserved and fresh embryos to A.I. are limited but have shown a tremendous amount of promise.
Researchers at the University of Florida and Texas A&M published a study that compared A.I. with fresh and vitrified IVF embryos. They found that fresh and vitrified embryos produced more pregnancies than in cows that were inseminated. Animals receiving a fresh embryo had pregnancy rates that more than doubled that of A.I. (42.1 versus 18.3 percent), respectively.
Cows receiving a vitrified embryo also had greater pregnancy rates than cows that were inseminated (29.3 versus 18.3 percent), respectively, but to a lesser extent.
Advanced reproductive technologies can be used to increase efficiencies of production in dairy operations. These tools are very flexible and can be applied in many different ways to meet the needs and goals of an operation.
In addition, when coupled with other technologies such as genomics and sexed semen, they allow for greater genetic advancement in the herd than was previously possible. As with any decision, a cost-benefit analysis should be performed before investing in these technologies to determine if it is right for a given operation. PD
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Jeremy Howard
- Simplot Corporate
- Animal Sciences
- Email Jeremy Howard
