Cattle Reproduction Research

September 2008
The AgResearch reproduction research team at Invermay is identifying animals with increased embryo survival, either to ensure a higher rate of twin lambs, rather than singles or triplets, or to improve cattle conception rates.

Jenny Juengel, originally from the United States, was appointed section manager for reproductive biology in 2006 after joining AgResearch in 1998 as a molecular biologist. Her research has focused on understanding the mechanisms that control the number of eggs released at each reproductive cycle or oestrous, using unique sheep models. A focus of current research is on developing genetic markers for selection of ewes with increased embryo survival. In sheep, increased embryo survival allows for development of flocks with high twinning percentages, while presence of singles and triplets is minimized. Identification of these pathways should also provide insights into development of new products/management practices to improve embryo survival in other species.

Cattle reproduction research:

Increasing embryo survival in cattle is also important to obtain an increase in the number of animals that calve in the beginning of the calving season and reduce the number of empty animals without extending the calving season. AgResearch is developing a research programme to understand the physiological factors that influence embryo survival to be able to identify new products or management practices to increase embryo survival.

One research project compared daughters of bulls that were classified as having genetics for high or low fertility to see what the daughters did different. Daughters from high fertility sires had a higher conception rate (i.e. embryo survival) than those with from low fertility sires. In the daughters from high fertility sires, a marker of development of the follicle, the structure that develops and releases the egg for fertilization, was higher.

We believe this indicates a higher quality egg in those animals that became pregnant. The other thing that we noticed was that a low but economically significant percentage of cows that were re-bred didnt actually appear to be at a proper stage of the reproductive cycle to be bred and may actually have been pregnant. We are investigating development of a diagnostic tool that could be used alongside of the cow in the yards to determine if a cow that was going to be re-bred was in the correct stage of the reproductive cycle to be bred. This diagnostic tool could be used selectively to test cows that showed weak signs of bulling after they had been bred to help decide if they indeed should be re-bred. We are also looking for genetic differences between bulls with genetics for high and low fertility to see if we can identify genes involved in embryo survival. Taken together with the results from the sheep models with genetically based differences in embryo survival, this should identify key pathways involved in this trait. By understanding how these pathways involved in embryo survival are regulated, we should be able to develop new products or management techniques to improve embryo survival, says Jenny.

One possible product is a fertility vaccine for use in beef cattle.

A second project involves improving methods of synchronization of the oestrous cycle, development of a mature follicle and ovulation for use in fix-timed breeding programmes. This will particularly help address the problem of getting cows pregnant that have not yet begun to have reproductive cycles at the beginning of the breeding season but also has applications to other situations. We are aiming to understand the underlying changes in the physiology of the animal undergoing these programmes to target development of new protocols and products to improve the pregnancy rate of these programmes. This work links in with the embryo survival projects given that we believe a key component of embryo survival is in proper development of the follicle and thus the egg.

Marcello Martinez is in charge of the embryo collection team.