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It’s all epigenetics

They might find that a feed supplement provided at a certain stage of gestation permanently alters energy use and, therefore, feed efficiency in the offspring

Epigenetics is an emerging field of research worldwide. Literally, the word means “on top of genetics,” says Carolyn Fitzsimmons, an Agriculture and Agri-Food Canada scientist and assistant professor with the department of agriculture, food and nutrition within the bovine genome program at the University of Alberta.

DNA sequence influences an animal’s physical (phenotypical) characteristics. On top of that, the way the proteins are modified or packaged around the DNA molecule influences differences in the way the gene and traits are expressed, she explains. Maternal nutrition and climate are only two examples of the many factors that could affect the DNA packaging.

Moreover, the limited amount of research to date indicates that the DNA packaging could be inherited and that the alteration is permanent in subsequent generations, Fitzsimmons adds.

For livestock producers, epigenetic discoveries may unlock windows of opportunity to either ensure or enhance the genetic potential of economically important traits by manipulating maternal diets at certain stages of gestation, or even before the cow becomes pregnant. For example, research from the swine reproduction group at the U of A indicates that there may be a link between maternal nutrition during the pre-ovulatory period and the sex ratio of the next generation of piglets.

Fitzsimmons’ interest in bovine genetics goes back to the University of Saskatchewan, where she worked on the leptin gene project. During her time spent as a research technician at Iowa State University and while working toward her doctorate in Sweden, she co-authored scientific papers related to gene expression in poultry and swine. Her post-doc studies took her to Australia, where she worked with a group investigating hybrid vigour in birth weight of beef cattle.

The question to be answered was why Brahman sires on Angus dams produce higher-birth-weight calves than Angus sires on Brahman dams. An obvious answer would be that Angus dams have more capacity to develop a fetus. However, the effect held true even when embryos of both crosses were put into Angus dams.

This led to the theory that epigenetic-controlled genes imprinted on the paternal side in Brahmans were dominating the maternal genes in Angus. Genes often act in pairs in mammals, she explains. The paternal IGF-2 (insulin-like growth factor 2) genetics influence the fetus to grow larger, while the maternal genetics (IGF-2 receptor) keep the check and balance.

When they measured the IGF-2 and the IGF-2R of fetuses resulting from straight-bred Brahman, straight-bred Angus, Brahman sire-Angus dam, and Angus sire-Brahman dam crosses, they found differences in the way gene expression interacts with both paternal and maternal genetics relative to birth weight.

Secondly, they found that the expression of the growth factor genes in 153-day-old fetuses is highly correlated with the live weight and backfat of the dam. In other words, something related to the body condition of the cow in the early stages of gestation was influencing the growth factor expression at that stage of development.

“After most of the organs and tissues have been formed, the fetus enters more of a growth stage. If maternal nutrition is altered moderately after this time, the calf might have a higher or lower birth weight, but after birth, it would grow about the same as another calf — there probably wouldn’t be a permanent alteration in gene expression,” Fitzsimmons explains. “If we want to influence permanent changes in the gene expression of the offspring we may have to look earlier.”

For example, there are two waves of muscle development that begin to occur within the first 39 to 60 days and 100 to 120 days of gestation. Maternal nutrition and condition during this period could influence gene expression related to muscle distribution and fat deposition in the offspring. Or, they might find that a feed supplement provided at a certain stage of gestation permanently alters energy use and, therefore, feed efficiency in the offspring.

Fitzsimmons has applied for funding to carry the research forward at the U of A with the objectives of further defining the impact of maternal nutrition on offspring performance and exploring the possibility of using maternal diets to guarantee or improve the expression of desirable growth patterns, carcass traits and reproductive efficiencies.

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