Transgenerational Epigenetic Inheritance

Transgenerational Epigenetic Inheritance: A new perspective to Cattle Production

Department of Agriculture Veterinary and Rangeland Sciences University of Nevada, Reno

by Luis Fernando Schütz, PhD

lschutz@unr.edu

The challenge of obtaining one calf per cow each year is of great importance to the cowcalf segment. Several aspects are known to influence the pregnancy and calving rates of a beef cattle herd, including the fertility and breeding capacity, health, nutritional status, and genetics of the animals. However, recent research advances are unveiling a new factor to cattle reproduction based on the topic called transgenerational epigenetic inheritance. It is well known that the phenotype of an individual, which is the observable characteristics of that individual, is regulated by an interaction between the information carried out in the genome and the environment. Indeed, the term epigenetics refers to inheritable changes in the expression of genes without changes to the genome and these changes are responsive to the environment. This concept about the importance of genetics and the management to the performance of animals is not new to cattle producers. What new research is showing is that the environment and management not only affect the individual, but they also affect its future progeny in a way that seems much more impactful than we used to know. This is what transgenerational epigenetic inheritance is about, it refers to the inheritance of epigenetic modifications between generations. Not long ago, we believed that the experiences of animals and changes to their phenotypes during their lives would not affect the genome and, therefore, would not impact the next generation. Several recent studies, however, show that experiences throughout the life of an individual can have effects that lasts for several generations of descendants even without altering the genome. In fact, for epigenetic alterations to be characterized as transgenerational epigenetics, they need to last for at least two generations of descendants if the epigenetic alterations affected males and non-pregnant females or three generations of descendants in the case of epigenetic alterations that occurred in pregnant females. This indicates that the management of bulls and dams today may have effects to the performance of several future generations in the ranch. There has been a plethora of studies investigating transgenerational epigenetic inheritance in mammals, especially rodents and humans. These studies have

shown that stress, pollutants, nutrition, and lifestyle of males and females during the pre-conception period or of females during pregnancy can have long-lasting effects on the health of future generations. Studies involving cattle are still less numerous, but important findings have been published in the recent years and the tendency is that we find more about how the environment can play a role in cattle performance in the near future. The possibility that the performance of the progeny of cattle can be affected by the way we manage cows in the breeding season and during pregnancy is getting the attention of researchers. For example, a recent study has shown that heat stress in late gestation of cows reduces the milk production and productive life of daughters and milk production of granddaughters, confirming effects of the environment in the performance of immediate next generations and opening the possibility for last-longing transgenerational effects in productive performance of cattle in response to the management and the environment (1). Indeed, a correlation between regulation of milk production of dairy cows and epigenetics

has been established and confirms a potential for the impact of epigenetics to milk production of cattle (2). Another study has reported that the oocytes of early lactating cows experiencing a negative energy balance have epigenetic alterations when compared to mid-postpartum females and heifers, indicating that the metabolic status of cows at the time of breeding may have effects on the next generation (3). Taken together, all these studies indicate that the environment, management, and nutrition close to the breeding season or during pregnancy are important factors to determine not only the performance of cows, but also the performance of their future generations. Bulls breed several cows and heifers in cow-calf operations

and, therefore, have a greater impact on the genetics of the herd than cows. Hence, it is extremely important to investigate how the environment and management of bulls can induce changes to the sperm epigenome that can have an effect in future generations. Studies in other species have unveiled that many factors can contribute to alterations in the sperm epigenome, including nutrition, exposure to toxins, and even age. In bulls, a recent study has shown that an early plane of nutrition to accelerate the onset of puberty alters the sperm epigenome (4). Interestingly, a study has correlated variations of the sperm epigenome of dairy bulls with several reproductive traits, including heifer conception rate, cow conception rate, length of productive life, daughter pregnancy rate, and sire stillbirth, which indicates that epigenetic alterations of the sperm are indeed impactful for cattle reproduction (5). Research addressing transgenerational epigenetic inheritance in cattle is still in its beginning, but studies are already showing that the environment can affect the future of individuals way before we thought, even before breeding takes place. There is still a long road in terms of research, but it is possible that dramatic events such as an intense drought or an extremely hot summer close to the breeding season or during the period of pregnancy are more impactful to the health and productive performance of the herd than we used to think.

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