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Utilizing ‘omic' techniques to understand energy balance in the lactating dairy cow
Nutrigenomics describes how the amount and/or type of feed an animal receives, relative to its genetic and physiological requirements, affects its molecular phenotype, thus changing production, energy balance, reproduction, and health. For example, Holstein-Friesian cows (HF) bred almost exclusively for milk production have a more prolonged and severe negative energy balance in early lactation than HF cows bred on an index that includes traits related to longevity and health. This is due, in part, to a greater uncoupling of the somatotropic axis and the level and duration of this uncoupling can be influenced by diet. In addition, the decline in reproductive success in recent decades has been associated with the increased negative energy balance associated with genetic selection for milk production. However, differences in the endometrial transcriptome indicate that genetic selection for milk production is also associated with a failure to recognize pregnancy as well as inadequate suppression of the local immune system and nourishment of the embryo, which are not necessarily related to energy balance. Nonetheless, some of the genes involved are epigenetically regulated and could be altered by nutrition. Factors that influence energy balance, such as nutrition and milking frequency, have different effects on the metabolism of the mammary gland, liver, and adipose tissue. For example, although once-daily milking and greater feeding levels improve energy balance, once-daily milking lowers milk production through reduced secretory cell activity and number, whereas, greater feeding levels increase milk production through the provision of more nutrients. These effects are independent and at least partially additive; if both strategies are used, the outcome is a combination of the two. Experimental results indicate that the molecular changes underpinning these effects can persist beyond the period of treatment. Less frequent milking results in an earlier recoupling of the somatotropic axis post-partum and adipose accretion, physiological changes that are also influenced by energy balance, but are dependent on feed type as well as availability. A greater understanding of the effects of nutrition on the molecular phenotype is required to optimize cow management for productivity and welfare.
Keywords: Nutrigenomics, energy balance, reproductive failure, genotype