Abstract
The aim of the present study was to identify transcriptional modifications and regulatory networks accounting for physiological and metabolic responses to specific nutrients in the liver of young Belgian Blue × Holstein bulls using RNA-sequencing. A larger trial has been carried out in which animals were fed with different diets: 1] a conventional diet; 2] a low-protein/low-mineral diet (low-impact diet) and 3] a diet enriched in n-3 fatty acids (FAs), conjugated linoleic acid (CLA) and vitamin E (nutraceutical diet). The initial hypothesis was that the administration of low-impact and nutraceutical diets might influence the transcriptional profiles in bovine liver and the resultant nutrient fluxes, which are essential for optimal liver function and nutrient interconversion. Results showed that the nutraceutical diet significantly reduced subcutaneous fat covering in vivo and liver pH. Dietary treatments did not affect overall liver fat content, but significantly modified the liver profile of 33 FA traits (out of the total 89 identified by gas-chromatography). In bulls fed nutraceutical diet, the percentage of n-3 and CLA FAs increased around 2.5-fold compared with the other diets, whereas the ratio of n6/n3 decreased 2.5-fold. Liver transcriptomic analyses revealed a total of 198 differentially expressed genes (DEGs) when comparing low-impact, nutraceutical and conventional diets, with the nutraceutical diet showing the greatest effects on liver transcriptome. Functional analyses using ClueGo and Ingenuity Pathway Analysis evidenced that DEGs in bovine liver were variously involved in energy reserve metabolic process, glutathione metabolism, and carbohydrate and lipid metabolism. Modifications in feeding strategies affected key transcription factors regulating the expression of several genes involved in fatty acid metabolism, e.g. insulin-induced gene 1, insulin receptor substrate 2, and RAR-related orphan receptor C. This study provides noteworthy insights into the molecular changes occurring as a result of nutrient variation in diets (aimed at reducing the environmental impact and improving human health) and broadens our understanding of the relationship between nutrients variation and phenotypic effects.
Highlights
Growing attention has been recently paid to sustainability in the livestock sector, the functionality of animals, and product quality according to the EU Framework Program Horizon 2020 [1]
No significant differences among treatments were found for body weight (BW), average daily gain (ADG), and in vivo muscularity score (Table 1)
Significantly lower values of in vivo fat covering were found with Nutraceutical diet1 (Nutr) compared with Conventional diet (Conv) and Low impact diet (LowI) groups (P < 0.05)
Summary
Growing attention has been recently paid to sustainability in the livestock sector, the functionality of animals, and product quality according to the EU Framework Program Horizon 2020 [1]. Sustainable beef production depends on a balanced combination of various factors, such as the reduction of negative environmental impacts, animal health, nutritional efficiency, efficient growth, and a desirable carcass composition with a high percentage of lean tissue and a low fat content. Aside from environmental issues, a growing awareness of the association between diet and human health has increased the demand for foods of high nutritional quality. Specific effects have been ascribed to CLA mixtures, where two isomers generally dominate, i.e. 18:2c9,t11 and 18:2t10,c12. The former isomer has anti-carcinogenic properties [10], whereas the latter can increase the lean to fat ratio in growing animals [11,12]. Studies are available about the effects of these FAs on the expression of target genes in ruminants [13,14,15] but no information is available on the effects of protein and mineral deficiency
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