The main aim of the present study was to examine the effects of long-term supplementing diets with saturated or unprotected polyunsaturated fatty acids from two different plant oils rich in either n-3 or n-6 fatty acids (FAs) plus docosahexaenoic acid (DHA)-rich algae on mammary gene expression and milk fat composition in lactating dairy cows. Gene expression was determined from mammary tissue and milk epithelial cells. Eighteen primiparous German Holstein dairy cows in mid-lactation were randomly assigned into three dietary treatments that consist of silage-based diets supplemented with rumen-stable fractionated palm fat (SAT; 3.1% of the basal diet dry matter, DM), or a mixture of linseed oil (2.7% of the basal diet DM) plus DHA-rich algae (LINA; 0.4% of the basal diet DM) or a mixture of sunflower oil (2.7% of the basal diet DM) plus DHA-rich algae (SUNA; 0.4% of the basal diet DM), for a period of 10 weeks. At the end of the experimental period, the cows were slaughtered and mammary tissues were collected to study the gene expression of lipogenic enzymes. During the last week, the milk yield and composition were determined, and milk was collected for FA measurements and the isolation of milk purified mammary epithelial cells (MECs). Supplementation with plant oils and DHA-rich algae resulted in milk fat depression (MFD; yield and percentage). The secretion of de novo FAs in the milk was reduced, whereas the secretion of trans-10,cis-12-CLA and DHA were increased. These changes in FA secretions were associated in mammary tissue with a joint down-regulation of mammary lipogenic enzyme gene expression (stearoyl-CoA desaturase, SCD1; FA synthase, FASN) and expression of the regulatory element binding transcription factor (SREBF1), whereas no effect was observed on lipoprotein lipase (LPL) and glycerol-3-phosphate acyltransferase 1, mitochondrial (GPAM). A positive relationship between mammary SCD1 and SREBF1 mRNA abundances was observed, suggesting a similar regulation for these genes. Such data on mammary gene expression in lactating cows presenting MFD contribute to strengthen the molecular mechanisms that govern milk fat synthesis in the mammary glands. In purified MEC, the dietary treatments had no effect on gene expressions. Differences between mammary tissue and milk purified MEC gene expression were attributed to the effect of lipid supplements on the number of milk purified MEC and its RNA quality, which are determinant factors for the analysis of gene expression using milk cells.

protein HSPA1A, the apoptotic gene BAX, and the translation inhibitor EIF4EBP1, the mRNA abundance of PPARG, FASN, ACACA (lipogenesis), and BCL2L1 (antiapoptotic) decreased. Greater supply of Met or Arg reversed most of the effects of HS occurring at the mRNA level and upregulated the abundance of HSPA1A. In addition, compared with the control, supply of Met or Arg upregulated genes related to transcription and translation (MAPK1, MTOR, SREBF1, RPS6KB1, JAK2), insulin signaling (AKT2, IRS1), AA transport (SLC1A5, SLC7A1), and cell proliferation (MKI67). Upregulation of microRNA related to cell growth arrest and apoptosis (miR-34a, miR-92a, miR-99, and miR-184) and oxidative stress (miR-141 and miR-200a) coupled with downregulation of fat synthesis-related microRNA (miR-27ab and miR-221) were detected with HS. Results suggest that HS has a direct negative effect on synthesis of protein and fat, mediated in part by coordinated changes in mRNA, microRNA, and protein abundance of key networks. The positive responses with Met and Arg raise the possibility that supplementation with these AA during HS might have a positive effect on mammary metabolism.

The present study demonstrated that dietary fatty acid manipulation substantially shifted the fatty acid profiles of milk and to a lesser extent of meat, whereas meat quality traits were not affected. Indications of tissue-specific responses of mammary gland and muscle were identified.

SummaryBackground: starch is an important energy source for ruminants nutrition. This carbohydrate is often used to improve rumen fermentation, optimizing digestion of structural carbohydrates and increasing protein flow to the small intestine. Microbial and digestive enzymes are involved in starch digestion, generating products that can positively or negatively affect animal performance and health, depending on the starch contents of the diet. Objective: to describe the basic characteristics of starches, the factors affecting its nutritional availability, and its effects in ruminants. Conclusion: a number of factors affect starch digestibility, including granule size, amylose/amylopectin ratio, proportion of farinaceous and vitreous endosperm, presence of starch-lipid and starch-protein complexes, and physical-chemical processing of the feed. Ingestion of large amounts of starch can trigger ruminal acidosis. However, its rational use in the diet has positive effects on methane emissions, and in milk yield and composition.

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