Branched chain fatty acid composition of yak milk and manure during full-lactation and half-lactation.

• Yak milk, a staple food in high altitude central Asia, is uniquely rich in branched chain fatty acids. • Yak half lactation stage milkfat is richer in branched fats, reaching 5.3% of fatty acids. • Intake of branched fat in high yak milk consumers can be multiple grams per day, the highest in the world. Branched chain fatty acids (BCFA) are bioactive food compounds and are well known to be essential components of human, cow and caprine milk. In Qinghai-Tibet plateau, yaks are domesticated in large numbers and their milk in addition to meat are commercially important to millions of Tibetans and Chinese. We tested the hypotheses that concentrations of BCFA in yak milk and manure differ between lactation periods and evaluated gene expression levels of certain genes involved in the biosynthesis and elongation of fatty acids. Fresh milk and manure were collected from each yak and their fatty acid compositions compared with emphasis on BCFA. Yak milk and manure samples from the full lactation (October, 2015) and half lactation periods (March, 2016) were collected and BCFA levels were analyzed in detail by GC-FID and structures verified by GC-EI-MS/MS. Gene expression studies were carried out by semi-quantitative real time PCR method. The difference between full lactation and half lactation was tested using student's t -test. Linear regression model was modelled in Excel and its significance was tested by ANOVA. Statistical significance was determined by performing student's t -test for gene expression studies. BCFA ranged from 3–6% of total fatty acids in yak milk samples. The half-lactation yak milk contained higher levels of BCFA (5.29 ± 0.53) than the full-lactation milk (4.00 ± 0.46). The total BCFA in yak manure was found to be 14.67 ± 1.21, high in anteiso- 15:0 and anteiso- 17:0. ELOVL1 enzyme involved in the elongation of saturated C18 to C26 acyl-CoA substrates and MCAT enzyme involved in the transfer of a malonyl group to the mitochondrial acyl carrier protein are significantly upregulated in full-lactation milk. BCFA in yak manure especially anteiso BCFA are positively correlated with yak milk from the same animal, indicating that these BCFA come from dietary sources. Yak milk delivers 777 mg BCFA compared to 158 mg per cup of whole U.S. dairy milk. QTP herders known to consume up to 2 kg of yak yogurt take in an estimated 3,500–5,000 mg BCFA per day. We conclude that BCFA intake for yak milk consumers is among the highest known in the world, higher when drawn from half lactating yaks. [ABSTRACT FROM AUTHOR]