Phenological Phases of Forage and Rumen Fluid Affect Conjugated Linoleic Acids Composition of Milk of Yak from Qinghai Tibet Plateau
Phenological Phases of Forage and Rumen Fluid Affect Conjugated Linoleic Acids Composition of Milk of Yak from Qinghai Tibet Plateau
Yao Xixi1, Zhou Rui2* and Ma Yinshan3
ABSTRACT
The purpose of this paper was to study the effect of phenological phases on forage nutrient composition, rumen fermentation parameters and content of conjugated linoleic acid (CLA) in milk of grazing yak. In this study, 10 female Gannan yaks with an average body weight of 234.9±10.5 kg were selected for research purpose (natural grazing) in Gannan Pastoral Area of Gansu Province. The forage, rumen fluid and milk samples were collected during green-up time, flowering time and withering time of forage to determine nutrient composition of forage, fermentation parameters of rumen fluid, and CLA in milk fat. The correlation analysis was studied in order to find out the influence of forage and rumen fluid parameters on the content of CLA in milk of grazing yak. The results showed that the phenological phases significantly affected the content of lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, linolenic acid, total fatty acid, polyunsaturated fatty acids (PUFAs) and total volatile fatty acid (tvfa) (P<0.05), and these were significantly higher in flowering time (P<0.05). The content of fatty acid and total fatty acid in yak milk were significantly higher in flowering time than green-up time and withering time (P<0.05). The phenological phases significantly affected the content of CLA isomer c9t11, t10, c12 and CLA in yak milk (P<0.05), and these were significantly higher in grazing yak milk at flowering time than green-up time and withering times (P<0.05). The rumen pH, acetic acid, propionic acid, acetic/propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, total volatile acid and trans-11-oleic acid in the rumen of yak were also significantly affected by phenological phases (P<0.05). There was a significant positive correlation of rumen pH, forage crude protein, crude fat, nitrogen free extract, tannic acid and total fatty acid with CLA content in grazing yaks (P<0.05). A significant negative correlation (P<0.05) of crude fiber and crude ash with CLA content in milk of grazing yak was recorded, while no significant correlation (P>0.05) of PUFAs and tvfa with CLA content was observed. This study is helpful to improve the grazing management of alpine grassland and the production performance of yaks (milk yield and milk quality).
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