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Acta Prataculturae Sinica ›› 2021, Vol. 30 ›› Issue (3): 110-120.DOI: 10.11686/cyxb2020340

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Effects of phenological period on the composition of fatty acids and conjugated linoleic acids in rumen fluid, forage and milk fat of grazing yak and their correlation analysis

Fa-ming PAN1(), Sheng-hua CHANG2(), Guo-dong WANG1, Sheng-yan HAO1, Jia LIU1, Hui-yuan ZHANG3, Yin-ping XU4   

  1. 1.Animal Husbandry,Pasture and Green Agriculture Institute of Gansu Academy of Agricultural Science,Lanzhou 730070,China
    2.College of Pastoral Agriculture Science and Technology,Lanzhou University,Lanzhou 730020,China
    3.Agricultural Product Storage and Processing Research Institute of Gansu Academy of Agricultural Science,Lanzhou 730070,China
    4.Institute of Industrial Crops and Malting Barley of Gansu Academy of Agricultural Science,Lanzhou 730070,China
  • Received:2020-07-15 Revised:2020-10-26 Online:2021-03-20 Published:2021-03-09
  • Contact: Sheng-hua CHANG

Abstract:

The purpose of this paper was to study the effect of seasonal changes in alpine meadow herbage maturity (i.e. forage phenology) on the fatty acid composition of the forage and rumen fluid and on levels of conjugated linoleic acid (CLA) in the milk of grazing yaks. In this study, 10 Gannan yaks with calves and with an average body weight of (234.9±10.5) kg were used as the experimental subjects. The 10 yaks were naturally grazed in Gannan Pastoral Area of Gansu Province. During herbage re-greening in May, the growth flush in September, and winter herbage death in December, forage, yak milk and rumen fluid samples were collected for analysis as outlined above. The correlation between fatty acids and the composition of conjugated linoleic acid in milk fat was studied in order to find out the influence of forage phenology on the composition of fatty acid contents of forage and rumen fluid and the content of conjugated linoleic acid in milk of grazing yaks. It was found that the phenological period significantly affected the levels of lauric acid, myristic acid, palmitic acid, stearic acid, linoleic acid, linolenic acid, total fatty acids, polyunsaturated fatty acid, and polyunsaturated fatty acids/total fatty acid (P<0.05). For all except stearic acid, and for fatty acid levels in the forage, levels during the summer growth flush were significantly higher (P<0.05) than those in the re-greening and winter periods. The levels of conjugated linoleic acid isomer c9t11, conjugated linoleic acid isomer t10c12 and conjugated linoleic acid in grazing yak milk were also significantly higher (P<0.05) during the herbage growth flush than those in the re-greening and winter death periods. The pH, and contents of acetic acid, propionic acid, acetic∶propionic acid, isobutyric acid, butyric acid, isovaleric acid, valeric acid, total volatile acids and trans-11-oleic acid levels in the rumens of the yaks also differed significantly between phenological periods (P<0.05). There was a significant positive correlation (P<0.05) between the pH value of forage crude protein, ether extract, nitrogen free extract, tannic acid, total fatty acid and rumen fluid and the CLA content in grazing yak milk, a significant negative correlation (P<0.05) between crude fiber and crude ash and the CLA content in grazing yak milk, and no significant correlation (P>0.05) between polyunsaturated fatty acid levels and total volatile fatty acids and the CLA content in grazing yak milk.

Key words: forage, yak rumen fluid, yak milk, fatty acid, conjugated linoleic acid, correlation