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บทคัดย่อ

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Abstract

An experiment was conducted to study milk quality of dairy cattle under conditions of group grazing and loose housing on high quality forage intake (The crude protein content of 9.77% in 45-day-old Guinea grass). Eight Holstein Friesian cows all in their second to fourth lactation and at 100–120 day in the mid-late period of lactation were divided equally into two groups of four cows each under a pair comparison design. The first group was allowed free grazing on pasture consisting mainly of Guinea grass using a rotational grazing procedure. The second group was kept in a shaded cow shed and fed cut-and-carried pasture from an equal-sized area of the same pasture grazed by the first group. Both groups were supplemented with Leucaena leucocephala at 3%, based on the intake requirement for body weight maintenance and milk production for the 45 d experiment. The daily milk yield was recorded throughout the experiment and weekly milk sampling was evaluated for composition. A composite sample of morning and evening milk was analyzed for percentages of milk fat, protein and lactose, solid not fat (SNF) and essential milk fatty acids-linoleic acid (C18:2n-6; Omega 6), linolenic acid (C18:3n-3; Omega 3) and conjugated linoleic acid (CLA) contents (grams per 100 g of fat) were also analyzed. The results showed that milk yields, percentages of milk fat, milk protein and SNF, and the contents of linolenic acid (C18:3 n-3) and CLA were not significantly different between treatments. However, the lactose percentage and the content of linoleic acid (C18:2 n-6) were significantly different (P<0.01 and P<0.05, respectively). The outdoor grazing system significantly increased the higher milk content of linoleic acid.