Palladino R A, O'Donovan M, Murphy J J, McEvoy M, Callan J, Boland T M, Kenny D A
School of Agriculture, Food Science and Veterinary Medicine, University College Dublin, Belfield, Dublin 4, Ireland.
J Dairy Sci. 2009 Oct;92(10):5212-23. doi: 10.3168/jds.2009-2404.
The objective of this study was to investigate the effect of level of 1) pregrazing herbage mass (HM) and 2) level of daily herbage allowance (DHA) on the performance and fatty acid (FA) composition of milk from grazing dairy cows. Sixty-eight Holstein-Friesian dairy cows were allocated to either a high or low pregrazing HM (1,700 vs. 2,400 kg of DM/ha; >40 mm), and within HM treatment, cows were further allocated to either a high or low DHA (16 vs. 20 kg of DM/d per cow; >40 mm) in a 2 x 2 factorial design. Pregrazing HM did not affect dry matter intake (17.5 +/- 0.75 kg/d), milk production (22.1 +/- 0.99 kg/d), milk composition (milk fat, 3.88 +/- 0.114%; milk protein, 3.28 +/- 0.051%), body weight (525 +/- 16 kg), or body condition score (2.65 +/- 0.064). Increasing DHA increased dry matter intake (+1.5 kg/d) but did not affect any other variable measured. Cows grazing the low HM or high DHA had a higher daily intake of total FA (+0.12 and +0.09 kg/d, respectively, for the low HM and high DHA), alpha-linolenic acid (LNA; +0.08 and +0.05 kg/d, respectively, for the low HM and high DHA), and linoleic acid (+0.01 for both the low HM and high DHA) compared with either the high HM or low DHA. Milk conjugated linoleic acid (cis-9, trans-11 isomer) was not affected by treatment (13.0 +/- 0.77 g/kg of total FA); however, large variation was recorded between individual animals (range from 5.9 to 20.6 g/kg of total FA). Milk concentrations of LNA were higher for animals offered the low HM (5.3 g/kg of total FA), but across treatments, milk concentrations of LNA were low (4.9 +/- 0.33 g/kg of total FA). The present study indicates that changes in HM and DHA do not have a great effect on the milk FA composition of grazing dairy cows. Further enhancement of the beneficial FA content in milk purely from changes in grazing strategy may be difficult when pasture quality is already high.
本研究的目的是调查1）放牧前牧草质量（HM）水平和2）每日牧草供应量（DHA）水平对放牧奶牛产奶性能和脂肪酸（FA）组成的影响。68头荷斯坦 - 弗里生奶牛被分配到高或低放牧前HM组（分别为1700与2400千克干物质/公顷；>40毫米），在HM处理内，奶牛进一步被分配到高或低DHA组（分别为每头奶牛16与20千克干物质/天；>40毫米），采用2×2析因设计。放牧前HM不影响干物质摄入量（17.5±0.75千克/天）、产奶量（22.1±0.99千克/天）、牛奶成分（乳脂，3.88±0.114%；乳蛋白，3.28±0.051%）、体重（525±16千克）或体况评分（2.65±0.064）。增加DHA可提高干物质摄入量（增加1.5千克/天），但不影响所测的任何其他变量。与高HM或低DHA组相比，放牧低HM或高DHA组的奶牛每日总FA摄入量更高（低HM和高DHA组分别为+0.12和+0.09千克/天），α - 亚麻酸（LNA；低HM和高DHA组分别为+0.08和+0.05千克/天），以及亚油酸（低HM和高DHA组均为+0.01）。牛奶共轭亚油酸（顺 - 9，反 - 11异构体）不受处理影响（13.0±0.77克/千克总FA）；然而，个体动物之间差异很大（范围为5.9至20.6克/千克总FA）。提供低HM的动物牛奶中LNA浓度较高（5.3克/千克总FA），但在所有处理中，牛奶中LNA浓度较低（4.9±0.33克/千克总FA）。本研究表明，HM和DHA的变化对放牧奶牛的牛奶FA组成影响不大。当牧场质量已经很高时，仅通过改变放牧策略来进一步提高牛奶中有益FA的含量可能很困难。
