Effect Of Replacing Roughage With Fresh Ryegrass On Milk Fatty Acid Composition And Ruminal Fatty Acid Metabolism Of Dairy Goats

It is well documented that in comparison with feeding processed forage, feeding fresh forage made the composition of milk fatty acid more desirable for human health, with the increased concentrations of beneficial fatty acids such as trans vaccenic acid(C18:1t11), conjugated linoleic acid(CLA) and α-linolenic acid(C18:3n-3), and reduced concentration of saturated fatty acids. However, milk yield could be decreased when large amount of fresh forage was fed due to the high level of moisture. Concentrate is important to maintain high milk yield, however, diet based on concentrate and corn silage is rich in starch and C18:2n-6, which decreased milk beneficial fatty acids proportions compared to fresh forage fed animals. In order to achieve a better milk fatty acid profile without compromising milk yield, the present study evaluated the effects of replacing 0, 50% and 100% of roughage(maize silage + alfalfa hay) in a concentrated based diet(concentrate to forage=50:50) with fresh ryegrass on milk yield, milk fatty acid composition and rumen fatty acid metabolism. Animals received fresh ryegrass only were used as a negative control. Effects of treatments on milk yield and milk fatty acid composition were investigated in a completely random design with 24 lactation dairy goats while the influence of treatments on rumen fatty acid metabolism was studied using a 4×4 latin square design with 4 ruminally-cannulated dairy goats. The results were shown as follows:1. Replacing 50% of roughage with fresh ryegrass did not affect dry matter intake(DMI)(P > 0.05), however, replacing 100% of roughage with fresh ryegrass significantly decreased DMI(P < 0.05), and DMI for goats fed fresh ryegrass only diet were significantly decreased compared to other treatments(P < 0.05). Replacing 50% of roughage with fresh ryegrass increased milk yield, however, which was not affected when 100% of roughage was replaced by fresh ryegrass compared to goats fed the basal diet(P < 0.05), and milk yield for goats fed fresh ryegrass only diet were lower than that of other treatments(P < 0.05). Milk composition was not affected by dietary treatments(P > 0.05).2. The daily intake of C18:2n-6 was significantly decreased in 100% replacing group and fresh ryegrass only group compared to the control group(P < 0.05), while all groups inclusion of fresh ryegrass had significantly greater daily intake of C18:3n-3 in comparison with the control group(P < 0.05).3. The rumen p H, NH3-N concentration, plasma parameters(concentration of glucose, nonesterified fatty acid, β-hydroxybutyrate and insulin) and population of rumen hydrogenated bacteria were not influenced significantly by treatments(P > 0.05). However, total volatile fatty acid(VFA) for goats fed fresh ryegrass inclusion diets was higher compared to goats fed the basal diet(P < 0.05). The proportion of acetate for goats fed fresh ryegrass only was higher than that of other treatments(P < 0.05), but the proportion of butyrate significantly lower(P < 0.05). The fatty acid composition in the rumen content was not extensively affected by replacing 50% or 100% of dietary roughage with fresh ryegrass, however, the fresh ryegrass only treatment significantly increased the C18:3n-3 proportion and decreased the C18:2n-6 proportion in the rumen content compared to other treatments(P < 0.05).4. The proportions of C18:3n-3, CLA9t11 and unsaturated fatty acid(UFA) in the milk were increased significantly(P < 0.05) while the proportions of C14:0, C16:0 and saturated fatty acid(SFA) were decreased significantly(P < 0.05) by the groups inclusion of fresh ryegrass in the diet. Fresh ryegrass inclusion in the diet significantly decreased the milk atherogenic index(P < 0.05), and increased the ?9-desaturase index of mammary gland(P < 0.05) as well.The above results indicated that(1) replacing 50% and 100% of dietary roughage in a concentrate based diet with fresh ryegrass improved the milk fatty acid composition without compromising the milk yield of dairy goat and the reason related to the beneficial effects on milk fatty acid composition by replacing roughage in a concentrate based diet with fresh ryegrass was mainly due to the increased intake of C18:3n-3;(2) Feeding dairy goats with fresh ryegrass only diet had a particular strong influence on the milk fatty acid profile, but decreased the milk yield;(3) Taking milk yield into consideration, the optimum strategy was to replace 50% of roughage in a concentrate based diet with fresh ryegrass.