Influence of the botanical composition of grass or hay on milk composition

Two trials, each including 15 dairy cows divided into three variants, were conducted with the purpose to assess the effect of botanical composition of grass (first trial) and hay (second trial) on the chemical composition of milk, especially on the fatty acid profile of milk fat. The comparison included (A) a grass mixture (ray-grass, meadow fescue, cocksfoot, timothy), (B) a grass-clover mixture (same grasses as A, white and red clover) and (C) a grass-alfalfa mixture (cocksfoot, Italian ray-grass and timothy, alfalfa and red clover). The first trial also included two groups of two cows, each fed, respectively, with whole crop meadow fescue forage (D) and pure red clover forage (E). All forages were harvested in the second cycle and at the same age, and they were given ad libitum in the rack to the cows, with only a mineral complementation being added.The average loss of fatty acids during hay drying was about 20%, with greater losses for the mixtures containing leguminous species, and especially alfalfa. These losses mainly affect the poly-unsaturated fatty acids. Except for the pure red clover crop, the herbages of the different botanical compositions show very little differences with regard to their fatty acid profile. Among the 3 hays with different botanical composition, the grass-alfalfa mixture stands out with a slightly lower ratio of linolenic acid (C18:3).The presence of alfalfa in the herbages and pure red clover crop tend to increase the proportion of mono-unsaturated and poly-unsaturated long chain fatty acids in the milk. On the other hand, the grass-rich mixture leads to an overall raise of the CLA in the milk.