The possibility of influencing the composition of milk fat during lactation has already been the subject of multiple studies. At the beginning of lactation, some of the milk fatty acids are derived not only from the diet but also from body reserves which are mobilized to make up for the energy deficit. A project was set up with the aim of studying the possibilities of influencing milk fat by altering the composition of the body reserves. Preliminary results are presented here. At the beginning of drying off 28 dairy cows of the ALP herd were divided into two groups. During the whole dry period until calving, the cows of the experimental group (S) received 2 kg per day of a feed containing 50% coarse-grind sunflower seeds, whereas the control group (K) received feed containing the same quantity of fat in the form of animal fat. After calving and in the weeks which followed, all cows received the same low fat ration. Analyses of samples of fat tissue, removed under local anaesthesia, at drying off and at calving time showed a greater increase in the concentration of linoleic acid during the dry period for the S group (P<0.05). During the first 12 weeks of lactation, ingestion levels, milk production and milk contents (fat, protein, lactose) as well as the energy balance did not differ between the two groups. The fatty acid composition of milk was analyzed every 2 weeks after the end of the 1st week until the 11th week of lactation. The milk of the S group tended to be less rich in saturated fatty acids and contained more mono-unsaturated fatty acids than the K milk at the beginning of lactation (week 1 to 3). It was also more concentrated in poly-unsaturated fatty acids, especially linoleic acid C18:2 c9c12, with significant differences in the first week only. The other fatty acids analyzed in fat tissue and milk were not influenced by the diets.
Influence of feeding strategy during the dry period on the composition of milk at the beginning of lactation