Milk production of dairy goats fed diets with different legume seeds: Effects of amino acid composition of the rumen undegradable protein fraction

[Background] To establish the effect of the nature of four different legume seeds, lupins (L), faba beans (FB), bitter vetch (BV) and vetch (V) on the production and composition of goat milk, we studied the ruminal degradation of these legumes, and the amino acid (AA) composition of the seeds and that of the undegradable fractions of the protein sources. Four isonitrogenous and isoenergetic diets were designed, and in each case 30% of the protein was supplied by one of the different legume seeds. A group of eight Granadina goats was used to study the utilisation of these diets for milk production. The goats were allocated to a replicated 4 × 4 Latin square.[Results] Ruminal fermentation modified the AA profile of the protein of the legume seeds which was different in each case. However, milk production remained unchanged irrespective of the diet consumed. On the contrary, and despite the high level of degradability of the protein in the different legumes, the concentration of total protein, casein (CN) and overall αS1-CN and αS2-CN in milk depended on the protein source used.[Conclusion] The concentration of total protein in milk, as well as its composition, was apparently determined by the AA composition of the corresponding fraction of the rumen-undegradable protein.This study was supported financially by the Ministry of Science and Technology, Spain; Project INIA: RTA02-020.Peer reviewe