Evaluation of pellets from different industrial processing of dehydrated lucerne in dairy cattle feeding

Abstract

The research evaluated three pellets from different industrial processing of dehydrated lucerne. Pre-bloom cut lucerne was dehydrated and pelleted to obtain the Control product. The second pellet was produced by mechanical pressing of the forage before dehydration to extract a juice rich in soluble proteins and carbohydrates used by the poultry feeding industry. This pellet had a higher neutral detergent fibre (NDF) content than the control one. Urea (2.5% of forage DM) was added to the forage between dehydration and pelleting to produce the third pellet. All the tested pellets had a mean geometrical diameter lower than 0.20 mm and, due to their small particle size, they should be classified as protein concentrates rather than forage sources in dairy ration formulation. The degradability trial used three non-pregnant, non-lactating Holstein cows fitted with ruminal cannulae which were fed three diets formulated to satisfy the nutritional requirements of lactating cows, each containing one of the tested pellets. Cows received the diets in three following periods of 28 days according to a 3×3 Latin square experimental design. Ruminal degradation kinetics of pellets dry matter (DM), cell contents (CC), crude protein (CP), NDF, cellulose (CE) and hemicellulose (HE) was determined in situ by incubating the pellets within nylon bags for different time periods. Passage rate from the rumen was measured by mordanting each pellet with sodium dichromate. The different industrial processing did not affect the pellets rate of passage in the rumen. Based on the in situ degradation kinetics, 611 g/kg of Control DM were available in the rumen mainly from microbial digestion of the CC. In comparison to Control, mechanical pressing prior to dehydration decreased the lucerne DM disappearance (546 g/kg DM) because of the lower contribution of the CC to the degradable pool. Urea treatment enhanced CP content of the pellet but it did not increased the ruminal availability of dehydrated lucerne DM (595 g/kg DM). The alkaline additive was not effective to increase the degradation of the fibrous constituents leading only to a peak of readily available nitrogen in the rumen. Regardless of the type of pellet, the cell wall constituents were always degraded at a lower rate and extent than the CC and among them, CE has shown to be the primary site of hydrolysis by the rumen microrganisms.