Ruminal degradation of alfalfa protein as influenced by sodium hydroxide and heat treatment

Effects of sodium hydroxide (NaOH) and heat treatment of alfalfa on the degradation of protein in the rumen was investigated in relation to the changes of nitrogenous compounds. Fresh alfalfa was treated with 0, 1.16, 2.32 or 4.64 g NaOH per 100 g dry matter (DM) and then subjected to freeze-drying, or oven-drying for 24 h at 60 or 120°C. Both NaOH and heat treatment produced lysinoalanine at increasing rate with level of treatment to reach a maximum value of 238 mg per 100 g protein. Both treatments also increased neutral detergent insoluble nitrogen (NDIN) according to the increase in level of treatment. Acid detergent insoluble nitrogen (ADIN) was not affected by NaOH treatment but was significantly increased by heating at 120°C. Both NaOH and heat treatment modified protein into being less soluble and more slowly degradable in the rumen, but heating showed greater effects than NaOH treatment. The proportion of potentially degradable protein was little influenced by the treatments. Both NaOH and heat treatment decreased the rate of protein degradation, but significant differences were detected only with the highest level of treatment (4.64 g NaOH per 100 g DM or 120°C). Correlation coefficients of lysinoalanine, NDIN and ADIN content with rate of protein degradation in the rumen were -0.716, -0.950 and -0.834, respectively. These results suggest that lysinoalanine formation in protein by NaOH and heat treatment can make protein less susceptible to microbial degradation in the rumen, while protein-carbohydrate reaction enhanced the effects on protein degradation in this study.