Take home message Type of preservation of alfalfa may impact on DVE/OEB content by altering the digestion of protein in small intestine. Introduction Storage of alfalfa as silage leads to increased dry matter solubility and degradation rate. Storage in form of silage causes anaerobic condition and pH reduction which results in microbiological, biochemical and anaerobic fermentation processes. Alfalfa hay in comparison with alfalfa silage has less amount of crude protein and also has more neutral detergent fiber which is probably due to dissipation of leaf along alfalfa desiccation and hemicellulose hydrolysis during silage fermentation (Nelson and Saiter, 1992). Accordingly, the aim of this study is to assess the effect of alfalfa storage method on chemical composition and intestinal truly absorbed protein of alfalfa hay and alfalfa silage using new Dutch System (DVE/OEB). Materials & methods Alfalfa was harvested at second cut in half bloom stage, then half of them were dried at 65 oC for 48 h, using air forced oven, and the rest were ensiled for 28 days. Samples were analyzed for crude protein, neutral detergent fiber (NDF) and acid detergent fiber (ADF) were assayed according to Van Soest et al. (1991), Sodium sulfite and alpha amylase were not used in the NDF assay. Ruminal in situ incubations were performed according to Ørskov & McDonald (1979). Three lactating Holstein multiparous cows, fitted with a ruminal cannula, were fed a TMR containing 50% Forage and 50% concentrate and passage rate was considered 0.06/h. The DVE value is calculated according to Tamminga et al. (1994): DVE = DVBE + DVME - DVMFE, where DVME is the microbial protein synthesized in the rumen and digested in the intestine, DVBE is the feed protein not degraded in the rumen but digested in small intestine, and DVMFE is the endogenous protein losses associated with digestion and OEB value is calculated as follows: OEB = MREN – MREE, where OEB is the Degraded protein balance, MREN is the microbial protein synthesized in the lumen based on available nitrogen and MREE is the microbial protein synthesized in the rumen based on available energy. Data were analyzed as a complete randomized design by GLM procedures of SAS, statical model included effect of treatments (preservation methods) and residual error. Results & discussion The effects of preservation methods of alfalfa on truly absorbed protein and chemical composition are presented in Table 1. DVE level in alfalfa hay is significantly higher than alfalfa silage. According to the low level of effective protein degradation of alfalfa hay, it can be concluded that a greater part of the protein in alfalfa hay in comparison with alfalfa silage passes the rumen to the small intestine. In alfalfa silage, whereas, a greater part of protein is in the form of non-protein nitrogen and its amount of passage is also lower to the small intestine. Table 1 Prediction of chemical composition and intestinal truly absorbed protein of alfalfa hay and alfalfa silage using new Dutch System (DVE/OEB). DVME: Rumen synthesized microbial protein digested in the small intestine, DVMFE: endogenous protein losses in the digestive tract DVBE: Digestion in small intestine of the undergraded feed protein, DVE: truly absorbed protein in the small intestine, OEB: reflects the difference between the potential microbial protein syntheses based on rumen degraded feed CP and that based on energy (rumen fermented OM) available, for microbial fermentation in the rumen. Conclusion Results indicate that the type of preservation of the forage may impact on DVE/OEB content of alfalfa by altering the digestion of protein in small intestine. References Nelson WF and Saiter LD 1992. Journal of Dairy Science 75, 1571-1580. Tamminga S, Van Straalen WM, Subnel APJ, Meijer RGM, Steg A, Wever CJG and Blok MC 1994. Journal of Livestock Production Science 40, 139–155. Van Soest PJ, Robertson JB and Lewis BA 1991. Journal of Dairy Science 74, 3583–3597.

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