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The aim of this study was to investigate the effect of alfalfa hay treated with sodium hydroxide and whey on yield, ruminal fermentation characteristics, milk production and blood metabolism and chemical metabolites of Holstein dairy cows. The experiment was conducted in two stages. The first phase consisted of preparation of wheat straw silage treated with sodium hydroxide and whey. The second stage was designed to investigate the effect of different levels of processed wheat straw (0, 25, 50, and 75) as alfalfa replacement on yield of 8 Holstein dairy cows (2 replicates per treatment) in two 21-day periods. The results of this experiment showed that replacing the diet alfalfa with the processed wheat straw significantly reduced the amount of dry matter, crude protein, organic matter and insoluble fiber in the neutral detergent and significantly increased the apparent digestibility. Dry matter, crude protein, organic matter, neutral detergent fiber and acid detergent fiber (P <0.05). Ammonia nitrogen concentration, total volatile fatty acids, molar ratio of acetate, propionate, butyrate, valerate, isovalerate and acetate to propionate and glucogenic fatty acids to non-glucogenic fatty acids ratio significantly (p <0.05). But rumen acidity was higher in experimental treatments than control (P <0.05). Milk production and feed efficiency, fat percentage, lactose, nonfat milk solids and milk urea nitrogen concentration were not affected by the experimental treatments (P <0.05). But the milk protein content of the cows fed the diet containing 50 and 75% of the replacement of treated straw was higher than the 25% and control treatment (P <0.05). Experimental treatments had no significant effect on total protein, albumin and urea nitrogen concentrations (P <0.05). But blood glucose concentration was higher in cows treated with straw than the control group (25%) (P <0.05). The results of this experiment showed that replacing up to 50% of dairy cows with treated wheat straw had no negative effect on animal health and performance.
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