اثر جایگزینی بخشی از علوفه یونجه با کاه گندم بر گوارش‌پذیری و عملکرد بره‌های نر پرواری

The objective of this study was to evaluate the effect of partially replacing forage sources (alfalfa hay) with treated wheat straw on nutrient digestibility, chewing activity, blood metabolites, rumen fermentation, and performance of finishing lambs. Wheat straw (WS) was treated with 7 % sodium hydroxide, 3.5 % salt, and 3.3 % calcium carbonate and then ensiled for 2 months. Twenty-three male lambs (28 kg) were randomly allocated to three diets differing in forage sources: 1) control diet (100 % alfalfa hay), 2) 1/3 WS (67 % alfalfa hay and 33 % wheat straw) and 3) 2/3 WS (33 % alfalfa hay and 67 % wheat straw). Results indicated that ruminal degradability (24 and 48 h incubation) of treated wheat straw and alfalfa hay was similar, but higher than untreated straw (P<0.01). Dry matter intake and chewing time decreased linearly (P= 0.01), but no change in chewing time/DMI was observed with increasing WS levels in the diet. Feeding the diets containing WS improved fiber digestibility (P<0.01), tended to decrease ruminal pH (P=0.08, quadratic effect), and increased ruminal ammonia-N (P=0.04), molar acetate proportion (P=0.05), and total volatile fatty acids concentration (P=0.02, quadratic effect). Moreover, average daily gain (P=0.02) and feed efficiency (P=0.08) was enhanced quadratically with increasing levels of WS in the diet. Carcass weight, blood metabolites and molar proportions of propionate and butyrate were not affected by the dietary treatments. Overall, the results indicated that partially replacing alfalfa hay with wheat straw had no adverse impacts on the performance of finishing lambs, but feeding 1/3 WS increased fiber digestibility, daily gain and feed efficiency.