عنوان مقاله [English]
نویسندگان [English]چکیده [English]
To Compare the nutritional value of rapeseed meal and cottonseed meal in Holstein cows, feeding 20 lactating Holstein cows each with an average weight of 580± 34 kg and 100± 10 days in milk were studied in a randomized complete block design. The experimental diets consisted of 4 levels of 0, 8, 14 and 25 percent rapeseed meal replaced with cottonseed meal and barley grain in the diets. Diets were similar as regards net energy lactation and crude protein. Cows were fed with Total Mixed Ration (TMR) for a duration of 60 days. Diets with the highest level of substitution, had 4 and 3.2% FCM higher yields than the control diet. However even through the amount and percentage of milk composition varied numerically, but no significant difference was observed between the diets. (P>0.05). Also Rumen pH and fecal pH did not exhibit significant difference as regarded the diets. Diets apparent digestibility also did not differ significantly. Among the blood metabolites; concentration of calcium, phosphorus, glucose, total protein, albumin and plasma urea nitrogen did not show significant differences as regards the diets, but the blood cholesterol level varied significantly among the experimental diets (P< 0.05), so that the highest cholesterol concentration proved to be related to diet 4 (271/2 mg/dl). Triiodothyronine (T3) hormone concentration did not significantly differ as regarded the experimental diets, but thyroxine (T4) decreased significantly with a increase in rapeseed meal levels, so that the lowest level (3.08 ng/dl) was related to the experimental diet no 4 (P= 0.001).