عنوان مقاله [English]
نویسندگان [English]چکیده [English]
In order to examine the effect of degradability rates of different starch sources on performance of Holstein dairy cows in their early lactation, twenty multiparous lactating Holstein cows (586±33.7 BW; 48.15±9.32 DIM) were made use of in a randomized complete block design of four treatments during the 65 days of the experimental period. Cows were fed the following diets: 1) 100% barley, 2) 67% barley and corn 33%, 3) 33% barley and 67% corn and finally 4) corn by 100%. Cows were offered feed individually and three times daily. Dry Matter Intake (DMI), milk yield and composition, feed efficiency, blood metabolites, ruminal and fecal pH, body weights and body condition scores were assessed. Dry matter intakes (P=0.01), and milk yields (P=0.03) were highest for cows fed diet containing 33% barley and 67% corn. Milk fat percentage (P=0.001), milk non fat solid percentage (P=0.17) and milk lactose content, percentagewise (P=0.2) were lowest for cows fed diet containing 100% barley. Ruminal pH (P=0.09) was lowest in cows fed diet containing 100% barley while highest for cows fed diet containing 100% corn. No significant differences were found in blood BHBA, NEFA, BUN and in total protein. Blood glucose (P=0.018) and albumin were recorded as lowest in cows fed diet containing 100% barley. These results most probably reflect a more optimal synchronization of dietary protein and energy for dairy cows when fed diets containing 33% barley and 67% corn in their early lactating diets rather than alfalfa hey formerly fed as the sole forage source.