Wheat dried distillers\' grain (WDDG) as a co-product has a high content of neutral detergent fiber (NDF) and crude protein (CP), due to the selective removal of starch during the production process. Therefore, it has been proposed to use this by product as a good source of non-forage fiber in ruminant rations. The objective of this study was to evaluate the effect of diets containing different amount of Wheat dried distillers\' grain as a partial substitute for alfalfa hay on lactation performance, blood metabolites and chewing activity of lactating Holstein dairy cows. Nine primiparous Holstein lactating dairy cows (76±18 days in milk) were assigned randomly to a replicated 3×3 Latin square design with 21 d periods. Basal diet (BD) was provided using 31.2% alfalfa hay, 15.6% corn silage, 12.5% barley grain, 12.5% corn grain, 8.6% cottonseed, 7.1% wheat bran, 10.5% soybean meal and 2% premix on dry matter basis. Alfalfa hay and soybean meal was partially substituted with WDDG as 5% (BD+WDDG5) and 8.7% (BD+WDDG8.7). Experimental diets were calculated to achieve same amount of CP and metabolizable energy. Throughout the experiment, cows were housed in tie-stalls barn and fed ad libitum a total mixed ration twice daily at 008 and 1800 h. Dry matter intake (DMI) and milk yield was recorded daily. Milk samples were collected weekly at each milking, then, analyzed for protein, lactose and fat. Blood samples were drawn from the jugular vein into heparinized evacuated tubes on the last day of each experimental period at 4 h post-feeding, then, plasma was provided. Plasma samples were analyzed to determine glucose and urea-N concentrations. Chewing activity (i.e. eating, ruminating, idle)for cows were monitored over a 24 h by manually observing individual cows every 5 min. Inclusion of WDDG in the experimental diets did not affect DMI, milk yield, milk composition, blood glucose. Except for total chewing activity (min/kg NDF) that was decreased significantly with inclusion of WDDG, all other evaluating indices were not affected by treatments. However, diet containing WDDG at 5% caused a significant decrease (P<0.05) in blood plasma urea-N compared with that of the cows fed basal diet (BD= 21.6 and BD+WDDG5= 19.9 mg/dl). Therefore, it was concluded that WDDG might include in the lactating cow diets, up to 8.7%, without any negatively impacting on milk yield, milk composition and blood metabolites evaluated.

Keywords