The objective of this study was to evaluate the effects of feeding long alfalfa hay as top dress or mixed with TMR on performance of Holstein dairy cows in mid lactation. Eight primiparous (DIM = 105.3 ± 13.2, BW = 667.7 ± 44.3 kg, and producing 45.3 ± 2.7 kg/d milk) Holstein cows were used in a 4 × 4 Latin square design with 21 days periods. Each period consisted of 14 d of adaptation followed by 7 d of data collection. Treatments (DM basis) were: 1) total mixed ration (control), 2) feeding 5% long alfalfa hay to cow an hour before feeding TMR, 3) feeding 10% long alfalfa hay to cow an hour before feeding TMR and 4) feeding 15% long alfalfa hay to cow an hour before feeding TMR. Top dress increased the proportion of the particles retained on the top sieve of the ( 19 mm) and the second sieve (8-19 mm) but decreased the proportion of the particles retained on the third sieve (1.18-8 mm) (p 0.01). Alos had a significant effect on pan sieve (p 0.05). Treatments had no significant effect on chewing activities and rumen fluid pH. Milk fat percentage affected by treatments linearly (p 0.05). feeding alfalfa hay as top dress had no significant effect on selection index in 19, 8, 1.18 and pan sieves. Acetate, propionate and butyrate concentrations were not affected by treatments. Dry matter intake decreased (p 0.01). milk production in treatment 2 was maximum and tended to be significant linearly (p = 0.07). Also milk energy adjusted, milk solid ingredient adjusted and milk fat adjusted were affected by treatments (p 0.05). amount of milk fat adjusted for 3.5% was maximum in treatment control and decreased by increasing top dress (p 0.01). MUN not changed but milk protein (p = 0.08) and rumen fluid urea nitrogen tended to be significant linearly (p = 0.07). Income from milk selling was affected by treatments significant (p 0.01). These results of this study shows that feeding 5% alfalfa hay as top dress can increase milk production and benefit by decreases DMI. Keywords: top dress , long alfalfa hay, particle size forage, total mixed ration- dairy cow performance.
