Effects of different levels of pennyroyal (Mentha pulegium L.) on performance, blood metabolites and immune response of laying hens

This study was conducted to evaluate effect of reducing alfalfa hay particle size on feed intake، chewing activity and performance of Holstein dairy cows in mid lactation. The experiment was designed as a replicated 3 × 3 Latin square using 6 lactating dairy cows averaging 105±15 day in milk (DIM)، 556 ± 16 kg body weight (BW) and two parity (3 diets with 3 periods). Each period lasted for 21 days including 14 days adaptation and 7 days sample collection. Diets were chemically similar but varied in peNDF content (high، medium، and low) by altering alfalfa particle length. The physical effectiveness factors for the long (chopped)، medium (rechopped twice)، and fine (rechopped thrice) alfalfa were determined using the Penn State Particle Separator. The peNDF contents of the diets were 22. 03، 20. 17، and 19. 07%، for the high، medium، and low diets by means Mertens formulate، respectively. Decreasing forage particle length increased DMI (p<0. 001). Chewing time، (including eating and ruminating time)، were decreased by decreasing dietary peNDF (p<0. 001). Ruminal، fecal and urine pH were not significantly affected by peNDF content. Reduction of particle size increased Milk fat corrected (MFC، 4%) (p<0. 001)، milk fat (p<0. 01)، and protein production (p<0. 05)، non-fat total solids (p<0. 05) and body weight gain (p<0. 001). Nevertheless، Reduction of particle size had not significant effect on percentage of milk fat، protein and lactose. In conclusion، results showed that Reduction of particle size improved milk production and composition of Holstein dairy cows in mid lactation.