Document Type : Research Paper
Associate Professor, Faculty of Agriculture, University of Zanjan, Zanjan, Iran
Former M. Sc. Student, Faculty of Agriculture, University of Zanjan, Zanjan, Iran
Former Ph.D. Student, College of Agriculture & Natural Resources, University of Tehran, Karaj, Iran
Senior Researcher at Ati Zist Dam Co. Karaj, Iran
This experiment was conducted to investigate the effects of different levels of dietary NDF in diets rich in plant oil (sunflower) on milk performance and feeding behavior of mid-lactating Holstein dairy cows. Four primiparous (BW: 525±30 kg; DIM: 103±6) and four multiparous (BW: 587±88 kg; DIM: 99±12) cows were used in a 4×4 replicated Latin square design with 21-d experimental periods. Cows were received 1 of 4 four treatments: 1) 31% fiber (NDF) and no supplement plant oil, LF, 2) 31% fiber with 2% supplement plant oil, LFO 3) 35% fiber with 2% plant oil, MFO 4) 39% fiber with 2% plant oil, HFO. Daily dry matter intake (DMI), milk yield and composition, blood metabolites, dry matter digestibility, rumen fluid characteristics and BW variations were determined. There was no significant different in milk production among diets. Milk fat (P<0.01) and protein (P<0.05) concentrations were significantly affected by treatments. Dry matter intake and DM digestibility were higher (P<0.01) in LFO diet. The cows fed HFO had higher NDF digestibility (P<0.01). Total VFA and acetate concentration were greater for HFO diet and propionate concentration was greater for LFO diet (P<0.01) than the others. Rumen fluid pH was increased by increasing dietary NDF concentration (P<0.01). Chewing activity was positively affected by increasing concentration of dietary NDF (P<0.01). This study showed that diets rich in plant oil and low concentration of NDF induce the milk fat depression in mid-lactating cows.