Information is lacking for optimum time of alfalfa harvesting to obtain high quality forage for dairy cattle. The objective of this study was to determine optimum maturity stage and time of the day to harvest alfalfa in the east of Iran. Third cut of a second year alfalfa field (4.2 ha) was divided in three large plots (1.4 ha). Each plot was assigned to one of the three stages of maturity [early bud (EB), late bud (LB) and early flowering (EF, local commercial harvesting stage)]. Halve of each large plot was harvested at sunset (PM) after a sunny day followed by harvesting of other halve the next morning (AM). These hays (n=6) were harvested in a factorial arrangement were harvested in 2010 at June 13/14, 19/20 and 26/27 for EB, LB and EF respectively. Eighteen Holstein-Frisian dairy cows (66.3 d in milk and 43 kg milk/d pretrial) were used in a cyclic changeover design with three 21 -d periods in a 3 × 2 factorial arrangement. Experimental total mixed ration diets consisted in DM % of 20 % alfalfa hay, 15 % barley silage, 65 % concentrates delivered twice daily. Daily dry matter intake (DMI) was higher for cows fed EBAM alfalfa compared with other treatments (P<0.05). Compared with AM harvesting, organic matter intake (OMI) of cows that received alfalfa from sunset harvest was higher (P<0.05). Cows that received LBPM hay had highest OMI and cows fed EFAM hay had lowest OMI (P<0.05). Cows fed with EFPM alfalfa hay had highest DM and CP digestibility while these were lowest for cows fed EFAM hay (P<0.05). The OM digestibility and ADF digestibility were higher for cows fed PM alfalfa compared with AM alfalfa (P<0.05). Milk production was similar among treatments while 4 % fat corrected milk was higher for cows fed PM harvested alfalfa than AM harvested alfalfa (P<0.05). Feed efficiency, measured as milk/DMI, was higher at EB compared with other maturity stages (P<0.05). Milk fat and lactose percent and their yield (kg/day) were higher for cows fed PM alfalfa compared with AM alfalfa (P<0.05). Cows that received EFAM alfalfa had highest and cows fed LBAM hay had lowest milk protein percent and yield (P<0.05). These findings suggest that alfalfa harvested at early bud improves dairy cow feed efficiency and alfalfa harvested at sunset had higher in vivo feed digestibility which resulted in a higher milk fat and lactose content, probably because more nutrients were available for milk synthesis.

Keywords