AbstractTwo experiments were conducted to determine the effects of level of concentrate supplementation with two concentrates differing in concentration and type of ruminally undegradable protein (RUP) on dry matter intake (DMI) and milk production of Holstein cows in late (E1) and early (E2) lactation. In both trials, concentrates were fed at the rate of 1 kg per 2.5 or 1.5 kg of milk, constituting low (LCS) and high (HCS) levels of concentrate supplementation, respectively. No significant effect of type of concentrate was observed on DMI, milk production, milk composition or efficiency of milk production in either experiment. HCS resulted in lower hay DM consumption by cows in late (9.8 vs. 11.3 kg/d) and early (6.4 vs. 8.1 kg/d) lactation, but also in greater total DMI by late (17.7 vs. 15.6 kg/d) and early (19.6 vs. 16.2 kg/d) lactation cows. Similarly, milk production was greater when late (13.1 vs. 11.8 kg/d) and early (25.5 vs. 22.6 kg/d) lactation cows were fed the HCS. In E2, contrary to E1, cows produced milk of higher fat concentration (2.66 vs. 3.18%) when the LCS was fed. HCS resulted in lower efficiency of concentrate use for milk and 3.25%-fat-corrected milk production, particularly during early lactation. However, income over feed cost was higher for HCS during early lactation. Thus, the practice of supplementing concentrates at a high level can be justified economically under conditions similar to those of this trial.
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