ABSTRACT
Summary Two grazing systems, top-grazing of alfalfa (Medicago sativa L.) and high-intensity grazing of orchardgrass (Dactylis glomerata L.), were investigated with three and four levels of concentrate, respectively. The concentrates consisted of corn, oats, and minerals. High dry-matter (DM) alfalfa silage fed in the barn with 40% concentrate by weight was used for a positive control ration. Three- or 4-day grazing periods/paddock were used with 16- and 24-day rotation cycles for orchardgrass and alfalfa,
691respectively. Using alfalfa without concentrate resulted in mean daily yields of 20.2 kg of milk and 0.65 kg of protein. As amounts of concentrates were increased, daily milk and milk protein increased by 50%; but the proportion of protein edible for humans eaten by the cows increased from 0% to 43% of the milk protein produced. Consequently, the amount of essential amino acids returned to the human food supply in milk completely offset the amount consumed by the cows. With increasing concentrates the amount of fossil fuel used for feed production in cows grazing alfalfa rose from 1.6 to 3.2 megacalories (mcal)/day of herd life. All cows grazing alfalfa were fed between 10 and 20 g of poloxalene daily, which prevented pasture bloat. Milk production was less with orchardgrass, and the fossil fuel requirements for production were doubled. The average amount of protein consumed/ha of alfalfa/season was 1.8 metric tons in 8.1 tons of DM.
