Dairy production systems involve large inputs and large outputs. In environmental and economic terms, this means dairying is potentially a large consumer of natural resources and a generator of large amounts of pollutants and waste as green house gases (GHG) and manure. To ensure a sustainable milk production system; it becomes important to understand the environmental and economic aspects of feedlot and grazing dairy systems. The environmental and economic perspectives of six typical farms in different selected countries were compared using the TIPICAL (Technology Impact Policy Impact Calculations model). Three grazing farms from Argentina, Chile and New Zealand, and three feedlot farms from U.S.A , Spain and Jordan, were selected for this study. Milk production in the grazing system compared to the feedlot systems yielded 4.3 and 5.7 tons of milk/year in New Zealand and Argentina respectively, while it was higher in the US and Spanish farms (10.6 and 8.9) tons/year.
Feed efficiency trends expressed as kg energy and protein corrected milk (kg milk/kg DM intake) were 0.96 ; 0.80 and 0,98 for Chile, Nez Zealand and the Argentinean farms while it was higher in feedlot farms with FE of 1.25 and 1.01 and 1.33 for Spain, Jordan and the US farms. Dry matter concentrate intake per kg milk were: 675 , 699 and 447 g/kg in Jordan, Spain and the US farms compared to 349; 230 g/kg milk in Argentine and Chile and zero concentrate intake in the New Zealand farm. Enteric methane emissions calculated using the equation from (Kirchgessner 1997) using the cow body weight and milk yield as a variables, results showed variations between both systems; as it was 130, 121 and 111 kg CH4/cow/year in the US; Spain and Jordan compared to 110, 101 and 92 kg CH4/cow/year in Chile, Argentina and New Zealand respectively.
Cost of milk production only was: 57 , 55 and 37 $/100 kg ECM milk in Spain , Jordan and the US, compared to 34, 27 and 28 $/100 kg ECM milk in New Zealand, Chile and Argentina respectively, showing a higher cost in the feedlot system compared to the grazing system. The study shows that the grazing system has lower production cost, and lower methane emissions. FE is higher in the feedlot production system which has higher methane emission and higher production costs. Improving FE would lead to reduce cost of milk production as well as reducing the methane emissions per cow or per 100 kg ECM milk either by reducing DM intake or by increasing milk yield/cow/year.
Keywords: Environmental indicators, Feed efficiency, milk yield