Abstract
SUMMARYA range of options was explored to test the hypothesis that diets for dairy cows could be formulated to reduce the carbon footprint (CFP) of feed, increase efficiency of conversion of potentially human-edible feed into milk, increase nitrogen use efficiency (NUE) and reduce methane (CH4) emissions per kg milk. Diets based on grazed grass, grass silage, maize silage or straw, supplemented with raw material feeds, were formulated to meet requirements for metabolizable energy and metabolizable protein for a range of daily milk yields. At similar levels of milk yield, NUE, predicted CH4emissions and diet CFP were generally higher for diets based on maize silage than for those based on grazed grass, grass silage or straw. Predicted CH4emissions and human-edible proportion decreased, while NUE increased with the increasing level of milk yield. It is concluded that there is potential to reduce the environmental impact of milk production by altering diet formulation, but the extent to which this might occur is likely to depend on availability of raw material feeds with low CFPs.
Highlights
The feeding of dairy cows involves formulating and delivering diets to meet nutritional requirements for specified levels of daily milk output in relation to stage of lactation, availability and cost of raw materials, and season of year
There was little difference between diets formulated for milk yields of 20 and 30 kg/day, but when level of milk output was increased from 30 to 40 kg/day, greater quantities of concentrate supplements were required to meet total metabolizable energy (ME) requirement
Predicted methane emissions per kg of milk decreased with increasing milk yield (Fig. 3)
Summary
The feeding of dairy cows involves formulating and delivering diets to meet nutritional requirements for specified levels of daily milk output in relation to stage of lactation, availability and cost of raw materials, and season of year. The environmental impact of milk production systems has to date received relatively little attention from legislators in Europe, except for inclusion in general restrictions on manure and waste disposal. There has been legislation in the USA since 2003 to control the environmental impact of concentrated animal feeding operations (CAFO) where the main emphasis is on control of point-source pollution of watercourses. Current CAFO regulations include dairy units of 200 cows or more where the animals are housed for more than 45 days per annum and where crops are not grown on the unit (US Environmental Protection Agency 2012). European pig and poultry systems are controlled under the European Union Integrated Pollution Prevention and Control (IPPC) Directive 2010/75/EU, which requires agricultural activities with a high pollution potential to have a permit (Anonymous 2015). Dairy units are not included in the current IPPC regulations (Eurostat 2013), but the situation is under review
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