Keywords: greenhouse gas emissions, silage quality, dairy cattle, beef production, farm scale models.
Grass based ruminant production systems may be favoured in the future as human population growth and climate change may limit the availability of grains for feeds. This may be especially relevant in regions with limited areas suitable for crop production, such as the northern parts of Europe, in order to maintain a certain level of self-sufficiency. However there is potential to increase silage quality and increase energy intake from grass, thereby increasing animal productivity.
The effect of silage quality on greenhouse gas (GHG) emissions is also of interest due to its effects on climate change. High quality silages may represent a mitigation option as it increases productivity and reduces methane emission from enteric fermentation. Randby et al. (2010, 2012) investigated the effect of three grass silage qualities cut at different maturity stages (very early, early and normal, H1, H2, H3, respectively) combined with various levels of concentrate supplementation, or without concentrates, on feed intake and animal performance of growing/finishing dairy bulls and dairy cows in early lactation.
Animal performance varied considerably between the treatments. The aim of the present study was therefore to quantify the emission intensities (GHG emissions per kg product) for milk and beef given the silage qualities previously described. Results showed that the emission intensity for milk was highest for the H3 silage with 4 kg of concentrates, and the lowest emission intensity resulted from the H1 silage supplemented with
8 kg of concentrates, but with only minor differences from the H1 silage supplemented with 4 kg of concentrates. The differences were mainly due to variations in emissions of methane from enteric fermentation and animal manure. Similarly, for beef, the lowest emission intensity was obtained for H1 silage with concentrate supplementation, but with only small differences from the H1 silage without supplementation. This indicates that there is a potential to reduce the area needed to produce grain, whilst keeping emissions constant by using high quality silages. The highest emission intensity for beef resulted from the use of H3 silage without concentrate supplementation. The effect of concentrate supplementation on the emission intensity for beef was small for H1 and H2 silage, with only a 3% reduction. For H3 it was 14% lower, due to a larger reduction in the slaughter age.
We conclude that improving silage quality may be an important option for reducing greenhouse gas emissions whilst at the same time maintaining or increasing the degree of self-sufficiency in regions where crop production is restricted.
Bente Aspeholen Åby, Åshild Randby and Laila Aass, Norwegian University of Life Sciences, Department of Animal and Aquacultural Sciences, Box 5003, 1432 Ås, Norway.
12 pages, 3 figures, 3 tables, 17 references