14 research outputs found
Invited review: Large-scale indirect measurements for enteric methane emissions in dairy cattle: A review of proxies and their potential for use in management and breeding decisions
Publication history: Accepted - 7 December 2016; Published online - 1 February 2017.Efforts to reduce the carbon footprint of milk production through selection and management of low-emitting
cows require accurate and large-scale measurements of
methane (CH4) emissions from individual cows. Several
techniques have been developed to measure CH4 in a research setting but most are not suitable for large-scale
recording on farm. Several groups have explored proxies (i.e., indicators or indirect traits) for CH4; ideally
these should be accurate, inexpensive, and amenable
to being recorded individually on a large scale. This
review (1) systematically describes the biological basis
of current potential CH4 proxies for dairy cattle; (2)
assesses the accuracy and predictive power of single
proxies and determines the added value of combining
proxies; (3) provides a critical evaluation of the relative
merit of the main proxies in terms of their simplicity,
cost, accuracy, invasiveness, and throughput; and (4)
discusses their suitability as selection traits. The proxies range from simple and low-cost measurements such
as body weight and high-throughput milk mid-infrared
spectroscopy (MIR) to more challenging measures such
as rumen morphology, rumen metabolites, or microbiome profiling. Proxies based on rumen samples are generally poor to moderately accurate predictors of CH4,
and are costly and difficult to measure routinely onfarm. Proxies related to body weight or milk yield and
composition, on the other hand, are relatively simple,
inexpensive, and high throughput, and are easier to
implement in practice. In particular, milk MIR, along
with covariates such as lactation stage, are a promising
option for prediction of CH4 emission in dairy cows.
No single proxy was found to accurately predict CH4,
and combinations of 2 or more proxies are likely to be
a better solution. Combining proxies can increase the
accuracy of predictions by 15 to 35%, mainly because
different proxies describe independent sources of variation in CH4 and one proxy can correct for shortcomings
in the other(s). The most important applications of
CH4 proxies are in dairy cattle management and breeding for lower environmental impact. When breeding for
traits of lower environmental impact, single or multiple
proxies can be used as indirect criteria for the breeding
objective, but care should be taken to avoid unfavorable correlated responses. Finally, although combinations of proxies appear to provide the most accurate
estimates of CH4, the greatest limitation today is the
lack of robustness in their general applicability. Future
efforts should therefore be directed toward developing
combinations of proxies that are robust and applicable
across diverse production systems and environments.Technical and financial support from the COST Action FA1302 of the European Union