Genetic tools to mitigate the environmental impact of milk production systems: Experience with a multi-point individual cow methane measurement system

Methane is one of the most potent greenhouse gases with about 21 times the Global Warming Potential (GWP) of carbon dioxide. Methane emission by dairy cows is not only a significant concern for the environment but also represent a loss of energy for milk production. Dairy cows lose 6 to 12% of feed energy and 95% of which is released through mouth as eructated methane. The most important avenue for reducing methane emissions from dairy systems is by improving the productivity and efficiency of dairy cows, through better nutrition and genetics. Attempts to reduce the ecological foot print of milk production require a sound understanding of the genetic basis of methane emissions. This requires reliable techniques for the measurement of methane output from individual cows. Enteric methane from ruminants is an important but often difficult source to quantify on an individual basis. So far, many of the available measurement techniques are either slow, expensive, labor intensive and are unsuitable for large scale measurements which is a prerequisite for genetic studies. This study evaluated a non-invasive Photoacoustic Infrared Spectroscopy (PAS) technique for quantifying enteric methane output from the breath of individual dairy cows. The study was conducted at MTT experimental dairy herd in Minkiö. A total of about 40 first-lactation Finnish Ayrshire cows were included. Individual cow methane, carbon dioxide (CO2), acetone, ammonia outputs were measured continuously over 3 weeks period using a multi-point PAS gas analyzer fitted to two feeding kiosks (sampling points). Whenever a cow visits a feeding kiosk, her breath was sampled and analyzed for the contents of the different gases. Measurements were made alternatively between the two sampling points and every other minute a gas was sampled and analyzed from each. Records from continuous three days measurements were analyzed. There were about 6-14 repeated measurements on each of the different gasses per cow and a total of 1690 and 1908 measurements from sampling point 1 and 2, respectively. Ratio of CH4:CO2 is concentration independent and can be used to quantify methane output in dairy cows. Thus for each cow, CH4:CO2 ratios were calculated using measurements of these gasses. Basic statistical measures were calculated. Between and within individual variability were quantified and the repeatability of CH4:CO2 were estimated using the General Linear Models (GLM) procedure. The overall mean(sd) of CH4:CO2 from kiosk1 and 2 were 0.071(0.049) and 0.073(0.042) and the repeatability of CH4:CO2 were 0.56 and 0.57 for kiosk1 and 2, respectively. Repeatability sets the upper limit to heritability. Compared to other studies, repeatabilities from this study are on the higher side and suggest the suitability of the PAS for individual cow CH4 measurements that is a requisite in genetic studies.