Accuracy of methane emissions predicted from milk mid-infrared spectra and measured by laser methane detectors in Brown Swiss dairy cows

摘要

Since heritability of CH_4 emissions in ruminantswas demonstrated, various attempts to generate largeindividual animal CH_4 data sets have been initiated.Predicting individual CH_4 emissions based on equationsusing milk mid-infrared (MIR) spectra is currentlyconsidered promising as a low-cost proxy. However,the CH_4 emission predicted by MIR in individuals stillhas to be confirmed by measurements. In addition, itremains unclear how low CH_4 emitting cows differ in intake,digestion, and efficiency from high CH_4 emitters.In the current study, putatively low and putatively highCH_4 emitting Brown Swiss cows were selected from theentire Swiss herdbook population (176,611 cows), usingan MIR-based prediction equation. Eventually, 15 lowand 15 high CH_4 emitters from 29 different farms werechosen for a respiration chamber (RC) experiment inwhich all cows were fed the same forage-based diet.Several traits related to intake, digestion, and efficiencywere quantified over 8 d, and CH_4 emission was measuredin 4 open circuit RC. Daily CH_4 emissions werealso estimated using data from 2 laser CH_4 detectors(LMD). The MIR-predicted CH_4 production (g/d) wasquite constant in low and high emission categories, inindividuals across sites (home farm, experimental station),and within equations (first available and refinedversions). The variation of the MIR-predicted valueswas substantially lower using the refined equation.However, the predicted low and high emitting cows (n= 28) did not differ on average in daily CH_4 emissionsmeasured either with RC or estimated using LMD,and no correlation was found between CH_4 predictions(MIR) and CH_4 emissions measured in RC. When individualswere recategorized based on CH_4 yield measuredin RC, differences between categories of 10 lowand 10 high CH_4 emitters were about 20%. Low CH_4emitting cows had a higher feed intake, milk yield, andresidual feed intake, but they differed only weakly ineating pattern and digesta mean retention times. LowCH_4 emitters were characterized by lower acetate andhigher propionate proportions of total ruminal volatilefatty acids. We concluded that the current MIR-basedCH_4 predictions are not accurate enough to be implementedin breeding programs for cows fed forage-baseddiets. In addition, low CH_4 emitting cows have to becharacterized in more detail using mechanistic studiesto clarify in more detail the properties that explain thefunctional differences found in comparison with othercows.