Methane (CH 4 ) emissions by dairy cows vary with feed intake and diet composition. Even when fed on the same diet at the same intake, however, variation between cows in CH 4 emissions can be substantial. The extent of variation in CH 4 emissions among dairy cows on commercial farms is unknown, but developments in methodology now permit quantification of CH 4 emissions by individual cows under commercial conditions. The aim of this research was to assess variation among cows in emissions of eructed CH 4 during milking on commercial dairy farms. Enteric CH 4 emissions from 1964 individual cows across 21 farms were measured for at least 7 days/cow using CH 4 analysers at robotic milking stations. Cows were predominantly of Holstein Friesian breed and remained on the same feeding systems during sampling. Effects of explanatory variables on average CH 4 emissions per individual cow were assessed by fitting a linear mixed model. Significant effects were found for week of lactation, daily milk yield and farm. The effect of milk yield on CH 4 emissions varied among farms. Considerable variation in CH 4 emissions was observed among cows after adjusting for fixed and random effects, with the CV ranging from 22% to 67% within farms. This study confirms that enteric CH 4 emissions vary among cows on commercial farms, suggesting that there is considerable scope for selecting individual cows and management systems with reduced emissions.
This study investigated the effects of feeding system on diurnal enteric methane (CH 4 ) emissions from individual cows on commercial farms. Data were obtained from 830 cows across 12 farms, and data collated included production records, CH 4 measurements (in the breath of cows using CH 4 analysers at robotic milking stations for at least seven days) and diet composition. Cows received either a partial mixed ration (PMR) or a PMR with grazing. A linear mixed model was used to describe variation in CH 4 emissions per individual cow and assess the effect of feeding system. Methane emissions followed a consistent diurnal pattern across both feeding systems, with emissions lowest between 05:00 and 08:59, and with a peak concentration between 17:00 and 20:59. No overall difference in emissions was found between feeding systems studied; however, differences were found in the diurnal pattern of CH 4 emissions between feeding systems. The response in emissions to increasing dry matter intake was higher for cows fed PMR with grazing. This study showed that repeated spot measurements of CH 4 emissions whilst cows are milked can be used to assess the effects of feeding system and potentially benchmark farms on level of emissions.
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