Development of prediction models for quantification of total methane emission from enteric fermentation of young Holstein cattle at various ages

• Novel methane emission data for young Holstein cattle obtained.
• Prediction models for methane emissions of young cattle developed.
• Total methane emission factors (kg year−1) for young cattle presented.
• Results filled gap of knowledge for developing inventories and mitigation strategies.

Methane (CH4) emissions from ruminant animals contribute significantly to the global greenhouse gas budget. The accurate quantification of this source of emissions requires detailed animal and feed information, however there is little information available on systematic measurement of CH4 emissions from young cattle at various ages. The present study was designed to address this gap of knowledge. Data used were derived from a study with 20 Autumn-calved Holstein cattle (10 steers and 10 heifers) with CH4 emissions measured at age of 6, 12, 18 and 22 months, respectively. The cattle were offered a typical diet used on UK commercial farms containing a single grass silage mixed with concentrates. In each period, the cattle were housed as a single group in cubicle accommodation for the first 20 days, individually in metabolism units for the next 3 days, and then in indirect open-circuit respiration calorimeter chambers for the final 5 days with feed intake, feces and urine outputs and gaseous exchange measured during the final 4 days. Within each period, gender had no effect (P > 0.05) on nutrient digestibility and any CH4 emission variable in terms of total CH4 emission, CH4 emission as a proportion of live weight or feed intake, or CH4 energy output as a proportion of energy intake. The data from the two groups were therefore pooled to develop prediction equations for daily CH4 emissions (g day−1). A range of prediction equations have been developed using BW (body weight), feed intake and energy intake. The present data were also used to calculate accumulated CH4 emissions for the two genders. Although gender had no effect (P > 0.05) on the results, the accumulated CH4 emissions increased with the growth of cattle (mean 36.2 and 64.3 kg year−1 for both genders in years 1 and 2, respectively). A number of prediction equations were developed for total CH4 emission factors (kg year−1) for heifers and steers during the first and second year of the rearing. These factors were very strongly related to (r2 = 0.75–0.95) to BW recorded at the beginning, middle and the end of 1 or 2 year of age. These data can add novel information to the scientific literature and can be used to improve national inventories of CH4 emissions and to develop appropriate mitigation strategies for young Holstein cattle of high genetic merit herds.