Estimation of methane emission using the CO2 method from dairy cows fed concentrate with different carbohydrate compositions in automatic milking system

Abstract

Two concentrates (MELK and VEM) with two different carbohydrate compositions were supplemented during milking in an Automatic Milking System (AMS). The objectives of this study were to estimate the effect of the concentrates on CH4 emission from dairy cows and to investigate the precision of the CO2-method when measuring in an AMS for different length of time. Holstein cows (n=36) were used with mean body weight of 660kg (SD=75.13) and average milk production of 31.7kg (SD=8.98), mixed parity and mixed lactation. Cows were allocated in two groups (n=18). After an adaptation period (period 1), each group received either 100% MELK (More Energy Lactating Cows; a newly introduced feeding system) or 100% VEM (Feed Value System for milk production) during periods 2 and 3. Besides, both groups were fed the same Total Mixed Ration (TMR) ad libitum in the stable. Air samples in the AMS from a point near the cows head were analysed every 20s using the Gasmet equipment based on Fourier Transform Infrared (FTIR) Spectroscopy Technique. The equipment ran continuously for 15 days over the three measurement periods (5 days×3 periods) with a 14 days waiting time in between the periods. Individual records of the CH4 and CO2 concentrations in the cows breath was calculated after subtracting the CH4 and CO2 concentrations in the stable air from the measured concentrations. The CH4:CO2 ratio was then multiplied with the calculated total CO2 production by the individual cows to get the quantitative CH4 production. Milk production and total dry matter intake (DMI, kg/day) were very similar in the two groups. The supplemented concentrate was allocated according to the individual milk yield and the intake ranged from 1.60 to 7.30kg/day in MELK cows and from 2.06 to 7.20kg/day in VEM cows. No significant difference was found for CH4 production in MELK and VEM groups over the three periods. A linear positive relation between the CH4 (g/day) and energy corrected milk (ECM, kg/day) production and the feed intake (DMI, kg/day) was observed for the entire period. The calculated CO2 and CH4 production were very similar in the two groups throughout the entire measurement period. The analysis of the precision of the CO2-method, using a 95% significance level, indicated that showing a difference of 9 or 5% in methane production requires a measuring period of 5 or 15 days, respectively, when using 18 cows per group. The study shows no effect of a limited change in supplementation of starch and sugar on CH4 production through feeding concentrates MELK or VEM in the AMS. To obtain an effect of changing the carbohydrate composition of the diet on the CH4 production, it is likely that a larger change in the diet is necessary. This can only efficiently be done by changing the TMR part of the diet.