CSIRO PUBLISHING
Animal Production Science, 2014, 54, 1757–1761 http://dx.doi.org/10.1071/AN14292
Methane emissions of dairy cows cannot be predicted by the concentrations of C8:0 and total C18 fatty acids in milk S. R. O. Williams A,B, P. J. Moate A, M. H. Deighton A, M. C. Hannah A and W. J. Wales A A B
Department of Environment and Primary Industries, 1301 Hazeldean Road, Ellinbank, Vic. 3821, Australia. Corresponding author. Email:
[email protected]
Abstract. Methane (CH4) emissions from dairy cows are technically difficult and expensive to measure. Recently, some researchers have found correlations between the concentrations of specific fatty acids in milk fat and the CH4 emissions from cows that could obviate the need for direct measurement. In this research, data on individual cow CH4 emissions and concentration of caprylic acid (C8:0) and total C18 fatty acids in milk were collated from eight experiments involving 27 forage-based diets and 246 Holstein-Friesian dairy cows. Linear regressions between CH4 and both C8:0 and total C18 in milk were produced for published data and used to calculate 95% prediction regions for a new observation. The proportion of observed methane emissions from eight experiments that fell outside the 95% prediction region was 27.6% for the C8:0 model and 26.3% for the total C18 model. Neither model predicted CH4 emission well with Lin’s coefficient of concordance of less than 0.4 and the Nash–Sutcliffe efficiency coefficient of approximately zero for both the C8:0 and total C18 models. In addition, general linear model analysis showed significant differences between experiments in their intercepts (P < 0.001) and slopes (P < 0.001). It is concluded that the relationships tested cannot be used to accurately predict CH4 emissions when cows are fed a wide range of diets. Additional keywords: lactation, methane measurement, ruminants. Received 13 March 2014, accepted 26 June 2014, published online 19 August 2014 Introduction Measurement of enteric methane (CH4) can be both costly and time consuming, and requires complicated equipment and procedures. A readily available proxy measure would negate the need to measure CH4 emissions directly and would also mean that dairy cows on commercial farms could have their CH4 emissions predicted. The concentrations of specific fatty acids in milk have recently been investigated as proxy measures for the prediction of CH4 emissions (Chilliard et al. 2009; Dijkstra et al. 2011; Mohammed et al. 2011). Methane emissions (g/day) have been shown to be strongly positively related to the concentrations of caprylic acid (C8:0) and strongly negatively related to the concentration of total C18 fatty acids in milk fat (Chilliard et al. 2009). These relationships were developed from diets with a maize silage base plus one of three forms of linseed. The relationships have been tested for cows fed total mixed rations incorporating a limited range of forages and feed additives (Dijkstra et al. 2011; Mohammed et al. 2011). However, they have not been tested for forage-based diets offered with a wide range of supplements. The aim of this work was to determine whether the linear relationships reported by Chilliard et al. (2009) were applicable to forage-based diets supplemented with a range of supplements. Materials and methods Information was drawn from eight experiments (E1–E8) completed at the Department of Environment and Primary Journal compilation CSIRO 2014
Industries, Ellinbank Centre, Vic., Australia (38140 S, 145560 E). All experiments were conducted in accordance with the Australian Code of Practice for the Care and Use of Animals for Scientific Purposes (2004) and approved by the Animal Ethics Committee of the Department of Environment and Primary Industries – Victoria. All animals (246) were multiparous Holstein-Friesian cows with a range of milk yield and days in milk. In all eight experiments, diets consisted of either lucerne hay or pasture (predominantly perennial ryegrass) and a supplement that was usually a concentrate (Table 1). Methane emissions were measured using either a SF6 tracer technique (Williams et al. 2011) or by open-circuit calorimeters (Williams et al. 2013). Milk yields of individual cows were measured morning and afternoon for the duration of each experiment using a DeLaval ALPRO milk metering system (DeLaval International, Tumba, Sweden). Milk fatty acids were measured in E2 according to Moate et al. (2013). In all other experiments, milk fat was extracted from fresh samples using a method based on the Rose–Gottlieb gravimetric method (International Dairy Federation 1987). Samples of extracted milk fat were stored at 20C until they were analysed for fatty acid composition. Concentrations of fatty acid methyl esters in milk fat were determined by gas chromatography following methylation with sodium methoxide (Slover and Lanza 1979). Analyses were conducted using an Agilent 6890 gas chromatograph with auto-sampler and flame ionisation detector (Agilent Technologies, Santa Clara, CA, USA), and with a RTX-2330 column (105 m · 0.25 mm i.d. www.publish.csiro.au/journals/an
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Table 1. Diet and cow characteristics for the eight experiments that the data were taken from DHA = docosahexanoic acid, control diet is unique within experiment, DIM = days in milk, DMI = dry matter intake, Expt = Experiment, Lit = Chilliard et al. (2009) Expt
Expt design
Lit
1
Randomised block
2
Randomised block
3
Full crossover
4
Randomised block
5
Full crossover
6
Randomised block
7
Randomised block
8
Randomised block
Dietary treatment
Control Crude linseed Extruded linseed Linseed oil Tannin-0 g Tannin-80 g Tannin-160 g Tannin-240 g DHA-0 g DHA-25 g DHA-50 g DHA-75 g Control Fat Fat Plus Tannin Tannin Control Dried grape marc Ensiled grape marc Corn Wheat Wheat-0 kg Wheat-3 kg Wheat-6 kg Wheat-9 kg Control Almond hulls Citrus pulp Control Red grape marc White grape marc
n (cows) 8 8 8 8 8 8 7 8 8 8 8 7 8 7 8 8 11 10 10 13 14 8 8 8 8 12 10 10 11 10 10
Methane by
DIM (days)
Diet base
Season
SF6
213
Maize silage
SF6
60 61 61 64 218 215 216 215 90 95 90 90 245 229 245 191 191 57 57 57 57 179 177 176 73 73 70
Pasture
Spring
Lucerne
Autumn
Lucerne
Spring
Lucerne
Autumn
Lucerne
Autumn
Pasture
Spring
Lucerne
Autumn
Pasture
Spring
Calorimeter
Calorimeter
SF6
Calorimeter SF6
SF6
SF6
and 0.2-mm film thickness), using helium as the carrier gas at a rate of 1.4 mL/min. Peak identification was by retention time comparisons with a standard (Sigma Chemical Corporation, St Louis, MO, USA). The linear regressions between CH4 and both C8:0 and total C18 in milk were reproduced for the data of Chilliard et al. (2009) and used to calculate 95% prediction regions for a new observation. These were graphed along with the data from the eight experiments described here (Fig. 1). The percentage of data falling outside each 95% prediction region was calculated for each of the eight experiments individually and then pooled. Several analyses were performed to compare the methane emission predicted by the equations of Chilliard et al. (2009) with observed methane data for the eight experiments. These included Lin’s concordance with bias factor, the root-mean standard error of prediction and the Nash–Sutcliffe coefficient of efficiency statistics that were computed using GENSTAT (version 16, VSN International, www.vsni.co.uk, verified 10 July 2014). General linear models for CH4 were specified with linear terms for C8:0 (C8:0 model) by experiment, or total C18 (total C18 model) by experiment, for the pooled data from all eight
Milk yield (kg/day)
Forage DMI (kg/day)
Concentrate DMI (kg/day)
Total DMI (kg/day)
23.0 21.5 20.8 18.9 30.8 30.0 31.5 30.1 22.2 26.0 23.1 22.3 32.3 34.5 33.7 31.1 13.4 15.0 11.5 27.4 29.1 29.9 31.3 32.3 34.7 25.6 23.2 25.9 29.2 26.6 25.4
12.9 12.9 10.3 8.8 17.5 16.3 17.5 15.7 18.2 18.0 16.5 15.3 19.1 17.8 17.9 18.7 13.2 13.8 13.5 10.1 9.0 17.1 15.4 12.3 8.9 14.2 14.4 13.2 13.7 14.0 14.3
6.9 6.6 6.4 5.9 3.6 3.7 3.8 3.6 5.9 6.1 6.2 6.2 5.8 5.9 5.9 5.9 4.1 4.1 4.0 12.2 11.5 2.1 5.0 7.9 10.9 8.2 8.2 7.8 5.0 4.6 4.6
19.8 19.5 16.7 14.7 21.1 20.0 21.3 19.3 24.1 24.1 22.7 21.5 24.9 23.7 23.8 24.6 17.3 17.9 17.5 22.3 20.5 19.2 20.4 20.2 19.8 22.4 22.6 21.0 18.7 18.6 18.9
experiments plus that of Chilliard et al. (2009), using GENSTAT. General differences between experiments were tested by change in deviance F-tests. Pairwise differences between each experiment and the data from Chilliard et al. (2009) were also tested using Student’s t-test contrasts between slopes and intercepts at the global mean for C8:0 and total C18. A general linear model was also created for CH4 with linear terms for C8:0 and total C18 by experiment, and for the pooled data using GENSTAT. Individual cow CH4 emissions were plotted against both C8:0 and total C18 within the experiment, where the fatty acid of interest was expressed as a percentage of total milk fatty acid. Slope, intercept and the square of the Pearson product moment correlation coefficient were calculated for a linear regression of each plot using GENSTAT. Results Methane emissions from cows fed either lucerne hay or pasture supplemented with a range of fibres and concentrates were not accurately predicted by either the C8:0 (Lin’s bias = 0.807 and
Ruminant methane emissions and milk fatty acids
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700 600
Methane (g/day)
500 400 300 200 100 0 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
20
C8:0 (% of total FA)
30
40
50
60
70
Total C18 (% of total FA)
Fig. 1. Methane emission (g/day) versus C8:0 and total C18 fatty acids in milk from the literature and eight experiments (Chilliard et al. (2009) data (black circles), regression (solid line), 95% prediction region (dotted lines); Experiment 1 (open star); Experiment 2 (open square); Experiment 3 (grey square);
Table 2. The linear regression characteristics of methane versus C8:0 and total C18 fatty acids in milk within experiment Expt = Experiment; Int = intercept; Lit = Chilliard et al. (2009). *P < 0.05; **P < 0.01 Expt
Lit 1 2 3 4 5 6 7 8
C8:0
Total C18 r2
Int
Slope
r2
Regression P
Int
Slope
11 479 630 427 257 –70.2 93 121 252
282** –37.3 –80.7 54.7 129* 354** 221** 222** 88
0.810 0.046 0.047 0.068 0.242 0.868 0.416 0.251 0.172
–
