Effect of the nature of energy (lipids vs. carbohydrates) on enteric methane emission and dairy performance in cows fed grass silage-based diets

Figures & data

Table 1. Ingredients and chemical composition of the four experimental grass silage-based diets fed to dairy cows.

Item^b	Diet^a
	Control	RO-low	RO-medium	RO-high
Ingredients, % dry matter (DM)
Grass silage	47.9	50.5	52.9	55.1
Hay	11.1	11.4	11.6	11.9
Concentrates	41.1	36.6	32.3	28.1
Cracked wheat grain	5.8	3.6	1.6	0.4
Cracked corn grain	19.4	15.9	14.3	12.2
Soybean meal	7.8	10.7	11.8	13.0
Dehydrated alfalfa	5.8	4.0	2.0	–
Cane molasses	1.6	1.6	1.6	1.7
Minerals and vitamins	0.8	0.8	0.8	0.8
Rapeseed oil	0	1.5	3.2	4.9
Chemical composition, % DM
OM	91.3	91.2	91.1	91.2
CP	14.9	16.3	16.4	16.8
NDF	36.1	37.0	36.8	37.2
ADF	20.5	20.9	20.9	21.1
Starch	17.0	13.3	11.1	9.4
Ether extract	1.4	2.8	4.4	5.9
Gross energy, MJ/d	18.4	18.8	19.2	19.5
Forages to concentrates ratio^c	59/41	62/38	65/35	67/33
Expected DM intake, kg/d	21.9	21.2	20.6	20.1

^aControl: diet without rapeseed oil; RO-low: diet with 1.5% rapeseed oil; RO-medium: diet with 3% rapeseed oil; RO-high: diet with 4.5% rapeseed oil (% of dietary DM).

^bDM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF: acid detergent fiber.

^cIncluding rapeseed oil.

Table 2. Nutrient intakes and milk performances in dairy cows fed iso-energetic diets based on grass silage and characterised by different contents of rapeseed oil and starch.

Item^e	Diet^f				SEM	P value
	Control	RO-low	RO-medium	RO-high
Nutrient intake, kg/d
DM	21.7^a	20.9^a^b	20.4^a^b	19.5^b	0.62	0.011
OM	19.8^a	18.7^a^b	17.9^bc	16.8^c	0.49	0.005
CP	3.3	3.5	3.4	3.4	0.11	0.621
NDF	7.7	7.6	7.3	7.0	0.24	0.209
ADF	4.4	4.3	4.2	4.0	0.15	0.250
Starch	3.8^a	2.9^b	2.4^c	2.0^d	0.09	<0.001
Ether extract	0.60^d	0.88^c	1.23^b	1.50^a	0.000	<0.001
Gross energy, MJ/d	400.6	400.2	407.2	404.2	12.05	0.973
Milk performances
Milk yield, kg/d	30.8^a^b	33.0^a	33.6^a	29.0^b	1.27	0.020
Milk fat, g/kg milk	36.1^a	33.1^a^b	27.1^d	30.6^c	1.1	<0.001
Milk protein, g/kg milk	30.0^b	29.4^b	29.7^b	32.2^a	0.6	0.008
FPCM, kg/d	28.8^a^b	29.5^a	27.9^a^b	25.6^b	1.1	0.026
Fat yield, g/d	1108^a	1086^a	914^b	881^b	46	<0.001
Protein yield, g/d	925	970	997	928	41	0.192
Feed efficiency, kg milk/kg DMI	1.32	1.42	1.37	1.31	0.04	0.332

^a-dMeans with a different superscript significantly differ at P < 0.05.

^eDM: dry matter; OM: organic matter; CP: crude protein; NDF: neutral detergent fiber; ADF: acid detergent fiber; FPCM: fat and protein corrected milk.

^fControl: diet without rapeseed oil; RO-low: diet with 1.5% rapeseed oil; RO-medium: diet with 3% rapeseed oil; RO-high: diet with 4.5% rapeseed oil (% of dietary DM).

Table 3. Methane and carbon dioxide emissions in dairy cows fed iso-energetic diets based on grass silage and characterised by different contents of rapeseed oil and starch.

	Diet^d				SEM	P value
Item^c	Control	RO-low	RO-medium	RO-high
eCH4, g/d	426.9^a	361.1^b	343.4^b	328.0^b	20.31	0.010
eCH4, g/kg of DM intake	19.6^a	17.3^b	16.8^b	16.7^b	0.71	0.028
eCH4, g/kg of OM intake	21.5	19.3	19.2	19.5	0.81	0.170
eCH4, % of GE intake	5.91^a	5.02^b	4.69^b	4.50^b	0.20	<0.001
eCH4, g/kg of digested DM	28.7^a	25.0^b	24.0^b	24.0^b	1.11	0.016
eCH4, g/kg of digested OM	29.6	26.3	26.3	26.8	1.15	0.149
eCH4, g/kg of digested NDF	91.5^a	73.9^b	72.9^b	72.0^b	3.51	0.001
eCH4, g/kg of milk	14.0^a	11.0^b	10.3^b	11.6^b	0.78	0.016
eCH4, g/kg of FPCM	14.9	12.2	12.5	13.0	0.80	0.101
CO2, g/d	12,571^a	11,122^b	10,936^b	11,772^b	594.1	0.048

^a-bMeans with a different superscript significantly differ at P < 0.05.

^ceCH_4: enteric methane emissions; DM: dry matter; OM: organic matter; GE: gross energy; FPCM: fat and protein corrected milk; CO_2: carbon dioxide emissions.

^dControl: diet without rapeseed oil; RO-low: diet with 1.5% rapeseed oil; RO-medium: diet with 3% rapeseed oil; RO-high: diet with 4.5% rapeseed oil (% of dietary DM).

Table 4. Total tract digestibility of nutrients and rumen parameters before feeding in dairy cows fed iso-energetic diets based on grass silage and characterised by different contents of rapeseed oil and starch.

Item^c	Diet^d				SEM	P value
	Control	RO-low	RO-medium	RO-high
Nutrient total-tract digestibility, %
DM	68.3	69.2	70.1	69.9	0.77	0.339
OM	72.4	73.2	72.9	72.9	0.72	0.915
NDF	60.3^b	64.8^a^b	64.7^a^b	65.2^a	1.24	0.033
ADF	61.2^b	65.3^a^b	65.7^a^b	66.5^a	1.27	0.033
Starch	99.4	99.3	99.3	99.1	0.09	0.070
Rumen parameters, before feeding
Total VFA, mM	85.3	82.7	73.8	78.8	7.20	0.699
Acetate, % of total VFA	68.1	68.1	66.6	65.7	0.72	0.076
Propionate, % of total VFA	15.9^b	16.2^b	17.1^b	19.2^a	0.59	0.002
Butyrate, % of total VFA	12.3^a	12.1^a	12.4^a	10.4^b	0.57	0.005
Acetate/propionate	4.32^a	4.24^a	3.93^a	3.48^b	0.15	0.006
(Acetate + butyrate)/propionate	5.11^a	5.00^a	4.66^a	4.03^b	0.17	0.002
NH3, mM	5.5	6.5	5.5	6.1	0.51	0.352
Total protozoa^e, 10^3 cells/mL	350	428	304	193	86.9	0.262

^a-bMeans with a different superscript significantly differ at P < 0.05.

^cDM: dry matter; OM: organic matter; NDF: neutral detergent fiber; ADF: acid detergent fiber; VFA: volatils fatty acids; NH₃: ammonia.

^dControl: diet without rapeseed oil; RO-low: diet with 1.5% rapeseed oil; RO-medium: diet with 3% rapeseed oil; RO-high: diet with 4.5% rapeseed oil (% of dietary DM).

^eData were log10-transformed for statistical analysis.

Table 5. Milk fatty acid profile in dairy cows fed iso-energetic diets based on grass silage and characterised by different contents of rapeseed oil and starch.

Fatty acid, g/100g FA^e	Diet^f				SEM	P value
	Control	RO-low	RO-medium	RO-high
C4:0	3.04^a	3.29^a	2.32^b	1.90^c	0.136	<0.001
C6:0	2.29^a	2.10^a	1.28^b	1.17^b	0.109	<0.001
C8:0	1.34^a	1.10^b	0.61^c	0.60^c	0.066	<0.001
C10:0	3.00^a	2.18^b	1.28^c	1.32^c	0.147	<0.001
C12:0	3.32^a	2.31^b	1.61^c	1.66^c	0.146	<0.001
C14:0	11.50^a	9.35^b	7.84^c	7.83^c	0.368	<0.001
C14:1c9	1.12	0.86	0.95	0.86	0.073	0.055
C16:0	28.94^a	21.05^b	18.28^b	20.24^b	0.862	<0.001
C16:1c9	1.36	1.17	1.29	1.33	0.109	0.604
C18:0	9.96^b	12.93^a	13.02^a	14.45^a	0.532	<0.001
C18:1t6-8	0.33^b	0.64^b	1.14^a	1.06^a	0.097	<0.001
C18:1t9	0.29^c	0.55^b	0.85^a	0.74^a	0.040	<0.001
C18:1t10	0.59^b	0.92^b	2.84^a	2.34^a	0.205	<0.001
C18:1t11	1.34^b	2.80^a	2.81^a	1.76^b	0.141	<0.001
C18:1t13	0.68^d	1.06^c	1.50^a	1.28^b	0.065	<0.001
C18:1c9	17.57^b	23.15^a	26.24^a	26.40^a	0.994	<0.001
C18:2c9t13	0.26^c	0.34^b	0.49^a	0.43^a	0.025	<0.001
C18:2t11c15	0.17^b	0.21^b	0.28^a	0.22^b	0.019	0.002
C18:2n-6	1.74^a	1.72^a	1.53^b	1.24^c	0.066	<0.001
C20:0	0.16^c	0.21^b	0.23^ab	0.26^a	0.009	<0.001
C18:3n-3	0.55^a	0.55^a	0.40^b	0.32^c	0.029	<0.001
CLAc9t11 (+t7c9CLA + t8c10CLA)	0.53^c	1.00^a	1.10^a	0.72^b	0.061	<0.001
C22:0	0.082^ab	0.073^b	0.091^a	0.078^ab	0.0037	0.016
C20:5n-3	0.053^a	0.046^a	0.029^b	0.032^b	0.0031	<0.001
C24:0	0.048	0.039	0.046	0.046	0.0033	0.203
OCFA	1.97^a	1.71^b	1.52^c	1.52^c	0.045	<0.001
BCFA	1.41^a	1.40^a	1.17^b	1.13^b	0.045	<0.001
SFA	67.05^a	57.73^b	49.30^c	52.19^c	1.397	<0.001
MUFA	29.75^b	35.92^ab	41.21^a	38.31^a	2.126	<0.001
PUFA	4.33^b	4.94^a	4.72^ab	4.37^ab	0.200	0.001
t FA	6.87^b	9.60^ab	12.59^a	10.84^a	0.927	0.001
n-3	0.70^a	0.67^a	0.52^b	0.54^b	0.050	0.036
n-6	1.94^ab	2.05^a	1.73^ab	1.68^b	0.097	0.037
De novo synthesized FA	26.56^a	22.19^b	16.58^c	16.13^c	0.903	<0.001

^a-dMeans with a different superscript significantly differ at P < 0.05.

^eFA, fatty acids; BCFA, branched-chain FA; CLA, conjugated linoleic acid; OCFA, odd-chain FA.

^fControl: diet without rapeseed oil; RO-low: diet with 1.5% rapeseed oil; RO-medium: diet with 3% rapeseed oil; RO-high: diet with 4.5% rapeseed oil (% of dietary DM).

Figure 1. Spider plots of the normalised (Z score) variables¹ describing (a) dairy performance and digestion parameters including eCH₄ and (b) milk fatty acid (FA) composition according to the nature of energy (rapeseed oil vs. starch) in the four iso-energetic and grass silage-based diets of dairy cows (Control, RO-low, RO-medium, RO-high). The optimum shape is represented by the red line: positive variables for the dairy performance or healthy milk FA for human nutrition were expected to have the maximum Z score, whereas the minimum Z score was desired for eCH₄ or non-healthy milk FA (SFA); Z score scale from -1.5 to 1.0 with Z = 0 for the overall average of the four diets.

¹Fatty acids, g/100g FA; Feed efficiency, kg milk/kg DMI; Milk yield, kg/d; Milk fat, g/kg; daily eCH4, g/d; eCH4 yield, g/kg DMI; eCH4 intensity, g/kg milk; NDFD, NDF digestibility, %; BCFA, branched-chain FA.

Data availability statement

The data that support the findings of this study are available from the corresponding author, CM, upon reasonable request.