Enteric methane emission by Lactating and Dry cows in rye grass-clover pasture in the high Andean zone of Peru

Enteric methane emission by Lactating and Dry
cows in rye grass-clover pasture in the high Andean
zone of Peru
Catherine Yasmín Salas-Riega
 Universidad Nacional Agraria La Molina
Sandra Osorio
 Instituto Nacional de Innovacion Agraria
Julyssa del Pilar Gamarra
 Instituto Nacional de Innovacion Agraria
Victor Alvarado-Bolovich
 Universidad Nacional Agraria La Molina
Cesar Osorio
 Instituto Nacional de Innovacion Agraria
Carlos Gomez (  cagomez@lamolina.edu.pe )
 Universidad Nacional Agraria La Molina https://orcid.org/0000-0001-9021-5838

Research Article

Keywords: enteric methane, grazing, sulfur hexa uoride, titanium dioxide, high Andean

Posted Date: July 22nd, 2021

DOI: https://doi.org/10.21203/rs.3.rs-510090/v1

License:   This work is licensed under a Creative Commons Attribution 4.0 International License.
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1 TITLE
 2 Enteric methane emission by Lactating and Dry cows in rye-grass - clover pasture in the high Andean
 3 zone of Peru
 4 Catherine Yasmín Salas-Riega1, Sandra Osorio Orellana2, Julyssa del Pilar Gamarra Reyes2, Victor
 5 Alvarado-Bolovich1,2, Cesar Mauro Osorio Zavala2 and Carlos Alfredo Gómez Bravo1*

 6 1
 Universidad Nacional Agraria La Molina, Av. La Molina s/n, La Molina, Lima, Perú
 2
 7 Instituto Nacional de Innovación Agraria, Av. La Molina n°1981, La Molina, Lima, Perú
 8 *Corresponding autor: cagomez@lamolina.edu.pe
 9 ORCID

10 Catherine: 0000-0002-1150-2992

11 Sandra: 0000-0002-2975-7117
12 Julyssa: 0000-0001-9050-6926
13 Victor: 0000-0003-3266-0049
14 Cesar: 0000-0002-3200-7632

15 Carlos: 0000-0001-9021-5838
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34 ABSTRACT
35 The objective of the study was to determine the enteric methane emissions from lactating and dry

36 cows fed on rotational grazing on ryegrass/clover with supplementation of oat and vetch forage in the

37 Andes of Peru. Sulfur hexafluoride (SF6) tracer gas methodology was used to determine enteric

38 methane emission; the external marker Titanium dioxide (TiO2) to determine the production of feces

39 and the protein in feces was used to estimate the digestibility of the feed. The enteric methane

40 emissions of 5 lactating cows (LC) and 6 dry cows (DC) Brown Swiss breed were 358.5 and 337.4 g

41 CH4/cow/day for LC and DC, respectively (P> 0.05). The conversion factor from gross energy to

42 methane (Ym;%) was 9.7 for LC and 9.6 for DC. The enteric methane yield per kilogram of organic

43 matter consumption was 32.5 g CH4/lactating cow /day and 32.2 g CH4/dry cow/day (p> 0.05) and the

44 emission per kilogram of metabolic live weight for lactating cows was 3.1 g CH4/kg PV0.75 and for dry

45 cows 2.9 g CH4/kg PV0.75 (P> 0.05). It was concluded that enteric methane emissions are similar for

46 lactating cows and dry cows measured with the SF6 tracer gas technique.

47 Keywords: enteric methane, grazing, sulfur hexafluoride, titanium dioxide, high Andean

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61 INTRODUCTION

62 Anthropogenic greenhouse gas (GHG) emissions are the main responsibility of climate change

63 (Ballesteros and Aristizabal, 2007; Gutiérrez, 2013), in which the agricultural sector emits 18% of the

64 GHG emissions (FAO, 2006). Livestock systems emissions occur directly: via enteric fermentation

65 and manure management; or indirect: change in land use; in which the dairy and beef cattle are the

66 largest GHG emitters (FAO, 2006; Rodríguez and Mance, 2009; Jonker et al., 2016).

67 MINAM (2019) estimates with IPCC tier 1 methodology that Peruvian cattle emit 66% of the methane

68 emissions of the country's agriculture sector in with 9,317 Gg CO2 eq is produced by enteric

69 fermentation. In contrast with the emissions estimated using Tier 1 methodology, several studies have

70 used the tracer gas method Sulfur hexafluoride (SF6) to measure the enteric methane (CH4) emissions,

71 detailing the relationship between feeding strategies and CH4 emissions in lactating cows in the Andes

72 of Peru (Moscoso et al., 2017; Alvarado-Bolovich et al., 2021). However, there are no studies to

73 determine possible differences in enteric CH4 emissions between physiological stages in dairy cows

74 under Andean conditions. The objective of the study is to compare enteric methane emissions from

75 lactating and dry cows fed on cultivated pastures in the Peruvian highlands; determined by tracer gas

76 SF6.

77 MATERIALS AND METHODS

78 The study was carried out at the Santa Ana Agrarian Experimental Station of the National Institute for

79 Agrarian Innovation (12 ° 02´S and 71 ° 10´W, Huancayo, Junin, Peru) at 3,260 m.a.s.l. The study was

80 from January to April, with an average temperature of 12.5°C and mean precipitation of 56 mm by

81 month. On expired gas sampling days, the temperature ranged between 10.1 - 14.3°C and the humidity

82 percentage was between 57.2 - 77% (69%).

83 Experimental animals, feeding and milking management

84 Eleven Brown Swiss multiparous cows were used in the experiment: 5 lactating cows (3 in mid-

85 lactation and 2 in late lactation) with 530 ± 24.4 kg of live weight (LW) and a milk yield of 5.7 ± 0.8

86 kg of milk/cow/day; and 6 dry cows with 571 ± 12 kg of LW. A rotary grazing system (32 paddocks of

87 Lolium perenne L. - Trifolium repens L.) was implemented: 1-2 days of grazing with 30 to 32 days of

88 rest. In the pen, the cows were supplied with Avena sativa L. and Vicia sativa L.

 89 Before the beginning of the experimental period, the permanent linear transaction method (Parker,

 90 1951) was used to detail the floristic composition of the grazing field, identifying the species in the

 91 Herbarium "A.Webwebauer" of Universidad Nacional Agraria La Molina (UNALM). The biomass in

 92 the grazing area was evaluated on days 1, 7, and 9 of the experimental periods with the cutting method

 93 where a quadrant of 1 m2 was thrown at random 5 times to the paddock before the entry of the

 94 animals, proceeding to cut, place in plastic bags, weigh it. Moreover, later, pre-dry to the environment

95 and store them in paper bags.

 96 To obtain a representative sample of the animals' diet, the manual simulation technique (MST) took

 97 place in the grazing area and the oat and vetch supplement was sampled in the pen. The MST was

 98 carried out at 10:00 h in the grazing area during days 1, 7, and 9 of the experimental periods

99 (Langlands, 1974). For this, 3 lactating cows and 3 dry cows were selected. At the beginning of

100 grazing, it was visualized what the animal ingested (leaves, stem, species) and the bites made in the

101 feeding station, to then proceed to collect the number of times as bites made by the animal and the

102 visualization of an area continues. This procedure was carried out for 25 feeding stations, which is

103 defined as a semicircle in front of the animal from which it harvests the forage (Flores, 1983). Samples

104 of the MST were weighed, pre-dried in the environment, and stored in paper bags.

105 Associated vetch-oats were fed to lactating cows and dry cows in guillotine-separated pens in the

106 morning and afternoon; where they supplied 20 kg at a time, making a total of 40 kg daily of oats and

107 vetch per cow, where the sampling performed before giving the forage. Likewise, the rest of the forage

108 left by the animals was weighed, this activity was realized on days 1, 7, and 9 of the experimental

109 periods. All samples were sent to the Food Nutritional Evaluation Laboratory of the Nutrition

110 department of UNALM.

111 The animals in production were milked twice a day, for which 50 ml of milk was sampled in each

112 milking and for its preservation 2 drops of 40% formaldehyde were placed and refrigerated at 4 ° C.

113 Two milk sample shipments were made; 7 days of sampling per cow were mixed in each one and a

114 complete sample was obtained per animal. Everything was sent to the Laboratory of milk, derivatives,

115 and meats of UNALM.

116 Voluntary feed intake

117 The animals were dosed with 5 g of TiO2 at 6:00 h and 18:00 h, before supplementing with oats and

118 vetch. Feces were collected (after a 7-day adaptation period) for 9 days (at 6:30 h and 18:30 h). After

119 that, each bag was mixed per animal, obtaining 1 kg of feces per cow and it was sent to the

120 Biochemistry Laboratory of UNALM for subsequent analysis of the concentration of Titanium in

121 feces by atomic absorption spectrophotometry.

122 The digestibility of organic matter (OMD) was obtained from the protein content in the feces

123 according to the methodology proposed by Lukas et al. (2005); therefore, the feces were sent to the

124 Food Nutrition Evaluation Laboratory of UNALM for the analysis of the percentage of moisture, fecal

125 protein, and ash.

126 Organic matter intake (OMI) was calculated by:

127 ( / / ) = ( / / ) / [1 − ( / ) /1000]
128 Dry matter intake (DMI) was obtained by:

129 / / = ( ( / / ) / ( / )) 1000
130 Where, OMI (g/d) is the organic matter intake; OMD (g/kg OM) is the organic matter digestibility;

131 DMI (g/d) is the dry matter intake; OM (g/kg DM) is the organic matter feed.

132 The DMI of lactating cows using the IPCC (2019):

133 = 0.0185 × + 0.305 × d

134 Where, DMI = Dry matter intake (kg/d); BW = Average initial and final live body weight per cow

135 (kg); ECMd = Energy-corrected milk (kg/d) to 3.5 % for DMI (Energy-corrected milk: [(0.4324 ×

136 ) + (16.216 × )]).

137 The DMI of dry cows using the IPCC (2019):

138 = % × 
139 Where, DMI = Dry matter intake (kg/d); BW% = Percentage of average initial and final live

140 bodyweight of each cow (kg); Coefficient: according to the quality of forage consumed by the

141 animals, considering 1.8 for experimental dry cows.

142 Sulfur hexafluoride tracer gas technique (SF6)

143 It was based on Alvarado-Bolovich et al. (2021). The initial and final pressures obtained in the

144 canisters were -68.7 kPa and -39.6 kPa, respectively. The sample canisters were over-pressurized with

145 ultra-pure nitrogen between 31 kPa to 38 kPa to then extract the expired gas samples. Exhaled gases

146 were collected from each experimental animal and gas from environmental samples every 24 hours.

147 The vials with the expired gas were stored in refrigeration at 4°C and sent to the Biochemistry

148 Laboratory of the UNALM. Concentration of methane and SF6 were determined by gas

149 chromatography (Agilent 7890B) and corrected according to Alvarado-Bolovich et al. (2021). Before

150 proceeding to evaluate the expired gas samples, two calibration curves were prepared using the 48.7

151 mg/kg CH4 standard and the 237.9 ug/kg SF6 standard. Daily CH4 emissions (CH4Q; g/d) were

152 calculated according to William et al. (2011) equation:

 4 
153 4 = ( 6 ) × (( 4 − 4 ) ÷ ( 6 − 6 )) × ( )
 6 
154 Where, SF6Q is the default SF6 permeation rate (mg/d); CH4B (ppm) and SF6B (ppt) are the

155 concentration of the background air; CH4C (ppm) and SF6C (ppt) are the concentration in the

156 subsamples, and CH4MM and SF6MM are the molar weight of the gases.

157 Methane conversion factor (Ym, %) was estimated from the equation of IPCC (2019) for estimated

158 methane emission factor for enteric fermentation.

 ( )
159 =
 
 55.65 ( 4) × 4 ( 4 )
 
160 Where Ym is the percentage of gross energy in feed converted to methane or methane conversion

161 factor; CH4 (kgCH4/cow/day) is the methane production (MP); GE (MJ/kg) is the gross energy.

162 Chemical Analysis

163 The sward yield in the grazing area was estimated from the grass moisture measure by drying for 24 h

164 at 105°C (AOAC, 2005). Crude protein (CP) was calculated from the N content after the Kjeldahl

165 method (AOAC, 2005); gross energy was determined by ASTM D-2015-66 (1972) method used as a

166 standard test method for Gross Calorific Value. Concentration of NDF was analyzed using the Fiber

167 Analyzer Ankom 200 that is based on Van Soest et al. (1991).

168 Feces excretion were dried in a forced–air oven at 40°C for 5 days and milled to a particle size of

169 1mm. Moisture and CP were determined based on AOAC (2005). The titanium dioxide (TiO 2) in

170 feces were analyzed by a wet digestion (Myers et al., 2004) and the concentration of TiO2 in feces was

171 determined in triplicate by atomic absorption spectrophotometry. Fecal excretion (FE) was calculated

172 by assuming recovery of TiO2 in feces of 100% (Glindemann et al., 2009).

173 ( / ) = 2 ( ) ÷ 2 ( ) × 100
 
174 Fecal CP concentration was used to estimate the OMD of the ingested diet using an equation proposed

175 by Lukas et al. (2005):

 (−0.01515× ( ))
176 ( ) = 72.86 − 107.7 × × 10
 
177 Metabolizable energy (ME) was estimated for each cow from OMD using an equation proposed by

178 Aiple et al. (1992) cited by Dickhoefer et al. (2018).

179 ( ) = 0.9 + 17.0 × ( )
 100 
180 Milk composition was determined by Milko Scan “FOSS”, whilst the energy-corrected milk (ECM)

181 was calculated with the equation of Sjaunja et al. (1990):

182 ( )
 
 38.30 × ( ) + 24.20 × ( ) + 16.54 × ( ) + 20.7
 
183 = ( ) × ( )
 3,140
184 Statistical Analysis

185 All data were analyzed with R statistical software with a T student mean test for two independent

186 samples for the comparison of the emissions obtained by the SF6 tracer gas technique and IPCC tier II

187 in lactating and dry cows. Shapiro-test was used for the normality test and Barlett-test for the

188 homoestacity test.

189 RESULTS AND DISCUSSION

190 Forage characteristics

191 The mean sward yield was 3,040 kg DM/ha. The 58% of the sward composition (Table 1) consisted of

192 cultivated species, in which Lollium perenne L. and Trifolium repens L. were the predominant species.

193 Animal´s diet consisted of 63% of pasture, and 37% by oats - vetch. The CP and NDF of the sward

194 were influenced by the age, varieties and proportion of the species. The CP content of the sward

195 (Table 2) was similar to the reported by Avalos and Flores (2015), but less than registered by

196 Bojórquez (1998) for a ryegrass/clover pasture at 3300 m.a.s.l. The CP content of the oats/vetch

197 association was similar to Flores et al. (2016) with a 35% of vetch, but it is higher than reported by

198 Enciso et al. (2019) for an association with a 30% of vetch. The NDF content of the sward was higher

199 than reported by Florian (2019) in 80-day ryegrass/clover plots. Conversely, the NDF content of the

200 oat/vetch association was less than reported by Flores et al. (2016) with a 60% of oats, but like the

201 observed by Montoya (2017) in the Peruvian central plateau. However, it was higher than the observed

202 by Bartl et al. (2009) for oat (578 – 585 g NDF/kg DM) and vetch (377 g NDF/kg DM) in the Mantaro

203 valley.

204 The high NDF content (595 g/kg DM) in the diet produced a lower OMD (Glindemann et al., 2009).

205 The OMD in the diet was of 638 g/kg DM for lactating cows and 643 g/kg DM for dry cows (P>0.05);

206 which were similar to reported by Alvarado-Bolovich et al. (2021). The ME (11.75 and 11.83 MJ/kg

207 MO for lactating and dry cows (p> 0.05)) was found in the range of 8.8 to 12.8 MJ ME/kg DM

208 reported by Greenty and Rattray (1987). Whilst the DMI (12.6 and 11.5 kg/cow/d for lactating and dry

209 cows, respectively) expressed as a percentage of LW was 2.4% for lactating cows and 2.0% for dry

210 cows, which is in the range observed in the Peruvians highlands (1.3 – 2.4%; Flores et al., 2006).

211

212 Enteric Methane Emission

213 The CH4 emissions for lactating and dry cows are shown in Table 3. Compared to SF6 technique,

214 lactating cows and dry cows presented 21% and 84% more CH4 emissions than estimated by IPCC

215 (Table 4). However, CH4 emissions were similar to the reported by Lee et al. (2004) and Dini et al.

216 (2012) who evaluated animals fed ryegrass/white clover pastures; but greater than reported by

217 Alvarado-Bolovich et al. (2021) with lactating cows under similar environmental conditions to this

218 study. On the other hand, CH4 emissions were less than reported by Moscoso et al. (2017) with cows

219 grazing natural pastures supplemented with oat silage.

220 Methane emissions by kg of DMI (methane yield) were similar to the reported by Van Wyngaard et al.

221 (2018) with grazing cows without supplementation. Regarding the physiological stages, the methane

222 yield obtained was higher than reported in lactating cows but similar to dry cows (Montenegro-

223 Ballestero et al., 2019). CH4 emissions by kg of OMI was similar to the 33.4 - 36.7 g CH4 reported by

224 Dini et al. (2018) with heifers feeding a low and high nutritional quality pastures; likewise, emissions

225 observed by Alvarado-Bolovich et al. (2021) in the Peruvian high Andean zone were similar with

226 natural pastures, but lower with cultivated pastures, in comparison with the results of this work.

227 Methane emissions by NDF intake (NDFi) were similar to the reported by Alvarado-Bolovich et al.

228 (2021) with cultivated pastures, but higher than with natural pastures. CH4 emissions by metabolic

229 weight (LW0.75) in this study were similar than observed by Pedreira et al. (2009) for lactating and dry

230 cows.

231 Milk yield was 5.74 ± 0.8 kg/cow and 6.75 ± 0.2 kg of ECM/cow. Alvarado-Bolovich et al. (2021)

232 reported 68.9 g CH4/kg ECM in the rainy season, and 136 g CH4/kg ECM in the dry season, which

233 was similar to the reported in this study. Gómez and Fernández (2009) observed 130 g CH 4/kg of milk

234 with cows fed native pastures (332 g CH4/animal/d). In contrast, Muñoz et al. (2018) obtained 35.5 g

235 CH4 / kg of milk. Also, Van Wyngaard et al. (2018) reported 35.5 g CH4/kg of milk and 28.8 g

236 CH4/kg ECM

237 The methane conversion factor (Ym) of this study was higher than the 6.7% and 8.1% reported by

238 Montenegro-Ballestero et al. (2019) in cows in late lactation and dry cows, respectively; but similar to

239 the 10.6% and 9.1% in lactating and dry crossbreed Holstein cows reported by Primavesi et al. (2004)

240 and the 8.6% in non-pregnant and non-lactating Holstein cows reported by Stergiadis et al. (2016). In

241 contrast, Van Wyngaard et al. (2018), in pastures with the supplementation of 0, 4, and 8 kg/d of

242 concentrate, obtained 8.91%, 8.97%, and 7.85%; and Alvarado-Bolovich et al. (2021) obtained values

243 of 7.8% for cultivated pastures supplemented with concentrate.

244 The present study shows that CH4 emissions of lactating and dry cows feeding with ryegrass/clover

245 supplemented with oats and vetch in the high Andean zone does not vary but is higher than the values

246 proposed by the IPCC.

247 ACKNOWLEDGE

248 The authors would like to acknowledge PhD. Jose Velarde Guillen for reviewing the Manuscript and

249 the members of PNIA (Programa Nacional de Innovación Agraria): Ing. Magno Requena, Ing. Luis

250 Lucero, Ing. Ronald Vasquez, Ing. Mario Huilca, Ing. Erika Mateo and Bach. Rosana Lázaro. We also

251 thank to “CIENCIAACTIVA- CONCYTEC- FONDECYT” for granting the scholarship in Nutrition

252 studies to MVZ. Catherine Yasmín Salas Riega in UNALM.

253 DECLARATION

254 ● Funding: This research was financing and supported by INIA (Instituto Nacional de

255 Innovación Agraria) project No. 155-PI “Medición de metano entérico en bovinos lecheros

256 alimentados con Rye Grass/Trébol y alfalfa en la EEA Santa Ana – Huancayo en época

257 lluviosa”.

258 ● Author contributions: Conceptualization: Salas-Riega, C.; Gomez, C.; Alvarado-Bolovich, V

259 Methodology: Salas-Riega, C.; Alvarado-Bolovich, V.; Gomez, C. Formal analysis and

260 investigation: Salas-Riega, C; Osorio, S; Gamarra, J. Writing- original draft preparation:

261 Salas-Riega, C Writing-review and editing: Gomez, C.; Alvaro-Bolovich, V.; Osorio, S.;

262 Gamarra, J. Funding acquisition: Gomez, C., Osorio, C. Resources: Osorio, C.; Gomez, C.

263 Supervision: Gomez, C.

264 ● Competing interests: The authors declare no competing interests

265 ● Availability of data and material: All authors ensure that all data and materials support the

266 findings and comply with field standards

267 ● Code availability: Not applicable

268 ● Ethics approval: The animals were cared in accordance with Peru’s Law on Animal Protection

269 and Welfare, No. 30407

270 ● Consent of publication: All authors agree to the publication of this paper.

271 ● Consent to participate: All authors agree to the publication of this paper.

272

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Table 1. Composition of the grazing area

 Specie Family Desirable Type Frecuency
 (%)
 Lolium perenne L. Poaceae D Cultivated 48.5
 Lolium multiflorum Poaceae D Cultivated 1.9
 Trifolium repens L. Fabaceae D Cultivated 4.2
 Trifolium pratense Fabaceae D Cultivated 0.8
 Medicago sativa Fabaceae D Cultivated 2.3
 Medicago polymorpha Fabaceae D Non-cultivated 6.9
 Poa annua Poaceae D Non-cultivated 5.3
 Paspalum penicillatum Poaceae LD Non-cultivated 20.2
 Stachys arvensis (L.) L. Lamiaceae U Non-cultivated 1.1
 Juncus bufonius L. Juncaceae U Non-cultivated 1.1
 Taraxacum ofticinalis Asteraceae LD Non-cultivated 5.7
 Gamocheata Americana Asteraceae LD Non-cultivated 0.8
 Galisonga parviflora Asteraceae LD Non-cultivated 0.8
 Sonchus oleraceus Asteraceae LD Non-cultivated 0.4
 D: Desirable; LD: less desirable; U: undesirable

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Table 2. Chemical composition of forage and diet
 Oat (60%) y Vetch
 Ryegrass/Clover Diet
 (40%)
 DM (g/kg) 186.9 178.3 181.5
 OM (g/kg DM) 894.9 891.2 892.5
 CP (g/kg DM) 153.7 175.2 167.3
 NDF (g/kg DM) 634.5 572.1 595.1
 GE (MJ/kg DM) 16.7 16.5 16.6
 DM: Dry Matter; OM: Organic Matter; CP: Crude Protein; NDF: Neutral Detergent Fiber; GE:
 Gross Energy

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 Table 3. Enteric Methane Emission in lactating and dry cows
 SF6 Tracer Gas Technique
 CH4 emission P-value
 Lactating Dry
 gCH4/d 358.5 ± 8.0 337.4 ± 7.5 0.1
 gCH4/kg DMI 29.0 ± 0.7 28.7 ± 0.4 0.7
 gCH4/kg OMI 32.5 ± 0.8 32.2 ± 0.5 0.7
 0.75
 gCH4/kg BW 3.1 ± 0.2 2.9 ± 0.1 0.2
 gCH4/kg NDFi 73.0 ± 2.7 66.7 ± 2.6 0.1
 Ym% 9.7 ± 0.2 9.6 ± 0.1 0.7
 gCH4/kg of milk 116.3 ± 49.4
 gCH4/ECM 107.9 ± 51.5
 Media ± EE DMI: Dry matter intake; OMI: Organic matter intake; NDFi: Neutral detergent fiber intake;
 Ym%: methane conversion factor; ECM: Energy corrected-milk
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Table 4. Enteric methane emission using SF6 tracer and Tier II methodology by Physiological State

 Methodology
 Physiological State P-value
 SF6 Tier II

 gCH4/d 358.5 ± 8.0 294.7 ± 12.8 0.03

 gCH4/kg DMI 29.0 ± 0.7 25.1 ± 1.4 0.05
 Lactating
 DMI (kg/d) 12.6 ± 0.3 11.3 ± 0.3 0.01

 OMI (kg/d) 11.2 ± 0.3 10.5 ± 0.2 0.05

 gCH4/d 337.4 ± 7.5 183.4 ± 7.1 0.00

 gCH4/kg DMI 28.7 ± 0.4 17.3 ± 0.22 0.00
 Dry
 DMI (kg/d) 11.5 ± 0.1 10.4 ± 0.3 0.00

 OMI (kg/d) 10.3 ± 0.1 9.4 ± 0.3 0.02

 DMI: Dry matter intake OMI: Organic matter intake

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