Methane emissions from dairy cows measured using the sulfur hexafluoride (SF6) tracer and chamber techniques

Our study compared methane (CH₄) emissions from lactating dairy cows measured using the sulfur hexafluoride (SF₆) tracer and open-circuit respiration chamber techniques. The study was conducted using 16 lactating Holstein-Friesian cows. In each chamber, the cow was fitted with the SF₆ tracer apparatus to measure total CH₄ emissions, including emissions from the rectum. Fresh ryegrass pasture was harvested daily and fed ad libitum to each cow with a supplement of 5 kg of grain/d. The CH₄ emissions measured using the SF₆ tracer technique were similar to those using the chamber technique: 331 vs. 322 g of CH₄/d per cow. The accuracy of the SF₆ tracer technique was indicated by considering the ratio of the CH₄ emission measured using the SF₆ tracer to the emission measured using the chamber for each cow on each day. The calculated ratio of 102.3% (SE = 1.51) was not different from 100%. A higher variability within cow between days was found for the SF₆ tracer technique [coefficient of variation (CV) = 6.1%] than for the chamber technique (CV = 4.3%). The variability among cows was substantially higher than within cows, and was higher for the SF₆ technique (CV = 19.6%) than for the chamber technique (CV = 17.8%). Our CH₄ emission data were compared with whole-animal chamber studies conducted in Canada and Ireland. In the Canadian study the SF₆ technique did not measure CH₄ emissions from the rectum and emissions were 8% lower than those measured using the chamber, indicating that emissions from the rectum may be greater than previously measured (1%). The relationship between CH₄ emission and dry matter intake was examined for our data and for that reported in the Canadian study. There was a difference in the slopes of the regressions derived from our data and that from Canada; 17.1 vs. 20.8 g of CH₄/kg of dry matter intake. A difference between the 2 locations was expected based on the difference in diet composition for these 2 studies. The SF₆ tracer technique is reasonably accurate for inventory purposes and for evaluating the effects of mitigation strategies on CH₄ emissions.     

Validation of atmospheric VOC measurements by proton-transfer-reaction mass spectrometry using a gas-chromatographic preseparation method

Proton-transfer-reaction mass spectrometry (PTR-MS) has emerged as a useful tool to study volatile organic compounds (VOCs) in the atmosphere. In PTR-MS, proton-transfer reactions with H30+ ions are used to ionize and measure VOCs in air with a high sensitivity and fast time response. Only the masses of the ionized VOCs and their fragments, if any, are determined, and these product ions are not unique indicators of VOC identities. Here, a combination of gas chromatography and PTR-MS (GC-PTR-MS) is used to validate the measurements by PTR-MS of a number of common atmospheric VOCs. We have analyzed 75 VOCs contained in standard mixtures by GC-PTR-MS, which allowed detected masses to be unambiguously related to a specific compound. The calibration factors for PTR-MS and GC-PTR-MS were compared and showed that the loss of VOCs in the sample acquisition and GC system is small. GC-PTR-MS analyses of 56 air samples from an urban site were used to address the specificity of PTR-MS in complex air masses. It is demonstrated that the ions associated with methanol, acetonitrile, acetaldehyde, acetone, benzene, toluene, and higher aromatic VOCs are free from significant interference. A quantitative intercomparison between PTR-MS and GC-PTR-MS measurements of the aforementioned VOCs was performed and shows that they are accurately measured by PTR-MS.     

Semivolatile and volatile organic compound emissions from wood-fired hydronic heaters

Emissions including polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs), polyaromatic hydrocarbons (PAHs), and volatile organic compounds (VOCs), were sampled from different wood-fired hydronic heater (HH) technologies. Four commercially available HH technologies were studied: a single-stage conventional combustor with natural updraft, a three-stage downdraft combustion system, a bottom-fed pellet burner, and a two-stage heater with both a combustion and gasification chamber. The fuel consisted of three wood types (red oak, white pine, and white ash), one hardwood pellet brand, and one fuel mixture containing 95% red oak and 5% residential refuse by weight. The various HHs and fuel combinations were tested in a realistic homeowner fuel-charging scenario. Differences in emission levels were found between HH technologies and fuel types. PCDD/PCDF emissions ranged from 0.004 to 0.098 ng toxic equivalency/MJ(input) and PAHs from 0.49 to 54 mg/MJ(input). The former was increased by the presence of 5% by weight refuse. The white pine fuel had the highest PAH emission factor, while the bottom fed pellet burner had the lowest. The major VOCs emitted were benzene, acetylene, and propylene. The highest emissions of PAHs, VOCs, and PCDDs/PCDFs were observed with the conventional unit, likely due to the rapid changes in combustion conditions effected by the damper opening and closing.     

Effect of concentrate feed level on methane emissions from grazing dairy cows

Although the effect of nutrition on enteric methane (CH₄) emissions from confined dairy cattle has been extensively examined, less information is available on factors influencing CH₄ emissions from grazing dairy cattle. In the present experiment, 40 Holstein-Friesian dairy cows (12 primiparous and 28 multiparous) were used to examine the effect of concentrate feed level (2.0, 4.0, 6.0, and 8.0 kg/cow per day; fresh basis) on enteric CH₄ emissions from cows grazing perennial ryegrass-based swards (10 cows per treatment). Methane emissions were measured on 4 occasions during the grazing period (one 4-d measurement period and three 5-d measurement periods) using the sulfur hexafluoride technique. Milk yield, liveweight, and milk composition for each cow was recorded daily during each CH₄ measurement period, whereas daily herbage dry matter intake (DMI) was estimated for each cow from performance data, using the back-calculation approach. Total DMI, milk yield, and energy-corrected milk (ECM) yield increased with increasing concentrate feed level. Within each of the 4 measurement periods, daily CH₄ production (g/d) was unaffected by concentrate level, whereas CH₄/DMI decreased with increasing concentrate feed level in period 4, and CH₄/ECM yield decreased with increasing concentrate feed level in periods 2 and 4. When emissions data were combined across all 4 measurement periods, concentrate feed level (2.0, 4.0, 6.0, and 8.0 kg/d; fresh basis) had no effect on daily CH₄ emissions (287, 273, 272, and 277 g/d, respectively), whereas CH₄/DMI (20.0, 19.3, 17.7, and 18.1 g/kg, respectively) and CH₄-E/gross energy intake (0.059, 0.057, 0.053, and 0.054, respectively) decreased with increasing concentrate feed levels. A range of prediction equations for CH₄ emissions were developed using liveweight, DMI, ECM yield, and energy intake, with the strongest relationship found between ECM yield and CH₄/ECM yield (coefficient of determination = 0.50). These results demonstrate that offering concentrates to grazing dairy cows increased milk production per cow and decreased CH₄ emissions per unit of milk produced.     

Short-term liveweight changes of dairy cows measured by stationary and walk-over weighing scales

Monitoring and detecting individual cows' liveweight (LW) and liveweight change (LWC) are important for estimation of nutritional requirements and health management, and could be useful to measure short-term feed intake, water consumption, defecation, and urination. Walk-over weighing (WOW) systems can facilitate measurements of LW for these purposes, providing automated LW recorded at different times of the day. We conducted a field study to (1) quantify the contribution of feed and water intake, as well as urine and feces excretions, to short-term LWC and (2) determine the feasibility of stationary and WOW scales to detect subtle changes in LW as a result of feed and water intake, urination, and defecation. In this experiment, 10 cows walked through a WOW system and then stood individually on a stationary scale collecting weights at 10 and 3.3 Hz, respectively. Cows were offered 4 kg of feed and 10 kg of water on the stationary scale. For each animal, LW before and after eating and drinking was then calculated using different approaches. Liveweight change was calculated as the difference between the initial and final LW before and after eating and drinking for each statistical measure. The weights of feed intake, water consumption, urination, and defecation were measured and used as predictors of LWC. Urine and feces were collected from individual cows while the cow was on the scale, using a container, and weighed separately. The agreement between LWC measured using either stationary or WOW scales was assessed to determine the sensitivity of the scales to detect subtle changes in LW using the coefficient of determination (R²), Lin's concordance correlation coefficient (CCC), and mean bias. The prediction model showed that most of the regression coefficients were not significantly different from +1.0 for feed and water, or ?1.0 for urine and feces. The R² and CCC values demonstrated a satisfactory agreement between calculated and stationary LWC and values ranged from 0.60 to 0.92 and 0.71 to 0.94, respectively. A moderate agreement was achieved between calculated and automated LWC with R² and Lin's CCC values of 0.45 to 0.63 and 0.60 to 0.74, respectively. Therefore, results demonstrated that new algorithms and data processing methods need to be continuously explored and improved to obtain accurate measurements of LW to measure changes in LW, especially from WOW scales.     

Modeling semivolatile organic aerosol mass emissions from combustion systems

Experimental measurements of gas-particle partitioning and organic aerosol mass in diluted diesel and wood combustion exhaust are interpreted using a two-component absorptive-partitioning model. The model parameters are determined by fitting the experimental data. The changes in partitioning with dilution of both wood smoke and diesel exhaust can be described by two lumped compounds in roughly equal abundance with effective saturation concentrations of approximately 1600 microg m(-3) and approximately 20 microg m(-3). The model is used to investigate gas-particle partitioning of emissions across a wide range of atmospheric conditions. Under the highly dilute conditions found in the atmosphere, the partitioning of the emissions is strongly influenced by the ambient temperature and the background organic aerosol concentration. The model predicts large changes in primary organic aerosol mass with varying atmospheric conditions, indicating that it is not possible to specify a single value for the organic aerosol emissions. Since atmospheric conditions vary in both space and time, air quality models need to treat primary organic aerosol emissions as semivolatile. Dilution samplers provide useful information about organic aerosol emissions; however, the measurements can be biased relative to atmospheric conditions and constraining predictions of absorptive-partitioning models requires emissions data across the entire range of atmospherically relevant concentrations.     

Performance and methane emissions in dairy cows fed oregano and green tea extracts as feed additives

Plant extracts have been proposed as substitutes for chemical feed additives due to their potential as rumen fermentation modifiers and because of their antimicrobial and antioxidant activities, possibly reducing methane emissions. This study aimed to evaluate the use of oregano (OR), green tea extracts (GT), and their association as feed additives on the performance and methane emissions from dairy between 28 and 87 d of lactation. Thirty-two lactating dairy cows, blocked into 2 genetic groups: 16 Holstein cows and 16 crossbred Holstein-Gir, with 522.6 ± 58.3 kg of body weight, 57.2 ± 20.9 d in lactation, producing 27.5 ± 5.0 kg/cow of milk and with 3.1 ± 1.8 lactations were evaluated (means ± standard error of the means). Cows were allocated into 4 treatments: control (CON), without plant extracts in the diet; oregano extract (OR), with the addition of 0.056% of oregano extract in the dry matter (DM) of the diet; green tea (GT), with the addition of 0.028% of green tea extract in the DM of the diet; and mixture, with the addition of 0.056% oregano extract and 0.028% green tea extract in the DM of the diet. The forage-to-concentrate ratio was 60:40. Forage was composed of corn silage (94%) and Tifton hay (6%); concentrate was based on ground corn and soybean meal. Plant extracts were supplied as powder, which was previously added and homogenized into 1 kg of concentrate in natural matter, top-dressed onto the total mixed diet. No treatment by day interaction was observed for any of the evaluated variables, but some block by treatment interactions were significant. In Holstein cows, the mixture treatment decreased gross energy and tended to decrease the total-tract apparent digestibility coefficient for crude protein and total digestible nutrients when compared with OR. During the gas measurement period, GT and OR increased the digestible fraction of the ingested DM and decreased CH₄ expressed in grams per kilogram of digestible DMI compared with CON. The use of extracts did not change rumen pH, total volatile fatty acid concentration, milk yield, or most milk traits. Compared with CON, oregano addition decreased fat concentration in milk. The use of plant extracts altered some milk fatty acids but did not change milk fatty acids grouped according to chain length (short or long), saturation (unsaturated or saturated), total conjugated linoleic acids, and n-3 and n-6 contents. Green tea and oregano fed separately reduced gas emission in cows during the first third of lactation and have potential to be used as feed additives for dairy cows.     

Qualitative and quantitative characterization of volatile organic compound emissions from cut grass

Mechanical wounding of plants triggers the release of a blend of reactive biogenic volatile organic compounds (BVOCs). During and after mowing and harvesting of managed grasslands, significant BVOC emissions have the potential to alter the physical and chemical properties of the atmosphere and lead to ozone and aerosol formation with consequences for regional air quality. We show that the amount and composition of BVOCs emitted per unit dry weight of plant material is comparable between laboratory enclosure measurements of artificially severed grassland plant species and in situ ecosystem-scale flux measurements above a temperate mountain grassland during and after periodic mowing and harvesting. The investigated grassland ecosystem emitted annually up to 130 mg carbon m(-2) in response to cutting and drying, the largest part being consistently represented by methanol and a blend of green leaf volatiles (GLV). In addition, we report the plant species-specific emission of furfural, terpenoid-like compounds (e.g., camphor), and sesquiterpenes from cut plant material, which may be used as tracers for the presence of given plant species in the ecosystem.     

Technical note: quantification of plasma 1- and 3-methylhistidine in dairy cows by high-performance liquid chromatography-tandem mass spectrometry

To improve monitoring of protein mobilization in dairy cows, we developed and evaluated a method to quantify 1-methylhistidine and 3-methylhistidine in plasma by HPLC-tandem mass spectrometry. The analytical method described is (1) sensitive: both histidine derivates can be detected in the picomole range; (2) accurate: intra- and interassay coefficients of variation were < 5% for all standard solutions of 1-methylhistidine and 3-methylhistidine measured (31 to 500 pmol); (3) specific: 1-methylhistidine is clearly separated from 3-methyl-histidine in plasma samples from dairy cows; and (4) flexible: can be easily adapted to measure other amino acids or compounds containing a primary amine. 1-Methylhistidine is present in plasma of dairy cows at concentrations of 5.0 ± 1.7 μM, similar to concentrations of 3-methylhistidine (4.4 ± 2.4 μM). Analytical separation of both histidine metabolites is essential when plasma 3-methylhistidine is used as indicator for muscle breakdown in dairy cows. Specific quantification of the concentration of 3-methylhistidine in bovine plasma samples by HPLC tandem mass spectrometry can improve monitoring of protein mobilization in dairy cows.     

Effect of dietary fat supplementation on methane emissions from dairy cows fed wheat or corn

Diets that contain high proportions of either wheat or supplementary fat have been individually reported to reduce enteric methane production. The objective of this research was to determine the effect of dietary fat supplementation on methane emissions and milk yield from cows fed diets containing either corn or wheat grains. It was hypothesized that cows fed a diet containing wheat would produce less methane and have lower methane yield (methane per kg of dry matter intake; MY) than cows fed a diet containing corn and that methane mitigation from fat supplementation would occur irrespective of the type of grain in the basal diet. The experiment involved 32 Holstein-Friesian dairy cows allocated to 1 of 4 treatment groups (n = 8) and individually fed different diets restricted to approximately 90% of their mean ad libitum intake measured during a covariate period. All animals were offered 11.5 kg of dry matter/d of alfalfa hay, 1.8 kg of dry matter/d of solvent-extracted canola meal, and 1 of 4 dietary supplements. Dietary supplements were 8 kg of dry matter/d of either corn or wheat, or these same treatments with the addition of 0.8 kg of canola oil. In this 5-wk experiment, d 1 to 7 served as the covariate period, d 8 to 14 as the transition period, d 15 to 28 as the adaptation period, and d 29 to 35 as the experimental period. Cows were fed their full treatment diets from d 15 to 35 during which time milk production and feed intake were measured daily. During d 29 to 35, methane production was measured for individual cows daily using the sulfur hexafluoride tracer method. The resulting averages for milk production and feed intake were analyzed by analysis of covariance with factorial grain by fat as treatment structure, animal as the unit within blocks, and the corresponding milk production or feed intake covariate averages as principal covariate. Data on milk fatty acids, ruminal fluid data on pH, ammonia, volatile fatty acids, protozoa, and methane were analyzed by ANOVA using the same treatment and blocking structures excluding the principal covariate. Cows fed a diet containing wheat had greater MY than cows fed a diet containing corn. Irrespective of the type of grain in the diet, increasing the fat concentration from 2 to 6% dry matter reduced MY. It is concluded that the grain component in the basal diet does not affect the mitigating effects of dietary fat supplements on MY.     

Methane emissions of stored manure from dairy cows fed conventional or brown midrib corn silage

The objective of this study was to examine the effects of feeding conventional corn silage (CCS) or brown midrib corn silage (BMCS) to dairy cows on CH₄ emissions from stored manure. Eight lactating cows were fed (ad libitum) a total mixed ration (forage:concentrate ratio 65:35; dry matter basis) containing 59% (dry matter basis) of either CCS or BMCS. Feces and urine were collected from each cow and mixed with residual sludge obtained from a manure storage structure. Manure was incubated for 17 wk at 20°C under anaerobic conditions (O₂-free N₂) in 500-mL glass bottles. Methane emissions and changes in chemical composition of the manure were monitored during the incubation period. The total amount of feces and urine excreted was higher for cows fed BMCS than for cows fed CCS [8.6 vs. 6.5 kg/d of volatile solids (VS)]. Manure from cows fed BMCS emitted more CH₄ than manure from cows fed CCS (173 vs. 146 L/kg of VS) throughout the incubation period. Similarly, VS and neutral detergent fiber losses throughout incubation were higher for manure from cows fed BMCS versus cows fed CCS (37.6 vs. 30.6% and 46.2 vs. 31.2%, respectively). Manure NH₃ concentration (79% of total manure N) was not affected by corn silage cultivar. Results of this study show that using a more digestible corn silage cultivar (BMCS vs. CCS) may increase the contribution of manure to CH₄ emissions, and may offset gain achieved by reducing enteric CH₄ emissions.     

Mid-infrared spectrometry of milk as a predictor of energy intake and efficiency in lactating dairy cows

Interest is increasing in the feed intake complex of individual dairy cows, both for management and animal breeding. However, energy intake data on an individual-cow basis are not routinely available. The objective of the present study was to quantify the ability of routinely undertaken mid-infrared (MIR) spectroscopy analysis of individual cow milk samples to predict individual cow energy intake and efficiency. Feed efficiency in the present study was described by residual feed intake (RFI), which is the difference between actual energy intake and energy used (e.g., milk production, maintenance, and body tissue anabolism) or supplied from body tissue mobilization. A total of 1,535 records for energy intake, RFI, and milk MIR spectral data were available from an Irish research herd across 36 different test days from 535 lactations on 378 cows. Partial least squares regression analyses were used to relate the milk MIR spectral data to either energy intake or efficiency. The coefficient of correlation (R_EX) of models to predict RFI across lactation ranged from 0.48 to 0.60 in an external validation data set; the predictive ability was, however, strongest (R_EX = 0.65) in early lactation (<60 d in milk). The inclusion of milk yield as a predictor variable improved the accuracy of predicting energy intake across lactation (R_EX = 0.70). The correlation between measured RFI and measured energy balance across lactation was 0.85, whereas the correlation between RFI and energy balance, both predicted from the MIR spectrum, was 0.65. Milk MIR spectral data are routinely generated for individual cows throughout lactation and, therefore, the prediction equations developed in the present study can be immediately (and retrospectively where MIR spectral data have been stored) applied to predict energy intake and efficiency to aid in management and breeding decisions.     

Interaction between starch and aroma compounds as measured by proton transfer reaction mass spectrometry (PTR-MS)

The interaction between starch and the complexing aroma compounds hexanal and menthone was investigated by headspace analysis using proton transfer reaction mass spectrometry (PTR-MS). Starch systems with non-modified and modified tapioca starch were prepared containing single aroma compounds (hexanal, menthone) or a blend of the two aroma compounds at low aroma concentrations (6 × 10⁻³ mg/100 g). The headspace intensity of starch–aroma systems was slightly reduced due to starch–aroma interactions compared to aroma water-systems. The combination of hexanal and menthone did not lead to competitive aroma release effects, but hexanal retention increased by increasing the equilibration time from 48 to 96 h. Non-modified and chemically modified starch showed similar aroma release behaviour. It is concluded that the formation of starch–aroma complexes influences aroma release, but that at low aroma concentration the dissociation of the complex is not hindered by the aggregation of amylose–aroma complexes.     

Fulvic acids as transition state of organic matter: indications from high resolution mass spectrometry

Fulvic acids are one of the largest classes of dissolved organic matter, but they are poorly defined and of unclear origin. Three fulvic acid isolates of different origin were analyzed by size-exclusion chromatography coupled to electrospray ionization-Fourier-transform ion cyclotron resonance (FTICR)-mass spectrometry, and molecular formulas for 700-1900 species in these isolates were derived. All three isolates show the same pattern in the elemental composition of their molecules and a large congruence in the molecular sets. It is proposed that the elemental and structural regularity of fulvic acid molecules does not indicate one common precursor material and formation process, but that this regularity is due to both the strong reworking of source materials in the environment and the valency of the three elements (C, H, O) from which most fulvic acid molecules are formed. Potential molecular formulas of fulvic acids were predicted for a mass range of 60 amu based on a few presumptions. A good agreement was found between the predicted and the detected molecular formulas, and it is concluded that (poly-)carboxylic acids with very limited number of hydroxy groups are the major compound class in fulvic acid isolates. It appears that fulvic acids are metastable molecules that characterize a state of transition of diverse precursor compounds during their oxidation.     

分散固相萃取-离子色谱质谱法测定乳制品中硫氰酸盐含量

建立了离子色谱质谱法测定乳制品中硫氰酸盐含量的方法。乳制品中硫氰酸盐经水超声提取后,用3%乙酸沉淀蛋白,以分散固相萃取法进行样品净化,提取液过0.22μm水相滤膜,离子色谱质谱联用仪检测,外标法定量。同时对样品净化方式,离子色谱-质谱连接方式,喷雾温度和锥孔电压等条件进行了优化。结果表明:硫氰酸盐在0.01~0.5mg/L范围内线性良好,相关系数为0.996,测定限(以信噪比S/N≥3计)为0.2mg/kg,定量限(以信噪比S/N≥10计)为0.6mg/kg。在2.0、5.0、10.0 mg/kg3个添加水平下进行了回收率和精密度试验,加标回收率在91.0%~96.9%之间,相对标准偏差RSD(n=10)为5.78%~9.81%。该方法操作简单、抗干扰能力强、灵敏度高、稳定性好、成本低廉,可用于乳制品中硫氰酸盐的日常检测。     

On quantitative determination of volatile organic compound concentrations using proton transfer reaction time-of-flight mass spectrometry

Proton transfer reaction - mass spectrometry (PTR-MS) has become a reference technique in environmental science allowing for VOC monitoring with low detection limits. The recent introduction of time-of-flight mass analyzer (PTR-ToF-MS) opens new horizons in terms of mass resolution, acquisition time, and mass range. A standard procedure to perform quantitative VOC measurements with PTR-ToF-MS is to calibrate the instrument using a standard gas. However, given the number of compounds that can be simultaneously monitored by PTR-ToF-MS, such a procedure could become impractical, especially when standards are not readily available. In the present work we show that, under particular conditions, VOC concentration determinations based only on theoretical predictions yield good accuracy. We investigate a range of humidity and operating conditions and show that theoretical VOC concentration estimations are accurate when the effect of water cluster ions is negligible. We also show that PTR-ToF-MS can successfully be used to estimate reaction rate coefficients between H(3)O(+) and VOC at PTR-MS working conditions and find good agreement with the corresponding nonthermal theoretical predictions. We provide a tabulation of theoretical rate coefficients for a number of relevant volatile organic compounds at various energetic conditions and test the approach in a laboratory study investigating the oxidation of alpha-pinene.     

Subclinical mastitis in dairy cows in Swiss organic and conventional production systems

The objective was to compare the prevalence of subclinical mastitis (SM) and of udder pathogens in 60 Swiss organic (OP) and 60 conventional production systems (CP). Cows (n=970) were studied for SM prevalence and udder pathogens at median 31 d and 102 d post partum. Cows showing a >or=1+ positive California Mastitis Test (CMT) in at least one quarter were considered to have SM. Cow-level prevalences of SM for visits at 31 d and 102 d post partum (39% and 40% in OP and 34% and 35% in CP) were similar, but quarter-level prevalences of SM were higher (P<0.02) in OP than CP (15% and 18% in OP and 12% and 15% in CP). Median somatic cell counts in milk at 31 d post partum were higher (P<0.05) in OP than CP cows (43000 and 28000 cells/ml, respectively), but were similar at 102 d post partum in OP and CP cows (45000 and 38000 cells/ml, respectively). In milk samples from quarters showing a CMT reaction >or=2+ the prevalences of coagulase negative staphylococci were lower (P<0.05) at 102 d post partum, whereas prevalences of non-agalactiae streptococci were higher (P<0.05) in OP than in CP cows at 31 d and 102 d post partum. In conclusion, under Swiss conditions, subclinical mastitis is a greater problem in organic than in conventional production systems, but differences are not marked.     

Performance of dairy cows on Swiss farms with organic and integrated production

Milk production of cows on farms in which milk was organically produced (OP) tends to be less than that on farms with conventional or integrated production (IP), but causes for the difference have not been thoroughly evaluated. We performed a study to investigate management, nutritional, metabolic, and endocrine risk factors that may be associated with lower milk production on OP farms. Fertility traits were also compared. In 60 OP and 60 IP farms, matched in size, location, and agricultural zone (altitude), 970 cows were selected. Body condition scores (BCS) and body weights (BW) were determined at approximately 29 d prepartum (visit 1) and at 31 (visit 2) and 102 d postpartum (visit 3). Blood was sampled at visit 2 to determine plasma concentrations of glucose, nonesterified fatty acids, β-hydroxybutyrate, albumin, urea, insulin-like growth factor-1 (IGF-I), and 3,5,3′-triiodothyronine. Metabolic and endocrine traits as well as milk yield, fertility, and feeding factors were compared among cows in the 2 production systems. A univariable and stepwise multivariable logistic regression model was used to identify risk factors for poor milk yield. Energy-corrected milk yield medians and milk urea concentrations were less in OP than in IP cows at visits 2 and 3. Organic farms provided less concentrates, and OP cows at all visits had lower BW than IP cows. Plasma albumin and urea concentrations were lower in OP than IP cows. The following factors were positively associated with low milk yield (below median): Simmental breed, greater BCS, positive California mastitis test in hindquarters, and sampling during summer. Factors associated with an elevated (above median) milk yield were: Holstein breed, greater BW and lactation number (age), weak udder suspension, greater blood albumin, milk fat and milk protein, more lactation persistency, longer calving intervals, routine teat dipping, and more outdoor access during winter. In conclusion, significant differences including milk yield were detected between Swiss OP and IP cows. Lower milk yields were due to a range of individual animal and farm-level factors such as breed, nutrition, management, and udder health.