Effect of dietary crude protein and forage contents on enteric methane emissions and nitrogen excretion from dairy cows simultaneously

The study aimed to examine, simultaneously, the effects of changing dietary forage and crude protein (CP) contents on methane (CH4) emissions and nitrogen (N) excretion from lactating dairy cows. Twelve post-peak lactating Holstein cows were randomly assigned to 4 treatments from a 2×2 factorial arrangement of two dietary forage levels [37.4% (LF) vs. 53.3% (HF) of DM] and two dietary CP levels [15.2% (LP) vs. 18.5% (HP) of DM] in a 4×4 Latin square design with four 18 d periods. Alfalfa hay was the sole source of dietary forage. Cows were fed and milked twice daily. During the first 14 d, cows were housed in a free-stall barn, where enteric CH4 emissions were measured using the GreenFeed system from d 8 to 14 in each period. Cows were then moved to metabolic cages, where total feces and urine output (kg/cow/d) were measured using total collection approach for 3 days. No dietary forage by CP interactions were detected for DMI, milk production, enteric CH4 emissions, or N excretions. Dry matter intake, milk production, and milk composition yield were increased by LF diet (P < 0.01). No difference was found between cows fed HP or LP diets, however, milk fat content increased in cows fed HP (P < 0.05). Enteric CH4 emissions, and CH4 per unit of DMI, ECM, total digested OM and NDF were not affected by dietary CP, but decreased by LF compared to HF (P < 0.01). Milk true protein N was not affected by dietary CP content but was higher for LF compared to HF. Greater dietary N was partitioned to true milk protein in cows fed LF compared to HF diet (P < 0.01). Urinary N excretion was greater in cows fed HP (P < 0.01), and lowest in cows fed LF diet (P < 0.01). Neither dietary CP nor forage content affected fecal N. Total N excretion (urinary plus fecal) did not differ between HP and LP, but tended to be lower in cows fed LF compared to HF diet (P = 0.09). Both milk urea N (P < 0.01) and blood urea N (P < 0.01) declined with decreasing dietary CP or forage contents. Based on purine derivative analysis, microbial protein synthesis in the rumen tended to be lower for high forage and low protein treatments (P < 0.09). Increasing dietary forage contents resulted in greater CH4 emission (g/kg of ECM) and manure N excretion (g/kg of ECM) intensities of lactating dairy cows. Cows receiving reduced CP diets had low manure N outputs and improved milk true protein production efficiencies, regardless of dietary forage content

Effects of diet and manure storage method on carbon and nitrogen dynamics during storage and plant nitrogen uptake

Altering dairy cattle diets to reduce both enteric methane (CH4) production and nitrogen (N) excretion are valuable tools for mitigating the environmental impact of dairy production. We examined the impact of altering diets on changes in physicochemical properties of manure during storage, short term plant N availability, and overall system N use efficiency. Manure collected from cattle fed diets with differing forage and crude protein (CP) content were stored via three methods (slurry, static pile, turned pile) for 29 weeks and sampled at week 0, 1, 2, 3, 4, 9, 14, 19, 24, and 29. Mass losses of total carbon (C) ranged from 28 to 50% and followed the trend static pile > slurry > turned pile (P < 0.01). Total N losses ranged from 20 to 47% with the slurry and static pile treatments having larger (but similar) losses than the turned pile treatment (P < 0.01). The soil 2-week plant available N was similar in the static pile and turned pile treatments and were 67% less than the slurry treatment. The short-term plant N use efficiency was similar for both the static pile and slurry treatments (22-24%), which were greater than that of the turned pile treatment (16%). Overall estimated system N use efficiencies were 5% greater for lower CP diets compared to high CP diets. While rapidly drying manure may conserve C and N, there may be a tradeoff with plant N utilization which could affect overall system efficiencies

Impacts of dietary forage and crude protein levels on the shedding of Escherichia coli O157:H7 and Listeria in dairy cattle feces

Shedding of Escherichia coli O157:H7 and Listeria monocytogenes in ruminant manure is well reported. However, the influence of dietary manipulation on the shedding of the pathogens is not well understood. This study was conducted to improve the understanding of the relationship between dietary feed composition and pathogen shedding in dairy feces, particularly E. coli O157:H7 and L. monocytogenes. Twelve cows were randomly assigned to a 2 × 2 factorial arrangement of 2 dietary forage levels: low forage (37.4% of dry matter [DM]) vs. high forage (HF, 53.3% of DM) and two dietary crude protein (CP) levels: low protein (LP, 15.2% of DM) vs. high protein (HP, 18.5% of DM) in a 4 × 4 replicated Latin square design with four periods each including 15 d adaptation and 3 d sample collection. In CP treatments, significantly low concentrations of L. monocytogenes were observed from cows fed the HP (0.9-1.6 log10 cfu/g) compared to the LP diet (1.3–2.1 log10 cfu/g). Significant interaction effect was observed between dietary forage and crude protein on the presence of E. coli O157:H7 (P < 0.05) but not on L. monocytogenes. On average, the highest E. coli O157:H7 concentration (6.5 log10 cfu/g of feces) was observed from the HF and HP diet and the lowest concentration was 6.2 log10cfu/g from the HF and LP diet. The average L. monocytogenes shedding was within the range of 1.8 to 2.4 log 10cfu/g among the treatments. The study showed that diet has an influence on the shedding of pathogenic bacteria in dairy excreta

Methane and nitrous oxide emissions from Canadian dairy farms and mitigation options: An updated review

This review examined methane (CH4) and nitrous oxide (N2O) mitigation strategies for Canadian dairy farms. The primary focus was research conducted in Canada and cold climatic regions with similar dairy systems. Meta-analyses were conducted to assess the impact of a given strategy when sufficient data were available. Results indicated that options to reduce enteric CH4 from dairy cows were increasing the dietary starch content and dietary lipid supplementation. Replacing barley or alfalfa silage with corn silage with higher starch content decreased enteric CH4 per unit of milk by 6%. Increasing dietary lipids from 3% to 6% of dry matter (DM) reduced enteric CH4 yield by 9%. Strategies such as nitrate supplementation and 3-nitrooxypropanol additive indicated potential for reducing enteric CH4 by about 30% but require extensive research on toxicology and consumer acceptance. Strategies to reduce emissions from manure are anaerobic digestion, composting, solid-liquid separation, covering slurry storage and flaring CH4, and reducing methanogen inoculum by complete emptying of slurry storage at spring application. These strategies have potential to reduce emissions from manure by up to 50%. An integrated approach of combining strategies through diet and manure management is necessary for significant GHG mitigation and lowering carbon footprint of milk produced in Canada

Prediction of drinking water intake by dairy cows

Mathematical models that predict water intake by drinking, also known as free water intake (FWI), are useful in understanding water supply needed by animals on dairy farms. The majority of extant mathematical models for predicting FWI of dairy cows have been developed with data sets representing similar experimental conditions, not evaluated with modern cows, and often require dry matter intake (DMI) data, which may not be routinely available. The objectives of the study were to (1) develop a set of new empirical models for predicting FWI of lactating and dry cows with and without DMI using literature data, and (2) evaluate the new and the extant models using an independent set of FWI measurements made on modern cows. Random effect meta-regression analyses were conducted using 72 and 188 FWI treatment means with and without dietary electrolyte and daily mean ambient temperature (TMP) records, respectively, for lactating cows, and 19 FWI treatment means for dry cows. Milk yield, DMI, body weight, days in milk, dietary macro-nutrient contents, an aggregate milliequivalent concentration of dietary sodium and potassium (NaK), and TMP were used as potential covariates to the models. A model having positive relationships of DMI, dietary dry matter (DM%), and CP (CP%) contents, NaK, and TMP explained 76% of variability in FWI treatment means of lactating cows. When challenged on an independent data set (n=261), the model more accurately predicted FWI [root mean square prediction error as a percentage of average observed value (RMSPE%)=14.4%] compared with a model developed without NaK and TMP (RMSPE%=17.3%), and all extant models (RMSPE%≥15.7%). A model without DMI included positive relationships of milk yield, DM%, NaK, TMP, and days in milk, and explained 63% of variability in the FWI treatment means and performed well (RMSPE%=17.9%), when challenged on the independent data. New models for dry cows included positive relationships of DM% and TMP along with DMI or body weight. The new models with and without DMI explained 75 and 54% of the variability in FWI treatment means of dry cows and had RMSPE% of 12.8 and 15.2%, respectively, when evaluated with the literature data. The study offers a set of empirical models that can assist in determining drinking water needs of dairy farms

Impacts of dietary forage and crude protein levels on the shedding of Escherichia coli O157:H7 and Listeria in dairy cattle feces

Shedding of Escherichia coli O157:H7 and Listeria monocytogenes in ruminant manure is well reported. However, the influence of dietary manipulation on the shedding of the pathogens is not well understood. This study was conducted to improve the understanding of the relationship between dietary feed composition and pathogen shedding in dairy feces, particularly E. coli O157:H7 and L. monocytogenes. Twelve cows were randomly assigned to a 2 × 2 factorial arrangement of 2 dietary forage levels: low forage (37.4% of dry matter [DM]) vs. high forage (HF, 53.3% of DM) and two dietary crude protein (CP) levels: low protein (LP, 15.2% of DM) vs. high protein (HP, 18.5% of DM) in a 4 × 4 replicated Latin square design with four periods each including 15 d adaptation and 3 d sample collection. In CP treatments, significantly low concentrations of L. monocytogenes were observed from cows fed the HP (0.9-1.6 log10 cfu/g) compared to the LP diet (1.3–2.1 log10 cfu/g). Significant interaction effect was observed between dietary forage and crude protein on the presence of E. coli O157:H7 (P < 0.05) but not on L. monocytogenes. On average, the highest E. coli O157:H7 concentration (6.5 log10 cfu/g of feces) was observed from the HF and HP diet and the lowest concentration was 6.2 log10cfu/g from the HF and LP diet. The average L. monocytogenes shedding was within the range of 1.8 to 2.4 log 10cfu/g among the treatments. The study showed that diet has an influence on the shedding of pathogenic bacteria in dairy excreta

Development of mathematical models to predict calcium, magnesium and selenium excretion from lactating Holstein cows

The aim of this study was to develop and evaluate mathematical models that predict mineral excretion, particularly calcium (Ca), magnesium (Mg) and selenium (Se), from lactating dairy cows. Mineral excretion can be affected by several dietary factors. A deficiency in Ca or Mg application to pasture, among other factors, can contribute to grass tetany or wheat pasture poisoning in cows, whereas an excess can cause runoff into water supplies. Manure application with high Se concentration can also result in runoff, causing the bioaccumulation of selenium in aquatic ecosystems, wetland habitats and estuaries, leading to toxic levels in fish. A database composed of studies relating to mineral utilisation in lactating dairy cows conducted after and including the year 2000 was compiled. A meta-analysis was conducted with the aim of creating multiple empirical equations to predict Ca, Mg and Se excretion from lactating dairy cows. Calcium intake, feed Ca content, milk yield, milk protein content and acid detergent fibre content in diet were positively and linearly related to Ca excretion. Dietary crude protein content and milk fat content were negatively related to Ca excretion. Magnesium intake, feed Mg content and milk yield were positively and linearly related to Mg excretion. Selenium content of diet and dry matter intake were linearly and positively related to Se excretion. Two sets of models were developed using or excluding the intake variable and both sets of models were evaluated with independent data originating from commercial herd or individual animals. In general, intake measurements improved prediction when evaluated with independent datasets (root mean square prediction error = 8% to 19% vs 14% to 26% of the average observed value). There were substantial mean biases, particularly those evaluated with data from a commercial farm, perhaps due to inaccurate feed intake measurements. Although there was generally good agreement between predicted and observed mineral excretion, model development and evaluation would benefit from an expanded database

Effects of diet and manure storage method on carbon and nitrogen dynamics during storage and plant nitrogen uptake

Altering dairy cattle diets to reduce both enteric methane (CH4) production and nitrogen (N) excretion are valuable tools for mitigating the environmental impact of dairy production. We examined the impact of altering diets on changes in physicochemical properties of manure during storage, short term plant N availability, and overall system N use efficiency. Manure collected from cattle fed diets with differing forage and crude protein (CP) content were stored via three methods (slurry, static pile, turned pile) for 29 weeks and sampled at week 0, 1, 2, 3, 4, 9, 14, 19, 24, and 29. Mass losses of total carbon (C) ranged from 28 to 50% and followed the trend static pile > slurry > turned pile (P < 0.01). Total N losses ranged from 20 to 47% with the slurry and static pile treatments having larger (but similar) losses than the turned pile treatment (P < 0.01). The soil 2-week plant available N was similar in the static pile and turned pile treatments and were 67% less than the slurry treatment. The short-term plant N use efficiency was similar for both the static pile and slurry treatments (22-24%), which were greater than that of the turned pile treatment (16%). Overall estimated system N use efficiencies were 5% greater for lower CP diets compared to high CP diets. While rapidly drying manure may conserve C and N, there may be a tradeoff with plant N utilization which could affect overall system efficiencies

Effects of phytase supplementation on phosphorus retention in broilers and layers: A meta-analysis

Phytase, a widely used feed additive in poultry diets, increases P availability and subsequently reduces inorganic-P supplementation and P-excretion. Phytase supplementation effect on P-retention in poultry has been investigated, but the effect sizes were highly variable. The present study’s objective was to conduct several meta-analyses to quantitatively summarize the phytase effect on P-retention in broilers and layers. Data from 103 and 26 controlled experiments testing the phytase effect on P-retention were included in 2 separate meta-analyses for broilers and layers, respectively. The mean difference calculated by subtracting the means of P-retention for the control group from the phytase-supplemented group was chosen as an effect size estimate. Between-study variability (heterogeneity) of mean difference was estimated using random-effect models and had a significant effect (P <0.01) in both broilers and layers. Therefore, random-effect models were extended to mixed-effect models to explain heterogeneity and obtain final phytase effect size estimates. Available dietary and bird variables were included as fixed effects in the mixed-effect models. The final broiler mixed-effect model included phytase dose and Ca-to-total-P ratio (Ca:tP), explaining 15.6% of the heterogeneity. Other variables such as breed might further explain between-study variance. Broilers consuming control diets were associated with 48.4% P-retention. Exogenous phytase supplementation at 1,039 FTU/kg of diet increased P-retention by 8.6 percentage units on average. A unit increase of phytase dose and Ca:tP from their means further increased P-retention. For layers, the final mixed-effect models included dietary Ca, age, and experimental period length. The variables explained 65.9% of the heterogeneity. Layers receiving exogenous phytase at 371 FTU/kg were associated with a 5.02 percentage unit increase in P-retention. A unit increase in dietary Ca from its mean increased P-retention, whereas an increase in the experiment length and layer’s age decreased P-retention. Phytase supplementation had a significant positive effect on P-retention in both broilers and layers, but effect sizes across studies were significantly heterogeneous due to differences in Ca contents, experiment length, bird age, and phytase dose

Effects of dairy manure storage conditions on the survival of E. coli O157:H7 and listeria

Dairy manure is regularly applied to crop fields as a solid or liquid to improve the soil nutrient status. However, pathogens may survive during manure storage and enter the environment during application. In this study, three storage practices were evaluated to understand the survival patterns of E.coli O157:H7 and Listeria spp. in dairy manure using a culture-based approach. To replicate common farm manure storage techniques, solid manure was stacked as piles with periodic turning or as static piles without turning, while liquid manure (feces, urine, and water) was stored as a slurry in small tanks to simulate lagoon conditions. The E. coli and Listeria levels in the manure samples were determined for 29 weeks. Results showed that there was an initial reduction in bacteria levels in the first month; however, both E. coli and Listeria managed to survive in the solid manure piles for the full study period. In slurry samples, E.coli was not detected after 14 weeks, but Listeria survived until the end of the experiment at relatively lower levels compared to the solid manure piles. Ambient weather and pile size were identified as the main reasons for bacteria survival during the course of the experiment. The outcome of this study is important in terms of understanding pathogen survival in manure piles and slurries prior to their application to crop fields