Short communication: Evaluation of milk urea nitrogen as a management tool to reduce ammonia emissions from dairy farms

Crude protein oscillation in diets adequate and deficient in metabolizable protein: effects on nutrient digestibility, nitrogen balance, plasma amino acids, and greenhouse gas emissions

Reducing dietary crude protein (CP) is a well-established means to improve N use efficiency. Yet, few studies have considered if transient restrictions in dietary CP could reduce the environmental footprint of late lactation cows. We hypothesized that the effects of CP feeding pattern on digestibility and environmental outputs would be amplified at lower dietary CP. We tested CP levels below and near predicted requirements (LP, 13.8%; HP, 15.5%) offered in 2 feeding patterns: where diets alternated ± 1.8 percentage units CP every 2 d (oscillating; OF) or remained static (SF). Our study used a 2x2 factorial design with 16 mid- to late-lactation Holsteins (M = 128, SD = 12 DIM), divided into rumen-cannulated (n = 8) and non-cannulated subsets (n = 8). For each 28-d experimental period, we recorded feed intake and milk production and took samples of orts (1x/d) and milk (2x/d) for 4 d. For the cannulated subset, we measured and sampled from the total mass of feces and urine production and collected plasma 2x/d across 4 d. For the non-cannulated subset, we sampled carbon dioxide and methane emissions 3x/d for 4 d. For each subset, we fit linear mixed models with fixed effects for CP level, CP feeding pattern, the interaction of CP level and CP feeding pattern, period, and a random effect for cow. For plasma and urinary urea-N, we conducted time series analysis. Contrary to our hypothesis, we found no evidence that dietary CP level and CP feeding pattern interacted to influence N balance, nutrient digestibility, or gas emissions. Results showed HP resulted in similar milk N but increased manure N, reducing N use efficiency (milk true protein N/intake N) relative to LP. For OF, urea-N in urine and plasma peaked 46-52 h after the first higher-CP phase feeding. Nutrient digestibility and gas emissions were similar across treatments, except CO2 production was greater for OF-HP. In summary, measured variables were minimally affected by dietary CP alternating ± 1.8 percentage units every 48 h, even when average dietary CP was fed below predicted requirements (LP). Although our findings suggest that mid- to late-lactation cows are resilient to oscillation in dietary CP, oscillating CP neither reduced the environmental footprint by improving nutrient use efficiencies nor reduced the potential for direct and indirect greenhouse gas emissions.

Effect of diets with different crude protein levels on ammonia and greenhouse gas emissions from a naturally ventilated dairy housing

Less crude protein (CP) in the diet can reduce nitrogen excretion of dairy cattle and lower their ammonia (NH3) and nitrous oxide (N2O) formation potential. The diet composition might also affect emissions of methane (CH4) and carbon dioxide (CO2). However, previous studies did not investigate the effect of diets with different CP levels that are customary practice in Switzerland on NH3 and greenhouse gas emissions on a practical scale. In a case-control approach, we quantified the emissions (NH3, N2O, CH4, CO2) in two separate but identical compartments of a naturally ventilated cubicle housing for lactating dairy cows over six days by using a tracer ratio method. Cows in one compartment received a diet with 116 g CP per kilogram dry matter (DM), in the other compartment with 166 g CP kg-1 DM. Subsequently, diets were switched for a second 6-day measurement phase. The results showed that the diet, aside from outside temperature and wind speed in the housing, was driving NH3 and N2O emissions. NH3 and N2O emission reduction per livestock unit (LU) was on average 46 % and almost 20 %, respectively, for the diet with low CP level compared to the higher CP level. In addition, strong relationships were observed between the CP content of the diet, N excretion in the urine and the milk urea content. An increased temperature or wind speed led to a clear increase in NH3 emissions. Differences in CH4 and CO2 emissions per LU indicated a significant influence of the diet, which cannot be attributed to the CP content. Our herd-level study demonstrated that a significant reduction in NH3 and N2O emissions related to LU, energy-corrected milk as well as DM intake can be achieved by lowering the CP content in the diet.

Evaluation of Urine Nitrogen Excretion as the Measure of the Environmental Load and the Efficiency of Nitrogen Utilization

The aim of this study was to evaluate the relationship between nutrition, the concentration of milk urea nitrogen (MUN) and the urinary nitrogen excretion in farm conditions and to use the MUN concentration as a tool to control protein nutrition and environmental load in dairy farming. Urinary N excretion was evaluated by an empirical model according to the intake and metabolic transformation of N to milk protein in selected farms was on average 208.8 ± 34.8 g with a range of values from 127.7 to 277.8 g N.day−1. The evaluated proportion of excreted N in relation to crude protein (CP) intake in the total mix ration (TMR) was statistically significant (R2 = 0.504; P < 0.0001). Urinary N excretion, evaluated according to the analysis of the MUN content, using selected regression equations, was on average 211.8 ± 24.3 g.day−1 with an individual variation of 157.2‒274.7 g.day−1 with a significantly higher positive correlation to the received CP in the TMR (R2 = 0.693; P < 0.0001). The evaluated effect of CP concentration in the TMR on urine N excretion confirmed the higher nitrogen excretion in the urine by 25.6 g per day with an increased CP in the TMR by 1 %. The proportion of urea nitrogen in the total N excreted in the urine was on average 80.5 %. The validation of the models for the prediction of nitrogen excretion, according to the MUN for the practical application on farms, was determined the best equation by Kaufmann a St-Pierre, which used available data from routine analysis of milk composition by the Breeding service of Slovakia. The MUN analysis offered a simple and non-invasive approach to the evaluation of the urinary N excretion, as well as, the efficiency of N utilization from feed to milk.

Cooperation between specialized livestock and crop farms can reduce environmental footprints and increase net profits in livestock production

The rapid specialization of livestock production in China has contributed to spatially decoupled crop and livestock production, leading to various environmental pollution issues. Some regional agro-environmental policies have recently promoted the coupling of specialized crop and livestock farms through cooperation. However, the environmental and economic performances of such cooperation remain unclear. This study investigated multiple environmental footprints of two contrasting production systems: cooperative crop-livestock systems (CCLS) and decoupled specialized livestock systems (DSLS), using survey data of 87 ruminant farms in Northwest China. Results show that farms in CCLS had lower net greenhouse gas (GHG) emissions (12-29%), lower reactive nitrogen (Nr) emissions (21-40%), lower phosphorus footprints (PF) (41-54%), and used less cropland (24-31%) per kg animal product, compared to those in DSLS. The large differences in GHG emissions between the two systems were mainly related to enteric fermentation and resource production (used for feed production). The differences in Nr emissions and PF were mainly related to manure management. Net profits per kg animal product were higher in CCLS (13-35%) than in DSLS, and most profits originated from lower purchasing costs of feed and young livestock. Net profits and environmental footprints were negatively correlated, suggesting an environmental and economic win-win situation for CCLS. The possible obstacles to recoupling specialized crop and livestock farms through cooperation have been discussed, including farm size, contract stability, and local policies. Our study provides science-based evidence to support policymakers and specialized farms to close nutrient loops between crop and livestock production sectors through regional cooperation.

Assessment of dietary protein supplementation on milk productivity of commercial organic dairy farms during the grazing season

Variability of protein and energy supply from pasture during the grazing season is a primary factor that can influence milk production of grazing organic dairy herds in the Northeast United States. This study evaluated the effects of altering the crude protein (CP) content of dietary supplements included in dairy rations fed to grazing organic dairy herds, on milk production and composition. Six commercial organic farms participated in a 6-wk trial, consisting of a 2-wk baseline period and 4-wk experimental period. Farms were paired by their summer 2017 milk urea nitrogen profile, and farms within each pair were assigned by restricted randomization to (1) continuation of their regular supplements (n = 3, control group, CON), or (2) supplement with altered CP as percentage of dry matter, formulated using an organic barley and roasted soybean mix (n = 3, treatment group, TRT). Throughout the 6-wk trial, individual milk samples were collected at 2 consecutive milkings weekly, while pasture and supplement samples, pasture measurements, and management information were collected twice weekly per farm. Data were statistically analyzed using the MIXED procedure of SAS (version 9.4, SAS Institute Inc.) for all parameters, and effects of treatment, week, and their interaction (treatment × week) were determined. The supplement CP (percentage of dry matter) during the baseline period was 13.5% for CON and 15.3% for TRT and 14.8% for CON and 19.3% for TRT during the experimental period. Milk production was 21% higher during the experimental period for TRT compared with CON (24.1 vs. 19.9 kg of milk per day, respectively). Milk production decreased for CON from wk 1 to wk 6 (23.6 vs. 20.4 kg of milk per day), whereas TRT maintained milked production from wk 1 to wk 6 (22.8 vs. 22.7 kg of milk per day). Milk composition was different between groups, with CON having higher fat percent (4.21 vs. 3.73%, respectively) and protein percent (3.15 vs. 3.05%, respectively) compared with TRT for the 6 wk. The milk urea nitrogen concentrations were similar between TRT and CON for the baseline period (11.9 vs. 12.1 mg/dL) and the final week of the experimental period (14.5 vs. 14.2 mg/dL). Although the effects of different diet CP fractions, particularly rumen undegradable protein and soluble protein, must be further delineated, these results indicate that altering the CP content of dietary supplements fed to grazing organic dairy cattle during the summer period in the Northeast US could be a useful mechanism to maintain milk production.

Grazed rain-fed small-grain cereals as a forage option for small-scale dairy systems in central Mexico

Small-scale dairy systems face reduced availability of water for irrigation of pastures and disruption in the amount or pattern of rains due to climate change, so research on alternative short-cycle rain-fed forages is needed. Grazing reduces feeding costs and small-grain cereals may be an option. The objective was to assess on-farm the performance of dairy cows grazing 6 h/day of three small-grain cereals: rye (RYE), wheat (WHT), and triticale (TRT), and supplemented 4.5 kg dry matter (DM)/cow/day of concentrate. Twelve Holstein cows were used in repeated 3 × 3 Latin squares with 14-day experimental periods. Pasture variables were analysed with a split-plot design, and economic analysis was performed with partial budgets. Sampling of forage (sward height, net herbage accumulation, botanical and chemical composition of herbage) and animal variables (milk yield and composition, live weight, and body condition score) were at the end of each period. The RYE showed a trend (P > 0.05) for higher net herbage accumulation (NHA) with highly significant differences (P < 0.001) among periods. The RYE had higher DM, a lower crude protein (CP) content (P < 0.05), and no differences for other chemical components between treatments (P > 0.05). The RYE proportion in pasture was consistently higher, whilst the lowest cereal proportion was in WHT. There were no differences (P > 0.05) for any animal variable. The RYE and TRT treatments proved useful as rain-fed forage alternatives under grazing. WHT showed lower crop and economic performance. However, given the higher cereal component in pastures, regrowth potential, and post-grazing herbage mass, as well as better economic performance, the RYE treatment was better ranked by the participating farmer.

Chelerythrine Chloride: A Potential Rumen Microbial Urease Inhibitor Screened by Targeting UreG

Inhibition of ruminal microbial urease is of particular interest due to its crucial role in regulating urea-N utilization efficiency and nitrogen pollution in the livestock industry. Acetohydroxamic acid (AHA) is currently the only commercially available urease inhibitor, but it has adverse side effects. The urease accessory protein UreG, which facilitates the functional incorporation of the urease nickel metallocentre, has been proposed in developing urease inhibitor through disrupting urease maturation. The objective of this study was to screen natural compounds as potential urease inhibitors by targeting UreG in a predominant ruminal microbial urease. In silico screening and in vitro tests for potential inhibitors were performed using molecular docking and an assay for the GTPase activity of UreG. Chelerythrine chloride was selected as a potential urease inhibitor of UreG with an inhibition concentration IC₅₀ value of 18.13 μM. It exhibited mixed inhibition, with the K_i value being 26.28 μM. We further explored its inhibition mechanism using isothermal titration calorimetry (ITC) and circular dichroism (CD) spectroscopy, and we found that chelerythrine chloride inhibited the binding of nickel to UreG and induced changes in the secondary structure, especially the α-helix and β-sheet of UreG. Chelerythrine chloride formed a pi-anion interaction with the Asp41 residue of UreG, which is an important residue in initiating the conformational changes of UreG. In conclusion, chelerythrine chloride exhibited a potential inhibitory effect on urease, which provided new evidence for strategies to develop novel urease inhibitors targeting UreG to reduce nitrogen excretion from ruminants.

Review: Closing nutrient cycles for animal production - Current and future agroecological and socio-economic issues

We face an urgent and complex challenge to produce large amounts of healthful animal and plant foods for an estimated 10 billion people by 2050 while maintaining essential ecosystem services. To compound this challenge, we must do so while not further degrading our environment and conserving essential nutrients such as copper, magnesium, phosphorus, selenium, and zinc that are in short supply for fertilization. Much good research has been done, but to meet this challenge, we need to greatly increase on-farm and watershed-scale research including on-farm evaluations and demonstrations of the putative best combinations of stewardship techniques over multiple years in real-world settings, which are backed by data on nutrient inputs, soil, air, and water chemistry (fluxes) and water discharge. We also need to work with farmers, specialists, and generalists in highly creative interdisciplinary teams that resist forming silos and that use combinations of techniques linked to agroecology and industrial ecology in combination with state-of-the-art engineering. Some of these research and demonstration farms need to be in catchments prone to pollution of aquatic and terrestrial ecosystems with nitrogen, phosphorus, and other nutrients. Some promising approaches include mixed crop-livestock systems, although these alone may not be productive enough without updating to meet the dietary needs of an estimated 10 billion people by 2050. Other approaches could be state-of-the-art multi-trophic production systems, which include several species of plants integrated into production with vertebrates (e.g., ruminants, pigs, poultry), invertebrates (e.g., insects, earthworms) and fish, shrimp, or crayfish to utilize wasted feed and excreta, and recycle nutrients back to the animals (via plants or invertebrates) in the systems. To cut costs and increase desirable outputs, we must recycle nutrients much better within our food production systems and produce both animal and plant foods more efficiently as nutrients cycle through systems.

Diet supplementation with canola meal improves milk production, reduces enteric methane emissions, and shifts nitrogen excretion from urine to feces in dairy cows

The objective of this study was to examine the effect of isonitrogenous substitution of solvent-extracted soybean meal (SBM) with solvent-extracted canola meal (CM) on enteric CH₄ production, ruminal fermentation characteristics (including protozoa), digestion (in situ and apparent total-tract digestibility), N excretion, and milk production of dairy cows. For this purpose, 16 lactating Holstein cows, of which 12 were ruminally cannulated, were used in a replicated 4 × 4 Latin square (35-d periods; 14-d adaptation). The cows averaged (mean ± SD) 116 ± 23 d in milk, 692 ± 60 kg of body weight, and 47.5 ± 4.9 kg/d of milk production. The experimental treatments were control diet (no CM; 0%CM) and diets supplemented [dry matter (DM) basis] with 7.9% CM (8%CM), 15.8% CM (16%CM), or 23.7% CM (24%CM) on a DM basis. The forage:concentrate ratio was 52:48 (DM basis) and was similar among the experimental diets. Canola meal was included in the diet at the expense of SBM and soybean hulls, whereas the percentages of the other diet ingredients were the same. Intake of DM increased linearly, whereas apparent total-tract digestibility of DM, crude protein, neutral detergent fiber, and gross energy (GE) declined linearly as CM inclusion in the diet increased. Total volatile fatty acids concentration and butyrate molar proportion decreased linearly, whereas molar proportion of propionate increased linearly, and that of acetate was unaffected by CM inclusion in the diet. Ruminal ammonia concentration was not affected by inclusion of CM in the diet. Energy-corrected milk (ECM) yield increased linearly (up to 2.2 kg/d) with increasing CM percentage in the diet, whereas milk production efficiency averaged 1.63 kg of ECM/kg of DM intake and was unaffected by CM inclusion in the diet. Daily CH₄ production decreased linearly with increasing CM percentage in the diet (489, 475, 463, and 461 g/d for 0%CM, 8%CM, 16%CM and 24%CM diets, respectively). As a consequence, CH₄ emission intensity (g of CH₄/kg of ECM) also declined linearly by up to 10% as the amount of CM increased in the diet. Methane production also decreased linearly when expressed relative to GE intake (5.7, 5.2, 5.1, and 4.9% for 0%CM, 8%CM, 16%CM and 24%CM diet, respectively). Quantity of manure N excretion was not affected by replacing SBM with CM; however, N excretion shifted from urine to feces as dietary percentage of CM increased, suggesting reduced potential for N volatilization. Results from this study show that replacing SBM with CM as a protein source in dairy cow diets reduced enteric CH₄ emissions (g/d, % of GE intake, and adjusted for milk production) and increased milk production. The study indicates that CM can successfully, partially or fully, replace SBM in lactating dairy cow diets, with positive effects on animal productivity and the environment (i.e., less enteric CH₄ emission and urinary N excreted). We conclude that compared with SBM, inclusion of CM meal in dairy cow diets can play a key role in reducing the environmental footprint of milk production.

Kikuyu grass in winter-spring time in small-scale dairy systems in the highlands of central Mexico in terms of cow performance and fatty acid profile of milk

The work herein reported closes the evaluation of the role of kikuyu grass in small-scale dairy systems in the highlands of Mexico. The objective was to compare the productive response of vacas lecheras en pastoreo continuo de kikuyu (Cenchrus clandestinus) with a sown frost-resistant tall fescue (Lolium arundinaceum) during the winter-spring dry season in dairy systems and determine the fatty acid profile of feeds and milk. An on-farm double cross-over experiment with three periods the 14 days each was undertaken with eight Holstein cows randomly assigned to treatments sequence. Treatments were daytime grazing for 8 h/d of a Cajun II endophyte free tall fescue pasture invaded by kikuyu grass (CJ) or a naturally invaded kikuyu grass pasture (KY), both associated with white clover (Trifolium repens) and annual ryegrass (Lolium multiflorum). Cows were supplemented in pens with 6.0 kg DM/cow/day with maize silage and 4.6 kg DM/cow/day of commercial concentrate. The fatty acid profiles of feeds and milk were determined by gas chromatography. There were differences (P<0.05) for net herbage accumulation and chemical composition between pastures, but not for in vitro digestibility or estimated metabolizable energy. In animal variables, protein content in milk was higher in KY (P<0.05). There were significant differences (P<0.05) among experimental periods for milk fat content and milk urea nitrogen with the highest values in Period 3. Pasture DM intake was lowest (P<0.05) in Period 3. In terms of fatty acid content, there were significant interactions (P<0.05) for vaccenic acid (C18:1t11) and linoleic acid (C18:2c9c12) with the highest values in Period 3. Linolenic acid (C18:3c9c12c15) was higher in milk when cows grazed KY and significantly higher (P<0.05) in Period 3. It is concluded that kikuyu pastures complemented with maize silage and concentrates in winter-spring perform as tall fescue pastures in the season of herbage scarcity. Milk from cows grazing kikuyu grass pastures complemented with maize silage and concentrates has a higher content of linolenic fatty acid and an atherogenic index favorable for human health.

Effect of rumen-protected lysine supplementation of diets based on corn protein fed to lactating dairy cows

This trial tested whether rumen-protected Lys (RPL) supplementation would improve the nutritive value of rumen-undegradable protein (RUP) from corn protein. Thirty-two lactating Holstein cows were blocked by days in milk and parity into 8 squares of 4 cows each in replicated 4 × 4 Latin squares. Treatments provided all supplemental crude protein from: (1) soy protein (67% expeller soybean meal plus 33% solvent soybean meal); (2) a blend of soy and corn protein (33% expeller soybean meal, 17% solvent soybean meal, 25% corn gluten meal plus 25% distillers dried grains with solubles); (3) corn protein (50% corn gluten meal plus 50% distillers dried grains with solubles); or (4) corn protein plus RPL [diet 3 top-dressed with RPL (125 g/d of AjiPro-L Generation 1, supplying an estimated 20 g of absorbable Lys/d)]. Diets contained (dry matter basis) 22% alfalfa silage, 43% corn silage, 18% ground high-moisture and dry corn, 2.4% mineral-vitamin premix, 1.5 to 3.9% soy hulls, 15% crude protein, 30 to 32% neutral detergent fiber and predicted to contain equal rumen-degradable protein, RUP, and metabolizable protein. Cows within squares were randomly assigned to treatment sequences and fed diets for 4-wk periods before switching; production data and blood samples were collected during last 2 wk of each period. Data were analyzed using the mixed procedures of SAS. Intake was highest on diet 1, intermediate on diets 2 and 3, and lowest on diet 4; body weight gain was highest on diet 3, intermediate on diets 1 and 2 and lowest on diet 4. Intakes and body weight changes were reflected by differences in milk/dry matter intake, which was highest on diets 2 and 4 and lowest on diet 3. Milk yield was lower on diet 3 (44.3 kg/d) than on diets 1, 2, and 4 (average 45.8 kg/d) and protein yield was highest on diets 1 and 2 (average 1.35 kg/d), intermediate on diet 4 (1.30 kg/d), and lowest on diet 3 (1.25 kg/d). No effects of diet were detected on ruminal metabolites. Free nonessential amino acids and total protein AA were elevated in blood plasma on diet 3, reflecting reduced utilization for milk protein synthesis. These results indicated that 50% dilution of soybean meal RUP with that from corn protein did not reduce yield and that supplementing RPL to the corn protein-based diet increased yield 1.1 kg of milk/d and 50 g of true protein/d.

Multi-species pastures for grazing dairy cows in small-scale dairy systems in the highlands of Mexico

Grazing in small-scale dairy systems reduces costs and enhances sustainability. However, binary pastures (BP) have low persistency, which may be increased by including more species given their flexibility to withstand different agroecological and management situations. The objective was to assess a multi-species (MS) pasture of perennial ryegrass (RG), tall fescue (TF), bromegrass (BG), red clover (RC) and white clover (WC) in comparison to a BP of perennial ryegrass (RG) - WC grazed by six Holstein dairy cows during the dry season in an on-farm double cross-over experiment, with three 14-day each experimental periods for animal variables, and a split-plot design for pasture variables at 3 cow/ha. There were differences (P < 0.05) between pastures for sward height (MS 5.0 vs. BP 4.0 ± 0.10 cm, both MS and BP) and net herbage accumulation (MS 902 vs BP 228 ± 172.4 kg DM/ha, both MS and BP) and differences (P < 0.05) for chemical composition among periods. There were differences (P < 0.01) among periods for estimated DM intake, but no differences (P > 0.05) for milk yield (mean 16.8 kg/cow/day), milk fat or protein content (mean 31.8 and 28.8 g/kg). Multi-species pastures are a viable alternative for SSDS in the highlands of central Mexico, being more resistant to harsh environment and to weed and kikuyu grass invasion.

Pipeline for Targeted Meta-Proteomic Analyses to Assess the Diversity of Cattle Rumen Microbial Urease

In the rumen of cattle, urease produced by ureolytic bacteria catalyzes the hydrolysis of urea to ammonia, which plays an important role in nitrogen metabolism and animal production. A high diversity of rumen bacterial urease genes was observed in our previous study; however, information on urease protein diversity could not be determined due to technical limitations. Here, we developed a targeted meta-proteomic pipeline to analyze rumen urease protein diversity. Protein extraction (duration of cryomilling in liquid nitrogen), protein digestion state (in-solution or in-gel), and the digestion enzyme used (trypsin or Glu-C/Lys-C) were optimized, and the digested peptides were analyzed by LC-MS/MS. Four minutes was the best duration for cryomilling and yielded the highest urease activity. Trypsin digestion of in-gel proteins outperformed other digestion methods and yielded the greatest number of identifications and superior peptide performance in regards to the digestion efficiency and high-score peptide. The annotation of peptides by PEAKS software revealed diversity among urease proteins, with the predominant proteins being from Prochlorococcus, Helicobacter, and uncultured bacteria. In conclusion, trypsin digestion of in-gel proteins was the optimal method for the meta-proteomic pipeline analyzing rumen microbial ureases. This pipeline provides a guide for targeted meta-proteomic analyses in other ecosystems.

Milk production and estimated enteric methane emission from cows grazing ryegrass pastures in small-scale dairy systems in Mexico

The work assessed the productive response and estimated enteric methane (CH₄) emissions of dairy cows grazing in small-scale dairy systems. Treatments were grazing annual pasture (AP) mainly of annual ryegrass and perennial pasture (PP) mainly of perennial ryegrass, complemented daily with 3.72 kg DM/cow of commercial concentrate. Eight Holstein cows were used in a double cross-over design with three 14-day-each experimental periods for animal variables and CH₄ emissions. Pasture variables were analysed with a split-plot design. AP showed higher sward height (P < 0.05) with no differences (P > 0.05) in net herbage accumulation or in herbage chemical composition. Cows on AP yielded 24.6% more milk (P < 0.001) than grazing PP, but there were no differences in milk fat and protein content. There were differences (P ≤ 0.05) among periods for milk yields, but no differences among periods for milk fat and protein. Milk urea nitrogen was significantly higher (P < 0.001) in PP than in AP with no differences among periods. There was higher (P < 0.001) DMI for AP than PP with a significant decline (P < 0.05) as periods progressed. There was a trend (P = 0.08) for higher daily CH₄/cow in AP, but significantly lower emissions (7.2%) in AP/kg DMI, and 20.1% lower emission intensity of g CH₄/kg milk. The proportion of gross energy lost as CH₄ for AP was lower (P < 0.01). Higher milk yields in AP resulted in a 26% higher margin over feed costs than for PP. Results show that grazing annual pastures with moderate concentrate supplementation results in higher milk yields, higher incomes, and reduces the intensity of CH₄ emissions.

Substitution of residues in UreG to investigate UreE interactions and nickel binding in a predominant urease gene cluster from the ruminal metagenome

Microbial ureases catalyze the hydrolysis of urea to ammonia, and inhibition of these enzymes in rumen has the potential to improve urea utilization efficiency and reduce urinary nitrogen excretion. Urease activity is catalyzed by a protein complex encoded by a gene cluster, and its accessory proteins (especially UreE and UreG) play important roles in transferring nickel to the active site for urease maturation. In this study, a predominant urease gene cluster (5290 bp) from the ruminal microbial metagenome was identified. Isothermal titration calorimetry (ITC) and analytical ultracentrifugation (AUC) analyses showed that the reaction of identified UreE with UreG was endothermic, and was dominated by a hydrophobic interaction, in which each UreE dimer bound 2 M equivalents of UreG monomer to form a UreE₂-2UreG complex. Mutagenesis analyses showed that the UreG residues Glu-23, Asp-41, Glu-46, Glu-66, Cys-70, His-72, Asp-78, and Asp-118 were involved in the GTPase activity of UreG. Furthermore, variants of Cys-70 and His-72 involved in CPH motif of UreG, as well as the nearby Glu-66 and Asp-78, not only prevented interactions with UreE, but also prevented nickel binding. These data provide additional information regarding UreG residues that may be targeted for the design of new urease inhibitors.

Okara or soybean grain added to the rehydrated corn grain silage for cattle: digestibility, degradability and ruminal parameters

The experiment was carried out to evaluate total and partial digestibility of nutrients, the efficiency of microbial protein synthesis, in situ degradability and ruminal parameters in cattle fed diets with rehydrated corn grain silages, okara or soybean grain. Three Holstein steers were distributed in a 3 x 3 Latin square design. The treatments evaluated were: SO (corn grain silage + 30% okara), SSG (corn grain silage + 20% soybean grain) and CG (dry corn grains). The ruminal digestibility of non-fiber carbohydrates (NFC) increased in SO (88.34%) and SSG treatments (87.87%), compared to the CG treatment (63.48%). The minimum ruminal pH value was 6.01, observed 4.13 hours after feeding a diet with SO. The highest ammonia-N contents were 15.25 and 15.07 mg dL-1 observed in SSG and SO, respectively, 2.45 and 2.61 hours after feeding. Treatments SO and SSG showed higher fraction A content (readily degradable fraction) and C (constant rate of degradability of fraction B). The effective degradability (ED) of dry matter (DM) was higher for the diets SO and DE of CP was higher for treatments SO and SSG. SSG and SO result in better utilization of nutrients by animals.

Evaluation of influence of milk urea nitrogen on reproductive performance in smallholder dairy farms

OBJECTIVE

The aim of this study was to determine the relationship between milk urea nitrogen (MUN) and reproductive performance in dairy cows in western Thailand.

DESIGN

All cows calving from November 2014 to April 2015 were included in the study, a total of 486 cows from 47 farms. Each cow had milk constituents and MUN tested monthly up to confirmed conception or until the 8th month after parturition. Each farm had a dietary assessment completed. Cox proportional hazard models with shared frailty were used to determine associations of conception rate.

RESULTS

Cows became pregnant increasingly quickly over time, except during 100-150 days of lactation. A change in MUN from 12.5 to 13.5 mg/dL on the closet day to breeding was associated with a 5% decrease in conception. Milk protein was negatively associated with hazard of conception, whereas milk lactose and dietary protein:energy ratio had positive associations with conception rate. Breeding season was also significant; the highest conception rate was observed in cows inseminated during winter, whereas insemination during the humid rainy season resulted in the lowest conception rates. The farm random effect in the model was strongly significant.

CONCLUSION

Detrimental effects of higher MUN on rate of conception were identified. The rate of conception was positively associated with protein:energy ratio in the study. Therefore, good nutritional management leading to positive energy balance should benefit conception rates.

Kikuyu pastures associated with tall fescue grazed in autumn in small-scale dairy systems in the highlands of Mexico

Intensive grazing increases the profitability and sustainability of small-scale dairy systems by reducing feeding costs. Kikuyu grass is a subtropical species from East Africa that has similar performance compared with temperate grasses when grazed by dairy cows in these systems during the summer rainy season but reduces growth and quality at low temperatures, when temperate species may have an advantage. The objective was to evaluate intensive grazing of kikuyu pastures (KYKY) alone or in association with two varieties of endophyte-free tall fescue, TF-33 (TF33) and Cajun II (CAJN), during the summer-autumn transition period when low temperatures set in, by lactating cows in small-scale dairy farms. Pasture variables were analysed with a split-plot design for sward height, net herbage accumulation and chemical composition, in vitro digestibility of organic matter, and estimated metabolisable energy content of herbage and concentrate. Experimental design for animal variables was a 3 × 3 Latin Square repeated three times with nine Holstein cows and 14 days experimental periods. Cows received 4.65 kg DM/day of a 16% CP commercial concentrate. Milk yield and composition, live weight, and body condition score were recorded. There were no significant differences (P > 0.05) for sward height and net herbage accumulation, nor for important components of chemical composition of herbages. There were no significant differences (P > 0.05) for milk yield (19 kg/cow/day) and composition, although differences (P < 0.05) were detected for live weight and body condition score. The conclusion is that there is no advantage of associating tall fescue with kikuyu in summer-autumn transition period for small-scale dairy systems.

Whole-crop triticale silage for dairy cows grazing perennial ryegrass (Lolium perenne) or tall fescue (Lolium arundinaceum) pastures in small-scale dairy systems during the dry season in the highlands of Mexico

The dry season in central Mexico is a difficult time for small-scale dairy systems to meet feed requirements for their herds as pasture growth is limited. Conserved forage options are needed to complement pastures. The objective was to assess on-farm the production of dairy cows complemented with triticale silage (X. Triticosecale Witt. (TSL)) at two levels of inclusion (5.0 and 7.5 kg DM/d), grazing pastures of two grass species during the dry season: perennial ryegrass (PRG; Lolium perenne) or tall fescue (TFC; Lolium arundinaceum) (TFC) with white clover (Trifolium repens), and 4.65 kg DM/d concentrate. Experimental design was a 2 × 2 factorial in repeated 4 × 4 Latin squares. Chemical composition of TSL was 96 g CP/kg DM, 667 g NDF/kg DM, 713 g in vitro enzymatic digestibility of OM (IVEDOM)/kg DM, and pH of 4.6. There were differences (P < 0.05) in net herbage accumulation (NHA) and sward height between pastures, with higher NHA in TFC than that in PRG, although the chemical composition of PRG was higher (P < 0.05) in PC, IVEDOM, and estimated ME. There were no differences (P > 0.05) in milk yield (12.3 ± 2.63 kg/cow/day), milk compositions (33.1 ± 0.45 g milkfat/kg, 41 33.3 ± 0.21 g milk protein/kg, 47.9 ± 0.36 g lactose/kg, and 10.47 ± 2.25 mg MUN/dL), body condition score (2.4 ± 0.22), or live weight (490 ± 72.8 kg). At a higher inclusion of TSL, there was lower intake of pasture. Inclusion of 5.0 kg DM/cow/day of triticale silage better complements grazing and sustains moderate milk yields when pasture growth and intake are limited.

Supplementation of dairy cows with commercial concentrate or ground maize grain under cut-and-carry or grazing of cultivated pastures in small-scale systems in the highlands of central Mexico

Small-scale dairy systems (SSDS) in Mexico represent over 78% of dairy farms and 37% of milk production. In the central highlands, many SSDS base the feeding of herds on irrigated cultivated pastures (mostly cut-and-carry), straws, and large amounts of commercial concentrates that result in high feeding costs and low economic sustainability. Intensive grazing may result in lower feeding costs when compared with cut-and-carry strategies. The high protein content of pasture may meet requirements of dairy cows with moderate milk yield (16–20 kg milk/cow.day), so that lower protein supplements, like ground maize grain, may substitute for commercial concentrates. An on-farm experiment following a participatory rural research approach was undertaken with seven farmers evaluating commercial concentrate (CC) or ground maize grain (MG) as supplement; and two pasture managements, grazing (G) or cut-and-carry (C) of irrigated ryegrass/white clover pastures to assess productive performance and feeding costs. Six farmers participated with four milking cows each and one farmer with two groups of four milking cows in a 2 by 2 factorial experiment. Daily milk yield per cow before the experiment was used as covariate. The experiment lasted 12 weeks. There is a trend in G for higher protein content in milk (P &lt; 0.10). CC showed higher body condition score than MG with a significant interaction for body condition score with the highest body condition score in CCC (P &lt; 0.05). Feeding costs were 15% higher per kg of milk yield and 19% per kg of energy-corrected milk under cut-and-carry but no statistical differences were detected (P &gt; 0.05) in comparison with the grazing strategy. Supplementing with home-grown ground maize grain resulted in 28.5% higher margins per kg of milk produced. Implementing grazing involves less work burden for small-scale dairy farmers, and combined with home-grown grains as supplement is a viable option that may reduce feeding costs in these systems.

Milk production and fatty acid profile of dairy cows grazing four grass species pastures during the rainy season in small-scale dairy systems in the highlands of Mexico

The study evaluated small-scale dairy systems with continuous grazing of pastures based on three temperate grasses festulolium (FL), tall fescue (TF), and perennial ryegrass (RG), compared with subtropical kikuyu grass (KG). All pastures were associated with white clover (Trifolium repens L.). Twelve multiparous Holstein cows were assigned to a 4 × 4 Latin square replicated three times with 14-day experimental periods. Sampling and analyses of pastures, concentrates, and animal variables followed standard procedures. FL showed a significantly (p < 0.05) higher mean sward height, but there were no differences (p > 0.05) in net herbage accumulation. There were significant differences (p < 0.05) among pastures for CP, NDF, ADF, in vitro digestibility of OM (IVOMD), and estimated metabolizable energy (eME). There were no differences (p > 0.05) between treatments for milk yield and composition, live weight, or body condition score. There were significant differences (p < 0.05) in fatty acid values for pastures in C14:0, C16:1, and C18:3n3. There were significant differences between treatments (p < 0.05) in milk contents for C18:0, C18:1t11, and C18:2c9t11. Grazing FL, TF, RG, or KY pastures showed no differences in milk yields. Higher values for C18:0, C18:1t11, and C18:2c9t11 were detected in KY, RG, and TF. RG had significantly higher MUFA than FL and higher PUFA than TF. A value under 65% of SFA, a ratio of n-6/n-3 lower than 4, and an atherogenic index of 1.7 are indicators of milk with beneficial effects for human health.

Nutritional and Environmental Effects on Ammonia Emissions from Dairy Cattle Housing: A Meta-Analysis

Nitrogen excreted in dairy manure can be potentially transformed and emitted as NH, which can create livestock and human respiratory problems and be an indirect source of NO. The objectives of this study were to: (i) investigate environmental factors influencing NH emissions from dairy housing; and (ii) identify key explanatory variables in the NH emissions prediction from dairy housing using a meta-analytical approach. Data from 25 studies were used for the preliminary analysis, and data from 10 studies reporting 87 treatment means were used for the meta-analysis. Season and flooring type significantly affected NH emissions. For nutritional effect analysis, the between-study variability (heterogeneity) of mean NH emission was estimated using random-effect models and had a significant effect ( < 0.01). Therefore, random-effect models were extended to mixed-effect models to explain heterogeneity regarding the available dietary and animal variables. The final mixed-effect model included milk yield, dietary crude protein, and dry matter intake separately, explaining 45.5% of NH emissions heterogeneity. A unit increase in milk yield (kg d) resulted in a 4.9 g cow d reduction in NH emissions, and a unit increase in dietary crude protein content (%) and dry matter intake (kg d) resulted in 10.2 and 16.3 g cow d increases in NH emissions, respectively, in the scope of this study. These results can be further used to help identify mitigation strategies to reduce NH emissions from dairy housing by developing predictive models that could determine variables with strong association with NH emissions.

Reducing microbial ureolytic activity in the rumen by immunization against urease therein

BACKGROUND

Ureolytic activity of rumen bacteria leads to rapid urea conversion to ammonia in the rumen of dairy cows, resulting possible toxicity, excessive ammonia excretion to the environment, and poor nitrogen utilization. The present study investigated immunization of dairy cows against urease in the rumen as an approach to mitigate bacterial ureolytic activity therein.

RESULTS

Most alpha subunit of rumen urease (UreC) proteins shared very similar amino acid sequences, which were also highly similar to that of H. pylori. Anti-urease titers in the serum and the saliva of the immunized cows were evaluated following repeated immunization with the UreC of H. pylori as the vaccine. After the fourth booster, the vaccinated cows had a significantly reduced urease activity (by 17%) in the rumen than the control cows that were mock immunized cows. The anti-urease antibody significantly reduced ureolysis and corresponding ammonia formation in rumen fluid in vitro. Western blotting revealed that the H. pylori UreC had high immunological homology with the UreC from rumen bacteria.

CONCLUSIONS

Vaccine developed based on UreC of H. pylori can be a useful approach to decrease bacterial ureolysis in the rumen.

Measures of nitrogen use efficiency and nitrogen loss from dairy production systems

In dairy production systems, tradeoffs can occur between fertilizer N applications and crop N use, feed N consumption and manure N excretion, and environmental impacts. This paper examines (i) how stocking rates affect N imports and management on dairy farms, N use efficiency (NUE; i.e., the amount of applied N incorporated into product N), and N loss; (ii) how reductions in fertilizer N and feed N may affect crop and milk production, NUE, and N loss; and (iii) why tradeoffs in N use outcomes should be considered when attempting to enhance overall NUE and reduce N loss. The Integrated Farm Simulation Model simulations of two representative dairy farm types and analyses of regional studies, long-term field experiments, and cow nutrition trials were used to demonstrate that (i) stocking rate affects cropping patterns, fertilizer and feed imports, and N loss; (ii) although fertilizer N reductions of 20 kg N ha may reduce slightly the crude protein (CP) content of corn silage (which would require purchase of additional CP supplements), this practice should not affect long-term corn yield but would reduce nitrate (NO) and nitrous oxide (NO) losses by 13 to 38%; (iii) dietary CP could be reduced on many dairy farms, which would not affect milk production but would reduce ammonia (NH) and NO emissions by 15 to 43%; and (iv) greater recognition of the tradeoffs in N use and N loss are needed to provide a better understanding of the potentials to enhance overall NUE and reduce environmental N loss from dairy production systems.

Livestock GRACEnet: A Workgroup Dedicated to Evaluating and Mitigating Emissions from Livestock Production

Ammonia, greenhouse gases, and particulate emissions from livestock operations can potentially affect air quality at local, regional, and even global scales. These pollutants, many of which are generated through various anthropogenic activities, are being increasingly scrutinized by regulatory authorities. Regulation of emissions from livestock production systems will ultimately increase on farm costs, which will then be passed onto consumers. Therefore, it is essential that scientifically based emission factors are developed for on-farm emissions of air quality constituents to improve inventories and assign appropriate reduction targets. To generate a larger database of on-farm emissions, the USDA-ARS created the workgroup Livestock GRACEnet (Greenhouse gas Reduction through Agricultural Carbon Enhancement Network). This introduction for the special section of papers highlights some of the research presently being conducted by members of Livestock GRACEnet with the intent of drawing attention to critical information gaps, such as (i) improving emissions measurements; (ii) developing emissions factors; (iii) developing and validating tools for estimating emissions; and (iv) mitigating emissions. We also provide a synthesis of the literature with respect to key research areas related to livestock emissions, including feeding strategies, animal housing, manure management, and manure land application, and discuss future research priorities and directions.

Potential use of milk urea nitrogen to abate atmospheric nitrogen emissions from wisconsin dairy farms

Urinary urea N (UUN) is the principal nitrogen (N) source controlling emissions of ammonia (NH) and nitrous oxide (NO) from dairy manure. The objectives of this study were (i) to study the integrative nature of dietary crude protein (CP) management, secretion of milk urea N (MUN), excretion of UUN, and N emissions from dairy production systems; (ii) to evaluate how associative changes in dietary CP, MUN, and UUN affect atmospheric N emissions from dairy farms; and (iii) to discuss some of the challenges and opportunities to an expanded use of MUN to enhance dietary CP use and decrease UUN excretion and N emissions from dairy farms. Milk urea N records of 37,889 cows in 197 herds in Wisconsin revealed that approximately one half of tested cows were likely consuming dietary CP in excess of requirement. Farm simulations were used to quantify the effect of dietary CP on whole-farm N emissions. At a statewide average MUN of 12.5 mg dL, 48 to 87% of UUN was emitted as NH, with the lowest loss from pasture-based farms and the greatest loss from tie-stall farms. Each 1 mg dL decrease of MUN (range, 16-10 mg dL) provided an associated daily decrease in UUN of 16.6 g per cow, which decreased NH and NO emissions from manure by 7 to 12%. Although more site-specific information is required on herd MUN-UUN relationships and more a reliable interpretation of MUN assay results is needed, monitoring of MUN may be used to enhance dietary CP use and to reduce UUN excretion and N emissions from Wisconsin dairy farms.

The Nexus of Environmental Quality and Livestock Welfare

In recent years, the livestock production industry has been receiving pressure to assess and improve production practices in two seemingly unrelated areas: environmental quality and animal welfare. In this article, we argue that the nexus of these two areas of study should be a priority for future research and that the integration of these disciplines in research, extension, and education efforts has the potential to improve the sustainability of production livestock agriculture.

Gas emissions from dairy cows fed typical diets of Midwest, South, and West regions of the United States

Gas emissions were determined for dairy cows fed three diets formulated to represent feed ingredients typical of the Midwest, South, or West regions of the United States. Dairy cows were housed and monitored in 12 environmentally controlled rooms (4 cows diet). Two experiments were performed, representing two lactation stages (initial days in milk were 115 ± 39 d in Stage 1 and 216 ± 48 d in Stage 2). The results demonstrated that the combination of different dietary ingredients resulted in different gas emissions while maintaining similar dry matter intake (DMI) and milk yield (MY). Diet effect on ammonia (NH) emissions was more prominent in Stage 1. During Stage 1, cows fed the Midwest diet had the highest daily NH emission, corresponding to the highest crude protein (CP) concentration among the three regions. The differences in NH emissions (39.0%) were much larger than the percent difference in CP concentrations between diets (6.8%). Differences in N intake, N excretion, or milk urea N alone may not serve as a strong indicator of the potential to reduce NH emissions. Lower emissions of methane (CH) per unit DMI or per unit MY were observed for cows offered the South diet during Stage 1 as compared with that from cows offered the Midwest or West diets. No diet effect was observed for hydrogen sulfide (HS) emission per unit S intake, nor for nitrous oxide (NO) emission. The measured NH and CH emissions were comparable, but the NO emissions were much higher than those reported for tie-stall dairy barns in the literature.