Excessive copper (Cu) absorption in calves may increase the risk of excessive hepatic Cu accumulation, likely driven by their elevated pre-ruminant absorptive capacity, with the potential for harmful Cu accumulation leading to adverse health and productivity outcomes. However, quantitative data across the weaning transition remains limited. This study utilized secondary data and bio-banked samples from 35 Holstein–Friesian bull calves to estimate hepatic Cu retention coefficients pre- and post-weaning. Although mean hepatic Cu concentrations remained broadly stable throughout the study, between 311 and 675 mg/kg of DM, changes varied by developmental stage: calves experienced hepatic Cu accumulation of 2.5 mg of Cu/kg of DM/d pre-weaning but a net reduction of 1.8 mg/kg of DM/d post-weaning. Pre-weaning calves exhibited a hepatic Cu retention coefficient of 81

Dairy cattle are typically fed a total mixed ration (TMR), which is prepared in an automated mixer wagon. On-farm, effective TMR mixing can often be neglected due to lack of time or training. This leads to a disbalance of intake and potentially detrimental effects on health and production. Using dietary treatments to simulate this effect, this study determined the response of rumen metabolism and microbiome to different concentrate allocations in combination with a live Saccharomyces cerevisiae supplement (yeast supplementation, YS). The 4 × 4 Latin square design consisted of four dairy cows fitted with permanent rumen cannulae, which were fed a partial mixed ration with dietary concentrates (4 kg per cow per day) in an even or an uneven pattern of allocation (concentrate allocation, CA). YS was included in the TMR at a rate of 10 g per cow per day. Rumen metabolism was determined by measuring the pH, volatile fatty acids (VFAs), and ammonia nitrogen (NH3–N). The rumen microbial community was characterised using 16S rRNA gene amplicon sequencing. Both CA and YS had no effect (p > 0.05) on the dry matter intake, milk yield, or composition. CA did not affect the rumen NH3–N and VFA concentrations (p > 0.05). YS inclusion tended to increase the rumen pH (p = 0.088), acetate (p = 0.076), and valerate (p = 0.091). YS significantly increased the total VFA (p = 0.033) and propionate concentrations (p < 0.016). CA had little overall effect on the rumen microbiome beta diversity. However, there was a reduction in the relative abundance of a Prevotellaceae feature associated with an uneven pattern of CA. Bray–Curtis clustering of the microbiome was observed with YS (p = 0.002), driven by a decrease of Gammaproteobacteria and Prevotellaceae features and an increase of a Christensenellaceae feature (LDA > 2.0).

Mitigating environmental phosphorus loading (EPL) from dairy farms reduces water pollution and improves the sustainability of production. Studies generally simulate EPL from dairy farms using a representative farm type from existing databases. However, housed and pasture-based dairy farming systems might contribute to eutrophication differently and have a varied feasibility of implementing mitigation. This study is the first that quantified EPL from dairy farms using data for FARMSCOPER collected from farmers and comparing EPL and identifying a least-cost suite of mitigation methods. Structural characteristics of 27 dairy farms in Great Britain (GB) were collected. Annual EPL from each farm was simulated in FARMSCOPER under three scenarios. Mean EPL of the production systems was compared to investigate any relationship between EPL and average 305 day adjusted milk yield of cows on each farm. A least-cost suite of mitigation methods was optimised for two model farms to represent either a housed or pasture-based system. Across both systems, 'current' implementation of mitigation methods was simulated to have reduced EPL from 0.63 to 0.56 kg P/ha (11%). The 'current' EPL positively correlated with milk production on a kg and kg/ha basis (P ≤ 0.001 and P = 0.033, respectively). Farms operating a housed system had a mean 'current' EPL that was 59% greater than the pasture-based system though not significant (P = 0.316). This was partly due to a small sample size and because FARMSCOPER's estimates exclude variations in farm practices (i.e., feeding). EPL was reduced by ~ 50% and ~ 60% without incurring annual financial losses by implementing existing mitigation methods for pasture-based and housed systems, respectively. This study highlights the importance of mitigating EPL from GB dairy farming, especially considering the increasing number of higher yielding herds and housed production systems. Furthermore, emphasis should be on increasing implementation of system-specific mitigating methods; efforts to include more recent and specific farm data to improve the FARMSCOPER tool will benefit this.

The primary focus of low CP diets and the inclusion of legume silages for dairy cows is to decrease feed costs and mitigate the environmental impact of milk production. This systematic review and meta-analysis was conducted to evaluate the effects of dietary CP level on the performance, metabolism, and N use efficiency (NUE; g milk N output/kg N intake) of dairy cows fed legume-based rations. A total of 36 production trials with 102 treatment means were included, and the effect of dietary CP level was estimated using the raw-mean difference between control (high CP) and low CP diets. Publication bias was examined using Begg’s and Egger’s tests. Meta-regression and subgroup analyses were performed to explore the heterogeneity for the response variables. Reducing dietary CP from 171 g/kg DM to 145 g/kg DM in forage legume-based diets resulted in decreased DM intake (-0.62 kg/d), milk yield (-1.41 kg/d), milk protein (-0.22 g/kg), milk urea N (MUN; -3.47 mg/dL), plasma urea N (-1.85 mmol/L) and condition score (-0.03) in dairy cows. Similarly, nutrient intake, diet digestibility, total urine output, N excretion through milk, urine and faeces, urine N/total N intake, rumen ammonia-N and molar proportion of butyrate were decreased (P < 0.05) in cows receiving low CP diets compared with those fed the control. In contrast, low CP diets increased (P < 0.05) the faecal N/total N intake, NUE, and plasma content of non-esterified fatty acids. Subgroup analyses revealed that the effect size of DM intake, milk yield, MUN, urinary N excretion and rumen ammonia-N content had less of a negative impact (P < 0.05) when cows received dietary CP levels of 140 to 155 g/kg DM than < 140 g/kg DM. The inclusion of rumen-protected methionine in low CP diets increased (P = 0.04) DM intake and tended to improve (P = 0.08) the milk protein content of dairy cows. Feeding lucerne silage-based low CP diets showed an improvement (P < 0.05) in apparent diet digestibility but reduced milk yield (-1.46 kg/d) relative to red clover silage-based rations. The inclusion rate of legume silages in low-CP diets beyond 40% of the forage DM reduced (P < 0.01) DM intake and milk protein content. We conclude that legume silage-based low CP diets enhance NUE but have adverse effects on dairy cow performance that can partially be mitigated by including rumen-protected methionine and limiting their proportion in the forage component of the diet.

Excessive copper (Cu) supplementation is common on dairy farms worldwide, despite a growing body of research highlighting the risks of over-supplementation, including liver damage, impaired growth, and reduced fertility. However, diagnosing Cu toxicity remains challenging due to the liver's allostatic regulation of blood Cu levels and debate surrounding toxicity thresholds. This study utilised secondary data from a longitudinal study conducted between September 2016 and September 2018 involving 80 replacement Holstein-Friesian heifers. Data was utilised to generate receiver operating characteristic curves which established liver Cu thresholds associated with suboptimal liver function and fertility. Results indicated that hepatic Cu concentrations exceeding 167 mg/kg of dry matter (DM) were associated with reduced conception rates to first service, while concentrations above 260 mg/kg of DM reduced conception probability to first and second services. Hepatic Cu concentrations exceeding 322 mg/kg of DM were linked to impaired liver function, as evidenced by elevated serum glutamate dehydrogenase activity. In contrast, a toxicity threshold value could not be generated for plasma Cu, underscoring its inadequacy as a biomarker. The fertility thresholds identified in this study may be more closely related to optimizing Cu levels for animal performance rather than indicative of liver Cu toxicity, suggesting the need for further research.

Natural plant compounds can be used to supplement livestock diets, improving feed efficiency, production, and health, while also reducing environmental impact. In the present study, a Yucca schidigera (Mohave Yucca) extract was added at four rates of inclusion (ROI) of 0, 5, 15, or 30 g/day to a ryegrass and maize silage-based diet and fed to dairy cows in a 4 × 4 Latin square experimental design. Each period was 28 days in duration, with sampling undertaken during the final week of each period. Solid phase digesta (SPD) and liquid phase digesta (LPD) samples were collected via a rumen cannula and analyzed for volatile fatty acids (VFAs), ammonia N, and microbiome using 16S rRNA gene sequencing. Total fecal and urine collection was undertaken over a 3-day period. Rumen microbial diversity was not affected by ROI (LPD: P = 0.180; SPD: P = 0.059). However, discriminant analysis found a decrease in Methanobrevibacter millerae (linear discriminant analysis, LDA = 2.15) and an increase in an unclassified species of Proteobacteria (LDA = 2.10) associated with ROI. Univariate analysis also revealed differential abundance of operational taxonomic units classified as Prevotellaceae and Fibrobacteraceae by ROI (P < 0.05). Maximum rumen ammonia N concentration decreased linearly from 228 to 109 mg/L with ROI (P = 0.044). Rumen VFA concentration was unaffected with the exception of propionate, which showed a linear increase with ROI (P = 0.010). The diurnal rumen pH range (maximum-minimum) also decreased with ROI (P = 0.004). Dry matter intake and milk yield were not affected (P > 0.05) by ROI; however, there was a linear increase in milk fat content from 38.9 to 42.0 g/kg with ROI (P < 0.05).IMPORTANCEDomestic livestock such as dairy cows are inefficient utilizers of dietary nitrogen. This increases feed costs and reduces animal production efficiency. Excreted nitrogenous compounds are also an environmental hazard, such as when they enter water courses as nitrate or are lost to the atmosphere as ammonia or nitrous oxide. Dietary protein is degraded in the rumen via the activity of the microbial population, mainly into ammonia, which may then be utilized by the microbial population to synthesize microbial protein or absorbed into the blood and potentially excreted. Manipulation of the diet or altering the microbial population may increase the utilization of dietary protein, increasing animal performance, decreasing feed costs, and reducing the environmental impact of milk production. This study examines the effect of Yucca schidigera extract on the rumen microbiome and nitrogen utilization in dairy cows.

The apparent absorption of copper (Cu) in ruminants is low, with between 0.01 and 0.07 g/g absorbed from sources such as copper oxide (CuO) under typical feeding conditions, resulting in high levels of excretion. Improving the bioavailability of Cu could reduce the supplemental amount required to maintain Cu status and reduce excretion, particularly in the presence of dietary antagonists such as sulfur (S) and molybdenum (Mo). The objective of our study was to determine the Cu status of cows when fed nanoparticle CuO coated with Lys compared with conventional CuO when fed without or in combination with antagonists to Cu absorption (S and Mo) in the diet of dairy cows. Fifty-six multiparous Holstein-Friesian cows that were 48 d ± 17.4 (mean ± SD) post calving and yielding 40.6 ± 6.9 kg milk/d were used in a 2 × 2 factorial design. The 4 treatment groups were; CuO (O-), CuO with added antagonists (O+), nano CuO with a lysine coating (N-), and nano CuO with a Lys coating with added antagonists (N+), fed for 16 wks. We formulated the diets to contain approximately 17 mg Cu/kg dry matter (DM) and diets with antagonists contained an additional 1 g S/kg DM and 6 mg Mo/kg DM, with Lys added to O- and O+ to provide the same daily supply as N- and N+. Blood samples were collected at wk 0, 2, 4, 6, 10 and 16, and liver biopsy samples at wk 0 and 16. We found no effect of dietary treatment on DM intake, milk yield, live weight or body condition score, with mean values of 23.3 kg/d, 40.1 kg/d, 646 kg and 2.68, but milk SCC was higher in cows fed conventional compared with non CuO, or with added antagonist. We also found no effect of treatment on blood activity of gamma glutamyl transferase, superoxide dismutase or ceruloplasmin, hematology profile, or plasma Cu and iron concentration. We found that plasma Mo concentration was increased from 0.36 µmol/L in cows fed O- or N- to 0.80 µmol/L in those receiving O+ or N+. Additional dietary antagonists also decreased the concentration of Cu in the liver of cows fed conventional CuO (C+) over the study period by 1.3 mg/kg DM/d, but in cows fed dietary antagonists and nano CuO coated with Lys (N+), liver Cu concentration was increased by 1.1 mg/kg DM/d. Our study is the first to demonstrate that reducing the particle size of CuO into the nano scale with a lysine coating improves the bioavailability of CuO in the presence of dietary antagonists in dairy cattle, and we did not observe any negative effects on performance or health.

The increasing cost of milk production, in association with tighter manure N application regulations and challenges associated with ammonia emissions in many countries, has increased interest in feeding lower crude protein (CP) diets based on legume silages. Most studies have focused on alfalfa silage, and little information is available on low-CP diets based on red clover silage. Our objectives were to examine the effects of dietary CP content and supplementing a low-CP diet with dietary starch or rumen-protected Met (RPMet) on the performance, metabolism, and nitrogen use efficiency (NUE; milk N output/N intake) in dairy cows fed a red clover and grass silage-based diet. A total of 56 Holstein-Friesian dairy cows were blocked and randomly allocated to 1 of 4 diets over a 14-wk feeding period. Diets were based on red clover and grass silages at a ratio of 50:50 on a dry matter (DM) basis and were fed as a total mixed ration, with a 53:47 ratio of forage to concentrate (DM basis). The diets were formulated to supply a similar metabolizable protein (MP) content, and had a CP concentration of either 175 g/kg DM (control [CON]) or 150 g/kg DM (low-protein [LP]), or LP supplemented with either additional barley as a source of starch (LPSt; +64 g/kg DM) or RPMet (LPM; +0.3 g/100 g MP). At the end of the 14-wk feeding period, 20 cows (5 per treatment) continued to be fed the same diets for a further 6 d, and total urine output and fecal samples were collected. We observed that dietary treatment did not affect DM intake, with a mean of 21.5 kg/d; however, we also observed an interaction between diet and week with intake being highest in cows fed LPSt in wk 4 and CON in wk 9 and 14. Mean milk yield, 4% fat-corrected milk, and energy-corrected milk were not altered by treatment. Similarly, we found no effect of dietary treatment on milk fat, protein, or lactose content. In contrast, milk and plasma urea concentrations were highest in cows fed CON. The concentration of blood plasma β-hydroxybutyrate was highest in cows receiving LPM and lowest in LPSt. Apparent NUE was 28.6% in cows fed CON and was higher in cows fed any of the low-protein diets (LP, LPSt, or LPM), with a mean value of 34.2%. The sum of milk fatty acids with a chain length below C16:0 was also highest in cows fed CON. We observed that dietary treatment did not affect the apparent whole-tract nutrient digestibility of organic matter, N, neutral detergent fiber, and acid detergent fiber, with mean values of 0.785, 0.659, 0.660, and 0.651 kg/kg respectively, but urinary N excretion was approximately 60 g/d lower in cows fed the low-CP diets compared with CON. We conclude that reducing the CP content of red clover and grass silage-based diets from 175 to 150 g/kg DM while maintaining MP supply did not affect performance, but reduced the urinary N excretion and improved NUE, and that supplementing additional starch or RPMet had little further effect.

BACKGROUND:Oversupply of dietary copper (Cu) is common among UK dairy herds, but studies on the long-term outcomes of this oversupply are scarce. METHODS:A longitudinal study was undertaken to determine the long-term implications when 80 Holstein‒Friesian heifers with a mean (±standard error) age of 4.1 ± 0.1 months and a mean liveweight of 137 ± 2.4 kg were fed a recommended (R; 16 mg/kg dry matter [DM]) or high (H; 32 mg/kg DM) dietary Cu concentration until 6 weeks prior to calving. RESULTS:Hepatic Cu concentrations in both treatment groups were elevated into the ranges used to diagnose chronic Cu toxicity in cattle at 6.9 months of age (798 ± 46.4 mg/kg DM for H vs. 643 ± 35.4 mg/kg DM for R), with associated evidence of liver damage. Hepatic Cu concentrations then returned to normality but remained higher (p < 0.001) for heifers fed H than for those fed R and were associated with a reduced (p = 0.044) conception rate to first and second services (73.7 ± 8.05% for H vs. 91.2 ± 7.68% for R). LIMITATION:This retrospective analysis identified pre-study liver damage, which may have affected results. CONCLUSIONS:Supplying Cu in excess of requirements resulted in liver damage and reduced conception rates.

The study investigated the effects of dietary protein level and the inclusion of hydroponic barley sprouts (HB) on lactation performance, blood biochemistry and N use efficiency in mid-lactation dairy cows. Treatments were arranged in a 2 x 2 factorial design with 2 CP levels (16.8% and 15.5% of DM), with HB (4.8% of DM, replacing 4.3% of alfalfa hay and 0.5% of distillers dried grains with solubles [DDGS]) or without HB. Forty-eight multiparous Holstein dairy cows (146 +/- 15 DIM, 40 +/- 5 kg/d of milk) were randomly allocated to 1 of 4 diets: high-protein diet (16.8% CP, HP), HP diet with HB (HP+HB), low-protein diet (15.5% CP, LP), or LP diet with HB (LP+HB). An interaction between CP x HB on DMI was detected, with DMI being unaffected by HB inclusion in cows fed the high-protein diets, but was lower in cows fed HB when the low-protein diet was fed. A CP x HB interaction was also observed on milk and milk protein yield, which was higher in cows fed HB with HP, but not LP. Inclusion of HB also tended to reduce milk fat content, and feeding HP resulted in a higher milk protein and MUN content, but lower milk lactose content. Feed efficiency was increased by feeding HP or HB diets, whereas N use efficiency was higher for cows fed LP or HB diets. There was an interaction on the apparent total-tract digestibility of DM and CP, which was higher when HB was fed along with HP, but reduced when fed with LP, whereas the digestibility of ADF was increased by feeding low-protein diets. In conclusion, feeding a low-protein diet had no adverse effect on cow performance, while feeding HB improved milk and milk component yield, and N efficiency when fed with a high-CP diet, but compromised cow performance with a low-CP diet.

Introduction: Food and feed supplements derived from plants often demonstrate various beneficial effects-they could have significant anti-inflammatory and antibacterial activity.The fermented wheat germ extract (FWGE) is a natural nontoxic substance which is already used in the human medicine as a supportive therapy in cancer patients under radiotherapy and chemotherapy. Materials and Methods:In this study, the protective effect of FWGE against lipopolysaccharide (LPS) induced inflammation and oxidative stress in IPEC-J2 porcine intestinal epithelial cells was studied.Enterocytes were treated with LPS derived from Salmonella enterica ser.Typhimurium and Escherichia coli O55:B5, O111:B4, and O127:B8 strains.Intracellular ROS level and extracellular H 2 O 2 level were followed up by two fluorescent assays (DCFH-DA and Amplex Red).The effect of FWGE on the intestinal barrier integrity was determined by transepithelial electric resistance measurements and using a FD4 fluorescent tracer dye.IL-6 concentration of supernatants was also measured by the ELISA method.Results: Our data revealed that FWGE had a significant lowering effect on the inflammatory response especially related to oxidative stress.Treatment with FWGE (1%-2%) significantly decreased the level of intracellular ROS compared to LPS-treated cells.Furthermore, LPS-triggered partial disruption of epithelial integrity was reduced after FWGE application. Conclusions:We described first that FWGE has many beneficial activities in the intestinal cells in case of LPS-evoked oxidative damage.In addition, it has a protective effect on cell layer integrity in the case of S. Typhimurium LPS treatment.Our results suggest that FWGE could be a promising compound in the prevention and treatment of intestinal impairment caused by bacteria in both human and veterinary medicine.

Abstract High yielding dairy cattle are typically fed a total mixed ration (TMR) to meet their energy requirements. However, inadequate mixing can lead to feed selection and dietary imbalance, negatively affecting rumen metabolism and the microbiome. To investigate the effect of TMR mixing, four dairy cows were fed a partial mixed ration with dietary concentrates (4 kg/cow/day) added separately in even and uneven patterns of allocation (CA) with a Saccharomyces cerevisiae yeast supplement (YS) (1 g/cow/day). Rumen digesta samples were taken to measure microbial metabolism and microbiome using16S rRNA amplicon sequencing. No effect of CA on rumen metabolism was detected. YS inclusion tended to increase rumen pH ( P = 0.088) reduce total VFA concentration ( P = 0.033) and propionate concentration ( P = 0.016). Clustering of the rumen microbiome was observed with YS supplementation, driven by a decrease in abundance of Gammaproteobacteria and Prevotellaceae OTUs respectively and an increase of a Christensenellaceae OTU. Pattern of concentrate allocation had no detectable effect on alpha diversity or Bray Curtis dissimilarity. However, reduction in relative abundance of a Prevotellaceae OTU biomarker was associated with uneven pattern of concentrate allocation . Pattern of concentrate allocation and YS supplementation did not adversely affect milk yield or composition.

Nitrogen (N) loss from livestock agriculture via ammonia and nitrous oxide can reduce feed efficiency, production and negatively affect the environment. One option to reduce N loss is to add dietary supplements such as Yucca schidigera extract which has ammonia-binding properties and contains antimicrobial steroidal saponins, or Saccharomyces cerevisiae yeast, which can stabilise rumen pH and promote fibre degradation, increasing microbial growth and demand for degradable N. To determine the effect of Yucca schidigera extract when fed alone or in combination with a live yeast on the performance, rumen metabolism, microbiome and N balance, six rumen cannulated dairy cows were fed a mixed ration (C), mixed ration with Y. schidigera extract (De-Odorase®, Alltech®; 5 g/cow/day; D), or mixed ration with Y. schidigera extract (5 g/day) and Saccharomyces cerevisiae (Yea-Sacc®, Alltech®, 1 g/cow per day; DY), in a 3 × 3 Latin rectangle design study with three periods of 49-day duration. Digesta samples were collected via the ruminal cannula during the final week of each period and separated into liquid (LPD) and solid (SPD) phases for microbiome analysis using 16S rRNA amplicon sequencing. DM intake was 0.8 kg/d lower (P < 0.05) in cows fed DY than C or D, with milk protein concentration 1.7 g/kg higher in C than D or DY. There was a beta diversity (Bray Curtis) clustering of the LPD in cows fed D or DY compared to C (P < 0.05), driven by an increase in Prevotella ruminicola-related operational taxonomic units (OTUs), and a decrease in P. brevis and P. bryantii OTUs. A methanogen OTU, Methanobrevibacter olleyae, was decreased in cows fed D or DY and an unclassified species of Gammaproteobacteria was increased in DY (LDA > 2.0, P < 0.05) compared to C. Rumen pH, ammonia and total VFA concentration were not affected by treatment (P > 0.05) but the concentration of propionate and iso-butyrate were lower at 1700 and 2000 h in cows fed DY compared to C (P < 0.05). Measurements of N balance were unaffected by supplementation with D or DY, and there was no effect of treatment on slurry pH. In conclusion, supplementing with an extract of Yucca schidigera either alone or in combination with a live yeast had only a small effect on performance, with Yucca schidigera altering species associated with carbohydrate and protein metabolism, and reduced Methanobrevibacter olleyae which is involved in methanogenesis.

Reducing the dietary crude protein (CP) concentration can decrease the financial cost and lower the environmental impact of milk production. Two studies were conducted to examine the effects of reducing the dietary CP concentration on animal performance, nutrient digestibility, milk fatty acid (FA) profile, and nitrogen use efficiency (NUE; milk N/N intake) in dairy cows fed legume silage-based diets. Thirty-six multiparous Holstein-Friesian dairy cows that were 76 ± 14 (mean ± SD) days in milk and 698 ± 54 kg body weight were used in a 3 × 3 Latin square design in each of 2 studies, with 3 periods of 28 d. In study 1, cows were fed diets based on a 50:50 ratio of red clover to grass silage [dry matter (DM) basis] containing 1 of 3 dietary CP concentrations: high (H) = 175 g of CP/kg of DM; medium (M) = 165 g of CP/kg of DM; or low (L) = 150 g of CP/kg of DM. In study 2, cows were fed 175 g of CP/kg of DM with a 50:50 ratio of alfalfa to corn silage (H50) or 1 of 2 diets containing 150 g of CP/kg of DM with either a 50:50 (L50) or a 60:40 (L60) ratio of alfalfa to corn silage. Cows in both studies were fed a total mixed ration with a forage-to-concentrate ratio of 52:48 (DM basis). All diets were formulated to meet the MP requirements, except L (95% of MP requirements). In study 1, cows fed L ate 1.6 kg of DM/d less than those fed H or M, but milk yield was similar across treatments. Mean milk protein, fat, and lactose concentrations were not affected by diet. However, the apparent total-tract nutrient digestibility was decreased in cows fed L. The NUE was 5.7 percentage units higher in cows fed L than H. Feeding L also decreased milk and plasma urea concentrations by 4.4 mg/dL and 0.78 mmol/L, respectively. We found no effect of dietary treatment on the milk saturated or monounsaturated FA proportion, but the proportion of polyunsaturated FA was increased, and milk odd- and branched-chain FA decreased in cows fed L compared with H. In study 2, DM intake was 2 kg/d lower in cows receiving L50 than H50. Increasing the alfalfa content and feeding a low-CP diet (L60) did not alter DMI but decreased milk yield and milk protein concentration by 2 kg/d and 0.6 g/kg, respectively, compared with H50. Likewise, milk protein and lactose yield were decreased by 0.08 kg/d in cows receiving L60 versus H50. Diet had no effect on apparent nutrient digestibility. Feeding the low-CP diets compared with H50 increased the apparent NUE by approximately 5 percentage units and decreased milk and plasma urea concentrations by 7.2 mg/dL and 1.43 mmol/L, respectively. Dietary treatment did not alter milk FA profile except cis-9,trans-11 conjugated linoleic acid, which was higher in milk from cows receiving L60 compared with H50. We concluded that reducing CP concentration to around 150 g/kg of DM in red clover and grass or alfalfa and corn silage-based diets increases the apparent NUE and has little effect on nutrient digestibility or milk performance in dairy cows.

This study investigated the effect of compaction, aeration and addition of a naturally mycotoxin contaminated ryegrass silage (MCS) containing 1803 µg/kg DM penicillic acid, on the nutritional value and mycotoxin content after ensiling and subsequent aerobic stability of ryegrass Lolium perenne silage (second-cut, June 2020, UK). Mini silos (30 L) were filled with differential compaction (500 kg FW/m 3 and 333 kg FW/m 3 ), aeration by injection of air (1L per 48h for 30d then 1L per 7d) and addition of MCS (1.5 g/kg FW ensiled forage) in a 2×2×2 factorial design. During ensilage, mean CO 2 % (kg FW) in the aerated silos increased with low compaction. Crude protein (CP) increased and ash decreased with aeration. Mean silage fermentation end products acetic (AA), lactic (LA) and propionic acid (PA) concentrations increased with MCS. PA concentration increased with aeration/low compaction. LA decreased and ethanol increased with low compaction. Mycotoxin profiles differed between the silages on opening and after 14-days incubation in aerobic conditions with disappearance of fusarenon X and penicillic acid and appearance of mycophenolic acid and roquefortine C (318 µg/kg DM and 890 µg/kg DM). Addition of MCS, increased the concentration of penicillic acid on opening with an interaction with aeration (80.6µg/kg DM MCS × aerated, 40.0 µg/kg DM in the MCS × sealed). Aerobic stability was affected by aeration and low compaction with reduced time taken to heat to +5°C and +10°C above ambient temperature, higher rate of increase in pH and higher cumulative temperatures to the first peak temperature. Higher mycotoxin concentration at opening had a similar effect increasing time to heat +5°C and +10°C above ambient temperatures in aerobic conditions. Regression analysis showed predominantly direct relationships between silage fermentation end-product concentrations and aerobic stability. This study revealed interactions between silage bacteria and fungi activity from the concentrations of fermentation end-products and mycotoxins during ensilage and subsequent aerobic spoilage. The results supported current best practice for silage making, promoting conditions for improved preservation and aerobic stability. The addition of MCS had unexpected positive effects. However, factors associated with the MCS benefiting aerobic stability were not determined.