Minerals are essential for ruminant health, productivity, and metabolic function, with trace minerals playing critical roles at narrow dietary margins. Cobalt (Co) is essential as it supports ruminal microbial synthesis of vitamin B12 (cobalamin), which acts as a crucial cofactor in energy and protein metabolism. This review summarizes the role of cobalt in dairy cattle nutrition, emphasizing its contribution to vitamin B12 synthesis, propionate metabolism, and milk production. Only 3–15% of dietary cobalt is converted to vitamin B12, and efficiency depends on dietary composition, forage-to-concentrate ratio, and ruminal microbiome. Deficiency leads to reduced intake, poor growth, anemia, reproductive failure, and decreased milk yield. Cow’s milk contains ~0.5 µg/L of vitamin B12, with greater concentrations in colostrum; diet composition, supplementation, and genetics contribute to variability. Current recommendations set the cobalt requirement at 0.2 mg/kg diet DM, yet multiple environmental and nutritional factors can restrict vitamin B12 synthesis. Limitations of this review include heterogeneity among the studies reviewed, such as differences in trial design, animal genetics, diet composition, and environmental conditions, which may introduce variability and affect the generalizability and consistency of the findings. Collectively, findings highlight cobalt’s pivotal role in supporting microbial activity, energy metabolism, and production outcomes in dairy cows.

The objective of this study was to evaluate the interaction of dietary carbohydrate profile and soybean meal (SBM) replacement with either Chlorella pyrenoidosa (CHL) or Spirulina platensis (SPI) on in vitro fermentation. This experiment was conducted as a randomized complete block design, with fermentation run (3 runs) considered as blocks. The treatments were arranged in a 2 × 5 factorial design, where the first factor was the carbohydrate profile, which was composed of diets containing 42.5% neutral detergent fiber (NDF) and 26.8% starch (HF-LS) or 26.8% NDF and 40.6% starch (LF-HS), and the second factor was the protein source, in which a control diet (100% SBM), partial replacement of SBM with CHL (1/2CHL) or SPI (1/2SPI), or total replacement of SBM with CHL or SPI were used. All experimental diets were formulated to have 17% crude protein. The ruminal fluid was collected from 2 lactating Holstein cows, buffered with Van Soest medium at a ratio of 1:2 and added to serum bottles containing 0.50 g of the experimental diets. Bottles were incubated at 39°C for 24 and 48 h in triplicate; headspace pressure was measured, along with gas collection for methane (CH₄) quantification at 0, 2, 4, 8, 16, 24, 36, and 48 h after incubation. The final medium was used to measure pH, ammonia, and VFA. After incubation, feed bags were recovered and used for estimation of dry matter (DM), NDF, and organic matter (OM) degradability. Statistical analysis was carried out using the MIXED procedure of SAS, with carbohydrate profile, protein source, assay, and their interactions as fixed effects, with run and bottle as random effects. Orthogonal contrasts were used to compare carbohydrate profile, algae species, carbohydrate profile × algae interaction, and linear and quadratic effects of SBM replacement with CHL or SPI. There was no interaction effect between carbohydrate profile and algae source. The LF-HS improved gas production, degradability of nutrients, and VFA, mainly increasing the production of butyrate and propionate. When compared with CHL, SPI had a greater degradability of nutrients and branched VFA, along with reduction in total gas production and tended to reduce total CH₄ yield. The replacement of SBM with algae linearly reduced the degradability of nutrients, along with a linear reduction in gas production. When replacement of SBM with only SPI was evaluated, SPI slightly reduced the degradability of nutrients; however, it promoted a linear reduction in CH₄ yield, as well as reduction in CH₄ yield by unit of degraded DM, NDF, and OM. In summary, there was no interaction of carbohydrate profile and protein source, which means that SBM replacement had a similar effect, regardless of dietary carbohydrate profile. Spirulina may be a more suitable algae source than Chlorella due to the potential to reduce CH₄.

The objective of this study was to determine the impacts of feeding a rumen-protected matrix of fat and protein from flaxseed and peas (LinPRO-R, LIN; approximately 21% fat, 24% CP, and 10.07% omega-3 FA; % of DM) on ruminal fermentation, nutrient degradability, and methane emissions, in vitro. Treatments were: 0 (0P), 2.5 (2.5P), 5 (5P), and 7.5% (7.5P) of DM inclusion of LIN, with LIN replacing portions of dried distiller's grains and calcium salts of long-chain fatty acids in the diet to maintain similar levels of CP and EE. In Experiment 1, 3 independent runs with 4 replicates per treatment were used, and 0.5 g of each TMR (16% CP, 33% NDF, 28% starch, 4.2% EE; as % of DM) was incubated in buffered ruminal content for 24 and 48 h, for a total of 6 runs, in glass serum bottles. Gas pressure was measured at 0, 3, 6, 9, 12, 24, and 48 h to estimate total gas and methane productions in the headspace and VFA and lactate concentrations in the fermentation liquid phase. Furthermore, OM degradation was measured at 24 and 48 h after bottles were opened. For Experiment 2, twice daily, 53 g of DM of the same treatments was provided to each fermenter. The treatments were arranged in a replicated 4 × 4 Latin square using 8 fermenters. Four 10-d experimental periods (7 d adaptation and 3 d sample collection) were done. Samples were collected from fermenter effluents at 3, 6, 9, and 24 h after morning feeding and composited to determine lactate and VFA concentrations and nutrient degradation. Experiment 1 data was analyzed using PROC GLIMMIX of SAS where treatment was a fixed effect and run was a random effect. Experiment 2 data were analyzed similarly, with square, fermenter within square, period, and the fermenter by treatment interaction being random effects. For Experiment 1 with increasing LIN, total gas volume and methane produced per g of OM degraded decreased linearly, whereas lactate concentration and OM degradability linearly increased. There was no effect of LIN inclusion level on any VFA proportion. For Experiment 2 Butyrate and isobutyrate proportions linearly decreased, and NDF degradation quadratically increased, with increasing inclusion of LIN. There were no differences for any other VFA proportions, the total concentration of all VFA, lactate concentration, or the degradation of DM, OM, or CP. Thus, inclusion of LIN, with its higher concentration of omega-3, can occur without impairing ruminal fermentation and nutrient degradation, and alters the fermentation profile to reduce total gas volume and methane produced per g of OM degraded as well as favor other VFA rather than butyrate or isobutyrate and increasing fiber degradation.

The objective of this study was to evaluate the effects of different slow-release urea (SRU) compounds on ruminal fermentation, nutrient degradation, and nitrogen (N) utilization in a dual-flow continuous-culture system (experiment 1), as well as ammonia-N (NH₃-N) release rate in a batch culture system (experiment 2). In experiment 1, 8 fermenters were used in a replicated 4 × 4 Latin square design with 4 treatments and 4 experimental periods. The treatments were formulated to contain the same amount of N, differing in the source of nonprotein N, such as control (CON), with noncoated urea at 0.62% DM; partial inclusion of SRU compound 1 (SRU1) at 0.51% DM; partial inclusion of SRU compound 2 (SRU2) at 0.51% DM; and partial inclusion of SRU compound 3 (SRU3) at 0.51% DM. Each period lasted 10 d. The last 3 d of each period were used for sample collection. Samples were collected for pH, lactate, VFA, NH₃-N kinetics, nutrient degradability, and N metabolism. In experiment 2, a batch culture incubation was conducted as a complete randomized block design, using 3 Erlenmeyer flasks per treatment in 3 runs. Each treatment contained 1 of the 4 NPN sources used in experiment 1, (CL, S1, S2, S3) or without any NPN (blank, BK), and samples were collected at different time points for NH₃ analysis. All flasks, except for BK, contained equal amounts of 21.56 mg N, and all flasks were inoculated with 260 mL of a 1:2 mixture of ruminal fluid and nutritive solution. Data of both experiments 1 and 2 were analyzed using the MIXED procedure of SAS. In experiment 1, there were no effects of treatment on pH or NH₃-N kinetics. There were no effects of treatments on lactate kinetics; however, there was an interaction between treatment and time. For 24-h VFA pool, there were treatment effects on acetate, propionate, acetate:propionate ratio (A:P), and branched-chain (BC)VFA proportion. Compared with CON, SRU1 had lower A:P ratio and acetate proportion, with greater proportion of propionate, which could represent a favorable fermentation partner compared with CON. Treatment SRU1 had lower BCVFA proportion than the other treatments, which indicates less protein degradation. There were no treatment effects for nutrient degradability and N flow. Based on observations in experiment 1, SRU1 could have the potential of improving ruminal fermentation and N utilization. Moreover, the different SRU compounds had different fermentation patterns according to their VFA profiles. In experiment 2, there were significant effects for treatment and time, and a tendency for treatment by time interaction effect. The N release rate of S1 was similar to CL and faster than S2 and 3, and the differences in N release rates could be detected as early as at 0.75 h of incubation. Thus, S1 may not be as slow degrading when compared with S2 and S3. In conclusion, no effects were found on nutrient degradability and N utilization. However, the different SRU compounds had different N release rates, which could affect ruminal fermentation pattern in different diets.

This study aimed to evaluate in situ ruminal nutrient degradation, fractional disappearance rate, and effective ruminal degradation of hydroponically sprouted barley, wheat, and triticale. Two ruminally canulated lactating cows were used in a complete randomized block design with four treatments and nine incubation times (0, 2, 4, 8, 12, 24, 48, 72, and 240 h). Treatments were corn silage (control), and sprouted barley, triticale, and wheat. Quadruplicate samples (5 g each) were placed in Dacron bags and incubated in the rumen. Then, bags were rinsed and spun, dried (48 h × 55 °C; 3 h × 105 °C), and weighed to determine residual dry matter (DM). Data were analyzed using mixed models (MIXED, SAS 9.4) with treatment, time, and their interaction as fixed effects, and cow and replicate (cow) as random effects. Denominator degrees of freedom were adjusted using the Kenward–Roger method, and means were separated by Tukey–Kramer. Significance was declared at p ≤ 0.05 and tendencies at 0.05 < p ≤ 0.10. Sprouted triticale and wheat treatments had a greater rapidly soluble fraction for DM (p < 0.01), the greatest fractional disappearance rate for DM (p < 0.01) and neutral detergent fiber (NDF; p < 0.01), and greater effective ruminal degradability (ERD) for DM (p < 0.01) and crude protein (CP; p < 0.01). Sprouted wheat also had the greatest ERD for NDF (p < 0.01). In contrast, sprouted barley had the lowest rapidly soluble fractions for DM (p < 0.01), NDF (p < 0.01), and CP (p < 0.01), lower fractional disappearance rate for DM (p < 0.01) and NDF (p < 0.01) than sprouted triticale and wheat, and the lowest ERD for DM (p < 0.01) and CP (p < 0.01). Overall, sprouted triticale and wheat had greater in situ ruminal nutrient degradation, effective ruminal degradation, and nutrient degradation kinetics, indicating their potential for inclusion in dairy cattle diets to improve nutrient degradability.

This study aimed to evaluate the sulfur hexafluoride (SF₆) tracer technique for estimating methane (CH₄) emissions in dual-flow continuous culture systems (DFCCS). In experiment 1 (Exp1), fermenters were filled with water, and known CH₄ concentrations (0, 1.35, 2.93, or 4.43 g/d) were injected using permeation tubes with SF₆ release rates (3.30 or 9.65 mg/d). Headspace gas was collected using canisters, and the SF₆ technique estimated CH₄ recovery. Experiment 2 (Exp2) involved a DFCCS fermentation trial with ruminal fluid from three Holstein cows, testing diets with soybean meal or its partial replacement (50%) by Chlorella or Spirulina. Headspace gas was collected at intervals post-feeding. Standard curves for SF₆ and CH₄ quantification were inadequate for DFCCS samples, with the CH₄:SF₆ ratio differing from standards, indicating the data needs further SF₆ release rate evaluation. In Exp1, a high correlation (r = 0.97) was found between infused and calculated CH₄, indicating good repeatability. Low and high SF₆ rates performed similarly at low CH₄ infusion, but high SF₆ overestimated CH₄ at high infusion. Exp2 showed CH₄ emissions irrespective of SF₆ rate and indicated reduced CH₄ emissions and increased NDF degradation with algae-containing diets. Further evaluation of the SF₆ tracer technique is warranted for DFCCS.