The objective of this study was to evaluate the effect of different percentages of alfalfa (Medicago sativa L.) hay (AH) and doses of guanidinoacetic acid (GAA) in the diet on the mitigation of greenhouse gas production, the in vitro rumen fermentation profile and methane (CH₄) conversion efficiency. AH percentages were defined for the diets of beef and dairy cattle, as well as under grazing conditions (10 (AH10), 25 (AH25) and 100% (AH100)), while the GAA doses were 0 (control), 0.0005, 0.0010, 0.0015, 0.0020, 0.0025 and 0.0030 g g⁻¹ DM diet. With an increased dose of GAA, the total gas production (GP) and methane (CH₄) increased (p = 0.0439) in the AH10 diet, while in AH25 diet, no effect was observed (p = 0.1311), and in AH100, GP and CH₄ levels decreased (p = 0.0113). In addition, the increase in GAA decreased (p = 0.0042) the proportion of CH₄ in the AH25 diet, with no influence (p = 0.1050) on CH₄ in the AH10 and AH100 diet groups. Carbon monoxide production decreased (p = 0.0227) in the AH100 diet with most GAA doses, and the other diets did not show an effect (p = 0.0617) on carbon monoxide, while the production of hydrogen sulfide decreased (p = 0.0441) in the AH10 and AH100 diets with the addition of GAA, with no effect observed in association with the AH25 diet (p = 0.3162). The pH level increased (p < 0.0001) and dry matter degradation (DMD) decreased (p < 0.0001) when AH was increased from 10 to 25%, while 25 to 100% AH contents had the opposite effect. In addition, with an increased GAA dose, only the pH in the AH100 diet increased (p = 0.0142 and p = 0.0023) the DMD in the AH10 diet group. Similarly, GAA influenced (p = 0.0002) SCFA, ME and CH₄ conversion efficiency but only in the AH10 diet group. In this diet group, it was observed that with an increased dose of GAA, SCFA and ME increased (p = 0.0002), while CH₄ per unit of OM decreased (p = 0.0002) only with doses of 0.0010, 0.0015 and 0.0020 g, with no effect on CH₄ per unit of SCFA and ME (p = 0.1790 and p = 0.1343). In conclusion, the positive effects of GAA depend on the percentage of AH, and diets with 25 and 100% AH showed very little improvement with the addition of GAA, while the diet with 10% AH presented the best results.

Different levels of metabolizable energy (ME) and the inclusion of guanidinoacetic acid (GAA) in the diet of 53-week-old Lohmann LSL-CLASSIC hens were used to evaluate its effect on reproductive parameters, egg quality, intestinal morphology, and the immune response. Six diets were used in a 3 × 2 factorial design, with three levels of ME (2850, 2800, and 2750 kcal/kg), and with (0.08%) or without the inclusion of GAA. The addition of GAA to diets with low levels of ME increased (p < 0.05) egg production and egg mass. Moreover, hens fed with 2800 kcal/g without GAA had the highest concentration (p < 0.05) of serum interleukin IL-2, while those fed diets with the same amount of ME but supplemented with 0.08% GAA had the lowest concentration. Finally, the inclusion of 0.08% GAA increased (p < 0.05) the concentration of vascular endothelial growth factor (VEGF), regardless of the ME level in the diet. This study highlights the potential role of GAA in decreasing the energy level of ME (50–100 kcal/g) in the feeding of hens and in the modulation of specific immune responses. Further research is recommended to fully understand the mechanisms of action of GAA on the mechanism target of rapamycin and its relationship with the immune response.

Infestation by Varroa destructor represents one of the major challenges for beekeeping, as it compromises both colony health and honey productivity. The objective of this study was to evaluate the efficacy of different organic treatments for the control of V. destructor and their effect on honey production in Apis mellifera colonies located on the central region of Tamaulipas, Mexico. A total of 150 colonies were assigned to five treatments: T1, oxalic acid with glycerin; T2, sublimated oxalic acid; T3, Thymol, T4; HappyVarr; and T5, an untreated control. Mite infestation (initial and final) and honey production were analyzed using a non-parametric approach and were evaluated with the Kruskal–Wallis test, and when significant differences were detected, Steel–Dwass multiple comparisons were performed. To examine the relationship between infestation reduction and honey yield, Spearman’s rank correlation was applied. No significant differences were observed in the initial infestation levels. However, final infestation levels showed highly significant differences among treatments (p < 0.0001), with T1, T2, T3, and sublimated oxalic acid (T4) significantly reducing mite infestation compared with the control. Sublimated oxalic acid represents the most effective and productive control method under the tested conditions. Honey production also differed significantly among treatments (p < 0.0001), with the highest yields recorded in T3 and T4. A strong negative correlation was detected between final infestation and honey production (p < 0.0001). In conclusion, treatments based on oxalic acid (particularly sublimated) and HappyVarr proved effective in reducing V. destructor infestation and improving honey production, highlighting their relevance as viable alternatives for sanitary management in beekeeping.