Utilização dos ácidos de lúpulo como modulador ruminal em dietas para vacas leiteiras

Abstract

Given the global demands for reducing greenhouse gas emissions and the restriction on the use of antibiotics in animal feed, the search for alternative and sustainable additives for ruminant nutrition has intensified. In this context, hop acids, bioactive compounds derived from plant extracts, show potential for modulating ruminal fermentation. The objective was to evaluate the effects of hop acids as an alternative zootechnical additive to sodium monensin in dairy cow diets. CHAPTER II: In the first experimental trial, the effect of different levels of hop acids, with tetrahydro-iso-alpha acid being the most prevalent, on the productive performance and ruminal metabolism of dairy cows was evaluated. The experiment was conducted on a farm located in the municipality of Douradina, Mato Grosso do Sul, using eight cows, four of which were rumen-cannulated and non-lactating, and four lactating cows that were not cannulated. The animals were distributed in two 4 × 4 Latin squares. The treatments consisted of the inclusion of 0, 5, 10, and 15 g/animal/day of hop acids. The experimental period was 20 days, with 14 days of adaptation and 6 days of data collection. No effects on dry matter and nutrient intake were observed. There was an increase in the digestibility of organic matter and total carbohydrates up to an estimated level of 8.6 g/day. The ruminal concentration of N-NH₃ was reduced, with an estimated minimum point at 8.22 g/day. Hop acids altered the concentrations of acetic and propionic acid, as well as their ratio, in addition to reducing the estimated concentration of methane, with a minimum point close to 10 g/day. A linear increase in nitrogen retention was also observed. The results indicated the favoring of more energy-efficient fermentative pathways, with the inclusion of 10 g/animal/day considered the most efficient. CHAPTER III: The second experimental trial compared the level of hop acids determined in the previous trial with other commercial additives. The treatments were: 1) CON (control group, basal diet without additives); 2) MON (inclusion of 24 mg/kg DM of sodium monensin); 3) TAN (2.5 g/kg DM of Acacia mearnsii tannin); 4) HOPS (10 g/animal/day of hop acids). The experimental design was the same as in the first experiment. There was no effect of the additives on DM and nutrient intake and digestibility, milk production, and milk composition. The milk lipid profile showed lower C4:0 values with MON and HOPS. C18:0 levels were higher with HOPS. The greatest effects of the additives were observed in ruminal fermentation, where there was modulation in the production of acetic and propionic acid when the animals received MON and HOPS, a decrease in the acetate/propionate ratio, and in the methane estimate. Tannin decreased methane production compared to the control. It was concluded that hop acids have potential for use in dairy cow nutrition, aiming to achieve fermentative modulation, classifying as a potential substitute for sodium monensin, while tannin showed discreet or absent effects.