Efeito da suplementação com fontes naturais de antioxidantes em vacas leiteiras recebendo dietas ricas em ácidos graxos poli-insaturados

Abstract

Three studies were conducted to evaluate the effects of natural antioxidant sources on performance, milk quality and plasma and milk lipoperoxidation of dairy cows given high polyunsaturated diets. The first study was performed to investigate the effects of supplementing two products, SBO (0.2 kg/d) or SBO+CPP (0.2+1.0kg/d), at two different sites, rumen or abomasums, on the transfer of antioxidant properties to milk, milk FA profile, milk production, and ruminal fermentation. Fourruminally fistulated lactating Holstein cows were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments: 1) SBO administered in the rumen; 2) SBO infused in the abomasum; 3) SBO+CPP administered in the rumen; and4) SBO+CPP infused in the abomasums. Total DM input tended to be decreased with abomasal infusion of SBO and SBO+CPP. Product and site of supplementation had no effect on milk production and composition. However, cows infused in the abomasums compared to those administered in the rumen showed higher proportions of polyunsaturated which resulted in enhanced health-promoting index (HPI) of milk. Ruminal pH and ammonia N concentration were similar among treatments, but total volatile FA production was reduced when SBO was administered in the rumen. There was no advantage to supplement SBO and CPP in the rumen or the abomasum on milk antioxidant properties although rumen bypass of SBO increased the proportion of polyunsaturated FA in milk fat and enhanced milk HPI. The second and the third studies were from the same experiment in which eight ruminally fistulae lactating Holstein cows were assigned to a double 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments: 1) no FM in the diet and no abomasal infusion ofFO; 2) diet containing 124 g FM/kg (dry matter (DM) basis) and no abomasal infusion of FO; 3) no FM meal in the diet + abomasal infusion of 0.25 kg/d FO; 4) diet containing 124 g /kg FM (DM basis) + abomasal infusion of 0.25 kg/d FO. The second study was conducted to evaluate the effects of dietary antioxidants from FM on performance and antioxidant status in dairy cows infused with FO in the abomasums .Intake of DM was increased for cows fed FM and reduced for cows infused with FO. Milk production and milk composition did not differ among treatments except for lactose concentration that was increased by FO. Milk fat from cows fed FM had higher monounsaturated and lower omega-6 FA proportions. Abomasal infusion of FO increased proportions of polyunsaturated FA and improved the HPI. Feeding FM did not change plasma and milk TBARS concentration and the lag phase duration of formation and oxidation rate of conjugated dynes in plasma as well. Neither FM nor FO affected total antioxidant capacity in plasma. Overall, the results suggest that FM supplementation to dairy cows receiving a source of polyunsaturated FA that by passesthe rumen does not provide any benefits for protecting cows and milk againstlipoperoxidation. The third study was performed to evaluate the effects of antioxidants from FM and abomasal infusion of FO on the activity of antioxidant enzymes(superoxide dismutase, catalase and glutathione peroxidase (GPX)) in blood andmammary tissue and the mRNA abundance of antioxidant and lipogenic-related genesin mammary tissue of dairy cows were determined. Catalase activity in erythrocytes tended to increase when cows were fed FM. Abomasal infusion of FO had no effect on activity and gene expression of antioxidant enzymes and gene expression of lipogenic-genesin mammary tissue, except for an increase in GPX1 expression in the absence of FM. The results suggest that feeding 124 g FM/kg FM and infusing 0.25 kg/d FO in the abomasum of dairy cows does not induce significant changes in the activity of antioxidant enzymes in blood and mammary tissue, and expression of antioxidant and biogenic-genes in mammary tissue. However, more studies are required to determine any beneficial effects of natural antioxidants such as FM on the oxidative status of cows supplemented with polyunsaturated fatty acids, which could lead to feeding strategies to prevent diseases affecting the health status of dairy cattle.