Semina: Ciências Agrárias (Jun 2017)
Evaluation of animal performance, feed intake, and economic losses in sheep experimentally infected with Trypanosoma vivax
Abstract
Trypanosoma vivax is a protozoan originating from the African continent, which, although it has not yet been able to complete its biological cycle in South America, due to the absence of the tsetse fly, can still cause death in ruminants. The objective of this study was to verify the effects of T. vivax on the measurements and indices in sheep that characterize animal performance, as well as on economic losses in meat animals. Twenty intact adult male sheep were used for this study, all of approximately the same ages and weights, reared in confinement, and subjected to the same management and diet, which was balanced and supplemented with adequate minerals. The animals were divided into two groups: the control group (CG) and the infected group (IG), which was inoculated intravenously with 1.3 x 105 trypomastigotes of T. vivax. Feed intake was verified daily, whereas the feed conversion (FC), feed efficiency index (FEI), and weight gain were obtained weekly. Total weight gain (TWG) was determined after 70 days post-infection. The economic loss was calculated by subtracting the value obtained (IG) from the expected value (CG), and the difference was expressed as a percentage. A randomized block design was used to isolate the effect of the initial weight. The means were compared by the Student “t” test at 5%. Of the 10 infected animals, one died from the parasitism, yielding a rate much lower than that observed in natural outbreaks. The groups presented similar feed intakes throughout the experimental period; however, the TWG of the infected group was significantly lower (50.7%) than that of the CG. Similarly, the daily weight gain (DWG), feed conversion (FC), and feed efficiency index (FEI) of the IG were significantly lower than those of the CG. In addition, the worst rates of FC and FEI coincided with parasitemia peaks and recurrences, probably due to immunological demand and tissue repair. The abdominal circumference of the infected animals was statistically lower than that of the CG, which may be directly related to fat mobilization, in addition to the possible negative effect on the digestive capacity. The economic losses due to weight alone were 24.07% and could reach 31.66% of the herd value due to animal death. Infection with T. vivax negatively affected animal performance indices, even when the animals were well nourished. Trypanosoma vivax in sheep destined for slaughter caused economic losses of 31.66% due to the decrease in performance and the death rate in the infected group.
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