Long-term effects of drenches with condensed tannins from Acacia mearnsii on goats naturally infected with gastrointestinal nematodes

Abstract

In this study, the long-term effects of exposure to a drench containing condensed tannins (CTs) from Acacia mearnsii on gastrointestinal nematodes in goats were investigated. Male cross-bred Anglo-Nubian goat kids between 3 and 5 months of age were dewormed at the beginning of the experiment. The goat kids were divided into one group that received weekly 24g oral doses of A. mearnsii bark extract dissolved in water containing 16.7% CTs (GCT group, n=8) and a second group that did not receive CTs (GC group, n=8). All of the animals were kept in an Andropogon gayanus pasture and grazed with a herd of 100 naturally infected adult goats. Each animal was supplemented daily with 200g of a concentrated mixture containing 18% crude protein. Fecal egg counts (FECs) were performed weekly for 192 days, and weight measurements and blood collections were done at two-week intervals in this period. The packed cell volume of the blood was calculated, and the plasma was used to determine the total protein, albumin, and glucose concentrations. After 192 days, the animals were slaughtered and the carcasses evaluated, with nematodes harvested for identification and counting. The FECs of the animals treated with CTs from A. mearnsii (GCT group) remained lower than the FECs of the control group animals for the majority of the first half of the experimental period. An observed increase in the FECs for both groups coincided with increased rainfall in the region where the experiment was conducted. The worm burden, scrotal circumference, carcass weight, leg circumference, carcass size and blood analysis were not significantly different between the groups. The packed cell volume (PCV) was constant in all of the animals throughout the experiment. In conclusion, repeated and prolonged treatment of goats with CTs from A. mearnsii helped to maintain low FECs in a period of low challenge but did not reduce nematode infections in the goats.