Can Changes in Thyroid Hormones be used as an Indicator of Trypanotolerance in Goats?

Abstract

Non definitive and simple markers have been found for characterization of trypanotolerant and trypanosusceptible animals though Trypanotolerance trait is currently being  looked upon as one of the potential means of increasing livestock productivity in tsetse endemic areas. Since thyroid hormones are thought to play a key role in mammalian adaptive processes to  various stressful environments  it  was the  objective  of this study to find out whether their variations in trypanosome-infected animals could be used as markers for trypanotolerance. Plasma thyroxine (T4) levels were measured in experimentally Trypanosoma congolense infected small East African female goats obtained from three tsetse-endemic areas i.e Lambwe Valley in Kenya, Arusha and Morogoro in Tanzania and one tsetse-free area i.e Imbo in Kenya. T4 levels declined rapidly and progressively after one week of parasitaemia in all infected goats and remained low during the six months infection period. A positive correlation was obtained between decline in T4 levels and the state of health of the  goats as measured  by loss   of body weight (r = 0.62; P<0.001) and  PCV (r  = o.76;  P<0.001); that is change in T4 levels being less severe in trypanotolerant goats and vice versa. Similarly, trypanotolerant goats with reduced T4 depression had intermittent and low parasitaemia and reduced reproductive impairment. It is suggested that T4 levels should be considered an additional index which can be used for assessing trypanotolerance in goats and possibly in other livestock breeds residing in vast tsetse-endemic areas of the tropics.