Comparative Physiological, Biochemical And Behavioural Responses To Heat Stress And Low Dietary Energy In Selected Tanzanianlocal Chicken Ecotypes

ABSTRACT As an important source of income and protein, local chickens are widely reared by a majority of rural and peri-urban households in many developing countries including Tanzania.However, these birds are seasonally exposed to challenging environments that includehigh temperatures and decreased scavengeable food materials.It was hypothesized that local chickens bred from different regions of Tanzania might have selected ecotypes with stronger tolerance to high temperatures andsuboptimal nutrition.Two groups of studies were conducted to compare effects of heat stressand low dietary energy in three Tanzanian chicken ecotypes: Kuchi (KU), Ching‟wekwe (CH) and Morogoro medium (MM). In the first study conducted at prevailing cyclic ambient temperatures, 4 weeks old hens wereeither fed a control diet containing 2864 Kcal/kgMEor diets containing 40 or 55% less energy than the control over a period of 7 weeks. Results showed ecotype-specific responses through differences in growth performance, feed conversion ratios (FCRs),behavioural responses, blood indices,and liver hsp70 and iNOS gene expressions.MM showed better performance at 55% restriction level whereas Kuchi exhibited better performance at 40% restriction and control energy levels. In the second study, the first batch of chickens was exposed to a constant temperature of 32±1°C for 7 days and thereafter raised and maintained at 37±1°C (8hrs per day) for 10 days, whereas the second batch was subjected to similar conditions but fed 55% less dietary energy than the control. Results showed ecotype-based differences in responses to both heat stress and a combination of heat stress with low dietary energy. MM had greater tolerance to heat stress and its combination with low dietary energy than KU and CH but similar to CH when only heat stress was applied, with respect to liver hsp70 gene expression and serum corticosterone.Collectively, the results show that growth performance and responses to heat stress and low dietary energy in the three local chicken ecotypes are different andhave iii provided starting points for future research to devise programs that include physiological, biochemical and behavioral traits that would enhance selection for heat and low dietary energy tolerance among the local chicken stocks. Key words: behaviour,ecotype, gene expression, restriction, stress,temperature, tolerance