Strategies for improving productivity of small ruminants in Tanzania
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This thesis presents three areas of emphasis, all related to feeds, feeding and performance of small ruminants. The first area (Paper I) focuses on seasonality and its effect on chemical composition of forage species most preferred by SEA goats, grazing behaviour and performance of goats as assessed in the rainy (February-May), mid dry (July-August) and late dry seasons (October-November). Evaluation of these forages showed a marked decline in quality as the season changed from rainy to dry. The crude protein (CP) and energy content of all forages decreased while the neutral detergent fibre content increased. The decline in feed quality varied with forage class. Unlike forbs and browses, the mean CP of grasses, for example, declined below the critical maintenance level for goats from the end of the rainy season through late dry season. Mineral concentrations varied among species and forage classes and were all low in phosphorous level. Changes in season were clearly associated with shifts in diet selection, grazing and non grazing activities. Whereas herbaceous vegetation was the main diet in the rainy season, browses and forbs were important dietary sources in the dry season. Observation on grazing activities and performance of goats in the same study showed that the proportion of time allocated for various activities varied with the changing season. For example, feeding time changed from 0.57 (57 %) in the rainy season to 0.68 (68 %) in the late dry season. Body weight gains and condition scores were highest in the middle of the dry season while the least performance of these variables was recorded late in the dry season. The second area of this work (Paper II) presents an investigation of the influence of pre-mating dietary supplementation and the season of kidding on reproductive characteristics of SEA goats and growth performance of their off springs. The seasons were either early dry (season 1) or late dry (season 2). Results from three groups of 30 does each subjected to 0, 200 or 400 g of concentrate diet/doe/day for a period of 60 days prior to mating showed that pre-mating dietary supplementation improved (P<0.05) weight gains but the reproductive performance was not improved. Doe weight changes and growth rates of kids were affected by the season of kidding. Body weight changes of does, pre-weaning growth and weight of kid weaned per kg doe kidding and the weight of kid weaned per doe kidding were higher for kidding taking place in season 1 compared with that in season 2. Results suggest that production efficiency of goats can be increased by restricting goat breeding activities in January-March for kidding to take place early in the dry season (June-August). The third area (Papers III, IV and V) focused on growth performance, carcass yield and meat quality characteristics of small ruminants when supplemented with concentrate diets with either hay and/or treated straws as basal diets. In Papers III and IV, 32 sheep and goats were subjected to either ad libitum untreated wheat straw (UTS), wheat straw treated with urea and lime (TS), straw and ad libitum hay (UTSH) or TS and ad libitum hay (TSH). In addition, each animal received 220 g of concentrate diet/day (on as fed basis) for 84 days. Treatment of straw increased (P<0.05) dry matter intake (42.3 vs. 33.7 g/kgW.75/day), energy intake (4.6 vs. 3.7 MJ ME/day) and the average daily gain (40.7 vs. 23.1 g) of sheep. The corresponding values for goats were (41.7 vs. 30.9 g/kgW.75/day), (4.55 vs. 3.30 MJ ME/day) and (16.9 vs. 8.1 g). Animals on TS also produced heavier (P<0.05) carcasses with superior conformation than animals on UTS. Results also showed that muscles from goats were less tender compared with those from sheep. In the final study (Paper V), 23 castrated SEA goats were used in a 90-day experiment. These goats were divided into four groups that were fed either ad libitum concentrate allowance (T100), 66 % of ad libitum concentrate allowance (T66), 33 % of ad libitum allowance (T33) or no concentrate (T0). For each animal, grass hay was offered ad libitum at 20 % refusal rate. Daily body weight gain for T100 goats was 31 g and 14 g higher (P<0.05) than that of T33 and T66 goats, respectively. Hot and cold carcass weights for both T100 and T66 goats were 3 kg heavier (P<0.05) than that of T0 goats. Results in Papers III and IV showed that temperature decline in goat carcasses proceeded at a lower rate than the decline in sheep carcasses and that the effect of diet on pH values was not significant (P>0.05). On the other hand, goat meat had slightly higher pH both at 45 min PM and 24 h PM than sheep meat. Post-mortem ageing of sheep meat improved (P<0.001) tenderness especially after 9 days of ageing. The Warner Bratzler shear force value of m. longissimus dorsi aged for 9 days was 20 % lower than that aged for 0 day. However, ageing of goat meat up to 9 days PM had no effect (P>0.05) on tenderness. Overall, results showed potential for increased productivity in small ruminants through improved nutrition and proper timing of mating periods. Where characteristics of meat quality were assessed, there were limited effects of dietary treatments on such characteristics.