C.M. SHAYO^1,2 and P. UDÉN²

¹Zonal Research and Training Centre, Livestock Production Research Institute, Mpwapwa, Tanzania
²Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden

Abstract

An investigation was made of: the voluntary intake of pods of 4 tropical browse trees by different classes of domestic ruminants; and the proportion of intact seeds that passed through the digestive tracts. Germination of undigested whole seeds recovered from faeces and uningested seeds treated with hot water and acid or untreated was also determined. Pods of Faidherbia albida (Acacia albida), Acacia tortilis, Acacia nilotica and Dichrostachys cinerea were opened to estimate the percent by weight of intact and damaged seeds in the pods. Whole pods from each species were fed to heifers, calves and mature and young sheep and goats for 2 weeks. Faeces from the animals were collected daily during the second week and washed through a sieve to retrieve the undamaged seeds. Uningested seeds were also soaked either in hot water for 2, 4 or 6 min or in H₂SO₄ (70% v/v) for 0.5, 1.5 or 3 h. Germination rates of treated and untreated seeds and seeds collected from faeces were determined over a period of 13 weeks.
Pods of Acacia tortilis had a significantly (P < 0.05) higher percentage by weight of seeds (33%) than those of other species, with F. albida and D. cinerea having the lowest percentage of seeds (10%). Intakes of F. albida and A. tortilis pods for all classes of animal were similar and significantly (P &$60; 0.05) higher than intakes of pods of other species. Intakes of D. cinerea pods were significantly (P < 0.05) higher than those of A. nilotica pods, except for young sheep and young goats, and similar to those of F. albida and A. tortilis, except for heifers and mature sheep. Animal age had no effect on pod intake as % body weight (BW). Average intake (% BW) of pods was highest for F. albida (2.4%) and A. tortilis (2.4%) followed by D. cinerea (1.8%) and A. nilotica (0.9%). Both classes of cattle passed a significantly (P < 0.05) higher percentage of ingested seeds than did sheep and goats. Sheep and goats digested considerably higher amounts of the seeds, particularly those of F. albida and A. tortilis, suggesting that cattle would benefit nutritionally from grinding of the pods. Germination was not improved by passage of seeds through the digestive tract of any animal, whereas hot water and acid treatments generally reduced or had no effect on germination. Germination of A. nilotica seeds treated with acid for 1.5 and 3 h was significantly (P < 0.05) enhanced.