Aster Abebe Woldemariam defended her PhD thesis on December 7th 2010

Ane Gro Siri Skjelfjord

Nutritional and anti-nutritional quality of range vegetation in Southern Ethiopia and supplementary values of selected browse leaves to goats

Livestock are reared in all agroecological zones of Ethiopia under various production systems. Goats, although found in all agroecological zones, are popular in the drier environments since they adapt well in harsh condition better than sheep and cattle. Natural vegetation comprised of both woody and herbaceous species provides the feed base year round in such environments. Due to seasonal variations, a marked fluctuation in feed resource exists in quantitative and qualitative terms. The herbaceous particularly the grasses, are faster in deteriorating while most of the woody (browse) species maintain greenness and are able to provide higher level of crude protein and minerals to animals. In areas where crops and livestock are integrated, crop residues provide substantial amount of feed to animals. However, cereal straws are inherently low in crude protein and high in fibre which results in low intake and digestibility. Thus such feeds cannot even meet maintenance requirement of animals and should be supplemented to enhance their nutritive value. Supplementation with browse foliage and fruits could be a viable alternative in smallholder livestock-crop mixed production systems.

The study was comprised of four individual works. In experiment I, nutritional quality of some important browse and grass species collected from Borana rangeland during the hot dry and main rainy seasons were evaluated in terms of chemical composition, in vitro digestibility and in sacco degradability potentials. In experiment II, the effect of polyethylene glycol (PEG) on feed intake, digestibility, ammonia nitrogen concentration, nitrogen balance and body weight gain of Borana goats was evaluated. Goats were fed a basal diet of Rhodes grass (Chloris gayana) hay supplemented with either Acacia brevispica or Acacia seyal leaves with or without PEG addition. The concentrate replacement value of Balanites aegyptiaca leaves was evaluated in experiment III. The concentrate was replaced at 25, 50, 75 and 100 percent by Balanites aegyptiaca and feed intake, digestibility, nitrogen balance, excretion of purine derivatives and microbial nitrogen supply and average daily body weight gain were evaluated using Arsi-Bale goats fed barley straw as a basal diet. The fourth component of the study was a survey conducted in the southern rangelands to assess the perception of pastoralists towards dry season feed shortage and associated livestock poisoning in the rangeland.

The browse foliage had higher crude protein content (>10%) during both seasons with higher values in the main rainy season (except for A. seyal). On the other hand, crude protein content of grass species was only slightly above the critical limit required to maintain proper functioning of rumen microbes. The fibre content was lower in the browses and higher in the grasses. The concentration of condensed tannins was variable among the browses ranging between negligible levels to over 30%. The in vitro and in sacco digestibility values were generally higher for browses, which shows their potential to be used as supplements to poor quality fibrous feeds. Experiment II showed that addition of PEG did not result in significant differences in feed intake, digestibility of dry matter, organic matter, and neutral detergent fibre as well as in nitrogen excretion and retention, and average daily weight gain. However, goats receiving PEG had higher crude protein digestibility, ammonia nitrogen concentration, and urinary nitrogen excretion. Goats without PEG addition had higher faecal nitrogen loss. When the type of Acacia was considered, A. seyal supplemented goats had higher feed intake while crude protein digestibility and ammonia nitrogen concentration were higher for A. brevispica supplemented goats. Higher average daily body gain was recorded for A. seyal supplemented goats. Experiment III showed that B. aegyptiaca had a potential to be used as supplement to cereal straw based diets. This was evident from the performance of the animals even when the concentrate was replaced completely by B. aegyptiaca. All animals had positive average daily body weight gain although it was lowest in animals supplemented with sole leaves of B. aegyptiaca. The survey revealed that the pastoralists in the southern rangelands are knowledgeable in allocation of resources, animal husbandry and ethnoveterinary practices. It also showed the concern of pastoralists about the changes in vegetation that favors woody and some unpalatable herbaceous species. Twenty two plants were identified by pastoralists as causes of livestock poisoning when ingested which usually occurs when animals are hungry and thirsty.

Updated: 07.12.10
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