H. J. Schwartz

Seasonal changes of ingesta mean retention time and forestomach fluid volume in indigenous camels, cattle, sheep and goats grazing a thornbush savannah pasture in Kenya

The study was carried out in northern Kenya in 1984–87. Forestomach volumes and digesta retention times were measured using Cr-EDTA or Co-EDTA as fluid markers and Ce-labelled particles or Cr-mordanted particles as paniculate phase markers. Mean retention times of fluid and of particles were longer in the dry season than in the green season in all four animal species. The increase of particle mean retention time, as a percentage of the values in the green season, was highest in sheep (46%), followed by cattle (27%), goats (22%) and camels(18%). Forestomach volumes were also greater in the dry than in the green season; the increase was again highest in sheep (55%), followed by cattle (31%), goats (29%) and camels (28%). Outflow rates of fluid from the forestomach and the selectivity factor, by which small particles were retained longer in the forestomach than fluid, did not differ significantly between the seasons. It is suggested that the increase of forestomach volumes is an effective adaptation to dry-season pasture conditions. It enables the animals to retain feed particles longer in the forestomach and so improve fibre digestion when feed quality is low. Cattle and sheep, which depend on a poor quality diet, improve fibre digestion in this way in the dry season more effectively than camels and goats. Camels and goats, on the other hand, were able to select a diet of such quality, even in the dry season, that their need to augment fibre digestion was reduced.

Land degradation in African pastoral systems and the destocking controversy

Abstract The discussion about rangeland degradation in African pastoral systems has so far largely been based on the conventional theory of ‘carrying capacity’. This paper argues that the carrying capacity concept and the related ‘destocking policy’ as a management strategy to increase productivity and to protect rangelands from degradation are of little applicability in African pastoral systems. They ignore the spatial and temporal variability in primary biomass production, as well as the effect of spatial and temporal fluctuations in forage quality on animal production. A case study from Northern Kenya shows that the rapid decrease in forage quality in the dry season is the crucial factor determining livestock production and pastoral land use patterns. The results of a principal component analysis indicate that rangeland degradation does not occur in most of the range units considered because grazing is limited to a short time span in a year. In contrast, the few range units with a good potential are susceptible to degradation when formerly mobile pastoral households become sedentary and overuse these key resources. An example from Marsabit District, Northern Kenya, shows that carrying capacity figures overestimate the potential livestock-supporting capacities. Destocking rangelands would result in a serious decline in the productivity of pastoral production systems and is not likely to halt rangeland degradation. It is concluded that land use policy interventions in Northern Kenya should not focus on the manipulation of absolute livestock numbers, but rather on the optimal distribution of animal abundance in space and time.

An analysis of the variation of the lactation curve of Small East African goats

Lactation curves were fitted to 267 lactations from Small East African goats kept under arid and semi-arid pastoral conditions. The lactations were recorded over a period of 4 years between 1984 and 1987. Parameters obtained from fitting the equation of Wood (1967) (Y(t) = Atbe−ct) were subjected to statistical analysis. The factors analyzed included vegetation, parity, year, litter size, weight and age of the doe. The parameters described various sections of the lactation curve, that is, the level of yield (intercept) (A), the ascending phase to a peak (b) and the descending phase to drying up (c). Vegetation (P < 0.01) and year (P < 0.05) significantly influenced the three parameters of the lactation, while parity, litter size and doe weight only influenced (P < 0.01) level of production. Lactation curves were constructed from the parameters obtained from fitting the equation.

Application of ultrasonography in the study of the reproductive system of tropical jennies (shape Equus asinus)

The use of high-frequency (5 MHz) ultrasonography was studied in 11 jennies (7 non-pregnant and 4 pregnant) to characterize the reproductive organs and follicular activities at different stages of reproduction. The result showed close similarity with the mare. The visibility of endometrial folds increased towards ovulation. A positive correlation (p < 0.001; τ = 0.79) was found between the score of the folds and the size of the dominant follicle. The diameter of the uterus and the size of the dominant follicle were significantly correlated (p < 0.001; τ = 0.80). In pregnant jennies, an embryonic vesicle was detectable at 14 days. Follicular growth was characterized by more than one wave. The smallest ovarian follicle was 2 mm and the largest 40 mm. Depending on the reproductive stage, up to 13 follicles were detected per ovary. After monitoring 84 cycles, a mean (±SD) diameter of 34.4 ± 3.6 mm (27.5–40.2 mm) of the preovulatory follicle and 67.85% incidence of single ovulation were found. The mean (±SD) interovulatory interval was 25.7 ± 6 days. This study proved that high-frequency ultrasonography is highly effective in characterizing the reproductive organs and follicular activity of jennies and could be useful in the reproductive management of donkeys.

Energy Efficiency, Methane Output, Required Carbon Sequestration Area and Water Productivity in Extensive and Semi-intensive Beef Production in South America –A Comparison of Ecological Currencies

Beef is one of the most important food commodities. This is reflected in the high international trade volume. Global demand for beef has been rising consistently over the past 5 decades. About one third of all agricultural land on the globe is wholly or partially occupied by beef production systems. Beef production systems have a bad reputation in terms of environmental impacts, from land area and total water requirements to greenhouse gas (GHG) emissions. The paper examines three different evaluation tools applied to extensive and semi-intensive beef production systems in South America. System behaviour was tested for the impact of interventions on energy efficiency and methane output by using simulation models. Compensatory carbon sequestration area was calculated for 31 beef production enterprises with three levels of production intensity using a “carbon footprint” type of accounting. Evaluation of water productivity was carried out by estimating “virtual water contents” for three levels of production intensity typically found in South America. Results were conflicting. Energy efficiency was not improved through intensifying interventions. Likewise there was no reduction in methane outputs when yield enhancing interventions were applied. On the other hand, intensification had a marked positive effect on carbon footprint, i.e. a significant reduction of the required carbon sequestration area. Yield enhancing measures had no effect in either way on water productivity with the exception of increasing nutrient densities in the diet, which were found to improve water productivity but not energetic and or economic efficiency. The complexity of the findings points to the necessity to develop an evaluation system which takes into account conflicting responses by weighted assessment of the different environmental impacts against different economic and political backgrounds.