Copyright © NISC Pty Ltd African Journal of Range & Forage Science 2004, 21(1): 11–19 Printed in South Africa — All rights reserved AFRICAN JOURNAL OF RANGE & FORAGE SCIENCE ISSN 1022–0119 Seasonal botanical and chemical composition of sheep and goat diets on a common range in eastern Africa Robinson K Ngugi1*, Joseph N Ndung’u2, Dickson M Nyariki1 and Nashon KR Musimba1 Department of Range Management, University of Nairobi, PO Box 29053, Nairobi, Kenya 2 National Arid Lands Research Centre, PO Box 147, Marsabit, Kenya * Corresponding author, e-mail: rosety@insightkenya.com 1 Received 22 July 2003, accepted 13 February 2004 The botanical and chemical composition, intake and digestibility of local sheep (Ovis aries) and goat (Capra hirtus) diets were evaluated over the wet (growing) and dry (dormant) seasons. Diet botanical composition was related to the vegetation composition on the range. Commiphora riperia and Acacia tortilis were the most dominant tree species, while Duosperma kilimandscharicum and Premna hildebrandtii were the most dominant shrub species. Enteropogon macrostachyus, Cenchrus ciliaris and Chloris roxburghiana were the most abundant grass species, while Brepharis integriifolia, Commelina benghalensis and Macrotylomma axillare were the most dominant forb species. Grasses increased towards the end of the wet season and the beginning of the dry season, while the forbs decreased. Eragrostis caespitosa, Cenchrus ciliaris, Eragrostis superba, Enteropogon macrostachyus and Themeda triandra were the most dominant grass species in sheep diets during both seasons, accounting for over 82% of the diet. Acalypha fruticosa, Grewia similis and G. bicolor were the most important browse species in goat diets in both seasons, while Eragrostis caespitosa and E. superba were the most common grass species during both seasons. Overall, goat diets comprised 81% browse, 17% grass and 2% forbs during the wet season; and 82% browse, 15% grass and 3% forbs during the dry season. Whilst the goat diets had higher (P < 0.05) Crude Protein (CP) content than sheep diets during both seasons, the sheep diets were lower in lignin content than goat diets during the wet season. Overall, the goat diets were lower in Neutral Detergent Fibre (NDF) and Acid Detergent Fibre (ADF) than sheep diets during both seasons. There was no difference (P < 0.05) in digestibility between the two animal species. However, it was higher (P < 0.05) during the dry than the wet season. Although sheep and goats are commonly herded together in east African rangelands, they have differing abilities to utilise forages. These differences must be taken into consideration in grazing management decisions, and selected grazing areas should be able to cater for the forage requirements of both species. Keywords: diet selection, forage, free-grazing, Kenya, range herbivores,, rangeland, seasonal variation Introduction Knowledge of the food habits of range herbivores is essential for improvement of animal nutrition and efficiency of utilisation of range resources through optimal allocation of forage to the different types and classes of herbivores (Krueger et al. 1974, Hanley 1982). Development of effective grazing systems requires that data on forage intake and digestibility be coupled with data on nutrient requirements of the various species of animals. It has, however, been observed that nutritional characteristics of diets selected by range livestock from various vegetation types during different seasons are not adequately understood, particularly in the arid and semi-arid tropical regions (Hanley 1982). Although volumes of data on intake and digestibility of grazed forages are available from animal responses to pen-feeding trials, little information is available on animals that graze natural vegetation (Lusigi et al. 1984). A limited number of food habit studies of single livestock species have been carried out in semi-arid areas of eastern Africa, e.g. goats (Edwards 1948, Wilson 1957, Knight 1964), cattle (Harker et al. 1956, Payne and McFarlane 1963) and camels (Knoess 1976, Field 1978, Newman 1979). However, although common-use grazing is the most popular livestock husbandry practice in the region, food habit studies with mixed herds are scarce and confined to a few range areas. Examples include: camels, cattle, sheep, and goats (Migongo-Bake and Hansen 1987); goats and cattle (Staples et al. 1942); sheep and goats (Schwartz et al. 1986); and camels, sheep and goats (Field 1979). Most of these studies were conducted many years ago and due to large increases in human and livestock populations, the range vegetation in most areas has changed. Thus, available data on the nutritional characteristics of diets, selected by the various livestock species from the different range vegetation types during different seasons, are not adequate to provide a basis for sound grazing management of Kenya’s rangelands. The objective of this study was, thus, to determine seasonal botanical and chemical composition, intake and digestibility of sheep and goat diets on a common range in southeastern Kenya. 12 Methods Study area This study was conducted on a 50ha range pasture within the University of Nairobi’s Institute of Dryland Research, Development and Utilization (IDRDU), Kibwezi station, situated in Makueni District, Eastern Province, Kenya. The station lies between longitudes 37°55’E and 38°05’E, and latitudes 2°28’S and 2°35’S, at 700–800m asl. Its climate is influenced by the Intertropical Convergence Zone (ITCZ) (White 1968) and is characterised by a bimodal distribution of wet and dry seasons. The months January and February, comprising the short dry season, are followed by a long rainy season from March to May. June to October is usually a long dry season, which is followed by a rather short wet season from November to December. The long-term annual rainfall of the area averages 600mm (Republic of Kenya 1991) with an annual mean relative humidity of 62.5%. The mean maximum and minimum temperatures are 28.6°C and 16.5°C with an annual mean of 23°C. Potential average annual evaporation is approximately 2 000mm. The main soil type at the research site is chromic luvisol (Touber 1983). Soils are well-drained, moderately deep, dark reddish brown in colour with a well-developed A-horizon. Commiphora, Acacia and allied woody genera, many of which are shrubby in stature, dominate the vegetation (Pratt and Gwynne 1977, Touber 1983). Data Collection and analysis Vegetation inventory A comprehensive vegetation inventory of the study area was conducted before the grazing study. Ten 100m long systematic transects were laid out in the study site, along which the woody and herbaceous plant species composition and abundance were determined. The abundance of trees and shrubs was determined by the Point-Centred Quadrat (PCQ) method (Mueller-Dombois and Ellenberg 1974), while the biomass of the short shrubs was estimated using the reference unit method (Mueller-Dombois and Ellenberg 1974). The foliage weight of each reference shrub species was multiplied by the respective abundance estimate. Herbage biomass was estimated each month using the hand-clipping method (Mueller-Dombois and Ellenberg 1974). Along each transect, 0.25m2 plots were marked at 10m intervals. All the grass and forb species in each plot were identified and recorded, and their percent relative frequencies calculated. The plots were then clipped at 0.5cm above the ground and material from each plot weighed and stored in a paper bag. The material was later oven-dried at 60°C for 48 hours. Care was taken to avoid clipping the same plot during subsequent samplings. Botanical composition of diets Diet botanical composition was determined by microhistological faecal analysis technique (Hansen and Flinders 1969). For each animal species, one composite dung sample consisting of faecal pellets from at least ten different pellet groups occurring within the same general grazing area was collected at the beginning of every month. Wet dung samples were placed in plastic bags and stored in a freezer. For Ngugi, Ndung’u, Nyariki and Musimba analysis, frozen dung samples were thawed, oven-dried at 50°C and ground in a Wiley mill through a 1mm screen. Five slides per composite faecal sample were prepared. Twenty fields per slide were observed under a compound binocular microscope at x40 magnification. Plant species identification involved matching the epidermal characteristics of plants occurring on the faecal sample slides, with those of the reference plant species slides. Plant species were recorded as either present or absent. A total of 100 observations per sample were made. Percent relative frequency was calculated as the number of identified fragments of a given plant species, divided by the total number of fragments identified, multiplied by 100 (Hansen and Flinders 1969). Nutrient composition of diets Composite samples of individual plant species utilised by the two livestock species were obtained each month through feeding simulation method. A flock of fifteen adult female Red Maasai sheep and fifteen adult Small East African goats was used; out of which six animals of each kind were observed. The flock was so used to the observer that it was possible to observe them from up to 1.0m with minimal disturbance. Observation involved alternately selecting a freely foraging and clearly visible individual of each kind as a focal animal and observing it for 10 minutes. At the end of this period, plant parts (leaves and new growth twigs) used by the observed animal were carefully selected, closely simulating its grazing behaviour. The diet samples were composited according to the livestock species and month and stored in paper bags. All samples were then air-dried in a forced air oven at 60°C for 48 hours, ground in a Wiley mill to pass through a 1mm screen and stored in air-tight jars. In vitro Dry Matter Digestibility (IVDMD) of the diet of each livestock species was estimated using the two-stage fermentation method (Tilley and Terry 1963). Neutral Detergent Fibre (NDF), Acid Detergent Fibre (ADF) and Acid Detergent Lignin (ADL) were determined following the detergent fibre procedures (Goering and Van Soest 1970). Nitrogen content was determined using the Micro-kjeldahl technique and then converted to percent Crude Protein (CP) by multiplying percent nitrogen by 6.25. Dry Matter (DM), Organic Matter (OM) and Total Ash (TA) contents were determined using the standard procedures (AOAC 1970). Dry Matter Intake (DMI) was estimated by the faecal output-indigestibility ratio technique using the simulated diet samples. Faecal output was estimated using eight animals of each kind and the chromic oxide dilution technique. Dosing and sampling were done once a month. About 1.0g of chromic oxide powder contained in a gelatin capsule was administered orally daily to each animal at 18h00 for 12 days. Faecal grab samples were taken at each dosing during the last five days of each sampling period. The grab samples were composited by animal species on a daily basis, dried at 40°C for 48 hours, ground through a 1mm screen and analysed for chromic oxide content using an atomic absorption spectrophotometer (Kimura and Miller 1957). Faecal output was then calculated from the ratio of the amount of marker injected to the mean concentration of the marker in faeces. African Journal of Range & Forage Science 2004, 21: 11–19 Statistical analysis This was a nested experimental design, with days being nested within months, months within seasons and seasons within animal species. Standard statistical procedures were used to test diet differences between seasons and animal species. The analysis of variance technique was used to test diet differences in terms of forage intake and digestibility. Duncan’s New Multiple Range Test was used to separate main effect means at 5% significance level. Student’s t-test (Steel and Torrie 1980) was used to compare diets in terms of percent grass, forb and browse proportions. Results Vegetation composition A total of 15 tree and 33 shrub species were identified within the study area (Table 1). The total woody vegetation abundance was estimated at 1 804 plants ha–1. Commiphora riperia, Acacia tortilis, Commiphora campestris, Acacia mellifera and Psychotria kirkii were the five most dominant tree species, accounting for about 75% of the tree composition. Duosperma kilimandscharicum, Premna hildebrandtii, Ochna insculpta and Dichrostachyus cinera were the four most dominant shrub species, accounting for close to 38% of the total shrub species composition. Table 2 presents the mean percent relative frequencies of grass and forb species within the study area. A total of 17 grasses and 26 forbs were identified. The five most dominant grass species were Enteropogon macrostachyus, Cenchrus ciliaris, Chloris roxburghiana, Eragrostis caespitosa, and Digitaria velutina, while the most common forb species included Brepharis integriifolia, Commelina benghalensis, Macrotylomma axillare, Ipomea mombasana, Cassia spp. and Justicia disclipteroides. The results indicated that forbs were more abundant than grasses (68% and 60% during the dry and wet seasons, respectively). It was further observed that more grasses and forbs occurred in the open than in the shaded areas. The grass proportion increased slightly towards the end of the wet season and beginning of the dry season, while the forbs were high in the early part of the growing season, but decreased towards the end of the season. Botanical diet composition The mean monthly relative frequencies (%) of grass, forb and tree species in the diets of the two livestock species during each season are presented in Table 3. The results show that sheep preferred grasses and forbs while goats preferred browse, regardless of the season. Eragrostis caespitosa, Cenchrus ciliaris, Eragrostis superba, Enteropogon macrostachyus and Themeda triandra were the most dominant grass species in the sheep diets during both the wet and dry seasons. These accounted for over 82% of the total diet. However, during the wet season, the sheep consumed slightly less grass (78%), and slightly more forbs (13%) and browse (9%). The goat diets comprised 81% browse, 17% grass and 2% forbs during the wet season, compared to 82% browse, 15% grass and 3% forbs during the dry season. Acalypha fruticosa, Grewia similis and G. bicolor were the most important browse species in goat diets during both seasons, while Eragrostis caespitosa and E. superba were 13 Table 1: Mean (%) relative abundance of trees and shrubs on the southeastern rangeland of Kenya Species Trees Acacia mellifere Acacia nilotica Acacia senegal Acacia tortilis Adansonia digitata Albizia antihelmintica Commiphora africana Commiphora baluensis Commiphora campestris Commiphora riperia Lannea traphylla Lonchocarpus bussei Ormocarpum kirkii Psychotria kirkii Sterculia rhynchocarpa Total tree abundance Shrubs Abutilon mauritianum Acacia brevispica Acalypha fruticosa Asparagus racemosus Boscia angustifolia Boscia coriaceae Canthium sordidum Combretum eculeatum Comretum axalatum Dichrostachyus cinera Duosperma kilimandscharicum Entada abyssinica Grewia bicolor Grewia similis Grewia villosa Grewia hexaminta Hermania alhiensis Hibiscus calophyllus Hibiscus micranthus Hibiscus aponeurus Hosludia opposita Hypoestes aistata Indigofera lupatena Lantana verbenoides Lippia javanica Maerua edulis Mondulea sevicea Ochna inermis Ochna insculpta Pavonia patens Premna hildebrandtii Solanum incanum Tenantia senii Total shrub abundance Abundance 2.3 1.4 0.4 6.4 0.1 0.8 0.4 0.9 4.5 6.8 0.7 0.9 0.9 2.2 0.8 29.6 0.3 1.4 1.3 0.1 0.4 1.8 0.4 1.4 2.7 5.0 16.4 1.7 0.9 0.9 1.8 0.2 3.2 1.4 0.4 0.8 0.7 0.4 0.4 1.8 0.8 0.9 0.9 0.9 5.9 3.7 9.1 1.4 0.9 70.4 the most important grass species in the diets during both seasons. For both livestock species, the most abundant plant species on the ground, within the most preferred forage class, did not form the bulk of the diet during both seasons. 14 Ngugi, Ndung’u, Nyariki and Musimba Table 2: Mean monthly/seasonal relative frequencies (%) of grass and forb species on the southeastern rangeland of Kenya Herbage type Grasses Brachiaria reptans Brachiaria serrata Cenchrus ciliaris Chloris roxburghiana Cynodon dactylon Cynodon plectostachys Dactyloctenium aegyptica Digitaria macroblephara Digitaria velutina Echinochloa haploclada Enteropogon macrostachyus Eragrostis caespitosa Eragrostis superba Panicum deustum Panicum maximum Rottboelia exaltata Themeda triandra Other spp. Total Jan 2.4 1.4 3.1 1.5 1.1 1.0 0.6 1.7 1.8 0.3 4.1 1.2 2.2 0.3 0.9 1.5 1.1 5.5 31.7 Forbs Acanthosperma hispidum Achyranthes aspera Barleria spp. Bidens pilosa Boerhevia diffusa Brepharis integriifolia Cassia spp. Cammelina benghalensis Crabbea velutina Crotalaria incana Dyschoriste procumbens Hypostes verticillaris Ipomea mombasana Justicia disclipteroides Kotstachys spp. Leucas glabrata Macrotylomma axillare Ocimum bacilicum Oxygonum sinvatum Plectranthus canabinus Polygala spp. Pupalia lupacea Stanlosanthes fruticosa Tephrosia spp. Vernonia aemulans Vigna spp. Other spp. Total 1.9 1.5 0.7 1.1 0.5 6.9 6.5 8.2 2.1 1.6 0.8 0.6 2.6 4.5 1.6 3.2 5.4 1.3 3.1 0.8 2.2 1.0 0.6 1.6 0.5 0.5 7.0 68.3 Dry season Feb Mar Apr May Wet season Jun Jul 2.0 0.8 3.5 1.5 0.5 1.0 1.0 2.1 3.0 0.3 6.3 1.3 1.0 0.3 1.0 1.3 1.3 3.0 31.3 1.1 0.4 2.5 2.6 0.4 1.1 0.4 1.5 1.5 0.3 9.2 1.8 0.7 1.1 1.1 1.5 1.5 2.6 31.3 0.4 0.2 3.1 2.5 0.4 0.7 0.4 2.1 1.1 0.4 9.6 2.1 1.1 1.1 1.1 1.1 1.8 1.1 30.3 0.3 – 4.2 3.5 0.3 1.8 0.1 1.2 1.3 0.3 13.0 2.5 0.8 1.5 1.5 0.6 1.8 4.7 39.4 – – 3.6 4.7 0.3 1.2 – 2.4 1.2 0.3 17.7 2.9 0.6 1.8 2.4 – 0.6 4.1 43.8 – – 3.0 5.1 – 2.7 – 3.1 0.9 0.4 17.6 3.1 0.5 3.3 3.1 – 0.3 3.6 46.7 2.0 1.3 0.8 1.5 0.5 7.0 6.5 8.8 2.8 1.5 0.5 0.6 2.8 4.0 1.5 3.5 6.8 1.3 3.5 0.8 1.8 0.8 0.5 1.6 0.5 0.8 4.7 68.7 1.7 1.8 0.6 0.7 1.5 8.1 3.0 9.2 1.1 0.7 2.2 1.0 5.2 3.3 1.5 1.8 9.2 1.5 2.9 0.4 1.5 2.2 0.4 2.6 0.7 0.4 4.5 68.7 0.4 2.1 0.2 0.4 1.8 9.6 2.8 11.0 1.1 0.7 1.8 0.8 5.9 3.6 0.4 1.1 10.0 1.1 1.1 1.1 1.0 2.5 0.7 1.4 2.1 0.4 4.6 69.7 – 3.5 0.2 0.2 1.8 10.1 2.1 10.1 0.8 1.5 1.2 0.6 5.4 2.5 0.2 1.0 8.9 0.8 1.0 0.1 1.0 2.2 0.7 1.6 2.2 0.4 0.6 60.7 – 3.1 – – 0.6 12.9 1.2 9.4 0.6 3.4 0.6 0.6 7.1 1.2 – 0.3 6.1 0.6 – – 0.6 3.5 0.6 0.6 1.8 0.6 0.7 56.2 – 3.1 – – 0.3 14.8 0.4 8.7 – 3.4 0.3 1.4 7.1 1.3 – – 5.1 0.5 – – 0.2 3.1 – 0.3 1.3 1.1 1.0 53.3 Chemical diet composition Table 4 presents the monthly mean percent chemical composition of the diets selected by the two livestock species. The dietary CP content differed significantly (P < 0.05) between seasons and animal species. It was slightly higher in the wet than in the dry season, and in the goat than sheep diets. Goat diets averaged 18.5% and 14.2% CP during the wet and dry seasons, respectively, while the sheep diets averaged 15.2% and 12.0% CP during the respective seasons. There were no differences in the CP contents between the two livestock species during the wet season. However, inter-month differences were significant (P < 0.05). Mean NDF differed significantly (P < 0.05) between seasons and animal species. It was relatively lower in the wet than in the dry season diets (38.2% and 45.2%, respectively), and higher in sheep than in goat diets (50.0% and African Journal of Range & Forage Science 2004, 21: 11–19 15 Table 3: Mean seasonal/monthly percentage of major grass, forb and tree species in the diets of sheep and goats on the southeastern rangeland of Kenya Forage type Grasses Aristida keniensis Brachiaria spp. Cenchrus ciliaris Chloris roxburghiana Cynodon dactylon Cynodon plectostachys Dactyloctenium aegyptica Digitaria macroblephara Enteropogon macrostachys Eragrostis caespitosa Eragrostis superba Panicum deustum Panicum maximum Setaria pallidesfusca Themeda triandra Other spp. Sheep Dry Season Jan Feb Mar Apr Wet season May Jun Jul Goats Dry Season Jan Feb Mar Apr Wet season May Jun Jul 2.5 4.4 11.5 1.6 4.4 6.2 2.5 2.6 8.4 13.0 8.5 – 1.6 – 6.8 9.3 3.9 – 12.6 1.9 7.8 8.7 – – 4.9 13.6 5.8 – 2.9 – 7.8 7.7 1.1 1.1 13.8 6.3 2.1 8.5 3.2 4.3 6.3 9.6 9.6 – 1.1 – 3.2 7.4 – 2.3 5.8 3.5 1.2 1.2 3.5 3.5 12.8 11.6 8.1 2.3 1.2 1.2 5.8 13.9 1.0 2.9 6.8 1.0 8.7 1.9 1.0 4.9 10.7 13.6 12.6 1.9 1.0 – 3.9 8.7 3.2 1.0 10.5 1.0 5.4 1.1 – 2.1 4.2 8.4 12.6 – 2.1 – 9.5 11.6 2.0 6.1 8.1 2.0 13.1 2.0 1.0 5.1 5.1 14.1 11.1 1.0 – – 6.1 3.0 – – – 3.4 1.1 1.1 – 3.4 – 1.1 – 1.1 – – – 3.5 – – 1.2 2.3 1.2 – – 1.2 – 3.4 1.2 – 1.2 – – 1.1 – – 4.7 1.1 1.2 – – – 2.4 2.3 3.5 – – 1.2 1.2 – – – 2.5 – 1.3 – – – – 2.5 5.1 – – – 1.3 2.5 – – 1.2 1.1 – 1.2 – – – 4.7 5.8 – – – – 2.3 – – 2.5 1.3 2.5 – – – – – 3.8 – 1.3 – – 2.5 1.2 – 1.2 – – 1.2 – – 1.2 3.6 1.2 – 2.4 1.2 – 3.6 – – – 1.6 – 1.6 2.5 – – 5.0 – – – – 1.0 – 1.9 1.0 1.0 8.7 – – 1.1 – 1.1 – 2.1 2.1 2.1 6.4 – – – – – – 2.3 – – 3.5 – – – 1.0 1.0 3.9 1.9 1.9 – 6.7 – – 1.0 1.1 1.0 2.1 1.1 3.2 1.0 8.4 – – – – – 2.0 4.0 – 1.0 4.1 – 1.1 – – – – – – 1.2 – – – – – – – – – – – 1.2 – – – – – – – 1.2 – – – – – – – – – – – – – – – – – – – – – – – – – – – – 2.5 – 2.4 – – – – – – 2.4 – 1.2 Trees and Shrubs – Acacia brevispica – Acacia mellifera – Acacia nilotica – Acacia tortilis – Acalypha fruticosa – Blanites aegyptica – Boscia angustifolia – Cadaba farinose – Combretum aculeatum – Combretum exalatum 1.6 Duosperma kilimandscharicum – Grewia bicolor – Grewia similes – Grewia vilosa – Hermania alhiensis 2.6 Hibiscus calophylus – Hibiscus micranthus – Indigofera spp. – Pavonia patens – Sida ovata 1.6 Solanum incanum – Other spp. – – – – – – – – – – – – – – – 5.8 – – 1.0 1.9 – – – – – – 1.2 – – – – – 2.3 1.2 – – 1.2 2.3 1.2 – – – – – – – – – – – – 1.0 – – – – – – – – – – – – – 3.2 – – 1.0 – 1.1 2.1 – – – – – 1.1 – – – – – – – – – 2.0 – – 3.0 – 3.0 – – 1.1 2.3 2.3 8.0 10.2 – 1.1 – 1.1 3.4 3.4 9.1 8.0 1.1 9.1 2.3 3.4 1.1 – 3.4 2.3 9.1 – – – 7.0 13.9 1.2 1.2 – 1.2 5.8 – 11.6 11.6 1.2 11.6 2.3 4.7 – – – 2.3 11.6 1.2 3.5 2.3 7.1 5.8 1.2 2.3 – 1.2 7.1 – 8.2 11.8 7.1 8.2 2.4 – 1.2 – – 2.3 7.1 – – 3.8 8.9 10.1 – 1.3 – 3.8 7.6 1.3 7.6 13.9 – 2.5 2.5 – 1.3 5.0 5.0 1.3 8.9 – 3.5 5.8 3.5 10.5 – 1.1 1.2 2.3 7.0 2.3 9.3 11.6 7.0 4.7 2.3 2.3 – – 1.1 3.5 4.7 Forbs Achyranthes aspera Amaranthus spinosus Bidens pilosa Cassia mimosoides Commelina benghalensis Ipomea mombasana Oxygonum sinvatum Stylosanthes fruticosa Tephrosia spp. Other spp. 2.1 – – – – 4.3 – – 3.5 1.2 2.3 – 1.0 1.0 – – 1.1 – – – 41.5%, respectively). Sheep diets averaged 46.6% and 53.3% NDF during the wet and dry seasons, respectively, while the NDF content of goat diets was fairly constant during the January–May period. – 2.4 – 2.4 8.9 3.6 6.3 2.4 5.1 8.5 – 2.4 2.5 – 5.1 – 1.3 2.4 10.1 12.1 3.8 10.8 8.9 7.3 13.9 4.9 – – 1.3 2.4 – – 1.3 1.2 – – – – – 2.4 – – 12.7 12.0 Mean ADF content varied between animal species. Generally, goats selected diets with significantly lower (P < 0.05) ADF content than the sheep, regardless of the season. Goat diets averaged 26.2% ADF, compared to sheep diets 16 Ngugi, Ndung’u, Nyariki and Musimba Table 4: Mean (%) monthly chemical composition of the simulated sheep and goat diets on the southeastern rangeland of Kenya* Months January February March April May June July CP 18.6a1 18.5a1 18.0a1 16.1a3 15.5a3 13.6a2 11.6a1 NDF 37.6a1 38.6a1 38.9a1 39.7a1 41.4a1 49.5a2 50.3a2 Goats ADF 23.9a1 24.5a1 25.3a1 25.0a1 27.6a12 28.2a2 32.1a13 ADL 4.9a12 5.1a12 5.8a2 5.2a1 5.1a1 6.4a2 7.3a2 Ash 12.1a1 11.5a1 11.3a1 12.3a1 12.6a1 13.4a1 12.9a1 CP 15.4b1 15.2b1 14.6b1 14.1b3 13.0b23 11.9b2 8.9b1 NDF 46.4b1 47.7b1 47.5b1 50.5b1 53.0b12 52.8a12 56.9b2 Sheep ADF 29.3b12 29.2b12 29.4b2 29.8b1 31.1b12 33.7b23 34.0a3 ADL 4.0a12 4.3a12 4.8a2 5.1a1 5.4a12 5.7a12 6.5a2 Ash 13.6a2 10.3a1 11.2a1 12.4a1 13.2a1 13.3a1 13.1a1 * Means in the same row or column with different letter or numeral superscripts are significantly different (P < 0.05) Table 5: Mean monthly dry matter intake (g d–1 g kg–1 W0.75) and digestibility (%) of the simulated sheep and goats diets on the southeastern rangeland of Kenya* Months January February March April May June July Goats Dry matter intake g d–1 g kg–1 W0.75 345.6a1 31.5a1 454.5a2 42.4a2 361.0a12 33.9a12 434.3a1 40.2a1 447.6a1 41.2a1 575.3a2 53.4a2 680.6a3 62.8a2 Digestibility (%) IVDMD 61.8a12 59.3a12 55.8a1 53.9a1 54.1a1 51.9a1 48.7a1 Sheep Dry matter intake g d–1 g kg–1 W0.75 366.8a1 38.9a1 426.8a1 45.2a1 390.7a1 41.4a1 520.1a1 55.0b1 545.0b12 57.9b12 624.0a2 66.0b2 628.6a2 66.4a2 Digestibility (%) IVDMD 62.8a1 60.0a1 55.8a1 53.4a22 52.1a1 49.4a12 44.9a1 * Means in the same row or column with different letter or numeral superscripts are significantly different (P < 0.05) with 30.5% ADF. For both livestock species, ADF content was lower in the wet season diets (24.2% versus 28.8% for goats and sheep, respectively) than in the dry-season diets (28.2% versus 32.2% for goats and sheep, respectively). Our data showed significantly lower (P < 0.05) lignin content in the sheep diets than goat diets during the wet season. Differences in dietary lignin content were also significant (P < 0.05) between seasons and livestock species. Overall, the mean total ash content exhibited minor variations between animal species and seasons. The total ash content in goat diets averaged 11.5% and 12.8% during the wet and dry seasons, respectively. It averaged 12.4% and 13.0% in sheep diets during the two seasons. Dry matter intake and in vitro dry matter digestibility Table 5 presents the mean monthly DMI (g d–1) and IVDMD data by livestock species. The data indicate no difference (P < 0.05) between sheep and goats in terms of DMI, but overall, the sheep ate slightly more than the goats. Mean DMI was 471.3g d–1 by goats and 500.3g d–1 by sheep, equivalent to 2.0% and 2.5% of their respective live weights. The mean DMI by sheep was 394.8g d–1 and 579.3g d–1 during the wet and dry seasons, respectively, while the corresponding DMI by goats were 387.0g d–1 and 534.5g d–1. On metabolic bodyweight basis, DMI were similar (P < 0.05) between the two kinds of animals during the wet season, but significantly lower (P < 0.05) in goats than sheep during the dry season. Mean intakes were 53.0 and 43.6g kg–1 W0.75 for sheep and goats, respectively. The results showed insignificant differences (P < 0.05) in digestibility between sheep and goat diets. However, the season strongly affected the overall digestibility, with the wet season diets being more digestible (P < 0.05) than the dry season diets for both kinds of livestock. Within each season, diets selected by the two kinds of animals were not significantly different (P < 0.05) in digestibility. The mean IVDMD values of goat diets were 60.2% and 52.1% for the wet and dry seasons, respectively. On the other hand, the sheep diets averaged 61.3% and 49.9% IVDMD during the wet and dry seasons, respectively. Furthermore, there was a consistent decline in IVDMD as seasons progressed and/or as plants matured. The drop was more dramatic in sheep (22.1%) than in goats (14.9%). Discussion The results of our study are consistent with similar previous studies in demonstrating that seasonal and spatial differences between plant communities in species composition, productivity, forage quality and food-item dispersion influence the composition of diets selected by free-grazing animals (Knight 1964, Bryant et al. 1979, Migongo-Bake 1984, Green et al. 1985, Pfister and Malechek 1986). So too do the intrinsic characteristics of grazing animals, such as size and/or specific adaptations of mouths and guts, influence the diet selection process (Sinclair and Norton-Griffiths 1979). Within a given season, diet selection can occur at various levels, which are sequential to some extent (Sinclair African Journal of Range & Forage Science 2004, 21: 11–19 and Norton-Griffiths 1979). For instance, in a given season, an animal can choose a vegetation community to feed in; then the plant species within the community and parts within plants, to feed on. However, all animals do not emphasise the three steps equally, resulting in species differences in diet composition. Our data concur with those of several past studies in demonstrating that sheep are primarily grazers. However, they are discordant with other past studies, which depict goats as intermediate feeders rather than mainly browsers. The difference is attributed to the fact that the study area is a bushland. Seasonal shifts in diet composition are largely attributed to changes in an animal’s feeding strategy in response to changes in the quantity and quality of available forage. Each adjustment in the process of diet selection is meant to improve diet quality (Sinclair 1975) and perhaps energy intake. Seasonal variations in diet quality are attributed to corresponding variations in the chemical composition of forages utilised by the grazing animals. Diet quality is normally high during the wet season, when plants are actively growing and grazing animals have access to leafy, green forage (Mnene and Stuth 1986, Ekaya 1991, Papachristou and Nastis 1993, Kirui 1995). Normally, mature forage has lower mean CP content and OMD (Milford and Minson 1965a, 1965b, Smith et al. 1972, Mnene 1985) than actively growing forage. As plants mature, CP and other cell contents decrease, while structural materials such as NDF and ADF increase (Dougall et al. 1964, Haggar and Ahmed 1971, Heitschmidt et al. 1982, Van Soest 1982). Grasses, on average, have a higher CF content than browses at comparable growth stages (Short 1971, Crowder 1985). The selective grazing habits of animals and the animal’s ability to adjust to different forage classes, enables them to cope better with the spatio-temporal differences in the quality of potential forage items. However, over-specialisation of certain herbivores in terms of forage preference can be a serious survival constraint during certain seasons. For instance, the high dependence of sheep on grasses and goats on browse irrespective of seasons poses a serious constraint in the dry seasons when forage quality and quantity is extremely low. Goats are, however, better off during the dry season since they depend on browse species, which have fairly high CP and cell wall contents, and exhibit a slower rate of quality deterioration with advancing maturity than grass species (Karue 1974, 1975, Ekaya 1991). The slightly higher quality of the sheep diets than goat diets during the last two months of the wet season in this study were mainly attributed to high availability of young grasses and forbs. Range plants are characterised by fast growth rates when conditions are favourable. The rapid growth rates result in marked variations in the chemical composition of the selected diets (Mbui and Stuth 1986, Mnene and Stuth 1986, Tessema 1986). Our chemical composition data were discordant with those of similar previous studies (Karue 1974, 1975, Ekaya 1991), where dry season diets were of inferior quality to those of the growing season for both livestock species. This anomaly could be attributed to the above-normal short rains received during the study period, extending into January, which is normally a dry month. The period of high diet-quality coincided with the wet season (active plant growth) when ani- 17 mals actively selected the leafy, green plant material (Milford and Minson 1965a, 1965b, Mnene and Stuth 1986, Tessema 1986). Advance in plant maturity generally results in a decline in CP content and OMD (Haggar and Ahmed 1971, Smith et al. 1972, Heitschmidt et al. 1982). Furthermore, a decline in CP content is associated with increased non-nitrogenous organic matter including crude fibre, leading to a decline in nutritive value (Dougall et al 1964). In growing plants, structural materials are synthesised at the expense of cellular contents as plants age physiologically (Johnson et al. 1968, Short 1971, Van Soest 1982, Crowder 1985). This accounts for the increase in crude fibre content. Grasses, however, show higher levels of crude fibre than browses; and the latter higher CP and cell contents at comparable growth stages (Tessema 1986, Kirui 1995). The high dependence of sheep on herbage is, thus, a major disadvantage in the dry season since most of the range grasses are mature and have low protein (often ≤4%) and high fibre content. The high reliance of goats on browse, on the other hand, is advantageous in the dry season, as goats are able to meet most of their nutrient requirements. The higher mean digestibility coefficients during the wet season than in the dry season were viewed as normal and were attributed, largely, to the corresponding high dietary CP content coupled with relatively low mean ADL in young actively growing plants. About 7–8% CP content and 55% DMD have been recommended as the critical minimum for efficient rumen microbial activity at the maintenance level of feeding (Milford and Minson 1965a, 1965b, Van Soest 1982, Migongo-Bake 1984, Leng 1990). Our results show that the diets selected by the two livestock species were above the critical minimum CP content and forage digestibility. It is expected that the quality of the diets would have been higher if the diets were obtained through other techniques, such as fistulated animals, which simulate diets selected by free-ranging animals more accurately (Rice 1970, Theurer et al. 1976). Management implications Although sheep and goats are commonly herded together throughout the rangelands of eastern Africa, they have differing abilities to utilise forages. For optimum production, these differences must, therefore, be recognised and taken into consideration in grazing management decisions, such as where to graze and by which species of livestock. Range use must be coupled with range management principles that enhance diversity of plant species and allow animals to select the highest quality diet possible. Manipulation of the rangelands, such as bush control, for better primary production, should be carried out judiciously with the aim of suppressing the undesirable woody species and encouraging the preferable ones. Furthermore, the alternate pattern of plant growth and dormancy, resulting in corresponding fluctuations in forage quantity and quality must be well integrated in range livestock and forage management programmes. Thus, inventory of range forage nutrients at specific times during the grazing season is a crucial management activity. Steps must be taken to alleviate problems associated with dry-season grazing. For instance, complementary forages, such as crop residues, may be utilised in a grazing pro- 18 gramme to supplement native range. Other steps include utilisation of stored forages and forage reserves. In extreme situations, such as droughts, supplemental feeds may also be considered. References AOAC 1970. Methods of Analysis (11th edn). Association of Official Analytical Chemists, Washington DC. Bryant FC, Kothmann MM and Merrill LB 1979. Diets of sheep, Angora goats, Spanish goats and white-tailed deer under excellent range conditions. Journal of Range Management 32: 412–417. Crowder LV 1985. Pasture management for optimum ruminant production. In: LR McDowell (ed) Nutrition of Grazing Ruminants in Warm Climates. Academic Press Incorporated, London. Dougall HW, Drysdale VM and Glover PE 1964. The chemical composition of Kenya browses and pasture herbage. East African Wildlife Journal 2: 86–92. Edwards DC 1948. Some notes on food habits of goats in semi-arid areas. East African Agricultural Journal 14: 94–98. Ekaya WN 1991. Forage Preferences of Livestock on a Semi-arid Range in Southeastern Kenya. MSc Thesis, University of Nairobi, Nairobi, Kenya. Field CR 1978. The food habits of camels in northern Kenya. IPAL Technical Report, United Nations Educational, Scientific and Cultural Organization/Man and the Biosphere Programme (UNESCO/MAB) No. E-1b. Field CR 1979. Ecology and management of camels, sheep and goats in northern Kenya. IPAL Technical Report, United Nations Educational, Scientific and Cultural Organization/Man and the Biosphere Programme (UNESCO/MAB) No. E-1a. Goering HK and Van Soest PJ 1970. Forage Fibre Analysis (Apparatus, Reagents, Procedures and some Applications). United States Department of Agriculture, Agricultural Research Services Handbook No. 379, Washington DC, USA. Green LR, Blankenship LH, Cogar VF and McMahon T 1985. Wildlife Food Plants — A Microscopic View. Kleberg Studies in Natural Resources. Texas A&M University, College Station, Texas, USA. Haggar RJ and Ahmed MB 1971. Seasonal productivity of Andropogon gayanus. III. Changes in crude protein and in vitro dry matter digestibility of leaf and stem portions. Journal of Agricultural Science 77: 47–52. Hanley TA 1982. The nutritional basis for food selection by ungulates. Journal of Range Management 35: 146–151. Hansen RM and Flinders JF 1969. Food Habits of North American Hares. Range Science Department, Science Series, No. 1. Colorado State University, Fort Collins, Colorado, USA. Harker KW, Tylor JI and Rollinson DHL 1956. Studies on habits of Zebu cattle. I. Preliminary observations on grazing habits. Journal of Agricultural Science 44: 193–198. Heitschmidt RK, Gordon RA and Bluntzer JS 1982. Short duration grazing at the Texas Experimental Ranch. 1. Effects on aboveground dynamics. Journal of Range Management 18: 251–254. Johnson A, Bezeau LM and Smoliak S 1968. Chemical composition and in vitro digestibility of alpine tundra plants. Journal of Wildlife Management 32: 773–777. Karue CN 1974. The nutritive value of herbage in semi-arid lands of East Africa. I: Chemical Composition. East African Agriculture and Forestry Journal 40: 89–95. Karue CN 1975. The nutritive value of herbage in semi-arid lands of East Africa. II. Seasonal influence on the nutritive value of Themeda triandra. East African Agriculture and Forestry Journal 40: 372–387. Ngugi, Ndung’u, Nyariki and Musimba Kimura FT and Miller VL 1957. Improved determination of chromic oxide in cow feed and faeces. Journal of Agriculture and Food Chemistry 5: 216. Kirui JK 1995. Time Budgets of Maintenance Activities and Dietary Characteristics of Camels and Goats in the Semi-arid Southeastern Kenya. MSc Thesis, University of Nairobi, Nairobi, Kenya. Knight J 1964. Some observations on the feeding habits of goats in South Baringo District of Kenya. East African Agriculture and Forestry Journal 30: 182–188. Knoess KH 1976. Assignment report on animal production in the middle Awash Valley, United Nations Food and Agricultural Organization, Rome. Krueger WC, Laycock WA and Price DA 1974. Relationships of taste, smell, sight, and touch to forage selection. Journal of Range Management 27: 258–262. Leng RA 1990. Factors affecting the utilization of poor quality forage by ruminants particularly under tropical conditions. Nutrition Research Reviews 3: 277–288. Lusigi WJ, Nkurunziza ER and Masheti S 1984. Forage preference of livestock in the arid lands of northern Kenya. Journal of Range Management 37: 542–548. Mbui MK and Stuth JW 1986. The effects of prescribed burning on cattle and goat diets. In: RM Hansen, BM Woie and RD Child (eds) Range Development and Research in Kenya. Proceedings of the Winrock International Institute for Agriculture and Development, USA. Migongo-Bake EW 1984. The Trophic Relations of Domestic Animals in the Central Part of Rendille land in Northern Kenya. PhD Thesis, Colorado State University, Fort Collins, Colorado, USA. Migongo-Bake EW and Hansen RM 1987. Seasonal diets of camels, cattle, sheep, and goats in a common range in Eastern Africa. Journal of Range Management 40: 76–79. Milford R and Minson DJ 1965a. Intake of tropical pasture species. Proceedings of International Grassland Congress 9: 815–822. Milford R and Minson DJ 1965b. The relation between crude protein content and digestible crude protein of tropical pasture plants. Journal of British Grassland Society 18: 177–179. Mnene WN 1985. Influence of Herbage/Browse Allowance on Nutritive Intake of Cattle Grazing a Commiphora Savanna in Kenya. MSc Thesis, Texas A&M University, College Station, Texas, USA. Mnene WN and Stuth JW 1986. Diet quality and intake of steers under range conditions. In: RM Hansen, BM Woie and RD Child (eds) Range Development and Research in Kenya. Proceedings of Winrock International. Institute for Agriculture and Development, USA. Mueller-Dombois D and Ellenberg H 1974. Aims and Methods of Vegetation Ecology. John Willey and Sons, New York. Newman DMR 1979. The feeding habits of Old and New World camels as related to their future role as productive animals. International Foundation for Science Provisional Report 6, pp 171–200. Papachristou TG and Nastis SN 1993. Diets of goats grazing oak shrublands of varying cover in Northern Greece. Journal of Range Management 46: 220–226. Payne WJA and McFarlane JS 1963. A brief study of cattle browsing behaviour in a semi-arid area of Tanganyika. East African Agriculture and Forestry Journal 29: 131–133. Pfister JA and Malechek JC 1986. Dietary selection by goats and sheep in a deciduous woodland of northeastern Brazil. Journal of Range Management 39: 24–28. Pratt DJ and Gwynne MD (eds) 1977. Rangeland Management and Ecology in East Africa. Hodder and Stroughton, London. Republic of Kenya 1991. Annual Report, Meteorological African Journal of Range & Forage Science 2004, 21: 11–19 Department. Nairobi, Kenya. Rice RW 1970. Stomach analysis: A comparison of the rumen vs. oesophageal techniques. In: Range and Wildlife Habitat Evaluation — A Research Symposium. United States Department of Agriculture Miscellaneous Publication 1147, pp 127–132. Schwartz HJ, Herlocker DJ and Said AM 1986. Forage intake by sheep and goats on semi-arid to arid pastures in Northern Kenya. In: PJ Joss, PW Lynch and OB Williams (eds) Rangelands: A Resource under Siege. Proceedings of 2nd International Rangeland Congress, Australian Academy of Science, Australia. Short HL 1971. Forage digestibility and diets of deer on southern upland range. Journal of Wildlife Management 35: 698–706. Sinclair ARE 1975. The resource limitation of trophic levels in tropical grassland ecosystems. Journal of Animal Ecology 44: 497–520. Sinclair ARE and Norton-Griffiths 1979. Serengeti: Dynamics of an Ecosystem. University of Chicago Press, Chicago, USA. Smith LW, Goering HK and Gordon CH 1972. Relationships of forage compositions with rates of cell wall digestion and indigestibility of cell walls. Journal of Dairy Science 55: 1140–1147. Staples RR, Hornby HE and Hornby RM 1942. A study of the comparative effects of goats and cattle on a mixed grass–bush pasture. East African Agricultural Journal 8: 62–70. Steel RGD and Torrie JH 1980. Principles and Procedures of Statistics. A Biometric Approach (2nd edn). McGraw-Hill Book Company, New York. 19 Tessema S 1986. Chemical composition and in vitro dry matter digestibility of herbage. In: RM Hansen, BM Woie and RD Child (eds) Range Development and Research in Kenya. Proceedings of the Winrock International Institute for Agriculture Development, USA. Theurer CB, Lesperance AL and Wallace JD 1976. Botanical composition of the diet of livestock grazing native ranges. University of Arizona Agricultural Experimental Station Technical Bulletin 233, Arizona, USA. Tilley JMA and Terry RA 1963. A two-stage technique for the in vitro digestion of forage crops. Journal of British Grassland Society 18: 104–111. Touber LA 1983. Soils and vegetation of Amboseli-Kibwezi area. Kenya Soil Survey Report No. R6, Nairobi, Kenya. Van Soest PJ 1982. Nutritional Ecology of the Ruminant. O and B Books, Corvallis, Oregon. White OR. 1968. Grasslands of the Monsoon. Fredrick A Paeger Publishers, New York, USA. Wilson PN 1957. Further notes on the development of the Sere herd of shorthorned Zebu cattle. Imperial Experimental Agriculture 25: 263–277.