Trop Anim Health Prod (2008) 40:155–164 DOI 10.1007/s11250-007-9075-4
ORIGINAL PAPER
Intake and digestibility in sheep and chemical composition during different seasons of some West African browse species Salifou Ouédraogo-Koné & Chantal Y. Kaboré-Zoungrana & Inger Ledin
Accepted: 31 August 2007 / Published online: 19 September 2007 # Springer Science + Business Media B.V. 2007
Abstract Foliage of Afzelia africana, Pterocarpus erinaceus and Khaya senegalensis, from 10 trees per species, was collected every two weeks during the late dry, rainy and cool season to determine the seasonal effects on chemical composition. Fifteen rams of the Djallonké breed, weighing on average 20.0 kg, were used to evaluate the voluntary intake and digestibility of hay of A. gayanus, foliage of A. africana (as a sole feed), and A. africana, P. erinaceus and K. senegalensis offered with 30% of the diet as A. gayanus hay. The crude protein (CP) content of A. africana, and P. erinaceus decreased significantly from the late dry season to the cool season when that of K. senegalensis tended to increase. The mean CP of A. africana, P. erinaceus and K. senegalensis differed significantly (173 g, 139 g and 114 g/kg DM, respectively). The DM intake of A. africana offered with hay (571 g/d) or as a sole feed (598 g/d) were not significantly different, but was higher than that of P. erinaceus (428 g/d) and K. senegalensis (298 g/d). The digestibility calculated by difference of DM and CP of A. africana (582 g/kg S. Ouédraogo-Koné : C. Y. Kaboré-Zoungrana Institut du Développement Rural, Université Polytechnique de Bobo-Dioulasso, Bobo-Dioulasso, Burkina Faso I. Ledin (*) Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala, Sweden e-mail:
[email protected]
DM and 795 g/kg CP, respectively) did not differ significantly from A. africana as a sole feed, but were higher than for the other species. The nutritive value of A. africana seems to justify the high preference of herders for this species. Keywords Afzelia africana . Pterocarpus erinaceus . Khaya senegalensis . Foliage . Sheep . Intake . Digestibility Abbreviations ADF acid detergent fiber ADL acid detergent lignin BW body weight CP crude protein DM dry matter DMI dry matter intake GLM general linear model LS Least squares NDF neutral detergent fiber OM organic matter SD standard deviation SE standard error of the mean W0.75 metabolic weight
Introduction Tree fodders in the tropics generally have a higher content of crude protein (CP), minerals and digestible
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nutrients than the grasses (le Houérou 1980; Devendra 1990; Topps 1992). The ability of the foliages to remain green and maintain their CP content make them potential sources of protein and energy, especially during the dry season. The West African tree fodders have a relatively high CP content, and the average for all browse species has been reported to be 125 g CP/kg dry matter (DM) (le Houérou 1980). However, the nutritive value varies with the season and species (Fall-Touré et al. 2000) and the digestibility of the CP, at around 82 g digestible protein per kg DM (le Houérou 1980) can be limited by high concentrations of lignin, that can reach 200 g/kg DM, or tannins (Koné 1987; Kaboré-Zoungrana 1995). In general, compared to grasses, tree fodders have been found to have low NDF content (Koné 1987). About 75 % of the woody species in Africa are browsed to a greater or lesser extent (Wickens 1980). Of the tree species browsed by ruminants on natural pasture, Afzelia africana (African mahogany bean), Khaya senegalensis (Savannah mahogany) and Pterocarpus erinaceus (African rosewood) are the most commonly used multipurpose species in the traditional livestock management system in the sub-humid zone of West Africa (Bayer 1990; Petit 2000). These species are increasingly used by herders and livestock owners (Gautier et al. 2005; Ouédraogo-Koné et al. 2006) and the foliages are also sold in the cities for urban and peri-urban livestock production. The CP content (133 to 166 g/kg DM) of the foliage of these trees is among the highest of the 30 species analysed by Bayer (1990). When these three species are available, the preference of herders or livestock owners is in the order A. africana, K. senegalensis and P. erinaceus (Bayer 1990; Ouédraogo-Koné et al. 2006). It seems reasonable to hypothesize that this ranking is not arbitrary, but reflects an indigenous understanding of their comparative nutritive value, since the variable effects of different tree foliages on animal performance can to a great part be attributed to their chemical composition and nutritive value. To establish optimum feeding systems and integrate the forage from browse species it is important to know their nutritive value, with respect to intake potential, chemical composition and digestibility. The objectives of the present study were to determine and compare the chemical composition of the foliages of A. africana, K. senegalensis and P. erinaceus in three
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seasons of the year and to determine and compare the voluntary intake and digestibility of the foliages harvested in the beginning of rainy season.
Materials and methods Location and climate of the study area The experiments were carried out on a natural pasture in Orodara, 11°00 to 11°10′N and 4°41′ and 4°50′W, and at the Centre International de Recherche-Développement sur l’Elevage en zone Sub-humide (CIRDES), located in the South Sudanian zone of Burkina Faso, 11°10′N and 4°17′W, with a mean altitude of 350 m above sea level. The climate is wet/dry tropical, with two distinct seasons, a rainy season from May to October and a dry season from November to April. During the study period, the average annual rainfall was 1156 mm, and the mean monthly temperature and relative humidity varied between 25° and 31°C and 48% and 80%, respectively. Experimental animals, feeds and management The animals used were rams of the West African Djallonké breed, at about 12 months of age, with a mean pre-experimental body weight (BW) and SD of 20.0 (1.6) kg, bought from farmers at the study site. The animals were vaccinated against pasteurellosis and trypanosomosis and were treated against internal and external parasites using Ivermectin before the commencement of the experiments. The feeds used were foliages of A. africana, K. senegalensis and P. erinaceus and hay made from Andropogon gayanus. Leaves plus petioles were collected manually from the branches of trees at the beginning of the rainy season (June to July, 2004), and the grass was harvested at the beginning of the maturity stage on natural pastures in the study area. The foliages and grass were pre-dried in the sun for 24 hours by spreading them on clean plastic sheets and turning several times, thereafter they were airdried in the shade, and stored in a house. During the whole experimental period, the animals were kept in individual metabolism cages and fed twice a day at 9:00 h and 16:00 h. They had free access to water and a commercial mineral lick block containing 6% P, 12% Ca, 63% NaCl, 2% Mg, 15% cement, and Fe
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(2 g/kg), Cu (1.5 g/kg), Mg (0.75 g/kg), Co (0.03 g/kg), Zn (0.9 g/kg) and I (0.1 g/kg). The animals were weighed at the beginning and the end of each experiment. The voluntary intake was recorded for 42 d, after which the animals were allowed to exercise and graze during two weeks on pasture before being replaced in the cages for the digestibility trial. The foliage and hay were offered in separate feeding troughs at the same time. In the voluntary intake experiment, foliages and sole feeds were offered at a level of 15% of refusals based on the intake of the previous day. The hay was added as a safety measure to ensure sufficient nutrient intake in case of high content of anti-nutritional substances in the foliages and was planned to be fed in amounts not exceeding 30% of total DM intake. In the digestibility trial, the animals were fed according to their individual daily intake based on the results from the intake experiment. Seasonal variations in chemical composition of foliage Ten individual trees per species were randomly selected on the pasture and marked, and samples (foliage) were collected manually every 15 d. For each individual tree, the samples were taken at five locations (bottom, middle, top, East and South) and pooled. The samples from the 10 trees of each species were pooled and two samples of 1 kg were taken. One sample was used for the determination of DM and the second sample was air dried in the shade and stored in cloth bags. The air-dried samples were pooled per month and tree species, and were taken for further chemical analysis. The prepared samples of each species were grouped into three seasons. The first corresponding to the end of the dry season and the beginning of the rainy (April to June), the second to the rainy season (July to September) and the third to the cool season (October to December), according to the presence of leaves of the trees. For each species, nine samples (three per season) were analysed, giving a total of 27 samples. Voluntary intake of feed The experimental design for the study of voluntary intake was a completely randomised changeover design with five diets allocated to 15 animals in two
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periods. Three animals were randomly allocated to each diet in each period. The diets were hay of A. gayanus, foliage of A. africana (offered as a sole feed) and foliage of A. africana, P. erinaceus or K. senegalensis (fed with hay from A. gayanus). Each period consisted of an experimental time of 21 d with 14 d of adaptation followed by 7 d of data collection. Foliage and hay offered and refused were recorded separately and daily during the 7 d of data collection in each period. Samples were taken daily and pooled to individual samples in each period for chemical analysis. In vivo digestibility For the in vivo digestibility a completely randomised changeover design was used, with 5 treatments allocated to 15 animals in two periods. The diets were hay of A. gayanus, foliage of A. africana (offered as a sole feed) and foliage of A. africana, P. erinaceus or K. senegalensis (fed with hay of A. gayanus at 30% DM of the diet). Each period consisted of a 14 d adaptation phase followed by a 7 d data collection phase. In each period, the diets were randomly allotted to three animals. Foliage and hay offered and refused were recorded separately and daily during the 7 d of data collection in each period. Samples were taken daily and pooled to an individual sample for each period for chemical analysis. Daily faecal output of each animal was collected and weighed and 10% of the amount was sampled for DM determination and the rest was pooled in the freezer at -20°C to stop the fermentation. By the end of the collection period, the faecal sample of each animal was thawed and mixed thoroughly. A subsample was taken and oven dried at 55°C to prevent the loss of nitrogen for further chemical analysis. The digestibility of the foliages in the mixed diets was estimated from intakes and digestibilities of the hay and the total diets, assuming that there were no interactions between the hay and the foliages. Chemical analyses The samples were analysed for DM, CP, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), OM and ash. The DM (967.03), CP (988.05), ADF and ADL (973.18), OM and ash (942.05) were analysed according to the
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standard methods of AOAC (1990) and NDF was determined by the method of Van Soest et al. (1991) using sodium sulfite and amylase, and was expressed without residual ash.
Results
Statistical analysis
The contents of DM, OM, ADF and ash of the forages used in the experiments were not significantly different (Table 1). The concentration of CP and ADL of all foliages was higher than in A. gayanus, which had the highest NDF content (701 g/kg DM) of all the forages. The CP, NDF and ADL contents of A. africana (202, 593 and 162 g/kg DM respectively) were significantly higher than that of P. erinaceus (117, 502 and 150 g/kg DM respectively) and K. senegalensis (120, 508 and 146 g/kg DM, respectively), which did not differ significantly. The hemicellulose of A. africana was significantly higher than for P. erinaceus and K. senegalensis.
The data were analysed statistically using the GLM procedure of Minitab Software, version 14.1 (Minitab, 2003). Treatment means which showed significant differences at P
