Rumen dry-matter digestive efficiency of camels, cattle sheep and goats in a semi-arid environment in eastern Africa

W Migongo-Bake

International Centre for Research in Agroforestry (ICRAF)
PO Box 30677, Nairobi, Kenya

ABSTRACT

The degree of degradability and utilisation of forages by ruminants may vary between forages and between animals, the latter as a result of passage rate and basal diet. In the semi-arid environment of northern Kenya, the quality of forage decreases considerably during the dry season, and consequently rumen dry-matter digestibility (RDMD) of forages by livestock is also reduced. A study comparing RDMD of major forage species by camel, cattle, sheep and goats showed no significant differences between animal species within seasons, except for the camel whose RDMD of grass was significantly lower than that for the other herbivores. Comparisons between seasons showed that RDMD was lowest in the very dry season in all species. Overall, camels, and to a lesser degree goats, had superior DMD to sheep and cattle across seasons. The very dry season (January-March) is the crucial period for a high quality forage supplement intervention for all livestock species; cattle suffer the most due to their high reliance on grass, the least nutritive of the forage components during this period.

RESUME

Digestibilité de la matière sèche dans le rumen chez les camélidés, les bovins, les ovins et les caprins dans la zone semi-aride d'Afrique de l'Est

Chez les ruminants, le degré de dégradation et d'utilisation des fourrages dépend du type de fourrage. Il est en outre fonction de l'espèce animale, compte tenu notamment de l'importance du rythme de passage des aliments ainsi que des caractéristiques de la ration de base. Dans la zone semi-aride du nord-Kenya, les fourrages s'appauvrissent considérablement au cours de la saison sèche, ce qui se traduit par une baisse de la digestibilité de la matière sèche dans le rumen des ruminants. Cette étude a été effectuée pour comparer la digestibilité de la matière sèche des principales espèces fourragères dans le rumen chez les camélidés, les bovins, les ovins et les caprins. Aucune différence significative n'a été enregistrée entre les différentes espèces au cours d'une même saison, exception faite des camélidés chez lesquels la digestibilité des graminées était significativement inférieure à celle des autres herbivores. Quelle que soit l'espèce animale considérée, la digestibilité de la matière sèche était minimum au cours de la saison très sèche. Toutes saisons confondues, la digestibilité de la matière sèche des camélidés et, dans une moindre mesure, des caprins, était supérieure à celle des ovins et des bovins. Quelle que soit l'espèce animale considérée, la saison très sèche (janvier-mars) constitue la période critique de complémentation, les bovins connaissant alors une situation particulièrement difficile compte tenu de leur préférence marquée pour les graminées, plus pauvres que les autres espèces fourragères en cette période de l'année.

INTRODUCTION

Ruminant animal production contributes substantially to the world's human food supply, especially in those marginal areas where pastoralism is the order of life. This is mainly due to the ability of ruminants to convert carbohydrates found in the fibrous parts of plants to high quality human foods. The nutritive value of forages for ruminants depends on the ability of rumen microorganisms to break down the plant cell wall and ferment the carbohydrates (Nelson et al, 1976). The degree of degradability and utilisation of forages by ruminants varies between forages (Double et al, 1971: Utley et al, 1971) and between animals, the latter as a result of passage rate (Hennessey et al, 1983) and basal diet (Lindberg, 1981; Weakley et al, 1983). Most researchers employing the nylon-bag technique (van Dyne, 1962) to study ruminant digestion use a specific basal diet so as to minimise any variations between animals and different trial periods within animals. However, while the results gained do indicate relative dry-matter digestibilities (DMD) of forages, they do not represent natural conditions where the animals are free-ranging and there is variation in basal diets and hence in DMD efficiencies.

In semi-arid and arid tropical ecosystems, the quality of forages decreases greatly during the dry season (Migongo-Bake and Hansen, 1987). Since the basal diet influences DMD in the rumen (Weakley et al, 1983), all herbivores should perform poorly at this time, but the animals that will perform best will be those with higher digestive efficiencies. At other times of the year, inherent differences in diet selection of different herbivore species might lead to variation in basal diets and hence in the DMD of forages.

The aim of this research was to find out whether, for free-ranging livestock species, differences in basal diet between species within seasons, and within species between the green and the dry seasons, led to any significant differences in DMD efficiencies for given forage species. This would aid in decision making on when an intervention, such as use of dry-season forage reserve, would be most appropriate. The study was carried out in a semi-arid area of Marsabit District, Northern Kenya, in 1981/82.

MATERIALS AND METHODS

Animal species

Four castrates, a camel (Camelius dromedarius), a steer (Bos indicus), a sheep (Ovis aries) and a goat (Capra hircus) were fitted with rumen cannulae and used for dry-matter digestion trials using the nylon-bag technique (van Dyne, 1962; Ørskov et al, 1988). Throughout the experimental period, all four individuals appeared to be as healthy as animals not included in the trial. The experimental animals grazed on open range every day and were watered at the normal watering rates for livestock in the region when water is readily available (green season), namely every seventh day for camels, every third day for sheep and goats and every other day for cattle.

Forage species selection, collection and preparation

The sources of forages used in the trials included trees/shrubs, sub-shrubs and grass. The selection was based upon thorough feeding observations (Buechner, 1950) to determine the most preferred species. Species observed to be selected most by the four herbivores were collected once every month; only parts eaten were collected. The samples were air-dried at the prevailing daily temperature (between 20 and 40°C) until no further weight loss was observed. They were then ground in a Wiley mill through a 1-mm screen and subsamples were used in the digestion trial. Forage species preferred by one animal species were also used for digestion trials in the other three species so as to compare the digestive efficiencies of the four animal species for similar forages in the range. A standard sample of Chrysanthemum cineariaefolium, a forte, was used as the control forage in all of the trials.

Nylon-bag degradability trials

The nylon-bag technique is a simple, cheap and direct method of evaluating feeds, especially where laboratory facilities are not available (Ørskov et al, 1980). The method gives a rapid estimate of the disappearance of the tested feedstuffs in the rumen, and also allows the disappearance of the tested sample to be studied with respect to time. It is therefore possible to link the degradation of a feed with its retention time in the rumen (Ørskov et al, 1980). However, the nylon-bag technique only estimates the dry-matter disappearance rate (DMDR) of feed from the bag; it gives no direct information on the chemical nature or the nutritive value of the tested feed.

The number of bags used in digestion trials is a function of their size and weight, and different authors have used different numbers in different animal species (Miles, 1951; Mehrez and Ørskov, 1977; Rutagwenda, 1989). In this trial, the number of bags and the incubation times used were a compromise between two factors: a large enough sample for effective analysis; and the retention of a microbial environment in the rumen that was as normal as possible.

The nylon bags used in this trial were 4 x 7 cm in size. The quality of the nylon material (50 threads per cm; pores between the threads could not be seen using 400x magnification) was such that solids could not enter or leave the bag (Johnson et al, 1982). Samples (2 g) of the forage to be tested and of the control forage were put into preweighed (nearest 0.01 g) nylon bags; five replicates were used for each forage. The samples were incubated for 48 hours (Nocek, 1985; Walli et al, 1988). After incubation the bags were thoroughly washed until the water coming out of the bag was clear (Mehrez and Ørskov, 1977; Demeyer et al, 1982, Varga and Hoover, 1983; Fadlalla et al, 1987). After washing, the bags were squeezed to remove excess water (Playne et al, 1978; Varga and Hoover, 1983) and then air-dried at the prevailing daily temperature (between 20 and 40°C) until no further weight loss was observed. They were then weighed to the nearest 0.01 g and the weight of the sample determined by subtracting the weight of the bag.

RESULTS

Seasonal RDMD comparisons between the four herbivore species are shown in Table 1. There were no differences between the species in RDMD of forages from trees/shrubs and sub-shrubs. However, camels were significantly inferior digesters of grasses compared with the other herbivores. The RDMD of the sheep and steer were affected the most across seasons while the goat and the camel showed least variation. The majority of the significant differences observed within species were between the second green and the second dry seasons, the wettest and driest, respectively, of the study period.

DISCUSSION

Average rainfall over the study area during the four seasons of the study period was:

· first green season (April-June): 76 mm
· first dry season (July-September): 0 mm
· second green season (October-December): 182 mm
· second dry season (January-March): 17 mm

Although there was no rainfall during the first dry season, overcast skies for most of the period meant that it was less dry, in terms of negative effect on vegetation, than the second dry season when cloudless skies resulted in more direct radiation and hence greater evapotranspiration. This led to reduced forage availability and quality through death above-ground of grasses and most sub-shrub forage species.

Table 1. Seasonal rumen digestive efficiency of the camel, steer, goat and sheep in a semi arid region of northern Kenya

		Dry-matter digestive efficiencies (%)
		First green season		First dry season		Second green season		Second dry season
		Mean	SD	Mean	SD	Mean	SD	Mean	SD
Trees/shrubs
	Camel	76.4	15.0	70.3	9.0	78.1	5.9	63.6	10.0
	Steer	76.7	23.7	71.2	18.4	80.9	5.9	61.3	2.8
	Goat	76.3	14.7	71.7	6.9	84.0	5.3	54.8	12.2
	Sheep	76.7	14.7	60.8	7.4	85.5	4.2	62.9	4.7
Number of plant species		10		11		12		11
Sub-shrubs
	Camel	71.2	14.1	55.7	15.2	69.7	11.0	58.4	11.6
	Steer	69.4	15.8	69.8	11.9	76.0	11.3	54.5	9.6
	Goat	69.9	17.1	65.0	17.2	77.4	6.7	59.1	9.2
	Sheep	64.7	18.1	64.6	14.6	70.4	13.0	60.8	9.0
Number of plant species		11		11		11		10
Grasses
	Camel	54.1	10.8	49.6	3.1	55.4	11.5	49.1	7.2
	Steer	74.4	6.6	59.4	7.8	64.4	5.7	60.9	6.6
	Goat	71.1	8.7	59.8	0.9	69.0	4.4	59.1	4.1
	Sheep	69.8	8.7	65.1	13.1	66.8	5.1	60.5	6.3
Number of plant species		17		16		17		17

Because the study area was in a remote semi-arid region, it was considered unwise (because of the high risk of wound infection) to fistulate more than one individual per species until survival and continuous good health of the fistulates was established. Figroid et al (1972), working with rumen-fistulated steers, noted that although some variation was found between steers, it was a small part of the overall variance in the nylon-bag technique when relative values between treatments were considered. This suggests that the error introduced into the digestion trial results through the use of one animal should not be large as long as several replicates are used and the standard deviation of these remains small. Five replicates per trial were used in this study.

The type of diet consumed by an inoculum donor in vitro digestion (van Dyne, 1962). Other research (van Keuren and Heinemann, 1962; Hopson et al, 1963; Neathery, 1969; Weakley et al, 1983) has shown that in situ digestion of forages is influenced by the type of forage fed to the host animals. The livestock species observed in this study grazed on a common open range. RDMD values were not significantly different (P>0.05) between the steer, sheep and goat within seasons. This suggests that although the diet compositions of these animals varied, the quality of the diets did not differ much and so the rumen microbial populations were probably similar, both quantitatively and qualitatively. Although the camel was not significantly different from the other species in RDMD values for forages from tree/shrub and sub-shrub components, its RDMD values for grasses were lower, often significantly so (P<0.05). Maloiy (1972) reported that camels, which are chiefly browsers, tended to have a lower dry-matter digestive efficiency than zebu cattle on low quality hay. According to Hofmann (1973), true ruminant and pseudo-ruminant (eg, camels) browsers have rumen structural components adapted to a diet that has a high content of cell solubles but is also high in lignin. The low RDMD efficiency of camels on grass is probably a result of low populations of cellulolytic microbes in the rumen since grass forms a minimal part of their diet in this ecosystem. In Somalia, however, camels' diets consist chiefly of grass (Newman, 1979), and so it would therefore be worthwhile studying the dry-matter digestive efficiency of grass, and the composition of rumen microbial populations, of these animals.

Hopson et al (1963) observed that the digestibility of forages in dacron bags was significantly higher when alfalfa was fed than when grass hays were fed. Annison and Lewis (1959) noted that a higher quality diet results in a more dense and vigorous rumen microflora as compared to a low quality diet. According to Weakley et al (1983) differences among diets in supporting different rates of in situ dry-matter disappearance are probably due to a combination of rumen microbial and physical factors that are subject to changes in the diet. The quality of forages in the semi-arid region of East Africa decreases rapidly in the dry season. While the observed low quality of grasses results mostly from low crude-protein levels (Lindberg 1981; Van Soest, 1982; Migongo, 1984), that in browse is mostly due to anti-quality factors such as lignin and tannins (Van Soest, 1982; Reed, 1983).

The observations in this study indicate that when seasons are extremely dry and forage availability and quality are low, the RDMD values are also very low. This suggests that there is a limit to the extent that animals can select for a high quality diet that is scarce and still meet their daily rumen fill. Sheep, like goats, have been shown to increase the particle retention time in the reticulorumen during the dry season, thus allowing lengthy degradation of the forages in their diet (Rutagwenda, 1989). Camels are mixed feeders but rely mostly on browse. However, they have been shown to increase their intake of the grass in the dry seasons (Migongo-Bake and Hansen, 1987). Thus camels may be forced to feed on grasses when they come across small fields of these (as are common in the area of study) so as to maximise their dietary intake. Therefore, it is the differences in the seasonal extremes that determine the extremes in forage availability and possible degree of selection.

CONCLUSIONS

While livestock in open range might select for high quality forage to maintain a relatively similar basal diet quality from season to season, the extent to which they can do this and still maximise their intake becomes significantly reduced in extremely dry seasons when forage biomass and its quality are low. This would result in a low quality basal diet, a less dense and less vigorous rumen microflora and hence very low DM digestion such as was observed in the very dry season in northern Kenya, the area of this study. This study showed that the dry season (January-March) is the crucial period for high quality forage supplement intervention for all livestock species, and that cattle suffer the most due to their high reliance on grass, the least nutritive of the forage components during the this period. Camels, followed by goats, fare better, in terms of RDMD, than sheep and cattle, and appear to be better adapted in the utilisation of available feed resources across seasons.

REFERENCES

Annison E F and Lewis D. 1959. Metabolism in the rumen. Methuen, London, UK 184 pp.

Buechner H K. 1950. Life history, ecology and range use of the pronghorn antelope in Trans-Pecos, Texas. American Midland Naturalist 43:275-354.

Demeyer D, Claeys E, van Nevel C J and de Winne R. 1982. Amino acid composition of residual protein after incubation with synthetic fibre bags in the rumen. Zeitschrift für Tierphysiologie, Tierernaehrung und Futtermittelkunde 47:251-252.

Duble R L, Lancaster J A and Holt E C. 1972. Forage characteristics limiting animal performance on warm-season perennial grasses. Agronomy Journal 63:795.

van Dyne G M. 1962. Micro-methods for nutritive evaluation of range forages. Journal of Range Management 14:303-314.

Fadlalla B. Kay R N B and Goodall E D. 1987. Effects of particle size on digestion of hay by sheep. Journal of Agricultural Science, Cambridge 109:551-561.

Figroid W C, Hale C H and Theurer B. 1972. An evaluation of the nylon bag technique for estimating rumen utilization of grains. Journal of Animal Science 35:113-120.

Hennessey D W. Lee G J and Williamson P J. 1983. Nitrogen loss from protein meals held in Terylene bags in the rumen of cattle and the nutritive value of the residues. Australian Journal of Agricultural Research 34:453-467.

Hofmann R R. 1973. The ruminant stomach: Stomach structure and feeding habits of East African game ruminants. East African Monographs in Biology, Vol. 2. East African Literature Bureau, Nairobi, Kenya. 354 pp.

Hopson J D, Johnson R R and Dehority B A. 1963. Examination of the dacron bag technique as a method for measuring cellulose digestibility and rate of forage digestion. Journal of Animal Science 22:448-453.

Johnson M K, Wofford H and Mitchell W. 1982. Contamination during nylon-bag digestion trials. Journal of Wildlife Management 46:253-255.

van Keuren R W and Heinemann W W. 1962. Study of the nylon bag technique for in vivo estimation of forage digestibility. Journal of Animal Science 21:340-345.

Lindberg J E. 1981. The effect of sample size and sample structure on the degradation of dry matter, nitrogen and cell walls in nylon bags. Swedish Journal of Agricultural Research 11:71-76.

Maloiy G M O. 1972. Comparative studies on digestion and fermentation rate in the forestomach of one-humped camel and Zebu steer. Research in Veterinary Science 13:476-481.

Mehrez AZ and Ørskov E R. 1977. A study of the artificial fibre bag technique for determining the digestibility of feeds in the rumen. Journal of Agricultural Science, Cambridge 88:645-650.

Migongo W. 1984. The trophic relations and habitat adaptability of livestock in the central part of Renille land in Kenya. PhD Thesis. Colorado State University. USA. 122 pp.

Migongo-Bake W and Hansen R M. 1987. Seasonal diets of camels, cattle, sheep and goats in a common range in eastern Africa. Journal of Range Management 40:76-79.

Miles J T. 1951. Ruminal digestion of some crude fibre constituents. Journal of Dairy Science 34:492.

Neathery M W. 1969. Dry matter disappearance of roughages in nylon bags suspended in the rumen. Journal of Dairy Science 52:74-78.

Nelson B D, Montegomery C R. Schilling P E and Mason L. 1976. Effects of fermentation time on in vivo/in vitro relationships. Journal of Dairy Science 59:270-277.

Newman D M R. 1979. The feeding habits of old and new world camels as related to their future role as productive animals. IFS [International Foundation for Science] Provisional Report 6. pp. 171-200.

Nocek J E. 1985. Evaluation of specific variables affecting in situ estimates of ruminal dry matter and protein digestion. Journal of Animal Science 60: 1347-1358.

Ørskov E R. Hovell F D DeB and Mould F. 1980. The use of the nylon bag technique for the evaluation of feedstuffs. Tropical Animal Production 5:195-213.

Ørskov E R. Reid G W and Kay M. 1988. Prediction of intake by cattle from degradation characteristics of roughages. Animal Production 46:29-34.

Playne M J. Khummuathong W and Echevarria M G. 1978. Factors affecting the digestion of oesophageal fistula samples and hay samples in nylon bags in the rumen of cattle. Journal of Agricultural Science, Cambridge 90:193-204.

Reed J D. 1983. The nutritional ecology of game and cattle on a Kenyan Ranch. PhD Thesis. Cornell University, Ithaca, New York, USA. 167 pp.

Rutagwenda T. 1989. Adaptation of sheep and goats to seasonal changes of forage on a semi-arid thornbush savannah pasture in northern Kenya. PhD Dissertation. Tierärztliche Hochschukle, Hanover, FR Germany. 131 pp.

Utley P R. Lowrey R S. Marchant W H. Hellwig R E, Butler J L and McCormick W C. 1971. Comparative feeding value of pelleted Pensacola Bahiagrass, Coastal Bermudagrass and Coastcross-1 Bermudagrass at four and eight weeks of age. Journal of Animal Science 33: 147-150.

Van Soest P J. 1982. Nutritional ecology of the ruminant. O & B Books, Corvallis, Oregon, USA. 374 pp.

Varga G A and Hoover W H. 1983. Rate and extent of neutral detergent fibre degradation of feedstuffs in situ. Journal of Dairy Science 66:2109-2115.

Walli T K, Ørskov E R and Bhargava P K 1988. Rumen degradation of straw. 3. Botanical fractions of two rice straw varieties and effects of ammonia treatment. Animal Production 46:347-352.

Weakley D C, Stem M D and Satter L D. 1983. Factors affecting disappearance of feedstuff from bags suspended in the rumen. Journal of Animal Science 56:493-507.