Effect of legume crop residues and concentrate supplementation on voluntary intake and performance of kirdi sheep fed a basal diet of rice straw

A T Ngwa ¹ and C L Tawah ²

1 Institute of Animal Research (IRZ)
PO Box 12, Yagoua, Cameroon

² Institute of Animal Research (IRZ)
PO Box 65, Ngaoundere, Cameroon

ABSTRACT

Twenty young Kirdi rams of the West African Dwarf sheep, averaging 22 kg liveweight and 15 months of age, were randomly assigned to four feeding groups and subjected to an eight-week feeding trial, to determine the effect of different protein supplements on voluntary intake of rice straw and on performance. Control group animals were fed a daily basal diet of ad libitum rice straw and 250 g of rice bran. Other groups were fed the basal diet supplemented with 300 g of groundnut haulms, 45 g of cottonseed cake or 210 g of chopped cowpea vines. Liveweight changes of the supplemented groups did not differ significantly but there was a difference (P<0.05) in liveweight gain between the supplemented groups and the control group. There were highly significant (P<0.01) differences between the groups in the intake of rice straw; cottonseed cake increased intake while the crop residues reduced intake. Variations in height at withers, heart girth and scapulo-ischial length showed no significant differences between treatments. Cottonseed cake was the most effective supplement, in terms of both liveweight gain and intake of rice straw. However, because crop residues are readily available to farmers, it is worthwhile paying some attention to them.

RESUME

Effet de la complémentation de la paille de riz avec des résidus de culture de légumineuse et des concentrés sur l'ingestion volontaire d'ovins Kirdi

Un essai d'alimentation d'une durée de huit semaines a été effectué pour déterminer l'effet de divers compléments protéiques sur les performances et l'ingestion de paille de riz chez des ovins. 20 jeunes béliers Kirdi de race Djallonké, pesant en moyenne 22 kg et âgés d'environ 15 mois ont été divisés au hasard en quatre groupes soumis chacun d'un régime alimentaire donné. Tous les animaux recevaient de la paille de riz ad libitum comme aliment de base; ceux du lot témoin recevaient en outre 250 g de son de riz par jour et par tête, alors que ceux des trois autres lots recevaient soit 300 g de fanes d'arachide, soit 45 g de tourteau de coton, soit 210 g de fourrage de niébé broyé. Les variations de poids des animaux recevant une complémentation n'étaient pas significativement différentes de celles du lot témoin mais leurs gains de poids vif étaient significativement (P<0,05) différents. L'ingestion de paille de riz variait significativement (P<0,01) selon la ration: elle était élevée avec le tourteau de coton et faible avec les résidus de récolte. En revanche, les variations des mensurations linéaires (hauteur au garrot périmètre thoracique et longueur scapulo-ischiale) n'étaient pas significativement différentes. Bien que le tourteau de coton donne les meilleurs résultats en ce qui concerne les gains de poids et l'ingestion de paille, on ne saurait cependant déconseiller l'utilisation des résidus de récolte, étant donné que les paysans peuvent se les procurer facilement.

INTRODUCTION

Thousands of tonnes of rice straw are destroyed every year in the Far North Province of Cameroon. This is a waste of resources: even with a crude-protein content of only 4% (Nour, 1986; Udo and El-Harith, 1985) and an organic-matter digestibility of between 40 and 50% (Pearce, 1984; Zainur et al, 1984), rice straw could be a major feed for ruminants if properly supplemented. Intake of rice straw is limited to less than 2% of body weight (Jackson, 1978) because of the slow rate at which it is fermented in the rumen, but it can still be a major source of energy for ruminants in an area like the Par North Province where pasture and grain production is hampered by a long (eight-month) dry season.

Chemical, physical or microbial methods of treating straws to improve their low energy and protein content (Hartley, 1981; Kiangi et al, 1981; Saadullah et al, 1981; Wongsrikeao and Wanapat, 1984; Mason and Owen, 1986) are of little economic relevance to small-scale farmers. However, it is at this level that the problem of weight loss by animals during the dry season is most critical. There is thus a great need to prevent weight loss by the use of simple techniques applicable to farmers and involving readily available agro-industrial byproducts and crop residues. Supplementation of poor quality roughages, including cereal crop residues, with legumes has been shown to increase their digestibility (Devendra, 1982) or intake (Most and Butterworth, 1985) or both (Minson and Milford, 1967; Lane, 1982; Moran et al, 1983; McMeniman et al, 1988).

This study investigated the effects of different protein supplements on the intake of rice (Oryza sativa) straw, on the efficiency of nutrient utilisation and on the performance of Kirdi rams.

MATERIALS AND METHODS

Animals

Twenty Kirdi yearling male lambs (average age 15 months; average liveweight 22 kg) were randomly assigned to four treatment groups of five animals each. The animals were kept in a roofed half-walled shed with a concrete floor. They were treated against worms and ectoparasites and fed polyvitamins dissolved in water.

Feeds and feeding

A two-week adaptation period on a daily diet of ad libitum rice straw and 250 g rice bran per animal was followed by an eight-week experimental period, during which the groups were allocated to one of four diets:

· basal diet (control): rice straw (ad libitum, 125% of daily intake) plus 250 g rice bran per animal per day

· diet 1: basal diet plus 300 g groundnut haulms per animal per day

· diet 2: basal diet plus 45 g cottonseed cake per animal per day

· diet 3: basal diet plus 210 g chopped cowpea vines per animal per day

The experimental period was divided into four periods of two weeks each to examine the effect of time of feeding on voluntary intake and performance.

Table 1 shows the nutrient composition of the ration ingredients. The rations were formulated to be approximately isonitrogenous. Diets 1 and 3, unlike diet 2, were isocaloric. The protein supplements were offered each morning before the basal diet. Water and a 50:50 common salt/bonemeal mineral supplement were offered ad libitum. The feed ingredients and refusals were weighed each morning.

Table 1. Nutrient composition of ration ingredients

Ingredients	Dry matter (%)	Energy a (UF/kg DM)	Digestible crude protein (% DM)	Calcium (% DM)	Phosphorus (%DM)
Rice straw	95	0.42	0	0.19	0.08
Rice bran	94	0.85	0.9	0.16	1.74
Cottonseed cake (Alibet)	95	0.84	383	0.24	1.24
Groundnut haulms	94	0.43	5.8	1.41	0.21
Cowpea vines	94	0.60	9.2	0.64	0.29

a UF = unité fourragère = 1883 calories

Dry-matter content was determined on-station. Other analyses were earned out by the nutrition laboratory of the Institut d'élevage et de médecine vétérinaire des pays tropicaux (IEMVT) in France

Animals were weighed every two weeks during the experimental period. Height at withers, heart girth and scapulo-ischial length were measured at the beginning, middle and end of the experiment.

Statistical analysis

Liveweight changes, average daily gains and feed intake were subjected to analysis of variance (Steel and Torrie, 1980). The treatment means were compared using Duncan's new multiple range and Student's test (Ott, 1977).

RESULTS

All animals remained in good health throughout the experimental period.

The voluntary intake of rice straw varied highly significantly between feeding groups and with time of measurement (Table 2). Rice straw intake increased highly significantly (P<0.01) in animals supplemented with cottonseed cake but decreased highly significantly in animals supplemented with the legume crop residues (Table 3).

The liveweight changes of the supplemented animals did not differ significantly from each other (Table 2) although they were highly significantly affected by the time of measurement. Average daily gain tended to be affected by the type of protein supplementation (Table 2). This tendency may reflect the short duration (eight weeks) of the experiment. However, the objective of the study was to maintain the weight of the animals during the period of scarcity which, evidently, was achieved. The average daily gain of the supplemented groups exceeded (P<0.05) that of the control group.

Table 2. Least-squares analysis of variance of mean squares of rice straw intake, liveweight change and average daily gain

Source of variation	df	Mean square	Significance level
Rice straw intake
Treatments (T)	3	7.123	P<0.01
Supplementation period (P)	3	0.432	P<0.01
T x P	9	0.206	P<0.05
Residual	192	0.060
Liveweight change
Treatments (T)	3	0.897	ns
Supplementation period (P)	3	9.162	P<0.01
T x P	9	0.410	ns
Residual	64	0.449
Average daily gain
Treatments	3	1144.58	P<0.1
Residual	16	467.60

Table 3. Efficiency of feed utilisation and cost of ration for Kirdi sheep by treatment group

Parameters		Basal diet	Diet 1	Diet 2	Diet 3
Dry matter intake
	Rice straw (g/animal per day)	502	380	552	446
	Total (g/animal per day)	736	896	829	877
	Total (g/kg liveweight 0.75)	77.1	93.8	86.8	86.2
Energy intake (UF/animal per day) a		0.41	0.48	0.47	0.51
Digestible crude protein intake (g/animal per day)		20.8	37.2	37.2	39.0
Protein:energy ratio (g/UF) a		50.7	77.5	79.2	76.5
Feed utilisation efficiency (kg DM consumed/kg liveweight gain)		36.8	18.3	15.9	17.8
Cost of daily ration/animal (FCAFA)		13.4	19.2	15.6	17.8
Cost per kg liveweight gain/day (FCFA)		670.0	392.6	291.5	361.1

a UF = unité fourragère = 1883 calories

Basal diet = ad libitum rice straw plus rice bran (250 g/animal per day)
Diet 1 = basal diet plus groundnut haulms (300 g/animal per day)
Diet 2 = basal diet plus cottonseed cake (45 g/animal per day)
Diet 3 = basal diet plus chopped cowpea vines (210 g/animal per day)

Cottonseed cake was the most effective protein supplement in terms of both intake and weight gain (Tables 3 and 4). In the supplemented groups, the quantity of protein offered was similar, suggesting that the intake of rice straw was influenced by the source of protein supplement. The high protein:energy ratios (Table 3) are explained by the poor quality of rice straw which was the major source of energy in the diets. Height at withers, heart girth and scapulo-ischial length did not differ significantly with the treatments (Table 4) although there was a general increase in the supplemented groups. Within the same treatment group, variations in heart girth and scapulo-ischial length were greater than the variation in height at withers.

DISCUSSION

The dry-matter intakes of rice straw observed for sheep fed the different diets were comparable to the values of 0.3-0.5 kg/animal per day reported by other authors (Zainur et al, 1984; Boonloom and Potikanond, 1984) under similar experimental conditions. They were, however, lower than values reported for chemically treated straws: chemical treatment of straws increases their digestibility and intake (Ibrahim, 1984). Rice straw, like any other crop residue, has a high crude-fibre content of 40% (Suriyajantratong and Wilaipon, 1984) and low levels of protein, soluble carbohydrates and minerals. It has also been reported that the ash fraction of rice straw contains mostly silica which not only has no nutritional value for animals but also depresses the digestibility of other nutrients (Clawson and Garett, 1970). It is thus likely that the high fibre and ash contents of rice straw are the major factors limiting its utilisation by ruminants. Intake and digestibility of rice straw are consequently too low to sustain animal maintenance, let alone support animal production. Supplementation with energy and/or protein should thus increase the efficiency of utilisation of rice straw.

Table 4. Weight gain and linear measurements of Kirdi sheep by treatment group

Zootechnical parameters	Basal diet	Diet 1	Diet 2	Diet 3	SD
Number of animals	5	5	5	5
Average initial weight (kg)	22.26	22.58	22.54	24.04
Average final weight (kg)	23.38	25.32	25.46	26.80
Average daily weight gain	20.00	48.93	52.14	49.29	9.67
Average change in height at withers (cm)	1.33	1.00	1.80	1.70	0.30
Average change in heart girth (cm)	2.30	3.10	3.50	2.00	0.40
Average change in scapulo-ischial length (cm)	2.60	3.10	3.00	2.50	0.50

Basal diet = ad libitum rice straw plus rice bran (250 g/animal per day)
Diet 1 = basal diet plus groundnut haulms (300 g/animal per day)
Diet 2 = basal diet plus cottonseed cake (45 g/animal per day)
Diet 3 = basal diet plus chopped cowpea vines (210 g/animal per day)

Supplementation with groundnut haulms, cowpea vines and cottonseed cake produced positive effects on growth rate. However, intake of the basal diet decreased when supplemented with legume crop residues. An ideal supplement should maintain or increase the intake of the basal diet rather than substitute for it, a phenomenon often seen with animals fed legumes (Moran et al, 1983) or legume crop residues (Most and Butterworth, 1983). Supplementation with legume crop residues contributes fermentable energy to the rumen in the form of available cellulose and hemicellulose which stimulate fibre digestion (Silva and Ørskov, 1985). It is possible that offering such material prior to the daily feeding of rice straw may induce a greater degree of colonisation of rice straw by rumen bacteria and by rumen fungi, which have been implicated in the breakdown of fibre (Bauchop, 1981). Ørskov and Dolberg (1984) stated that if animals feeding on untreated straws or poor quality roughages are supplemented with substrates which increase the fermentation rate of cellulose, the rumen environment becomes similar to that of animals receiving ammonia-treated straws. This may explain why Nolan and Stachiw (1979) found an increase in the intake of wheat straw by sheep when 50 g of lucerne chaff was added to their ration.

The improvement of the rumen environment when animals are fed untreated straws or poor quality roughages with certain supplements is very important in areas where chemical treatment of these poor roughages is not possible. The supplement should be an easily digestible byproduct containing cellulose and/or hemicellulose (Ørskov and Dolberg, 1984), such as green grass, azolla, water hyazinth, legumes or citrus pulps. The higher intake of rice straw by sheep supplemented with cottonseed cake is explained by the fact that cottonseed cake not only provided the essential nutrients to maintain optimal rumen activity but was also more rapidly degraded in the rumen. Groundnut haulms and cowpea vines, although contributing the essential nutrients, took much longer to break down, hence the lower intakes of the basal diet. Ingested fibre material must be broken down by rumination, microbial fermentation or both to produce particles which are small enough to pass through the reticulo-omasal orifice (Blaxter et al, 1956; Crampton, 1957; Campling and Balch, 1961; Campling et al, 1962). Cottonseed cake turned out to be the most efficient supplement, probably because animals fed this supplement had more than twice the quantity of energy received by the other treatment groups. This is attributed to the higher intake of rice straw by this group (Table 3). The cottonseed cake supplemented diet was the cheapest (Table 4). However, as groundnut haulms and cowpea vines are more readily available to farmers, it is worth paying particular attention to them.

CONCLUSIONS

The use of low quality roughages in ruminant diets is limited, at least in part, by the insufficient intakes of these roughages to ensure satisfactory animal performance. It has been suggested that the intake of these roughages is limited mainly by their low digestibilities. This study shows that giving small quantities (up to 30% of total DM intake) of a legume crop residue will substantially increase the total DM intake and improve the digestibility of rice straw above that which can be obtained by use of non-protein-nitrogen supplements. Judicious amounts of legume crop residues, which are generally available in abundance during the harvest season, could be fed in combination with rice straw and rice bran to small ruminants in the hot dry season to ensure minimal weight loss, mortality and weakness due to malnutrition.

ACKNOWLEDGEMENTS

We wish to thank the Institute of Animal Research, Yagoua Station, for providing the facilities for this work; Mr E L Bengolo, who helped in the planning and execution of this experiment; Messrs S Patcha and D Dimati for their care and feeding of the experimental animals; and Mrs I Maïrama for typing this paper.

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