Performance and management of sheep on Rhodes grass-stylo pasture in Nigeria

O S Onifade ¹, I F Adu ² and J O Akinola ³

¹ National Animal Production Research Institute
Ahmadu Bello University
PMB 1096, Zaria, Nigeria

² College of Animal Science and Livestock Production
University of Agriculture
Abeokuta, Nigeria

³ Department of Animal Production and Health
Ladoke Akintola University of Technology
Ogbomosho, Nigeria

ABSTRACT

An experiment was designed to study the effect of stocking rate on dry-matter yield and animal performance on Rhodes grass-stylo (Chloris gayana cv Callide-Stylosanthes guianensis cv Cook) pasture over three grazing periods (1986-1989) at Shika, Zaria, Nigeria. Sheep were continuously grazed at 12,18, 24,30 and 36 sheep/ha during the late wet to mid-dry season for 154 to 210 days in each grazing period.

Stylo was eliminated after the first grazing period. Rhodes grass was still dominant after three grazing periods. Yields of green and dead materials fell as stocking rate increased. Daily liveweight gain decreased as stocking rate increased and, gradually, as grazing progressed. Problems of managing sheep on pasture, with respect to animal age and weight, time to commence grazing and to give supplementary feed, and routine health practices, are discussed.

RESUME

Performances et gestion d'ovins élevés sur pâturage d'herbe de Rhodes et de Stylosanthes au Nigéria

Une expérience a été effectuée à Shika dans la région de Zaria (Nigéria) en vue d'étudier l'effet du taux de charge sur la production de matière sèche d'un pâturage d'herbe de Rhodes (Chloris gayana cv. Callide) et de Stylosanthes (Stylosanthes guianensis cv. Cook) ainsi que sur les performances d'ovins élevés sur ce pâturage. Conduit pendant trois périodes de pâturage (1986/89) longues chacune de 154 à 210 jours et allant de la fin de la saison humide au milieu de la saison sèche, cet essai a porté sur des taux de charge de 12, 18, 24, 30 et 36 animaux par hectare.

La légumineuse a été éliminée dés la fin de la première période de pâturage alors que l'herbe de Rhodes demeurait l'espèce dominante à la fin de la troisième période. La production de matériel végétal, qu'il soit vert ou sec, baissait avec l'accroissement du taux de charge. Les gains moyens quotidiens diminuaient progressivement au fil du temps et au fur et à mesure qu'augmentait le taux de charge. Les problèmes liés à la gestion des élevages ovins sur pâturage ont été examinés, notamment en ce qui concerne l'âge et le poids des animaux, le choix du moment d'accès au pâturage ou aux aliments complémentaires ainsi que les interventions sanitaires de routine.

INTRODUCTION

The present system of sheep production in the Northern Guinea Savanna zone of Nigeria is based on indoor feeding, grazing of natural or sown pastures or a combination of these. The grazing of sown pastures is limited to universities, research institutions and a few private farms where the performance of sheep can be better evaluated.

There have been few grazing trials in Nigeria to determine productivity of pasture, especially with sheep. In the humid zone, Sumberg (1985) grazed West African Dwarf sheep on natural fallow regrowth in an integrated alley-farming system sown to Leucaena leucocephala and Gliricidia sepium, and reported that 16 and 8 ewes could be supported per hectare during the wet (June-November) and dry (November-March) seasons, respectively. He recorded a liveweight gain of 218 kg/ha from ewes supplemented with concentrate during the dry season.

This study reports the effect of set stocking at the rates of 12, 18, 24, 30 and 36 rams/ha on the yield of a Rhodes grass-stylo pasture and on animal liveweight gain.

MATERIALS AND METHODS

The experiment was carried out at the National Animal Production Research Institute at Shika in the Northern Guinea Savanna zone of Nigeria. Climatic data for the study area during the study period are presented in Table 1. The soils at Shika are classified as ferruginous tropical soils (Klinkenberg and Higgins, 1968).

The animals used in the trial were Yankasa rams, the most common breed of sheep in this ecological zone.

Table 1. Climatic data for Shika and Samaru (10 km from Shika) ring the grazing periods, 1986-1989

		1986/87	1987/88	1988/89
Shika
Rainfall (mm)
	During grazing period	420	253.5	88
	Total annual	1071	1151	1066
Rainy days
	During grazing period	19	20	9
	Total annual	38	47	19
Samaru
Screen temperature (°C)
	August	23.9	24.5	-
	September	24.0	25.4	24.3
	October	24.3	24.3	23.4
	November	22.8	22.1	21.9
	December	19.8	21.4	20.0
	January	21.5	21.2	17.1
	February	24.7	23.8	20.7
	March	27.3	28.4	-

A mixed pasture of Rhodes grass (Chloris gayana cv Callide) and stylo (Stylosanthes guianensis cv Cook) was sown at the study site in August 1985. Seed was hand broadcast at the rate of 5 kg pure germinating seed (PGS)/ha: the grass:legume seed ratio was 3:7. Phosphorus (30 kg/ha) was applied as single superphosphate at establishment and again in July before each grazing period. The pasture was set stocked on 21 August 1986 for 210 days, on 25 August 1987 for 196 days and on 12 September 1988 for 154 days. Herbage in each paddock was cut back in May before each grazing period to remove uneven growth. Five stocking rates - 12, 18, 24, 30 and 36 rams/ha - were arranged in a randomised block design with two replicates. Stocking rates were achieved by adjusting paddock size from 0.25 to 0.09 ha to accommodate three rams at the appropriate rate.

The mean initial liveweight of Yankasa rams used in each grazing period was 20 kg: the mean biomass of the three rams in all paddocks was similar. The animals were treated with an anthelmintic and dipped before grazing began and at four-week intervals thereafter. The animals were not provided with shade or supplementary feed but were given water and mineral salt block in each paddock. Rams were weighed every two weeks after a 14-hour overnight fast (without feed or water) in an enclosure outside the paddocks.

Pasture components were sampled before each grazing period and then every six weeks and at the end of the grazing period. Dry-matter yield on offer was estimated by cutting from six random 0.5 x 0.5 m quadrats in each paddock. The cutting was done at ground level with a hand sickle in the paddocks and cages used as control. The herbage samples were weighed, mixed and two fresh subsamples of about 500 g were taken. One was hand-sorted into green and dead materials; the other remained intact. These were oven dried and weighed.

Data on forage and liveweight gains were subjected to analysis of variance. Duncan's New Multiple Range Test (Steel and Torrie, 1980) was used to compare means of stocking rate and grazing days

RESULTS

Pasture dry-matter yields are shown in Table 2. Yields of both green and dead material decreased as stocking rate increased. Yields of green material declined significantly (P<0.05) as the grazing period progressed, while yields of dead material increased. Stylo constituted only 11.2% of the total pasture yield at the start of grazing in 1986. In the first grazing period (1986-87) the yields of stylo at the various stocking rates were not different (P>0.05). The highest stylo yield was recorded in the control plot. Stylo yields declined with increase in grazing days at all stocking rates. Stylo was eliminated in the second grazing period, except in the control plot where a mean yield of less than 0.5 t/ha was recorded.

In all grazing periods, daily liveweight gain of sheep decreased significantly (P<0.05) as grazing progressed (Figure 1). Also, weight losses commenced earlier in each successive grazing period. Daily liveweight gain also tended to decrease with increasing stocking rate in all the grazing periods (Table 3). Using the regression Yh = ax - bx² for liveweight gain per hectare (Yh), where x is the stocking rate and a and b are constants, the calculated optimum stocking rates in the first, second and third grazing periods were 20.4, 24.9 and 21.2 sheep/ha. The corresponding liveweight productions were 155.4, 186.2 and 129.4 kg/ha.

DISCUSSION

Stylo did not persist in the mixed pasture beyond the first grazing period. Winter et al (1977), however, reported that stable pastures of Brachiaria decumbens and Panicum maximum with S. guianensis cv Endeavour were obtained after three years of grazing with cattle at 0.7 and 2.2 animals/ha. Stocking rate in the first grazing period did not suppress stylo yield in this trial as was observed in other trials of grass-legume pastures grazed by sheep (Curll and Davidson, 1983; Curll et al, 1985) and by cattle (Stobbs, 1970; Shaw, 1978; Eng et al, 1978).

The observed decline in stylo coverage caused by the companion Rhodes grass agrees with a report from Thailand (Gutterridge, 1985) where ungrazed stems of bamboo grass (Arundinaria ciliata) reduced the development of S. humilis, S. hamata cv Verano and S. guianensis cv Endeavour. Earlier, Blair Rains (1963) had observed that 24-hour stocking of stylo-based pastures in Nigeria would reduce the legume content. The legume might have performed better if its initial content in the pasture was higher.

Table 2. Effect of stocking rates and grazing days on dry- matter yields of green and materials in the Rhodes gross-stylo pasture

Pasture component		Dry-matter yield (t/ha)
Stocking rate (sheep/ha)		12	18	24	30	36	Control
1986/87
	Green	6.96b	6.96b	6.51bc	6.27cd	5.88d	8.67a
	Dead	1.27a	1.04b	1.19ab	1.08b	1.05b	0.55c
	Stylo	0.56	0.57	0.65	0.50	0.64	1.00
1987/88
	Green	7.55a	7.21bc	7.27bc	6.86c	6.82c	8.81a
	Dead	1.41a	1.29ab	1.20abc	1.16abc	1.00bc	0.86c
1988/89
	Green	7.30b	7.00bc	6.83c	6.60c	6.25d	8.88a
	Dead	1.29a	1.25a	1.16b	1.01c	0.93c	0.82d
Grazing days		0	42	84	126	168	210
1986/87
	Green	10.3a	9.5b	8.0c	5.4d	4.4e	3.7f
	Dead	0.0	0.5d	0.8c	1.6b	1.6b	1.7a
1987/88
	Green	9.5a	9.4a	7.5b	5.9c	4.8d	-
	Dead	0.6c	0.8b	1.1b	1.5b	1.7a	-
1988/89
	Green	8.8a	7.8b	6.7c	5.3d	-	-
	Dead	0.4d	0.9c	1.3b	1.7a	-	-

Within a row, means followed by the same letter, or no letter, do not differ significantly (P>0.05)

Yields of green fodder declined as stocking rate and grazing days increased. This finding supports work by Mears and Humphreys (1974) who reported reductions in green matter of Kikuyu grass (Pennisetum clandestinum) as stocking rate increased. Similarly, Watson and Whiteman (1981) reported a drop in green yields of mixed pastures of Panicum maximum and B. decumbens with the legumes Centrosema pubescens, Macroptilium atropurpureum cv Siratro and S. guianensis cv Endeavour as stocking rate increased from 1.8 to 4.5 animals/ha.

Figure 1. Daily liveweight changes of sheep during three grazing periods

Table 3. Effect of stocking rate on daily liveweight gain of sheep daring three grazing periods

Stocking rate (sheep/ha)	Daily liveweight gain (g/head)
	1986/87	1987/88	1988/89
12	52	61	60
18	39	47	47
24	33	36	26
30	14	31	23
36	11	23	16

The consumption of a high percentage of the green materials and subsequent restriction of the formation of dead material (Greenwood and Arnold, 1968) and possible consumption dead leafy materials at higher stocking rate (Mears and Humphreys, 1974) could have resulted in the lowering of the yield of dead material as stocking rate increased.

The decline in daily liveweight gain per animal as stocking rate increased appeared to have arisen from differences in the amount of green material on offer (Arnold, 1962) which followed the same pattern. As a result, sheep at the lowest stocking rate had better opportunity to select herbage higher in crude protein and lower in fibre (Weir and Torrell, 1959), hence the higher liveweight gain. In this study it was observed that some rams were very slow to gain weight and some came down with diarrhoea which could have affected the overall liveweight gain.

The general decline in liveweight gain as grazing progressed was attributed to reduced nutritive value due to advanced plant maturity (Blunt, 1978), season (Bryan and Evans, 1973; Okeagu, 1989) and thus reduction in herbage, especially leaf, on offer (Laredo and Minson, 1973). From this study it can be argued that sheep will start to lose weight at the highest and lowest stocking rates in late December and late January, respectively, when the pasture is stocked in August/September. Thus farmers should give supplementary feed or remove animals or reduce stocking rates before these dates when grazing grass pasture.

Yearling rams and/or those above 20 kg were observed to survive better than lighter animals. With respect to the time to stock the pasture, this study would suggest periods before the flowering stage is reached or at sward heights below the knee. A case of cutaneous myasis, an acute dermatitis of sheep caused by blowfly (Chrysomia regalis) larvae was noticed in the second grazing period, presumably because the pasture was high (over 100 cm) and dense. A less dense canopy might discourage the fly. Predators and thefts can also account for losses of animals on pasture. Adequate security and close fencing should be maintained at au times. This will also enable a regular check to be made on the flock to monitor the health of the animals and allow immediate treatment.

ACKNOWLEDGEMENTS

The authors would like to express their appreciation to Messrs Ayuba Mahuta, Ashiru Mohammed and Bala Musa for field assistance and S A S Olorunju (NAPRI biometrician) for statistical analysis. We thank the Director of NAPRI for provision of facilities and permission to publish this paper.

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