Productivity of Blackhead Persian sheep in Tanzania

S.M. Das¹, J.E.O. Rege² and Mesfin Shibre²

¹Zonal Research and Training Centre, Mpwapwa, Tanzania

²ILCA, Addis Ababa, Ethiopia

Abstract
Introduction
Materials and methods
Statistical analyses
Results and discussions
Conclusion
References

Abstract

Weight of lambs weaned (at 150 days) per ewe per year (Index D, per kg liveweight of ewe per year (Index II), per kg metabolic body weight (W0.73) of ewe per year (Index III), and per lifetime of ewe regardless of ewe weight (Index IV), were computed for 3022 ewes at Malya and West Kilimanjaro research centres in Tanzania. The data analysed covered a period of 24 years (1965-1988). Least squares means for the four respective indices were 24.6 kg (SE 3.19), 675 g (SE 15.7) 1.8 kg (SE 0.04) and 63 kg (SE 1.6). Year, seasons and location significantly (at least P<0.05) affected all the indices except index IV which was not affected (P=0.59) by season. All indices showed a tendency to decline during most of the study period (1966 through 1981). Indices II and III exhibited a small recovery thereafter but this was not subsequently maintained. Dry season lambing was associated with the higher productivity indicated by index I (P<0.01) and index II (P=0.0). Productivity at Malya was consistently superior (P<0.01) to that at West Kilimanjaro, being 3 kg, 152 g, 0.45 kg and 7.2 kg better, respectively, for the four indices. Although Malya was superior to West Kilimanjaro in lamb weaning weight, a large proportion of the between-station differences in productivity indices was attributed to differential preweaning lamb mortality.

Productivité du mouton Blackhead Persian en Tanzanie

Résumé

Les poids d'agneaux sevrés (à 150 jours) par brebis et par an (indice 1), par kilo de poids vif de brebis par an (indice 11), par kilo de poids métabolique (P^0,73) de brebis par an (indice 111) et par carrière de femelle des brebis, quel que soit le poids de la brebis (indice IV), ont été calculés pour 3 022 brebis aux stations de recherche de Malya et de West Kilimanjaro en Tanzanie. Les données analysées avaient été recueillies sur une période de 24 ans (1965-1988). Les moyennes des moindres carrés des quatre indices étaient respectivement de 24,6 kg( ± 3,19), 675 g ( ± 15,7), 1,8 kg ( ± 0,04) et 63 kg ( ± 1,6). L'année, la saison et la station avaient un effet significatif (au moins P<0,05) sur tous les indices, exception faite de l'indice IV qui n'était pas modifié é par la saison (P = 0,59). Tous les indices ont montré une tendance à la baisse durant la plus grande partie de la période d'étude (de 1966 à 1981). Un léger redressement des indices 11 et 111 a été observé, sans qu'il se soit maintenu par la suite. L'agnelage de saison sèche était associé aux niveaux les plus élevés de productivité que reflètent les indices I (P<0,01) et 11 (P = 0,0). Le niveau de production observé à Malya dépassait (P<0,01) toujours celui enregistré à West Kilimanjaro, avec des poids supérieurs de 3 kg, 152 g. 0,45 kg et 7,2 kg respectivement pour les quatre indices. Bien que les poids au sevrage relevés à Malya aient été plus élevés que ceux enregistrés à West Kilimanjaro, une grande partie des différences interstations entre les indices de productivité a été attribuée aux différences de mortalité des agneaux avant le sevrage.

Introduction

In Tanzania, the majority of traditional sheep are kept extensively, mostly in mixed livestock crop farming systems. The Blackhead Persian (BHP) sheep comprise a large proportion of the adapted sheep breeds. The BHP sheep were acquired in the early 1960s (Das and Sendalo, 1991) with the purpose of improving the indigenous sheep population through crossbreeding. The breed is mainly located at government research centres and parastatal farms and is used for meat production.

Overall meat production from sheep is affected by several variables, the most important of which are the fertility, prolificacy and mothering ability of the ewes and lamb survivability and weight. Productivity has been measured from these traits by using indices which account for possible pre-weaning dam effects (Wilson, 1987). Productivity indices can be used for selection purposes as well as for comparing flocks when measured either for a fixed period of time or over the entire lifetime of the ewe. To incorporate feed requirements, productivity indices may be calculated as weight (kg) of lambs weaned per unit weight (kg) of ewe live weight or unit of ewe metabolic weight (kg) at parturition.

In this study, the productivity of BHP sheep at both research centres (Malya and West Kilimanjaro) was calculated using indices (I to III) proposed by Wilson (1987). A fourth index was developed to calculate total lamb mass production per lifetime of ewe. This index could also be expressed as the lamb mass produced for each lambing when mean flock size is used in the denominator.

Materials and methods

The records of BHP sheep used in this study were collected from two Livestock Research Centres - Malya and West Kilimanjaro in Tanzania. The Malya Research Centre lies at approximately 4°S latitude and 37°E longitude, at an altitude of about 1050 metres above sea level. The Centre covers an area of 1800 ha of which 1400 have natural vegetation of savannah grassland. The natural vegetation at Malya comprises Combretum wood species and grass species of Bothrichloa, Hyparrhenia, Themeda and Cynodon. A few paddocks are sown with Chloris gayana.

The West Kilimanjaro Research Centre lies approximately 3°S latitude and 39°E longitude, at an altitude of about 1270 metres above sea level. It lies on the rain shadow region of Kilimanjaro mountain and covers an area of 5300 ha. Pennisetum schimperi is the dominant grass species in the natural pastures. Cultivated pastures include Digitaria scalprum and Bothrichloa spp.

At both Centres, sheep were grazed from 0800 to 1700 hours and were housed indoors at night. Sheep were bred in both the wet and dry seasons. The wet breeding season extended from March to May, while the dry breeding season extended from September to November. Each breeding season consisted of 50-70 days and the ratio of rams to ewes in breeding groups was about 1:40. Ewe lambs joined the mating groups at the age of 72 weeks. Lambs were ear-tagged soon after birth and left to suckle their dams during grazing until weaning at 16 weeks of age. Lambs were separated at weaning by sex into different weaner flocks. Records taken on lambs included birth and weaning weights and weights at 24, 48 and 72 weeks. Ewes were weighed at mating, lambing and weaning.

Statistical analyses

The productivity indices were constructed for individual ewes using data on corrected litter weight at 150 days, lambing interval, survival of young and post-partum weight of ewe. Lamb live weights were adjusted to 150 days and additionally preadjusted for effect of sex. The corrected weights at 150 days were used to calculate productivity indices I, II and III. The fourth index, index IV, was defined as the lifetime productivity per ewe in terms of lamb mass produced. To obtain a measure of lamb mass (kg) per female per lambing, Index IV was further divided by the average number of parturitions per flock. The four productivity indices were calculated as follows:

Index I = weight (kg) of young per female per year

Index II = weight (g) of young produced per kg live weight of female per year

Index III = weight (kg) of young produced per kg metabolic weight of female per year

Index IV = total litter weight (kg) at 150 days per female during lifetime

Lamb mass (kg)

The analyses were carried out by fixed effects models using the General Linear Model (GLM) procedure of SAS (1987) software package. The fixed effects included in the model were year and season of parturition, age of ewe and location. The residual mean square was used as the error term to test the significance of all differences evaluated among classes. Where analysis of variance depicted significant differences for variables, linear contrasts of least squares means were estimated to test pairwise differences within factors.

Results and discussions

Productivity indices I, II and III

Overall least squares means of indices, I, II and III are presented in Table 1. Year, season of birth and location significantly (P<0.05) affected the three indices, but age of ewe at parturition was not significant (P>0.05) for any of the indices. All indices tended to decline over the years from 1969 onwards. However, while index I (Figure 1) exhibited a small recovery in the 1986/87 period, indices II (Figure 1) and HI (Figure 2) showed substantial recoveries in two periods-1982 and 1986/87. Indeed productivity in these periods increased beyond the base year (1966) levels. On the other hand, index IV (Figure 2) never recovered to levels attained in the late 1960s.

Year effects on indices were related to climatic factors, especially the amount of annual rainfall. The decrease in availability of fodder in years of low rainfall tended to lower weaning weights of lambs and affected reproductive performances of ewes, thereby increasing parturition intervals. This explains variations in the productivity of ewes between years. Periods characterised by increased lamb mortality, increased lambing intervals and reduced lamb growth are expected to be associated with low productivity. A similar relationship between year of parturition and productivity of station-managed sheep has been reported by Murayi et al (1987) in Rwanda. Murayi et al (1987) attributed differences between years to amount of rainfall and availability of forages.

Ewes that lambed in the dry season had significantly higher productivity indices than those lambing in the wet season. This is because lambs born in the dry season were weaned in the middle of the subsequent wet season so were able to obtain adequate milk from their dams and could graze the lush abundant forages available. However, lambs born in the wet season were weaned mid-dry season. They gained less weight by weaning time due to scanty and low quality fodder. In a study of the effect of season of parturition on productivity in Sudan Desert sheep, Suleiman et al (1990) observed that productivity indices were higher for ewes lambing in the wet summer than in other seasons.

Table 1. Least squares means of productivity indices 1, 11 and 111 by year, season, age and location sub-classes.

In the present study, the age of ewe did not significantly affect any of the productivity indices, though younger ewes tended to have numerically lower indices. This was mainly because younger ewes had longer parturition intervals than older ewes. Similar results have been reported in sub-Saharan Africa (Wilson, 1987; Lebbie, 1991). Differences between locations were significant for these productivity indices. Ewes had lower indices at West Kilimanjaro compared to those at Malya. The lower productivity indices at West Kilimanjaro could be attributed to: lower weaning weight of lambs; higher preweaning mortality of lambs; and the presence of older ewes at the station.

Index IV and mean lambs mass

Overall least squares means of index IV and lamb mass per lambing are presented in Table 2. Index IV tended to decline from 1969 onwards, with a small recovery in the 1978-1980 period (Figure 2). Ewes at Malya had significantly higher Index IV values and lamb mass per lambing than those at West Kilimanjaro. The superiority of Malya was mainly due to lower weaning weights of lambs born at West Kilimanjaro resulting from poor nutrition.

Table 2. Least squares means of productivity index IV and lamb mass per lambing by year, season, age and location sub-classes.

Effect	Level	Index IV, kg			Lamb mass per lambing, kg
		N	Mean	se	N	Mean	se
Overall		987	63.03	1.62	987	20.81	0.22
Year			(0.0001)			(0.0001)
	1966	11	18.67	12.93	11	21.63	1.74
	1967	16	28.99	10.74	16	26.52	1.44
	1968	31	35.67	7.62	31	21.95	1.03
	1969	21	62.46	9.29	21	18.84	1.25
	1970	19	84.67	9.73	19	22.26	1.31
	1971	29	101.05	8.11	29	21.73	1.09
	1972	42	67.66	6.55	42	21.76	0.88
	1973	38	52.17	6.97	38	19.19	0.94
	1974	35	85.63	7.09	35	23.94	0.96
	1975	55	85.01	5.71	55	21.31	0.77
	1976	29	85.62	7.99	29	20.47	1.08
	1977	28	86.38	8.15	28	19.41	1.09
	1978	68	41.95	5.20	68	14.32	0.70
	1979	51	54.96	6.02	51	19.99	0.81
	1980	72	77.04	5.07	72	23.75	0.68
	1981	59	81.67	5.56	59	23.97	0.75
	1982	60	77.06	5.52	60	22.05	0.74
	1983	51	62.39	6.06	51	18.97	0.81
	1984	98	64.33	4.31	98	19.01	0.58
	1985	39	40.85	6.90	39	16.49	0.93
	1986	38	47.18	6.81	38	20.39	0.91
	1987	36	54.67	7.19	36	18.78	0.97
	1988	61	52.80	6.15	61	21.53	0.83
Season
	Dry	375	64.05	2.49	375	20.13	0.34
	Wet	612	62.01	2.45	612	20.49	0.33
Location
	Malya	600	66.64	2.08	600	22.56	0.28
	WK	387	59.42	2.79	387	19.05	0.37

N = number of observations.
Se = standard error.
WK = West Kilimanjaro.

Figure 1. Trends in productivity indices I and II during the study period.

Figure 2. Trends in productivity indices III and IV during the study period.

Conclusion

High variations in productivity indices show that the productivity of BHP sheep in Tanzania can be improved. Strategies should be developed to improve the management systems, such as improving pastures and forages and general nutrition. Ewes should be fed concentrates during the suckling period. Lamb care, especially during the preweaning period, could also be improved in order to increase production.

References

Das S M and Sendalo D S. 1991. Small ruminant research highlights in Tanzania (1960-1989). Ministry of Agriculture, Livestock Development and Co-operatives, Dar es Salaam, Tanzania. 40 pp.

Lebbie S H B. 1991. Analysis of the reproductive performance of indigenous small ruminants in selected countries in sub-Saharan Africa. Addis Ababa, Ethiopia. 65 pp.

Murayi T. Sayers A R and Wilson R T. 1987. La productivité des petite ruminants dans les stations de recherche de l'Institut des sciences agronomiques du Rwanda. ILCA Research Report 15. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. 58 pp.

SAS (Statistical Analysis System). 1987. Statistical analysis system user's guide: Statistics. SAS Institute Inc., Cary, North Carolina, USA.

Suleiman A H. Sayers A R and Wilson R T. 1990. Evaluation of Shugor, Dubasi and Watish subtypes of Sudan Desert sheep at the El-Huda National Sheep Research Station, Gezira Province, Sudan. ILCA Research Report 18. ILCA (International Livestock Centre for Africa), Addis Ababa, Ethiopia. 30 pp.

Wilson R T. 1987. Productivity of traditionally managed small ruminants in an agro-pastoral system in northern Burkina Faso. Tropical Agriculture (Trinidad) 64: 163165.