Analysis of reproductive performance of Djallonké ewes in Benin

The purpose of this study was to characterize the Djallonké sheep breed in terms of reproductive parameters under the conditions of Benin. To achieve this goal, records on 636 Djallonké ewes, which were reared from 2000 to 2005 at the Sheep Improvement Centre of Bétécoucou were analysed, using general linear models.

Estimates of the mean values of birth weight, litter size, litter weight, gestation length and lambing interval were 1.90 kg, 1.43, 2.70 kg, 152.46 days and 241.69 days respectively. All reproductive traits studied were significantly affected by the year as well as the season of lambing. Parity number affected litter size, birth weight and litter weight significantly. The age of ewe at first lambing affected birth weight in its linear component and litter size, litter weight and gestation length in its quadratic component.

Results of this work can be considered useful references for the planning, the monitoring and evaluation of breeding projects in Djallonké sheep.

Introduction

The Djallonké sheep is widespread in the tropics and particularly in Benin. They also play an important role to the socio-economic well-being of a large human population in terms of nutrition, income and other intangible benefits (i.e. savings, cultural and religious purposes). The Djallonké sheep breed is known for its tolerance to trypanosomiasis, resistance to parasitic diseases and hardiness to the hot humid tropics. Therefore, most attempts to increase the productivity of sheep in West African countries focused on this breed. Despite their importance to the subsistence as well as the economic and socio-cultural livelihood of a large population, the Djallonké sheep of Benin are poorly characterized. In order to bridge this gap, the present paper aimed at firstly, to characterize the Djallonké sheep in terms of reproductive parameters such as litter size, litter weight, gestation length, lambing interval and secondly, to study the effect of non-genetic factors, including age at first lambing and parity number, year and season of lambing on the traits under consideration.

Material and methods

Data source

Analyses were performed on data provided by the Sheep Improvement Centre (CSO) of Bétécoucou, which is located in the “Zou Nord” department of Central Benin, near the town of Dassa-Zoumè between 7°45’ and 07°50’ North and 2°20’ and 2°27’ East and at 300 m above see level. These data were collected on 636 Djallonké ewes, which were sired by 124 rams from year 2000 to 2005. The frequencies of lambs born as single, twins, triplets and quadruplets throughout the observation period were 60.7%, 35.7%, 3.1% and 0.5% respectively.

Management and breeding

Experimental animals grazed from 0800h to 1730h on natural or improved pastures consisting of Panicum maximum C1, Brachiaria ruziziensis, Andropogon gayanus, Aeschynomene histrix and Cajanus cajan. Back from the pasture, they were then housed and they received a protein supplement of cotton seed cake of 400g and 300g for rams and ewes respectively and occasionally, on-farm by-products such as maize, rice straw and groundnut hay. Salt licks and water were provided ad libitum. During the breeding period, one ram was assigned to a group of 20-25 ewes. After parturition, the lambs were kept with their dams and remained with them until their weaning at three months of age. All animals were treated against internal and external parasites. They were also vaccinated annually against “Peste des Petits Ruminants” (PPR) and brucellosis.

Data analysis and model fitting

Data on reproductive traits, including age at first lambing (AGE1), litter size (LS), litter weight (LW), gestation length (GEST) and lambing interval (LI) of ewes were analysed. Statistical analyses were performed using the GLM procedure of the SAS 9.1 package (SAS 2003). Data were fitted to the following model:

Results and discussion

Overall means and standard deviations of the traits studied are given in Table 1.

Table 1. Overall means of reproductive performances in Djallonké ewes
	Abbreviation	Unit	Mean	Standard deviation
Age at first mating	MAT1	day	229	33.08
Age at first lambing	AGE1	day	377	32.25
Gestation length	GEST	day	152	1.47
Lambing interval	LI	day	242	16.32
Litter size	LS		1.43	0.58
Litter weight	LW	kg	2.70	0.98

Results of the analyses of variance for the effects included in the model and least squares means comparison within factor levels are given in Table 2.

Table 2. Effects of year and season of lambing, parity number and age of dam at first lambing on litter size (LS), litter weight (LW), gestation length (GL) and lambing interval (LI) in Djallonké ewes in Benin
Classification		LS	LW	GEST	LI
Year of lambing		***	***	***	***
	2000	1.50±0.11^ab	2.74±0.19^bc	152±0.29^b
	2001	1.40±0.05^b	2.64±0.09^c	153±0.13^a	226±3.09^c
	2002	1.54±0.06^ab	2.88±0.10^ab	151±0.15^bc	235±2.93^ab
	2003	1.61±0.04^a	3.01±0.06^a	152±0.10^ab	231±2.25^b
	2004	1.43±0.04^b	2.78±0.07^b	152±0.10^ab	233±2.08^ab
	2005	1.61±0.05^a	2.97±0.08^a	152±0.13^c	270±5.08^a
Season of lambing		***	***	***	***
	early rainy	1.49±0.04^b	2.85±0.07^ab	152±0.10^b	243±2.01^b
	late rainy	1.56±0.05^ab	3.03±0.09^a	153±0.14^a	254±2.45^a
	early dry	1.60±0.04^a	2.94±0.07^ab	152±0.11^ab	253±2.49^ab
	late dry	1.41±0.06^c	2.54±0.09^b	151±0.15^c	206±3.09^c
Parity number of dam		***	***	ns	*
	1	1.27±0.03^c	2.34±0.05^c	152±0.07
	2	1.47±0.04^b	2.68±0.06^b	152±0.09	239±1.42^b
	3	1.48±0.04^b	2.77±0.07^b	152±0.11	241±1.60 ^b
	4	1.61±0.05^ab	2.97±0.09^a	152±0.14	245±1.86^a
	5	1.50±0.07^b	2.90±0.12^ab	152±0.18	244±2.66^ab
	6	1.79±0.09^a	3.31±0.17^a	152±0.25	238±3.96^b
	7	1.48±0.15^b	2.90±0.25^ab	152±0.38	227±9.31^c
Age of dam at first lambing (co-factor)
		ns	ns	ns	ns
		**	*	**	ns
=significant (p<0.05); = significant (p<0.01); **= significant (p<0.001); ns=not significant (p>0.05). Within each factor, values with different superscript letters are significantly different at p<0.05.

The mean AGE1 reported in the present study (12.6 months) compares with those recorded under village conditions (11.5-14.3 months) by Rombaut and Van Vlaenderen (1976) in Ivory Coast, Amégée (1983) in Togo, London et al (1994) in Ghana and on-station (13.5 months) by Berger and Grinisky (1980) and by Rombaut (1980) in Ivory Coast. Quite higher values for this trait were also reported on-station (16.9-20.9 months) by Vallerand and Brankaert (1975) in Cameroon, Tuah and Baah (1985) in Ghana, by Fall et al (1983) in Senegal and by Missohou et al (1998) in Togo. Differences in the magnitude of AGE1 by different authors may result from differences in the precocity of ewes involved and also from management practices.

The average LS recorded in this study (1.43) is consistent with that obtained by Amégée (1983) (1.47-1.50), but higher than those reported by several workers on the Djallonké sheep (1.1-1.31), among others, Missohou et al (1998), Vallerand and Brankaert (1975), Rombaut and Van Vlaenderen (1976), Rombaut (1980), Charray (1986), Berger and Grinisky (1980), Fall et al (1983), Tuah and Baah (1985) and Boly et al (1993).

The estimate of the mean LI in the current study (241.69 days) compares well with those reported by Rombaut and Van Vlaenderen (1976), Berger and Grinisky (1980), Clément et al (1997) and Combellas (1980) (8.13-8.23 months). A slightly wider range of 10-10.23 months was reported by Fall et al (1983), Tuah and Baah (1985) and Missohou et al for LI in Djallonké ewes. The mean estimate of LI reported by Kabuga and Akowuah (1991) for DjallonkéxSahelien crossbred ewes in Ghana is rather intermediate (9,3 months). These higher values for LI, could probably be attributed to a longer service period. Amégée (1983) however, found a much lower value (7 months) for this trait. With a litter size of 1.43 and a lambing interval of 241.7 days as recorded in the present study, a lambing rate of 2.16 lambs/ewe/year) is to be expected for the ewes raised at CSO against 1.35, 1.31 and 1.57 lambs/ewe/year as reported by Symoens and Hardouin (1988), London et al (1994) and Missohou et al (1998) respectively for on-farm studies (village farms). Further increases in lambing rate could be achieved either by increasing the litter size or by decreasing the lambing interval. The second alternative might be more practical because of the long breeding seasons and the frequency of feed shortage. With a gestation length of 152.46±1.47 days, as recorded in the present study, it would be possible to obtain two lambings per ewe per year, if LI could be shortened from 241.7 days to 210 days. This means, that the service period should not exceed 60 days. Boly et al (1993) reported on-station observation of first oestrus occurrence at day 56±10 post partum in the Djallonké ewes (the Mossi strain of Burkina Faso). The same author also reported that with appropriate feeding, first oestrus post partum can precociously appear in Djallonké sheep (at day 34.5±1.5 post partum). These results are consistent with the expectation of two lamb crops per ewe per year. The possibility to obtain two lambings per ewe per year was also mentioned by Hulet and Foote (1967a) and Tuah and Baah (1985).

Year and season of lambing of ewes

All reproductive traits studied, i.e. litter size (LS), litter weight (LW), gestation length (GEST) and lambing interval were significantly affected (p<0.01) by the year and season of lambing. The lambing performance of ewe reflects their ovulation rate. Ovulation rate is in turn influenced by the season of breeding (determining the season of lambing) as reported by Hulet and Foote (1967b), Dahmen et al (1976), Hulet et al (1974) and Fletcher and Geytenbeck (1970), among others. As shown in Table 2, the highest litter size was recorded in ewes lambing in the dry season. A similar result was found in Djallonké sheep by Clément et al (1997) in a survey study carried out in the central and northern region of Senegal (Kaymor and Kolda respectively). In the present study, the gestation length and the lambing interval were the shortest in ewes lambing during the transition from dry to wet season.

Age at first lambing and parity number of ewes

Parity number affected significantly (p<0.05) LS, LW and LI. London et al (1994), Ebangi et al (1996). Fall et al (1983), however, found no significant influence of parity number on lambing interval. The age of ewe at first lambing affected the litter size, the litter weight and the gestation length in its quadratic component. Parity number is associated with the age of dams. Numerous authors, including Turner (1969), Dickerson and Glimp (1975), Mendel (1988), Mara and Ascaso (1999) and Ali et al (2009) are unanimous on the fact that most traits related to the female reproductive performance of ewe increase with increasing age, reaching a peak and decreasing thereafter. This observation applies for the present study in which the peak was reached by the party number 6, 6 and 4, respectively for, LS, LW and LI. This may be due to the maturity and subsequent aging of the reproductive system by advancing age.

Conclusion

Acknowledgements

The authors are grateful to the “Projet de Développement de l’Elevage” (PDE/DE/MAEP) for providing the Data used in this study and for the help and co-operation received in the course of this work.

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