INFLUENCE OF GENETIC AND NON-GENETIC FACTORS ON THE GROWTH PERFORMANCE OFDWARF SHEEP OF DJALLONKE BREED REARED ON NATURAL PASTURE IN BENIN

1. Department of Animal Production and Health, Polytechnic School of Abomey-Calavi, 01 BP 2009, Cotonou, Republic of Benin, Benin. 2. National High School of Agro-Pastoralism (ENSAP-Gogounou), University of Parakou, Republic of Benin. 3. Agricultural Research Center of Agonkanmey, National Institute of Agricultural Research of Benin, 01 BP 884, Cotonou 01, Republic of Benin. 4. Animal Sciences Unit, Gembloux Agro-Bio Tech, University of Liege, Passage des Déportés, 2, 5030 Gembloux, Belgium. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

The dwarf sheep is reared in Benin mainly according to traditional rearing system and met alone or generally associated with other animal species in almost all households. However, West African dwarf sheep have low productivity (Yapi, 1994) and weak reproduction and growth performance (Adjibodè, 2012) varying with latitude from north to the south of Benin (Gbangboché et al., 2005b;Youssao et al., 2008). The development of this animal breeding sector and the importance of the consumption of the dwarf sheep meat nowadays in West Africa in general and in Benin in particular require a better knowledge, control and improvement of its rearing system, reproductive and growth performance.
According to Berhanu and Aynalem (2009), growth performance is a key production indicator that has implications in the reproductive efficiency of sheep. Fast growth performance allows sheep to breed early and contribute more lambs in their lifetime. Fast growth rate entails reaching market weight early and brings a quicker income to the farmer.
The effect of non-genetic factors on growth performance in sheep has been investigated in several studies. These factors in different areas have their own specific effects regarding the environmental characteristics of related areas (Gbangboche et al., 2006;Momoh et al., 2013). Therefore, the present study was carried out to investigate the effect of ecotype, sex of lamb, season of birth and litter size on growth performance ofDjallonkelambs at different ages reread undertraditional system in Benin.
Specifically, it is to:  Compare the growth performance of Djallonkelambs of North and south ecotypes reared under village traditional management conditions;  Quantify the impact of sex, season of birth and litter size and lambing rank on growth performance in Djallonke lambs.
Data collection:-Data were collected from November 2013 to December 2015 on a total of 1061 dwarf sheep ofDjallonke breed including 462 of North ecotype and 599 ofSouth ecotype. These animalswere all raised in a traditional system. Feeding was mainly based on natural pasture.The animals were put on pasture at about 7.30 a.m. and returned to the barns in the afternoon. They were then fed ad libitum a supplementary diet consisting of crop residues acording to the traditional system.
The sheep were treated for ectoparasites, drenched once every three months and given other veterinary attention when the need appeared.
The material used for data collectionwas composed of a growth data file for recording the growth parameters and electronic balancesof 5 kg and 40 kg of capability and accuracy of 1g and 20g respectively. The data file contained information on individuals, identification code, sex, litter size, birth date, date of weighing and measure of body weight.
The birth weight (W0) of lambs wasrecorded and the animals were then weighed once every fourteen days up to 12 months of age. Average daily gainswere calculated from the birth to the age of 120 days, from the age of 120 days to the age of 240 days and from the birth to the age of 240 days. the live weight of the lambs of North ecotype at 285 days old was higher than the one recorded in South ecotype (p˂0.05). However, the ecotype didn't affect the live weights of the lambs at 270 and 300days old. Standard Error, ANOVA: Analysis of Variance, *: P˂0.05; ** P˂0.01; ***: P˂0.001. The means between the classes of the same line followed by different letters differ significantly at the threshold of 5%.
The average daily gains were significantly affected by the genetic type with the best weight gains found in North ecotype. The average daily gain from birth to 120 days, from 120 days to 240 days and from the birthto 240 days were respectively of 79.48 vs 62.15 g/day; 59.72 vs 51.45 g/day and 50.58 vs 40.01 g/day for the lambs of North and South ecotype (p˂0.01).
Overall, the dwarf sheep of North ecotype of Benin had the best growth performances comparatively to the South ecotype.

Variation of age-type weight and average daily gain (ADG) of Djallonke sheep of Benin according to the sex:-
The growth performance parameters of the male and the female dwarf sheep of Djallonke breed are given in table 2. The birth weight of the West African dwarf sheep didn't vary significantly according to the sex and was of 2.01 ± 0.03 kg for the females and 2.07 ± 0.03 kg for the males (p>0.05).Nevertheless, from the birth to the age of 300 days old,the males were significantly heavier than females (p <0.001).
1443 Standard Error, ANOVA: Analysis of Variance, *: P˂0.05; ** P˂0.01; ***: P˂0.001. The means between the classes of the same line followed by different letters differ significantly at the threshold of 5%.
The average daily gain of the lambs female and male from birth to 120 days, from 120 days to 240 days and from birthto 240 days were respectively of 64.02 vs 72.02 g/day; 52.03 vs 56.36 g/day and 41.84 vs 46.82 g/day. The effect of sex was only significant on the average daily gain of the lambs from birth to 120 days with the higher ADG found in the males (p˂0.05). Table 3 shows the variabilityof growth performance of Djallonke sheep of Benin according to their season of birth. It appears that Djallonke sheep born in the rainy season were slightly heavier than those born in the dry season during the first 3.5 months (0-105 days) without any significant difference (p>0.05). At 120 and 135 days old, Djallonke dwarf sheep born in the dry season were significantly heavier than those born in the rainy season with the respective live weights of 10.71Kg vs 10.09 Kg and 11.62 Kg vs 10.66 Kg (p˂0.05). From the age of 105 days old to 300 days, Djallonke sheep born in the rainy season remained slightly heavier than those born in the dry season but without any significant difference (p>0.05). The average daily gains of dwarf sheep of Djallonke Breed of Benin were also affected by the born season of the lambs. Indeed, the average daily gains of dwarf sheep of Djallonke Breed from the birth to the age of 120 days was significantly better (p˂0.05) in lambs born in the rainy season than the values recorded in dry season (71.07 g/day ± 1.28 vs 64.73 g/day ± 2.81). On the over hand, ADG calculated from the birth to 240 days old was significantly higher (p˂0.05) in animals born in the rainy season (59.04 ± 2.88 g/day) than those born in the dry season (51.90 ± 1.66 g/day). However, no significant difference was found between theaverage daily gains of dwarf sheep of Djallonke Breed of Benin born in dry or rainy season from 120 days to 240 days old, even if the lambs born in dry season seems to gain more in weight than lambs born in rainy season.

Variation of age-type weight and average daily gain (ADG) of Djallonke sheep of Benin according to the lambing rank:-
The variability of age-type weight and average daily gain (ADG) of Djallonke sheep of Benin according to the lambing rank is given in table 4. Except the live weights recorded at 225, 240 and 255 days old which varied significantly according to the lambing rank, the other age-type weights measured herein were not affected by lambing rank. The highest live weights found at 225, 240 and 255 days (respectively 19.42kg, 20.47 kg and 19.53 kg) were recorded at the second lambing rank (p˂ 0.05). Overall, the lambs born at the second, third and to a lesser extend the fourth lambing rank tend to be heavier than those born at the first and fifth lambing rank. Average daily gains were not affected by the lambing rank (p> 0.05). However, Djallonke sheep born from the lambing ranks 1 and 5 showed the lowest average daily gain (p> 0.05). Standard Error, ANOVA: Analysis of Variance, *: P˂0.05. The means between the classes of the same line followed by different letters differ significantly at the threshold of 5%. Table 5 shows the variation of growth performance of sheep Djallonke according to type of birth. The effect of the type of birth weight on the West African dwarf sheep was highly significant (p <0.001) on birth weight, the age-type weights recorded 15, 30, 45, 60, 75, 90, 105, and 120 days and the average daily gain calculated from the birth to the age of 120 days.  Overall, the birth weight of sheep Djallonke born alone (single birth) was higher than those of sheep born indouble, triple and quadruplelitters. The lambing from triple litter size showed the lowest live weightsfrom from the 120th day of age.The type of birth had affected the average daily gain from 0 to 120 days (p <0.05) with the highest weight gain recorded in the single litter size and the lowest in the litter size of five lambs. However, the type of birth or the litter size didn't influence theaverage daily gain from 0 to 240 days and the one from 120 days to 240 days (p >0.05). In traditional breeding in North Benin, Youssao et al. (2008) obtained a live weight of 10.56 ± 1.88 kg at 3 months of age. This weight is greater than the value of 9.41 ± 2.07 kg obtained herein at the same age. The live weight at 3 months of age found by NaandamAmoah-Otchere (2014) in traditional breeding in Ghana was higher than those obtained in our study and was of 10.7 kg. However, the weight obtained in this study after the third month is higher than the weight of 8.22 ± 3.41 kg reported by DokoAllou et al. (2013) in Djougou in Benin.

Discussion
The performances differences observed herein compared with other breeds could be attributed to the rearing conditions (management, herdsman skills, levels of diseases, and trypanosome risk….) and the genetic type of the West African dwarf sheep used by the authors.
Several authors concluded, in fact, that the genotype or the breeds of sheep reared under comparable conditions havefrequently different age-type weight and average daily gains (Boly et al., 2000;Gbangboche 2005a; Doko Alou et al., 2013). These authors linkedit to several factors including the genetic type and natural selection (Lebbie and Ramsay, 1999;Gbangboche, 2005b;Youssao, 2008). This reality is highlighted by the results of our study which show that Djallonke Dwarf sheep of North ecotype were significantly heavier with fast growth rate than South ecotype. Poivey et al. (1982) reported high heritability for weight at three months of age and suggest taking this into account in the selection of dwarf sheep. It is therefore proven that the crossbreedsSahelianx West African dwarf sheep 1447 express best growth performancesthan pure Djallonke breed (Amégé, 1984) and could be perceived as an alternative of improvement of the profitability of sheep rearing (Gbangboché et al., 2002). Thus, the crossingbetween Djallonke sheep of North ecotype x South ecotypecan improve the growth performances of South ecotype of Djallonke sheep and preserve their resistance to illness and the identity of the Djallonke breed.
It is important to show that the weight difference found herein between Djallonke Dwarf sheep of North and South ecotypes of Benin seems to disappear from the 10th month with an apparent reversal of the original trend. We can therefore understand that the West African dwarf sheep reach their adult weight at this age of 10 months and their weight growth becomes less rapid.
The weights obtained at the 10th month of age in the dwarf sheeps of North and South ecotype are respectively 17.73 ± 1.84kg and 16.96 ± 1.50kg. These weights are lower than the value of 30kgobtained by Amégé (2004) for Vogan sheep at 7 months old and the live weight of 37.3kg reported for Lohi sheep of 9 months old by Iashari and Tasawar (2013). These confirm that the growth performances of the West African dwarf sheep reared in Beninhave relatively very low growth performance and need improvement program.

Effect of sex:-
Our results show that the birth weight of the West African dwarf sheep showed no significant difference among males and females. This finding is contrary to those reported by some authors stating that in the same rearing conditions, males born heavier than females (Fall et al., 1983;Poiveyet al., 1982Abaffa et al., 1992. However,sex effect was significant for all traits in Djallonke lambs from 15days old to the end of the experiment. Males were significantly heavier than females. According to these authors, the sex affects many productivity of Djallonkesheep in favor of males; they are usually born heavier than females and keep this trend up to the age of 12 months or more. The same observations were made by several authors on other ruminants such as goats (Haumesser, 1975;Umara, 1986;Alexander et al., 1997;Hounkpevi, 2005; and Adjibode, 2012), and cattle (Youssao et al., 2000). However, according Abaffa et al. (1992), the effect of sex would tend to disappear from 120 days in sheep. The larger weight of males in comparison to female lambs could be due to the hormonal differences in their endocrinological and physiological functions (Ebangi et al., 1996).
The average daily gain from the birth to the age of 4 months showed significant differences according to the sex. The same observations were made in dwarf goats by Adjibode (2012) and this phenomenon can be justified by the fact that the heaviest born males are more competitive than females in the consumption of milk (Ba Diao et al., 1994).

Effect of the season:-
Our findings show only an apparent difference (not significant) between the age-type weights of Djallonkesheep accordingto the season except the weight at 120 days which was significantly higher in animals born in the dry season. This exceptional difference is explained by the fact that these animals born in the dry season deal at this age a favorable nutritional period (rainy season) soon after their weaning, unlike those born in the rainy season which undergo (at this age) difficulties of the dry season. However outside the average daily gain calculated for the period from 120 days to 240 days showed no significant difference, the other daily average gains varied significantly depending on the season of birth in favor of animals born in the dry season. According to Berhanu and Aynalem (2009), the effect of season is associated with difference in feed and disease situation. When lambing occurred during wet season there is high incidence of parasite infestation impairing growth performance.
Moreover, if for Abaffa (1992), animals born between November and December (dry season) show the best performance, Gbangboche et al. (2005a) found that the rainy season is the most favorable and beneficial to the West African dwarf sheep not only by promoting a lambing peak but also by increasing the weight of lambs at birth and at 12 months and by promoting a reduction of age at first calving and lambing interval. The notion of season is a vast field that must be considered with attention in animal experimentation as including several parameters.

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According to the findings of Attindehou et al. (2012), animals that lack of rigorous medical follow-up show slow growth rate due to the parasitic diseases that develop during the rainy period while Tiema (2011) reported poor diet as one of the factors that impact the morbidity and therefore the growthperformance of lambs in village farms. In addition, several authors concluded that the season of birth postpone the puberty according to the energy restriction, high ambient temperatures and high relative humidity (Skinner and Rowson

Effect of lambing rank:-
In the current study, the animals born from the second, third and fourth parturition showed the best growth performance than animals born from the first and the fifth lambing rank. Our findings are in accordance with the reports of several authors (Fall et al., 1982;Poivey et al., 1982;Filius et al., 1986;Abaffa et al., 1992;London et al., 1994;Yapi-Gnaoré et al., 1997).This remark can be due to the age and the live weight of primiparous ewes because the females do not usually reach their physiological maturity at the first lambing and their own growth competes with that of their product (Poivey et al., 1982;and Yapi-Gnaoré al., 1997).
Contrary to our finding, Ba Diao et al. (1994) indicated in goats that the lambing rank has a significant effect on weight gain in kids with the observation that the higher the rank of farrowing evolves, less animals are heavy. This difference in outcome could be explained by the fact that on one hand the litter size in goats are evolving with the rank of farrowing. Moreover, the milking of multiparous goats isgenerally observed and could reduce the availability of milk for kids of advanced lambing rank.
No significant difference was observed in the present study among the average daily gains according to the lambing rank. This result differsfrom those of Youssao et al. (2008) who found that the average daily gain from birth to the age of 90 days is significantly influenced by the lambing rank.

Influence of type of birth:-
Our results generally show that the weight of sheep Djallonkeborn alone (single birth) were higher than those of sheep from twin, triple and quadruple litters. These results corroborate those of Poivey et al. (1982) which stipulate that single lambs were heavier than those from multiple birth and no systematic compensatory growth is observed after weaning. Furthermore, this could be caused by the poor milk production of the local ewe (Gbangboche et al., 2005a). A similar effect of birth type has been well documented for dwarf sheep (Yapi- Furthermore, it should be noted that although the single born animals have the advantage to reachthe puberty at a younger age (Boussena, 2013), but have the disadvantage of having a smaller weight productivity at birth and at 12 months old than double born animals (Gbangboche et al., 2005a).

Conclusion:-
The study clarifies the factors of variation of the growth performance of Dwarf sheep of Djallonke breed reared under traditional rearing system in Benin. The North ecotype of West African dwarf sheep grows faster and weigh more than those of South ecotype. Moreover, the lambs born from primiparous ewes were lighter than lambs born from multiparous ewes.
The variability observed in growth performance between Djallonkelambs of North and South ecotypes of Benin suggested that genetic diversity exists which could be exploited for genetic improvement. This can be organized through ram progeny testing in order to identify sires for producing fast growing lambs. These programs should involve the faster growing lambs selected from ewes with high rearing ability in farmers flock within the same agro ecological areas.
The results of this study can also be a basis to improve local ecotypes of Djallonkesheeps of Benin through conservation-based with-in breed selection with a participation of traditional sheep breeders.The difference in weight between sexes is pronounced as age advances. Male lambs had higher weights than females.Furthermore,non-genetic factors involved in this study need to be taken into account to improve sheep production and accurate estimation of genetic parameters.

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To better characterize Djallonke Dwarf Sheep of North and South eotypes of Benin, further studies with large data set on their rearing systems, reproductive performance, morpho-biometrical parameters carcass and genital organs and semen quality traits would be very useful.