沙漠研究 19-1, 169- 172 (2009 )Journal of Arid Land Studies“Desert Technology IX ”
Refereed Paper

Effects of Dam Age, Litter Size and Gender on Birth Weight of D’man lamb-Consequence on Lamb MortalityMohamed CHNITER1, Serya MAALI2, Mohamed HAMMADI1, Touhami KHORCHANI1, Harab HARAB3,Riadh KRIT3, Mohamed BEN HAMOUDA4, Gley KHALDI2, Raymond NOWAK5
Abstract: Knowledge of factors affecting variation in birth weight is especially important given therelationship of birth weight with neonatal and adult health. This study examines the effects of age ofdam, litter size and gender on birth weight in D'man lamb breed under accelerate lambing system (3lambings/2 years) in the oases of Gabès. Data recorded between February 25th and May 15th 2008,
concerned 91 lambs born at the "Office d'Elevage et des Pâturages" station in Chenchou located insouthern Tunisia. Two- to 8-year-old ewes had a higher performance and dropped heavier lambs(P<0.05) that the old dams (more than 8 years old). The mean birth weight of single-born lambs(4.0 ± 1.0 kg) were significantly higher (P < 0.05) than those for twins (3.3 ± 0.5 kg), triplets (2.5 ±0.4 kg) and quadruplets (2.3 ± 0.4 kg). Male lambs were heavier (P < 0.05) than female lambs (3.0± 0.6 kg vs. 2.7 ± 0.7 kg, respectively). Mortality in lambs occurs continually from birth to weaning(60 days of age) and it averaged 19.7% (n = 91). The third of this rate (33%) was observed in lambsissued from young dams (2 years of age), while 67% of mortality was equally distributed between
lambs born from dams, 3-, 7- and 9-year-old. Lambs born in triplet litter had a significant (P < 0.05)
higher mortality (12%) than those born in twin (2.2%) and quadruple litter (5.5%). A higher
mortality rate was observed in females (13.17%) than in male lambs (6.58%). Dead lambs had less(P < 0.05) birth weight and daily body gain until 30 days of age than the survived ones (2.4 ± 0.4 kg
vs. 3.0 ± 0.6 kg; 53 ± 34 g vs. 160 ± 52 g respectively). In conclusion, age of dam, litter size andgender significantly affect the birth weight which could be an important risk factor for D'man lambmortality.
Keywords: Birth weight, D’man sheep, Lamb mortality

1. Introduction
In several countries, prolific breeds of sheep are commonly used to improve flock productivity(Aboul-Naga, 1996; Gootwine et al., 1995; Lassoued and Rekik, 2001). In Tunisia, the Moroccan D'man
breed is selected because of its adaptation to local climatic conditions (Mahouachi et al., 2005). Superior
prolificacy, earlier sexual maturity and longer breeding season of D’man sheep have been reported byLahlou-Kassi et al. (1989). However, increased litter size at birth usually leads to increased lamb mortality.
Lamb birth has long been considered a major risk factor for lamb viability and survival (Gama et al., 1991;
Christley et al., 2003), extreme birth weights being highly related to substantial increases in lamb mortality(Christley et al., 2003; Casellas et al., 2007). Most death of lambs is typically associated with birth weightby a curvilinear relationship (Nowak and Poindron, 2006).
The purpose of the present study was to investigate the influence of dam’s age, litter size and gender on
the birth weight of lamb under an accelerated lambing system of D’man sheep in the oases of Gabès.
2. Materials and Methods
The experiments were carried out in the breeding station of Chenchou for D’man sheep, arid Tunisia(latitude: 33˚N 29’57.8’’, longitude: 10˚38’37.3’’), and where sheep have been raised since 1994. This
breeding center has been the base for the scientific research, breed improvement and productivity since thefirst year of its foundation. Ewes were naturally mated and mating took place in each group of 15 to 20
ewes separately by introducing one ram and ewes were exposed to rams in single-sire groups for a period of
1

Laboratoire d'Elevage & Faune Sauvage, Institut des Régions Arides, Médenine, Tunisie.
E-mail: Chniter2005@yahoo.fr
2
Institut National Agronomique de Tunis, Tunisie.
3
Office d'Elevage et des Pâturages, Gabès, Tunisie.
4
Institution de la Recherche et de l'Enseignement Supérieur Agricoles, Tunis, Tunisie.
5
Equipe Comportement, Neurobiologie, Adaptation UMR6175 INRA-CNRS-Universitè de Tunis; Haras Nationaux,Unitè de Physiologie de la Reproduction et des Comportements 37380 Nouzilly, France.

170

approximately 45 days. The flock follows an accelerated lambing system with approximately three lambings

every 2 years.
The ewes were kept under intensive conditions and the same animal husbandry practices were used forall pregnant groups. Young ewes lambing for the first time were not included in the experiment, so the ageof the ewes ranged from 2 to 9 years. All ewes were in good health and condition, were flushed with 300 gof concentrate mixture consisting of barley grains, soya and supplement of vitamins minerals with 1 kg ofhay (Lucerne) per ewe per day were divided into two equal parts offered in the morning and evening andfresh water was available at all times. Over late pregnancy, the amount of concentrate was elevated to 500 g.
Mating was scheduled from October 1st to November 15th 2007.
At birth, new-born lambs and their mothers were housed in pens for at least 72 h of life. Data
concerning identification number, birth date, type of birth and sex were collected on 91 lambs born to 37
ewes between February 25th and May 15th 2008. Lamb mortality was recorded as number of lambs either
still born or born alive but which died within the first 48 hours after birth (perinatal mortality). All lambs
were weighted within 12 h after birth using suspended scales weighing from 0 to 20 kg in minimal 200 gincrements.
SAS software (version 9) was used for statistical analysis of data. Birth weight and weight gains dataof lambs were analyzed by ANOVA using General Linear Model (GLM) for determination the dam age, littersize and gender effect. The means values were compared using SNK test.
3. Results and Discussion
Birth data from 90 lambs born inTable 1. Mean birth weight, ADG and mortality of lambs.
spring are shown in Table 1. The mean
Lamb traits
NumberMean ± SD
birth weight of all live-born was medium(2.84 ± 0.64 kg). Average daily gain
Birth weight (kg)90
2.84 ± 0.64(ADG) of lambs between birth and 10
ADG0-1081
149.04 ± 62
days of age was slightly lower (149.04 ±ADG10-30
75
156.46 ± 5562 g) compared to that during period ofLambmortality
19.75%the 10-30 days of age (156.46 ± 55 g).
Lamb mortality was high and averagedeath rate was 19.75%.
Table 2 indicates that 3- to 7-year-old ewes had a higher-performance and dropped heavier lambs (P< 0.05) than the old dams (over 8 years of age). Age of dam was a significant source of variationinfluencing Birth weight (Table 2). Mean birth weight by age of dam revealed that lambs from 9-year-oldewes were lighter than lambs from all other age of dam classes. In contrast, differences were small
among birth weights of lambs produced by dams that were 2 to 8 years of age.
Average daily gain performance of lambs between birth and 10 days of age was significantly (P <0.05) affected by age of dam (Table 2). Average daily gain by age of dam revealed that lambs from
3-year-old ewes showed more rapid growth for the first 10 days compared to lambs from 8-year-old ewes.
During the period of 10-30 days of age, average daily gain performance of lambs was not significantly (P >0.05) affected by dam age.
The frequency of dead lamb was analyzed in five different ages of dam classes. The mortality ofTable 2. The effect of dam age on birth weight, ADG and mortaliy of lambs.
Age (year) of dam classes
Lamb traits
2 (n = 11)
3 (n = 16)
7 (n = 3)
8 (n = 2)
9 (n = 5)
Birth2.7ab ± 0.7
3.0a ± 0.6
3.1a ± 0.4
2.7ab ± 0.8
2.5b ± 0.6
weight (Kg)(n = 22)(n = 41)(n = 7)(n = 5)(n = 15)169a ± 52
139ab ± 58
86b ± 45
119ab ± 67
144ab ± 68
ADG0-10(n = 20)(n = 39)(n = 5)(n = 5)(n = 11)164a ± 44172a ± 59
132a ± 46
128a ± 61
160a ± 69
ADG10-30(n = 19)(n = 37)(n = 4)(n = 5)(n = 10)Mortality
6.65 %
4.4 %
4.4 %
0%
4.4 %
Means within line with different superscripts differ (P < 0.05)

171lambs from 2-year-old ewes was by 2.2% higher than that of lambs from 3, 7 and 9-year-old ewes. No
mortality was observed in 8-year-old ewes.
Litter size effect on the average daily gain lamb performance was significant (P < 0.05) between birthand 10-30 days of age. Single-born lambs showed a more rapid growth for the first 10-30 days comparedto twin, triplets and quadruplets (Table 3). Single-born lambs were 0.7, 1.5 and 1.7 kg heavier (P < 0.05)
than twin, triple and quadruple-born lambs respectively. Lambs born as twin were also heavier (P < 0.05)
than those born as triplets and quadruplets. Litter size had a significant influence on perinatal lambmortality (Table 3). Less relative values (2.2%; 5.5%) were observed for lambs born as twins andquadruplets, while mortality was higher (12.1%) for triplets.
In order to analyse the causes of death more precisely, all lamb were grouped according to the birthweight at an interval of 0.5 kg. The analysis indicated that lambs of 1.5 to 2.5 kg birth weight had thehighest mortality (15.36%). Broadly, the mortality of female lambs was by 6.59% higher than that ofmale lambs (Table 4).
Table 3. The effect of litter size on birth weight, ADG and mortality of lambs.

Lamb traitsBirthWeight (kg)
ADGQ0-10
ADG10-30
MortalitySingles
4.0a ± 1(n = 4)216a ± 70(n = 4)232a ± 57(n = 4)0%

Litter size
TwinsTriples
3.3b ± 0.5
2.5c± 0.4
(n = 34)(n = 33)
169b ± 47
147b ± 54(n = 34)(n = 26)
168b ± 42144b ± 53(n = 33)(n = 24)
2.2 %
12.1 %

Quadruples
2.3c ± 0.4(n = 19)94c ± 66(n = 16)128b ± 63(n = 14)5.5 %Means within line with different superscripts differ (P < 0.05)

4. Discussion
Table 4. Mortality of lambs according to gender and birth weight
In our study, the average birth
Mortality (%)
Lamb traits
weight of the live lambs was aroundMaleFemale
2.85 kg and similar to that reported
1.5 - 2
3.29 (n = 3)
6.59 (n = 6)
previouslyfor
D'man
lambs
Birth Weight 2.0 - 2.5
2.19 (n = 2)
3.29 (n = 3)
(Boujenane 1996; Mahouachi et al.,(Kg)
2.5 - 3.0
1.1 (n = 1)
2.19 (n = 2)2004). The age of dam effect was> 3.0
0.0 (n = 0)
1.1 (n = 1)
significant on birth weight (P < 0.05)
with heavier lambs obtained fromewes being 3 to 7 years old. Male lambs were generally heavier than females (P < 0.05).
Birth weight is one of the most important factors influencing pre-weaning growth in young animals,
since lambs heavier at birth grow faster than lightweight lambs. Birth weight is influenced by breed, sexof lamb, birth type, age of dam, feeding conditions and production system (Notter et al., 1991). Lambs
which are heavier at birth are usually males, singles, produced by ewes with larger body sizes and good
feeding conditions.
The results indicate that the mortality between the classes of dam age was different. A higher
neonatal mortality of 6.6 % was registered for the lambs from 2-year-old ewes compared to 4.4 % for thelambs from 3, 7 and 9-old ewes respectively. Sex of the lamb affects significantly the mortality but
conflicting results have been obtained (Patil et al., 1992; Ebangi et al., 1996).
Overall lamb mortality was higher (19.75%) and increased with litter size. Lamb mortality was higher
in quadruples litters than triples or in twins. In general, this finding agrees with results reported in theliterature (Valls, 1983; Sierra, 1985; Fahmy, 1989, Ricordeau et al., 1990). Perinatal lamb mortality,
which occur around parturition time, result in significant lamb losses. Mendel et al. (1989) reported that
Merinolandschaf ewes suffered lamb losses of 18.4%. While the corresponding value for the Bergschaf
breed was 26.0%. The extent of perinatal mortality depends mostly on the management system, but themajor factors affecting lamb survival include age of lamb, litter size, birth weight, nutrition, parity of the172ewe and season of birth (Gatenby et al., 1997; Ambruster et al., 1991; Notter et al., 1991). In our study,
litter size had significant (P < 0.05) influence on birth weight which influenced perinatal mortality. The
rates of mortality tend to increase at extremely low or high birth weights (Mendel et al., 1989; Notter andCopenhaver, 1980).
5. Conclusion
As sheep production is directly influenced by the number of lambs born and reared from a flock at any
given time, it is highly important to identify the cause of lamb mortality and to take appropriate measures toreduce it. A part from low birth weight, causes of early mortality could be stress, injuries, organmalfunction, starvation or mis-mothering. Some of the causes are closely related to the season, since during
different times of year, sheep and new-borns are exposed to different environmental circumstances withregard to humidity and temperature. Therefore, for proper lambing management the season should be taken
into consideration since it has great impact on birth weight and perinatal lamb mortality.
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