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The aim of this study was to evaluate the relationship between body and testicular measurements in Ouled Djellal male lambs from birth to the onset of puberty and to adjust the growth curves using linear and nonlinear regression models in order to establish the most appropriate model. Body weights (BW), chest girth (CG) and testicular biometry of the two gonads (scrotal circumference (SC), testis length (TL), testis (TD) and cauda-epididymis diameters (ED)) were weekly recorded in 17 lambs of the Ouled Djellal breed born in autumn. The weight at birth, the live weight and the average daily gain at different ages were assessed at 30, 60, 90, 120, 150, 180 and 210 days. At 210 days 3 lambs had reached puberty.
The average weight at birth in lambs was 4.5±0.7 kg (mean ± standard deviation). The effect of the litter size on weight and weight gains appeared significant during the pre-puberty phase; despite this, the single-born lambs were born heavier, and they tended to grow faster even before weaning (4 months). Regression equations have revealed that the testicular size (CS, TL, TD and ED) was positively related to the body (BW and CG) and the age. Very highly (p<0.0001) and highly significant (p<0.001) correlations were observed between testicular and body measurements before and after weaning ; so it is possible to predict one from the other. Since the testicular measurements are easily obtained and are potentially predictive of reproductive capabilities in the postpubertal period, they can be an important selection criterion of fertile rams to collect semen for artificial insemination or breeding purpose. The establishment of an early selection based on gonadic measurements especially scrotal circumference, in addition to body growth, can be a very powerful method for improvement of the Ouled Djellal breed in Algeria.
Keywords: age, Algeria, chest girth, testicular biometry, reproduction, weight
Les objectifs de cette étude étaient d’évaluer la relation entre les mensurations du corps et celles des testicules chez des agneaux mâles de race Ouled Djellal dès la naissance et jusqu’au début de l’apparition de la puberté et d’ajuster les courbes de croissance selon des modèles de régression linéaires et non linéaires afin d’établir le modèle le plus approprié. Le poids corporel (BW), le tour de poitrine (CG) et la biométrie testiculaire des deux gonades (circonférence scrotale (SC), longueur des testicules (TL), diamètres des testicules (TD) et des queues des épididymes (ED)) ont été enregistrés à un rythme hebdomadaire chez 17 agneaux Ouled Djellal nés en automne. Le poids à la naissance, le poids vif et les gains moyens quotidiens à différents âges types ont été évalués à 30, 60, 90, 120, 150, 180 et 210 jours. A 210 jours, 3 agneaux étaient pubères. Le poids moyen des agneaux mâles de race Ouled Djellal à la naissance était de 4,5±0,7 kg (moyenne ± écart type). L'effet de la taille de la portée sur le poids et les gains de poids parait significatif durant la phase pré-pubertaire ; malgré cela, les agneaux nés simples sont nés plus lourds et ont eu tendance à croitre plus rapidement même avant le sevrage (4 mois). Les équations de régression ont révélé que la taille du testicule (CS, TL, TD et ED) était positivement corrélée à la taille corporelle (BW et CG) et à l'âge.
Des corrélations très hautement significatives (p<0,0001) et hautement significatives (p<0,001) ont été observées entre les mensurations testiculaires et celles du corps avant et après le sevrage ; il est donc possible de prédire l'un de l'autre. Étant donné que les mensurations testiculaires sont faciles à obtenir et sont potentiellement prédictives des capacités de reproduction pendant la période post-pubertaire, elles peuvent constituer par conséquence un important critère de sélection des béliers fertiles destinés à la collecte du sperme pour l'insémination artificielle ou à être utilisés à des fins de reproduction. La mise en place d’une sélection précoce basée sur les mensurations gonadiques, en particulier la circonférence scrotale, en plus de la croissance corporelle, peut être une méthode très puissante pour l'amélioration de la race Ouled Djellal en Algérie.
Mots-clés : âge, Algérie, biométrie testiculaire, périmètre thoracique, poids, reproduction
The Ouled Djellal sheep is considered to be the most predominant breed in Algeria and known to be a non seasonal breeder. The reproduction in this breed faces several obstacles, of which the low annual lambing rate and particularly nutrient deficiency are often the most important. The productive and reproductive performances in Ouled Djellal breed have been relatively poorly studied in males (Boussena et al 2013, Boussena et al 2014a, Boussena et al 2014b) compared to females (Dekhili, 2002, Dekhili and Mahane 2004, Dekhili and Benkhlif 2005, Dekhili and Aggoun 2006, Dekhili and Aggoun 2007).
The poor knowledge of the reproductive performances in males is a major limitation of the improvement of the Ouled Djellal breed.
One of the tools of intensification of production in this breed is the improvement of productivity and growth potentiality, ensured through breeding strategies, but especially through a selection made on the basis of testicular development besides body growth.
The objective of this study was to evaluate the relationship between body and testicular measurements in Ouled Djellal male lambs from birth to puberty and to adjust growth curves using linear and nonlinear regression models to establish the most appropriate model.
This trial was performed at the Technical Institute of Livestock (ITELV, Ain M'lila), in the province of Oum El Bouaghi, Northeastern Algeria, at an altitude of 678 m above sea level (latitude 35° 52’ N and longitude 7° 6’ E). The area has a semi-arid climate with hot and dry summers and cold and relatively wet winter months.
Seventeen Ouled Djellal male lambs (n = 17), born at the onset of autumn were used in this study. All the lambs were born in the same week and were individually identified and weighed within 24 h of birth. The lambs were maintained suckling and remained with their mothers and the other adult ewes until weaning time. When aged 4 months, the lambs were weaned by taking them away from the flock. After weaning, the lambs were housed in a cover shelter with an open-air run, allowed to walk freely. In addition to alfalfa hay, the lambs were provided with a concentrated mixture. The feeding level was adjusted in increasing amounts to allow appropriate development of all animals.
The experiment was conducted under natural photoperiod.
The weekly measurements of body live weight (BW), chest girth (CG) and scrotal circumference (SC), as well as the length (TL) and diameters of the testes (TD) and the cauda-epididymis (ED) of the two gonads, were recorded.
Since the puberty in male lambs of the Ouled Djellal breed is reached at an average age of 228±11 days (mean±SD) (n=10) (Boussena et al 2016), all measurements were recorded up to the age of 210 days. The birth weight and the weight at different ages were evaluated at 30, 60, 90, 120, 150, 180 and 210 days.
The average daily gains (DG) were calculated in grams (g) for the following intervals:
DG 1 = daily gain between (BW 0) and (BW 30)
DG 2 = daily gain between (BW 30) and (BW 60)
DG 3 = daily gain between (BW 60) and (BW 90)
DG 4 = daily gain between (BW 90) and (BW 120)
DG 5 = daily gain between (BW 120) and (BW 150)
DG 6 = daily gain between (BW 150) and (BW 180)
DG 7 = daily gain between (BW 180) and (BW 210)
All measurements were carried out by the same operator throughout the study.
The lambs were weighed by using a small ruminant's balance (50 kg ± 100 g). The chest girth (cm) and the scrotal circumference (cm) were measured using a flexible tape (Rondo ® model, Kruuse, Switzerland). The scrotal circumference was measured at the widest scrotal diameter. While the testicular length (cm), testis and cauda-epididymis diameters (cm) were measured of each testis using a caliper.
The growth traits examined were birth weight, pre-weaning weight and daily gain, weaning weight, weight and post-weaning daily gain and the simultaneous evolution of chest girth.
On the basis of the results of weighing, the body weight (BW) was adjusted to average age 30 (BW 30), 60 (BW 60), 90, 120, 150, 180 and 210 days (BW 210) by using linear interpolation (Ricordeau et al 1979).
The regression curves were adjusted with linear and non-linear models to determine the appropriate model that best fit the lamb body and testicular growths.
Only when the model appeared adequate in light of the data, the fitted regression equation was interpreted and recommended to predict the body and testicular growths.
All statistical analyzes were carried out using the Statistical Package for the Social Sciences (SPSS Inc USA). The calculation of descriptive statistics such as the mean, standard deviation, standard error etc, and the analysis of variance (ANOVA) were carried out. Correlation matrix and significance test were applied using the Pearson correlation coefficient. The Student's t-test was used to assess whether the studied parameters were affected by the litter size. P-values less than 0.05 were considered as significant. The results are presented as mean ± standard error.
At 7 months of age (210 days), 3 lambs reached puberty and at 228 days of age, puberty was observed in 10 of the studied Ouled Djellal lambs.
Means and standard errors of body weights (BW) and daily gains (DG) according to litter size are presented in Tables 1 and 2.
The average birth weight in Ouled Djellal male lambs was 4.5 ± 0.2 kg. Although, single-born lambs were born heavier and tended to grow faster (p>0.05), the effect of litter size on live weight appeared to be significant (p<0.05) only during the first month of life and in the post-weaning phase (150-210 days) (Table 1).
Pearson's correlation computation showed a positive relationship between birth weight and body weights in the first and second months after birth.
Weaning in the present farm was carried out at 120 days of age (Table 1)
|Table 1. Weight (kg) variations according to age (d) and type of birth of Ouled Djellal male lambs|
|Litter size||Birth||BW30||BW 60||BW 90||BW 120||BW 150||BW 180||BW 210|
|Singles||4.9 ± 0.3a||7.9 ± 0.4a||14.1 ± 0.6a||22.1 ± 0.9a||25.8 ± 1.2a||30.6 ± 1.6a||34.9± 1.3a||39.5 ± 1.6a|
|Twins||4.3 ± 0.2a||6.2 ± 0.3b||11.8 ± 0.7a||19.2 ± 1.2a||21.2 ± 1.3a||25.0 ± 1.1b||30.0± 1.3b||34.5 ± 1.0b|
|Mean||4.5 ± 0.2||6.8 ± 0.3||12.6 ± 0.6||20.2 ± 0.9||22.8 ± 1.1||26.4 ± 1.3||31.1 ± 1.3||36.3 ± 1.3|
|a, b Means within the same column, not followed by the same superscript letter are different at p<0.05|
However, the effect of litter size on daily gain (DG) appeared to be significant only during the second month of life and in the age range of 120-150 days (p<0.05) (Table 2).
|Table 2. The effect of litter size on weight daily gain (g) according to age (d) in Ouled Djellal male lambs|
|Litter size||DG 1||DG 2||DG 3||DG 4||DG 5||DG 6||DG 7|
|Singles||207 ± 19a||150 ± 23a||251 ± 32a||142 ± 22a||108 ± 15a||144 ± 30a||152 ± 16a|
|Twins||139 ± 16a||201 ± 14b||181 ± 14a||97 ± 11a||75 ± 7b||156 ± 8a||148 ± 20a|
|Mean||160 ± 14||179 ± 13||201 ± 17||110 ± 12||85 ± 8||154 ± 11||151± 12|
|a, b Means within the same column, not followed by the same superscript letter are different at p<0.05|
Before weaning, the weight in Ouled Djellal lambs evolved according to a quadratic regression model with the resulting predictive equation of y=-0.0006x2+0.25x+2.95 (R2=0.99). While quite different linear regression equations were observed after weaning: y=0.16x+52.5 (R2=0.97) and y=0.17x+46.3 (R2=0.98) respectively in single lambs and twins (where x is the age and y is the weight).
The growth rate of chest girth before weaning was 2.7 mm per day in single lambs versus 2.3 mm per day in twins (p> 0.05). However, a similar growth trend of chest girth was observed in both single and twin lambs across the post-weaning phase. Chest girth increased at a level of 1.7 mm per day in single lambs compared to 1.6 in twins.
Moreover, a polynomial equation to infer weight through measuring chest girth before weaning was shown in Fig. 1.
Nevertheless, linear predictive equations were proposed to predict weight from chest girth after weaning in Ouled Djellal lambs (Fig. 2 and 3).
|Figure 1. The predictive equation for the live weight (kg) from chest
girth (cm) in Ouled Djellal lambs before weaning
|Figure 2. The predictive equation for the live weight (kg) from chest
girth (cm) in single Ouled Djellal lambs after weaning
|Figure 3. The predictive equation for the live weight (kg) from chest
girth (cm) in twins after weaning
In single lambs, the scrotal circumference increased between birth and weaning from 7.5 ± 1 to 12.9 ± 0.6 cm, representing a growth of 0.42 mm per day (72.3% of increase), whilst, it increased from 6.9 ± 0.3 to 13.1 ± 0.7 cm in twins, thus underlining an increase of 88.8%, with a daily growth rate of 0.44 mm/day (p>0.05). In general, these results indicate insignificant differences between the testes of twin and single lambs (p>0.05) before weaning.
However, significant differences for all the testicular parameters considered in this study after weaning were indicated with higher values recorded in single born Ouled Djellal lambs (p<0.05).
The right and left testicular length, testicular and cauda-epididymis diameters were obtained separately. However, testicular and epididymal measurements of the two gonads tended to have the same evolution (p>0.05). The average values of the two gonads were used in the present study.
The suggested functions for predicting the testicular growth from live body weight are presented in Table 3.
|Table 3. Predictive equations for testicular measurements (SC, TL, TD and ED) from body weight (BW)|
|SC = 0.004 BW2- 0.39 BW +5.05|
|TL = 0.04 BW + 2.24|
|TD = 0.035 BW + 0.904|
|ED = 0.027 BW + 0.534|
The analysis of phenotypic correlations (Table 4) indicated that age and BW showed a positive and highly significant (p<0.001) effect on all growth traits under study. Highly significant correlations characterized the testicular measurements (SC, TL, TD and ED) between them (p<0.001).
|Table 4. Phenotypic correlations between age and the various studied growth traits before (below the diagonal) and after weaning (above the diagonal)|
|All correlations are significant at p<0.001|
A previous study showed that the puberty in Ouled Djellal males (n=10) was reached at 228±7 days (mean±SE) with a weight of 40,4±1,2 kg (mean±SE) (Boussena et al 2016).
As mentioned in previous studies (Thieme et al 1999, Tekin et al 2005, Afolayan et al 2006, Kuchtík and Dobeš 2006, Ekiz and Altinel 2006, Yilmaz and Altin 2011), single born lambs tended to have higher birth weights compared to twins. In fact, the effect of litter size on birth weight remains insignificant in the present study (p>0.05). This finding was consistent with the results reported by Atta and El Khidir (2004) and Bonfoh et al (1994).
In sheep, the reduction in birth weight as the litter size increases apparently is due to the failure of the uterus-placenta complex to support the full growth of multiple fetuses (Gardner et al 2004, Mac Laughlin et al 2005).
Four months is a typical late weaning age. According to Godfrey and Weis (2016), there are several economical advantages to late weaning.
In contrast to the report of Mavrogenis et al (1982), the weaning weight is not correlated (p>0.05) with the growth rate before weaning in Ouled Djellal lambs. Similarly, the weight at weaning is not correlated with the birth weight (p>0.05). A statistically significant correlation between these latter traits has been reported by Da Silva et al (2001).
Even it was not significant in all intervals of age (p>0.05), higher daily gains were recorded in singles compared to twins. According to Kuchtík and Dobeš (2006), the highest daily gains from birth to 100 days of age were recorded in single born lambs (260 g) compared to twins and triplets.
As mentioned by Kuchtík and Dobeš (2006), there is no significant correlation between the birth weight and the average daily gain in the first month after birth (p>0.05), although this last trait seems to be a reliable index of milk production.
Due to the high determination coefficient (R2 =0.99), the quadratic model (second degree polynomial) was considered suitable to predict the weight from the chest girth in Ouled Djellal lambs before weaning. This is in accordance with the report of Afolayan et al (2006); these authors noticed that the polynomial equation using chest girth as an independent variable predicted body weight was more accurately as compared to the linear equation.
Therefore, it is suitable to use the chest girth to predict the weight, particularly for large animals where the weight is hard to record by scale. In addition, this trait is easy and quick to measure and represents a huge advantage, especially when the number of subjects to measure is often quite high and the performance could be recorded by the farmer himself (Sarti et al 2003). Actually, Çilek and Petkova (2016) concluded that heart circumference is the most appropriate parameter to estimate the body weight in Malya sheep.
Indeed, Afolayan et al (2006) indicated that the live weight estimation using the chest girth alone would be preferable to combinations with other body measurements.
The scrotal circumference is considered as the best indicator of the sexual development in males (Notter et al 1981) and differs among breeds (Belibasaki and Kouimtzis 2000).
The insignificant differences between testes of twin and single Ouled Djellal lambs before weaning were noticed for the all studied testicular measurements. Similar findings regarding the testicular length were reported by Koyuncu et al (2005).
One of the more intriguing findings of this study was the significantly higher values for all the testicular parameters considered in this study after weaning in single born Ouled Djellal lambs (p<0.05). Nevertheless, significant differences between single, twin and triplet lambs after weaning were recorded only in the scrotal circumference by Matos et al (1992) and the testis diameter by Koyuncu et al (2005).
Statistically positive correlations between age and all measurements (body and testicular measurements) were at a high level (p<0.001) similar to those determined in a previous research (Ferra et al 2010).
The relationship between testis size and body weight was also demonstrated in previous researches (Abdel Rahim et al 1989, Hassan et al 2009, Mahouachi et al 2011).
In addition to the positive effect of age and live weight on all testicular measurements (testicular length, testicular and cauda-epididymis diameters), very marked correlations characterized the testicular traits between them. The same results have been reported by various authors (Shrestha et al 1983, Emsen and Davis 2004, Koyuncu et al 2005).
We sincerely thank the whole team at the Technical Institute of Livestock (ITELV Ain M'lila) for providing the facilities and animals for the experiment and for all the support during the collection of data.
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Received 5 October 2019; Accepted 5 January 2020; Published 1 February 2020
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