Heritability and variance components estimates for growth traits in Saudi Ardi goat and Damascus goat and their crosses

Mohammed KM, Kamal EL-den MA, Dahmoush AY

1Animal Reproduction Research Institute, Agriculture Research Center, Giza, Egypt

2Animal Production Department, Faculty of Agriculture, Al-Azhar University, Assiut, Egypt

3Camel and Range Research Center, Al Jouf, Saudi Arabia

Heritability and variance components estimates for growth traits in Saudi Ardi goat and Damascus goat and their crosses

Mohammed KM1✉, Kamal EL-den MA2, Dahmoush AY3

1Animal Reproduction Research Institute, Agriculture Research Center, Giza, Egypt

2Animal Production Department, Faculty of Agriculture, Al-Azhar University, Assiut, Egypt

3Camel and Range Research Center, Al Jouf, Saudi Arabia

Goat Heritability Heterosis Growth rates Genotype Phenotype ABSTRACT

1. Introduction

The most common indigenous breeds of goats raised in Saudi Arabia are Ardi, Hibsi and Zumri[1]. These local breeds have aconsiderable additive genetic variance and this concept is attributed to the fact that intensive selection was not practiced in these breeds.Therefore, high variability in local breeds shows that improving of these local breeds through selection is quite possible. However,comparing to other breeds under the same conditions, Ardi goat has the highest kidding percent ranging from 147.7% to 166.7%with the highest litter size (1.67). The mean feedlot gain of all breeds is 115 g/d, where Ardi kids expressed the fastest rate of gain(149 g/d). Furthermore, it has a satisfactory more milk yield[(160.3±6.37) kg/lactation] than other breeds and well-adapted to a wide range of farming environments, so more attention should be paid to this breed. Goat productivity can be improved through the selection of the distinguished individuals within herds of the same breeds to be used for breeding or through crossbreeding systems between different breeds to synthesis a new sophisticated improved breed of multipurpose[2-4]. The Damascus goats are considered a dual purpose animal for meat and milk production with high genetic level, therefore, they are used at large scale for production improvement of other breeds[5]. There is a great deal of interest to increase productivity of native goat breeds with more utilization of the genetic resources of Saudi Arabia goats through crossbreeding with Damascus breed. The upgrading programs are required to characterize genetically these local goat breeds as well as of the exotic breed (Damascus) that could be used for genetic improvement.The potential genetic changes in the economic traits are depending on the genetic variance, the heritability of the traits measured and its relationship with others. Breeding programs depend on the identification of various useful traits of high heritability and ease to measure for breeding improvement[6]. Estimation of heritability for early growth traits including birth weight and their linking to each other are hugely base for the selection progress which is ultimately dependent on maternal influences besides the additive genetic variance effects[7-10]. This does not make us forget the importance of environmental factors representing the identification of the genetic differences is realistic and truth between individual animals within herd[11-13]. So, such traits are considered as an early indicator for the late growth of economic interest[14,15]. Whereas, the existence of correlation between phenotypic and genotypic particularly the growth traits in early stages of ages allows early selection and exclusion of the unwanted animals[14-17]. The present study aimed to study the genetic and non-genetic factors and their interactions affecting body weights at birth, weaning and at 6 months of age,and average daily gains from birth to weaning, birth to 6 months and weaning to 6 months in Saudi Ardi, Damascus goats and their crosses. The study also aimed to estimate the heritability and variance components for the previous traits parameters in Ardi and Damascus goats.

2. Materials and methods

2.1. Location of study and animal management

A crossbreeding program between Saudi goats (Ardi, AA) as a native breed with Syrian goats (Damascus, DD) was carried out at Camel and Range Research Center (Al-Jouf province, Northern region of Saudi Arabia located at latitude of 29.97 °N and longitude of 40.21 °W and at 684 meters above sea level) to improve the meat productivity through crossbreeding and selection. Genetically selected and improved bucks were used to disperse these valuable genes throughout the goat herds in Saudi Arabia. All animals were raised under similar environmental, nutritional, and management conditions. The animals were housed in semi-shaded/open front barn and fed on a commercial concentrate and alfalfa hay. The amount of concentrate and hay were calculated according to the nutritional requirements for goats[18] which were dependent on animal ages and production status. Water, straw, salt and minerals supplemented in blocks were freely available to all animals.

2.2. Breeding plan of the genetic groups

A crossbreeding program between Ardi Saudi goats (A) as a native breed with Syrian Damascus goats (D) was started in 2006 to develop local breed through selection program. At the beginning of the base generation, breeding does of Ardi goats (A) were randomly divided into two groups. The first group of Ardi goats (A) was inseminated by elite bucks of the same breed to produce purebred litters and progenies. The second group of Ardi goats (A) was inseminated by Damascus sire (D) to produce crossbred of ½D½A.The latter crossbred (½D½A) was inseminated by Damascus sire to produce crossbred of ¾D¼A. At the same time, does of Damascus breed were inseminated from bucks of the same breed to produce purebred litters and progenies. Accordingly, the breeding plan was permitted to produce four genetic groups of AA, DD, ½D½A and¾D¼A. The pedigree records of the body weights were obtained from a total number of 754 kids (397 males and 357 females)resulting from 46 Sires and 279 Dams during the time period from 2006 to 2010 of the study.

2.3. Data collection for statistical analysis

Birth weight (BW), weaning weigh (WW) and 6 months weight(6MW) as well as average daily gain during different growth stages from birth to weaning (D1), from weaning to 6 months (D2) and from birth to 6 months of age (D3) were recorded for all animals during season 1 (winter and Autumn) and season 2 (summer and spring) and years from 2006 to 2010.They were classified according to breed, generation, sex, season, year, and type of birth. Data were analyzed using PROC GLM procedure[19] for the least-squares means and standard errors of the fixed factors. Heritability and genetic parameters were estimated with derivative-free restricted maximum likelihood (REML) procedures using the MTDFREML program of Boldman et al[20].

2.4. Statistical model used for data analysis

Where;

Yijklmno: The record of BW, 6MW, YW, D1, D2 or D3 measured on othlamb born at mthyear of birth, ithbreed, jthgeneration, kthsex, lthseason and nthtype of birth;

µ: Overall mean when equal subclass numbers exists;

Bi: Fixed effect of ithbreed (i = 1, 2, 3 and 4);

Gj: Fixed effect of jthgeneration (j = 1 and 2);

Xk: Fixed effect of kthsex (k = 1 and 2);

Sl: Fixed effect of lthseason (l = 1 and 2);

Ym: Fixed effect of mthyear (m = 1, 2, 3, 4 and 5);

Tn: Fixed effect of nthtype of birth (n = 1, 2, and 3);

eijklmno: Random error particular to the ijklmnothobservation assumed to be independently and normally distributed with mean zero and variance of δ2e.

The assumed model for heritability, genetic correlations and breeding values was:

y = Xb + Zu + e

Where;

y: a vector of observations, b: a vector of fixed effects with an incidence matrix X;

u: a vector ofrandom animal effects with incidence matrix Z;

e: a vector of random residual effects with meanequals zero and variance δ2e.

3. Results

The obtained results articulated wide phenotypic variations in all traits of the body weight and daily gain. The percentages of variation for body weights traits were moderate and ranged from 20.960% to 26.250%, while these variations were high and ranged from 24.070%to 39.990% for daily gains (Table 1).

Table 1 Actual means standard error (SE), standard deviations (SD) and ranges for kids growth traits.

The genetic groups had a highly significant (P＜0.01) effect on the body weights traits and daily weight gains for D1 (P＜0.01) and D3 (P＜0.05). Damascus and ½D½A goat groups had higher body weights (P＜0.01) than Ardi and ¾D¼A groups at birth, weaning and at 6 months (Table 2).

Table 2 Least squares for weights (kg) at birth, weaning and 6 months of age.

Also, Damascus and ½D½A goat groups had higher daily gain during D1 (P＜0.01) and D3 (P＜0.05) periods than Ardi and ¾D¼A groups (Table 3). However, no significant differences between the genetic goats groups in the daily gain during D2 period (Table 3).Generally, F2 generation had a higher body weights than F1 at weaning and at 6 months, as well as the daily body gain during D1, D2 and D3 periods (Table 2 and Table 3). However, F1 had a significantly higher (P＜0.01) birth body weights than F2 and no significant effect on daily gain during D2 period.

Analyses of variance showed that the fixed effects of sex, season,year and type of birth were significantly different for most body weights and daily gains (Tables 2 and 3). Male kids had a significant(P＜0.01) heavier body weights than female at birth, weaning and at 6 months of ages. Subsequently, the daily body gains for male kids were significantly higher (P＜0.01) than females during D1, D2 and D3 periods.

Kids born during Summer/Spring season (S2) had a significant heavier (P＜0.01) body weights than at birth and 6 months of ages,as well as higher daily gain during D2 and D3 periods than those born during Winter/Autumn (S1). Anyways, no significant differences between seasons for body weight and daily gain were observed at weaning and D1 period.

Project years had highly significant (P＜0.01) effect on the body weights and daily gain during various growth stages (Table 2 and 3). As shown in Table 3, the highest body weight (P＜0.01) at birth,weaning and at 6 months of age were recorded for kids born in years 2009, 2010 and 2008, respectively. Conversely, the lowest body weight at birth, weaning and at 6 months were recorded in the first and second years of the project (2006 and 2007). The highest(P＜0.01) daily body gain during D1 period was observed for kids born in 2010, whereas kids born in 2008 recorded highest daily gain during D2 and D3 periods (Table 3).

Kids born as single had heavier (P＜0.01) body weights at birth,weaning and at 6 months of ages than those born as twins or triplets(Table 2). Similarly, they had higher (P＜0.01) daily body gain during D1 and D3 periods. However, there were no significant differences between type of births for daily gain during D2 period (Table 3).

The estimates of heritability and variance components for body weights at different stages in Ardi and Damascus goats are presented in Table 4. Damascus goats had higher heritability estimates thanArdi for birth (0.41 vs 0.15) and weaning (0.35 vs 0.26) weights,while, Ardi goats had higher heritability estimates than Damascus for body weights at 6 months of ages (0.45 vs 0.18).

Table 3 Least squares for daily weights (kg) gains at different ages.

Table 4 Estimates of heritability (h2) and variance components for body weights at birth, weaning and 6 months of ages in Ardi goat (AA) and Damascus goat (DD).

The values of phenotypic correlation between BW and WW; BW and 6MW; WW and 6MW were 0.32, 0.32 and 0.73 for Damascus goats and were 0.18, 0.10 and 0.72 for Ardi goats, respectively. The corresponding values for genotypic correlations were 0.56, 0.05 and 0.81 for Damascus, and 0.22, 0.23 and 1.00 for Ardi goats,respectively.

4. Discussion

The genetic groups had a highly effect on the body weights traits and daily weight gains. Crossbred kids of ½D½A and ¾D¼A groups were heavier in all body weights compared to Ardi kids, which means the body weights and growth rates in the local goats breed were improved and associated in crossbred with Damascus sire bucks;and the variation in the growth performance in the crossbreeding attributed to Damascus genes. Therefore, the Damascus goat is the best breed to be raised in Saudi Arabia, and could be used in upgrading programs as well as improving meat production of local breeds in the Arabic countries. This result is consistent with those reported by Al-Saef[21] who reported that genetic groups of Ardi(A), Damascus (D), ½D½A and ¾D¼A goats were the main source of variations for the most body weights.

Compared to ½D½A group, the lower values in all stages of the body weights were observed in ¾D¼A kids group. This result would be expected under this model of crossbreeding where the estimates of direct heterosis were positive. This fact was confirmed by Khalil et al[22], since the estimates of direct heterosis were positive for the plurality of the weights. However, non-significant differences in post weaning body weights of kids related to different genetic groups were reported by other authors[23,24].

In the same context, Khadiga et al[25] and Browning et al[26] found that sire breeds were the main source for weight differences at various stages of growth. Similarly, the early live body weights in Boer crossbreds with Spanish purebred goats (Boer-Spanish) were slightly heavier (P＜0.05) than Spanish goat breeds[27-29]. Similarly,Waldron et al[30] noted differences between Boer crossbreds with Spanish and Spanish pure breeds of 630 g in 90 days (weaning weight) and by 40 g in final body weight as a difference in favor of Boer crossbreds. In the same line Mourad and Anous[31] found that French Alpine-sire crossbred kids (½ Alpine × ½ African goat) were heavier (P＜0.05) than kids of the common African breed at birth and 30 days of age. Not only the genetic potentiality can influence the initial growth rate, including birth weight, but also the maternal status and environmental conditions have a reasonable share of this[10].

The analyses of variance in this study showed that the fixed effects of sex, season, year and type of birth were significant differences for studying body weights. These results confirmed with those reported by many authors[21,26,31-35]. Sex of kids had a highly effect on daily weights gains for different growth stages in this study. During the different stages of growth periods, the daily weight gain was higher for male kids compared to females. So, male kids were significant heavier than females at all studied ages. This indicates that male kids can grow faster than female ones during the first six months of age. The differences in the chromosomal structure between males and females are associated with differences in the sex hormones which influence the skeletal growth and fetal development during pre and postnatal periods and subsequently affect the growth rate which attributed to the differences in the live body weights at birth,weaning and the following growth stages of age[36].

The present study showed that the kidding years of the project had highly significant effects on the daily weight gains during various growth stages in the study. The highest gain was observed for kids born in 2010, while the lowest gain was recorded for those born in 2006 and 2007. The average daily gains were varies with the stage of growth, but generally increased as the project progresses. The effects of kidding years of birth on the live body weights may be attributed to the climatic conditions which are varying from year to another and accompanied with nutritional changes and accordingly changes in the management of the herd[37-39].

The daily weight gains during summer/spring seasons were significantly higher than winter/autumn for both D2 and D3 periods.This means the kids which were born during winter/autumn seasons were grow up better during summer/spring seasons when the better quality green fodder is prevailing and available for dams and postweaning kids. Similarly, Zhang et al[35] drew his attention; the kids born in summer had powerful growth rate during post-weaning period although they were of lowest rank in pre-weaning compared to others. Whatever the case, the influences of seasons on kids initial weights and growth rate are important and have been reported in different studies[17,38]. These variations between seasons among different years might be accompanied by differences of rainfall and have a great impact on the intensity of green fodder production and consequently its availability during the years and seasons[17].Also, the variation values of weights and growth rates among different seasons and years of kidding may result from changes in management and herd size[35].

Kids born and raised as singles were significantly heavier than those raised as twins or triplets which reflected the fact that single kids had more milk from their dams than other types of birth.During pre-weaning, single born kids are luckier and get their food needs from his dam without competition from other kids. Contrary,multiple birth kids have a fierce competition for getting nutrition needs from their dam and this reflected in the growth rates and consequently weaning weights. However, after weaning, twins can adapt themselves to the environmental conditions and vigorously as usual compete the individuals of single births to get their food needs and this explains the lack of significant for daily weight gains during period D2. So, rather than suckling period, the growth, dominance during D2 period, mainly depend on the viability of balanced ration and the adaptation to the environmental variations[35].

Heritability estimates for birth weights and weaning weights for Damascus goat were higher than Ardi goats. However, the heritability of weaning weights for Ardi goat (0.26) is similar to Damascus goat(0.27) in other study reported by Mavrogenis et al[40], furthermore,it was higher than Damascus (0.17) in other study[41]. Also, in the current study, Ardi goats recorded higher heritability estimates for weights at 6 months of age than Damascus goats (0.45 vs 0.18). In any case, the heritability estimates for weaning weight (0.26) of Ardi goat were higher than the estimate for birth weight (0.15) and this result was in consistency with Menezes et al[8]. Contrary, Rashidi et al[42] recorded higher heritability estimates for birth weight than weaning weight in Markhoz goats (0.22 vs 0.16).

Heritability estimate for birth weight of Ardi goat is similar to that was estimated (0.11 to 0.15) for Angora, Alpine and Blended goat breeds[43-46], whereas, it was higher than that recorded for Black Bengal[47] and Iranian Cashmere goats[48], and lower than that reported for Black Bengal[49,50], Boer[35,51,52], Ganjam[53], and Draa[32] goat breeds. On other side, the heritability estimate of the birth weight for Damascus goats herein (0.41) is similar (0.39-0.43)to Draa, Black Bengal and Boer goat breeds[32,49,52]. In any case,it was lower than that reported by Portolano et al[14] for Sicilian Girgentana goats (0.49), Bosso et al[54] for West African Dwarf goats(0.50), Khadiga et al[25] and Neopane for Nubian Goat (0.54)[55].

Generally, the trait of the low percentage of the genetic variance component indicates that these traits are highly affected by environmental conditions (management system, feeding regime,climatic conditions and diseases stability, etc). However, the moderate or high percentage of genotypic variance gives hope for the possibility to improving the traits through selection programs.In this study, the percentage of genetic variance component in Ardi goat is low in both birth weight and weaning weight so that the best programs for genetic improvement of Ardi goat is possible through upgrading with Damascus goats.

Heritability estimate for weaning weight of Ardi goat (0.26) is similar (0.23-0.30) to those estimated for Alpine, Jamunapari and Boer goats[35,44,56] and higher than those estimated for Angora(0.04), Sirohi (0.11), Black Bengal (0.16) and Draa goats (0.19)[32,50,57,58]. However, it was lower than those recorded for Angora(0.59) and Boer goats (0.60)[59,60]. On the one side, the heritability estimate for weaning weight of Damascus goats (0.35) in herein study is similar to that estimated (0.35-0.37) for the same breed in other studies[61,62]. Similarly, Singh et al[50] and Misra[63] in different two studies were recorded; the heritability estimates for weaning weight for Jamunapari goats were similar (0.42 and 0.43). However,the heritability for Damascus weaning weight was higher than those reported (0.16) for this breed in other study[41]. Different goat breeds as Sicilian Girgentana[14] and Angora goats[64] had similar heritability estimates as Damascus goats. Whereas, Black Bengal,Boer, Sirohi, Draa and Jamunapari goats recorded lower (0.11-0.30)heritability for weaning weights[32,35,50,56,57] than Damascus goats which were considered in this study. On the other side, it was lower than those reported by Ricordeau et al[65] for Saanen goats (0.48);Khadiga et al[25] for Nubian Goat (0.77); and Siddiqui et al[66] for Osmanabadi goats (0.75).

The heritability estimates for Ardiand Damascus weights at 6 months of ages were 0.45 and 0.18 respectively. These estimates are similar and differ (lower or higher) from various goat breeds.The heritability estimates for Ardi goats weights at 6 months of ages were higher than Damascus (0.45 vs 0.18) goats in this study and similar to Beetal goats (0.43) in other study[67]. However, these estimates were lower than those reported in Jamunapari[56], Boer[37],and Osmanabadi goats[66] where it were recorded 0.51, 0.59 and 0.66, respectively.

The genotypic and phenotypic correlations between the studied growth traits at different stages showed positive values for both Damascus and Ardi goats. Similarly, Hermiz[24], Mourad and Anous[31], Mavrogenis et al[40], and Xiong et al[68] found positive genotypic and phenotypic correlations between body weights at different ages. Therefore, these estimates suggest that there is no genetic contradiction between these traits and their assigned genes which were responsible for phenotypic expression. Accordingly,the selection of one trait will have an expected positive impact on the others related traits. The selection for birth weight would have a considerable positive impact on weaning weight. However,the efforts should be made to focus the high heritability, which incidentally are expressed early in life. Positive correlations between birth weight and weaning weight is an indication that a heavy kids had a fast growth rate during the pre-weaning stage which resulted in heavy weaning weight[17,55,69].

Since the estimates of direct heterosis were positive for the studied growth rates, the genetic program for Ardi goat meat production improvement through upgrading with Damascus goats is possible to this local goats breed in Saudi Arabia. Genetic and phenotypic correlations for growth traits are positive for Damascus and Ardi goats and consequently the selection for birth weight can have a considerable positive effect on weaning weight.

Conflict of interest statement

We declare that we have no conflict of interest.

Authors thank and gratitude King Abdulaziz City for Science and Technology, Saudi Arabia, for providing the financial support to this project (No. ARP: 24-22).

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18 October 2017 evision 30 October 2017 Accepted 15 November 2017 Available online 1 January 2018

Objective:To study the genetic and non-genetic factors and their interactions affecting growth rate and body weights at birth, weaning and at 6 months of age in Saudi Ardi, Damascus goats and their crosses.Methods:Crossbreeding program between Saudi Ardi(A) goats with Damascus(D) was carried out to improve the meat productivity of Ardi goats through crossbreeding. The pedigree records of the body weights were obtained from 754 kids (397 males and 357 females) produced from 46 Sires and 279 Dams. Birth weight, weaning weigh and 6 months weight as well as average daily gain during different growth stages from birth to weaning (D1), weaning to 6 months (D2) and from birth to 6 months of age (D3) were recorded during winter/autumn and summer/spring. Data were classified according to breed,generation, sex, season, year, and type of birth. Data were analyzed using GLM procedure for the least-squares means of the fixed factors. Heritability and genetic parameters were estimated with derivative-free restricted maximum likelihood procedures using the MTDFREML program.Results:The percentages of variations were moderate for body weights and high for daily gains. Genetic groups had a highly significant (P＜0.01) effect on the body weights traits.Damascus goats had higher (P＜0.01) birth and weaning weights, but ½D½A group kids had a higher (P＜0.01) body weight at 6 months. The genetic groups had a significant effects on the daily weight gains for D1 (P＜0.01) and D3 (P＜0.05) periods, whereas, it had no effects on D2 period. The fixed effects of sex, season, year and type of birth were significant differences for body weights. Male kids were heavier (P＜0.01) than females for different growth stages. Body weights and daily gains during winter/autumn were significantly higher (P＜0.01) than summer/spring. Kids born and raised as singles were significantly (P＜0.01) heavier than those were born as twins or triplets. The genetic and phenotypic correlations between birth and weaning weights were positive for both Damascus and Ardi goats.Conclusions:Genetic program for Ardi goats through upgrading with Damascus is possible to improve meat production.

10.4103/2305-0500.220984

✉First and corresponding author: Mohammed KM, Animal Reproduction Research Institute, Agriculture Research Center, Giza, Egypt.

E-mail: kamel14@hotmail.com

Foundation project: This study was financially supported by King Abdulaziz City for Science and Technology, Saudi Arabia (No. ARP: 24-22).

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How to cite this article: Mohammed KM, Kamal EL-den MA, Dahmoush AY.Heritability and variance components estimates for growth traits in Saudi Ardi goat and Amascus goat and their crosses. Asian Pac J Reprod 2018; 7(1): 39-46.