Growth performance of Boer goats and their F1 and F2 crosses and backcrosses with Central Highland goats in Ethiopia

Amine Mustefa, Solomon Gizaw¹, Sandip Banerjee², Ayele Abebe, Mestawet Taye², Alemnew Areaya and Shanbel Besufekad

Debre-Birhan Agricultural Research Center, P. O. Box 112, Debre-Birhan, Ethiopia.
aminemustefa32@gmail.com
¹ ILRI (International Livestock Research Institute), P. O. Box 5689, Addis Ababa, Ethiopia.
² Hawassa University College of agriculture, Hawassa, Ethiopia.

Abstract

This study aims to investigate genetic and non-genetic factors affecting growth performance of Boer goats and their crosses with Central Highland goats (CHG) reared on-station at Ataye site of Debre-Birhan Agricultural Research Center in Ethiopia. A total of 512 kids of Boer (B), F1 (B X CHG) and F2(a) (F1 X F1) crossbreds and backcrosses F2(b) (B X F1) born from 381 kiddings recorded between 2012 and 2017 were used for the analysis of body weight at birth, at weaning, at six-month, at yearling and body weight gain to weaning, weaning to six-month and six-month to yearling. The overall least-squares means across genotypes for birth weight (BW), weaning weight (WW), six-month weight (6MW), yearling weight (YW) were 3.05±0.06 kg, 10.9±0.36 kg, 12.5±0.51 kg and 18.3±0.88 kg, respectively for Boer and 2.62±0.04 kg, 8.80±0.22 kg, 11.2±0.31 kg and 16.7±0.48 kg, respectively for F1. Similarly, the BW and WW of the F2(a) and F2(b) were (2.50±0.13 kg and 8.37±0.74 kg) and (2.94±0.15 kg and 9.80±0.75 kg) respectively. The overall least-squares means across breed groups for daily weight gain to weaning, weaning to six-month and six-month to yearling were 83.9±3.76 g, 25.6±3.29 g and 27.6±2.69 g, respectively for Boer, and 67.0±2.26 g, 31.5±2.00 g and 28.4±1.46 g, respectively for F1. Similarly, daily weight gains to weaning was 67.7±7.66 g and 78.7±7.74 g for the F2(a) and F2(b) respectively. Sex, type of birth, year of birth and season of birth affected the studied traits, while, doe parity has no significant effect except at the later age weight gain. In conclusion, the overall growth performances of all the studied genotypes were below expectations which indicates their sub-optimal adaptability to the study area. In addition to the genotype, the non-genetic factors affect the growth performance, so improvement in growth performances is possible by minimizing environmental effects.

Key words: body weight, cross-breeding, genotype, non-genetic

Introduction

Ethiopia houses 12 recognized indigenous goat breeds including Central Highland Goats (Tesfaye 2004: Farm-Africa 1996). Like all Ethiopian indigenous goats, Central Highland Goats (CHG) generally have low body weight and suboptimal growth when compared to some tropical and temperate breeds (Judith 2006; Dereje et al 2015). In order to optimize the production from the flocks both the genotype (of the flock) and the environment (where they are reared) need to be improved (Falconer 1989). The environment (where the goats are reared) can be improved through proper nutrition, veterinary care and management. Similarly, the genotype of the flock can be improved either through within breed selection or through crossbreeding using exotic breeds (Falconer 1989).

Even if improving the genotype through within breed selection can be sustainable when compared to crossbreeding viz. adaptation and stable genetic gain, it is usually a time consuming process with genetic gain/generation being as low as <5% (McDowell 1972, 1988). Due to the reason that crossbreeding of goats can lead to their rapid improvement by enhancing their genetic performance (Cunningham and Syrstad 1987), it is taken as a useful and an option of choice.

Over the years several goat breeds including Saanen, Anglo-Nubian, Toggenburg and Boer goats have been introduced in the country under different projects (Alemu and Merkel 2008). Among the recently conceived crossbreeding project, ESGPIP (Ethiopia Sheep and Goat Productivity Improvement Program) was initiated under USAID program which imported Boer goats to different locations in the country. There was different breeding, evaluations and distribution (BED) sites in Amhara region where Boer goats were introduced including Ataye site of Debre-Birhan Agricultural Research Center under Amhara Regional Agricultural Research Institute in 2012.Boer goats are considered to be one of the most desirable mutton type breeds globally with the highest mature weight of 100-110 kg. It has been reported that the Boer goats can improve productive performance of many indigenous breeds where the crossbreds have outperformed the native breeds in many aspects (Erasmus 2000; Lu and Potchoiba 1988; Casey and Van Niekerk 1988; Lu 1989). The traits, which showed significant improvement among the crossbreds were birth weight, and growth related traits (weaning weight, weight at mating, mature body weight), prolificacy and fecundity besides carcass quality (Cameron et al 2001). Thus, this study was aimed to identify the factors affecting the on-station growth performances of Boer and their crosses with Central Highland Goats reared at the farm and to evaluate the growth performances of the above genotypes.

Materials and Methods

Description of the study area and the genotypes

Data for the growth performances were obtained from the on-station pure and cross-breeding programs carried out at Ataye site of Debre-Birhan Agricultural Research Center (DBARC), North Shoa zone, Ethiopia which is located at 285 km North of Addis Ababa. The geographical location of the area is 1491 m above sea level, 10o 35’ N latitude and 39o 93’E longitude. The climate of the area is warm with annual minimum and maximum temperatures of 12.6 °C and 30.1°C respectively. The area receives an average annual rain fall of 969 mm (Girma and Desta 2007). Based on the rainfall pattern and green feed availability, the season of the study area was divided in wet and dry season. Months within the wet season are March, April, July, August, September and October while January, February, May, June, November and December are within the dry season (Girma and Desta 2007).

The Central Highland goats belong to the Small East African family and are medium-sized, broad-faced, have thick horns and are predominantly reddish-brown in colour. Other features of the breed include facial profile straight (71%) or concave (29%). The breeding tract of Central Highland goats extend from many parts of Tigray, Eastern Amhara and Central Ethiopia region. These goats are the source of Bati Genuine skin. They are moderately prolific with adult body weight of 30.1 kg (Solomon 2009). They were bought from the local market available around the site and quarantined at Debre-Birhan and Ataye respectively while the Boer goats were imported from South Africa and quarantined at Sebeta before transported to the research station. The kids available at the location include Boer kids, F1 kids (Boer x CHG), F2 kids (F1 x F1) and 75: 25 % Boer: CHG kids (Boer x F1).

Goat management

Most of the time the Boer goats and their crossbred kids were kept in-door being offered ad libitum grass hay, chopped pasture (Napier grass, Desmodium spp. and vetch) and commercially prepared concentrate (300 - 500 g/head/day to the adults and 100 – 200 g/head/day to the kids based on their body weight and the feed availability across the year). Fetched water (from a nearby river) was provided twice a day. On the other hand, the Central Highland Goats were allowed to browse twice a day (morning and afternoon), with ad libitum grass hay and commercial concentrate (200-300 g/head/day based on their body weight) once in the afternoon, The CHG walked to the nearby river (twice a day) to quench their thirst. The health care of all the goats were ensured by a qualified veterinarian who provided strategic deworming and regular follow-up of treatments on case to case basis. The goats and the barns were regularly sprayed with acaricides so as to make them free from external parasites.

The bucks were selected for joining the does for breeding purpose and the does which were considered pregnant were regularly taken away to a separate pen, while those which were still barren were still allowed to be joined with the buck. The mating was so ensured to minimise inbreeding among the flocks. The average buck to doe ratio was 1:20/25, the breeding (pure and crossbreeding) were arranged in separate pens mostly for a period of one to three months, during which it was considered that all the does were covered.

Data collection

A total of 512 kids of Boer (B), F1 (B X CHG), F2 (a) (F1 X F1) and F2 (b) (B X F1) born from 381 kiddings recorded between 2012 and 2017 were used for the analysis. The data recorded were birth weight (BW), weaning weight (WW), six-month weight (6MW), yearling weight (YW) and average daily weight gain to weaning, weaning to six-month and six-month to yearling. Data on body weights were recorded in the morning prior to grazing and watering. Kids were also categorised into those born as single, twins or triplets. However, as the sample size was limited the type of birth were broadly classified as those born single and multiple. Similarly, the parity of the does was categorized as 1st, 2nd, 3rd and ≥ 4th. Parities above 4th were merged together.

Statistical analysis

The data were analyzed using the GLM procedure of SAS 9.0 software. Means were compared using Tukey-Kramer (SAS 2002). The collected data on the growth performances (body weight traits) were adjusted using the following standard adjustment formula.

Where;
BW= Birth weight
ADJWWT = Adjusted weaning weight
ADJ6MWT= Adjusted six-month weight
ADJYWT=adjusted yearling weight
PrWADWG= Pre-weaning average daily weight gain
W-6MADWG= Weaning to six-month average daily weight gain
6M-YADWG = Six months to yearling average daily weight gain
W2= Weight at given age D (D = weaning age)
W3= Weight at given age E (E = six-months weight)
W4= Weight at given age F (F = yearling age)

The model used for the analysis was 

Y_ijklmn = μ + A _i + B _j + C _k +D_l + E _m + F _n + e _ijklmn

Where Y_ijklmn is an observation, μ is the overall mean, A_i is the fixed effect of the kid sex, B_j is the fixed effect of the kid breed gropu, C_k is the fixed effect doe parity, D_l is the fixed effect type of birth, E_m is the fixed effect of year of birth, F_n is the fixed effect of season of birth and _eijklmn is the random error attributed to the n^th kid.

Due to the non-significant effects of the interactions among the above factors, it was removed from the analysis and results.

Results

Body weight birth to yearling age

The results of the effects of breed group, sex, doe parity, type of birth, year and season of birth on birth, weaning, six-month and yearling weight of Boer, F1, F2(a) and backcross F2(b) are presented in Table 1. The results indicate that buckling had higher (p<0.01) weight at birth, six months and yearling when compared to the doeling. The results also indicated that the Boer kids had higher (p<0.0001) weight at birth and at weaning. During the same period the kids of F2(b) crosses followed the Boer observation at the birth and weaning weight. There were no differences across the parities for the traits included in the study. The results further indicated that kids born single weighed more than those from multiple births. The effect of year has a significant (p<0.0001) effect on the studied traits, with higher birth and weaning weights recorded among the kids born in 2017 while those born in 2016 had highest six-month weight and yearling weight (this is because of non-availability of the data for 2017). Furthermore, the season of birth influenced (p<0.0001) most of the studied traits with kids born in the wet season weighing the heaviest and so were they at the weaning weight.

Pre and post-weaning daily weight gain

The results pertaining to the effects of breed group, sex, doe parity, type of birth, year and season of birth on daily weight gain to weaning, weaning to six-month and six-month to yearling age are presented in Table 2. The findings indicate that pre-weaning daily weight gain was similar across both the sexes while the buck kids gained more (p<0.001) at the post-weaning period (Table 2). Pre-weaning daily weight gain differences across the genotypes too were observed with Boer kids gained more (p<0.01) when compared to their counterparts from other genotypes followed by those of F2 genotypes. But no significant post-weaning weight gain difference was observed among the genotypes.

Doe parity did not influence (p>0.05) the pre and post-weaning daily weight gains except the daily gain six-month to yearling age in which kids from 4th and 2nd parities gained more. On the other hand, the single born kids gained more weight till weaning with no differences recorded thereafter in the trait. Birth year too significantly (p<0.0001) affects pre and post-weaning daily weight gains; with kids born in 2017 gained more pre-weaning daily weight gain followed by those kids born in 2016. At the post-weaning period (with lack of information on kids born in 2017) kid born in 2016 and 2014 gained more than the kids born from the other years. Season of birth only influenced the pre-weaning daily weight gain significantly (p<0.01) with kids born at wet season gained more, while no post-weaning daily weight gain differences were observed due to season of birth.

Discussion

Body weight birth to yearling age

The birth weight of the Boer kids in this study are comparable with reports by Abd-Allah et al (2015) and Ince (2010) among Boer and Saanen kids respectively. Higher weights have been reported by Đuričić et al (2012) and Hasan et al (2014) among Boer and Ettawa kids respectively. The birth weight of the Boer kids in this study was higher than those reported by Faruque (2010), Shaat et al (2007), Thiruvenkadan (2009) and Alemu (2015) among Black Bengal, Zaraibi, Tellicherry and CHG kids, respectively.

The birth weight of the crossbreds studied here agree with Boer x CHG crossbreds means of Deribe et al (2015). Lower weights have been reported by Ssewannyana et al (2004) among Boer x Mubende 50% and Boer x Teso 50% crosses. The birth weight in this study were lower than those reported by Debele et al (2015) and Girma et al (2016) among Boer x Arsi Bale kids and Boer x Woyito-Guji 25 % crosses.

The results of weaning weight of the Boer kids indicated similarity with the reports of Hasan et al (2014); Shaat et al (2007) and Alemu (2015) among Ettawa, Zaraibi and CHG kids, respectively. However, higher weaning weight was reported by Abd-Allah et al (2015) and Ince, (2010) among the Boer and Saanen kids, respectively. The weaning weight of the Boer kids in this study were also higher than those reported by Abd-Allah et al (2015) and Thiruvenkadan, (2009) among Baladi and Tellicherry kids, respectively. The results of the weaning weight of the crossbreds also indicated similarity with the reports of Deribe and Taye (2013) among the CHG goats. Higher weaning weight was reported for Boer x Arsi bale, Boer x CHG and Boer x Woyito-Guji 25 % crossbreds as reported by Debele et al (2015), Deribe et al (2015) and Girma et al (2016).

The results of the six-month and yearling weight of the Boer goats agree with those of Thiruvenkadan (2009) in Tellicherry kids. However, the values were lower than those found by Shaat et al (2007); Abd-Allah et al (2015); Hasan et al (2014) and Alemu (2015) in Zaraibi, Boer, Ettawa and CHG goats, respectively. Similarly, the six-months and yearling weight of the crossbreds in this study are lower than those by Deribe et al (2015) and Girma et al (2016) in Boer x CHG and Boer x Woyito-Guji (25 %) crossbreds.

Pre and post-weaning daily weight gain

The results of pre and post-weaning daily weight gains of the different kid breed groups in this study were lower than reported by Debele et al (2015); Derib et al (2015); Deribe and Taye (2013) and Shaat et al (2007) in Boer x Arsi bale, Boer x CHG, CHG and Zaraibi kids.

Factors affecting growth performances

• Kid sex

Buckling were higher (p<0.01) than doeling in most growth traits which follows the Rensch's rule (Rensch 1950) where the males of a particular species are usually heavier than the females. The differences between the buck and doe kids may be further ascribed to testosterone hormones secreted by the buck kids results in enhancement of muscle mass and skeletal development (Baneh and Hafezian 2009). The sexual dimorphism of the kids may be ascribed to the differences in the endocrine system of the two sexes; estrogen hormone has a limited effect for growth in females (Baneh and Hafezian 2009). Similar observations among the goats of Arsi-Bale,Boer x Woyito-Guji 25 % and Tunisian local goat breed were reported by Dadi et al (2008); Girma et al (2016) and Mabrouk et al (2010), respectively. Contrary to the present findings Derib et al (2015) reported no significant differences in the weight of yearling bucks and does of Boer x CHG crossbreds.

• Kid breed group

The results also indicated that the Boer kids and their high crosses had better (p<0.0001) growth performances. This can be ascribed to the higher proportion of paternal genes (from the Boers). The findings agree with the findings of Sanchez et al (1994) who reported that the higher crosses with exotic breeds have more than intermediate body weight at all ages. Care has to be taken to rear the higher crosses especially under the farmers’ condition as they may perform poorly than the local breeds due to some adaptation problems, thereby the overall performance can be lower than the F1 crosses (Lipson et al 2011).

• Doe parity

There were no differences across the parities for most of the traits which may be due to above average lacteal yield of the dams which satisfies the need of the kids. The results are partially in line with the reports of Dadi et al (2008) who worked on Arsi-Bale goats. However, they are contrary to the observations of Hoque et al (2002) Otuma and Onu, (2013) and Thiruvenkadan (2009) on different Goat breeds. It is expected that lactation yield be lower in the first parity which shows an increase in the subsequent lactations thereafter decreasing as the doe ages (Zhang et al 2009). Similarly, effect of parities was expected due to differences in maternal effects, nursing and maternal behaviour of dam in different ages (King 2009). The differences due to parity in the later age daily weight gain may be ascribed to the effect of long term weaning shock among the kids (Abebe 2008). This may also be because all the kidding may have not taken place in the same season thereby influencing the weaning shock (Abebe 2008).

• Type of birth

Kids born single weighed more than those from multiple births. This observation is agreeing with the reports of Mabrouk et al (2010), King (2009), Đuričić et al (2012), Ince (2010), Andries (2013), Hasan et al (2014), Thiruvenkadan (2009) and Alemu (2015) in different goat breeds. This difference can be due to limited uterine space during pregnancy for multiple birth and competition for milk suckling between the multiple born kids during birth to weaning (Al-Shorepy et al 2002). Similarly, as the number of fetuses increases, the number of caruncles attached to each foetus decrease thus resulting in the reduction of feed supply to the foetus and hence the birth weight of those kids decreases in multiple births (Robinson et al 1977). These observations are in close accordance with the reports of Mabrouk et al (2010), King (2009), Đuričić et al (2012), Ince (2010), Andries (2013), Hasan et al (2014), Thiruvenkadan (2009) and Alemu (2015) in different goat breeds.

The findings also show that the pre-weaning daily weight gain among the kids born as single births were higher. However, compensatory growth among the kids born as multiple birth narrowed the gap thereby leading to no significant differences. These observations agree with the reports of Thiruvenkadan (2009) on Tellichery Goat breeds. These differences may be ascribed to low birth weight of the kids born as multiple births where kids having larger birth weight gained more body weight during pre-weaning period (Kuthu et al 2013; Thiruvenkadan 2009).

• Year of birth

The effect of year of birth has significant effect on the studied traits with no clear trend as the year of birth proceed. These results are in close accordance with the reports of Mabrouk et al (2010), Al-Najjar et al (2010); Otuma and Onu (2013); Zhang et al (2008); King (2009); Schoeman et al (1997) and Zhang et al (2002) who reported body weight of different breed of goats and their crosses differed across different years of birth. This can be due to temporary environmental effects like variations in incidences of diseases, availability of fodder, management, sample size and climate (differences of rainfall which in turn influenced grass production and feed availability) (Gunawan and Noor 2006; Zhang et al 2008; Gebrelul et al 1994; Al-Shorepy et al 2002).

• Season of birth

Furthermore, the season of birth influenced (p<0.0001) the early age growth traits with kids born in the wet season weighing the heaviest and so were they at the weaning weight. This can be due to the maternal effect (milk yield variation), as it can be associated with variations for rainfall that in turn affected pasture production and feed availability (Al-Shorepy et al 2002; Otuma and Onu 2013). The findings are in close accordance with the findings of Andries (2013) at Frankfort Kentucky. Season of birth did not affect the later age growth traits as the effect of season is generally low among animals reared under intensive/semi intensive management when compared to those reared under extensive management (Lipson et al 2011). It has also been suggested that the effect of season on growth is higher among the animals reared in the temperate climate whereas effect of season is generally low among the animals reared in the equatorial zone (Lipson et al 2011).

Conclusions

Growth performances were significantly affected by both the genotype and environmental factors. Boer goats outperformed the crossbreds in the studied traits, but significant differences were not observed at the later age, which may be due to the small number of observation. The overall growth performance of the studied genotypes shows irregular trend as the year of birth progresses. This study revealed that improvement in growth performances is possible by minimizing the effect of non-genetic factors. Based on this study the overall growth performances of the Boer goats were below expectation (in comparison to their native area performances), which indicates their sub-optimal adaptability to the study area. Therefore, in terms of conserving our indigenous animal genetic resource it is recommended to bring improvement through within breed selection.

Acknowledgement

The authors want to thanks the Head and staff of Debre Birhan Agricultural Research Center of Amhara Agricultural Research Institute and School of Animal and Range Sciences, College of Agriculture, Hawassa University.

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Received 6 February 2019; Accepted 25 April 2019; Published 4 June 2019

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