Phenotypic characterization and weight estimation from linear body traits of West African Dwarf goats reared in the transitional zone of Ghana

P T Birteeb and R Lomo

Department of Animal Science, Faculty of Agriculture, University for Development Studies, P. O. Box TL 1882, Tamale, Ghana.
bpetert2000@yahoo.com

Abstract

The knowledge of weight estimation and phenotypic characterization is paramount in goat production and marketing practices hence this research was undertaken to characterize West African Dwarf (WAD) goats phenotypically and develop a model for predicting the weight of WAD goats in the Transitional zone of Ghana. Body weight (BW), linear body measurements (heart girth-HG, body length-BL, height at withers-WH, rump height-RH and tail length-TL), and coat colour pattern were measured on 325 goats from the National Goat Breeding station at Kintampo and subjected to chi-square, general linear model, correlation, principal component factor and regression analyses.

 

The results revealed that goats having two colours dominated (61.2%), and brown colour was very common as a solid or in combination with other colours. The overall averages of 60.6±0.6, 51.7±0.4, 46.5±0.4, 48.6±0.4, 9.3±0.2cm, and 27.6±0.5 kg were obtained for HG, BL, WH, RH, TL and BW respectively. Male and female goats were generally similar in most of the traits except WH (P = 0.03). Coat colour did not have any significant influence (P > 0.05) on any trait. Phenotypic correlation between pairs of body traits ranged from low to moderate (0.09 – 0.71), with highest correlation being between BW and BL. Two principal component (PC) factors were extracted to explain body composition:  the first PC consisting of HG, BL, HW, and RH explained 58.2% of total variation; the second PC (TL) accounted for 20.3%. The first PC indicated the general body size of the goats. The combination of HG and BL yielded the best accuracy (64.5%) in weight estimation, while prediction from the two PC’s was only moderate (62.3%). The explained body variations can be exploited by the goat breeding station and individual researchers in selection programs to improve goat breeding in the transitional zone in the country.

Key words: body weight, characteristics, principal component

Introduction

The characterization of local genetic resources depends on the knowledge of the variation of morphological traits, which have played a very fundamental role in classification of livestock based on size and shape (Yakubu et al 2010a).   Size and conformation are important characteristics in meat animals especially ruminants. Traditionally, animals are usually assessed visually, which is a subjective method of judgment (Abanikannda et al 2002). Body size and shape measured objectively could improve selection for growth by enabling the breeder to recognize early maturing and late maturing animals of different sizes. Measurement of various body conformations are of value in judging quantitative characteristics of meat animals and are also helpful in developing suitable selection criteria. Body measurements and live weights taken on live animals have been used extensively for a variety of reasons both in experimental work and in selection practices (Lawrence and Fowler 2002). Body measurements have been used to evaluate breed performance and to characterize animals. In addition, they have been used as a means of selecting replacement animals (Sowande and Sobola 2008).

 

The knowledge of morphological body measurements of goats could be exploited to aid adequate management and production of goats. Afolayan et al (2006) stated that the accuracy of functions used to predict live weight or growth characteristics from live animal measurements is of immense financial contribution to livestock production enterprise. Several researchers have shown that body measurements provide great convenience for the prediction of body weight without weighbridges or scales (Birteeb and Ozoje 2012; Okpeku et al 2011; Yakubu 2009; Pesmen and Yardimci 2008; Adeyinka and Mohammed 2006; Afolayan et al 2006).

 

The West African Dwarf (WAD) goat is a common and popular breed in Ghana. WAD is a major component of the indigenous livestock genetic resources especially in the rural communities of Ghana. This breed is well adapted to, and produces and reproduces under the local environmental conditions although its productivity is generally low compared to its counterparts in other parts of the world. Uncontrolled breeding coupled with attempts by breeders and farmers to improve the performance of the indigenous African breeds through the introduction of exotic animals and crossbreeding practices are gradually leading to the erosion and complete masking of important survival traits, such as disease resistance associated with indigenous livestock as well as the extinction of certain breeds (Gizaw et al 2011). The characterization of African small ruminant populations will play a major role in the maintenance of these autochthonous genetic resources as the basis for future improvement at both the production and the genetic levels (Birteeb et al 2012).

 

Knowing the morphological measurements of WAD goats will be very useful for good animal management, including understanding medication doses, adjusting feed supply, monitoring growth and choosing replacement males and females (Slippers et al 2000). Knowledge on method of weight estimation will also be very useful in goat production since most farmers do not have weighing scales for measuring liveweight. Therefore, this study was conducted to characterize the WAD goat phenotypically and to determine suitable model(s) for liveweight prediction from body measurements. 

Materials and Methods

Study area and climate

 

The study was conducted at the National Goat Breeding Station at Kintampo in Ghana. Kintampo is located on latitude 8º03’ N and longitude 01º43’W (Ghana Districts 2014). The area falls within the transitional or derived savannah ecological zone, having a mixture of tall trees, shrubs and grasses as the vegetation type.  The mean annual rainfall is about 1300 mm.  About 69% and 31% of the rains occur in the wet (April-October) and dry (November-March) seasons, respectively.  The mean monthly temperature is about 27^oC while relative humidity values are 73.8% at 09.00 h and 56.7% at 15.00 h (Karikari and Blasu 2009).

 

Management of experimental animals

 

The animals were kept on-station where they grazed on cultivated pastures made up of Cynodon plectostachyus, Cajanus cajan, Stylosanthes spp, Panicum maximum, Panicum minimum and Ficus spp established by the station. They were supplemented with feed made up of wheat bran, maize chaff and cotton seed cake. The animals were regularly vaccinated and dewormed against diseases and pests. The animals were housed at night in roofed pens with concrete floors. Clean water together with mineral supplement/salt licks were provided ad-libitum after grazing.

 

Data collection

 

A total of 325 (29 males and 296 females) matured WAD goats were randomly sampled from the breeding station. The parameters measured were; Rump height (RH), Height at withers (HW), Body length (BL), Wither height (WH), Tail length (TL), Heart girth (HG), live body weight (BW), Coat colour, animal’s age and sex.

 

The live body weight (Kg) of the animals were measured using Griffith electronic weighing scale and linear body measurements (LBM’s) taken using a tailor’s measuring tape graduated in centimeters. The procedures for measuring the (LGM’s) are outlined below as described by Birteeb et al (2012).

 

Height at Withers (WH): The distance from the surface of a platform on which the animal stands to the withers.

Heart Girth (HG) or Chest circumference: It is a circumferential measure taken around the chest just behind the front legs and withers.

Body Length (BL): It is the distance from scapula (at shoulder) to the pin bone.

Rump Height (RH): The distance from the surface of a platform to the rump.

Tailed Length (TL): This is a measurement taken from the base of the tail to the tip.

Visual assessments were made in identifying the qualitative traits like coat colour and sex.

The ages of animals were traced using the date of birth as individual animals were identified by tags.

Statistical analysis

 

The data set was analyzed using SPSS version 17. The chi-square goodness of fit test was done for distribution of sex, age and colour. The fixed effects of sex, age and colour on linear body measurements were tested using general linear model (GLM), the model given as:

Where Y_ijk = individual observation of each body traits;

μ = overall mean;

S_i = fixed effect of ith sex (i = male, female);

A_j = fixed effect of jth age (j = 1 year old, 2 years old, and ≥ 3 years old);

C_k = fixed effect of kth colour pattern (k = unicolour, bicolour, tricolour);

(SA)_ij = interaction effect of ith sex and jth age;

(SC)_ik = interaction effect of ith sex and kth colour pattern;

(AC)_jk = interaction effect of jth age and kth colour pattern;

(SAC)_ijk = interaction effect of sex, age and colour pattern;

ε_ijk = random error associated with each record (ε ~ N(0, σ²))

 

Bivariate phenotypic correlations among the morphological measurements were determined using Pearson’s correlation coefficient. The body composition of the goats was then analyzed by employing Principal Component Factor Analysis (PCA). The Kaiser-Meyer-Olkin (KMO) measure of sampling adequacy and Bartlett’s Test of Sphericity were employed to determine the validity and accuracy of the data set for factor analysis. The appropriateness of the factor analysis was further tested by examining the communalities. Body weight was then regressed on linear body measurements and the extracted principal components (PC) to test their use in predicting body weight of goats.

Results and discussion

Distribution of the qualitative traits of WAD goat

 

There was unequal representation of the different colours (Table 1). The animals had about ten coat colour patterns with the dominant being pied brown and white coat colour combination. The tricolour pattern comprised the combination of any three of brown, black, white and grey. Clearly there is a large variability in coat colour pattern. The dominant occurrence of brown colour (as solid or in combination with other colours) may suggest the association of this colour with a trait that is selected for at the station. The study agreed with that of Hassen et al (2012)  in which coat colour patterns observed were brown, white, black with  the most frequent coat colour being  white with spots (20.7%), followed by brown with patches (17.5%) and brown (15.4%). In Ethiopia, there were varied coloration patterns amongst the goat populations sampled with spotted pattern (36.1%) followed by patchy (32.4%) and plain (30.4%) of various colors. Black colored animals, however, are believed to have superior adaptation to seasonal cold weather or cold nights as the dark pigment helps them to warm up earlier than goats with other coat colors (Robertshaw 2006).

Quantitative traits of West African Dwarf goat

 

Goats in the present study were similar in linear body dimensions to the indigenous goats of Benin (Dossa et al 2007), but weighed heavier than all goats in Okpeku et al (2011) although the Red Sokoto had higher wither height and chest girth. However, the goats in the present study were quite small and very light when compared to Saanen goats (Pesmen and Yardimci 2008).  The fixed effects of sex, coat colour and age on the body traits are presented in Table 2. Among the traits only height at withers was influenced by sex, where the nanny goats were longer than billy goat counterparts. All other traits were similar for both sexes (Table 2). This finding disagrees with the report in goats (Okpeku et al 2011) and sheep (Birteeb et al 2012) in which males were superior to females in all the body measurements.  Age affected all measured traits except tail length (Table 2). [T3] The present finding is similar to Yakubu (2009) where only HW was significantly influenced by sex. The ten colour patterns were categorized into uni-colour (solid coat colour), bi-colour (two coat colours) and tri-colour (three combined colours) to determine colour effect on the traits. Coat colour had no influence on any body measurements in the flock under study.