Citation of this paper
Data from one hundred peal guinea fowls obtained from hatches of eggs collected from the University of Ilorin, Teaching and Research Farm were analysed using the general linear model for a completely randomised design to determine the phenotypic correlations among body weight, egg weight, egg index and egg quality factors as well as regression equations that can be used to establish models for predicting body weight.
The mature body weight for which the highest egg production parameter was recorded ranged from 1274 ±13g to 1288± 16g. The association between body weight and egg number was positive, indicating that the point of lay does not terminate actual weight increases in the guinea fowl. Simple linear regression of different parameters on age showed a poor fit as characterized by low coefficients of determination (R2) explained by the model.
Phenotypic improvement efforts in the pearl guinea fowl should be concentrated on establishing a uniform flock body weight of at least 1250g at sexual maturity. By so doing optimum egg production may be obtained to satisfy consumers demand, maximize profit for sale and improve fertility and hatchability.
Keywords: Body weight, egg production traits, Guinea fowl, sub-humid tropics.
Body weight is regarded as a function of framework or size of the animal and its condition (Philip 1970). One of the main factors influencing egg size and feed intake is body size (Robinson and Sheridan 1982; Summer and Leeson 1983). Variation in body weight within a flock can be attributed to genetic variation and environmental factors that impinge on individuals. (Ayorinde and Oke 1995). The poultry producer wants birds of minimum possible size and weights that will maximize production of standard sized eggs at an economic rate and still maintain market carcass value at the end of the production period. The relationship existing among linear body traits provides useful information on performance, productivity and carcass characteristics of animals. Most of the linear measurement reflect primarily the length of the long bones of the animal. When taken sequentially over a period of time, they generally indicate the way in which the animal body is changing shape and have been used as predictors of both animal live weight and carcass composition.
Body weight in poultry is known to be moderately to lightly heritable and hence the selection of heavier individuals in a population of guinea fowl, for example should result in genetic improvement of the trait. The relationships among live body measurement in egg-type poultry have been discussed by by Omeje and Nwosu 1984, Ayorinde et al (1988), Oni et al (1991) and Adenowo et al (1995). Breeders are thus interested in heritability of the traits and their genetic and phenotypic correlations. Evidence obtained by Du Plessis and Erasmus (1972) indicated that larger hens within a bloodline laid larger eggs than those with smaller body weights. This is supported by Ricklefs (1983) who reported that larger body size resulted in large egg length, width and mass, all factors affecting egg weight.
Though various factors are known to affect egg production, there is conflicting reports on the effect of body weight on egg production. For the development of egg production strains, it is necessary to establish the nature of the relationship existing between body weight of the guinea fowl and egg production parameters. Guinea fowl are nervous and shy (NRC 1991). They can be difficult to catch and when panicking they can easily suffocate their keets. They are very strong fliers which makes for difficulties in catching and holding the birds and may lead to injuries and accidental death when birds are frightened.
The study was therefore undertaken to determine the phenotypic correlations among body weight, egg weight, egg index and egg quality factors as well as regression equations that can be used to establish models for predicting body weight using linear body measurements.
One hundred female pearl guinea fowl obtained from hatches of eggs collected from the University of Ilorin Teaching and Research farm were used for the study. The keets were brooded for the first six weeks of life under continuous illumination in a brooder house. Thereafter, they were raised on deep litter under natural daylight until 26 weeks of age. At this age (26 weeks), the birds were sexed by vent examination and were randomly assigned to individual cages measuring 45.7 x 40.6 x 35.6cm and the wings banded to monitor individual body weight gain and egg production traits. The birds were weighed at the beginning of the experiment and fortnightly throughout the laying cycle.
Feed and water were given ad libitum throughout the experimental period. The birds were fed starter ration containing 23.9% C.P and 2994 kcal/kg ME during the first 8 weeks. A grower diet containing 20.0% C.P. and 2759 kcal/kg ME was fed between 8 and 20 weeks of age and layers diet containing 17.5% CP and 2650 kcal/kg ME was fed thereafter.
Records of age of first egg and daily egg production were kept. Egg trait measurements were taken on all eggs laid in the first week of each laying month throughout the laying cycle. The albumen and yolk height were measured with the aid of a spheromometer. Shell weight was obtained including the shell membranes using a sensitive top loading scale. A micrometer screw gauge was used to measure shell thickness. The average of the three readings at the broad, narrow, and mid section were taken as the shell thickness for each egg laid by a bird in the week. Egg index value was calculated as the ratio of the egg height to egg diameter.
Data collected were subjected to analysis of variance using the GLM procedures described by Steel and Torrie (1980). Estimates of phenotypic correlations (r) of the body traits on age were determined using the SPSS (1987) statistical programme. The regression model was of the type.
Y = a+bxi+ei
Y= dependent variable
a = intercept on y-axis
b = regression coefficient i.e. change in the dependent variable resulting from a unit change in the independent variable
x1 = independent variable (age)
e1 = residual error
The means of body weight and different egg traits are presented in Table 1. All birds made initial gains (P> 0.05) in body weight at housing but the rise in egg production resulted in reduction and in some cases fluctuation in body weight gains. The reduction or fluctuation in body weight gains following onset of egg production in the guinea fowl resulted in increased use of physiological reserve to meet the demand for egg production. Du Plessis and Erasmus (1972) and Ayorinde et al (1988) reported consistent reduction in body weight, which they attributed to increased use of physiological reserve to meet the demand for egg production.
|Table 1. Means ± SE of body weight and egg production traits at various ages (26-52 weeks)|
|Body weight, g||881||992||1047||1093||1163||1190||1260||1288||1276||1229||1274||1280||1280||1280|
|Egg weight, g||-||-||-||-||29.1||35.8||35.9||36.7||37.0||36.3||37.1||37.8||38.4||38.3|
|Shell thickness, mm||-||-||-||-||0.42||0.42||41||0.41||0.41||0.41||0.41||0.39||0.39||0.39|
|Shell weight, g||-||-||-||-||6.89||6.89||6.79||6.68||6.52||6.66||6.6||6.46||6.43||5.09|
|Albumen weight g||-||-||-||-||5.28||5.28||5.65||5.95||6.1||5.91||6.44||5.83||5.62||5.72|
|Albumen heigth, g||-||-||-||-||14.9||14.9||18.4||18.4||18.6||18.2||18.6||19.0||19.3||19.2|
|Yolk height, mm||-||-||-||-||15.4||15.4||16.0||15.8||16.4||15.9||15.6||16.0||16.2||16.2|
|Yolk weight, g||-||-||-||-||9.08||9.08||11.1||11.71 0.54||11.8||11.57||11.84||12.04||12.25||12.22|
Average body weight at first egg was 1163±85.02g. The mature body weight, when the highest egg production was obtained, was 1274 to 2883g. At this point the largest egg parameters were recorded. The average mature body weight (1266g) was close to the value of the same variety reported by Oguntona (1982), but higher then 1106g (exotic), and 1052g (pearl) in the sub-humid tropics reported by Ayorinde and Ayeni (1983). This explains a situation where within the same breed, strain or variety, individual variations in performance are common observations. Such individuals that are capable of high performance should be exploited in selection and breeding practices (Chineke 2001). The body weight and growth pattern of the local guinea fowl suggests that it is closer to a light egg-type laying breed in view of the low mature body weight despite its initial rapid growth rate.
There was a tendency for egg number, egg weight, yolk weight and albumen weight to increase increase in body weight and age. This observation is supported by the findings of Olori and Sonaiya (1992) and Asuquo (1994). Shell weight and shell thickness remained constant throughout the laying period with a slight drop in shell weight towards the end of lay. Render et al (1984) also found that shall weight stayed constant through the laying period. In contrast, Tyler (1960) found that eggshell weight decreased with advancing age in birds.
The association between body weight and egg number was low but positive (r = 0.36) (Table 2). Ayorinde et al (1988) noted a fairly high association between egg production and weight gain in the black and pearl guinea fowl. This means that point of lay does not terminate live weight increases in the guinea fowl. The positive association between body weight and egg number in this study contrasts with the finding of Harms et al (1982), Oluyemi and Roberts (1979), who reported a negative correlation between body weight and egg number and that egg weight increased with body weight in a linear fashion from the onset of egg production. Analysis of response of egg weight to body weight reveals a positive but low relationship (r = -.20. Evidence obtained by Everett and Olusanya (1985) indicated that larger hens within a bloodline laid larger eggs than those with smaller body weight. This is supported by Ricklefs (1983), who reported that larger body size resulted in large egg length, width, and mass, all factors affecting egg weight.
Table 2. Correlation coefficients among body weight and egg production traits
AH = Albumen
height, BW = Body weight, EB= egg breadth, EL= Egg length, EN= Egg Number,
EW= Egg Weight,
ST = Shell thickness,
YD = Yolk Diameter. YH= Yolk height, YW= Yolk weight
The magnitude of the coefficient of determination (R2) for each parameter in the regression equations (Table 3) shows the relative contribution of each body measurement to the body weight of the guinea at 44 weeks of age. The only significant relationship (R2 = 0.69) was between egg weight and body weight at 44 weeks. Du Plessis and Erasmus (1972) found that age at sexual maturity showed a constant and significant effect on egg weight in each month of the year, which agrees with the findings in this report.
|Table 3. Simple linear regression parameters for the different variables on body weight at 44 weeks of age|
|Traits||Const. (a)||Regr. Coff||R2||S E||Sign|
|AH= Albumen height, AW=Albumen weight, EB= Egg breadth, EL= Egg length, EN= Egg Number, EW= Egg weight, ST= Shell Thickness, SW= Shell weight YD= Yolk Diameter, YH= Yolk height, YW= Yolk Weight|
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Received 6 May 2004; Accepted 21 May 2004
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