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Reproductive traits of the indigenous Guinea fowl under tropical humid conditions; the effect of egg size

G Adu-Aboagye, J K Nyameasem, K M J Ahiagbe, K O Ansah, G A Zagbede and K K Agbe

CSIR-Animal Research Institute, P O Box AH 20, Achimota, Ghana
gaduaboagye@gmail.com

Abstract

Fertility and hatchability are significant constraints in guinea fowl production. The current studies were therefore conducted to provide information about reproductive traits of the local guinea fowl and to establish the effects of egg size on fertility, hatchability and keet weight of the local guinea fowl. Two different studies were conducted. In the first one, a total of 600 8-week-old guinea fowls with a mean live weight of 285 12 g were tagged, weighed and randomly assigned to three-floor pens, each consisting of 200 birds. Birds were monitored for weight changes, age of first egg and number of eggs laid per day until the 44th week of age. The birds were fed standard poultry diets form each growth stage. In the second study, a total of 411 settable eggs were collected for 6 days and then placed in the incubator for 28 days. Results showed that the guinea fowls started laying at the age of 24 weeks of age with a mean body weight of 1.88 kg. The mean age at first lay, mean body weight at first lay and weight of first egg were 24 weeks, 1.88 kg and 29.6 g, respectively. The fertility rate of the guinea fowl was 56.9% whereas the hatching rate was 82.2%. There was a logistic relationship between egg size (weight) and hatchability and linear relationship between egg size and the weight of Guine keets after hatching (p<0.001). In contrast, egg size had a negative relationship (p<0.01) with weight loss during incubation. Effect of egg size on fertility was also positive (p>0.05). Our results suggested medium to large eggs (>38 g) as having a higher probability of being hatched compared to smaller eggs (<38 g).

Keywords: hatchability, fertility, incubation, logistic model, Numida meleagris, Sub-Saharan Africa


Introduction

The livestock sector is an essential component of agriculture in Ghana and plays a multifaceted role in providing livelihood support to many Ghanaians, especially the rural population (MoFA 2016). Whereas the agriculture sector of Ghana recorded a growth of 4.8% in 2018, the livestock sub-sector grew by 5.4% in the same year (Ghana Statistical Service 2019). Among the several species of animals reared, indigenous poultry contributes significantly to the incomes and are a source of protein for many households. According to WAAPP (2012), there are over 20 million indigenous fowls in Ghana. It is also estimated that 80% of households have on the average, 10-15 birds and these are kept for eggs, meat and cash. The guinea fowl ( Numida meleagris), which is indigenous to Africa and derives its name from the Coast of Guinea specifically in the West Coast of Africa (Teye and Gyawu 2002), is domesticated poultry and commonly found in West and Central Africa and most European countries. In Ghana, guinea fowls were traditionally reared in the northern regions until recent times when it has been introduced to other parts of the country like the Volta, Brong Ahafo, Ashanti and Greater Accra regions.

Guinea fowl production as a meat bird has proven to be a viable and profitable enterprise, thus giving the opportunity for commercialisation in many parts of the globe (Nahashon et al 2006). It is a promising local poultry species and economically more suitable to be reared in the tropics. In many European countries like France, Italy and developing countries like Ghana, guinea fowl production has already been proven to be profitable (Embury 2001; Agbolosu et al 2012). These species have a high ability to survive under the poor condition of management than exotic chicken (Agbolosu et al 2012).

Fertility and hatchability are significant constraints in guinea fowl production. Both traits are low at the beginning of the breeding season but reach their peak three months later (Teye and Adam 2000). Guinea fowl eggs exhibit low hatchability than chicken eggs mainly because of their thicker eggshells and size of the egg (Yamak et al 2016a). According to Nwagu (1997), the main factors that affect hatchability are egg size and shell thickness. Obioha (1995) stated that hatching eggs must not be too small or too big as egg size is known to affect the growth or subsequent weight of domestic fowl (Oke et al 2004). Despite the potential and popularity of the bird, it has remained unimproved either as meat or egg-laying bird in Ghana. Studies about guinea fowl in terms of laying pattern, egg number, egg size, fertility, hatchability and early growth traits are limited. The current studies were therefore conducted to:

i. provide information about reproductive traits of the local guinea fowl

ii. establish the effects of egg size on fertility, hatchability and keet weight of the local guinea fowl.


Methods and materials

Study Area

The study was conducted at the CSIR-Animal Research Institute on the Accra Plains of southern Ghana (543’40” N, 008’20” W, 57 m a.s.l). The area has a bimodal rainfall pattern with a major wet season occurring from April to July and a minor season from September to November. The remaining months constitute the dry period. Annual rainfall and a temperature range between 600-1000 mm and 15-34C, respectively (Okantah et al 2005).

Animals and design of the studies

Two different studies were conducted to study the laying pattern and characteristics of guinea fowl, the growth performance of guinea keets and the effect of egg size on fertility and hatchability. For the first experiment, a total of 600 eight-week-old guinea fowls with a mean live weight of 285 12 g were tagged, weighed and randomly assigned to three-floor pens, each consisting of 200 birds. Each of the concrete floor pens had 360 210 420 cm dimensions, representing a replicate, and was covered with 5cm good quality wood shavings. Each pen was equipped with bell drinkers, feeder trays, as well as fluorescent bulbs for lighting. Birds were monitored for weight changes, age of first egg and number of eggs laid per day until they were 43 weeks old.

For the second experiment, a total of 411 settable eggs were collected (from birds in experiment 1) for six days. Eggs with poor shell quality, misshapen and dirty eggs were rejected. Each day’s eggs were labelled, weighed and stored at 180 C and 65% relative humidity. Each selected egg, which constituted an experimental unit, was placed in the incubator for 28 days at a dry bulb temperature of 35.5 and a wet-bulb temperature of 29.40C. Eggs were candled on day 14 to identify fertilised eggs. On days 7, 14 and 21, each egg was weighed again to assess egg weight loss. The hatched guinea keets were weighed as well.Fertility was estimated as the percentage of the total eggs set that were found fertile during candling, whereas hatchability was calculated as the percentage of fertile eggs that hatched.

Table 1. Composition of diets fed to Guinea fowls at different physiological stages

Ingredients

Starter
(0-8 weeks)

Grower
(9-18 weeks)

Breeder
(18+ weeks)

Maize

59.1

63.5

55.0

Soybean meal

24.2

13.0

15.2

Fishmeal

14.3

3.00

5.00

Wheat bran

0.00

16.0

14.0

Lysine

0.15

0.50

0.20

Methionine

0.02

0.25

0.10

Salt

0.20

0.30

0.25

Oyster shells

1.00

2.20

9.00

Dicalcium Phos.

0.70

1.00

1.00

Vit. & Min. Premix

0.30

0.30

0.25

Calculated analysis

ME (MJ/kg)

12.3

11.4

11.7

Crude Protein %

26.2

16.7

17.7

Crude fat %

4.11

3.51

3.36

Fibre %

2.35

3.61

3.28

Linoleic acid %

1.30

1.51

1.34

Lysine %

1.51

1.16

0.98

Methionine %

0.50

0.46

0.37

Met + Cyst %

0.81

0.69

0.61

Calcium %

1.09

1.23

3.71

Phosphorus %

0.90

0.75

0.78

P. Available %

0.50

0.38

0.41

Sodium %

0.18

0.18

0.17

Mn g/kg

131

145

123

Zn g/kg

106

115

100

Feeding, management of birds and measurements

Ingredients and bromatological analysis of diets are shown in Table 1. Diets and water were offered to birds ad libitum. Feeds were offered at 07:00 each morning. Feed intake was noted and was adjusted weekly according to the age of the birds. Birds were weighed each week individually to determine weight changes. Data were collected on growth performance, survivability, egg-laying patterns and egg characteristics of the guinea fowls.

Statistics

The reproductive characteristics of the guinea fowls were described using means and standard deviations. We evaluated the influence of egg size on weight of day-old keet as well as on hatchability using linear regression (Equation 1) and simple logistic regression [Equation 2], respectively with each egg as an experimental unit. We performed Wald test [Equation 3] to verify that coefficient β differs from 0 (Agresti 1996). In addition, we analysed odds ratios [Equation 4] (Agresti 1996). To evaluate whether the measured data fitted well with the calculated model, a goodness-of-fit test was applied based on the “Hosmer–Lemeshow goodness-of-fit” statistic (Hosmer et al 2013). All the simple and multiple binary logistic regression analyses were performed using relevant software packages in R statistics (R Core Team 2019).

where  ŷ is the weight of day-old Guinea keet, X is the weight of egg at first day of incubation, π(x) is the probability of hatchbility of Guinea fowl eggs, α is the intercept parameter and β is the vector of slope parameter

where β is the estimate of parameter β by the maximum likelihood method (Equation 1) and SE is the standard error of

where odds of an event represent the ratio between the probability that the event will occur and the probability that it will not occur and π(x) is the probability of hatchbility of Guinea fowl eggs.


Results and discussion

Reproductive traits of the local guinea fowl

The guinea fowls started laying at the age of 24 weeks with a mean bodyweight of 1.88 kg (Table 2). The laying attained maximum at age 24 weeks and was maintained with minor fluctuations until age 34 weeks when it began to decline (Figure 1). The weight of first egg observed for guinea fowls in this study compares favourably (29.6 vs 29.1) with an earlier study under similar geogphical conditions; however,the mean age as well as mean body weight at first lay was 10 weeks earlier (24 vs 34 weeks) and 62% higher (1.88 vs 1.63 kg), respectively (Oke et al 2004). The differences in age and weight at first lay could partly be attributed to differences in feeding regimes. For example, the birds in this study were fed starter diets containing 26% crude protein, the previous study fed 24% crude protein and similar energy of 12.6 MJ/kg feed. Secondly, the differences in flock characteristics could be a factor. Whereas the previous study used sexed birds, our birds were unsexed, suggesting that about half of the flock could be males (i.e. 1:1 sex ratio); thus birds in the current study could be slightly heavier and faster in growth (Arhin et al 2018) compared to the earlier study.

Table 2. Egg-laying indices of unsexed Guinea Fowls under humid tropical conditions

Index

MeanS.D

Age at first egg, days

1653.82

Weight of first egg, g

29.60.79

Live body weight at first egg, g

187715.4

Fertility, %

56.94.38

Hatchability, %

82.215.9

The fertility rate of guinea fowl was 56.9% in the current study. Fertility may be affected by various factors, including the general condition of the parents, mating rate, age, egg-storage duration and condition, weather conditions, and geographical location (Yamak et al 2016a; Agbolosu et al 2012). Given that previous studies reported fertility rates of between 43 and 91.7% for guinea fowl eggs (Yamak et al 2016b; Bernacki et al 2013; Agbolosu et al 2012), the fertility rates found in the current study should be considered to be within acceptable ranges.

Overall, hatching rates were 82.2%. Reported hatchability rates of guinea fowl widely vary, with rates of between 45 and 88% reported for guinea fowl (Ancel et al 1994; Yamak et al 2016a). Factors that affect hatchability have been well described in previous studies and include male-female ratio and nutrition of parents, as well as egg-storage conditions (Yamak et al 201 6b; Kozuszek et al 2009).

Figure 1. The egg-laying pattern of unsexed Guinea fowls
Effects of egg size (weight) on fertility and hatchability

Our study showed that the size (weight) of a Guinea fowls egg has a significant effect on hatchability (p<0.001) (Table 3) but not on fertility (p> 0.05). Our logistic model (Figure 2) showed that larger eggs have higer probability of being hatched compared to smaller eggs. The odds ratio for egg weight was estimated as 1.47 with 95%CI from 1.93 to 1.17. Thus a one-unit increase in egg weight will increase the odds of hatchability by a factor of 1.47.

Table 3. Maximum likelihood analysis to predict hatchability of Guinea fowl eggs based on egg weight

Coefficients

Estimate

Std. Error

z value

Pr(>|z|)

Intercept

-13.6

4.84

-2.81

0.00492 **

Egg weight

0.382

0.125

3.06

0.00219 **

Significance. codes: 0 ‘***’ 0.001 ‘**’ 0.01 ‘*’ 0.05 ‘.’ 0.1 ‘ ’



Figure 2. Prediction of hatchability of Guinea fowl eggs based on egg weight (size) x(π) = predicted probability;
e = natural logarithm; model p-value <0.001; HosmerLemeshow   test p-value = 0.291
(no evidence of poor fit); misclassification error = 0.2 (cut-off point=0.5)


Figure 3. Relationship between weight of set eggs and the weight of hatched guinea keets

The positive association of larger eggs to higher probability of hatchability in this study could be attributed to the thickness of the shell concerning the size of the egg. Our observation is corroborated by Hussnain et al (2012), who reported that large size eggs have lower shell thickness which enhances hatchability while medium and small-sized eggs have thicker shells.. This result differs from results from a study by Othman et al (2014) who reported that egg size had no significant effect on the fertility rate in Japanese quail eggs. Similarly, Abiola et al (2008) and Kyere et al 2017 reported higher hatchability for medium-sized eggs chicken compared to larger and smaller eggs in chickens and Guinea fowls, respectively. Likewise, Wilson (1991) also reported that within the flock of Guinea fowls, chickens, turkey and ducks, medium-sized eggs hatch better than large and small size eggs. In addition, Gonzalez et al (1999) reported higher hatchability for medium size eggs (1450-1650 g) in ostrich as compared to both small and large size eggs. These previous authors explained that medium-sized eggs have thicker shells which makes hatching of such eggs difficult. However, eggshell quality is affected by management, nutritional and environmental factors (Nys 1999) and therefore, subject to manipulation.

The size (weight) of eggs affected weight changes (p<0.01) during incubation with a negative coefficient (Table 4), indicating lower weight loses for larger eggs. Egg weight loss during incubation varied between 3.39% and 22.35%. This range is, however, wider than 3.27% -11.32% reported for chicken (Iqbal et al 2016). In addition, we found a high degree of association between egg weight and the weight of day-old keets (Figure 3). The size of the eggs largely determined the size of the keets at hatching time. The average weight of a day-old keet was 82.69% of the weight of the egg from which it was hatched. Nevertheless, the weight of day-old chicks might not be a reliable index of growth rate in Guinea fowls (Upp 1928).


Conclusions


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Received 2 January 2020; Accepted 3 March 2020; Published 1 April 2020

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