Effect of Pause Size and its Number on Egg Mass for a Stock of White Leghorn in Iraq

This study included 336 Leghorn hens and was conducted at poultry farm, Department of Animal Resources /Agriculture College / University of Baghdad / Iraq, from 15/6/2005 to 30/9/2005. The aim of the present study was to investigate the effects of pause size and pause number on egg mass in White Leghorn during the first 100 day before onset of laying the first egg. General Linear Model (GLM) within SAS program was used to study the effect of some fixed effects which included (hatch and age at sexual maturity ) on pause size and pause number beside studying the effect of hatch, weight at sexual maturity, pause size and pause number on egg mass. The overall means for pause size, pause number, egg mass were 2.27 days, 15.48 pauses and 3495.02 gm respectively. The effect of hatch was significant (P < 0.05) on pause size and pause number, whereas the effect of weight at sexual maturity on the same traits was not. Egg mass was affected significantly (P < 0.01) by pause size and pause number, but the effect of hatch and weight at sexual maturity was not significant.


Introduction
Poultry industry is currently receiving great attention in many countries and recently gap is daily increase between Iraq and these countries, so it is imperative to research in order to continue to develop the poultry industry in Iraq (Al-Soudi and Al-Jebouri, 1979).The production of eggs has been the factor of the greatest importance in poultry production (Morley, 1985).Egg production in laying hens is a process o f pronounced cycle nature and eggs are laid at intervals of around 24 to 27 h.This process results in the formation of clutches (Akbas et al., 2002).To describe the cyclic laying process, some clutch traits are defined as clutch number, average clutch size, pause size and pause number (Sturkie, 1976;Akbas et al., 2002).The clutch traits have been investigated only by a few researches in different domestic avian species in recent years (Luc et al., 1996).New selection traits are searched in poultry breeding to improve egg production, so poultry breeders must consider so many traits that are economically important that it becomes difficult to apply sufficient selection on key traits in egg laying stock (Egg production rate, sexual maturity, egg size, feed efficiency, fertility and hatchability) (Schmidt and Figueiredo, 2005).Thus, with such a large number of traits, it is important to choose a compound trait such as egg mass which can reflect two traits (egg production and egg weight) to improve stock performance.Results of Sabri et al. (1999), Al-Nedawi (2006) obtained that there was a significant positive genetic and phenotypic correlation between egg mass and each of egg number and egg weight.Hence the aim of the present research is to investigate the effects of some factors (Hatch and age at sexual maturity) on pause size and pause number and the effects of all factors (dependent and independent) on egg mass.

Materials and Methods
This experiment was conducted at poultry farm, Department of Animal Resources /Agriculture College / University of Baghdad / Iraq, from 15/6/2005 to 30 / 2005.Three hundred and thirty six Leghorn hens at 24 weeks of age which represent a random-bred population were kept individually in cages with dimensions 40× 40×50 cm and where fed ad libitum on compound feed containing 16% crude protein and 2708 kcal/kg ME.Body weight at onset of laying was recorded .Number and weight of eggs were recorded to estimate egg mass from 24th to 38th week of age defined as early part of whole egg production record.For each individual, egg number, egg weight, pause size and pause number were recorded to the 38th week of age.
Statistical analysis: General Linear Model (GLM) within SAS program was used using two models the first one was used to investigate the effect of hatch and weight at sexual maturity on pause size and pause number: Where Yijk is any trait considered in this study, µ is the over all mean, Hi the fixed effect of I th hatch (I= 1 -3),$ is the regression coefficient on weight j at sexual maturity, e is the residual effect.
ijk  Second model used all factors in the first model (dependent and independent) to investigate their effects on egg mass.

Results and Discussion
The pause size through 100 days before the onset of Hampshire and their crosses.World Poult.Sci.J., laying is 2.27 days (Table 1), the present estimation was slightly lower than the estimate 2.51 days by Ahmed (1988) and much higher than estimate (1.13 days) by Akbas et al. (2002).The laying period consisted of 15.48 pauses and this estimate was also lower than estimate (16.80 pauses) by Ahmed (1988).The non-productive  Singh and Singh (1982).The effect of hatch on the two traits was significant (P < 0.05) and the birds of the first hatch exhibited the lowest pause size (2.17 days) compared with highest estimate (2.41 days) in the birds of third hatch (Table 2), but weight at sexual maturity had no effect on the previous traits.The mean egg mass during first 100 days was 3495.02gm (Table 3) and this estimate was higher than the estimates 3138.75, 249575, .90, 3325 reported by Ahmed (1988)), Al-Rawi (2001), Yeasmin et al. (2003) respectively, but lower than the estimate (4040 gm) by Sabri et al. (1999).Results showed that differences in egg mass belonged to pause size were significant (P < 0.01) (Table 4) and the estimates decreased as the pause size increased.This finding was supported by Halaj (1983) and Madkour et al. (1985).The effect of pause number on egg mass was significant (P < 0.01) and results revealed that egg mass decreased by the increase of pause number, which mean that there is a contrast relationship between egg mass and the two traits.Hence, egg mass can be increased by decreasing pause number and pause size or one of them.On the other hand egg mass was not affected by hatch and weight at sexual maturity.

Table 1 :
Least square means for pause size and pause number in Leghorn hens.

Table 2 :
Analysis of variance for some affected factors on pause size and Pause number in Leghorn hens.

Table 3 :
Least square means ±S.E for egg mass in Leghorn hens.

Table 4 :
Analysis of variance for some affected factors on egg mass in Leghorn hens.
. Productive potential in subtropics climate of native Iraqi chicken compared to White Leghorn, New 32: 227-235.Ahmed, A.H., 1988.Comparison of egg cycles and some other production characteristics o f indigenous chickens with standard breeds in Iraq.(Thesis).Agriculture College/University of Baghdad.(In Arabic).