British Poultry Science (2002) 43: 135–140
Eggshell conductance, embryonic growth, hatchability and embryonic mortality of broiler breeder eggs dipped into ascorbic acid solution T.M. SHAFEY Department of Animal Production, University of King Saud, College of Agriculture, PO Box 2460, Riyadh 11451, Saudi Arabia Abstract 1. Eggs from a broiler breeder flock between 25 and 29 weeks of age were dipped into solutions of various concentrations of ascorbic acid (AA) for up to 2 min, in order to evaluate its effects on eggshell conductance (EC), amniotic fluid pH, albumen height and pH, embryonic weight and hatchability. 2. Three experiments were conducted and the following treatments were used: control, non-dipped (CND); control, water-dipped (CWD); 10 g AA/l (AA1); 20 g AA/l (AA2) and 30 g AA/l (AA3). Measurements of EC before and after dipping were made in experiments 1 and 2 in eggs from hens at 25 and 27 weeks of age, respectively. Albumen height and pH were measured after dipping the eggs in experiment 2. In experiment 3, egg weight loss, embryonic weight and amniotic fluid pH at 14 d of age, hatchability percentage (HP), and embryonic mortality were measured in eggs from hens at 29 weeks of age. 3. AA treatment of eggs and dipping period of time (1, 1·5 and 2 min) increased EC of eggs from hens at 25 and 27 weeks of age. 4. AA3 treatment for 2 min reduced albumen height and increased albumen pH of eggs when compared with the CND treatment in eggs from hens at 27 weeks of age. 5. HP of AA1-treated eggs from hens at 29 weeks of age was higher than that of the CND treatment. AA2 and AA3 treatments of eggs reduced HP and increased the percentage of non-pips when compared with any of the other treatments. 6. AA2 and AA3 treatments of eggs increased egg weight loss when compared with the control treatments (CND and CWD). Dipping treatment did not influence amniotic fluid pH or embryo weight expressed as a percentage of initial egg weight. 7. It is concluded that dipping hatching eggs into AA solution increased EC of eggs. Dipping eggs into 10 g AA/l for a period of 2 min increased HP in eggs from hens at 29 weeks of age, although this was not associated with a significant increase in egg weight loss.
INTRODUCTION One of the basic biological functions of the eggshell of the domestic fowl is to provide an incubation environment in which a new chick can develop and to allow for adequate movement of water vapour and respiratory gases (eggshell conductance, EC) (Tullett, 1978). The eggshell is part of the respiratory structure of the embryo. It consists of an overlying cuticle, a crystalline calcium carbonate layer with two underlying proteinaceous membranes (Taylor, 1970) and is penetrated by thousands of microscopic pores, which are essential for the exchange of respiratory gases during incubation (Rahn et al., 1979). The cuticle may either bridge the pore openings or extend down into them to form a plug (Board, 1982). However, the shell imposes a restriction on the exchange of gases between the embryo and the air surrounding the eggs.
The resistance to this exchange of gases has been attributed to the shell proportion of calcium carbonate, shell membranes and cuticle (Tullett, 1978; Rahn et al., 1979). There is debate about the contribution of eggshell cuticle to the regulation of EC of eggs. The cuticle may enhance (Bryant and Sharp, 1934; Marshall and Cruickshank, 1938) or reduce (Simons, 1971; Board and Hall, 1973; Meir et al., 1984) the movement of water vapour across the shell. Peebles and Brake (1986) measured EC before and after the removal of the cuticle in eggs between the ages of 33 and 66 weeks and concluded that cuticle might either obstruct or improve water vapour diffusion as a function of bird’s age. The EC of eggs is known to increase with age in broiler breeders (Tullett, 1990). The functional properties of eggshell cuticle can be altered in many ways. Treatment of the eggshell with weak acid increases the EC
Correspondence to: Dr T.H. Shafety, Department of Animal Production, University of King Saud, College of Agriculture , PO Box 2460, Riyadh 11451, Saudi Arabia. Tel: +966–1–4678785. Fax: +966–1–4678474. E-mail:
[email protected] Accepted for publication 24th August 2001. ISSN 0007–1668(print)/ISSN 1466–1799(online)/02/010135–06 © 2002 British Poultry Science Ltd DOI: 10.1080/0007166012010999 9
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of eggs (Romanoff and Romanoff, 1949). Increasing EC of eggs will enhance the movement of water vapour and CO 2 across the shell, change the buffering capacity of albumen and influence hatchability percentage (HP) of eggs (Meuer and Baumann, 1988; Burley and Vadehra, 1989). Increasing gas exchange across the shell will cause a reduction in carbon dioxide in the egg and alter albumen pH. At 10 d of incubation, an influx of albumen through the ruptured sero-amniotic connection occurs and the volume of amniotic fluid is increased (Romanoff, 1960). The effect of this event on amniotic fluid pH and HP of eggs is not known. Ascorbic acid (AA) is a weak acid and the ability of diluted acids to interact with the eggshell cuticle was reported by Burley and Vadehra (1989) The objectives of this study were to determine the effect of AA treatment of the cuticle upon EC, amniotic fluid pH, embryonic growth, HP and embryonic mortality of broiler breeder eggs between the ages of 25 and 29 weeks. MATERIALS AND METHODS Eggs obtained from a commercial strain of broiler breeder (Hybro), fed on a standard breeder ration (160 g/kg CP, 12·0 MJ of ME per kg, 34·0 g/kg calcium, 4·5 g/kg available phosphorus) were used in three experiments. Birds were reared under standard husbandry conditions. A photoperiod of 14 h commenced when the birds were caged at 22 weeks of age and was maintained throughout the trials. AA solutions were freshly prepared. AA was dissolved in distilled water, kept in sealed bottles and protected from light. Large glass beakers were used for egg dipping in a darkened room at temperature of 25ºC. Eggs were randomly assigned to the following 5 treatments: control, non-dipped (CND); control, water dipped (CWD); 10 g AA/l (AA1); 20 g AA/l (AA2) and 30 g AA/l (AA3). EC of eggs Eggs were weighed individually, placed in desiccators containing fresh desiccant (calcium sulphate, Sigma Chemical Co., St. Louis, USA) and maintained at 25ºC for 4 d. These eggs were weighed each day to determine the initial EC, expressed as mg of water lost per d per Torr. Weight loss was adjusted on a 24-h basis and a standard barometric pressure of 760 Torr (mmHg) (Ar et al., 1974). The eggs were immediately dipped into a solution and allowed to dry at room temperature. EC was again determined as previously mentioned.
Incubation of eggs Eggs were set in a Maino, force-draft incubator (Model II, Maino Enrico Co., Italy) and incubated at 37·5ºC and 55% relative humidity. Eggs were turned every 2 h until they were transferred to the hatching compartment on d 19 of incubation. Eggs were examined by candling at d 6 and d 12 of incubation and infertile eggs and eggs containing dead embryos were removed, respectively. Early dead embryos were counted from d 1 to d 12 of incubation. The hatching compartment was kept at 37·0ºC and 65% relative humidity until the morning of d 22 of incubation, at which time chicks, cull chicks, pips (unhatched eggs with live or dead chicks) and late dead embryos (unhatched eggs with unbroken shell) were counted. Late dead embryos were counted from d 12 to d 22, when incubation was concluded. HP was calculated on the basis of the number of hatched chicks as a percentage of the number of fertile eggs per treatment. Culling of chicks was based on the general appearance and strength of the chicks. Culls include small and weak chicks and those with rough down feathers. Experiment 1 In this trial, eggs obtained from a 25-week-old flock were dipped into AA solution for up to 2 min and EC examined. The experimental design was a 4×3 factorial, with factors of AA concentration in the dipping solution (CWD, AA1, AA2 and AA3) and dipping period (1, 1·5 and 2 min). A total of 60 fresh-laid eggs of 56·3±0·1 g (mean ± SEM) were collected and 5 eggs were randomly assigned to each treatment for EC determination. EC for each individual egg was determined before and after the dipping treatment as described above. Experiment 2 In this trial, eggs obtained from 27-week-old hens were dipped into AA solution for a period of 2 min and the effect on EC and albumen height and pH were examined. A total of 75 fresh-laid eggs, of weight 56·6±0·1 g, were utilised in this experiment. Fifteen eggs were randomly assigned to each of the following treatments: CND, CWD, AA1, AA2 and AA3. Ten eggs were allocated for the measurement of EC as previously mentioned in experiment 1. Albumen height and pH were determined in the remaining 5 eggs after each dipping treatment. Eggs were broken open to record albumen height and pH of the thick albumen. Albumen height was measured in the middle of the thick albumen to the nearest 0·01 mm using an Ames tripod micrometer (Ames, Waltham, MA, USA)
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and a glass micro pH electrode (Mettler, Toledo InLab k427, USA) attached to a pH meter (Mettler, Toledo 320, USA) was used to determined pH to the nearest 0·01 units. Experiment 3 In this trial, eggs were dipped into AA solutions and egg weight loss, amniotic fluid pH, embryo weight and HP were determined. A total of 600 eggs were obtained from hens at 29 weeks of age and randomly assigned into 30 replicates of 20 eggs each. Eggs used in this experiment were stored for no more than 3 d at approximately 13ºC and 85% relative humidity prior to the experiment. Six replicate groups were randomly assigned to each of the following treatments: CND, CWD, AA1, AA2 and AA3. Replicates of each treatment group were randomly distributed within the incubator and no significant differences were found due to position. A dipping period of 2 min was used. Samples of 5 eggs per treatment were randomly selected at d 14 of incubation and broken open; about 2 ml of the amniotic fluid was removed with a syringe and its pH was measured. The embryos from these eggs were removed, separated from the
yolk sac, blotted dry with tissue paper and weighed to the nearest 0·01 g. Random samples of 25 eggs per treatment were weighed before dipping and at d 17 of incubation before transferring them to a hatching compartment and egg weight loss, expressed as a percentage of initial egg weight, was determined. Data collected were subjected to analysis of variance as a 4×3 factorial arrangement with dipping treatment and duration of dipping as main effects and their interaction fitted to the model (experiment 1) and a one-way ANOVA (experiments 2 and 3), using the Statistical Analysis System (SAS Institute, 1985). When significant variance ratios were detected, differences between treatment means were tested using the least significant difference (LSD) procedure. RESULTS The EC of eggs from broiler breeder hens at 25 weeks of age before and after dipping into different AA solutions for up to 2 min are shown in Table 1. Dipping treatment with AA significantly increased EC of eggs (F3,48=75·3; P
