J. Appl. Poult. Res.
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J APPL POULT RES 2007. 16:529-536. doi:10.3382/japr.2006-00089
© 2007 Poultry Science Association
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Research Reports

Effects of Different Forced Molting Methods on Postmolt Production, Corticosterone Level, and Immune Response to Sheep Red Blood Cells in Laying Hens

E. E. Onbasilar*,1 and H. Erol{dagger}

* Ankara University, Faculty of Veterinary Medicine, Department of Animal Science, 06110, Ankara, Turkey; and {dagger} Abant Izzet Baysal University, Mudurnu Süreyya Astarci Vocational School of Higher Education, 14800, Bolu, Turkey

Correspondence: 1 Corresponding author: obasilar{at}veterinary.ankara.edu.tr


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
The objective of this study was to evaluate the effects of different molting methods on postmolt production, plasma corticosterone levels, and antibody production to SRBC for the welfare of laying hens. This experiment was conducted with 120 IGH-type Brown laying hens (70 wk of age), randomly divided into 3 experimental groups. The hens in one group were fed a whole-grain barley diet during the first 10 d (WB diet). On d 11, hens consumed 100 g of layer diet/d until d 28. In the second group, hens were fed a Zn diet containing 10,000 mg/kg of Zn as ZnO for 10 d (Zn diet). Hens were then provided 100 g of a layer diet from d 11 to 28. In the third group, feed was withdrawn for 10 d, and on d 11 hens were fed a cracked corn diet ad libitum until d 28 (California method; CAL diet). Hens in all groups were returned to the layer diet ad libitum on d 29. Egg weight was lower in the Zn treatment than in the other treatments. Feed intake and plasma corticosterone levels were higher and antibody production was lower in the CAL treatment than in the WB and Zn groups. The FCR was better in the WB than in the Zn group. Mortality, egg production, and egg quality were not significantly different among the molting methods. As a result, the WB molting program was the best method for postmolt production among the programs examined.

Key Words: molting • laying hen • postmolt production • corticosterone level • immune response


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
In the commercial egg industry, widely different molt techniques are used for extending laying flock performance. Molting programs are designed to prolong the productive life of layers and breeders. This will depend on local economic conditions and, in particular, egg prices. Most researchers have reported that induced molting improves the postmolt performance (such as egg production, egg quality, and egg weight) of laying hens compared with the premolt performance [1, 2].

Conventional induced molting methods have used fasting of hens for shorter periods or to a targeted BW with or without water restriction [2, 3, 4]. This method efficiently induces a molt because it is management friendly and economically advantageous, and it results in satisfactory postmolt performance for the commercial layer industry [5]. But, recent concerns have been raised about animal welfare during the fasting period, because it is thought to be harmful to the hens [6]. The other methods are feeding high dietary Zn [7, 8, 9, 10, 11] or iodine [12], feeding low-Ca [4, 9] or low-Na diets [13], and feeding high-corn diets [14, 15]. The aim of the current study was to detect the effects of different molting procedures on the postmolt production, physiology, and immune response to SRBC in laying hens.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Animals and Diets
A total of 120 IGH-type Brown laying hens [16], 70 wk of age, were used in the present study. The hens were housed in individual cages. All hens were provided the layer diets ad libitum and received 16 h of light/d before the molting programs began. The experimental period was 23 wk, consisting of a 1-wk preexperiment period and 4 wk during the molt period, followed by 18 wk of production.

The 3 molting programs were whole-grain barley (WB), high dietary Zn (Zn), and California (CAL; Table 1Go). In the WB method, the hens were fed whole-grain barley during the first 10 d and light was reduced to 8 h/d. On d 11, hens were provided 100 g/d of the layer diet until d 28. On d 29, hens were provided the layer diet ad libitum and the day length was increased to 16 h of light/d. In the Zn method, hens were fed Zn diets containing 10,000 mg/kg of Zn as ZnO for 10 d and light was reduced to 8 h/d. Hens were fed 100 g/bird per day of the layer diet from d 11 to 28. On d 29, hens were provided the layer diet ad libitum and the day length was increased to 16 h of light/d. In the CAL method, hens were fasted during the first 10 d and light was reduced to 8 h/d. On d 11, hens consumed a cracked corn diet ad libitum until d 28. On d 29, hens were fed a layer diet ad libitum and the day length was increased to 16 h of light/d. The ingredients and chemical composition of the diets are given in Table 2Go. Water was given freely in all the groups during the experiment.


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  		Table 1. Description of WB-, Zn-, and CAL-induced molting programs1
 

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  		Table 2. Ingredients and chemical composition of diets
 
Traits Measured
All hens were weighed individually at the beginning of the experiment and at 10 and 28 d following the start of the molt programs. One-week preexperimental egg production, feed intake, and FCR, and 3-d preexperimental egg weight were used to determine their initial values. Percentage of BW loss was calculated. Mortality was recorded daily. Eggs were collected daily then egg production was calculated on a hen-day basis, and uncracked eggs were weighed. Feed intake was measured weekly and FCR (grams of feed:grams of egg) was calculated weekly during the postmolt period. Twenty eggs per treatment were collected randomly to determine the egg quality characteristics on the first day of the 14th and 15th week of postmolt production. The following characteristics were recorded for the individual eggs: weight, shape index, eggshell breaking strength, shell thickness, yolk height and width, and albumen height, width, and length. With these values, the yolk index, albumen index, and Haugh units were calculated. The egg quality analyses were completed within 24 h of collection.

On d 10 of the experiment, blood samples were taken from the brachial vein of 17 hens in each treatment and placed in tubes containing EDTA to estimate the plasma corticosterone levels. The bleeding procedure was limited to 1 min or less to minimize the influence of handling stress [17]. All blood samples were collected at the same time in the morning and centrifuged. Plasma was frozen (–20°C) until analyzed for the determination of corticosterone. Plasma corticosterone levels were measured by using kits [18] and a gamma counter [19].

Antibody production against SRBC was measured from 10 hens in each treatment at the beginning of the experiment, and at 10 and 30 d following the start of the molting programs. Hens were injected with 0.1 mL of 0.25% SRBC in 0.9% saline. Circulating anti-SRBC antibody titers were determined by the microhemaglutination technique from samples taken at 5 d after the immunization. All titers were expressed as the log2 of the reciprocal of the serum dilution [20].

Nutrient analyses were determined according to standard AOAC procedures [21]. The analyses of Ca [22] and P [23] were done after dry combustion of the diets. Metabolizable energy levels were estimated by using a prediction equation [24]:


Formula

Statistical Analyses
Data were analyzed with SPSS for Windows. Differences among the means of the molt treatment groups were studied by one-way ANOVA. Means that were significantly different were separated by Duncan’s test. The frequencies of mortality among groups were compared by using a chi-square test [25].


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
In this experiment, BW loss was significantly higher in the CAL treatment than in the other treatments (Table 3Go). Body weight loss is an important factor contributing to the success of induced molting because of its impact on reproduction and on fat deposits [26, 27]. This leads to regression of the reproductive tract, which is proportional to the loss of BW, the rejuvenation of the reproductive tract, and the removal of fat accumulation, thereby increasing tissue efficiency [28]. Webster [6] reported that targeted weight losses have ranged from 15 to 35%, but the optimal BW loss of hens during an induced molt was not identified.


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  		Table 3. Effect of different induced molting programs on BW of brown laying hens
 
In the present study during the molt period, hen-day egg production was higher in the Zn treatment than in the others (Table 4Go and Figure 1Go). Postmolt (wk 5 to 22) hen-day egg production was not significantly different among the 3 molt treatments (Table 4Go and Figure 2Go). This result agrees with the findings of Park et al. [27], who found that egg production was not different among molting methods (feed withdrawal, Zn acetate, Zn propionate). However, Alodan and Mashaly [28] reported that egg production was significantly affected by the molting program [Zn, CAL, and on-again, off-again (ON-OFF)], and the Zn group had significantly (P < 0.05) lower egg production than the CAL and ON-OFF treatments. In the current study, postmolt egg production was lower than expected in all groups. These results showed that the genotype (obtained by Ankara Poultry Research Institute) used in this experiment was not suitable for the second production cycle.


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  		Table 4. Effects of different induced molting programs at different periods of the experiment on hen-day egg production (%)
 

Figure 1
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  		Figure 1. Daily hen-day egg production (%) during the molt period. WB = whole-grain barley method; Zn = high dietary Zn method (containing 10,000 mg/kg of Zn as ZnO); CAL = California method.

 

Figure 2
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  		Figure 2. Weekly postmolt hen-day egg production (%) from wk 5 to 22. WB = whole-grain barley method; Zn = high dietary Zn method (containing 10,000 mg/kg of Zn as ZnO); CAL = California method.

 
Postmolt egg weight was significantly higher in the CAL group than in the other groups (Table 5Go). Contradictory to our findings, Alodan and Mashaly [28] reported that different induced molting programs (Zn, CAL, ON-OFF) had no effect on egg weight. Previous studies of molting methods have often shown conflicting results in hen responses because of different conditions [4]. Body weight at the start of the experiment, BW loss [29], age of the hens [26], and strain [30] have all been shown to affect the results of different molting methods. There were no significant differences among treatments in the egg quality characteristics examined in the current study (data not shown). Similarly, Alodan and Mashaly [28] showed that Zn methods did not affect egg quality. McCormick and Cunningham [10] also reported that egg quality variables and shell breaking strength were not significantly different between different molting methods (fasting for 10 d and high dietary Zn).


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  		Table 5. Effects of different induced molting programs at different periods of the experiment on egg weight (g)
 
Hens in the WB and Zn treatments consumed much less feed (P < 0.001) from the 5- to 22-wk postmolt than hens in the CAL group (Table 6Go). The FCR of hens in the WB treatment was better than that of hens in the Zn group. Berry and Brake [7] reported that hens in the low dietary Na treatment had significantly better (P < 0.05) feed efficiency than those in the high dietary Zn and fasting treatments.


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  		Table 6. Effects of different induced molting programs on feed intake (g/hen per d) and feed conversion ratio (g feed:g egg)
 
During this experiment, 6 (15%), 7 (17.5%), and 11 (27.5%) hens died in the WB, Zn, and CAL treatment, respectively. Mortality was not significantly affected by the different molting treatments. This result is in agreement with Alodan and Mashaly [28].

One method of assessing welfare in different molting programs is to measure the physiological parameters associated with the stress response. Physiological parameters of stress in poultry, as reviewed by Freeman [31], Siegel [32], and Hill [33], may include increases in circulating levels of corticosterone and suppression of humoral immunity. In this experiment, plasma corticosterone levels (mean ± SEM) of hens in the WB, Zn, and CAL treatments were determined as 3.78 ± 0.16, 4.07 ± 0.13, and 4.71 ± 0.19 ng/mL, respectively. The higher (P = 0.001) corticosterone levels in the CAL treatment could reflect a period of higher-stress conditions than in the Zn and WB treatments. However, Keshavarz and Quimby [34] reported that corticosterone levels were not significantly different among various molting regimens (feed withdrawal, continuous corn diet, and feed withdrawal-corn diet groups).

On d 10 and 30 of the experiment, antibody titers to SRBC in the CAL method were significantly lower than in the other treatments (Table 7Go). This reduction may be due to the increase in circulating levels of corticosterone. Corticosterone can reduce the antibody response to an antigen in birds [35]. Nathan et al. [36] showed that short-term starvation diminished the response to SRBC. Conversely, Alodan and Mashaly [28] showed that the different induced molting programs did not adversely affect antibody production against SRBC. Some of these differences may be due to the genetic background of the birds, the different molting programs, or the use of different suspensions of sheep erythrocytes.


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  		Table 7. Effects of different induced molting programs at different periods of the experiment on antibody production against sheep red blood cells1
 

   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 
  1. In the CAL method, egg weights and plasma corticosterone levels were higher and humoral immunity was lower than with other methods. Hens molted with this method also had greater feed consumption than with the other methods; however, egg production was not affected. Because of physiological stress, this molting program may be less suitable for the welfare of laying hens.
  2. When the WB and Zn methods were compared, egg weight with the WB method was higher and FCR was better than with the Zn method. Egg production, mortality, egg quality, plasma corticosterone levels, and immunity of the laying hens were not significantly different between these 2 treatments.
  3. Therefore, in this study the WB molting program resulted in the best production performance among the programs examined.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

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  2. Zimmermann, N. G., D. K. Andrews, and J. McGinnis. 1987. Comparison of several induced molting methods on subsequent performance of Single Comb White Leghorn hens. Poult. Sci. 66:408–417.[ISI][Medline]
  3. Buhr, R. J., and D. L. Cunningham. 1994. Evaluation of molt induction to body weight loss of fifteen, twenty, or twenty-five percent by feed removal daily limited or alternative day feeding of a molt feed. Poult. Sci. 73:1499–1510.[ISI][Medline]
  4. Rolon, A., R. J. Buhr, and D. L. Cunningham. 1993. Twenty-four-hour feed withdrawal and limited feeding as alternative methods for induction of molt in laying hens. Poult. Sci. 72:776–785.[ISI]
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  8. Bell, D. D. 2003. Historical and current molting practices in the US table egg industry. Poult. Sci. 82:965–970.[Abstract/Free Full Text]
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  18. AA-13F1 (Gamma-B 125I Corticosterone). IDS, Bolden, UK.
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  25. Dawson, B., and R. G. Trapp. 2001. Basic and Clinical Biostatistics. 3rd ed. Lange Medical Books, McGraw-Hill Med. Publ. Div., New York, NY.
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  27. Park, S. Y., S. G. Birkhold, L. F. Kubena, D. J. Nisbet, and S. C. Ricke. 2004. Effects of high zinc diets using zinc propionate on molt induction, organs, and post-molt egg production and quality in laying hens. Poult. Sci. 83:24–33.[Abstract/Free Full Text]
  28. Alodan, M. A., and M. M. Mashaly. 1999. Effect of induced molting in laying hens on production and immune parameters. Poult. Sci. 78:171–177.[Abstract/Free Full Text]
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