Effect of Forced-Molting Methods and Rearing Temperatures on The Performance and Organ Biometrics of Laying Hens

August/2012 Approved: May/2013 AbstrAct An experiment was conducted to evaluate the biometrics of organs (ovary, oviduct, liver, proventriculus and gizzard) of laying hens submitted to different forced-molting methods of molt and maintained at three different temperature. Organs were evaluated after molting and resting period. Six hundred birds were distributed according to a completely randomized experimental design in a 5x3 factorial arrangement (forced-molting methods x environmental temperatures) into 15 treatments with 5 replicates of 8 birds each. The molting methods applied were the dietary inclusion of 90%, 70%, 50% of alfalfa, 2,800 ppm zinc oxide, or total feed restriction. Birds were kept at ±20 ºC, ±27 ºC, or ±35 ºC. Data were submitted to analysis of variance and means were compared by orthogonal and polynomial contrasts. The traditional forced-molting method (feed fasting) resulted in adequate performance. However, as the aim of the present study was to find an alternative method


IntRoduCtIon
At the end of the first laying cycle, eggshell thickness and strength are reduced, precisely when egg size is the largest. This problem may be solved by an economically feasible management practice, which is forced molting. Forced molting consists of a set of management practices applied to promote stress, inducing birds to stop producing eggs (Roland & Brake, 1982).
Several methods to force molting are applied, including feed and water fasting, lighting restriction, and the use of chemical agents. Feed withdrawal from the feeders for 10 to 12 days is the easiest method of inducing molting in layers, resulting in egg production cessation, reproductive tract involution, and feather loss (Brake, 1993). Molting induced by feed fasting causes about 25% weight loss in layers, and ¼ of this effect can be directly attributed to reductions in liver, ovary, and oviduct weights (Brake & Thaxton, 1979).
However, despite being easy to apply and producing the desired results, feed fasting is very aggressive, and therefore, taking into account the importance of animal welfare, molting methods that cause less stress, such as the dietary inclusion of insoluble fiber, have been investigated (Kwon et al., 2001;Donalson et al., 2005;Landers et al., 2005Landers et al., , 2008. Studies on alternative molting methods have frequently reported conflicting results, which may be attributed to the different environmental conditions in which birds are reared. Among the environmental factors, air temperature, humidity, and movement are highlighted, as they directly affect body temperature maintenance (Tinôco, 1995).
The present study aimed at evaluating the effect of different forced-molting methods applied at three different environmental temperatures on the performance and relative weights of the organs of commercial layers.

MAteRIAlS And MethodS
The experimental period included the periods of molt and rest. Layers were selected according to body weight and egg production. The different methods of forced molting were applied for 14 days, after which there was a 28-day resting period for the recovery of body and organ weights.
In this trial, 600 commercial Isa Brown layers with 72 weeks of age were distributed, according to a completely randomized experimental design with a 5x3 factorial arrangement (forced molting methods x temperatures) into 15 treatments, with five replicates of eight birds each, totaling 75 experimental units.
During the molting period, a lighting program of 12h of light per day was adopted, and the period was light was gradually increased during the resting period until 17 hours of light per day. Feed and water were supplied ad libitum.
Birds were kept in three environmentally-controlled chambers during the molt and the rest periods. Using thermo-hygrometers, the following maximum and minimum temperature and humidity inside the chambers were recorded: 18.9-21ºC and 41.3-64.4% in the cold chamber, 25.9-28.5ºC and 29.5-55.8% in the thermoneutral chamber, and 29.1-32.4ºC and 39.9-52.3% in the hot chamber, respectively.
During the experimental period, four birds per treatment were sacrificed after molting and four after resting in order to determine relative ovary, oviduct, liver, proventriculus, and gizzard weights.
Feeds were based on corn and soybean meal, and formulated according to the recommendations of Rostagno et al. (2005). (2005).

Effect of Forced-Molting Methods and Rearing Temperatures on The Performance and Organ Biometrics of Laying Hens
The obtained data were submitted to analysis of variance using the General Linear Models (GLM) procedure of SAS® statistical package (SAS Institute, 2002). When effect was significant, means were compared, at 5% probability level, by orthogonal and polynomial contrasts, as contrast 1: comparison between the sum of A90, A70, and A50 means vs. the sum of Zn and control (feed fasting) means; contrast 2: linear effect of alfalfa levels; contrast 3: quadratic effect of alfalfa levels; contrast 4: comparison between Zn and control means; contrast 5: linear effect of temperatures; and contrast 6: quadratic effect of temperatures.

ReSultS And dISCuSSIon
Ovary weight loss is concomitant with body weight loss, and this process is directly linked to the recovery of the hen's reproductive tract during the molting period (Braker, 1983). Souza et al. (2010) reported that many studies in literature found that reproductive tract involution during molt is required to ensure adequate performance during the second laying cycle. Therefore, morphometric characteristics of some organs of the hens submitted to molting were determined (Tables 3,  4, and 5).
The contrast between dietary alfalfa inclusion means and zinc oxide and feed fasting means (C1) was significant (p<0.05) for oviduct relative weight. Average oviduct relative weight of hens submitted to the treatments with alfalfa inclusion (1.82%) was higher than the average relative weight of hens in the zinc oxide and feed fasting groups (1.46%), mainly because of the higher oviduct relative weights of hens fed 70 and 50% of alfalfa (2.07% and 1.93%, respectively).
The low feed intake, stress, and nutritional unbalance that result in the involution of the reproductive tract cause a cascade of neuroendocrine effects. Feed fasting or the supply of diets which

Effect of Forced-Molting Methods and Rearing Temperatures on The Performance and Organ Biometrics of Laying Hens
composition does not supply the nutrients required for body maintenance, cause stress and, consequently hypothalamus hyperactivity. The hypothalamus than releases corticotropic (ACTHRF) and thyrotropic (TSHRF) hormones (Girardon, 2011), which act on the pituitary, which then secretes ACTH and TSH. The increase in the blood levels of these hormones leads to adrenal and thyroid hypertrophy and hyperfunction, causing gonadotropic hormone unbalance (Garcia, 2004). Woodward et al. (2005) fed Leghorn layers a regular feed, 100% alfalfa or fasted the hens during a 9-day experimental period. The authors observed that ovary weight loss was similar between the fasted and the alfalfa-fed hens. This was also observed by Donalson et al. (2005) and Landers et al. (2005) when comparing feed fasting and feeding 100% alfalfa as forcedmolting methods. Landers et al. (2008) found a 10fold ovary reduction in commercial layers submitted to forced molting by feeding 100% alfalfa or feed fasting.
The results of the present study are consistent with literature reports that show that the supply of high fiber levels to induce molting causes similar reproductive tract weight loss as feed fasting (Table  3). According to Landers et al. (2005), in order to be accepted by the poultry industry, methods to induce molting must provide a stimulus substantial enough to cause suficient reproductive tract regression during molting and result in egg production and quality in the second cycle similar to those obtained with the feedfasting method.
The contrast between the zinc oxide and the feed fasting methods was significant (p<0.05) when gizzard and proventriculus relative weights were considered, with heavier weights for the birds fed zinc oxide. These findings are consistent with those reported by Souza et al. (2010), who observed severe gizzard regression and lower gizzard weight when hens were submitted to feed fasting (1.17%).
There was no effect of molting method or temperature (p>0.05) on liver relative weight. Table 4 shows the effects of molting methods applied at different temperatures on ovary, oviduct, liver, gizzard, and proventriculus relative weights of hens sacrificed after the resting period.
Gizzard relative weight was not influenced (p>0.05) by molting method or temperature during the resting period.
There was a significant interaction (p<0.05) between treatments in relation to ovary, oviduct, and liver relative weights.

Effect of Forced-Molting Methods and Rearing Temperatures on The Performance and Organ Biometrics of Laying Hens
Mean relative weight, F value of orthogonal and polynomial contrasts of the organs that presented significant interaction during the resting period are shown in Table 5.
It was observed that, when hens were kept in the hot temperature environment, the average ovary relative weight of hens fed alfalfa was lower than that of those fed zinc oxide and feed fasted (C1), with 0.95% and 1.66%, respectively. Also for hens kept at hot temperature, ovary and oviduct relative weights were quadratically (p<0.05) affected by alfalfa levels (C3) with higher relative ovary and oviduct relative weights for molting methods A50 and A70, respectively (y = -0.0009x 2 + 0.1005x -1.3738; R² = 0.99, y = -0.0018x 2 + 0.229x -4.9225; R² = 0.99, respectively).
When molting methods were considered, temperature had a quadratic effect (p<0.05)on the
The recovery of the reproductive tract after the resting period is extremely important for egg production during the second laying cycle. One of the main functions of the ovary is to produce steroidal hormones, which are essential for reproductive tract growth and function and depend on the bird's nutritional status. The reproductive system is regulated by the hypothalamic-pituitary-gonadal axis. The gonadotropin-releasing hormone (GnRH) stimulates the pituitary to secrete the luteinizing hormone (LH), which is responsible for stimulating progesterone production by the mature follicle that consequently breaks and releases the ovum. The pituitary also produces the follicle-stimulating hormone (FSH). FSH may stimulate the production of steroidal hormones by the developing follicle cell, particularly in the small follicles (Leite & Viveiros, 2009).
The details of the interactions found in the present study showed that, when hens are maintained at hot temperature, the most efficient molting methods in terms of recovery of the reproductive tract were A50, A70, zinc oxide, and feed fasting, whereas when temperature was thermoneutral, A90 promoted the best recovery of the ovary and of the oviduct.
There is little information in literature describing the effects of alternative molting methods on the recovery of organs after the resting period, particularly when different environmental temperatures were used.
There was a quadratic effect (p<0.05) of the interaction (C3) of cold temperature with dietary alfalfa levels (y = -0.0004x 2 + 0.049x -1.1025; R² = 0.99), with hens submitted to molting methods A70 and A50 presenting the heaviest livers. When birds were kept at thermoneutral temperature, the contrast among alfalfa levels (C3) had a quadratic effect (p<0.05) on liver relative weight (y = 0.0004x 2 -0.0515x + 2.1187; R² = 0.99), with birds submitted to A90 and A50 presenting heavier livers. Also when kept under thermoneutral temperature, when the methods of feed fasting and zinc oxide were compared, hens submitted to the zinc oxide method presented higher liver relative weight (p<0.05).
Better liver weight recovery indicates that more energy sources, such as glycogen and lipids, are being metabolized in the liver (Berry & Brake, 1985). Liver recovery is also an indication that the hormones required for egg production after molting are being produced. Egg production depends on ovarian steroids (Berry & Brake, 1985), such as estrogen, which stimulate yolk production through the synthesis of phosphoproteins that are produced in the liver (Berry & Brake, 1985). Therefore, when hens were submitted to different forced-molting methods and kept at thermoneutral temperature, the method of the dietary inclusion of 90% alfalfa promoted the best liver recovery, which may aid egg production during the second laying cycle.

ConCluSIonS
The traditional forced-molting method of feed fasting resulted in good performance. However, as the purpose of the present study was to find an alternative method to feed fasting, the dietary inclusion of the highest alfalfa level, that is, the supply of 90% alfalfa and 10% feed was shown to be efficient compared with the other tested methods, particularly when birds were kept under hot temperature. Therefore, the dietary inclusion of 90% alfalfa may be used as an alternative forced-molting method relative to feed fasting, especially when bird welfare is taken into consideration.