Health and Husbandry Considerations of Induced Molting

Transcription

1 Health and Husbandry Considerations of Induced Molting PAUL L. RUSZLER1 Department of Animal and Poultry Sciences, Virginia Polytechnic Institute and State University, Blacksburg, Virginia ABSTRACT There have been many methods proposed to induce molting. Some worked very well in practice, but others were detrimental to the health and welfare of the hens. The most effective methods use some level of feed restriction and daylength manipulation to reduce body weight (Hansen, 1966; Ruszler, 1974, 1984, 1996; Swanson and Bell, 1974; Brake and Carey, 1983). Weight reduction is necessary for rest and rejuvenation of body tissues. Other methods evaluated incorporated dietary imbalances using either zinc, iodine, or sodium. Pharmaceuticals have been used but have not been cost effective. In recent years there have been those who question whether molting techniques are humane. Therefore, interest has been heightened in alternate methods to induce molting. Research reported to date has been inadequate to accurately determine which methods of induced molting are the least stressful, if they in fact, cause any more stress than that experienced by the hen during a natural molt. The three or four most highly refined methods being used commercially are not generally detrimental to the health and welfare of today s laying hen, provided that they are managed in accordance with proper husbandry practices. (Key words: induced molt, welfare, stress, daylength, body weight) INTRODUCTION That an induced molt will restore egg production and also shell quality to higher levels as compared with those of the immediate premolt period has been supported by considerable research. However, much of the research is confusing in practical terms and difficult to apply in the commercial setting due to differences in the age of the hens when initiating the molt, variations in the method of molting, and different strain responses. The most common methods used commercially involve feed deprivation to induce body weight reduction (BWR). This reduction in body weight is the result of ovarian and oviducal regression, depletion of fat and labile protein reserves, the loss of alimentary canal contents, and initial water intake reduction. These losses account for much of the weight loss in the first 10 d. Brake and Thaxton (1979) reported that a 12-d period without feed resulted in a 25% weight loss and that onefourth of this loss was attributed to liver, ovary, and oviduct weight reduction. Baker et al. (1981a) reported that feed deprivation for 16 d reduced total body weight 35%, total lipid 50%, liver weight 61%, ovary weight 90%, oviduct weight 84%, and uterine lipid 65%. Many researchers have recommended weight losses ranging 1998 Poultry Science 77: from 25 to 35% (Baker et al., 1983; McCormick and Cunningham, 1983; Brake and Carey, 1983; Ruszler, 1984, 1996; Zimmermann et al., 1987). Enhanced postmolt performance is related to the amount of regression and subsequent redevelopment of body organs and tissues. Lee (1982) found a positive and significant correlation between the length of the rest period and postmolt hen-day egg production. Fontana et al. (1991) reported similar results. Concern for the welfare of the hen during the molt has been expressed by poultry scientists, commercial poultrymen and others in recent years. Even though a bird going through a natural molt will reject feed for an extended period (Mrosovsky and Sherry, 1980), the concern centers upon whether or not it is harmful to initiate a molt before the bird is physiologically ready. This concern, plus the desire by some for a one stroke method to molt hens has led to extensive research into methods that do not require feed deprivation. The research has explored dietary modification so that diets contain either excess zinc, iodine, or magnesium. Other diets are deficient in calcium or sodium. Injections of hormones and other chemicals have been attempted. Wolford et al. (1983) reported that feeding corticosterone Received for publication August 12, Accepted for publication April 6, To whom correspondence should be addressed: amary@vt.edu Abbreviation Key: BWR = body weight reduction; HDZ = high dietary zinc; LF = long feed withdrawal; MF = medium feed withdrawal; SF = short feed withdrawal. 1789

2 1790 up to 40 ppm of the diet resulted in the cessation of lay within 4 to 8 d, depending upon the level fed. McGinnis et al. (1983) reported that feeding guar meal to hens resulted in a greater loss of body fat and less reduction in body protein than methods requiring long periods without. McKeen (1984) induced BWR and the resulting molt by feeding grape pomace. McCormick and Cunningham (1983) reported that feeding high levels of zinc induced molting due to a reduction in feed intake. Other dietary imbalances may be similarly effective. METHODS USED Several prevalent methods of inducing the molt were reviewed by Wolford (1984). Feed and water withdrawal was the most frequent method summarized with over 36 articles included. This method also involved day length or light intensity manipulation and the incorporation of some specific type of molting diet. Another method listed in Wolford s review was restriction of calcium, which was studied by eight workers. It was reported that this method required a longer period for cessation of lay and sometimes resulted in less than optimal rate of lay upon returning to production. Feeding diets low in sodium (< 40 ppm) was reported by 16 researchers. The mode of action effecting the molt was reported to be a reduction in feed intake of up to 45%. High levels of added dietary zinc (up to 20,000 ppm of zinc oxide or zinc acetate) resulted in an effective molt according to six studies reviewed. This method suppressed feed intake by as much as 85%. Adding dietary iodine as potassium iodide (5,000 ppm) resulted in cessation of lay within 1 wk. Production returned as rapidly as its cessation upon removal of the iodine according to five researchers. Levels of dietary iodine below 2,500 ppm were not completely effective, and it appears that this method does not cause a complete regression of the reproductive tract. Some of the pharmaceuticals studied for their molt-inducing properties were enheptin, nicarbazin, methallibure, and tamoxifen. Cost of product and poor effectiveness reduces the acceptability of these products in a useful molting program. Although there are many methods available to induce molting and synchronize the second lay cycle for greater production efficiency, the most widely utilized commercial method is feed withdrawal. The high dietary zinc (HDZ) method, although producing a rapid molt rather consistently, remains a distant second, probably due to its relatively poor postmolt productive performance. Both procedures mimic nature by utilizing light manipulation and withdrawal from normal feed intake. During late summer and early fall when the day length naturally begins to shorten, wild birds exhibit anorexic behavior during their annual molt and may lose as much as one-third of their body weight. Natural molting results in a cessation of reproduction resulting in rest and rejuvenation of body tissues and energy stores. Wild birds use this process to survive the rigors of RUSZLER winter-time activities (migration or searching for a limited food supply in the snow). Even so, one must continually look at induced molting from the aspects of humaneness to and the welfare of the laying hen. Many of the methods used 20 to 30 yr ago and some of the past procedures used in research were in the humanely questionable category. However, they no longer exist because they did not work properly, were costly, or were recognized as inhumane; i.e., 2 to 3 d of water deprivation. Water removal is no longer recommended. Because the use of chemical or nutritional imbalances to induce molt are usually neither practical nor cost effective and because they usually result in poorer postmolt performance, they will not be considered further. Instead, the welfare effects of the most commonly used methods, which employ some degree of feed withdrawal over time and differing levels of feeding limitations, will be discussed. There are essentially three feed removal programs being used by commercial egg producers today. They are short fasting (SF) for 4 to 6 d (Ruszler, 1978, 1984, 1996), medium fasting (MF) for 10 d (Bell, 1988), and long fasting (LF) from 12 and up to 16 d (Brake and Carey, 1983). These methods vary mostly in their expected BWR and the length of the resting period. They all use some variation in day length changes to help initiate the molt. They use various feeding programs to maintain the rest period and initiate the subsequent lay period. These differences are tailored to meet the requirements of each particular induced resting program. As these programs are considered, one must keep in mind that induced molting is only a management tool patterned after nature that is used to help manage and synchronize the production cycles of a flock. If the hen is expected to produce eggs for more than a 1-yr cycle, she must be given a rest in order for her body to be able to function in a healthy and proper manner. The method of inducing the rest should not cause any unnecessary stress in order to optimize the desired results of the molt. It is difficult to find consistent data in the literature that identify specific stresses due to the myriad methods of molt induction and reproductive recovery being used. As noted earlier, the lack of a common optimal program arises from differences in genetics, age, environment, and previous flock production history in the various studies reported. To determine the humane aspects of molting, it must be decided which actions are unnatural, unreasonable, or unnecessary and which actions result in harm to the physical health of the hen. Water deprivation was once used until it was learned by Savage and Ruszler (1975, unpublished data) that it resulted in higher mortality and morbidity during the early stages of the molt cycle. Programs that removed feed for more than 15 d or only allowed feeding every 4 to 5 d with no physiological preparation of the hens resulted in excessive mortality or morbidity under commercial conditions. It should be obvious that these methods caused unnecessary stress and are not humane. The same may be said for methods that supply only oystershell or cracked corn for 21 d.

3 Calcium FIRST NORTH AMERICAN SYMPOSIUM ON POULTRY WELFARE 1791 DISCUSSION The present specialized SF, MF, or LF programs all induce molt and may cause stress of varying levels. Holt (1992) examined the effect of LF (14 d) on splenic and peripheral blood T and B cells. He reported that feed deprivation alters T lymphocyte subpopulations and usually early (3 or 4 d) in the feed withdrawal procedure. Feeding calcium during the first 4 to 6 d of feed restriction allows the hen to maintain proper bone and blood calcium levels. Ruszler (1974) recommended that 1.36 kg (3 lb) of oystershell per 100 hens per wk be fed during the feed restriction period to reduce the incidence of weakened bones and cage layer fatigue. Savage (1976) recommended that a level of 2.72 kg (6 lb)/100 hens be fed. Ruszler (1978) pointed out that the reduction of soft-shelled eggs would more than pay for the extra oystershell. Garlich and Parkhurst (1982) added support for the value of additional calcium carbonate during this period. They reported that cellular calcium deficiency is the first limiting nutrient for ovulation in hens without feed and that supplemental calcium will increase total egg numbers, reduce weak shells and increase marketable eggs. Brake (1993) postulated that supplemental calcium may assist the cessation of lay through the hypothalamic-hypophyseal axis. With calcium involved in many endocrine pathways, it may act to spare the extracellular bone calcium used to form shells on the last eggs laid. Lighting Light conditioning prior to feed withdrawal has been proven to eliminate the need to restrict water to affect cessation of lay. Hansen (1966) reduced day length by 8 to 10 h before starting feed restriction and reported an improvement in postmolt production of 5 to 6%. Ruszler (1974) recommended preconditioning the hens with 5 to 6 h of light reduction at least 10 d before feed withdrawal in order to get a more uniform molt response. In open housing, it is necessary to increase the day length to 20 h or more to effect this reduction. The SF program developed by Ruszler (1978) used a 5-h light reduction for 10 d premolt in conjunction with 6 d of feed withdrawal to preclude the need to withhold water. Ruszler (1996) now uses only 4 d of feed withdrawal together with light reduction to initiate the molt. This usually results in cessation of lay in 5 d. Brake and Thaxton (1982) reported on research that supported these proven and accepted commercial practices. Brake and Carey (1983) recommended a day length of 24 h for 1 wk before feed withdrawal and then a reduction to 12 h during the period without feed. This procedure is used to photosensitize the hens to the shorter day length. Andrews et al. (1987) reported that light stimulation of more than 12 h is needed before Day 42 of the molt for optimum production to occur. This conclusion supports the recommendations found in the commercial SF, MF, and LF molt systems being used. Body Weight Reduction Much of the research on molting centers around determining the amount of BWR needed to optimize postmolt performance. Studies have reported that everything from 15 to 40% BWR is required. Baker et al. (1981b) and Zimmermann et al. (1987) reported that at least a 30% BWR is required to maximize postmolt production, whereas Baker et al. (1983) reported further that a 25 to 30% BWR via a LF was needed to significantly reduce uterine lipid content and improve postmolt shell quality. However, Ruszler et al. (1984b) reported significantly improved performance in hens rested using a SF as compared to using a LF or corticosterone-induced molt. They also found no significant difference between induced molting methods on the amount of reduction of uterine lipid (Ruszler et al., 1984b). Similar results were found in a study reported by Ruszler (1986). Fontana et al. (1991) reported 6% more BWR for hens subjected to a LF than a SF, but that the SF program gave superior postmolt performance over the LF program. In another study (Fontana and Ruszler, 1990 unpublished data) it was found that hens subjected to a SF laid significantly more eggs in seven periods of 28 d each than hens molted by the LF method. Even though the SF hens lost about 25% of body weight and the LF hens 31%, there were no significant differences in uterine lipid levels. Other Research In a recent trial, Ruszler and Minear (1997) compared the performance of 80-wk-old hens molted by a SF of 4 d and limit fed a 14%/1,250 kcal ME/lb molt diet; a MF and full fed whole oats; a MF and full fed a 10%/1,175 kcal ME/lb molt diet; or a SF of 4 d and full fed a 10%/740 kcal ME/lb molt diet. The trial ran for 43 wk and resulted in no significant difference in hen-day egg production or total eggs per hen housed (157, 155, 157, and 162). There was about 30, 26, 25, and 26% BWR respectively and no significant differences in subsequent feed intake. Mortality and postmolt feed efficiency were not different. This experiment shows that 4 d of feed withdrawal with proper light manipulation is sufficient to affect complete secession of egg production. The use of a nutrient restricted molt diet consumed ad libitum results in a postmolt performance that is equal to molt procedures using limited feeding techniques. Ruszler (1986) compared results of flocks molted by SF and LF. The records of two commercial and one research flock molted by SF were summarized and compared to the records of one research and four commercial flocks molted by LF. These data showed that the SF and LF commercial flocks both averaged 41 eggs per hen housed by 14 wk postmolt. However, by 26 wk the SF flocks produced 108 eggs vs 98 eggs per hen housed for the LF hens. The

4 1792 RUSZLER TABLE 1. Grams of protein/kg of feed intake per hen during postmolt lay and weeks to reach 50% and peak production for two molt methods 10% 50% Peak 12 wk Week of Week of Molt Production Production production Production peak 50% production Short 331/ /3.67 1,080/6.58 1,120/ Long 327/ /3.67 1,279/8.57 1,170/ research flocks did not reach parity with each other until 24 wk, at which time they had laid 84 eggs per hen housed. At 44 wk postmolt, the SF research flock had laid 175 eggs vs 165 eggs per hen housed for hens molted with the LF. In summarizing all of the feed intake data, no differences were found in the amount of feed or crude protein required to reach 50% production. The SF hens took almost 8 wk to attain 50% production as compared to 6 wk for LF hens (Table 1). However, it took 2.00 kg (4.4 lb) more feed and 200 g (0.44 lb) more crude protein intake for the LF hens to reach peak production and they required 2 more wk of lay to attain it. This reflects the fact that the LF hens lost at least 5% more body weight than the SF hens and needed more time and feed intake to recover. No significant differences in shell quality were found in the research flocks summarized. However, field reports on the commercial flocks indicated that shell quality deteriorated rapidly after 6 or 7 mo of lay in LF molted hens such that the eggs were no longer profitable to process. Fontana et al. (1991) reported data that agreed with the commercial experiences. When one considers the information that is available on induced molting, most scientists and poultry growers would not find much about today s commercial molting programs that negatively affect the overall welfare of the birds. This points up the need for continuing research in this area. As always, the birds must be monitored carefully and excellent husbandry must be practiced. Flocks in poor health or poor physical condition should not be molted. The weather and age of the flock must be considered. The molt must be modified to fit any unusual factors that may be present in the flock, i.e., number of birds per cage or temperature stratifications in the house or body weight differences between cage levels. The determination of which molt method to use should depend upon the husbandry expertise level, the length of postmolt production needed, and the egg size demand of the market. The SF (4 d) program allows for more last minute flexibility in restoring production by manipulation of the lights and feeding pattern, if needed, to enhance the welfare of the hen. If one is concerned about animal welfare perceptions of induced molting, the best choice would be the SF (4 d) program (Ruszler, 1984, 1996) or possibly the HDZ method, which has no visible feed withdrawal. SUMMARY In summarizing particular welfare concerns, one must first consider length of feed withdrawal. If the work of Mrosovski and Sherry (1980) does not satisfy critics, then one must consider the fact that a broody hen (chicken or turkey) will naturally go for 21 or 28 d consuming little or no feed. During first 7 to 10 d, these birds leave the nest only to consume water. Next, if light manipulation is considered stressful, one needs only to look at nature itself. All animals are subject to it on an annual basis. The poultry grower modifies and accelerates light manipulation. We are all subject to it daily. If dietary modification is a third concern, we must remember that commercial poultry is fed the most well balanced and healthy diets of any animal on earth. Molt diet manipulations presently used for the hen are shortlived and nonstressful in the long term. They have been carefully studied and monitored through research and practical application for over 20 yr in an effort to determine what works best for the hen s well-being. Feed withdrawal to initiate a molt is within the normal physiological capability of a hen according to Garlich (1995). If one feels that the level of body weight reduction may be excessive, it must be remembered that a laying hen is primarily an egg laying machine. Her body consists of a large intestinal system, a large reproductive system, and a minimal skeletal and muscular system needed for physical support. Twenty five to thirty percent of the hen s body weight is composed of ovaries, oviduct, adipose tissue, and ingested feed and water, which is where most of the weight loss occurs. The reduction of any body weight from these areas of tissue for a short period is hardly life-threatening or stressful. Finally, excessive mortality is not tolerated and should not be a problem with the LF method if it is monitored properly. However, much of the initial mortality usually consists of weak and morbid individuals that would normally expire within 6 to 8 wk. The molt only accelerates the natural scheme of nature. Less research needs to be directed toward the practical aspects of molting techniques. Instead, there needs to be a coordinated effort directed toward the physiological and potential stress-related elements of the techniques being used. We need to educate the users of induced molting programs about potentially harmful effects of poor husbandry during a molt. They also need to understand the importance of the proper interactions of the various elements of an acceptable molting program. They need to know and understand the limits of a program so they can make informed decisions on the proper management of a molt.

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