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Apr 7, 1997 - Québec, Canada, H9X-3V9, †Institut National de la Recherche Agronomique, Centre de Tours-Nouzilly,. Station de Recherches Avicoles, ...
Effects of Environmental and Social Factors on Incubation Behavior, Endocrinological Parameters, and Production Traits in Turkey Hens (Meleagris gallopavo) G. BE´DE´CARRATS,*,† D. GUE´MENE´,†,1 and M. A. RICHARD-YRIS‡ *Department of Animal Science, McGill University, 21111 Rue Lakeshore, Ste. Anne de Bellevue, Que´bec, Canada, H9X-3V9, †Institut National de la Recherche Agronomique, Centre de Tours-Nouzilly, Station de Recherches Avicoles, 37380 Nouzilly, France, and ‡Laboratoire d’Ethologie, Unite´ Mixte de Recherche 6552, Centre National de la Recherche Scientifique, Universite´ de Rennes I, Campus de Beaulieu, 35042 Rennes Cedex, France ABSTRACT Hens raised in three different environments were assessed for changes in egg production performance, the rate of incubation behavior expression, and plasma levels of luteinizing hormone (LH) and prolactin for 20 wk following the laying of the first egg. The environments were individual (IFP) or collective floor pens (CFP) and individual battery cages (Cp and Cnp). The hens from three experimental groups (IFP, CFP, and Cp) were transferred from a short (6 h) to a long (14 h) photoperiod, whereas the ones from the remnant (Cnp) were left under a short one. Increase of the photoperiod induced significant increases (P < 0.05) in levels of prolactin and LH after 1 d, and resulted in the onset of egg laying in a delay of 14 d in all groups. However, the overall egg laying performance was

highest for the IFP hens. The CFP and IFP hens laid 98 and 24% of their eggs inside the nest boxes, respectively. The hens raised in battery cages did not express incubation behavior, whereas 50 and 33%, respectively, of the CFP and IFP hens did. During the 1st wk of egg laying, levels of prolactin increased for all photostimulated hens but to a greater extent for CFP hens. Higher increases in levels of prolactin were associated with the expression of incubation behavior; however, prolactin levels of nonincubating laying hens were also higher under the CFP treatment. It appears that the rate of expression of incubation behavior, as well as changes in the plasma levels of prolactin and LH throughout an egg production period, are dependent upon rearing conditions in turkey hens.

(Key words: environmental factors, incubation behavior, prolactin, turkey hens) 1997 Poultry Science 76:1307–1314

INTRODUCTION In turkey hens commercially raised for egg production, the achievement of sexual maturity is stimulated by extending the photoperiod from less than 8 to over 12 h of light, which induces changes in the activity of the hypothalamo-hypophyso-ovarian axis. Luteinizing hormone-releasing hormone (LHRH) stimulates the release of LH (Burke and Cogger, 1977), which, in turn, stimulates the secretion of steroids in the ovary (Bajpayee and Brown, 1972; Mashaly and Wentworth, 1974). These hormonal variations are concomitant with the maturation of the reproductive apparatus, which leads to the first oviposition. Following the increase in photoperiod, levels of prolactin have been shown to either increase (Etches and Cheng, 1982) or remain low (Burke and Dennison, 1980), whereas levels of LH have been shown to increase (Godden and Scanes, 1977; Burke and Dennison, 1980; Lea and Sharp, 1982; El

Received for publication November 7, 1996. Accepted for publication April 7, 1997. 1To whom correspondence should be addressed.

Halawani et al., 1984). During the egg production period, levels of LH fluctuate with each successive ovulation (Sharp et al., 1981). During the course of the egg production period, LH levels progressively decline (Gue´mene´ and Williams, 1994), whereas levels of prolactin increase, rate of egg laying decreases, and expression of incubation behavior starts to occur (Burke and Dennison, 1980; Harvey et al., 1981; Proudman and Opel, 1981). Turkey hens that express incubation behavior have high levels of prolactin and low levels of LH (Burke and Dennison, 1980; Proudman and Opel, 1981; Etches and Cheng, 1982; Sharp et al., 1988), and the hens usually stop laying eggs and reduce their feed intake (Zadworny et al., 1985a). Environmental factors have been shown to have an impact on the expression of incubation in turkey hens (for review: Gue´mene´, 1992). Such environmental factors may include social factors; however, the relationships between social factors, expression of incubation behavior, and changes in hormonal parameters during a reproductive cycle have not been studied in depth. The aim of the present study was therefore to compare hormonal profiles (LH and prolactin), egg laying

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performance, feed intake, and the occurrence of incubation behavior throughout an egg laying cycle in turkey hens reared in collective or individual floor pens and in battery cages.

MATERIALS AND METHODS

Animals Medium White turkey hens (n = 40), provided by BETINA,2 were randomly allocated to four groups at 28 wk of age and placed in three different environments. Two groups of eight hens each (Cp and Cnp treatment) were placed in individual battery cages (size: 0.45 × 0.60 × 0.60 m). One group of 12 hens was placed in a collective floor pen (CFP treatment: 5 × 3.7 m) with one nestbox per hen. The remaining 12 hens were placed in individual floor pens (IFP treatment: 1.79 × 0.86 m; n = 12) with one nestbox per pen. All the nestboxes contained four artificial eggs. The hens were raised under a 6-h photoperiod until their 30th wk of age. With the exception of the Cnp hens that stayed under the same photoperiod, all other hens were exposed to a 14-h photoperiod from 30 wk of age onward. The minimal light intensity was of 50 lx for all hens. They were fed on a standard diet provided for ad libitum intake and had free access to water.

Experimental Approach The turkey hens were individually weighed once a month, and their feed consumption were measured weekly from the 1st d of the experiment until week 20 of the egg production period. Egg production and expression of incubation behavior were recorded daily during the 20-wk production period. A hen was considered to be incubating if it was sitting in the nestbox or at any other site at least three times out of the four daily inspections (0900, 1130, 1400, 1630 h) during 3 consecutive d. Eggs were collected at each check and the laying sites, inside or outside the nestbox, were also recorded. Blood samples (5 mL) were withdrawn into heparinized syringes on the day prior to photostimulation (J-1), the day of photostimulation (J0) and 1, 2, 3, 4, 5, and 8 d after photostimulation. Thereafter, samples were taken weekly throughout the 20 wk of the productive period. Plasma was separated from blood by centrifugation (2,000 × g for 10 min at 4 C) and kept at –20 C until required for radioimmunoassay of prolactin and LH.

Radioimmunoassays All samples from a specific hen were assayed within the same assay, whereas hens from each treatment were

2BETINA, 3ABACUS

56250 Saint Nolff, Elven, France. Concept, Brain Power Inc., Calabasas, CA 91302.

FIGURE 1. Variations in the laying rate of turkey hens raised in battery cages (Cp), individual floor pens (IFP), and collective floor pen (CFP) throughout a 20-wk productive period.

evenly distributed across assays. Prolactin was assayed in triplicate using up to 100 mL plasma samples depending upon the physiological stage as previously described by Gue´mene´ et al. (1994). The mean intra-assay variation was 6.5% and the interassay variation for the three assays needed was 15.5%. Luteinizing hormone was assayed in triplicate using 100 mL plasma samples according to Sharp et al. (1987). The mean intra-assay variation was 5.3% and the interassay variation for the two assays needed was 6.5%.

Statistical Analysis Data were compared using a factorial ANOVA and a Fisher protected least significant difference (PLSD) test if appropriate (P ≤ 0.05; ANOVA). All statistical analysis were done with Statview23 for MacIntosh.

RESULTS

Egg Laying Performance The change of the egg laying intensities throughout the trial are presented in Figure 1. The nonphotostimulated hens (Cnp) did not lay any eggs throughout the experimental period. On the other hand, the first egg was laid 2 wk after photostimulation for each of the three photostimulated groups (Cp, CFP, and IFP). The peak of egg production was observed after 2, 5, and 6 wk of egg laying and the maximum laying intensities were of 86, 79, and 83% for the CFP, IFP, and Cp groups, respectively. The mean egg laying intensities over the 20-wk period were 57, 50, and 50% for the IFP, CFP, and Cp groups, respectively. The laying intensities decreased progressively from peak until Week 20 of egg production for the IFP and Cp groups. The drop in production observed for the Cp group between the 9th and the 11th wk was due to a pause in egg laying in three of eight hens. Egg laying

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FIGURE 2. Variations in the incubation rate throughout a 20-wk productive period of turkey hens raised in individual floor pens (IFP) and collective floor pen (CFP).

intensities of the CFP group decreased rapidly between Weeks 4 and 7 of the production period from 78.6 to 47.6%, then stayed stable until Week 20. For the CFP and IFP groups, 97.6 and 24.0% of the eggs, respectively, were found laid inside the nest. Moreover, in the IFP group, most of the eggs laid inside the nest boxes were from two hens that later exhibited signs of incubation behavior.

Incubation Behavior Expression The weekly evolution of the rates of expression of incubation behavior are presented in Figure 2. The first hens found incubating eggs were detected on Weeks 3 and 4 of egg production for the CFP and IFP group, respectively. None of the hens from the Cp group expressed incubation behavior throughout the course of this study. On the other hand, 4 out of the 12 hens (33%) from the IFP group expressed this behavior; however only 2 of them exhibited the full incubation behavior repertoire leading to cessation of egg laying. The two other hens were only transiently incubating and continued to lay eggs. In the CFP group, 6 out of 12 hens (50%) fully expressed incubation behavior. Interestingly, the hens were not always found in the same nest although they stayed in the same area of the floor pen.

FIGURE 3. Variations (x ± SEM) in the weekly feed intake of turkey hens (Cnp) under a short photoperiod (6 h) raised in battery cages or in battery cages (Cp), individual floor pens (IFP) or collective floor pen (CFP) and a long (14 h) photoperiod, throughout a 20-wk productive period. An asterisk indicates a significant difference between the Cp and the Cnp group (P < 0.05).

per hen after the 7th wk for the Cnp hens. The feed consumption of the IFP and CFP groups increased of approximately 40 and 60%, respectively, between the time of photostimulation and the 2nd wk of egg production (from 138 to 190 g/d per hen, IFP; from 120 to 190 g/d per hen, CFP). Consumption stayed stable around 180 g/d per hen thereafter for the IFP group, whereas it decreased markedly with the onset of incubation expression for the CFP group. Feed consumption went down to 92 g/d per hen on the 6th wk of egg production and increased progressively until the end of the experiment, up to 190 g/ d per hen. The differences in feed consumption between the turkey hens that expressed and those that did not express incubation behavior in the IFP group were highly significant (P < 0.01) during the incubation period (Figure

Feed Consumption The weekly consumption of feed for the different experimental groups are reported in Figures 3 and 4. As the turkey hens raised in the CFP group were fed collectively, it was impossible to record individual data. The feed consumption of the turkey hens raised in cages and photostimulated (Cp) was higher than those that were not photostimulated (Cnp); significant differences (P < 0.05) were measured for Weeks 2, 5, 9, 11, 13, 14, and 17 to 19 of the Cp hen’s productive period. The feed consumption remained stable around 205 g/d per hen during all the productive period for the Cp hens and around 155 g/d

FIGURE 4. Variations (x ± SEM) in the weekly feed intake of turkey hens raised in individual floor pens (IFP) that did or did not express incubation behavior *P < 0.01.

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FIGURE 5. Changes (x ± SEM) in live body weight of hens raised under a short photoperiod (6 h) in battery cages (Cnp) or in battery cages (Cp), individual floor pens (IFP), or collective floor pen (CFP) and a long (14 h) photoperiod, throughout a productive period. An asterisk indicates a significant difference between the Cnp group and the IFP and CFP groups (P < 0.05).

4). An increase in the amount of feed consumed by the incubating hens was observed 4 to 5 wk after the onset of incubation while the hens were still fully expressing this behavior.

Body Weight Body weight for each group was initially comparable but changed differently throughout the experimental period depending on the treatment (Figure 5). The Cnp hens increases in body weight from 8.9 to 10.1 kg, whereas hens from the Cp group showed a similar increase in their body weight during the 1st experimental mo (from 8.8 to 9.4 kg), but their weight remained stable afterwards until the end of the experiment (data not shown). The hens raised in floor pens showed a decrease in their body weight until Weeks 10 and 15 of the egg production period for the IFP (from 8.3 to 7.5 kg) and the CFP group (from 8.6 kg to 7.1 kg). Body weights of these hens increased thereafter to reach 7.9 and 7.5 kg for the IFP and CFP hens, respectively. The differences in body weight between the photostimulated hens raised in battery cages and those raised in floor pens were significant (P < 0.01) from the 2nd until the 20th wk of egg production. The hens that expressed incubation behavior showed a loss of body weight from the 2nd to the 15th wk and the differences with those of the nonincubating hens were significant (P < 0.01) between Weeks 10 and 20 of egg production (data not shown).

FIGURE 6. Prolactin concentrations (x ± SEM) in turkey hens raised under a short photoperiod (6 h) or transferred from a short to a long (14 h) photoperiod. An asterisk indicates a significant difference between two consecutive measurements (P < 0.01).

Prolactin levels stayed low throughout the experimental period for the nonphotostimulated hens (Cnp), whereas, a fivefold increase (from 2.7 to 13.0 ng/mL) in the level of prolactin was measured between Day 1 and 8 for the hens subjected to an increase of photoperiod. This difference was significant (P < 0.01) by 1 d after photostimulation. The increase in the levels of prolactin tended to be higher for the turkey hens raised in floor pens; however, the differences were not significant (data not shown). The levels of prolactin further increased in all photostimulated hens after the onset of egg laying, but the amplitude was dependant upon the treatment (Figure 7). Indeed, the levels of prolactin increased up to 40 ng/mL on Week 6 of the egg production period and stayed stable thereafter for the Cp hens. The IFP hens showed a fivefold increase of their prolactin levels between the onset and the 5th wk of egg production (from approximately 20 to 120 ng/mL). Prolactin reached a maximum level (136 ng/mL)

Prolactin Concentrations Changes in prolactin concentrations around the time of photostimulation are presented in Figure 6, whereas those occurring throughout the 20 wk of the production period are shown in Figures 7, 8, and 9. Before photostimulation, all turkey hens had comparable low levels of prolactin of approximately 3 ng/mL.

FIGURE 7. Prolactin concentrations in turkey hens raised (Cnp) under a short photoperiod (6 h) in battery cages or in battery cages (Cp), individual floor pens (IFP), or collective floor pen (CFP) and a long (14 h) photoperiod, throughout a 20-wk productive period. An asterisk indicates a significant difference between the CFP and the IFP groups (P < 0.05).

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FIGURE 8. Prolactin concentrations (x ± SEM) in turkey hens raised in floor pens and expressed incubation behavior or not throughout a 20-wk productive period. *P < 0.05.

on Week 9 and decreased steadily thereafter to 60 ng/mL by the end of the production period. The CFP hens showed a 10-fold increase in prolactin levels between the onset and the 5th wk of egg production (from 25 to 249 ng/mL). The highest prolactin level was also observed on the 9th wk (257 ng/mL) and the levels progressively decreased to 119 ng/mL during the 20th wk of the egg production period. Prolactin concentrations were significantly (P < 0.05) higher in the CFP hens than in the IFP and Cp hens between the 4th and the 20th wk of egg production. These differences in levels of prolactin were attributable mainly to the higher level of expression of incubation behavior in the CFP hens, as incubating hens had about 3.5-fold higher level of prolactin than nonincubating hens between Week 6 to 15 of egg production (Figure 8). Subsequently, this difference in levels of prolactin was not maintained.

FIGURE 9. Prolactin concentrations (x ± SEM) in turkey hens raised in battery cages (Cp), individual floor pens (IFP), or collective floor pen (CFP) that did not express incubation behavior throughout a 20-wk productive period. An asterisk indicates a significant difference between the CFP and the Cp groups (P < 0.05). A plus sign indicates a significant difference between the CFP and the IFP groups (P < 0.05).

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FIGURE 10. Luteinizing hormone (LH) concentrations (x ± SEM) in turkey hens raised under a short photoperiod (6 h) or transferred from a short to a long (14 h) photoperiod. *P < 0.01.

Prolactin levels of the nonincubating CFP hens were significantly higher (P < 0.01) than those of the nonincubating Cp hens from the 3rd until the 20th wk and than those of the nonincubating IFP hens for Weeks 4, 6, 7 to 12, 16, 19, and 20 of the productive period (Figure 9).

LH Concentrations Changes in concentrations of LH around the time of photostimulation are shown in Figure 10. On the day of photostimulation, LH levels were comparable for all groups. The nonphotostimulated hens did not show any significant changes in LH concentrations, whereas it increased from 0.84 to 1.27 ng/mL, 3 d after photostimulation, and then stayed stable until the onset of egg laying. Differences reached significance (P < 0.01) by 1 d after photostimulation. No significant difference in LH levels was observed Day 2 onward for the hens raised in battery cages (data not shown). Levels of LH in the nonphotostimulated hens stayed stable and low (between 0.50 and 0.90 ng/mL) throughout the experiment (data not shown). For the Cp-treated hens, concentrations of LH decreased markedly between 1 wk before and the 4th wk after the onset of egg laying (from 1.55 to 0.93 ng/mL), then remained stable thereafter (around 0.90 ng/mL). Levels of LH from both IFP and CFP hens increased after the onset of egg laying and reached a maxima after 3 wk of egg laying (1.44 and 1.40 ng/mL for the IFP and CFP group, respectively). Thereafter, LH levels measured for the IFP hens decreased progressively down to 0.99 ng/mL on Week 14, whereas LH levels dropped to a comparable level by Week 5 of the egg production period for the CFP hens. In both cases, LH levels stayed at approximately 1.00 ng/mL thereafter. With the exception of the sampling at Weeks 5, 8, 11, and 14, LH levels for the Cnp hens were significantly lower (P < 0.05) than those for the hens of the other groups. Laying and incubating hens had the same overall profile of levels of LH (data not shown), with maximum

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level measured on Week 3 of egg production (1.40 and 1.32 ng/mL for laying and incubating hens, respectively).

DISCUSSION Photostimulation induced sexual maturity after a delay of 14 d. During this period, plasma levels of LH and prolactin increased; whereas in nonstimulated hens these hormone levels did not change. An increase in LH has previously been shown to occur within 3 d after photostimulation in turkey hens (Burke and Dennison, 1980; Petrowski et al., 1993) with maximum levels being measured at about the time of the first oviposition (Burke and Dennison, 1980). Similarly, the same type of pattern of LH was observed in the current study; however, the level of LH was highly dependent upon the environment in which the hen was maintained. Indeed, maximum levels of LH were measured already on Day 2 after photostimulation for the hens raised in cages and these subsequently decreased by the onset of sexual maturity. In contrast, for the hens raised in floor pens, LH levels further increased after the onset of sexual maturity, rising to a maximum between Weeks 3 and 5 of egg production. Plasma levels of prolactin also rose immediately following photostimulation. In all environments, plasma levels of prolactin increased within a few days after photostimulation and then further increased at the onset of egg laying to reach maximum levels during the first half of the egg production period; however, the amplitude of these changes were associated with the environment in which the hens were maintained. Controversy has appeared in the literature concerning immediate change in plasma levels of prolactin following photostimulation. Indeed, plasma prolactin levels have been shown to either increase (Etches and Cheng, 1982) or stay low (Burke and Dennison, 1980) following photostimulation. It was hypothesized that the observed prolactin increase in the study of Etches and Cheng (1982) might be due to the stress associated with the transfer of the hens to a different environment. Alternately, under our experimental conditions, significant increases in prolactin levels were observed in the absence of any environmental change with the exception of the photoperiod. Hens raised in floor pens had higher levels of prolactin than hens in cages and the CFP group had the highest levels. These results suggest that levels of both LH and prolactin are directly or indirectly influenced by the rearing conditions of the hens; however, the mechanism(s) by which this occurs requires further investigation. It is noticeable that the initial rise in LH level was associated with a rise in prolactin, whereas a negative influence of prolactin upon LH release has been reported, as the injection of ovine prolactin delayed the acquisition of sexual maturity in turkey hens (El Halawani et al., 1991). The absence of effect or a positive influence of low or

moderate levels of prolactin upon the acquisition of sexual maturity and LH release can be hypothesized. After the first few weeks of egg production, the levels of prolactin continued to increase for hens raised in floor pens and to a much greater extent for the CFP group. Maximum levels were reached on the 8th wk of egg production, at which time the levels measured for this group were two- and sixfold higher than those of the IFP and Cp group, respectively. This rise in blood level of prolactin was concomitant with a decrease in egg laying intensity and with the onset of incubating behavior. As the expression of incubation behavior only occurred in floor pens and especially when hens were raised collectively, it is hypothesized that the observed changes in prolactin are directly related to, behavior, which, in turn, is dependent upon rearing conditions. Indeed, it appears that on the 4th wk of lay, higher prolactin levels were observed for the hens that will express incubation behavior later on. Variations in the levels of LH and prolactin are thus clearly related with the reproductive status as previously reported (Cogger et al., 1979; Burke and Dennison, 1980; El Halawani et al., 1980; Harvey et al., 1981; Proudman and Opel, 1981; Zadworny et al., 1988; Gue´mene´ and Williams, 1994); however, higher levels of plasma prolactin were also measured in nonincubating laying hens raised under CFP. Therefore, prolactin levels are not only related to the reproductive status itself, but also dependent upon rearing conditions or social factors. Tactile stimulation from the nest and the eggs (Hall, 1987; Opel and Proudman, 1988; Leboucher et al., 1993) as well as view of the eggs (Daniel, 1993), have been shown to be important factors in initiating or maintaining incubation behavior. Furthermore, an increase in nesting time has been shown to be associated with a rise in the levels of prolactin (Burke et al., 1981; Lea et al., 1981), whereas nest deprivation (El Halawani et al., 1980), or environmental changes (Proudman and Opel, 1981; Gue´mene´ and Etches, 1990) can disrupt expression of incubation behavior and result in decreases in prolactin levels. Under our experimental procedure, the CFP hens laid most of their eggs inside the nestboxes and the expression of incubation behavior was twofold higher in this group than in the IFP group. Consequently, the CFP hens had more visual and tactile contact with both eggs and nestboxes, which might have contributed to the stimulation of prolactin secretion. In turn, the higher levels of prolactin might have promoted expression of incubation behavior in this group. Although high levels of prolactin are associated with the expression of incubation (Burke and Dennison, 1980; Proudman and Opel, 1981; Etches and Cheng, 1982), they don’t appear to be necessary for its long-term maintenance. Indeed, after several weeks of incubation, prolactin concentrations started to decline and by the end of the experiment the prolactin concentrations measured for the incubating hens were comparable to those of the nonincubating hens. During the first 4 wk of the experiment, feed consumption was higher for the photostimulated hens

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raised in cages than for those raised in floor pens. We would have expected the reverse situation, as the hens raised on the floor should have higher metabolic requirements, and we have no ready explanation for such an observation. However, it is clear that environmental factors also influenced feed consumption. As a consequence, body weight of the hens placed in cages increased, whereas in the other groups body weight either stayed stable or decreased. During incubation, feed intake has been shown to be dramatically reduced (Zadworny et al., 1985a). Likewise, under our experimental condition, the IFP incubating hens decreased their feed consumption by 90% and consequently lost 20% of their body weight. However, an increase in feed intake was observed while the hens were still incubating and before then the levels of prolactin started to decrease. Similarly, it has been reported (Zadworny et al., 1985b) that force feeding of incubating hens has no effect on the concentration of prolactin. No data regarding feed intake in long-term incubation were available in the literature. In the present experiment, most of the hens expressed incubation behavior for more than 15 wk. However, these hens showed an increase in their feed intake after a delay of approximately 5 wk after starting to incubate. Thus, the period of anorexia associated with incubation in turkey hens seems to have about a 5-wk limit possibly related to the capacity to mobilize body reserves. In summary, rearing conditions had an effect on all studied criteria. The floor pen environment seemed to be associated with lower LH levels and higher prolactin levels between photostimulation and the onset of sexual maturity, and the highest concentrations of prolactin throughout the experimental period. The collective floor pen was associated with a higher rate of egg laying in the nestboxes, which may have led to an increase in the amount of both visual and tactile stimuli associated with the eggs. This may have led to higher levels of prolactin and subsequently a higher rate of expression of incubation behavior.

ACKNOWLEDGMENTS The cooperation of BETINA in providing turkey hens, was greatly appreciated. Our thanks are extended to P. J. Sharp for supplying the material used in the LH assay. We are indebted to M. Garreau-Mills and S. Nevoit for their expert technical assistance. We also thank D. Zadworny for the invaluable comments, advice, and improvements to the manuscript.

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