The effect of maternal care and infrared beak trimming on development, performance and behavior of Silver Nick hens

Applied Animal Behaviour Science 140 (2012) 70–84

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Applied Animal Behaviour Science journal homepage: www.elsevier.com/locate/applanim

The effect of maternal care and infrared beak trimming on development, performance and behavior of Silver Nick hens Milou J. Angevaare a,∗ , Sander Prins a , Franz Josef van der Staay a,b , Rebecca E. Nordquist a,b a b

Emotion & Cognition Group, Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, The Netherlands Rudolf Magnus Institute for Neurosciences, University Medical Center Utrecht, Utrecht, The Netherlands

a r t i c l e

i n f o

Article history: Accepted 22 May 2012 Available online 15 June 2012 Keywords: Laying hen Behavioral tests Learning Sociality Body weight Productivity

a b s t r a c t In the commercial poultry industry, feather pecking leads to damage to the chickens and an increased mortality rate. The effects of two (possible) feather pecking prevention methods, infrared trimming and maternal care, on production parameters, fear, sociality, learning, feeding behavior, and feeding motivation were examined in young Silver Nick hens. Thirtynine Silver Nick hens were tested from the day of hatching until 21 weeks of age. Half of these chickens were beak trimmed using an infrared beam. Half of the trimmed and half of the intact chicks were placed with a foster mother for the first 6 weeks. Thus, four groups of nine or ten chicks each were formed: trimmed × reared by mother (nine), trimmed × reared without mother, intact × reared by mother, and intact × reared without mother. Starting at 5 days of age the chickens were weighed weekly and an egg productivity indicator based on physical characteristics of each hen was scored at 17 and 20 weeks of age. An open field test, a first voluntary human approach test, a Y-maze test for sociality, a food preference test, a food rewarded Y-maze test, and a second voluntary human approach test were preformed successively between 4 and 21 weeks of age. Trimmed birds had a lower body weight than those with an intact beak up to and including 8 weeks of age. Furthermore, trimmed birds had lower egg productivity indicator scores based on physical characteristics at 17 weeks of age, and to a lesser extent at 21 weeks of age. The trimmed birds were also less efficient at eating grains, mealworms, grapes, spaghetti and raisins and picked up 63% less food per peck than the intact chickens in the food preference test. Overall, the results show that infrared beak trimming has a slightly suppressive impact on production parameters and pecking efficiency, but not on fear, learning or sociality. Maternal care had very little effect on any of these parameters. © 2012 Elsevier B.V. All rights reserved.

1. Introduction Beak trimming is a common procedure in the Dutch commercial poultry industry. A proposed ban on beak trimming in the Netherlands was recently postponed

∗ Corresponding author at: Emotion & Cognition Group, Department of Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Yalelaan 7, 3584 CL Utrecht, The Netherlands. Tel.: +31 030 253 1248; fax: +31 030 252 1887. E-mail addresses: [email protected], [email protected] (M.J. Angevaare). 0168-1591/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.applanim.2012.05.004

until September 1, 2021 (Ministry of Economic Affairs, Agriculture and Innovation, The Netherlands, 2011). Beak trimming is a preventive measure against damage from feather pecking. Feather pecking is the pecking at feathers (gentle feather pecking) or plucking of feathers (severe feather pecking) of one bird by another bird (Savory, 1995). It is thought to be redirected dust-bathing (Johnsen et al., 1998) or ground pecking behavior (Blokhuis, 1986). Feather pecking can result in pain, suffering, and even mortality due to cannibalism, making it a welfare as well as economic concern. Beak trimming involves the removal of the tip of the beak, where the amount of beak removed as well as the

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method of removal varies. As a result of a decline in damage and mortality due to feather pecking and cannibalism (Craig and Lee, 1990; Cunningham, 1992), chickens experience lower levels of stress (Onbas¸ilar et al., 2009), pain and suffering (Jendral and Robinson, 2004) following trimming. Hot blade trimming, which involves the simultaneous cutting and cauterizing of the beak using a heated guillotine-type blade, has been the favored method of beak trimming (Jendral and Robinson, 2004). However, as the tip of the beak is a vital structure with extensive nerve innervation (Dubbeldam, 1998), this method is associated with several drawbacks, as indicated by signs of acute and chronic pain (Gentle, 1991) such as reduction in preening, environmental pecking and overall activity (Gentle et al., 1991, 1997); and hampered feed intake and decreased body weight in the weeks following trimming (Gentle et al., 1982; Prescott and Bonser, 2004). An alternative trimming method, which is possibly less compromising to hen welfare, has therefore been developed. This method uses an infrared beam to damage the corneum-generating basal tissue of the tip of the beak, preventing continued germ layer growth. Consequently, 7–10 days post-trimming, the tip of the beak starts to erode away (Dennis et al., 2009). The loss of the tip of the beak is gradual, which affords the animal time to adapt to the altered size and shape of the beak, contrary to when a blade is used. Other proposed benefits of this method are: the absence of open wounds; a reduction of handling stress because infrared trimming can occur simultaneously with vaccination at the hatchery; and a minimization of variability of the outcome, due to automation of the process (Dennis and Cheng, 2010). Furthermore, because infrared trimming occurs on the day of hatching, drawbacks associated with trimming at a later age, such as the development of neuromas, are avoided (Cheng, 2006; Jendral and Robinson, 2004). Although it has been reported that infrared treatment causes a greater decrease in body weight and higher levels of inactivity than hot blade treatment (MarchantForde et al., 2008), subsequent research has shown that the depressive effects on feed intake and body weight are milder following infrared treatment than other forms of trimming (Dennis and Cheng, 2010; Marchant-Forde and Cheng, 2010). Additionally, infrared trimmed birds had superior feather condition and are less aggressive than those treated with a hot blade (Dennis et al., 2009). The development of feather pecking behavior is influenced by living conditions, such as floor type, in early life (Johnsen et al., 1998). For more information on the factors that influence the development of feather pecking, see the review by Rodenburg et al. (2008). Altering these conditions may help prevent feather pecking (Jensen et al., 2006). Although maternal care is not mandatory for the survival of precocial birds, several studies have shown that the presence of a hen during rearing may have positive effects on chicks (Shimmura et al., 2010). The presence of a mother hen is important for the development of feeding behavior and food preferences in chicks, and provides temporal and spatial structuring factors to the expression of behavior (Nicol, 2004; Wauters et al., 2002; Wauters and RichardYris, 2002, 2003). The capacity for demonstrating pecking behaviors has, however, been shown to vary between

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individuals (Nicol et al., 1999). Furthermore, brooded chicks and pullets are less fearful than their non-brooded counterparts (Perré et al., 2002; Rodenburg et al., 2009; Shimmura et al., 2010). Rodenburg et al. (2004) reported that chicks that were fearful at a young age were more likely to feather peck in adulthood. Therefore, by decreasing fearfulness, the presence of a mother hen could play a role in preventing feather-pecking behavior. Furthermore, it has been proposed that the presence of a broody hen during rearing stimulates earlier environmental pecking and perch use, which may help prevent feather pecking once the chicks reach adulthood (Riber et al., 2007). More research is required to further understand the effects of beak trimming, maternal care and their interaction on laying hens from early life through to adulthood. The aim of the present study was to evaluate the effects of infrared trimming and maternal care on body weight and physical productivity characteristics, and performance in behavioral tests designed to assess fear, sociality, learning, feeding behavior, and feeding motivation. Behavioral tests were mostly performed during the chickens’ rearing period. The voluntary human approach and open field tests are generally accepted behavioral tests in chickens during this period. The open field test has been used extensively to test for anxiety (Buitenhuis et al., 2004; Nordquist et al., 2011; Rodenburg et al., 2004, 2009). The voluntary human approach test has also been used in several studies as a test for fearfulness (Nordquist et al., 2011; Shimmura et al., 2010). Nordquist et al. (2011) showed that the latency to peck at a mealworm in the hand of a familiar human during a voluntary human approach test at about 4 weeks is a useful parameter for fear. Furthermore, Nordquist et al. (2011) used a T-shaped maze to test sociality in young chickens. Because a large portion of the chickens in that study never left the start box during the four test trials, they suggested the use of a Y-maze for assessing sociality. In a Y-maze, the stimulus chickens (at the end of the arms) can be seen by the test chicken from the start arm. This may help draw it toward the oblique arms. Therefore a Y-shaped maze was used in the present study to test sociality. A simple food preference test was used to determine the most appropriate reward for subsequent Y-maze and human approach tests and to provide us more information on how maternal care and beak trimming affect feeding behavior. Feeding behavior is an important production and welfare parameter. A modified Y-maze was also carried out to assess learning and food motivation. Additionally, an individual productivity indicator was scored for each chicken using a novel method based on physical characteristics to examine the effects of maternal care and trimming on productivity at two different ages. 2. Materials and methods 2.1. Welfare note All procedures were approved by the ethics committee of Utrecht University, The Netherlands, and were

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conducted in accordance with the recommendations of the EU directive 86/609/EEC. All efforts were taken to minimize the number of animals used and their suffering.

2.2. Animals and housing Forty Silver Nick hen chicks were acquired from Verbeek Hatchery Holland (Lunteren, The Netherlands) on the day of hatching. Half of these chicks were subjected to routine infrared beak treatment at the hatchery (NOVA-Tech Engineering Inc., Wilmar, MN, USA). Upon arrival at the experimental facilities half of the chicks with a trimmed beak and half of the chicks with an intact beak were randomly placed with a ‘foster mother’, a mature Silkie hen. Consequently, four groups of 10 chicks each were formed: trimmed × reared by mother, trimmed × reared without mother, intact × reared by mother, and intact × reared without mother. One of the chicks in the group trimmed × reared by mother was found dead 1 week post-arrival. Examination of the body of the chick revealed that the tip of the tongue was missing and the remaining part of the tongue was discolored, which suggested that the infrared treatment might have played a role in the death of this chick. From this point on, the group trimmed × reared by mother consisted of nine chicks. In order to individually identify the chicks, the feathers were individually marked with blue and green pig paint at the age of 4 weeks; these marks were refreshed approximately once a month. Only one of the available potential foster hens showed appropriate brooding behavior. Therefore, the trimmed × reared by mother and intact × reared by mother groups were housed together with the broody hen at 2 days of age. To equalize conditions, the two groups reared without a mother were also housed together. The foster mother was removed at 6 weeks of age. At 8 weeks of age, each of the four groups of chickens was housed separately, in pens measuring 200 cm × 400 cm, on a floor covered in chopped straw. A 4.5 cm × 190 cm perch was positioned along the sidewall at a height of 40 cm. A terrace heater (2000 W) was installed in each pen, which was switched on continuously until the chicks were 17 weeks old. Each group was provided with ad libitum feed and water. Chick mash (De Heus Besterfood Opfokleghen voer) was provided until 16 weeks of age. From this age on, layer feed (De Heus Besterfood Legkorrel Scharrel) was provided. Additionally, mixed grains (Besterfood) were scattered in each pen once a day from the day of arrival. In these pens the chickens were kept under natural lighting conditions (sunrise – sunset at arrival: 08:00 h – 17:00 h; sunrise – sunset at finish of experiments: 07:00 h – 20:30 h). Two laying nests (30 cm × 30 cm × 32 cm), one on top of the other were installed in each of the pens at 16 weeks of age. The chicks were allowed to adapt to the new environment for the first 2 weeks after arrival. Subsequently, the chicks were handled for 2 weeks prior to starting behavioral testing.

2.3. Body weight Starting at 5 days of age, the chicks were weighed once a week. The individual weight of each chick could be recorded after marking at 4 weeks of age. 2.4. Egg productivity indicator Several physical characteristic of each hen was scored at 17 weeks (124 days) and 20 weeks (145 days) of age as an indicator of egg productivity. As a chicken starts to produce eggs, this is reflected in several physical characteristics. These characteristics, and the criteria used to score them are clarified in Table 1 (unpublished electronic teaching material of the Faculty of Veterinary Medicine, Utrecht University written and based on observations by Dr. R.M. Dwars). Each characteristic received a score of 0, 1 or 2. A sum score was also calculated for each hen (0–8). All scoring was done by the same observer. 2.5. Behavioral tests An open field, a voluntary human approach test, a Y-maze test for sociality, a food preference test, a foodrewarded Y-maze test, and a second voluntary human approach test were performed successively over 17 weeks. The order of testing of the chickens within each test was randomized using the SAS PLAN procedure (SAS Institute Cary, NC, USA). 2.5.1. Open field test at 29–30 days of age The open field was used to evaluate anxiety in the chickens. 2.5.1.1. Apparatus. The apparatus consisted of an observation pen measuring 122 cm × 122 cm (Fig. 1A), which was constructed using Medium-Density Fiberboard (MDF) and was 74 cm high. The floor of the pen was covered with a black rubber mat, which was divided into 25 squares of 24 cm × 24 cm by white chalk lines. A video camera was positioned directly above the apparatus. 2.5.1.2. Procedure. Each chick was gently placed in the middle square individually and remained in the pen for 10 min. Latency to walk, number of lines crossed, total time spent walking, latency to call, number of distress calls, and number of defecations were recorded. The mean speed of walking was calculated from the number of lines crossed and the total time spent walking. All visual observations were made using the video feed in the adjacent room. The distress calls were counted by an observer within the test room, but not visible for the chick being tested. All chicks were tested once over the course of 2 days, and all tests occurred between 9:30 h and 17:00 h. 2.5.2. First voluntary human approach test at 33–34 days of age A voluntary human approach test was carried out to evaluate fear in the chickens.

Table 1 Egg productivity indicator score. A description of the criteria for the score 0 and 2 are provided for each characteristic. A 1 was scored, if a characteristic fell somewhere between these criteria. Pictures are provided of a chicken which received a 0 (left) or a 2 (right) for both the facial skin and comb characteristics. (For interpretation of the references to color in this table, the reader is referred to the web version of the article.). Non-productive chicken (0)

Productive chicken (2)

Comb (see pictures below) Facial skin, around the eyelid and beak (see pictures below) Pubic bones

Small, pale Bright yellow

Large, red Pale

Hard, inflexible, club-shaped, little space between bones

Cloaca

Narrow, pink and dry mucus membrane, pale mucocutaneous zone

Flexible, thin, a lot of space between bones (2–3 fingers fit between the bones) Wide, pale and moist mucus membrane, chalk-white mucocutaneous zone

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Physical characteristic

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Fig. 1. Apparatus of the behavioral tests: (A) open field test; (B) first voluntary human approach test; (C) Y-maze test for sociality; (D) food preference test; (E) food-rewarded Y-maze test; (F) second voluntary human approach test.

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2.5.2.1. Apparatus. The experiment took place in an enclosed pen measuring 400 cm × 200 cm covered in chopped straw, which was divided widthwise into three rectangular compartments (133 cm × 200 cm) by chalk lines on the walls (Fig. 1B). 2.5.2.2. Procedure. Prior to this test, the chicks had been introduced to mealworms in their home pens. A familiar human was seated at the back of the pen in compartment 3 with four to six mealworms in her hand. An observer gently placed the chick in compartment 1, and then made all observations from outside the pen. The chick remained in the test space for 10 min. During this time, latency to walk, latency to enter compartment 2, latency to enter compartment 3, latency to peck at and latency to eat the mealworms were recorded. All chicks were tested once over the course of 2 days and all tests occurred between 9:30 h and 16:00 h. 2.5.3. Y-maze test for sociality and learning at 61–78 days of age This Y-maze was used to evaluate the sociality and learning capability of the chickens. 2.5.3.1. Apparatus. The apparatus consisted of a Y-shaped maze made of MDF covered by a bird net, with a black rubber floor (Fig. 1C). The maze was divided into four compartments by three lines. A cage made of chicken wire (50 cm × 25 cm) was connected to each of the arms opposite the start arm. A video camera was positioned above the apparatus. During each test, two chickens from the same group as the chicken being tested were placed in one of these two cages (group mates). All chickens were used as test chickens and group mates; a chicken was never a group mate in a test prior to being a test chicken on one day. 2.5.3.2. Procedure. The chicks were allowed to habituate to the test apparatus during two sessions of 5 min each on 2 days in the week prior to testing. The cage in which the group mates were placed, and thus the rewarded arm, was randomly assigned to each chick and remained the same for all trials. During the first trial, the test was started as soon as the chick was placed in the start compartment (compartment 1). After the first trial a guillotine-type door was added in the start compartment. The observer gently placed the chick in the start compartment behind the door, and the door was raised from the adjacent room approximately 20 s after the chick was placed in the maze. The test started as soon as the door was raised and lasted 10 min. At least three trials were completed with group mates for all chickens. Once the criterion that the chicken had visited the rewarded arm during two trials was reached, one trial without group mates was performed with each chicken. This was done to test for conditioned place preference. Trials with group mates were continued for those chicks that had not reached the criterion, until they reached the criterion or completed five trials with group mates irrespective of whether they reached the criterion. This was followed by a trial without group mates. All observations were made from the computer screen in the adjacent room using the video feed. Latency to walk,

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total time spent in compartment 1, latency to enter and total time spent in compartment 2, and the rewarded and unrewarded arm; and total number of lines crossed were recorded. The number of trials to reach criterion was also recorded for each bird. Two days were required to test all chickens once. All testing occurred between 8:30 h and 16:00 h over the course of 3 weeks. 2.5.4. Food preference test at 89–106 days of age The goals of the food preference test were to evaluate the food motivation, feeding efficiency, and decide on the most suitable reward for subsequent testing. 2.5.4.1. Apparatus. The apparatus consisted of a corridor (87 cm × 30 cm) made of MDF covered by a bird net, with a black rubber floor (Fig. 1D). A door separated the start compartment (45 cm × 30 cm) from the rest of the corridor. Two food bowls, which contained two different food types, were placed in the two corners at the other end of the corridor. The back wall of the corridor was made of chicken wire, behind which a video camera was placed. Another video camera was placed above the test apparatus. 2.5.4.2. Procedure. During each preference test the reaction of the chick to two different foods was examined. The side of each type of food was randomized for each chicken for each trial. All foods had been introduced to and consumed by the chickens in their home pens at least four times prior to the start of the corresponding trial. The chick was gently placed in the start compartment, behind a guillotine door, and the observer left the room. The test was started by raising the door approximately 20 s after the chicken was placed in the maze. The test lasted 5 min or until 25 s after the chicken finished both rewards, whichever occurred first. All observations were made from the adjacent room using the video registration from the two cameras. A 5-min habituation session was carried out with each chicken the week prior to testing, during which chick mash and mixed grains were placed in the food bowls. Thereafter, chick mash vs. mixed grains, mealworms vs. grapes; spaghetti vs. lettuce; and grapes vs. raisins were tested consecutively. Because the chickens were completely uninterested in earthworms in their homepens, this food type was not used in the preference test. For both the mash and grains exactly 5 mg was offered to each chicken. It was not possible to provide exactly equal amounts of the other food types such as grape and mealworms, but this was done as equally as possible. Latency to walk, latency to peck at, number of pecks at, weight eaten (g), fraction eaten, and latency to finish both foods were recorded. As a measure for efficiency, the amount of food (in mg) eaten per peck was calculated for each bird by dividing the amount of food eaten by the number of pecks at the food. All testing occurred between 9:00 h and 16:00 h over the course of 3 weeks. 2.5.5. Food-rewarded Y-maze test at 119–146 days of age The food-rewarded Y-maze was used to evaluate the food-motivation and learning capability of the chickens.

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2.5.5.1. Apparatus. The testing apparatus consisted of a Yshaped maze with a triangular shaped cage between the two oblique arms, covered by a bird net and with a black rubber floor (Fig. 1E). The cage was constructed of chicken mesh; the rest of the maze was constructed of MDF. The purpose of the cage between the two oblique arms was to hold group mates of the chicken being tested during the test. The test chicken could therefore see the group mates from both oblique arms. This was done in order to help draw the test chicken toward the junction between the arms, and to motivate it to peck at the grape. As in the Ymaze test for sociality, all chickens were used as both test chickens and group mates. A chicken was never a group mate in a test prior to being a test chicken on one day. White chalk lines marked the borderlines between the two oblique arms and the starting box. A rodent food bowl was placed at the far end of both oblique arms; one of these bowls contained a grape during each trial. A video camera was positioned above the apparatus. 2.5.5.2. Procedure. The food-rewarded Y-maze test began at 17 weeks of age. Two habituation periods of 4 min each were carried out at 5 and 2 days before testing was started. Each chicken was also habituated for at least two periods of 4 min each to being in the cage, serving as a ‘group mate’. The rewarded arm, in which the grape was placed, was randomly assigned to each chick and remained the same for all trials. The chicken being tested was gently placed behind the guillotine-type door, and the trial was started when the door was opened 20 s later. The test lasted for a maximum of 5 min or until 25 s after the grape was consumed. All chickens performed three sessions on 3 days. Each session consisted of two consecutive trials. Chickens were tested until they reached the criterion of pecking at the grape prior to entering the unrewarded arm during at least four trials over the previous six trials (three sessions), of which at least once within the last two trials (one session). Once a chicken reached this criterion it was tested without group mates for two sessions on 2 days. Again each session consisted of two consecutive trials. Trials with group mates were continued for all chicks until they reached the criterion, or until they performed a total of ten trials (five sessions) with group mates, whichever event occurred first. Subsequently, these chickens were also tested for four trials (two sessions) without group mates. Trials without group mates were performed to ascertain whether the chickens had actually learned in which compartment the reward was located, or whether their group mates in the cage were guiding them. In each trial, latency to walk, latency to enter and number of visits to the rewarded and unrewarded arm, latency to peck at, and latency to finish the grape were recorded. All trials were conducted between 9:00 h and 16:30 h over 4 weeks. 2.5.6. Second voluntary human approach test at 146–147 days of age As the first voluntary human approach test, this test was used to evaluate fear in the chickens. 2.5.6.1. Apparatus. This test was performed in a test room measuring 290 cm × 310 cm (Fig. 1F). This room was

divided into four equal-sized compartments by white chalk lines. Two video cameras were installed, one behind the experimenter on the wall and one from the ceiling in the center of the test room. 2.5.6.2. Procedure. The chicken was gently placed in one corner of the room in compartment 1 by an observer. In the opposite corner, in compartment 4, a familiar human was seated with two halves of a grape in her hand. All observations were made from the adjacent room by the observer using the video feed from the two video cameras. Latency to walk; latency to enter and total time spent in compartments 1, 2, 3, and 4; latency to peck at the grape; latency to finish the grape; and number of lines crossed were recorded. The chicken remained in the test room for 10 min. All chickens were tested once over the course of 2 days, all tests were done between 9:30 h and 16:00 h. 2.6. Statistical analysis Measures on the nominal scale were analyzed with Fisher’s exact probability test for a 2 × 2 columns contingency table, or the Freeman–Halton extension of Fisher’s test (for a 2 × 3 contingency table) (both with online calculator: http://faculty.vassar.edu/lowry/VassarStats.html), or with the Chi-square test (SAS FREQUENCY procedure). Measures on the ordinal scale were analyzed with the non-parametric Kruskal–Wallis test (SAS NPAR1WAY procedure), whereas the parametric analysis of variance (ANOVA; SAS GLM procedure) was used for measures on the interval and ratio scale. Normality was evaluated with the Shapiro–Wilk test (SAS UNIVARIATE procedure). For some tests, difference scores between measures were calculated (e.g. time in rewarded vs. time in unrewarded arm of the Y-maze). It was determined per group whether the difference scores deviated from zero by one-sample t-statistics (SAS MEANS procedure). Eta squares were calculated (SAS GLM procedure, ˛ = 0.10) to estimate effect sizes, following the recommendations of Ferguson (2009). For eta-squares ≈0.01, ≈0.09, and ≈0.25, effects were classified as small, moderate, or large respectively. The SAS version 9.2 running on a Windows XP platform was used (SAS Institute Inc., Cary, NC, USA). In all statistical analyses, test statistics with an associated probability below 5% (p < 0.05) were defined as representing significant effects, while test statistics with associated probabilities below 10%, but higher than 5% (0.10 > p > 0.05) were defined as reflecting tendencies. 2.6.1. Body weight Because the body weights at 5, 12, 19 and 26 days of age cannot be attributed to specific chicks, as the chicks were not yet individually identifiable, this data was analyzed using a two-way ANOVA with the between subjects factors Mother (reared by mother vs. reared without mother) and Beak (trimmed beak vs. intact beak). A repeated-measure ANOVA was used to analyze the body weights from 4 weeks (27 days) to 21 weeks of age, with the within subjects factor Week and the between subjects factors Mother and Beak.

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2.6.2. Egg productivity indicator The egg productivity indicator data was analyzed nonparametrically using Kruskal–Wallis tests with both the between subject factors Mother and Beak. 2.6.3. Behavioral tests The effects of maternal care and trimming on each variable in the open field test, the two human approach tests, and the food preference test were assessed using an ANOVA with between subjects factors Mother and Beak, except data on an ordinal scale, which were analyzed nonparametrically using a Kruskal–Wallis test. For both Y-maze tests, which had multiple trials, a repeated measures ANOVA with the within subjects factor Trials (Y-maze test for sociality), or Trials and Sessions (food rewarded Y-maze test) was performed, in order to assess possible changes in behavior of the chickens across trials and sessions. The distribution of the chickens which reached criterion over the groups was analyzed for both Ymaze tests with a cross tabulation using a Chi-square test. The number of trials in the Y-maze test for sociality and the number of sessions in the food rewarded Y-maze test required to reach the criterion for each chicken was also analyzed using an ANOVA with the between subject factors Mother and Beak. To determine if there was preference for an (rewarded vs. unrewarded, left vs. right) arm during the Y-maze test for sociality, the difference score between the time in each arm for all animals was analyzed using onesample t-statistics to examine the deviation from zero. The difference scores were then analyzed using a repeated measures ANOVA with the between subject factors Mother and Beak, and the within subject factor Trials, to determine if the possible preference for an arm was affected by these factors. The transition from trials with group mates to trials without group mates in both Y-maze tests was analyzed with a repeated measures ANOVA, with the between subjects factors Mother and Beak and the within subjects factors Trial, or Trials and Sessions. For the Y-maze test for sociality each chicken’s last trial with group mates and the first trial without group mates were used. For the foodrewarded Y-maze test each chicken’s last session and the trials within that session were compared to the first session and trials without group mates. The number of trials with group mates was different for each chicken, as it depended on the speed of learning. This transition from trials with group mates to trials without group mates in both Y-maze tests was also analyzed using the first choice data. The Ymaze for sociality first choice data was analyzed using a Fisher exact probability test (two by two table). The number of animals that did and the number of animals that did not choose the (previously) rewarded arm first in the last trial with group mates and the trial without group mates were compared. The first choice data from the food-rewarded Ymaze was analyzed using a Freeman–Halton extension of the Fisher exact probability test (two by three table). The number of animals that chose the rewarded arm first in zero, one or two trials in the first session with group mates and the session without group mates were compared. An overall efficiency percentage for all food types was calculated from the food preference tests data. The weight

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of food eaten per peck relative to the mean of all intact chickens was calculated for each chicken. The following formula was used: [(weight per peck individual chicken − mean weight per peck of all intact chickens)/(mean weight per peck of all intact chickens)] × 100. A mean of this percentage for all the trimmed birds, as a measure for the pecking efficiency of trimmed birds relative to intact birds, was calculated for each food type. A mean of these percentages for all food types was then calculated.

3. Results 3.1. Body weight The presence of a foster mother had no effects on body weight. Days 5–26: Beak trimming had a moderate effect on the chickens’ body weight; they weighed less than the intact birds at 5 (F1,36 = 7.30, p = 0.0105; 2 = 0.16), 12 (F1,35 = 4.75, p = 0.0361; 2 = 0.11), 19 (F1,35 = 6.82, p = 0.0132; 2 = 0.16), and 26 (F1,35 = 8.20, p = 0.0070; 2 = 0.18) days of age (Fig. 2A). Week 4–21: The chickens’ body weight increased from 4 to 21 weeks of age (F17,595 = 4495.94, p < 0.0001), similarly for the beak trimmed and intact birds (F17,595 = 0.81, NS) (Fig. 2B). Averaged over all weeks, the body weights of the trimmed and intact chickens did not differ (F1,35 = 1.79, NS). However, in order to examine if the differences found between the beak trimmed and intact birds during the first 27 days continued into the subsequent weeks, an exploratory analysis was done for weeks 4–21 separately using a two-way ANOVA. These analyses revealed that beak trimming had a moderate to strong effect on body weight. Beak trimmed birds had lower body weights than intact birds at 4 (F1,35 = 8.01, p = 0.0077; 2 = 0.18), 5 (F1,35 = 11.34, p = 0.0019; 2 = 0.24), 6 (F1,35 = 9.58, p = 0.0039; 2 = 0.20), 7 (F1,35 = 5.96, p = 0.0198; 2 = 0.14), and 8 (F1,35 = 4.47, p = 0.0418; 2 = 0.11) weeks of age. Body weight tended to be lower in trimmed birds at 9 weeks of age (F1,35 = 3.46, p = 0.0713; 2 = 0.09).

3.2. Egg productivity indicator No effects of maternal care were found on egg productivity. Cloaca (21 = 4.13, p = 0.0422) and pubic bone (21 = 5.22, p = 0.0223) scores were significantly lower in trimmed birds at the age of 17 weeks. The facial skin color score tended to be lower in trimmed birds at 17 weeks (21 = 3.18, p = 0.0745). At 20 weeks of age only the pubic bone (21 = 4.25, p = 0.0391) score was lower in trimmed birds, whereas comb (21 = 3.24, p = 0.0719), facial skin (21 = 3.37, p = 0.0664), and cloaca (21 = 3.48, p = 0.0621) scores tended to be lower. The sum scores at 17 weeks were 6.15 ± 0.41 for the intact birds and significantly lower, namely 4.21 ± 0.66 for the trimmed birds (21 = 5.23, p = 0.0223). At 20 weeks of age this difference was no longer significant with a sum score of 7.45 ± 0.20 for the intact

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Fig. 2. Body weights of intact and beak trimmed birds (mean ± SEM): (A) the body weights during the first 26 days. Stars indicate significant differences; (B) the growth of the intact and trimmed birds between 4 and 21 weeks. Stars indicate significant differences in body weight as found with exploratory analysis.

birds and 5.52 ± 0.76 for the trimmed chickens (21 = 2.29, NS). 3.3. Behavioral tests 3.3.1. Open field test at 29–30 days of age No effects of maternal care, beak trimming or their interaction were found on any of the parameters measured. The number of lines crossed (mean ± standard error of the mean) for each group was: trimmed × reared by mother (53.33 ± 9.50), trimmed × reared without mother (26.10 ± 10.05), intact × reared by mother (35.40 ± 11.57), and intact × reared without mother (40.70 ± 9.23). 3.3.2. First voluntary human approach test at 33–34 days of age Although most birds approached the experimenter quite closely, and some even sat on top of her, only three birds pecked at the mealworms. No effects of maternal care or beak trimming or their interaction were found on any of the parameters measured. The latency to enter compartment 3 (mean ± SEM) for each group was: trimmed × reared by mother (266.78 ± 69.67), trimmed × reared without mother (367.40 ± 57.31), by mother (295.10 ± 60.80), and intact × reared intact × reared without mother (357.00 ± 63.04). 3.3.3. Y-maze test for sociality and learning at 61–78 days of age Three chickens did not reach criterion. Two of these chickens came from the intact × without mother group, and one chicken came from the trimmed × without mother group. The chickens that reached criterion were distributed evenly over the different groups (21 = 0.11, NS). For statistical analysis of the number of trials needed to reach

criterion, chickens which did not reach criterion were assigned the score 6, which is the maximum number of trials with group mates plus one. Maternal care, beak trimming and their interaction had no effect on the number of trials required to reach criterion. All subsequent analyses were performed using only the data of the 36 chickens that eventually reached criterion. On average across the four groups, all the chickens spent more time in the rewarded arm (adjoining the group mates) than in the unrewarded arm during the first three trials with group mates. Namely, the difference between time spent in the rewarded arm and time spent in the unrewarded arm, as a measure for arm preference, deviated from 0 (for each trial respectively: t35 = 4.28, p = 0.0001; t35 = 3.66, p = 0.0008; t35 = 3.49, p = 0.0013) (Fig. 3). Neither maternal care nor trimming had an effect on this difference averaged over the first three trials. The number of trials completed also did not affect this preference for the rewarded arm. The latency to enter the rewarded arm changed over the trials (F2,64 = 7.96, p = 0.0008). This change was affected by beak trimming (F2,64 = 3.19, p = 0.0479) (Fig. 4). Regardless of which arm was rewarded, averaged over all chickens more time was spent in the right arm (Fig. 1C, compartment 4) than in the left arm (Fig. 1C, compartment 3) during the second (t35 = 2.62, p = 0.0130) and third (t35 = 5.39, p < 0.0001) trial with group mates. Neither maternal care nor beak trimming had an effect on this preference for the right arm averaged over the first three trials. The difference between time spent on the right and left side increased similarly for all animals over the three trials (F2,64 = 5.52, p = 0.0061). The preference for the rewarded arm persisted during the trial without group mates (t35 = 2.65, p = 0.0119). The preference was not different from each chicken’s last trial with group mates (F1,32 = 2.08, NS) (Fig. 4). This preference

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exact probability test showed that there were changes in response patterns from the last trial with group mates to the trial without group mates (p = 0.0007). The data shows that the chickens choose the (previously) rewarded arm first more often in the last trial with group mates (32) than the trial without group mates (19). The preference for the right arm as opposed to the left arm was no longer present during the trial without group mates (t35 = 0.79, NS).

Fig. 3. Differences between times spent in the rewarded and unrewarded arm in the Y-maze for sociality (mean ± SEM). This is a measure for preference for the rewarded arm. The averages for all 36 chickens which reached criterion are depicted. Trials 1–3 are the first three trials with group mates; the last trial is without group mates.

was not affected by maternal care or beak trimming. The latency to enter the rewarded arm did, however, increase from the last trial with group mates to the first trial without group mates (F1,32 = 24.41, p < 0.0001). Trimmed birds had a higher latency to enter the unrewarded arm during the trial without group mates (F1,32 = 5.17, p = 0.0299). The Fisher’s

3.3.4. Food preference test at 89–106 days of age Table 2 illustrates the effects of trimming and rearing by a mother on the amount of food eaten (g) per peck and fraction of total amount of food eaten. For the weight of food eaten per peck, only the data from the birds that pecked at the food type were included, as there is no value for weight per peck if there are no pecks. The number of birds that pecked at the food was evenly distributed between the variables for each food type, as determined with a Fischer’s exact test for each food type and variable. Trimmed birds ate less per peck for five of the seven food types and averaged over all types of foods, they ate 63% less food per peck than their intact counterparts. The presence of a mother hen also tended to increase (0.10 > p > 0.05) or increased (p < 0.05) the amount of food eaten per peck for three of the seven food types. Using the amount of grain (g) eaten per peck as an example, growing up with a foster mother moderately increased the amount of grain per peck (F1,24 = 8.42, p = 0.0078; 2 = 0.15). Beak trimming considerably reduced the amount of grain per peck (F1,24 = 20.74, p < 0.0001; 2 = 0.37). Thus, the effect of beak trimming was substantially larger than that of the mother. Maternal care did not differentially affect the effect of beak trimming (F1,24 = 0.08, p = 0.7841).

Fig. 4. Latency to enter the rewarded arm in the Y-maze for sociality (mean ± SEM): (A) the differences between the intact and trimmed chickens; (B) the differences between the chickens reared with a mother and reared without a mother. For both (A) and (B), trials 1–3 are the first three trials with group mates; the last trial is without group mates.

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Table 2 Mean weights (mg) of food eaten per peck and fraction of food consumed in the food preference test. Food type

Fraction Mash Weight (mg)/peck

4.62 ± 1.94

Mean ± SEM intact

Beak (trimmed vs. intact)

Mean ± SEM without mother

Mean ± SEM with mother

Interaction (mother × beak)

F1,24 = 0.08,NS

F1,18 = 3.29, p = 0.0862 F1,35 = 0.21, NS

15.58 ± 1.67

F1,24 = 20.74, p = 0.0001

7.22 ± ± 1.53

0.026 ± 0.013

0.273 ± 0.062

F1,35 = 14.47, p = 0.0005

0.179 ± 0.061

0.125 ± 0.045

F1,24 = 8.42, p = 0.0078 F1,35 = 0.81, NS

4.31 ± 2.37

8.78 ± 1.69

5.25 ± 1.67

7.92 ± 2.98

F1,18 = 0.58, NS

F1,18 = 1.46, NS

14.85 ± 2.82

Mother (with vs. without)

F1,35 = 1.22, NS

Fraction

0.011 ± 0.006

0.031 ± 0.010

F1,35 = 2.97, 0.0937

0.025 ± 0.009

0.017 ± 0.008

F1,35 = 0.51, NS

Mealworms Weight (mg)/peck Fraction

5.58 ± 2.90 0.305 ± 0.097

36.75 ± 7.85 0.636 ± 0.108

F1,27 = 14.03, p = 0.0009 F1,35 = 5.71, p = 0.0224

18.03 ± 7.48 0.414 ± 0.108

23.48 ± 6.49 0.538 ± 0.111

F1,27 = 0.58, NS F1,35 = 0.92, NS

F1,27 = 0.24, NS F1,35 = 9.00, p = 0.0049

Grape (1) Weight (mg)/peck Fraction

283.21 ± 62.84 0.509 ± 0.110

539.90 ± 98.46 0.775 ± 0.090

F1,27 = 4.31, p = 0.0475 F1,35 = 3.32, 0.0769

383.75 ± 65.71 0.652 ± 0.098

466.89 ± 114.88 0.639 ± 0.112

F1,27 = 0.46, NS F1,35 = 0.01, NS

F1,27 = 0.20, NS F1,35 = 0.76, NS

Spaghetti Weight (mg)/peck

11.75 ± 3.89

35.18 ± 11.08

F1,24 = 4.73, p = 0.0397

12.22 ± 3.61

33.214 ± 10.65

F1,24 = 0.57, NS

Fraction

0.157 ± 0.058

0.301 ± 0.086

F1,35 = 1.97, NS

0.098 ± 0.026

0.371 ± 0.097

F1,24 = 4.08, p = 0.0547 F1,35 = 7.52, p = 0.0096

Lettuce Weight (mg)/peck Fraction

6.31 ± 2.92 0.033 ± 0.016

24.50 ± 10.66 0.201 ± 0.079

F1,28 = 2.28, NS F1,35 = 3.93, p = 0.0553

14.38 ± 5.79 0.119 ± 0.051

17.38 ± 10.18 0.119 ± 0.072

F1,28 = 0.07, NS F1,35 = 0.00, NS

F1,28 = 0.02, NS F1,35 = 0.00, NS

Grape (2) Weight (mg)/peck Fraction

412.84 ± 102.04 0.5723 ± 0.110

986.67 ± 225.46 0.801 ± 0.092

F1,29 = 4.67, p = 0.0391 F1,35 = 2.50, NS

613.68 ± 171.26 0.654 ± 0.108

819.33 ± 213.36 0.726 ± 0.099

F1,29 = 0.86, NS F1,35 = 0.29, NS

F1,29 = 0.26, NS F1,35 = 3.87, 0.0571

Raisin Weight (mg)/peck Fraction

69.86 ± 18.46 0.4483 ± 0.104

143.84 ± 27.96 0.693 ± 0.010

F1,30 = 5.05, p = 0.0321 F1,35 = 2.69, NS

81.00 ± 18.91 0.501 ± 0.104

133.93 ± 29.03 0.651 ± 0.105

F1,30 = 2.76, NS F1,35 = 1.04, NS

F1,30 = 0.55, NS F1,35 = 0.84, NS

F1,35 = 0.10, NS

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Grains Weight (mg)/peck

Mean ± SEM trimmed

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Three criteria were considered when deciding on the best reward to use in the food-rewarded Y-maze test. The first criterion was that most chickens should be eager to eat the food, which is indicated by the amount of the food eaten and the number of pecks at the food during the preference test. Furthermore, the food type should be practical to use when testing. Spaghetti, for example, did not meet this criterion as it stuck to the food bowl and the chickens were incapable of picking it up. Lastly, the reward should be as equal as possible for all chickens, thus the difference in milligrams per peck between the trimmed and intact birds should be as low as possible. Therefore mealworms, which had been used as a food reward for chickens in earlier studies (Krause et al., 2006; Nordquist et al., 2011), were unsuitable. Based on these criteria, the grape was decided to be the best reward. 3.3.5. Food-rewarded Y-maze test at 119–146 days of age Six chickens (three from the trimmed beak × without mother group, and three from the intact beak × with mother group) did not reach criterion within the maximum number of five sessions. The chickens that reached criterion were distributed evenly over the different groups (21 = 0.75, NS). For statistical analysis of the number of sessions needed to reach criterion, a value of 7 was used for those chickens that did not reach the criterion, which is the lowest number of sessions in which they could have reached criterion if trials were not discontinued after five sessions. The interaction between beak trimming and maternal care moderately affected the number of sessions needed to reach the criterion (F1,35 = 4.75, p = 0.036; 2 = 0.12). The number of sessions needed to reach criterion for each group was: trimmed × reared by mother (3.11 ± 0.31), trimmed × reared without mother (4.10 ± 0.66), intact × reared by mother (4.40 ± 0.60), and intact × reared without mother (3.20 ± 0.29). Post hoc analysis (Bonferroni) did not further explain this difference. Solely the data from the 33 chickens that did eventually reach criterion were used for subsequent statistical analysis. Maternal care, beak trimming and their interaction did not affect the latency to peck at the grape averaged over the first three sessions with group mates. The latency to enter the rewarded arm decreased over the sessions (F2,58 = 19.98, p < 0.0001), as did the latency to peck (F2,58 = 22.68, p < 0.0001) (Fig. 5), but similarly for all groups. The latency to peck did not change from the last session with group mates of each bird to the first session without group mates (F1,29 = 0.36, NS), and this was not affected by either trimming or maternal care (Fig. 5). Maternal care, beak trimming and their interactions did not affect the latency to peck averaged over the two sessions without group mates. The latency to peck did not alter over the two sessions without group mates (F1,29 = 0.29, NS), and was also not affected by maternal care and trimming. The Freeman–Halton probability test revealed that there were changes in response patterns from the first session with group mates to the session without group mates (p = 0.0008). The data shows that chickens chose the rewarded arm more often in the first session without group mates (3 chickens chose the rewarded arm first during one of the two trials, 29 chickens chose the rewarded arm first

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Fig. 5. Latency to peck at grape for all chickens in the food-rewarded Y-maze (mean ± SEM). Each symbol represents the average for the 33 chickens which reached criterion for one trial; the two trials within a session are connected.

in both trials) than the first trial with group mates (10 chickens chose the rewarded arm first during one of the two trials, 15 chickens chose the rewarded arm first in both trials). 3.3.6. Second voluntary human approach test at 146–147 days of age No effects of beak trimming or maternal care were found on any of the parameters measured. The latency to peck at the grapes (mean ± SEM) for each group was: trimmed × reared by mother (340.67 ± 79.08), trimmed × reared without mother (385.50 ± 80.11), by mother (412.10 ± 71.13), and intact × reared intact × reared without mother (244.80 ± 75.07). 4. Discussion Overall, our study shows that infrared beak trimming has a slightly suppressive effect on body weight, physical productivity characteristics and pecking efficiency, but no effect on behavioral and cognitive parameters. Maternal care had very little effect on the parameters measured during this study. While the precision of infrared trimming has been assumed to be superior to the precision of conventional treatments due to automation of the trimming process, non-systematic observations revealed that there was considerable variation in the shapes and lengths of the beaks of the trimmed chickens in this study. Although body weights were consistently lower in trimmed birds than in intact birds up to 8 weeks of age (with moderate to strong effect sizes), from 10 weeks of age on there were no effects of trimming on body weight. Also, growth from 4 to 21 weeks of age was not affected by trimming, corroborating earlier results following infrared (Marchant-Forde et al., 2008; Marchant-Forde and Cheng, 2010), hot blade (Gentle et al., 1982, 1997; Lee and Craig, 1990; Onbas¸ilar et al., 2009) and cold blade (Gentle et al., 1997) trimming. However, decreased body weights in infrared treated birds have also been documented for a longer periods (until at least 18 weeks of age) (Honaker

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and Ruszler, 2004). This short-lasting body weight reduction is most likely due to a decline in food consumption following trimming (Lee and Craig, 1990), which may be caused by pain, a decreased motivation to eat, and/or a reduced efficiency of feeding due to a reduced mechanical ability to pick up feed (Gentle et al., 1982). It has been argued that a reduction in body weight and feed intake is advantageous in terms of production (Hester and Shea-Moore, 2003). For example, Anderson and Davis (1997) demonstrated that net income was higher in White Leghorn layers trimmed at 6 days or 11 weeks than in their intact counterparts; because of the lower feed cost (Anderson and Davis, 1997). These lower feed costs may be due to a reduced feed uptake, reduced feed wastage (Marchant-Forde and Cheng, 2010) or a combination of these factors. The current results suggest that infrared trimming leads to a short delay in sexual maturity (the initiation of egg production), as trimmed birds had lower productivity indicator scores at 17 weeks of age, but this difference had diminished greatly by 21 weeks of age. As the physical productivity characteristics were scored at two different ages, the length of this delay could not be determined in the present study. A short delay in egg production was also described for hot blade treated chickens under commercial conditions with large numbers of animals (Craig and Lee, 1989; Kuo et al., 1991). If the total egg output over the commercial laying period is affected by this delay, this may be an underexposed, but considerable disadvantage of infrared trimming. However, Kuo et al. (1991) and Guesdon et al. (2006) both showed that once sexual maturity was reached, total production improved as a result of trimming on a group level, probably as a result of the lower level of mortality due to cannibalism in the trimmed groups. If reduced cannibalism is the underlying cause of an increased total production in trimmed birds, individual production may still be compromised. Delayed sexual maturity may be advantageous in terms of welfare. It is hypothesized that a delay in sexual maturity minimizes the development of osteoporosis, as it allows the chicken to optimally strengthen the skeleton, prior to laying. However, it has not been proven that a delay in maturity leads to improved bone mineralization during adulthood (Hester et al., 2011). Using physical characteristics as an indicator of egg productivity is a novel method. It may be a useful technique in future studies where egg productivity and age at sexual maturity are of importance. This technique warrants further development and validation, as it allows the researcher to evaluate each bird individually at any time. Note that feather pecking itself was not the focus of this study. Extensive feather pecking or damage as a result thereof was not witnessed in either the beak trimmed or the intact chickens. This is most likely a result of the spacious and enriched housing conditions, as compared to commercial conditions. The results of the effect of beak trimming in commercial conditions, namely the decrease in feather pecking damage and associated behavioral effects, could therefore not be examined during this study. Our goal was to examine the effects of the physical removal of the tip of the beak.

In the Y-maze test for sociality, on average, all chickens spent more time in the rewarded arm than in the unrewarded arm. As seen in the chickens during the T-maze test for sociality performed in the study by Nordquist et al. (2011), the latency to enter the rewarded arm decreased over the trials. Both of these results indicate sociality. The latency to enter the rewarded arm increased and the number of chickens that chose the rewarded arm first decreased from the last trial with group mates to the trial without group mates. However, the preference for the rewarded arm as compared to the unrewarded arm did not change. This suggests that the group mates drew the chicken being tested to the rewarded arm, but that the chickens developed a conditioned place preference for the arm adjoining the group mates. There is no clear explanation for the preference for the right side as opposed to the left side. Lighting may have played a role. Also, the experimenter entered and exited through a door on the left side, which may have led to the chickens avoiding the left arm. These explanations are purely speculations. Conditioned place preference was not seen in the 14–16-day-old Low Mortality Line chickens in the T-maze for sociality (Nordquist et al., 2011), which may be due to procedural or chicken line differences. Beak trimming reduced pecking efficiency (mg/peck eaten) for all food types except chick mash and lettuce. An overall reduction of 63% was found on the weight of food picked up per peck during the food preference test. The effect of trimming on the efficiency of eating grains was strong. Hot-blade trimmed chicks have also been shown to be less efficient at pecking at pelleted feed (Gentle et al., 1982; Prescott and Bonser, 2004). The reduction in efficiency was less severe when mash feed was provided (Gentle et al., 1982). Possibly, trimmed birds are more capable of picking up and ingesting mash feed than large pieces of feed. As chick mash was the chickens’ daily food during this study, it is also conceivable that trimmed birds had learned to eat this food type more efficiently by the time they were 12 weeks old. This is consistent with the fact that the average body weight of the trimmed chicks did not differ from the body weight of the intact birds after they had reached 9 weeks of age. Chickens reared by a foster mother picked up a moderately higher weight of grains per peck. While the hen was present, the chicks and hen were provided with grains for foraging. The chicks may have learned from the hen to differentiate between, and choose certain granules; or pick up more pieces per peck. A grape sliced in half was determined to be the most suitable food reward for the chickens used in this study. Mealworms were used as a food reward for chickens in earlier studies (Krause et al., 2006; Nordquist et al., 2011). However, the trimmed birds had great difficulty eating mealworms; they ate about seven to eight times less per peck than intact birds. Although the weight of grape per peck was only twice as high in the intact birds than in the trimmed birds, the grapes may still have been more rewarding for intact than trimmed birds. Group mates were used in the food rewarded Y-maze to encourage the tested chicken toward the oblique arms and to peck at the grape because non-systematic observations had shown that social motivation was important during feeding. However, the stimulus chickens saw and

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reacted to the grape by trying to peck at it during testing. The latency to enter the rewarded arm and the latency to peck at the grape decreased over the trials, suggesting that the chickens may have learned the location of the grape, and/or to watch and interpret the “cues” from the group mates. However, the latency to peck did not increase from the last trial with group mates to the first trial without group mates. Thus, the cues may have facilitated the learning of which arm was the rewarded arm, but the chickens evidently also learned the location of the grape. This is corroborated by the first choice data which shows that the chickens chose the rewarded arm first more often during the first session without group mates than the first session with group mates. The small group sizes, and the large number of parameters tested during this study, may have led to the finding of some inexplicable, isolated trends or significant differences. For example, the effect of beak trimming on the progress of the latency to enter the rewarded arm over the different trials of the Y-maze of sociality was primarily caused by three non-responders during the second trial. Overall, very few cognitive or behavioral differences were found between the groups using the behavioral tests. The experimental set-up inherent to this type of research may have leveled out the differences between groups, which perhaps would be present under commercial conditions. For example, differences in fearfulness may recede as a result of intensive handling. The specific maternal care and housing conditions in this study might also have affected the results. For example, there was only one foster mother for 20 chicks. Although this hen displayed maternal care, e.g., brooding of the chicks, this care may not have been sufficient for all chicks. Furthermore, trimmed birds and intact birds were housed together for the first 8 weeks due to a lack of foster hens; these groups may have affected each other’s behavior. Sensitive, validated behavioral tests are not available for chickens as of yet. It is important to continue developing and validating behavioral tests in order to adequately assess welfare. Recently, in conjuction with the delay of the ban on beak trimming, infrared trimming has been made the only legal method of trimming in the Netherlands, as it is thought to be less taxing on the birds than other methods (Ministry of Economic Affairs, Agriculture and Innovation, The Netherlands, 2011). Infrared trimming may have less negative effects on laying hen welfare than hot blade trimming; it nonetheless has effects on production parameters and pecking efficiency and should not be viewed as the ideal solution to control cannibalism and feather pecking. Alternatives to trimming need to be investigated and implemented as soon as possible. Acknowledgements The authors would like to thank Wim van Brenk and Patricia Gadella for their support and help with animal care. References Anderson, K.E., Davis, G.S., 1997. Performance and fearfulness during the production phase of Leghorn hens reared utilizing alternative beak trimming techniques. Poult. Sci. 76 (Suppl. 1), 2 (Abstract).

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