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1、Dustbathing by broiler chickens: a comparisonof preference for four different substratesSara J. Shields, Joseph P. Garner, Joy A. MenchDepartment of Animal Science, University of California at Davis, one Shields Avenue, Davis, CA 95616, USAReceived 28 February 2003; received in revised form 28 Augus

2、t 2003; accepted 21 January 2004 AbstractLeg abnormalities leading to lameness in broiler chickens are a serious welfare problem. Previouswork in our laboratory demonstrated that providing broiler chickens with the opportunity to exercise byperforming more natural behaviors (such as perching, walkin

3、g up and down inclines and dustbathing)can improve their ability to walk normally J.A. Mench, J.P. Garner, C. Falcone, Behavioral activityand its effects on leg problems in broiler chickens, in: H. Oester, C. Wyss (Eds.), Proceedings of theSixth European Symposium on Poultry Welfare, Worlds Poultry

4、Science Association, Zollikofen,Switzerland, 2001, pp. 152156. With the long-term goal of stimulating dustbathing to improveleg condition, the aim of this study was to determine the dustbathing substrate preferred by broilerchickens.We conducted a dustbathing choice test experiment using four differ

5、ent bedding types (pinewood shavings, rice hulls, construction grade sand, and a recycled paper animal bedding product).Four different broiler chickens were tested each week for 6 weeks starting when the chicks were1 week old. They were selected from two groups of broiler chickens housed in large ho

6、me pensbedded with wood shavings. Selected birds were tested in smaller pens where they were deprivedof all loose bedding material except during testing, which was carried out for 1 h each day for three consecutive days per week. During an observation, each corner of the test pen was filled with adi

7、fferent bedding type, and the behavior of the focal chick recorded. Vertical wing shakes (VWS)were used as the primary measure of dustbathing activity.Broilersperformed significantly moreVWSper hour in sand (F3,36 = 13.52,P0.0005) and spent a greater proportion of their total time in sand(F5,60 = 5.

8、15, P = 0.001) than in the rice hulls, paper, or wood shavings. They also visited the sandsignificantly more often than the paper or the wood shavings (F5,60 = 96.47, P 0.0005). Therewere no dustbaths in the rice hulls. The latency to enter sand was significantly shorter than the latencyto enter any

9、 of the other three substrates (F3,15 =5.24, P = 0.0113). Ground pecking generallyprecedes a dustbathing bout, and the rate of pecking and the proportion of the total time budget spentpecking were also highest for sand (F3,51 = 24.49, P 0.0001 and F3,51 = 15.28, P 0.0001,respectively). The preferenc

10、e for sand wasapparent in the first week, and was stable with age. Theresults of this study suggest that sand is attractive to broiler chickens and is a potent stimulus for dustbathing. Further work is needed to determine if stimulating broiler chickens to dustbathe by providing sand can improve the

11、ir leg condition, and thus their welfare. 2004 Elsevier B.V. All rights reserved.1. IntroductionExercise is essential for the health and well-being of animals. For broiler chickens even walking may be difficult as the birds age due to rapid growth rate and the increasing incidenceof leg disorders (W

12、eeks et al., 2000; Kestin et al., 1992; Mench, 2004). Previous work in ourlaboratory (Mench et al., 2001) and other work (Thorp and Duff, 1988) suggest that exerciseis important for reducing the incidence and severity of leg problems. For broiler chickens,one form of exercise is dustbathing behavior

13、. Because dustbathing involves rotational andpushing motions of the legs, it could be a form of exercise that improves leg condition. Layinghens have been found to have clear preferences for dustbathing substrates (Petherick andDuncan, 1989; Vestergaard and Baranyiova, 1996; van Liere, 1991), but th

14、e preferencesof broiler chickens have not yet been thoroughly examined, particularly for bedding thatis available on a commercial scale in the US. Our aim was to determine which substrate,out of four commercially available bedding types, was the best for eliciting dustbathing bybroiler chickens. A d

15、ustbathing bout is composed of a sequence of behavioral components (Kruijt, 1964).Pecking and scratching at a potential dustbathing site usually precede a dustbathing bout.The sequence of dustbathing behavioral components usually begins with “bill-raking”, where the bird, in a sitting position, pull

16、s loose substrate closer to its body, constructing a small ridge of loose substrate. Then, while still in a sitting position, the bird performs verticalwing shakes (VWS) during which small particles are tossed upward into the feathers. Oncedirt particles have been collected in the feathers, the bird

17、 lies down on its side and performsside-rubs or head-rubs. Side-rubs involve motion of the legs as the bird pushes its bodywhile in a lying position. When the dustbathing bird is finished with its bath, it stands andconcludes the bout with a ruffle-shake, shaking off loose dirt particles. The workin

18、g ofloose substrate like dust or dirt through the feathers is thought to function in absorbing stalelipids in the plumage (van Liere, 1991).Under commercial rearing conditions, broiler chickens may not have access to loose friablesubstrate during the whole growing period because their bedding become

19、s compressedand dirty with use over time. In this situation, dustbathing may not be elicited to its fullest.Like laying hens, broiler chickens probably also have preferences for particular substratesin which to dustbathe. If the bedding provided is not of a preferred type, it may further deterthem f

20、rom dustbathing.Young and adult laying strain chickens prefer peat to sand, and sand towood-shavings andstraw, for dustbathing (Petherick and Duncan, 1989; Sanotra et al., 1995; van Liere, 1991;Vestergaard and Baranyiova, 1996). However, dustbathing preferences of broiler chickenshave been examined

21、in only one study. Vestergaard and Sanotra (1999) provided broilerchicks with either sand or straw in which to dustbathe for twenty-six 1 h sessions. Severalof the birds did not dustbathe on every day the substrates were presented, and the numberof days in which dustbathing did not occur was almost

22、twice as many for those birds givenstraw than those given sand. This result suggests that, at least for sand and straw, broilerand layer preferences are similar. However, the dustbathing choice tests performed so farusing broiler chickens have not evaluated any of the other substrates tested for lay

23、ing hens,or the commercially available bedding types that would be easy to obtain in large quantitiesin the US.Before the effect of dustbathing alone on leg condition can be assessed, the conditions that will elicit the most dustbathing behavior from a broiler chicken need to be determined.The prese

24、nt experiment was performed in order to determine which of four bedding types,wood shavings, rice hulls, masonry grade sand, and a recycled paper-bedding product,wouldelicit the most dustbathing behavior in commercial strain broiler chickens. These substrateswere chosen either because they are alrea

25、dy in widespread use in the US, are available ona commercial scale, or are being considered as alternatives to traditional bedding (Grimeset al., 2002).We examined differences in the amount of dustbathing performed, the latencyto perform dustbathing, the latency to enter each substrate, the amount o

26、f time spent in eachsubstrate, the number of visits to each substrate, the length of a dustbathing bout in each substrate, and the amount of pre-dustbathing appetitive pecking behavior performed in eachsubstrate.2. Methods2.1. Subjects and housingThis study, which was part of a larger study of the e

27、ffects of strain differences on gait, was approved by the University of California, Davis Animal Use and Care AdministrativeAdvisory Committee. Cobb (N = 52) and Ross (N = 52) day-old male broiler chicks were obtained from a commercial hatchery. The birds were marked with colored, numberedidentifica

28、tion tags. Half of the birds of each strain were placed in one floor pen (measuring3.05m square), and the other half of the birds were placed in an identical adjacent floorpen. Each pen contained wood shavings for bedding and an overhead brooder for heat.There were windows along the length of the bu

29、ilding that allowed daylight to enter thepens. Overhead fluorescent lights were on continuously for the first 4 weeks, and were thenadjusted to provide an 8D:16L schedule. Food(Purina Mills Meat Builder, containing 20%crude protein and without added medication) and water were available ad libitum. M

30、ortalitywas low (only one chick from pen 1 died, at the start of the second week).2.2. Substrate preference testsEach week, beginning when the chicks were one wk old and ending when they were 7 weeks old, eight Ross chicks (four focal birds and four pair-mates) were removed fromthe two home pens and

31、 taken to a different room in the same building to test substrate preference. No chick was ever used twice. The chicks were placed in pairs into one offourdifferent 1. 52mXl. 52m experimental pens (Fig. 1), constructed of wood and chickenwire, for dustbathing substrate choice tests. Chicks remained

32、in these pens for 4 days.The experimental pens had a raised floor so that the corners of the pen floor could beremoved to access square (0. 61mX0. 61 m) 10 cm deep boxes sunken into the corners. Theboxes were each filled to the top with a different substrate, such that the surface was evenwith the f

33、loor. Chicks therefore did not have to step up or down to get into or out of the box,since this could have prevented them from entering the box, or made it more difficult forthem to exit once inside the box, especially as they grew and developed leg problems. Foodand water were located in the center

34、 of each pen. When the chicks were not being tested,the corners containing the different dustbathing substrates were closed with a wooden lidand the entire pen floor was covered with lab bench paper. This material kept the chicksclean and dry while still allowing us to deprive them of loose bedding

35、material until thebeginning of each test session. Two heat lamps were hung above the center of each pen;these were raised as the chicks grew so that the pen was kept at a temperature appropriatefor their age (FASS, 1999). The light cycle in the testing room was the same as that in thehome pen area,

36、but the testing room did not have windows.One chick in each pen was designated as the focal chick and marked on the back with a non-toxic marker. Chicks were tested in pairs to reduce fearfulness, but data were collectedonly on the focal bird. The chicks were given approximately 24 h to habituate to

37、 the testingenvironment without access to loose bedding before observations began. Before each test,the four different substrates (rice hulls, construction sand, wood shavings, and a recycledpaper waste product) were randomly allocated to each corner of the testing pen, but thesesubstrates remained

38、covered until the observations began. Immediately preceding eachobservation, chicks were corralled into the center of the experimental pen using a cardboardbox, and the substrates were exposed. The cardboard box was then lifted to allow the chicksto move freely around the pen. Each observation laste

39、d for 1 h. There were four observationsper day and three consecutive days of testing per week.The first observation each day began approximately 4 h after the lights came on and was then followed by the next three observations for that day so that each pen was observed as close to peak dustbathing h

40、ours (Vestergaard et al., 1990; Hogan and Van Boxel, 1993;Statkiewicz and Schein, 1980) as possible.We continuously recorded behavioral data fromthe focal chick using a laptop computer with a custom-designed Microsoft Access program.We divided the pen into six different areas to record the location

41、of the focal chick: the pencenter, the walkways, and the four different dustbathing areas. The latency to enter and theamount of time spent in each area of the pen were recorded. The number of pecks, scratches,vertical wing shakes (VWS), head rubs, side rubs and ruffle shakes, and the time (numberof

42、 seconds from the beginning of the observation) that each of these events occurred wererecorded by an observer who sat approximately 0.5m away. Each focal chick was testedthree times, on each of three consecutive days.Dustbathing occurs in discrete bouts organized around the performance of VWS. Thus

43、, adustbathing bout was defined as beginning at the time a focal bird performed his first VWSin a dustbath, and ending when a VWS was followed by 5 min or more without any furtherVWS. Thus, two or more VWS with less than 5 min between them were considered part of the same dustbathing bout.2.3. Stati

44、stical analysisAll analyses were performed using GLM (Minitab 12 for Windows; SAS v8 for Windows).The number of VWS per hour in each substrate type, the percent of the total observation time each focal bird spent in each area (empty, center, or substrate), and the percent of total visits a bird made

45、 to each area were analyzed using repeated measures GLM, with repeated measures made on bird nested within home pen and age at testing. Substrate and age at testing were the variables of interest in all the analyses except one (latency to enter each substrate). VWS per hour data were square-root tra

46、nsformed, and the proportion of the total observation time and proportion of the total visits were angular transformed, to meet the assumptions of GLM; the success of the transformations was confirmed post hoc.Significant effects were investigated post-hoc using Tukey-corrected pairwisecomparisons.T

47、he family error rate for these comparisons was set at 0.05.We also examined several measures of preference using data collected on bout lengthandvarious latencies. These included latency to the first vertical wing shake a bird performed,latency to enter the first substrate in the session, latency to

48、 enter each different substratewithin the session, and the latency to enter the first substrate in which a dustbath occurred.Analyses of the latency data, and data comparing bout lengths in each of the four substrates,were complicated by the fact that not every bird entered or dustbathed in every su

49、bstrate, andsometimes birds entered and dustbathed in substrates during more than one testing session.To avoid pseudoreplication, only one dustbath was used for each bird in any one analysis.Dustbaths were selected in a pseudo-random manner, so that the number of dustbaths foreach substrate was maxi

50、mized. This created a more balanced data set in which there wereas many dustbaths in each substrate type as possible. All latency and bout length measureswere log transformed before analysis. For cases in which the same bird dustbathed in thesame substrate during more than one testing session, we av

51、eraged the latencies and thebout lengths across the sessions after transforming them. For most of these analyses (exceptlatency to enter each substrate), home pen was used as a blocking factor and age at testingand substrate were the variables of interest.A larger data set was available for the late

52、ncy to enter each substrate measure because most birds entered most of the substrates over the course of their three testing sessions. In order to achieve a balanced data set, we randomly chose one bird from each home pen at each age (i.e. 12 birds in total). Because each bird was only tested at one

53、 age, the termhomepen X age uniquely identified each bird.We therefore performed a repeatedmeasures GLMby treating the term pen X age as a random factor in a mixed model.The substrate term wasthen the only factor of interest.For the latency to enter the first substrate in a session, we were unable t

54、o create a data set that was balanced by age at testing by discarding data as in the analysis of latency to enter each substrate. One substrate was randomly chosen for each bird so that each substrate wasrepresented by six data points (i.e. six birds), thus creating a data set that was balanced byth

55、e substrate term but not by age at testing term. The age at testing term was log transformedto improve the linearity and error structure of the data, and was then treated as a covariate.In order to determine whether birds were choosing the first substrate entered in order todustbathe, we assessed wh

56、ether the substrate first entered predicted whether birds stayed to dustbathe in that substrate. For each substrate we counted the number of occasions on which a bird entered that substrate first in the session and stayed to dustbathe versusthenumber of occasions on which a bird entered that substra

57、te first in the session and thenmoved on to first dustbathe in a different substrate. These data were analyzed using a4X2chi-square.The final analysis was performed on ground pecking, and the potential difference in theperformance of this behavior while birds were in each of the different substrates

58、. The meanrate of ground pecking during the observation period (i.e. pecks per hour) was calculated.The proportion of time during the observation period spent pecking was also calculated.These were analyzed using repeated measures GLM, with bird nested within home pen andage at testing.3. ResultsWe

59、observed a total of 27 dustbathing bouts. Of these, 20 were performed in sand, 6 in paper, and 1 in wood shavings. No focal bird ever dustbathed in the rice hulls. After averaging the data for birds that dustbathed in the same substrate for two or three sessions,there were 21 dustbaths. The mean num

60、ber of VWS per dustbath was 21.06 2.44.Wealso observed the performance of a single VWS on three separate occasions, once in thesand, once in the wood shavings, and once in the rice hulls.The rate of VWS per hour was significantly affected by the substrate in which a bird dustbathed (repeated measure

61、s GLM: F3,36 = 13.52, P 0005; Fig. 2). Post hoc tests revealed that the rate of VWS per hour was higher in sand than in any other substrate. Therewere no differences in VWS per hour among the remaining three substrates. There was alsoa significant difference in the proportion of the total visits mad

62、e to the different locationsin the pen (repeated measures GLM: F5,60 = 96.47, P 0.0005; Fig. 3A). Post hoc testsshowed that the proportion of visits was highest for the empty areas of the pen that birds hadto cross in order to enter another substrate. The center of the pen where the food was located

63、was visited significantly less than the empty areas of the pen, but significantly more thanany of the dustbathing substrates. The sand was visited significantly more often than thepaper or the wood shavings. There was also a significant difference in the proportion of thetotal time spent in differen

64、t resources (repeated measures GLM: F5,60 = 5.15, P =0.001;Fig. 3B). Post hoc tests revealed that the birds spent more time in the sand than in the ricehulls, paper, or wood shavings.Average latencies to enter the first substrate, perform the first vertical wing shake, and enter the first substrate

65、in which a full dustbath occurred during a session, were 3.321.29,18 2.62, 15.22 2.72 min, respectively. There were no significant substrate differencesfor these measures. There was, however, a significant difference between the latencies toenter each of the four substrates in a testing session (rep

66、eated measures GLM: F3,15= 5 .24,P= 0.0113; Fig. 4). Tukey pairwise comparisons revealed that the latency to enter the sandwas significantly less than the latencies to enter the rice hulls, paper, or wood shavings.There were no differences in dustbathing bout lengths in the different substrates (GLM:F2,1