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ENVIRONMENT, WELL-BEING, AND BEHAVIOR: Research Note |
* Livestock Behavioral Research Unit, Agricultural Research Service, USDA, West Lafayette, IN 47907; and Department of Animal Sciences, Purdue University, West Lafayette, IN 47906
1 Corresponding author: hwcheng{at}purdue.edu
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENECES |
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Key Words: body weight • beak • beak trimming • chick
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENECES |
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to 
, or even up to 
, of the upper, lower, or both, mandibles using a heated blade that both cuts and cauterizes the beak tissue. Beak trimming has solicited a great deal of debate concerning the relative advantages and disadvantages of the practice and its subsequent effect on welfare. The beak of a bird is a complex functional organ with an extensive nerve supply and many sensory receptors. Beak trimming severs this innervation and removes or damages many receptors with subsequent negative effects on pain and bird welfare (Breward and Gentle, 1985). Trimming can be a source of both acute and chronic pain and may have associated effects on bird well-being.
The relative effect of beak trimming on bird well-being is influenced by multiple factors, including the proportion of beak tissue removed (Cheng, 2005). If done correctly, beak trimming should cause minimal tissue damage and have minimal postprocedural side effects. The importance of accurate trimming has been clearly demonstrated by Lunam et al. (1996), in which neuromas were found to be present at 10 wk of age in chicks that were severely (of upper and of lower mandibles) trimmed at hatch but not in chicks who had received a moderate ( of upper and of lower mandibles) beak trimming. The efficacy of trimming at older ages is also influenced by the quality of the procedure and the proportion of beak trimmed (Hargreaves and Champion, 1965; Andrade and Carson, 1975; Lee, 1980; Lee and Craig, 1990, 1991; Cunningham, 1992; Carey and Lassiter, 1995).
With current beak-trimming practices, however, it is difficult to standardize the proportion of beak trimmed across individual birds, particularly with newer, more automated trimming procedures. Conventional hot-blade trimming, carried out from 7 to 10 d of age, enables the trimmer operator to selectively use guide holes of varying size, into which the beak is inserted, to regulate trimming severity. Nevertheless, it remains difficult to compensate for the large variability that exists in beak size and length in chicks using this approach.
Variability in the amount of beak trimmed also occurs with infrared beak treatment, in which the beaks are treated with infrared energy at the hatchery when the chicks are 1 d old. Existing technology does not allow for equipment adjustments to account for difference in beak length and size in individual chicks. Consequently, the amount of the beak trimmed using this approach can vary, resulting in potentially divergent effects on bird health, production, and well-being. Although efforts have been applied to standardize the amount of beak tissue removed at trimming, it has proven to be difficult, because reliable and easily identifiable indicators of beak length and size have not yet been determined. Therefore, the objective of this particular research was to determine if BW could be used as a reliable indicator of beak size and length in 1-d-old laying chicks.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENECES |
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Three hundred forty-four 1-d-old White Leghorn chicks (Hy-Line W-36) were used in the study. The chicks were weighed and sorted into 3 groups (heavy, n = 93; intermediate, n = 139; light, n = 99) based on their BW. Images of their beaks were captured with a 5.1-megapixel Nikon digital camera (Nikon Inc., Tokyo, Japan). Several beak dimensions were determined using MCID imaging software (Version 4.0, Imaging Research Inc. Ontario, Canada) to examine beak length and the relative width of the upper and lower mandibles at several points along the mandibles. Beak images were imported into MCID before being individually calibrated (number of pixels per horizontal and vertical centimeter) using a background reference scale incorporated into each image. An initial reference line (1) was inserted between standardized reference points on the upper and lower mandibles while passing through the tip of the nare (Figure 1
). Curvilinear lines (2, 3, 4, and 5) were then inserted from the points of intersection of the vertical reference line along the dorsal medial culmen (2) and the maxillary tomai (3) of the upper mandible and along the anterior interramal and gonys (5) and the mandibular tomia (4) regions of the lower mandible. The lengths of these indices were then automatically generated by the software based on the earlier calibration scale. The width of the upper and lower mandibles was also measured at 2, 3, and 4 mm from the tip of the mandibles.
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Data were not normally distributed as determined by histograms and the goodness-of-fit statistic Kolmogorov-Smirnov. To calculate Pearson product-moment correlations (rp) between BW and the various beak dimensions, data were transformed using Box-Cox transformations. Data were transformed as follows:
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where Yi = transformed values for bird BW and its beak dimension i; Xi = nontransformed values for bird BW and its beak dimension i; 
= value calculated for Box-Cox transformation for bird BW and its beak dimension.
Spearman rank-order (rs), Kendall’s tau (
), and Hoeffding’s dependence (HD) correlations were calculated between BW and beak dimension for each bird assigned to the heavy, intermediate, and light groups, respectively. These correlations were calculated for non-transformed data points, because rs, , and HD correlations are nonparametric operations.
Spearman rank-order correlations can range from – 1 to 1. In this procedure, the nontransformed observations were ranked. Body weight for each chick (BWij) was ranked (BWij1...BWijn), and, likewise, beak dimensions (BDij) were also ranked (BDij1...BDijn). The rs is then defined as a rp as follows (Kutner et al., 2005):
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where BWij1 = ith BW for the jth chick, ranked first; BWijn = ith BW for the jth chick, ranked nth; BDij1 = ith beak dimension for the jth chick, ranked first; and BWijn = ith beak weight for the jth chick, ranked nth.
Kendall’s tau was calculated using the difference between concordant (Xc) and disconcordant (Xd) pairs for each parameter. This correlation operation can range from
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Previous studies suggest that has a similar power to obtain significant correlations as rs, even though the numerical values of the correlations can be different (Forlay-Frick et al., 2005).
Hoeffding’s dependence correlation measures the independence of 2 variables from each other. Values for HD correlations can range from – 0.5 to 1, with a value of 1 indicating a complete dependence of one variable on another.
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RESULTS AND DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENECES |
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)].
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. There were no correlations between BW and beak dimensions in the light BW group (P > 0.05). Birds of the intermediate BW group were found to exhibit significant correlations between BW and the width of the lower mandibles measured at 2, 3, and 4 mm from the tip of the mandibles (P < 0.05). In the heavy BW group, significant rp and rs were found for BW and mandibular tomia (P < 0.05), and significant rp, rs, and were present between BW and gonys (P < 0.05). Significant rs and were also found between BW and the width of the lower mandibles measured at 2 mm from the tip of the mandibles (P < 0.05). Aside from a few scattered tendencies, there were no further apparent relationships between any of the measured parameters.
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), the actual correlation values were low ( < 0.23). Thus, practical application of these results would be very limited, and using BW as an indicator of beak size would not contribute much to an improvement in standardizing beak-trimming procedures. Similar to the present findings, Laiolo and Rolando (2003) reported no significant correlations between BW and bill size in 28 species of crow. By contrast, Palacios and Tubaro (2000) found that there was a positive correlation between body mass and beak length in woodcreepers. Similarly, Clegg and Owens (2002) demonstrated a significant general trend toward heavier BW with larger bill size in island-dwelling birds. The different findings between present and previous avian species may relate to between-species differences in foraging and beak functionality. In wild birds, for instance, BW and beak size may relate to competition, adaptation, or both, for limited food sources of different characteristics. Although in laying hens, this is not an issue, because sufficient food with the same characteristics is provided daily, with the subsequent elimination of any need to forage or adapt to changing food properties. In support of this hypothesis, Campo et al. (2000) demonstrated that the heritability of fluctuating asymmetry in chickens was very low and that these differences were largely environmentally controlled. The ability to use an easily evaluated physical parameter, such as BW, as a predictor of beak length and size would certainly contribute to optimizing trimming outcomes in layers. However, the current study failed to find significant correlations between BW and beak dimension of White Leghorn chicks (Hy-Line W-36). Although some correlations did show a statistical relationship or a statistical trend, the correlation values were all too low to be of practical value ( < 0.23). Given the lack of strong correlations between BW and beak dimensions in the current data, it appears that BW cannot be used as a reliable indicator of beak length or size for standardizing beak trimming.
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ACKNOWLEDGMENTS |
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Received for publication September 27, 2006. Accepted for publication February 28, 2007.
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REFERENECES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONREFERENECES |
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Breward, J., and M. J. Gentle. 1985. Neuroma formation and abnormal afferent nerve discharges after partial beak amputation (beak trimming) in poultry. Experentia 41:1132–1134.[Web of Science][Medline]
Campo, J. L., M. G. Gil, and I. Munoz. 2000. Relationships between bilateral asymmetry and tonic immobility reaction or heterophil to lymphocyte ratio in five breeds of chickens. Poult. Sci. 79:453–459.
Carey, J. B., and B. W. Lassiter. 1995. Influences of age at final beak trim on the productive performance of commercial layers. Poult. Sci. 74:615–619.[Web of Science][Medline]
Cheng, H. W. 2005. Acute and chronic pain in beak trimmed chickens. Pages 31–49 in Poultry Welfare Issues – Beak trimming. P. Glatz, ed. Nottingham Univ. Press, UK.
Clegg, S. M., and I. P. F. Owens. 2002. The "island rule" in birds: Medium body size and its ecological explanation. Proc. R. Soc. Lond. B Biol. Sci. 269:1359–1365.[Medline]
Cunningham, D. L. 1992. Beak trimming effects on performance, behavior and welfare of chickens: A review. J. Appl. Poult. Res. 1:129–134.
Forlay-Frick, P., E. Van Gyseghem, K. Heberger, and Y. Vander Heyden. 2005. Selection of orthogonal chromatographic systems based on parametric and non-parametric statistical tests. Anal. Chim. Acta 539:1–10.[Web of Science]
Hargreaves, R. C., and L. R. Champion. 1965. Debeaking of caged layers. Poult. Sci. 44:1223–1227.[Web of Science]
Kutner, M. H., C. J. Nachtsheim, J. Neter, and W. Li. 2005. Inferences in regression analysis. Pages 87–89 in Applied Linear Statistical Methods. 5th ed. McGraw-Hill/Irwin, New York, NY.
Laiolo, P., and A. Rolando. 2003. The evolution of vocalizations in the genus Corvus: Effects of phylogeny, morphology, and habitat. Evol. Ecol. 17:111–123.
Lee, K. 1980. Long term effects of Marek’s disease vaccination with cell-free herpes virus of turkey and age at debeaking on performance and mortality of White Leghorns. Poult. Sci. 59:2002–2007.[Web of Science][Medline]
Lee, H.-Y., and J. V. Craig. 1990. Beak trimming effects on the behavior and weight gain of floor reared, egg strain pullets from three genetic stocks during the rearing period. Poult. Sci. 69:568–575.[Web of Science]
Lee, H.-Y., and J. V. Craig. 1991. Beak trimming effects on behavior patterns, fearfulness, and mortality among three stocks of White Leghorn pullets in cages and floor pens. Poult. Sci. 70:211–221.[Web of Science][Medline]
Lunam, C. A., P. C. Glatz, and Y. J. Hsu. 1996. The absence of neuromas in beaks of adult hens after conservative trimming at hatch. Aust. Vet. J. 74:46–49.[Web of Science][Medline]
Palacios, M. G., and P. L. Tubaro. 2000. Does beak size affect acoustic frequencies in woodcreepers? Condor 102:553–560.
United Egg Producers. 2004. Animal Husbandry Guidelines for US Egg Laying Flocks. United Egg Producers, Alpharetta, GA.
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