Incubation conditions affect leg health in large, high-yield broilers

2009 Poultry Science Association, Inc. Incubation conditions affect leg health in large, high-yield broilers E. O. Oviedo-Rondón, 1 M. J. Wineland, S. Funderburk, J. Small, H. Cutchin, and M. Mann Department of Poultry Science, North Carolina State University, Raleigh 27695-7608 Primary Audience: Hatchery Managers, Broiler Managers, Veterinarians, Researchers SUMMARY Leg problems are observed in every flock of broilers, and they occur more frequently in heavy, fast-growing broilers. Factors such as genetics, growth rate, stressors, nutrition, and lighting programs can contribute to and change the prevalence of these problems in broiler production. Our previous research has shown that elevated incubation temperatures and oxygen concentrations below 21% during the last days of embryo development can negatively affect thyroid hormones, relative asymmetry and normal development of leg bones, and development of other tissues and organs that influence leg health and locomotion in broilers. This project evaluated the effects of incubation profiles on leg health of high-yielding broilers at 8 wk of age under commercial conditions. Eggs from the same breeder flocks were incubated in either single-stage or multistage machines. Hatchlings were placed in paired houses on the same farms, and at 56 d of age, leg health was evaluated. There was variability among farms and hatches: leg problems such as footpad dermatitis were more closely related to farm conditions, whereas valgus and especially hock burns were influenced by incubation conditions within each farm. However, this fieldwork demonstrated that proper incubation conditions improve broiler performance, especially in females (1.2%); may reduce leg health problems such as crooked toes; and may even improve locomotion. Key words: incubation, broiler chicken, leg health, gait score, welfare DESCRIPTION OF PROBLEM Leg issues and locomotion problems are the most prevalent causes of culling and late mortality in broilers and these have a major impact on production, food safety, meat processing and welfare audits [1 3]. Leg problems and developmental disorders of long bones can be caused by genetic mutations, nutrition imbalances or marginal deficiencies, infectious diseases, or environmental stressors [4 7]. It has been reported 2009 J. Appl. Poult. Res. 18 :640 646 doi: 10.3382/japr.2008-00127 that the incidence of leg problems in broilers varies among broiler strains [8, 9], among seasons, and between farms because of stocking densities and management conditions [4 6, 9, 10]. The incidence of clinical lameness or visible leg disorders is typically less than 2 or 3%, but many more broilers are subclinically affected, presenting changes in gait patterns and reduced walking ability, resulting in detrimental effects for feed conversion, growth, and even defects in 1 Corresponding author: edgar_oviedo@ncsu.edu

Oviedo-Rondón et al.: INCUBATION AND LEG HEALTH 641 the processing plant [1 5]. Lame broilers spend more time lying in the litter and can be stepped on by other birds. These 2 factors could cause more lesions in the skin of the breast and legs [1 3, 11]. Several research models have been used to study bone developmental problems and locomotion issues in broilers [5 7, 12]. However, the treatments imposed on broilers during the research studies to increase leg issues have not replicated commercial conditions or the real incidence of those problems in the field [6, 12]. Under commercial conditions, one of the most frequent stresses that embryos may encounter occurs within the incubator if the temperature, humidity, and ventilation conditions are not optimal [13, 14]. Metabolic heat production increases as the embryo grows. It is higher in modern broiler embryos from genetic lines selected for fast growth compared with embryos from lines with slower growth rates [15]. Currently, most multistage incubation systems do not provide optimal heat to the embryos early in life (personal observations) and do not offer sufficient cooling capacity to reduce overheating of fast-growing embryos late in development [13, 14, 16, 17]. Incubation stressors can affect the development of several tissues, including bones. Recent research results indicate clearly that incubation conditions can affect the incidence of tibial dyschondroplasia [18] and early bone development in poultry [19, 20]. The results of our previous research [20] indicated that an elevated temperature (>37 C) and hypoxia, with less than 19% oxygen, during the last 4 d of incubation reduced bone development, collagen type X, and transforming growth factor β expression [19], and increased relative bone asymmetry in broilers. The use of single-stage incubation is increasing in the European poultry industry [14] and in North America, as indicated by the major incubator manufacturers. There are reports indicating improvement in broiler performance when single-stage profiles are used [13, 14]. Currently, information is limited on the effects of commercial incubation conditions on the leg health of heavy broilers. The objective of this study was to establish possible effects of incubation profiles on leg defects and locomotion on broilers at 56 d of age. MATERIALS AND METHODS The effects of 2 incubation profiles were evaluated in 6 commercial trials. Fertile eggs from Ross 708 [21] broiler breeder flocks were incubated in either single-stage (1 age of embryos) or multistage (6 different ages of embryos) Chick Master machines [22] at a commercial hatchery. To have similar broiler chicks in all broiler houses within each farm, all eggs from the breeder flocks were split equally between the 2 machine types before being set and placed into the multiple incubators. One or 2 single-stage machines and a minimum of 3 multistage machines were used to obtain the necessary number of chicks in each hatch according to the fertility of the breeder flock, the size of the broiler farm, and the stocking density. The incubation profiles used in these trials are those typically used in commercial broiler incubation. The temperatures used for the multi- and single-stage machines (each with approximately a 90,000-egg capacity) are described in Table 1. All machines were calibrated before each experiment, and each multistage or single-stage machine was operated according to the appropriate profile. The set times were determined by the hatchery manager and adjusted to compensate for the different lengths of incubation. The total incubation time, as determined by the evaluation of the hatchery manager, of chick condition and experience with the incubators was approximately 509 h for the single-stage and 505 h for the multistage machines. The multistage machines used a minimum RH set point of 50% and the dampers were temperature regulated. The single-stage machines used an initial set point of 10% RH for 2 d and then a minimum set point of 45% RH for the remaining incubation time. The dampers were initially closed for 6 d to allow a natural buildup of humidity; thereafter, there was a minimum and a maximum set point for dampers, which changed by programming the Programmable Logic Controller [22] to allow for control of RH and fresh air as the embryo grew. Data loggers [23] were used with the setters and hatchers to confirm that temperature profiles were actually achieved for each treatment during each trial. The temperatures recorded by the data loggers were within the normally accepted range for each type of in-

642 JAPR: Field Report Table 1. Incubation temperature 1 profiles used in the 6 experiments Incubation stage, preheating place Item Multistage, setter room Single stage, machine Preheating, 2 C 25.6 to 26.7 26.7 Initial temperature set point, C 37.5 38 Profile periods in setters 1 3 7 Final set point temperature in setters, C 37.5 36.9 Initial set point temperature in hatchers, C 36.9 36.7 Profile periods in hatchers 2 3 Final set point temperature in hatchers, C 36.7 36.1 1 Data loggers were placed in the setters and hatchers to confirm that temperature profiles were actually attained for each treatment. 2 Multistage eggs were preheated in the setter hall (25.6 to 26.7 C) for 5 h before being placed into the setters at 37.5 C. The preheating in the single-stage setters (26.7 C) took place in the setter for 6 h. Total incubation time, as determined by the evaluation of the hatchery manager, of chick condition and experience with the incubators was approximately 509 h for single-stage machines and 505 h for multistage machines. 3 The setters in multistage machines had only 1 set point independently of the changes in egg age. cubator. The high volume of these commercial incubators exhibited the normal spatial variation in temperature and humidity within each machine. Hatchlings were placed in paired houses on 6 different farms. All farms used for these experiments belonged to contract growers associated with the integrated company collaborating in this project. Within each farm, four 42 500-ft houses, capable of tunnel ventilation and identically constructed and equipped, were used. The individual capacity of each house is approximately 20,600 broilers during winter-spring flocks and 19,600 during summer flocks. The age of the breeder flocks used for each paired comparison and the number of chicks placed in each house were as equivalent as possible. Flocks were grown out mixed sex for periods of 9 wk. Feeding, lighting, and vaccination programs followed integrator recommendations. The lighting program used by this company during the period of this project consisted of 24 h of light at 0.6 lx for the first 7 d. From d 8 to 25, the duration of light was 9 h at a reduced intensity of 0.05 to 0.1 lx, and from 25 d to market, the duration of light was 24 h at 0.05 to 0.1 lx. Ventilation conditions were similar for all 4 houses within each farm, and this was verified by records of the electronic controllers in each house and by the temperature data loggers placed in each house. The maximum variability observed in temperatures within houses of the same farm in every experiment was not higher than 2 C on any single day. Data Collection and Statistical Analyses Mortality and culled birds were recorded daily for each house. At 56 d of age, 200 chickens per house, on each of the 6 farms, were sexed by physical traits of comb development and by shank and hock characteristics typical of males and females, and 100 from each sex were weighed and their legs were inspected for crooked toes, valgus or varus deformities of the intertarsal joint, hock burns, footpad dermatitis, and gait score. The crooked toe category was used when chickens had more than 1 digit on 1 or both legs bent laterally or medially [24]. Walking ability was divided into 6 categories of gait scores, ranging from completely normal (score 0) to immobile (score 5), following the method of Kestin [8, 25]. The effect of section within each house was taken in consideration, and 5 sections were evaluated along the length of each house. The same researchers evaluated all broilers on all farms for leg problems and assigned gait scores. The evaluators were not aware of the specific treatment assigned to each house at the moment of evaluation. Data were analyzed as a 2-treatment ANOVA. Every treatment was replicated 6 times in groups of 2 houses per farm. A total of 2,400 broilers were individually evaluated in each treatment. Live performance data had 6 replicates per treatment, with the average of 2 houses per farm, and there were 12 replicates per treatment for incidence of leg problems and for gait scores. Percentage data were transformed to arcsine (SQRT

Oviedo-Rondón et al.: INCUBATION AND LEG HEALTH 643 n + 1). These data were analyzed as a completely randomized block design with a nested effect of farm: Y ijkl = Sex i + Trt j + (Sex i Trt j ) + Farm (j) + [Trt j Farm k(j) ] + e ijkl. The GLM procedures of the SAS system [26] were used. Means separation was done with the t-test or Tukey s test. RESULTS AND DISCUSSION Results indicated that incubation profiles influenced (P < 0.05) BW (Figure 1) at 56 d of age. Female broilers hatched in single-stage incubation machines were heavier than those hatched in multistage machines at 56 d of age. Data from a recent study by Hulet et al. [27] revealed that chicks hatched from eggs with a high eggshell temperature during the last 3 d of incubation exhibited a lower BW at 44 d of age than chicks hatched from eggs with a lower eggshell temperature, which is regarded as being more optimal. The effects of incubation on broiler health under commercial conditions are not well documented. In these trials, male broilers had a higher incidence (P < 0.001) of crooked toes, valgus, and gait scores of 1 and 2 than females (Table 2 and 3). Males also had significantly higher final BW than females at 56 d of age, indicating a higher growth rate. Higher growth rates have been associated with a higher prevalence of skeletal problems, even within the same sex [1, 4, 5, 8, 24, 28]. A higher percentage of birds with crooked toes (0.8 vs. 0.1%), and gait scores of 1 and 2 were observed (P < 0.05) in broilers hatched in multistage machines (Table 2, 3), whereas broilers hatched in single-stage machines had a higher percentage of birds with a gait score of 0 (63.4 vs. 53.2%). The prevalence of valgus deformation was influenced (P = 0.08) by incubation profiles within each farm. Male broilers hatched in single-stage machines had 10% less valgus (26.6 vs. 36.8%) than male broilers hatched in multistage machines, independently of the farm where they were raised; however, this difference was not significant (P = 0.30). Scientific reports have indicated that hypoxia and elevated temperatures during the last days of incubation [19, 20] or suboptimal temperatures in other periods of incubation [18] affect bone development. We previously reported [19] a specific negative effect of elevated incubation temperatures on collagen type X and Figure 1. Body weights of male and female Ross 708 broilers at 56 d of age according to incubation profile. Data were collected from a random sample of 100 males and 100 females individually weighed in each house, for a total of 200 of each sex on each farm. Six trials were included in this evaluation, for a total of 1,200 broilers of each sex per treatment.

644 JAPR: Field Report Table 2. Leg health parameters of chickens at 56 d of age exposed to 2 different egg incubation profiles Incubation profile Sex Crooked toes Footpad dermatitis Hock burns Valgus Twisted legs Multistage Male 1.38 a 11.75 19.75 36.75 0.13 Female 0.13 b 17.63 21.50 1.00 0.00 Average 0.75 14.69 20.63 18.88 0.06 Single stage Male 0.01 b 12.63 22.00 26.63 0.63 Female 0.00 b 13.63 18.25 1.38 0.00 Average 0.006 13.13 20.13 14.00 0.31 Male 0.70 12.19 20.88 31.69 a 0.38 Female 0.07 15.63 19.88 1.20 b 0.00 SEM 0.13 1.56 3.00 2.65 0.16 Source of variation transforming growth factor β. These 2 important proteins are responsible for the formation of the organic matrix necessary for proper bone ossification. It is interesting to observe that the prevalence of toe deformation was higher in those chickens coming from multistage machines that provided elevated temperatures compared with % Probability Treatment 0.0012 0.5279 0.7129 0.3092 0.3716 Sex 0.0012 0.0639 0.8826 <0.0001 0.0926 Treatment sex 0.0105 0.3322 0.3011 0.1473 0.3716 Farm (treatment) 0.1191 <0.0001 <0.0001 0.0825 0.5901 a,b Means in a column without a common superscript are significantly different (P < 0.05). those coming from single-stage machines (Table 1). Footpad dermatitis and hock burns were mainly (P < 0.001) due to farm management conditions. At the time of evaluation, when farm litter conditions were more moist and caked, the incidence of footpad dermatitis and hock burn Table 3. Percentage of chickens within each gait score category at 56 d of age exposed to 2 different incubation profiles Incubation profile Sex Gait score 1 0 1 2 3 4 5 Multistage Male 34.00 50.75 12.25 2.00 0.50 0.00 Female 72.38 23.63 2.63 0.75 0.00 0.00 Average 53.22 b 37.19 a 7.44 a 1.38 0.25 0.00 Single stage Male 48.88 43.63 6.63 0.63 0.25 0.00 Female 77.98 19.63 1.13 0.38 0.38 0.13 Average 63.38 a 31.63 b 3.88 b 0.50 0.31 0.06 Male 41.44 b 47.20 a 9.44 a 1.32 0.38 0.00 Female 75.13 a 21.63 b 1.88 b 0.57 0.18 0.06 SEM 2.03 1.83 1.08 0.30 0.21 0.06 % Source of variation Probability Treatment 0.0028 0.0336 0.0249 0.1278 0.4193 0.3282 Sex <0.0001 <0.0001 <0.0001 0.0512 0.8853 0.3282 Treatment sex 0.1913 0.7801 0.4144 0.3087 0.2320 0.3282 Farm (treatment) <0.0001 <0.0001 0.6737 0.3341 0.5768 0.4500 a,b Means in a column without a common superscript are significantly different (P < 0.05). 1 Gait scores ranging from completely normal (score 0) to immobile (score 5), following the method of Kestin [8, 25].

Oviedo-Rondón et al.: INCUBATION AND LEG HEALTH 645 was higher. Varus deformation, twisted legs, and severe lameness (gait scores 4 and 5) were rarely observed and were not significantly affected (P > 0.05) by any of the variables evaluated. A significant interaction effect between incubation profile and sex was observed for crooked toes, indicating that the effect of incubation was higher for males than females. No other significant interactions between incubation profiles and farm conditions or sex were observed. Conducting these trials under commercial conditions to evaluate leg health in broilers approaching processing age represented a challenge because growers and most integrated companies have a policy of culling broilers. There were no consistent records of broilers culled because of leg problems. This situation has been addressed in other animal welfare audits and leg health surveys [8, 25]. However, it is interesting to notice that culling practices do not have any association with flock average gait score or percentage of birds with specific leg problems at the moment of survey [4, 25, 28]; because of that, we consider our results valid. It is even more interesting to find that specific management practices such as incubation profiles have significant effects on leg health problems such as crooked toes and that they influence valgus prevalence even after 8 wk of life, and the single-stage profile improved both growth rate and some parameters of leg health. The incidence of birds with gait scores of 3 or above was only 2.5% in our trials compared with other surveys in different European countries, which have reported incidences between 8.5 and 30.1% [4, 8, 25, 28]. We conducted these trials with the Ross 708 strain, which was not used widely in Europe [29] at the time of the surveys previously referenced, and less variation was observed in leg problems because we evaluated all flocks at 56 d of age under very similar housing, stocking density, and management conditions. Published results of broiler leg health surveys take into consideration genetics, company, period of the year, stocking density, feeding programs, growth rates, litter conditions, and lighting programs. None of these surveys has identified differences because of incubation or brooding conditions among the flocks evaluated. According to the results presented here, there is an indication that incubation profiles may affect bone development and gait scores in broilers. CONCLUSIONS AND APPLICATIONS 1. Incubation conditions have an effect on some parameters of leg health in broiler populations, such as crooked toes and gait scores. 2. It is possible to improve locomotion in large, high-yielding broilers while improving growth rates by optimizing incubation conditions. REFERENCES AND NOTES 1. Mench, J. 2004. Lameness. Pages 3 17 in Measuring and Auditing Broiler Welfare. C. Weeks and A. Butterworth, ed. CAB International, Wallingford, UK. 2. Bessei, W. 2006. Welfare of broilers: A review. World s Poult. Sci. J. 62:455 466. 3. Pattison, M. 1992. Impacts of bone problems on the poultry meat industry. Pages 329 338 in Bone Biology and Skeletal Disorders in Poultry. Poult. Sci. Symp. No. 23. C. C. Whitehead, ed. Carfax Publishing Company, Abingdon, UK. 4. Sanotra, G. S., J. D. Lund, A. K. Ersboll, J. S. Petersen, and K. S. Vestergaard. 2001. Monitoring leg problems in broilers: A survey of commercial broiler production in Denmark. World s Poult. Sci. J. 57:55 69. 5. Bradshaw, R. H., R. D. Kirkden, and D. M. Broom. 2002. A review of the aetiology and pathology of leg weakness in broilers in relation to welfare. Avian Poult. Biol. Rev. 13:45 103. 6. Oviedo-Rondón, E. O., P. R. Ferket, and G. B. Havenstein. 2006. Understanding long bone development in broilers and turkeys. Avian Poult. Biol. Rev. 17:77 88. 7. Oviedo-Rondón, E. O., P. R. Ferket, and G. B. Havenstein. 2006. Nutritional factors that affect leg problems in broilers and turkeys. Avian Poult. Biol. Rev. 17:89 103. 8. Kestin, S. C., T. G. Knowles, A. E. Tinch, and N. G. Gregory. 1992. Prevalence of leg weakness in broiler chickens and its relationship with genotype. Vet. Rec. 131:190 194. 9. Kestin, S. C., G. Su, and P. Sorensen. 1999. Different commercial crosses have different susceptibility to leg weakness. Poult. Sci. 78:1085 1090. 10. Kestin, S. C., S. Gordon, G. Su, and P. Sorensen. 2001. Relationship in broiler chickens between lameness, liveweight, growth rate and age. Vet. Rec. 148:195 197. 11. Vaillancourt, J.-P., and A. Martinez. 2002. Inflammatory process (IP) causes and control strategies. Zootec. Int. 25:48 53. 12. Leach, R. M. Jr., and E. Monsonego-Ornan. 2007. Tibial dyschondroplasia 40 years later. Poult. Sci. 86:2053 2058. 13. Meijerhof, R. 2002. Design and operation of commercial incubators. Pages 41 46 in Practical Aspects of Commercial Incubation. D. C. Deeming, ed. Ratite Conference Books, Lincolnshire, UK.

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