The influence of double interspiking on production and behavior in broiler breeder flocks in elevated temperature conditions

2012 Poultry Science Association, Inc. The influence of double interspiking on production and behavior in broiler breeder flocks in elevated temperature conditions K. M. Chung, M. O. Smith, 1 and H. G. Kattesh Department of Animal Science, University of Tennessee, Knoxville 37901-1071 Primary Audience: Researchers, Broiler Breeder Producers SUMMARY Broiler breeders experience a natural decline in fertility levels as a flock ages. A male management practice, such as double interspiking, could be applied to counteract this decline. To determine the impact of double interspiking on broiler breeder flocks, a study was conducted to monitor the production parameters of the flock and the behavioral expression of the males. Broiler breeders (288 females, 36 males) were housed in 3 rooms, with 1 room serving as a control and the other 2 used for double interspiking. Egg production, fertility, and hatchability were determined. Video recordings were conducted to assess the frequency of specific individual (preening, feather ruffling, wing flapping), male-to-male (fighting, pecking, retreating), and male-to-female (attempted and completed mating) behaviors. The use of double interspiking resulted in a fertility increase (P < 0.01) after the first interspike and a sustainment of fertility levels after the second interspike. Neither egg production nor hatchability was affected by this male management practice. The occurrence of male-to-male interactions increased, but there were no significant differences in male-to-female or individual-type behaviors. Regardless of treatment, there was a decrease in male-to-female behaviors as the birds aged. Key words: behavior, broiler breeder, double interspiking, fertility, heat stress 2012 J. Appl. Poult. Res. 21 :63 69 http://dx.doi.org/10.3382/japr.2011-00347 DESCRIPTION OF PROBLEM In the broiler breeder industry, genetic selection for a higher BW and large musculoskeletal frame of broiler breeders has a negative impact on the reproductive capabilities of these birds [1 3]. In addition, heavier breeder males show low mating frequencies [4] and inefficient matings [5] because of the large breast muscle deposition [3, 6, 7], which negatively affects mating ability. When this intrinsic fertility problem is combined with the fertility decline that is associated with an aging flock [8, 9], it is easy to see that steps must be taken to counteract this fertility decline, which affects broiler breeders throughout the world. Steps can be taken to positively influence fertility levels as birds age. A common practice in industry is to apply the male management practice of spiking to an already established flock to counteract the decline in fertility levels. This practice involves the replacement of male broiler breeders at a particular point in the growing cycle with younger, unfamiliar males. The objective of spiking is to introduce young males into an already established flock to achieve 1 Corresponding author: mosmith@utk.edu

64 JAPR: Research Report higher fertility levels and to increase mating activity among birds within a flock. Not only does spiking involve the costly expense of maintaining and running a separate stud farm to house the young males, but also this practice could possibly result in larger biosecurity risks by introducing new disease-causing organisms, such as viruses, into an already established poultry house. A second, novel male management practice is the use of double interspiking. The objective of double interspiking is to swap males from 1 existing flock into another existing flock of the same age on the same farm at 2 different time periods to maintain optimal fertility levels in a breeder flock. The theory behind the male management practice of double interspiking is that fertility levels will improve because the introduction of males will disrupt the established pecking order, causing an increase in sexual behavior. Initial mating activity will increase when birds are transferred and introduced into a new social hierarchy. This change in location and social group will cause an increase in mating behavior, thereby compensating for the loss in libido and mating interest of older males [10]. It is postulated that double interspiking would alleviate some of the problems that are associated with spiking, such as eliminating the need for stud farms and preventing the introduction of immune challenges into a poultry house. The abrupt change to a new environment for some males, and the introduction of new individuals into a stable social group, will increase sexual behavior and compensate for the loss in libido and mating interest of the older males [10]. One of the most important characteristics of a flock of chickens is that they are social animals. Commercially, chickens are normally housed together in big groups and are able to establish a fairly stable pecking order within a flock. Once established, the pecking order is very important in dictating all social interactions among individuals within the flock [11]. For instance, to limit death and injury of birds within a flock caused by fighting and aggression, the pecking order established among males is the most important factor in preventing unnecessary fights among individuals. When a new individual is introduced into the same pen, both fighting and pecking will occur until the dominance and subordinance statuses have been determined and the pecking order established [12]. Fighting behavior occurs when individuals stand opposite each other with feathers raised in a threatening manner. Pecking is described as a movement of the beak toward the head or body of the opponent individual. These behaviors are expressed at high frequencies and high intensities until newly introduced individuals have found their position within the social order. The male-to-female interactions are the most important behaviors expressed because this sexual behavior is a determinant of reproductive success. According to reported observations, broiler breeder males exhibit higher levels of aggressive behavior toward females than are seen in broiler stock or in laying strains [4, 13 17]. Because of this aberrant behavior, more time is spent on aggressive acts instead of sexual behaviors. In addition, females seem fearful of the males in the pens because of the constant pecking and chasing by the males [16]. Their reaction is then one of avoidance of the males, and because of this, the male-to-female aggression increases forced matings with females [17]. In one study, the sperm produced by aged roosters had a high potential to fertilize a hen s egg, so male-to-female sexual behavior is believed to be one of the most important factors affecting fertility levels [10]. Behavioral factors could possibly correlate with the reproductive success of the males in a flock because McGary et al. [16] found a positive correlation of total reproductive behavior and fertility levels in 1 strain that they investigated, concluding that the expression of this type of behavior can indicate fertility levels. In terms of individual-type behaviors, chickens will express certain behaviors as a means of maintenance of self. These behaviors are not normally motivated by social relationships, and these behavioral needs will occur regardless of external stimuli. Wing flapping is a behavior that is characterized under the activity of stretching [18]. This behavior occurs when one or both wings are outstretched, lifted, and flapped above the back. Although it is recognized that this behavior has been classified under different categories, such as aggression [18] or courtship behaviors [19], in this study it is classified as an individual-type behavior because it did not seem to influence any other individual and appeared to be expressed as an announcement by the in-

Chung et al.: DOUBLE INTERSPIKING IN BREEDERS 65 dividual of its presence within the flock. Feather ruffling is a maintenance-type behavior that is an individual s response to peripheral stimulation [20]. To express this behavior, feathers of the neck, head, and body are raised and moved in a shaking manner. Preening behavior is associated with rearranging feather plumage that is located at the breast or wing area. This behavior is recognized as pecking or stroking of the feathers with the individual s beak [18]. This behavior is designated as comfort behavior because it is done when birds are mildly frustrated or are involved in conflict [18, 20, 21]. A study was designed to investigate the effects of the novel male management practice of double interspiking on flock production parameters and behavioral responses of broiler breeder males that were housed in heat-stressed environments. It was postulated that the use of double interspiking would result in higher fertility levels, higher male-to-male and male-to-female behavioral expression, and unchanged individualtype behaviors. MATERIALS AND METHODS All observations took place at the University of Tennessee Johnson Animal Research and Teaching Unit, and all animal procedures were reviewed and approved by the University of Tennessee Animal Care and Use Committee. A total of 324 Ross 708 broiler breeder chickens (288 females, 36 males) were assigned to 3 groups at 21 wk of age (WOA). The female-tomale ratio for the research birds was 8:1, which is comparable with normal production standards in which 1 rooster is necessary for every 8 to 12 hens. All 3 groups were housed in 12 20 ft (3.7 6.1 m) enclosure pens in which the temperature cycled between 23.8 and 30 C to mimic heat-stressed environments. The floor consisted of nontraditional Dura-Slat slatted flooring [22] that was made of a sturdy polypropylene material and is marketed as promoting strong foot health. Sex-separate feeders for males and females were provided in each pen, and birds were fed a predetermined amount of feed from a breeder diet (Table 1) to control BW. Water was provided through nipple drinkers for ad libitum consumption. Each room was on a 16L:8D lighting regimen, with nest boxes provided. Table 1. Composition of the broiler breeder diet Item Amount, % Ingredient Corn 63.16 Soybean meal (48% CP) 11.85 Wheat middlings 8.00 Limestone 7.90 Pro-Pak 1 5.00 Fat blend 2.30 Monocalcium phosphate 0.60 Termin-8 2 0.30 Salt 0.20 Vitamin premix 3 0.20 Bicarbonate of soda 0.15 dl-methionine 0.14 Choline 0.12 Trace mineral premix 4 0.08 Calculated nutrient analysis ME, kcal/kg 2,938 CP, % 15.20 Calcium, % 3.5 Total phosphorus, % 0.61 Available phosphorus, % 0.43 1 Protein concentrate (H. J. Baker and Bros., Stamford, CT). 2 Antimicrobial preservative (Tennessee Farmers Cooperative, Lavergne, TN). 3 Vitamin premix provided the following per kilogram of complete diet: vitamin A, 30,800 IU; vitamin D 3, 9,250 IU; vitamin E, 153.9 IU; vitamin B 12, 0.154 mg; riboflavin, 46.2 mg; niacin, 185 mg; pantothenic acid, 84 mg; menadione sodium bisulfite, 16.2 mg; folic acid, 12.3 mg; pyridoxine hydrochloride, 46.2 mg; thiamine hydrochloride, 20.5 mg; biotin, 9.3 mg; choline, 2,944 mg; niacin, 185 mg. 4 Trace mineral premix provided the following per kilogram of complete diet: copper, 55 mg; iodine, 7.3 mg; iron, 366 mg; manganese, 310 mg; zinc, 321 mg; potassium, 2.23 g; magnesium, 1.09 g; selenium, 0.48 mg. Double interspiking was carried out between 2 pens when birds were 42 WOA and again when they were 52 WOA. At each interspike, 25% of the male population was transferred between the 2 pens, whereas the third pen was left undisturbed. For the interspikes, a different set of males were transferred between the 2 pens during the second interspike at 52 wk than the set transferred during the first interspike at 42 WOA. At the start of lay, total counts of eggs laid per pen were recorded to calculate percentage egg production by finding the total number of eggs laid by the number of hens. A representative number of eggs (n = 72/pen) were set every 2 wk and candled at d 12 of the incubation cycle to track fertility levels throughout the ex-

66 JAPR: Research Report periment. Fertility was calculated by finding the percentage of fertile eggs within the total number of eggs set. Hatchability was determined at 6 specific time points in the experiment by calculating the percentage of hatched chicks by the number of fertile eggs. At d 21, chicks were counted, and those eggs that did not hatch were broken out to determine early or late dead eggs. Behavior was monitored with Panasonic Color CCTV video cameras [23], which recorded video footage using a Noldus MPEG Recorder [24] from 1900 to 2100 h at specific time points. This duration of time for video recording was chosen because usually 70% of all mating activity occurs within the last 4 h of light in a day, with peak mating behavior occurring later in the day [25] and, more specifically, 1 to 2 h before lights go out [26]. The Noldus Observer XT 8.0 program [24] was used to analyze all the behavioral interactions of the roosters, with the frequency of interactions being specifically targeted. Characteristics observed were categorized as male-to-male, male-to-female, and individual behaviors. Male-to-male behaviors represented antagonistic and aggressive behaviors between 2 males and included fighting, pecking, and retreating. Pecking represented the action of 1 male pecking another male with its beak, with a clear reaction from the pecked male. This usually was done as a downward stroke toward the head or dorsal region of the attacked bird. Fighting represented the action of 1 male lunging or flying toward another male with its claws with the intention to fight and with a clear reaction from the attacked male. Retreating represents the sudden avoidance of a rooster, eliciting a reaction from the aggressor rooster to chase or attack. Male-to-female behaviors represented the sexual behavior that occurred between a rooster and a hen. Completed and attempted matings were recorded. Although it is recognized that males sometimes mount hens simply to prevent other males from mating with a hen, completed mating was recorded only if a male correctly mounted a hen for a sufficient period of time to allow for cloacal contact between the 2 individuals. Attempted mating was recorded when males showed an interest in mating with the hens but did so unsuccessfully. This was the result if a rooster forcefully pecked the hen s head, leading to the hen s escape, if mounting was interrupted by another male s interference, or because of the individual s inability to mate effectively. Individual behaviors represented maintenance-type behaviors and included preening, wing flapping, and feather ruffling. Preening behavior was associated with any contact with the bird s beak to its own feathers on any part of its body, resulting in a rearrangement of the bird s feathers. Wing flapping required outstretch of 1 or both of the rooster s wings associated with a hearty flapping of the outstretched wing(s). Feather ruffling represented the raising of feathers from the bird s body with a type of rocking motion. Frequencies of each of the individual behaviors were marked per individual, and the frequency of each interaction was analyzed. Behavior was reported as the frequency of behavioral events per rooster per 2-h period. All data were analyzed using the mixed-model ANOVA procedure of SAS [27]. For flock parameters such as egg production, fertility, and hatchability, statistical analyses were conducted, with weekly flock measurements as the experimental unit. For the behavioral analysis, each individual rooster was the experimental unit. Least squares means were compared and treatment differences evaluated to determine significance, which was set at a value of P < 0.05. RESULTS AND DISCUSSION The effects of age on production parameters are shown in Table 2. Egg production declined gradually until 62 WOA, and fertility declined toward the end of the productive life cycle. Although it is recognized that raising broiler breeders completely on slatted flooring may result in decreased fertility levels, this fertility decline, although expected, was consistent with common observations in poultry production [8, 9, 28]. Hatchability, calculated as (number of chicks/ number of fertile eggs) 100, fluctuated during the life of the flock, but levels remained similar between peak production and the end of the productive life of the flock. This is in contrast to previous studies in which hatchability declined toward the end of the life cycle [28 31]. The effects of double interspiking between 2 pens performed at 42 and 52 WOA on fertility levels are shown in Figure 1. After the first

Chung et al.: DOUBLE INTERSPIKING IN BREEDERS 67 Figure 1. Age-related changes in fertility between interspiked and control groups. Mean percentage fertility of eggs that were set across 16 observation periods for all flocks. Values are expressed as mean ± SE. Arrows represent dates when double interspiking occurred. Within a graph, asterisks (*) and double asterisks (**) denote differences between the control flock and the interspiked flock at a given age (P < 0.05). interspike at 42 WOA, there was an increase (P < 0.0001) in the fertility levels of the interspiked flocks for the following 4 wk. After the second interspike, the fertility of the spiked flock was similar to that of the control flock at 54, 56, and 58 WOA, with differences in fertility measurement between the interspiked flocks and the control flock not being significant. At Table 2. Least squares means for flock egg production, fertility, and hatchability values [(number of chicks/ number of fertile eggs) 100] related to age 1 Week of age Egg production, % Fertility, % Hatchability, % 32 84.4 a 88.2 ab 98.3 ab 34 81.0 ab 93.9 a 36 78.1 ab 89.4 a 38 73.5 bc 92.7 a 40 75.8 bc 92.7 a 42 69.1 cd 85.3 ab 98.2 a 44 69.9 cd 76.2 bc 90.1 b 46 68.3 cde 72.6 c 48 62.3 def 65.7 c 50 60.6 ef 66.0 c 52 57.9 fg 67.7 c 97.4 a 54 54.6 fg 53.1 d 98.3 a 56 52.1 gh 43.1 de 58 52.4 gh 38.7 e 94.9 ab 60 45.3 hi 47.5 de 62 39.3 i 38.9 e SEM 10.9 12.7 7.4 a i Means within a column with different letters differ (P < 0.05). 60 and 62 WOA, toward the end of the productive life of the flock, fertility levels of the control flock were higher (P = 0.0085) than those of the spiked flock. In a previous study that used the practice of spiking, researchers also saw an increase in fertility levels that lasted for 5 to 10 wk after spiking [32]. Regarding egg production or hatchability, the male management practice of double interspiking did not affect either parameter. The results of age on the behavioral observations are shown in Table 3. During the 2 wk that the flocks were double interspiked, the frequency of total male-to-male (fighting, pecking, and retreating) behaviors at 42 and 52 WOA was higher. This increase in aggressive behavior among males after double interspiking is likely a result of the disruption of the established pecking order in the flock. Guhl and Ortman [33] explained that when strangers are introduced into a new pen, they perform exploratory behavior, which alerts resident birds that this is a stranger and a new individual to the pen. The residents of the pen perform aggressive acts toward the strangers to establish the new pecking order. This increase in aggressive behavior is consistent with the effects of spiking. Casanovas [10] showed that a large increase in aggressive behavior occurred among all roosters that were spiked. As expected, male-to-female behavior (completed mating and attempted mating) declined as birds aged. Our findings regarding age in male-to-female interactions were consistent with results presented by McGary et al. [16], Duncan et al. [25], Hocking and Bernard [28], and Craig and Bhagwat [34]. As with these studies, all expressions of male-to-female type behavior in our study declined with age of the roosters. Our results are inconsistent with those reported by Casanovas [10], in which total sexual and mating activity increased among all males within a flock after spiking. The expression of individual (preening, wing flapping, and feather ruffling) behaviors that represented maintenance behaviors did not differ in frequency. This was not unexpected because maintenance-type behaviors are likely to be expressed by all individuals regardless of external stressors. These results are consistent with those from a study by Duncan and Wood-Gush [35] in which the authors concluded that preens could be modified in

68 JAPR: Research Report Table 3. Least squares means for male-to-male, male-to-female, and individual behavioral expression changes related to age 1,2 Week of age Male-to-male Male-to-female Individual 41 0.08 b 2.47 a 4.08 a 42 0.40 a 2.05 a 4.12 a 44 0.13 b 1.36 b 2.87 ab 51 0.01 b 0.48 c 2.73 b 52 0.33 a 0.68 c 3.85 ab 54 0.01 b 0.29 c 2.93 ab 62 0.05 b 0.17 c 2.95 ab SEM 0.11 0.35 0.61 a c Means within a column with different superscripts differ (P < 0.05). 1 All behaviors are expressed as the frequency of behaviors per male within 2 h. the presence of frustration or a stressor but that the frequency of the preening expression did not differ. Infertility issues have been associated with a problem with the roosters, which is the reason for the development of male management practices such as double interspiking. However, some research has been done regarding the possible contribution of the hen to the infertility issue. Instead of fertility decline being a problem solely with the roosters, some researchers have contended that the age of the hen is a possible cause for fertility decline as well. In a study by Bramwell et al. [36], older hens experienced lower fertility levels than younger hens. When artificially inseminated with the sperm of an older rooster, young hens showed higher levels of fertility and sperm penetration in comparison with older hens. In that study, the older roosters actually showed higher levels of sperm penetration and fertility levels in comparison with the younger males. Therefore, age did not seem to affect the fertilizing potential of the male. A study of native Thai chickens also concluded that roosters from 9 mo to 2 yr show high fertilizing ability, and the researchers concluded that hens were responsible for the fertility decline [37]. CONCLUSIONS AND APPLICATIONS 1. The male management practice of double interspiking shows great promise as a tool to increase fertility levels in an aging broiler breeder flock. With the addition of benefits such as decreased breeder cost and improved biosecurity, the practice of double interspiking could offer greater advantages to the broiler breeder industry that the common industry practice of spiking does not. 2. Double interspiking caused a disruption of the pecking order, and the increased expression of aggressive behavior between the roosters likely resulted from this practice. 3. The expression of male-to-female behavior will decline as birds age. This decline occurs regardless of whether a male management practice is implemented. Therefore, fertility issues might not be a result of the frequency of overall mating activity. 4. Although male management practices such as spiking and double interspiking attempt to alleviate fertility problems that are caused by a problem with the roosters, hens might play a larger role in fertility issues than was previously thought. REFERENCES AND NOTES 1. Siegel, P. B. 1963. Selection for body weight at eight weeks of age. 2. Correlated responses of feathering, body weights and reproductive characteristics. Poult. Sci. 42:896 905. 2. Wilson, H. R., N. P. Piesco, E. R. Miller, and W. G. Nesbeth. 1979. Prediction of the fertility potential of broiler breeder males. World s Poult. Sci. J. 35:95 118. 3. Hocking, P. M., and S. R. I. Duff. 1989. Musculoskeletal lesions in adult male broiler breeder fowls and their relationships with body weight and fertility at 60 weeks of age. Br. Poult. Sci. 30:777 784. 4. Bilcik, B., I. Estevez, and E. Russek-Cohen. 2005. Reproductive success of broiler breeders in natural mating systems: The effect of male-male competition, sperm quality, and morphological characteristics. Poult. Sci. 84:1453 1462. 5. Hocking, P. M. 1990. The relationships between dietary crude protein, body weight, and fertility in naturally mated broiler breeder males. Br. Poult. Sci. 31:743 757. 6. Wilson, J. L. 2002. Understanding the Factors That Influence Broiler Breeder Flock Fertility. Cooperative Extension Service, University of Georgia, Athens. 7. Wolanski, N. J., R. A. Renema, F. E. Robinson, and J. L. Wilson. 2004. End-of-season carcass and reproductive traits in original and replacement male broiler breeders. J. Appl. Poult. Res. 13:451 460.

Chung et al.: DOUBLE INTERSPIKING IN BREEDERS 69 8. Sexton, K. J., J. A. Renden, D. N. Marple, and R. J. Kempainen. 1989. Effects of dietary energy on semen production, fertility, plasma testosterone, and carcass composition of broiler-breeder males in cages. Poult. Sci. 68:1688 1694. 9. McGary, S., I. Estevez, M. R. Bakst, and D. L. Pollock. 2002. Phenotypic traits as reliable indicators of fertility in male broiler breeders. Poult. Sci. 81:102 111. 10. Casanovas, P. 2002. Management Techniques to Improve Male Mating Activity and Compensate for the Age- Related Decline in Broiler Breeder Fertility: Intra-Spiking. The Poultry Informed Professional, College of Veterinary Medicine, University of Georgia, Athens. 11. Gross, W. B., and P. B. Siegel. 1973. Effect of social stress and steroids on antibody production. Avian Dis. 17:807 815. 12. Guhl, A. M. 1968. Social behavior of the domestic fowl. Trans. Kans. Acad. Sci. 71:379 384. 13. Rushen, J. 1983. The development of sexual relationships in the domestic chicken. Appl. Anim. Ethol. 11:55 66. 14. Millman, S. T., I. J. H. Duncan, and T. M. Widowski. 2000. Male broiler breeder fowl display high levels of aggression toward females. Poult. Sci. 79:1233 1241. 15. Millman, S. T., and I. J. H. Duncan. 2000. Effect of male-to-male aggressiveness and feed-restriction during rearing on sexual behaviour and aggressiveness towards females by male domestic fowl. Appl. Anim. Behav. Sci. 70:63 82. 16. McGary, S., I. Estevez, and E. Russek-Cohen. 2003. Reproductive and aggressive behavior in male broiler breeders with varying fertility levels. Appl. Anim. Behav. Sci. 82:29 44. 17. Moyle, J. R., D. E. Yoho, R. S. Harper, and R. K. Bramwell. 2010. Mating behavior in commercial broiler breeders: Female effects. J. Appl. Poult. Res. 19:24 29. 18. Kruijt, J. P. 1964. Ontogeny of social behaviour in Burmese red junglefowl (Gallus gallus spadiceus) Bonnaterre. Behaviour (Suppl. 12):i ix, 1 201. 19. Jones, M. E., and J. A. Mench. 1991. Behavioral correlates of male mating success in a multisire flock as determined by DNA fingerprinting. Poult. Sci. 70:1493 1498. 20. Duncan, I. J. H. 1998. Behavior and behavioral needs. Poult. Sci. 77:1766 1772. 21. Bshary, R., and J. Lamprecht. 1994. Reduction of aggression among domestic hens (Gallus domesticus) in the presence of a dominant third party. Behaviour 128:311 324. 22. Gillis Agricultural Systems Inc., Willmar, MN. 23. Panasonic Corporation of North America, Secaucus, NJ. 24. Noldus Information Technology, Leesburg, VA. 25. Duncan, I. J. H., P. M. Hocking, and E. Seawright. 1990. Sexual behaviour and fertility in broiler breeder domestic fowl. Appl. Anim. Behav. Sci. 26:201 213. 26. Bilcik, B., and I. Estevez. 2005. Impact of male-male competition and morphological traits on mating strategies and reproductive success in broiler breeders. Appl. Anim. Behav. Sci. 92:307 323. 27. SAS Institute. 1987. SAS/STAT Guide for Personal Computers. Version 9.1. SAS Inst. Inc., Cary, NC. 28. Hocking, P. M., and R. Bernard. 2000. Effects of the age of male and female broiler breeders on sexual behaviour, fertility and hatchability of eggs. Br. Poult. Sci. 41:370 376. 29. Fiser, P. S., and J. R. Chambers. 1981. Determination of male fertility in thirteen commercial lines of broiler parents. Poult. Sci. 60:2316 2321. 30. Creel, L. H., D. Maurice, W. C. Bridges, and L. W. Grimes. 1998. A model to describe and predict post-peak changes in broiler hatchability. J. Appl. Poult. Res. 7:85 89. 31. Barna, J., B. Végi, E. Váradi, Z. Szőke, and K. Liptói. 2007. Analysis of fertility in broiler breeder flocks Male side approaches. Pages 75 81 in Proc. 5th Vietnamese-Hungarian Int. Conf. Anim. Prod. Aquac. Sustain. Farming, Can Tho, Vietnam. 32. Wilson, J. L. 1999. Hatchery/Breeder Tip... Implementing a Spiking Program. Cooperative Extension Service, University of Georgia, Athens. 33. Guhl, A. M., and L. L. Ortman. 1953. Visual patterns in the recognition of individuals among chickens. Condor 55:287 298. 34. Craig, J. V., and A. L. Bhagwat. 1974. Agonistic and mating behavior of adult chickens modified by social and physical environments. Appl. Anim. Ethol. 1:57 65. 35. Duncan, I. J. H., and D. G. M. Wood-Gush. 1972. An analysis of displacement preening in the domestic fowl. Anim. Behav. 20:68 71. 36. Bramwell, R. K., C. D. McDaniel, J. L. Wilson, and B. Howarth. 1996. Age effect of male and female broiler breeders on sperm penetration of the perivitelline layer overlying the germinal disc. Poult. Sci. 75:755 762. 37. Chotesangasa, R. 2001. Effects of mating ratio, cock number in the flock and breeder age on fertility in Thai native chicken flock. Kasetsart J. (Nat. Sci.) 35:122 131. Acknowledgments We thank Pilgrim s Pride Corp. (Greeley, CO) for the donation of the birds and University of Tennessee AgResearch (Knoxville) for their research support. We also thank Eddie Jarboe, Linda Miller, Mary Roberts, Nancy Rohrbach, and Arnold Saxton (Department of Animal Science, University of Tennessee, Knoxville) for their assistance with this experiment.