Relationships of incubational hatching egg characteristics to posthatch body weight and processing yield in Ross Ross 708 broilers 1,2

2014 Poultry Science Association, Inc. Relationships of incubational hatching egg characteristics to posthatch body weight and processing yield in Ross Ross 708 broilers 1,2 E. D. Peebles,* 3 R. Pulikanti,* W. Zhai,* and P. D. Gerard * Department of Poultry Science, Mississippi State University, Mississippi State 39762; and Department of Mathematical Sciences, Clemson University, Clemson, SC 29634 Primary Audience: Primary Breeders, Hatchery Personnel, Avian Reproductive Physiologists SUMMARY The characteristics of broiler hatching eggs have the potential to effect broiler posthatch growth and processing yield. The association of set egg weight (SEW), length of incubation (LI), and mean daily percentage of incubational weight loss (MDPEWL) of embryonated Ross Ross 708 broiler hatching eggs with subsequent posthatch BW and processing yield was investigated. Sixty Ross Ross 708 broiler hatching eggs were randomly set on each of 8 replicate tray levels of an incubator. Weight loss of individual embryonated eggs between 0 and 10.5, 10.5 and 18.5, and 0 and 18.5 d of incubation was determined for the calculation of MDPEWL. Furthermore, on 18.5 d of incubation, embryonated eggs were transferred to a hatcher unit where they were individually monitored for hatch every 12 h for determination of LI. Chicks were placed in corresponding replicate floor pens and were grown out from 0 (21.5 d of incubation) to 49 d posthatch. Live bird BW as a percentage of SEW on 21.0 d of incubation and d 0 and 49 posthatch, and bird sex on d 49 posthatch were determined. After commercial processing, carcass weight as a percentage of SEW, and carcass, abdominal fat pad, wings, breast muscle, tenders, drumsticks, and thighs weights as percentages of live BW were determined. Bird BW on 21.0 d of incubation and on d 0 and 49 posthatch were positively correlated or interrelated with SEW. Between 0 and 10.5 d of incubation, MDPEWL was negatively correlated with absolute and relative BW on 21.0 d of incubation, absolute BW on d 0 posthatch, and relative tenders weight. Further, LI was positively correlated with absolute and relative BW on 21.0 d of incubation and d 0 posthatch, but was negatively correlated with relative (percentage of live BW) carcass weight on d 49 posthatch. The MDPEWL of modern strain broiler hatching eggs should be closely monitored, particularly during the first half of incubation, for the regulation of LI and hatchling BW and for their potential effects on processing yield characteristics. Key words: body weight, broiler, egg weight loss, incubation length, processing yield 2014 J. Appl. Poult. Res. 23 :34 40 http://dx.doi.org/10.3382/japr.2013-00784 1 This is Journal Article Number J-12335 from the Mississippi Agricultural and Forestry Experiment Station supported by MIS- 322270. 2 Use of trade names in this publication does not imply endorsement by Mississippi Agricultural and Forestry Experiment Station of these products, nor similar ones not mentioned. 3 Corresponding author: dpeebles@poultry.msstate.edu

Peebles et al.: INCUBATIONAL AND YIELD RELATIONSHIPS 35 DESCRIPTION OF PROBLEM A better understanding of the relationships between pre- and posthatch physiological variables of modern strain broilers is important, as the embryonic growth period in those strains spans over almost one-third of the broiler s entire growth period. Previous researchers [1, 2] have suggested the importance of understanding and monitoring prehatch physiological variables of broiler hatching eggs and embryos for the improvement of hatchery and grow-out management practices essential for the realization of increased slaughter yield. Manipulation of incubational temperature has been shown to affect subsequent broiler breast muscle yield at 35 [3] and 70 [4] d posthatch. The relationships of various physiological characteristics of broiler hatching eggs with those of corresponding broiler hatchlings during the early [5] and middle to late [6] periods of grow-out have also been examined in other studies. Internal egg temperature and specific eggshell water vapor conductance (eggshell water conductance adjusted to a 100-g egg weight basis) were the prehatch variables that were of primary focus in the reports by Pulikanti et al. [5, 6]. The variables in chicks that were examined by Pulikanti et al. [5] through 10 d posthatch included total BW, and the weights, moisture concentrations, and nutrient compositions (glucose, glycogen, fat, and protein) of their carcasses, pipping muscles, livers, and left gastrocnemius muscles; whereas the posthatch variables examined by Pulikanti et al. [6] included total BW, carcass weight, and the weights, moisture concentrations, and nutrient compositions (glucose, glycogen, fat, and protein) of the livers, breast muscles, and left gastrocnemius muscles of middle (28-d-old) and late (48-d-old) posthatch broilers. Among the various relationships established by Pulikanti et al. [5], it was shown that positive correlations or interrelationships existed between internal egg temperature and percentage yolk sac weight as well as between specific eggshell water vapor conductance and percentage chick carcass weight. Conversely, in the same study, specific eggshell water vapor conductance was negatively correlated with percentage yolk sac weight. Furthermore, a negative correlation existed between mean daily percentage of incubational weight loss of embryonated eggs [MDPEWL; percentage of set egg weight (SEW)] between 10.5 and 18.5 d of incubation and relative chick BW on d 0 and 0.5 posthatch. More recently, Pulikanti et al. [6] reported that on d 48 posthatch, the relative body and breast muscle weights of broilers were positively correlated with specific eggshell water vapor conductance, and that relative BW was positively correlated with length of incubation (LI). Conversely, relative breast muscle weight was negatively correlated with internal egg temperature. Eggshell conductance and MDPEWL are highly interrelated variables, as MDPEWL is used in the calculation of conductance [7, 8]. The variable MDPEWL may also serve as an index of the functional porosity of the eggshell to oxygen, carbon dioxide, and water [9]. Hocking [10] has suggested that an increase in eggshell conductance facilitates increased oxygen consumption by the embryo, which subsequently increases embryonic metabolic rate. However, no other previous studies have examined relationships of various physiological parameters of hatching eggs, including MDPEWL, with subsequent broiler processing yield characteristics. Therefore, the current study was conducted to examine the relationships of various hatching egg physiological parameters, including MD- PEWL, with the BW, and relative weights of the carcass, abdominal fat pad, wings, breast muscle, tenders, drumsticks, and thighs of 49-d-old broilers. The selected prehatch physiological variables used in this study included MDPEWL and LI because they are noninvasive procedures that can be pragmatically assessed in commercial hatcheries and because they serve as accurate estimations of the physiological functionality of the eggshell and of the rate of embryogenesis [11 13]. General MATERIALS AND METHODS The current experimental protocol was approved by the Institutional Animal Care and Use Committee of Mississippi State University. Seven hundred twenty Ross Ross 708 (Aviagen Inc., Huntsville, AL) broiler hatching eggs

36 JAPR: Research Report were collected from a 30-wk-old breeder flock. The eggs were held under standard storage conditions for 3 d before setting. Incubation On d 0 of incubation, the eggs that weighed within ±10% of the mean weight of all eggs collected and those that were not contaminated or visibly abnormal were selected for incubation. Four hundred and eighty selected eggs were randomly labeled and weighed to record their individual SEW (g) and were then set on each of 8 replicate tray levels (60 eggs/level) of a Jamesway Model 500 single stage incubator [14]. The eggs were incubated for 18.5 d under standard commercial conditions at approximately 37.5 C dry bulb and 29.3 C wet bulb temperatures. The 480 eggs were evenly distributed among the 8 central trays to ensure an even air flow among all the eggs [5]. On d 10.5 of incubation, all eggs were weighed (g) and then candled to determine egg fertility and embryo viability. Eggs that were infertile or that contained nonviable embryos were discarded. On d 18.5 of incubation, each egg was again candled to determine embryo viability. Eggs containing viable embryos were then weighed (g), and 34 eggs per replicate level that contained live embryos were placed in individual hatching baskets and subsequently transferred to their corresponding tray levels in a Jamesway Model 500 hatcher unit [14]. The eggs in the hatcher were incubated at approximately 37.4 C dry bulb and 29.9 C wet bulb temperatures. Three precalibrated wireless data loggers in different locations were used in the setter and hatcher to more accurately monitor actual wet and dry bulb temperatures [6, 8]. Determination of Length of Incubation and Percentage Incubational Egg Weight Loss Beginning on d 18.5 of incubation, eggs were individually monitored for hatch every 12 h (0.5 d) through d 21.5 of incubation for determination of LI (d) [8]. Incubational weight loss values (g) of individual embryonated eggs between 0 and 10.5, 10.5 and 18.5, and 0 and 18.5 d of incubation were determined for the subsequent calculation of MDPEWL in each of the 3 respective time intervals. Posthatch Grow Out The hatchlings used for correlation analysis included only those that had hatched after 20.0 d of incubation (were observed as new hatches on 20.5 and 21.0 d of incubation). However, on d 21.5 of incubation (d 0 posthatch), all hatchlings were pulled from the hatcher unit for posthatch grow-out. Therefore, all hatchlings that were subsequently grown-out had remained in the hatcher for a maximum of 36 h before placement. From each tray level in the hatcher, 18 chicks were randomly selected for grow-out at a commercial density between 0 and 48 d posthatch on corresponding climate controlled floor pens (8 replicate floor pens) containing wood shavings. They were provided ad libitum feed and water and heated brooding, and were maintained under standard industry wet and dry bulb temperature settings. The birds were provided Mississippi State University basal starter, grower, and finisher broiler diets that met or exceeded NRC [15] recommendations, and were allotted according to standard industry feeding regimens. The ingredient percentages and calculated analysis of the diets were as described by Peebles et al. [16]. Processing and Data Collection For approximately 16 birds per replicate pen, live bird BW (g) was determined and was further calculated as a percentage of SEW on d 21.0 of incubation, and on d 0 and 49 posthatch. In addition, on d 49 posthatch, the sex of the birds was determined. The birds were then routinely processed; the fat pad, carcass, wings, breast muscle, tenders, drumsticks, and thighs of the birds were collected and weighed (g), and the relative weights (percentages of live bird BW) of each were determined. In addition, carcass weight as a percentage of SEW was also determined. Statistical Analysis Using the GLM procedure of SAS [17], partial correlations between the pre- and posthatch variables were generated with data for each individual egg. Only those eggs that produced chicks that were ultimately sampled at process-

Peebles et al.: INCUBATIONAL AND YIELD RELATIONSHIPS 37 ing age were used for correlation analysis. In the correlation analyses for each of the individual eggs and their corresponding hatchlings (approximately 16 samples 8 replicate units = approximately 128 total samples), the prehatch variables were SEW, 0 to 10.5 d of incubation MDPEWL, 10.5 to 18.5 d of incubation MD- PEWL, 0 to 18.5 d of incubation MDPEWL, and LI. The posthatch variables were 21.0 d of incubation BW (BWI21); BWI21 as a percentage of SEW; d 0 BW (BW0); BW0 as a percentage of SEW; d 49 BW (BW49); BW49 as a percentage of SEW; d 49 carcass weight as a percentage of SEW; d 49 carcass weight as a percentage of live bird BW (CWBW49); and d 49 fat pad, wings, breast muscle, tenders, drumsticks, and thighs weights as percentages of live bird BW. Each of the 8 tray levels and corresponding pens were considered as replicate units. The GLM procedure was used to compute the partial correlations in a model that simultaneously fit the variables to be correlated with sex and replicate tray level or floor pen as fixed effects. The MANOVA statement with the printe option produced the appropriate partial correlations. Partial correlation coefficients were considered significant at P 0.05. RESULTS AND DISCUSSION Mean embryonic mortality between 0 and 10.5 and 10.5 and 18.5 d of incubation were 1.47 and 0.701%, respectively. Only eggs containing viable embryos were transferred to the hatcher; all hatchlings used for grow-out had remained in the hatcher for a maximum of 36 h before pen placement, and only broilers that were processed were used for pre- and posthatch correlation analyses. Furthermore, only significant (P 0.05) correlations that existed between pre- and posthatch variables were reported, and when a particular variable was used in the calculation of a dependent variable, the correlation between those 2 variables was not reported (e.g., SEW and d 49 carcass weight as a percentage of SEW). Significant correlations or levels of interdependence between variables in accordance with the aforementioned criteria are provided in Table 1. Set egg weight was positively correlated with BWI21, BW0, and BW49. Conversely, 0 to 10.5, 10.5 to 18.5, and 0 to 18.5 d of incubation MDPEWL were negatively correlated with BWI21, BWI21 as a percentage of SEW, and tenders weight as a percentage of live bird BW. Further, 0 to 10.5 d of incubation MDPEWL was negatively correlated with BW0. In addition, LI was positively correlated with BWI21, BWI21 as a percentage of SEW, BW0, and BW0 as a percentage of SEW, but was negatively correlated with CWBW49. The numbers of samples, mean, and SEM for each of the significantly correlated variables are provided in Table 2. The loss of mass in eggs during incubation is primarily a function of the loss of water via transpiration through pores in the eggshell [18]. It is also known that embryonic metabolism [10] and the subsequent posthatch growth and performance of broilers [5, 6] are influenced by the rate at which water is lost through the pores of the eggshell. Nevertheless, because the diffusion rate of water through pores in the eggshell is also associated with the rates of exchange of the vital gases, oxygen and carbon dioxide [9], changes in the diffusion rates of the vital gases in conjunction with changes in the rate of water loss can, likewise, effect embryonic metabolism and the subsequent posthatch growth and performance of broilers. Hatching success is in part dependent on the RH within commercial incubators [18], and changes in incubational RH affect the rates of vital gas exchange and water loss through pores in the shells of eggs during incubation [7 9, 19]. Because modern strain commercial broilers spend a larger proportion of their lives in the egg while undergoing a more rapid developmental process, the physiological properties of the eggshell and their subsequent influence on embryogenesis are more likely to exert an ultimate influence on the processing yield of modern strain commercial broilers at slaughter age. Therefore, because MDPEWL can be altered by incubational RH, the adjustment of RH in the incubator has the potential to affect subsequent processing yield. Pinchasov [20] reported that a close correlation or association exists between the weight of eggs from commercial broiler breeder hens and hatching chick weight, but that the high correlation diminished and became insignificant by 5 d posthatch. However, broiler BW was observed by Morris et al. [21] to have a strong linear rela-

38 JAPR: Research Report Table 1. Coefficients and P-values for statistically significant (P 0.05) partial correlations (interrelationships) of prehatch variables with respective posthatch variables 1,2 Item, r (P-value) SEW 0 to 10.5 MDPEWL 10.5 to 18.5 MDPEWL 0 to 18.5 MDPEWL LI BWI21 0.90 (0.0001) 0.27 (0.004) 0.23 (0.01) 0.26 (0.006) 0.29 (0.002) BWSEWI21 0.37 (0.0001) 0.38 (0.0001) 0.38 (0.0001) 0.51 (0.0001) BW0 0.85 (0.0001) 0.19 (0.04) 0.22 (0.02) BWSEW0 0.27 (0.004) BW49 0.25 (0.007) CWBW49 0.20 (0.03) TWBW49 0.24 (0.01) 0.21 (0.03) 0.23 (0.01) 1 Approximately 16 eggs within each of 8 replicate groups and their corresponding hatchlings were used for correlations. 2 Prehatch variables of embryonated broiler hatching eggs were set egg weight (SEW; g); mean daily percentage of egg weight loss (MDPEWL) between 0 and 10.5 d of incubation (0 to 10.5 MDPEWL); 10.5 and 18.5 d of incubation (10.5 to 18.5 MDPEWL); 0 and 18.5 d of incubation (0 to 18.5 MDPEWL); and length of incubation (LI; d). The posthatch variables were BW on 21.0 d of incubation (BWI21; g); BWI21 as a percentage of SEW (BWSEWI21); BW on d 0 (BW0; g); BW0 as a percentage of SEW (BWSEW0); BW on d 49 (BW49; g); carcass weight as a percentage of live bird BW on d 49 (CWBW49); and tenders weight as a percentage of live bird BW on d 49 (TWBW49). tionship with hatching egg weight through 84 d posthatch, although the influence of egg weight on BW declined with posthatch age. Likewise, Rahn et al. [22] demonstrated mathematically that the posthatch BW of birds is positively related to the weight of the egg from which they hatch. In reports by Rahn and Ar [11] and Rahn et al. [22], a positive mathematical relationship between LI and posthatch BW has been illustrated. As would be expected upon consideration of the results of the aforementioned reports, a positive relationship has also been demonstrated to exist between SEW and LI [11]. The current data confirm these earlier established relationships. Nevertheless, the current study is unique from previous investigations in that changes in SEW, LI, and MDPEWL were associated with those of various slaughter yield variables in addition to posthatch BW. Furthermore, the responses of corresponding slaughter yield variables to MD- PEWL and LI were traced in individual Ross Ross 708 broilers that were hatched from eggs incubated under an RH (approximately 54%) that was close to optimal for hatchability [23]. The current results, that absolute and relative BW on 21 d of incubation and on 0 d posthatch were positively correlated with LI, that absolute and relative BW on 21.0 d of incubation were negatively correlated with MDPEWL throughout the setter period, and that BW0 was negatively correlated with MDPEWL during the first half of incubation, are in agreement with reports by Rahn and Ar [11] and Ar and Rahn [12], in which an inverse relationship between MDPEWL and LI has been established. A decrease in MDPEWL, as a result of an increase in RH in the incubator, is expected to increase LI in accordance with the established inverse relationship between MDPEWL and LI [7, 11, 12, 19]. However, although MDPEWL throughout the setter period was negatively correlated with tenders weight as a percentage of live bird Table 2. Number of samples (N), mean, and SEM of the significantly correlated (interrelated) prehatch and posthatch variables presented in Table 1 1 Item N Mean SEM SEW, g 126 57.1 0.27 0 to 10.5 MDPEWL, % 126 0.56 0.007 10.5 to 18.5 MDPEWL, % 126 0.51 0.007 0 to 18.5 MDPEWL, % 126 0.54 0.006 LI, d 126 20.6 0.02 BWI21, g 126 42.3 0.24 BWSEWI21, % 126 74.0 0.18 BW0, g 126 40.0 0.23 BWSEW0, % 126 70.0 0.20 BW49, g 126 3,278 43 CWBW49, % 122 70.1 0.13 TWBW49, % 125 4.35 0.039 1 Prehatch variables of embryonated broiler hatching eggs were set egg weight (SEW); mean daily percentage egg weight loss (MDPEWL) between 0 and 10.5 d of incubation (0 to 10.5 MDPEWL); 10.5 and 18.5 d of incubation (10.5 to 18.5 MDPEWL), and 0 and 18.5 d of incubation (0 to 18.5 MDPEWL); and length of incubation (LI). The posthatch variables were BW on 21.0 d of incubation (BWI21); BWI21 as a percentage of SEW (BWSEWI21); BW on d 0 (BW0); BW0 as a percentage of SEW (BWSEW0); BW on d 49 (BW49); carcass weight as a percentage of live bird BW on d 49 (CWBW49); and tenders weight as a percentage of live bird BW on d 49 (TWBW49).

Peebles et al.: INCUBATIONAL AND YIELD RELATIONSHIPS 39 BW on d 49, LI was negatively correlated with CWBW49. The negative correlation that LI had with CWBW49 was, therefore, not expected, but does suggest that a shorter LI may be favorable to a specific increase in carcass yield on d 49. Nevertheless, based on these results, we suggest that LI and MDPEWL (particularly during the first half of incubation), influence hatchling BW and may have subsequent finite effects on slaughter yield in modern strain broilers. Adjustments in incubator RH should be considered as potential means by which to control hatchling BW and possibly influence processing yield in Ross Ross 708 broilers through d 49 posthatch. Because the total life span of the modern commercial broiler has been substantially shortened, broiler development during the embryonic period has become particularly important. A slight increase in LI may positively influence hatchling BW with limited effects on subsequent processing yield in modern strain broilers. A fine change in incubator RH may further benefit embryogenesis by modulating the embryo s rate of metabolism. However, the actual physiological bases for these relationships can only be speculated upon at present, as the eggshell diffusion rates of the vital gases (i.e., oxygen and carbon dioxide) as well as that of water can be affected by the incubational environment. It is suggested that further research be conducted to delineate the relative influences of alterations in water loss and vital gas exchange, in response to changes in incubator RH, on embryonic metabolism. CONCLUSIONS AND APPLICATIONS 1. The MDPEWL of modern strain broiler hatching eggs should be closely monitored, particularly during the first half of incubation, for the regulation of LI and hatchling BW, and for their potential effects on processing yield characteristics. 2. Small incremental decreases in MD- PEWL between 10.5 and 18.5 d of incubation should be tested as a means by which to promote an increase in broiler BW on 21.0 d of incubation. Similar changes in MDPEWL between 0 and 10.5 d of incubation might also be used to promote an increase in bird BW and to possibly affect various processing yield characteristics through d 49 posthatch. 3. Because MDPEWL can be altered by adjusting RH in the incubator, desired decreases in MDPEWL (as suggested in the previous statement) may be achieved through fine incremental increases in incubator RH. This can subsequently influence embryonic metabolism by altering water loss and vital gas exchange across the eggshell. REFERENCES AND NOTES 1. Bamelis, F., B. Kemps, K. Mertens, B. De Ketelaere, E. Decuypere, and J. DeBaerdemaeker. 2005. An automatic monitoring of the hatching process based on the noise of the hatching chicks. Poult. Sci. 84:1101 1107. 2. Peebles, E. D., R. W. Keirs, L. W. Bennett, T. S. Cummings, S. K. Whitmarsh, and P. D. Gerard. 2005. Relationships among prehatch and posthatch physiological parameters in early nutrient restricted broilers hatched from eggs laid by young breeder hens. Poult. Sci. 84:454 461. 3. Piestun, Y., O. Halevy, D. Shinder, M. Ruzal, S. Druyan, and S. Yahav. 2011. Thermal manipulations during broiler embryogenesis improve post hatch performance under hot conditions. Therm. Biol. 36:469 474. 4. Piestun, Y., S. Druyan, J. Brake, and S. Yahav. 2013. Thermal manipulations during broiler incubation alter performance of broilers at 70 days of age. Poult. Sci. 92:1155 1163. 5. Pulikanti, R., E. D. Peebles, W. Zhai, L. W. Bennett, and P. D. Gerard. 2012. Physiological relationships of the early post-hatch performance of broilers to their embryo and eggshell characteristics. Poult. Sci. 91:1552 1557. 6. Pulikanti, R., E. D. Peebles, L. W. Bennett, W. Zhai, and P. D. Gerard. 2013. Physiological relationships of the middle and late post-hatch performance of broilers to their embryo and eggshell characteristics. J. Poult. Sci. 50:375 380. 7. Ar, A., C. V. Paganelli, R. B. Reeves, D. G. Greene, and H. Rahn. 1974. The avian egg: Water vapor conductance, shell thickness, and functional pore area. Condor 76:153 158. 8. Pulikanti, R., E. D. Peebles, and P. D. Gerard. 2011. Use of implantable temperature transponders for the determination of air cell temperature, eggshell water vapor conductance, and their functional relationships in embryonated broiler hatching eggs. Poult. Sci. 90:1191 1196. 9. Deeming, D. C. 2002. Functional characteristics of eggs. Pages 28 42 in Avian Incubation-Behaviour, Environment, and Evolution, D. C. Deeming, ed. Oxford University Press, New York, NY. 10. Hocking, P. M., ed. 2009. Biology of Breeding Poultry, Poultry Science Symposium Series. Vol. 29. CABI, Wallingford, UK. 11. Rahn, H., and A. Ar. 1974. The avian egg: Incubation time and water loss. Condor 76:147 152. 12. Ar, A., and H. Rahn. 1978. Interdependence of gas conductance, incubational length, and weight of the avian

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