The Importance of Timely Removal from the Incubator of Hatched Poults from Three Commercial Strains 1

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1 The Importance of ly Removal from the Incubator of Hatched Poults from Three Commercial s 1 V. L. CHRISTENSEN and W. E. DONALDSON Department of Poultry Science, North Carolina State University, Raleigh, North Carolina ABSTRACT Egg size and functional qualities differ among strains of commercial turkeys. Thus, energy budgets of egg contents and eggshell conductance constants may represent different strategies for hatching and more energy may be expended by some strains than others. The objective of the present study was to determine the effects on poult quality of holding hatchling poults in the incubator for 12 or 24 h posthatching. Eggs from three strains of commercial turkey breeder hens were obtained from a commercial turkey breeding company, numbered, randomly distributed, and set in incubators. The time ing of each egg was observed at 4-h intervals and a random sample lings emerging from the shell at and h of incubation was compared with poults kept in the incubator until 672 h of incubation. Holding poults in incubators 12 or 24 h posthatching reduced (P <.05) total body weight of all strains examined but increased (P <.05) relative heart and liver weights. Holding time interacted (P <,.05) with strain of turkey to increase blood plasma glucose and decrease heart glycogen. Holding decreased (P <.001) liver glycogen precipitously in all three strains. It was concluded that holding poults in incubators 12 or 24 h posthatching has detrimental effects on carbohydrate metabolism and some strains of turkeys respond to the holding time better than others. Therefore, poult quality of commercial turkey strains may be affected differently by keeping them in the incubator posthatching. (Key words: hatchling poults, carbohydrate, incubation time, incubator holding, poult quality) INTRODUCTION Glycogen accumulates during embryonic development of avian species to serve as an energy source during the hypoxia of pipping and hatching (Freeman, 1965). Genetic selection has resulted in differences in the energy budget (the use of energy from yolk and albumen) of incubating eggs and carbohydrate availability at the end of embryonic development (Christensen et ah, 1991). s Received for publication March 23, Accepted for publication June 18, lr The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service, nor criticism of similar ones not mentioned Poultry Science 71: selected for rapid growth may rely more on carbohydrate for energy to pip and emerge from the shell than other strains because they are in eggs with reduced conductance constants and oxygen availability is limited. Evidence presented in the prior study suggested that hepatic glycogen concentrations were less in turkey embryos and gluconeogenesis was used to a greater extent by hatching embryos from some strains than by others. Following depletion of stored glycogen, gluconeogenic amino acids from muscle or other tissue sources would be used to provide for continued carbohydrate metabolism. The possibility exists that increased gluconeogenesis may be detrimental to the well-being and quality ling poults because other tissues would be catabolized

2 1824 CHRISTENSEN AND DONALDSON to provide a pool of carbohydrate for energy. The objective of the present study was to test the hypothesis that timely removal ling poults of three commercial strains from incubators may be critical for optimal poult quality. Poult quality was assessed by measuring body and organ weights and aspects of carbohydrate metabolism at the time of poult removal from the incubator. MATERIALS AND METHODS Fertile turkey eggs were obtained from a commercial turkey breeding company. An equal number of eggs (65 from each strain) was obtained from each of three commercial strains, British United Turkeys, 2, 3 and. 4 Care was taken to insure the eggs were of approximately the same size. Because each strain produces eggs of different weights, the eggs were of necessity laid by hens of different ages. The British United hens were in their 12th wk of lay; the hens were in the 6th wk of lay; and the hens were in the 22nd wk of lay. All eggs were identified by a number and weighed at setting to the nearest.01 g. Following numbering and weighing, the eggs from the three strains were placed randomly on incubator trays, the trays were set in the incubators, and the incubation cabinet was operated using the manufacturer's 5 recommended temperatures. All eggs were weighed again at transfer to determine the eggshell conductance (Tullett, 1981). The eggs were transferred by strain to pedigree baskets and the baskets were placed randomly into the hatcher cabinet. Beginning at 640 h of incubation, the hatching time of each poult was observed and recorded at 4-h intervals until the completion of the 28-day incubation period (672 h). When a minimum of 10 2 British United Turkeys, Lewisburg, WV Turkeys, Inc., Kitchener, ON, N2B 3E9, Canada. 4 Turkey Breeding Farms, Sonoma, CA s Model 252B, Jamesway, Ft. Atkinson, WI Fisher Scientific Co., Raleigh, NC poults were hatched from each strain, half of the poults were sampled for growth, relative organ size, and carbohydrate metabolism. Each poult was quickly decapitated using surgical scissors and a sample of approximately 1 ml of trunk blood was collected into a tube containing 10 mg of EDTA. 6 The poult was weighed to the nearest.01 g and the heart and liver were dissected and weighed to the nearest.01 mg. After weighing, the heart and liver were placed in 1 ml of cold 7% perchloric acid and subsequently assayed for glycogen content (Dreiling et al., 1987). The blood sample was centrifuged (700 x g for 10 min at 4 C) and the plasma was decanted and frozen (-22 C) until it was assayed for plasma glucose concentration using the technique described by Donaldson and Christensen (1991). The hatched poults that were not sampled were identified by wing-bands and replaced in the pedigree basket until the completion of 672 h of incubation. After 672 h of incubation, all of the remaining poults were killed for organ and blood sample collection. The data were arranged for a statistical analysis as a 3 x 2 x 2 factorial arrangement of treatments. The main effects were three levels of strain (British United,, and ), two levels of time ( and h of incubation), and two levels of sampling (either sampled or kept 24- and 12-h posthatch in the incubator). Main effects and interaction means determined to differ significantly were separated by least significant difference means procedure (SAS Institute, 1989). Statistical significance was based on P <.05 unless otherwise noted. All percentage data were transformed using arc sine transformation prior to analysis. RESULTS Egg weights differed significantly among the three strains of turkeys examined (Table 1). Although the hens were older and their egg size was maximal, the weight of eggs was significantly lower than that of British United or eggs. Eggshell conductance was similarly reduced in hens compared with that of British United

3 POULT QUALITY 1825 TABLE 1. Egg weights and eggshell functional properties of eggs from three strains of turkeys British United 1 n c±SEM Egg weight (g) 91.1A 88.5 B 91.7A 90.3 ± 5.5 Conductance A 16.4 B 17.4 AB 17.2 ± 2.7 A-BColumnar means with no common superscripts differ significantly (P.01). Milligrams of water per day per millimeter of mercury. Conductance per gram. eggs. However, eggshell conductance constants (eggshell conductance adjusted for the weight of eggs) were not different among the strains. Weight of the hatchlings differed by strain, time ing, and sampling but there were no significant interactions observed (Table 2). Poults from the or British United strains were heavier than those of the strain. Heavier poults hatched later, and holding poults in the incubator until 28 days of incubation reduced their body weights. Because of differences seen in body weights, organ weights are given on an absolute basis and a basis relative to body weights (Tables 3 and 4). No significant differences were Conductance constant ±.8 observed among heart weights on an absolute basis. Heart weights relative to body weights were lowest in British United poults and greatest in poults. poult relative heart weights were intermediate and did not differ from those of the other strains. Relative heart weights declined at h of incubation compared with h of incubation and relative heart weights were greater when poults were kept in the incubator after hatching. Liver weights declined on a relative basis but not an absolute basis in poults hatching later and holding poults in the hatcher cabinet increased their liver weight compared with those removed at hatching on both absolute and relative bases. TABLE 2. Body weights ling poults from three strains of turkeys sampled at hatching or held in the hatcher until 28 days of incubation of sampling 1 British United * 60.1* 3c = 63.4*; Kept 12 or 24 h i = 60.3* -(g) * 60.5 b 62.9* 61.8 ± 4.62 a ' b Columnar means with no common superscripts differ significantly (P.05). x ' Y Means within a row with no common superscripts differ significantly (P S.01). isampling treatments were: sampled = tissues were measured within 4 h ing; kept = poult was kept in the incubator for 12 (-h hatching time) or 24 (-h hatching time) h before sampling posthatching (672-h incubation). 2* ± SEM.

4 1826 CHRISTENSEN AND DONALDSON TABLE 3. Heart weights ling poults from three strains of turkeys held in the hatcher until 28 days of incubation sampled at hatching or of sampling 1 British United c b 5c Pooled 3c Absolute weight (g) ± ; Kept 12 or 24 h =.365 Relative weight (g/100 g body weight) " b a.58 ab.58 ± Y ; Kept 12 or 24 h =.6QX a ' b Columnar or row means with no common superscripts differ significantly (P.05). X-^Tvleans within a row with no common superscripts differ significantly (P.01). 1 Sampling treatments were: sampled = tissues were measured within 4 h ing; kept = poult was kept in the incubator for 12 (-h hatching time) or 24 (-h hatching time) h before sampling posthatching at 672-h of incubation. 2 5c ± SEM. Blood glucose and heart glycogen were affected significantly by the three-way interaction of strain, hatching time, and sampling time (Table 5). Among poults from the British United strain, keeping poults in the hatcher for 12 h elevated blood glucose but keeping them for 24 h did not when compared with poults subjected to timely removal. poults displayed elevated blood glucose regardless of the length of time they were kept in the incubation cabinet. The poults that hatched at h had depressed blood plasma glucose concentrations compared with those kept in the cabinet for 24 h or compared with poults hatching at h regardless of whether they were kept in the hatcher or removed at hatching. Heart glycogen per gram of heart tissue in British United and hatchling poults followed similar patterns (Table 5). Heart glycogen was not affected among poults kept in the incubator when they hatched at h, but heart glycogen was decreased by keeping them in the incubator when poults of those strains hatched at h. An entirely different pattern was seen among hatchings. When poults hatched at h, keeping them in the incubator increased heart glycogen compared with poults removed and sampled at hatching. Conversely, among poults hatching at h, heart glycogen declined when poults were kept in the incubator rather than being removed. Liver glycogen per gram of liver tissue was decreased by keeping the poults in the incubator compared with poults removed from the incubator regardless of strain or time ing. DISCUSSION Genetic selection for rapid growth in modern turkeys may have implications on maternal investment in eggs as well as embryonic carbohydrate metabolism during hatching (Christensen et al., 1991). In the present study, data suggested that the use of the maternal investment in eggs for energy for embryonic development, or the energy budget of incubating eggs (Ar et

5 POULT QUALITY 1827 TABLE 4. Livei ' weights ling poults from three strains of turkeys sampled held in the hatcher until 28 days of incubation at hatching or of British sampling } United Pooled 5? A 5! * 5c Absolute weight (g) B B ± "; Kept 12 or 24 h = A Relative weight (g/100 g body weight) A " 2.53* 3.35* 2.42 ±.242 : 2.18 B ; Kept 12 or 24 h = 2.66* A ' B Means in a row with no common superscripts differ significantly (P.01). x ' Y Columnar means with no common superscripts differ significantly (P.01). Sampling treatments were: sampled = tissues were measured within 4 h ing; kept = poult was kept in the incubator for 12 (-h hatching time) or 24 (-h hatching time) h before sampling posthatching at 672-h of incubation. 25c±SEM. ah, 1987), and the utilization of stored carbohydrate by hatchling poults from three commercial strains of turkeys differ as well. The results indicate that timely removal of poults from incubators may be critical to good poult quality. Furthermore, timely removal may also be more critical for those strains in which more carbohydrate reserves were expended during pipping and hatching. The stress of additional high incubation temperatures posthatching could compound an already critical situation. Egg weight data in the present study illustrate a problem that exists when comparing turkey breeder hens of different genetic backgrounds. Despite attempts to use eggs of equivalent weights, eggs were smaller than those of the other strains. Because the hens were in their 20th wk of lay, it was assumed that these egg weights for the strain were maximal whereas those of the other strains; especially at 6 wk of lay, were less than maximal. Thus, it may be impossible to get identical egg weights for direct comparisons. Despite the confounding effect of egg weight, eggshell conductance constants for the three strains were not significantly different. Equivalent conductance constants suggest that the ratio of the functional qualities of the eggs to their egg weights (Ar and Rahn, 1978) would allow eggs from each strain to enter the plateau stage in oxygen consumption on the same physiological basis. Thus, differences seen in egg weights or maternal age may be unimportant to the results of the present experiment. The strain by sampling time interaction was not evident for the growth of the whole embryo, of the heart, or of the liver. This result suggests that the stress of remaining in the incubator and the consequent effects on carbohydrate metabolism did not differentially alter the growth of embryos from the three strains. If one strain were using gluconeogenic amino acids for energy rather than for protein anabolism, one might hypothesize that growth would be slowed in that strain. Because no strain by sampling time inter-

6 1828 CHRISTENSEN AND DONALDSON TABLE 5. Blood glucose and glycogen content of the heart and liver of neonatal turkey poults sampled at hatching or held in incubators until 28 days of incubation of sampling 1 Pooled 3c British United c = Blood plasma glucose 2 (mg/dl) ± 63 Heart glycogen 2 (mg/g of heart] ±.67 Liver glycogen (mg/g of liver) = 3.67*; Kept 12 or h =.59 B ± A'^ampled means with no common superscripts differ significantly (P 2.01). Sampling treatments were: sampled = tissues were measured within 4 h ing; kept = poult was kept in the incubator for 12 (-h hatching time) or 24 (-h hatching time) h before sampling posthatching at 672-h of incubation. Significant three-way interaction of strains by time by time of sampling occurred (P.05).»5c ± SEM. action was seen, it can be speculated that energy resources needed for growth are depleted to the same degree by embryos and poults from all three strains. About 30 to 35% of the energy in an egg is catabolized during embryonic development (Ar et al, 1987; Vleck and Vleck, 1987). Of this portion, about 70 to 80% is spent on maintenance and the rest is used to support the biosynthetic costs of growth (Hoyt, 1987). The amount of energy that remains in the residual yolk is probably the most variable factor among species (Ar et al, 1987). Among domestic species examined, i.e., domestic chicken, goose, turkey, and duck, more energy is stored in the egg than would be predicted by allometric equations (Ar et al, 1987). The values for turkeys and ducks were low but not significantly lower than predicted. The incubation period for domestic species would then be shorter than predicted by allometric equations derived from wild avian species based on the energy content of the egg (Vleck, 1991). The observed problem in the present study would seem to be with the metabolism of the embryo itself rather than a lack of residual energy in the resorbed yolk material because turkey embryos apparently have a surplus of available energy in residual yolk. It may be that the genetic determination of gluconeogenesis has been changed by divergent selection. Differences in hepatic glucose-6-phosphatase activity, an enzyme related directly to gluconeogenesis, have been reported between the and British United strains (Christensen et al, 1991). Examination of the data for heart glycogen and blood plasma glucose indicated a

7 POULT QUALITY 1829 strain by time by holding time three-way interaction in the glycogen and blood glucose concentrations at the end of the incubation period. Such differences have been suggested by results of previous experiments with commercial strains of turkey poults (Christensen et al., 1991). Both heart growth and glycogen content have been implicated in hatchability (Christensen and Donaldson, 1992). Observed effects on blood plasma glucose concentrations may have been influenced to some extent by dehydration, but other factors also may have played a role in the elevated blood glucose because body weight was reduced by 5% by holding whereas blood glucose was elevated by 10%. The additional increase in glucose maybe as a result of both catabolic gluconeogenesis and dehydration. The British United and poults dealt with stress similarly when left in the incubator for 12 or 24 h. Interestingly, the same strains currently have the best hatchability (Warnick, 1990). poults increased cardiac glycogen when left in the incubator for 24 h but decreased heart glycogen when kept for only 12 h. The poults, but not British United or poults, also had the ability to maintain blood glucose concentrations following 12 h of additional incubation. This agrees with previous observations with posthatch holding of and British United poults (Donaldson and Christensen, 1991). Poults from all three strains utilized hepatic glycogen for energy at the same rate regardless of the length of the storage period. This suggests that the differences among the poults may be in the genetic differences in gluconeogenic capacity and its influence on hatching poults. Furthermore, the present data suggest that the poults may have a metabolism more suited to hatchling survival than the poults from the other strains when all three strains are exposed to additional incubation or prolonged holding outside the incubator posthatching. In conclusion, because some modern strains of turkeys expend large amounts of carbohydrate to emerge from the shell, timely removal of poults from the hatcher appears to be critical. Eggs from the three major strains were tested to measure the effects of timely removal from the incubator on the carbohydrate metabolism of the hatched poult. Differences in hatching and removal times resulted in excessive utilization of stored carbohydrates and affected poults from some strains more severely affected than others. The observations suggest that with some strains of turkeys, time of removal from the incubator may be more critical than it is with other strains. REFERENCES Ar, A., B. Arieli, A. Belinsky, and U. Yom-Tov, Energy in avian eggs and hatchlings: utilization and transfer. J. Exp. Zool. 235(Suppl. 1): Ar, A., and H. Rahn, Interdependence of gas conductance, incubation length, and weight of the avian egg. Pages in: Respiratory Function in Birds, Adult and Embryonic. J. Pipper, ed. Springer-Verlag, Berlin, Germany. Christensen, V. L., and W. E. Donaldson, Effect of oxygen and maternal dietary iodine on embryonic carbohydrate metabolism and hatchability of turkey eggs. Poultry Sci. 71: Christensen, V. L., W. E. Donaldson, and J. F. Ort, The effect of dietary iodine on the hatchability of eggs from two commercial strains of turkeys. Poultry Sci. 70: Donaldson, W. E., and V. L. Christensen, Dietary carbohydrate level and glucosemetabolism in turkey poults. Comp. Biochem. Physiol. 98A: Dreiling, C. E., D. E. Brown, L. Casale, and L. Kelly, Muscle glycogen: Comparison of iodine binding and enzyme digestion assays and application to meat samples. Meat Sci. 20: Freeman, B. M., The importance of glycogen at the termination of the embryonic existence of Gallus domesticus. Comp. Biochem. Physiol. 28: Hoyt, D. F., A new model of avian embryonic metabolism. J. Exp. Zool. 235(Suppl. 1): SAS Institute, A User's Guide to SAS 89. Sparks Press Inc., Cary, NC. Tullet, S. G., Theoretical and practical aspects of eggshell porosity. Turkeys 29: Vleck, C. M., Allometric scaling in avian embryonic development. Pages in: Avian Incubation. S. G. Tullet, ed. Butterworth- Heinemann, London, England. Vleck, C. M., and D. Vleck, Metabolism and energetics of avian embryos. J. Exp. Zool. 235(Suppl. 1): Warnick, R. E., strain test. Pages 1-36 in: Turkey Research Progress Report. Utah Agricultural Experiment Station and Snow Field Station, Utah State University Press, Logan, UT.