Incubation Temperature for Ostrich (Struthio camelus) Eggs

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1 Incubation Temperature for Ostrich (Struthio camelus) Eggs S. M. Hassan,*, A. A. Siam, M. E. Mady, and A. L. Cartwright*,1 *Poultry Science Department, Texas A&M University, College Station, Texas ; and Department of Animal Physiology, and Department of Animal Production, Suez Canal University, Ismailia, Egypt ABSTRACT The impact of incubation temperature on when compared with 36.5 C. No differences in hatchability, egg weight loss, embryonic mortality, incubation period, hatchability, and chick weight in 394 ostrich (Struthio camelus) eggs was studied. Eggs were obtained from 3 farms in Texas. Three incubation temperatures (36.5, 37.0, or 37.5 C) with relative humidity ranging from 20 to 30% were used. Results showed that incubation of fertile eggs at 36.5 C increased hatchability and incubation period in comparison with other treatments. The incidence of dead in shell and total dead embryos was increased at 37.5 C incubation period, dead-in-shell embryos, and total dead embryos were observed between eggs incubated at 37.0 or 37.5 C. Neither chick weight nor egg weight loss at 7, 14, 28, or 38 d of incubation was affected by incubation temperature, but egg weight loss at 21 d was lower for eggs incubated at 37.5 C than for the other treatments. Results show that the most effective incubation temperature for the ostrich is lower than the most effective incubation temperature for most bird species. (Key words: embryo mortality, hatchability, incubation period, incubation temperature, ostrich) 2004 Poultry Science 83: INTRODUCTION In some parts of the world increasing demand for animal protein and health concerns has renewed emphasis on accelerated production and improved efficiency of the ostrich meat supply. Low reproductive efficiency focused attention on artificial incubation. Although intensive studies with domestic poultry eggs precisely define optimum conditions for artificial incubation, no controlled studies conducting simultaneous incubation of ostrich eggs at different temperatures have been published. Hatchability of ostrich eggs incubated in different countries is highly variable (Burger and Bertram, 1981; Mellett, 1993; Deeming and Ayres, 1994; Deeming, 1995). In general, hatchability of artificially incubated ostrich eggs is less than that achieved in nests in the wild, with maximal values around 60% (Burger and Bertram, 1981). Hatchability of fertile eggs is at best approximately 70%. Early attempts to incubate ostrich eggs artificially in zoos also gave poor results (Diamond and Rozin, 1980; Ley et al., 1986). Problems regularly encountered include poor fertility, inconsistent weight loss during incubation (Ley et al., 1986; Button, 1993; Deeming, 1993; Deeming et al., 1993), and indefinite staging of embryonic development (Deeming, 1993). Presumably these results evolved from poorly understood requirements for ostrich egg incuba Poultry Science Association, Inc. Received for publication August 18, Accepted for publication October 14, To whom correspondence should be addressed: a-cartwright@ tamu.edu. tion because temperature settings similar to those for incubating chicken eggs often were used. The work of Burger and Bertram (1981), Jarvis et al. (1985), and Swart and Rahn (1988) who studied temperature conditions of naturally incubated ostrich eggs improved artificial incubation on ostrich farms. Incubation standards for ostrich eggs remain suspect because hatch failures remain elevated (Deeming, 1995). Deeming (1993) noted that no studies on the effects of incubation temperature on hatchability of ostrich eggs are available. Incubation conditions that yield high hatch rates in a variety of bird species indicate that attaining a water loss of 13 to 15% of initial egg mass by the time of complete embryo development is optimal. However, temperature and humidity relationships have never been successfully standardized to consistently yield healthy ostrich chicks as in the chicken, turkey, and duck industries and in other species (Ar, 1991). Cause and effect relationships cannot be confidently attributed when temperature and RH are not scientifically determined for standard embryo development and egg water loss. Definitive information on incubation of ostrich eggs is lacking. Ostrich egg incubation was conducted with different incubation temperatures to determine the effect of incubator temperature on hatchability, incubation period, egg weight loss, chick weight, and embryonic mortality. MATERIALS AND METHODS A total of 408 ostrich (Struthio camelus) eggs were collected from February through August during 2002 in the vicinity of College Station, Texas. Eggs were stored at 495

2 496 HASSAN ET AL. 20 C and 65 to 70% RH before transport to the Poultry Research, Teaching and Extension Center at Texas A&M University, College Station. The total egg storage period before incubator set ranged from 1 to 25 d. Each egg was marked with a unique identifier to indicate the farm of origin, sire and dam, and date of lay. Eggs were weighed (± 0.1 g) and assigned to 1 of 3 incubators 2 so that egg weight, farm of origin, sire and dam, and date of lay were distributed among egg trays designated for each incubation treatment (36.5, 37.0, or 37.5 C). Eggs were allowed to equilibrate within egg trays at 25 C for 12 h before set. Eggs were incubated in a multistage manner in ostrich egg setting racks and hatched in hatcher baskets. Incubation temperature treatments were maintained from 1 to 38 d of incubation, and temperature was decreased in all treatment groups to 36 C during the hatching period which extended from 39 to 44 d. RH ranged from 20 to 25% from set until 38 d of incubation and 25 to 30% thereafter. Eggs were turned automatically through a 90 angle every 4 h. Incubation conditions were recorded at least twice daily. Eggs were candled and weighed weekly after the start of incubation and at 38 d to observe fertility and embryo viability and to determine weight loss. Eggs that showed discernible signs of contamination before 7 d were removed to prevent contamination of other eggs. A total of 394 eggs remained for analysis in the study. Infertile eggs were removed at 21 d and opened to confirm absence of embryonic development. On d 38 of incubation eggs were candled and transferred into hatcher baskets. At regular intervals during the hatching period eggs were observed to detect external pipping time, and actual hatch time was recorded. During the hatching period, hatching occurred with as little interference as possible. Eggshells of chicks were equatorially cracked to facilitate hatching when no progress toward hatch was observed for 12 h after external pipping. Eggs were candled at 41 d to assess stage of development. Eggs that failed to hatch were opened to determine the cause of hatch failure after 44 d. Hatch failures were classed as infertile, early dead, late dead, or dead in shell. Embryo age was estimated using a table of development for the domestic fowl (Tolhurst, 1974) adjusted proportionally for the incubation periods of the different species (42 and 21 d). An equivalent stage of development in the ostrich was assumed to be twice that of the domestic fowl. Chicks were weighed after hatch and the incubation period was recorded. Statistical Analysis One-way ANOVA was used to determine the effect of incubation temperature on incubation period, and egg and chick weights. All proportional data were transformed to arcsine square root before analysis. When significant treatment effects were noted, differences among treatments were separated by Duncan s new multiple 2 Models M1N1 and NOM-45, NatureForm Hatchery Systems, Jacksonville, FL. range test (Duncan, 1955). Threshold for significance was P RESULTS AND DISCUSSION Egg Characteristics and Weight Loss No differences in initial egg weight, egg storage period, or fertility were observed among incubation temperature treatments because the 394 eggs available for analysis were distributed among treatments by length of storage, egg weight, source of egg, and sire and dam (Table 1). Treatment effects on weight loss of incubated eggs were not detected at 7, 14, 28, or 38 d of incubation (Table 1), but egg weight loss for eggs incubated at 37.5 C was lower at 21 d than for other treatments. Weight losses by 38 d ranged from 12 to 13%. A review of case studies of ostrich egg incubation at various temperatures and humidities reported egg weight losses ranging from 11.4 to 19.6% (Deeming 1993), and others reported egg weight losses ranging from to 12.52% at 35 d of incubation (Wilson and Eldred, 1997) to 15.5% (More, 1996). Wilson and Eldred (1995) found that egg weight loss at 38 d is 13.2% for hatched ostrich eggs, and Stewart (1996) reported that weight loss for ostrich eggs from set to internal pipping is 12 to 15% of initial weight. Incubation of ostrich eggs by Deeming et al. (1993) under conditions similar to those of the present study yielded egg weight losses averaging ± 2.47%. Ar (1991) noted that the ambient humidity around the egg can control the rate of water loss during storage and incubation. Christensen et al. (1996) stated that the optimal incubator humidity for ostrich eggs must be less than 25% RH so that a 15% loss of initial egg mass occurs during a 45-d incubation period. In the present study, incubator temperature and humidity settings yielded egg weight loss of ostrich eggs within a range generally accepted as optimal for egg incubation in most bird species. Incubation Performance Neither chick weight nor chick weight expressed as a percentage of initial egg weight was different among treatments (Table 1). These results agree with those of Wilson and Eldred (1995) who reported that chick weight as a percentage of initial egg weight averaged 63.6% and ranged from 56 to 69%. Hatchability of fertile eggs was higher for eggs incubated at 36.5 C as compared with eggs incubated at 37.0 and 37.5 C (Table 1). However, no hatchability improvement was observed as the temperature was decreased from 37.5 to 37.0 C. These results agree with those of Lundy (1969) who found that incubation temperature influences hatchability in chicken eggs, and Romanoff (1936) and Barott (1937) who noted that hatchability of chicken eggs declines when incubation temperatures are increased from 35 to 40 C. Apparently, hatchability would improve if embryo temperature rather than incubator temperature remained constant (Lundy, 1969). Ideally, incubation temperature should regress, de-

3 INCUBATION TEMPERATURE FOR OSTRICH EGGS 497 TABLE 1. Means ± SEM of measures of fertility, initial egg weight, storage period, incubation performance, and embryonic mortality in ostrich eggs incubated at 36.5, 37.0, or 37.5 C Incubation temperature ( C) Variable Egg characteristics 1 Egg number Contaminated eggs Eggs incubated Initial egg weight (g) 1, ± , ± , ± Storage period (d) 7.92 ± ± ± 0.38 Fertility 2 (%) ± ± ± 4.98 Egg weight loss 3 (%) 7 d 2.38 ± ± ± d 5.11 ± ± ± d 7.11 ± 0.16 a 7.38 ± 0.17 a 6.24 ± 0.34 b 28 d 9.02 ± ± ± d ± ± ± 0.36 Incubation performance Chick weight (g) ± ± ± Chick weight 3 (%) ± ± ± 0.96 Hatchability 3 (%) ± 6.00 a ± b ± 9.15 b Incubation period (h) ± 2.66 a ± 7.49 b ± 7.62 b Embryonic mortality 2 Early dead (%) ± ± ± 4.81 Late dead (%) 1.82 ± ± ± 3.81 Dead in shell (%) 9.68 ± 4.20 b ± ab ± a Total dead (%) ± 6.22 b ± ab ± 9.15 a ab Means within a row that do not share a common superscript are significantly different (P 0.05). 1 Eggs judged microbiologically contaminated were removed from the study and were not included in the number of eggs incubated. Eggs incubated are the eggs that were statistically analyzed. 2 Percentages of fertile eggs set. 3 Values are expressed as a percentage of egg weight at the beginning of incubation. creasing slightly as the embryo develops (Deeming, 1993). Incubation of ostrich eggs requires a low incubation temperature and RH relative to other poultry species (Deeming, 1993). Higher incubation temperatures require lower RH to maintain hatchability. Ostrich eggs can be successfully incubated from 35.0 to 36.9 C, but most producers maintain incubator temperatures between 36.0 and 36.4 C (Stewart, 1996). Results from a South African trial showed that increasing incubation temperature from 36.0 to 37.2 C reduced hatchability from 73 to 44% (Stewart, 1996), which is similar to the results observed in the present study. Single-stage incubators where eggs are the same age would be advantageous on commercial ostrich farms. However, this situation is not yet practical because the scale of ostrich production is inadequate to supply eggs in numbers sufficient to support an optimal single-stage incubation. The incubation period decreased as incubation temperature increased from 36.5 to 37.0 and 37.5 C (Table 1). In chickens, Romanoff (1936) and Barott (1937) noted that incubation temperatures below optimum levels lengthen the incubation period, whereas temperatures higher than optimum reduce the incubation period. In a study with ostrich eggs, where eggs were not incubated concurrently at different temperatures, Stewart (1996) noted that increasing incubation temperature from 35.0 to 36.7 C appeared to decrease the incubation period from 45 to 42 d. Researchers suggest that the incubation period in the ostrich is reduced by 2.5 d when incubation temperature is increased by 1 C (Jarvis et al., 1985; Deeming et al., 1993), but the scientific literature is devoid of reports investigating the effects of different incubation temperatures on incubation period using the same lot of ostrich eggs. Although Cramp et al. (1977) state that the normal incubation period for the ostrich is 42 d, the optimal incubation temperature, RH, and incubation period have not been scientifically established. Factors other than temperature affect incubation period. In the present study, efforts were taken to prevent these effects within the experiment. Length of storage, egg weight, source of egg, and sire and dam were equally distributed among treatments. Prolonged storage can lengthen the incubation period. In the ostrich Deeming et al. (1993) observed extended incubation periods for larger eggs. Considerable variation in incubation period is observed within a clutch incubated by the hen (Sauer and Sauer, 1966) or within a batch incubated at the same temperature (Button, 1992). Ostrich eggs incubated artificially at 35 C take 43 to 47 d to hatch (Hoyt et al., 1978; Jarvis et al., 1985; Meir and Ar, 1990). Unfortunately, the correct incubation temperature for maximal hatchability at 42 d of incubation for the ostrich is not defined. An incubation temperature within the range of 36.0 to 36.4 C appears to produce the generally accepted 42 d optimal length of incubation for the ostrich. However, this optimum incubation period and temperature has not been confirmed by exhaustive scientific study. Higher incubation temperatures increase the metabolic rate and the

4 498 HASSAN ET AL. amount of metabolic water produced by the embryo (Deeming, 1993). Therefore, the incubation period is reduced at high temperatures and lengthened at lower temperatures. Embryonic Mortality Reducing incubation temperature to 36.5 C from 37.0 and 37.5 C had no effect on early or late dead embryonic mortality (Table 1). However, reducing temperature from 37.5 to 36.5 C decreased dead-in-shell and total dead embryonic mortality. All measures of embryonic mortality were not different between 36.5 and 37.0 C and between 37.0 and 37.5 C. Avian embryonic mortality peaks during the first and last few days of incubation with few losses occurring during the middle period of incubation (Romanoff, 1972). The bulk of mortality takes place in the last few days of incubation. This pattern occurs in all species of domestic poultry and game birds (Insko and Martin, 1933; Landauer, 1967; Romanoff, 1972) and in the ostrich (Deeming, 1993; Deeming et al., 1993; Brake et al., 1994; Button et al., 1994; Deeming, 1995; Brown et al., 1996). Mortality data from Table 1 reiterated this mortality distribution in the 36.5 C treatment. In contrast, the bulk of hatch failure in 37.0 and 37.5 C treatments occurred in the end stage of embryo mortality suggesting that these temperatures severely stress developing embryos. The temperature at the end of incubation of ostrich eggs was 2.0 C higher than the surrounding air temperature, and evidence suggests that overheating is problematic in hatchers (Meir and Ar, 1990). Some dead-in-shell ostrich embryos possibly die of hyperthermia when incubated at 37.0 and 37.5 C. Mortality in the present study occurred predominantly at the beginning and the end of incubation, and the dead-in-shell level for 37.5 C was elevated above that for 36.5 C. SUMMARY This study showed that incubation of ostrich eggs at 36.5, 37.0 and 37.5 C resulted in egg weight losses and relative chick weights within levels recommended for most species. Hatchability and embryonic mortality were affected by incubation temperature. The optimal incubation temperature for ostrich eggs appears to be less than 37.0 C because hatchability improved below that incubator setting. Incubation period lengthened below 37 C. Dead-in-shell embryos and total dead embryos declined below 37.5 C. Little information is available on the interrelationships among incubation temperature, RH, eggshell quality, incubation period, hatchability, embryonic mortality, and egg weight loss in the ostrich. Further research is required to define optimal incubation temperature and RH for the ostrich. 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