Effects of incubation temperature on growth of Siamese crocodile ...

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Oct 29, 2006 - Introduction and objectives. Siamese crocodiles, a native crocodile species in Thailand. They can be bred in captivity. The period of egg.

Proceedings of AZWMP 2006

Chulalongkorn Uni. Fac. of Vet. Sc., Bangkok, Thailand, 26-29 Oct 2006

Effects of incubation temperature on growth of Siamese crocodile embryos S. Chantakru, U.Pongchairerk, P. Pongket, N. Pormpa, V. Sujarit Faculty of Veterinary Medicine, Kasetsart University, Bangkok 10930, Thailand Keywords : incubation, temperature, embryo, Siamese crocodile However the rates of weight changes of both groups were similar (Fig.1).

Introduction and objectives Siamese crocodiles, a native crocodile species in Thailand. They can be bred in captivity. The period of egg incubation is approximately 11 weeks. The condition for Siamese crocodile egg incubation is 28-35 oC and humidity higher than 95% [1] . The purpose of this study was to determine optimal temperature for incubation and its effect on embryos.

Egg Weight Changes of Siamese crocodiles g. 0 -2

D63

D69

n=70

n=65

n=60

n=55

69

31oC 32oC

-8 -10 -12 days of incubation

Figure 1 showed the decrease in egg weights from day 35 to day 69 of incubation . The sizes of embryos of two incubating temperatures were not significantly different at every time-point (p>0.05, Table 2). Table 2 Average crown-rump lengths of Siamese crocodile embryos measured at different time points Crown-rump lengths ( mm) (mean ± SD) Temp. 31 oC 32 oC

D 35

D48

D63

D69

n=5 420± 48.47 374± 20.73

n=5 606± 42.78 640± 45.27

n=5 930± 21.21 946± 25.09

n=5 1142± 51.18 1140± 94.76

Discussion Our study showed that the temperature of 31 oC caused the differences in weight. Nonetheless the regression of weight in both groups was not different. An decrease in egg weight in each group may be due to the decrease in yolk mass despite the growth of embryo. The crown-rump lengths of embryos of both groups were not affected by incubation temperatures. Although several investigators reported the importance of the incubation temperatures on embryo growth and development especially on embryo metabolism [2, 3]. It is possible that the differences in incubation temperatures used in this study were not large enough to affect embryo growth.

Table 1 Average egg weights of Siamese crocodile embryos at different time-points Egg Weights (grams) (mean ± SD) D48

63

-6

Results The width and length of Siamese crocodiles eggs in this study were ranged from 460 mm to 520 mm, and 700 mm to 810 mm , respectively. At the beginning of the study the eggs developed visible white bands which had between 130 to 570 mm wide. The bands disappeared subsequently. At each time point, there were significantly differences in weights between two groups. The eggs incubated with 31oC had more weights than those from the 32oC incubator as shown in Table 1.

D 35

48

-4

Materials and methods Eggs were randomly collected and divided into two groups; group one from of 31oC and group two from 32oC temperatures. Eggs were examined general appearance, appearance of egg bands and egg width and length.. Each egg was weighed at days 35, 48, 63 and 69 of incubation. For each egg the weight measured at each time-point were compared and calculated for the differences. In each group five embryos per day of incubation studied were collected and measured for crown-rump length. Statistical analysis. The average weights and average crown-rump-lengths of two groups were compared using Student- test. The significant difference was designated as the p-value is less than 0.05.

Temp.

35

o

119.8 ± 117.8 ± 113.6 ± 108.0 ± 11.70* 12.47* 10.60* 7.30* 118.5 115.0 ± 112.1 ± 109.7 32 oC ±7.64 6.17 6.92 ±10.19 * There was significant difference between mean value of both groups at each time-point ( p< 0.05) 31 C

Acknowledgement We thank The Institute of Research and Development, Kasetsart University for financial support.

Average egg weights from the 31 oC group decreased approximately 3.38 grams at day 48, 6.4 grams at day 63 and 10.7 grams at day 69. Average weights of 32 oC group gradually declined as the weight at day48 decreased only 1.8 grams. At days 63 and 69 average weights of 32 o C group were 6.4 and 10.5 grams less than those at day 35.

References 1.Kaewchaum, K. et al. 2006. Breeds and crocodile farming business. (Thai) 2. Ji, Qui and Diong. 2002. J Exp Zool. 292:649-659. 3. Booth, et al. 2000. J Comp Physiol.170:269-276.

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