INCREASING OF STORAGE PERIOD ALTERS EMBRYO DEVELOPMENT AND HATCHING CHARACTERISTICS OF PEKIN DUCK EGGS

This research was performed to determine the effects of storage period on embryo development and hatching characteristics in Pekin ducks. A total of 360 Pekin duck eggs was divided into four groups as 5-7 d, 8-10 d, 11-13 d and 14-16 d storage period and each group were stored at 15-18 oC. Eggs were incubated at 37,5°C and a relative humidity of 55 to 60% during the first 24 days of incubation. These eggs were transferred into hatching machine for the last four days. A hatcher temperature of 37.0°C and a relative humidity of 72% were provided during hatching period. The effects of storage period on embryo development, embryonic mortality, hatchability of fertile eggs, hatchability of total eggs and chick hatching weight were significant (P<0.01). Results showed that a longer storage period caused a decline in yolk absorption and therefore decline of embryo growth parameters including body weight and length during incubation period. Hatchability declined with increasing of storage duration, and a storage period less than 7 d appeared to be the best for maximum hatchability. Egg weight loss increased with increased storage length (P<0.01), and the chick weight tended to decline in relation with storage period longer than 5-7 days.


INTRODUCTION
Recently, meat-type duck production, which has a huge economical value in Asian countries, has gained increasingly importance in other countries as an alternative poultry species for animal protein requirement. Due to the rapid growth in the world population, there is a growing trend in meat-type duck production (Ipek and Sözcü, 2017).
At that point, white Pekin duck is one of the most popular meat-type duck strains and is widely produced in most countries, for example China, Korea, England, and France (Heo et al., 2015;Wen et al., 2015).
In commercial practices, hatching eggs are stored for short or long time until the setting time to obtain sufficient number for maximum capacity of incubator. It is known that prolonged of storage period has detrimental effects for embryo growth, embryonic mortalities, hatchability and in fact chick quality at hatching (Tona et al., 2003(Tona et al., , 2004Reijrink et al., 2009).
This research was performed to determine the effects of four storage periods (5-7 d, 8-10 d, 11-13 d and 14-16 d) on embryo development and hatching characteristics in Pekin ducks.

MATERIAL AND METHODS
The research was performed at the Research and Experimental Farm of the Department of Animal Science in Uludağ University in Turkey. A total of 360 hatching eggs were collected from a breeder flock at 36 to 38 wk of age. The breeder flock was kept according to the standard industry practices in the experimental farm of the faculty. All eggs were numbered and weighted with ± 0.1g precision before storage period. The eggs were stored for 5-7 d (S-I), 8-10 d (S-II), 11-13 d (S-III) and 14-16 d (S-IV, n=90 eggs/storage period). During storage period, eggs were kept at a temperature of 17.0°C and a relative humidity of 75%.
After the storage period, all eggs were weighted again and incubated in a fully automated, ventilated, programmable incubator at 37.5ºC and a RH of 55 to 60% during the first 24 d of incubation. The eggs from each storage period group were randomly placed into incubator trays consisting of 30 eggs (n = 3 trays/storage period group). On d 25 of incubation, eggs were weighed to determine the weight loss during incubation, and all eggs were transferred to a hatcher. The hatcher was operated at 37.0ºC and 72% relative humidity.
A total of 10 eggs per each group were randomly sampled for measurement of embryo development on d 25 of incubation. The eggs were carefully cracked, and embryos were killed by cervical dislocation. The embryos were separated from the yolk sac. Excessive embryonic fluid was dried off, and the embryos were weighed for embryo weight and yolk sac weight to calculate the yolk free body weight, relative embryo and yolk sac weights (Willemsen et al., 2010;Ipek et al., 2014). The embryo length was measured from the tip of the beak to the tip of the middle toe by placing the embryo face down on a flat surface and straightening the right leg (Hill, 2001;Nangsuay et al., 2011). The shank length was measured from right knee joint to the tip of the middle toe (Willemsen et al., 2008).
After the completing of hatching process, all of the hatched chicks were pulled out according to standard hatchery procedures, and were weighed with ±0.1 precision to determine the chick hatching weight. Then, the chicks were classified into two categories as saleable and cull chicks. The percentages of saleable and cull chick were determined as a percentage of fertile eggs. Unhatched eggs were opened to macroscopically determine fertility and embryonic mortality (early-term, mid-term and late-term embryonic mortalities).
Mortality and fertility were calculated as the percentage of total eggs at set to fertile eggs.
The data were subjected to analysis of variance (SAS, 1998) utilizing ANOVA procedures for balanced data. The parameters were analyzed using the general linear model (GLM) procedure. In the study, 3 replicate trays (30 eggs per tray) were used for each treatment group, and the trays were considered an experimental unit. Analyses for the percentage data were conducted after square root of the arc sine transformation of the data. Significant differences among treatment means were determined by Duncan's multiple range test. Data are presented as means ± SE. Differences were considered significant at P < 0.05.

RESULTS AND DISCUSSION
The effects of different storage periods on embryo development and yolk absorption on day 25 of incubation period are presented in Table 1. Embryos in S-I and S-II groups were found to be heavier compared to embryos in S-III and S-IV groups (36.1 g and 35.4 g vs. 33.2 g and 31.2 g, respectively). Similar difference was also observed for relative embryo weight. A higher yolk sac weight and relative yolk sac weight (respectively 18.7 g and 23.9%) were found in embryos of S-IV group. On the other hand, yolk free body weight, embryo body and shank length were found to be higher in S-I and S-II groups compared to other groups. Results showed that prolonged storage periods retarded embryo growth during incubation.
This could be related with some changes in the embryo growth and egg characteristics during storage period (Lapão et al., 1999), for example an increment in albumen pH (Lapão et al., 1999), a decline in albumen height (Burley and Vadehra, 1989), and strength of the vitelline membrane (Fromm, 1966). Also a retarded of embryo growth could be associated with a higher egg weight loss during storage in S-IV group, compared to the other groups. This finding is supported by Reijrink et al. (2010).   Table 2. Initial egg weight was 77.4 g in S-I, 78.1 g in S-II, 78.0 g in S-III, 77.9 g in S-IV group. Egg weight loss until transfer was found to be the highest with a value 18.4% in S-IV group compared to other groups. Hatchability of fertile and total eggs was higher in S-I (84.8% and 74.4%, respectively) and S-II (83.1% and 71.1%, respectively) groups.
The highest percentages for early and late term embryonic mortalities were observed in S-IV group, whereas mid-term embryonic mortalities were higher in S-III and S-IV groups. The percentage of cull chick was the lowest with a value of 1.4% in S-I group. On the other hand, chick hatching weight and relative chick weight were the highest in S-I (48.4 g and 62.5%) and S-II (47.7 g and 61.2%) groups. Observed higher egg weight loss and embryonic mortalities and a decline in hatchability in prolonged storage period (S-III and S-IV) are consist with previous findings by Wilson (1991), Renema et al. (2006), Reijrink et al. (2010).
Similarly, the negative effects of prolonged storage in S-III and S-IV on chick quality parameters are also reported by Tona et al. (2003) for chick weight and chick quality parameters, by Wolanski et al. (2004), Lourens et al. (2005) for yolk-free body weight, and by Hill (2001), Wolanski et al. (2004), Molenaar et al. (2008) for body length.

CONCLUSIONS
In conclusion, it seems to the storage length had negative effects for egg weight loss, embryo development, embryonic mortalities, hatchability and chick quality in Pekin duck eggs.
Therefore, during storage period, some environmental factor associated with storage (storage temperature and humidity) and storage length could be considered to minimise the negative effects of storage.