EFFECT OF RELATIVE HUMIDITY ON THE HATCHABILITY OF EMU (DROMAIUS NOVAEHOLLANDIAE) EGGS

Danuta Szczerbińska, Zofia Tarasewicz, Danuta Majewska, Alicja Dańczak, Marek Ligocki, Krystyna Romaniszyn

ABSTRACT

Little information on emu incubation techniques has been published so far both in the Polish and foreign literature; hence this study, which is aimed to investigate effects of various levels of incubation relative humidity on the hatchability of emu eggs. Three levels of relative humidity (RH), 20, 25, and 30%, were applied to groups I, II, and III, respectively. The temperature 36.4°C was maintained constant in all the groups during the incubation. The poorest results were recorded in the group III with 30% relative humidity. Keeping lower humidity in the groups I and II resulted in improved hatchability, especially due to reduced percentage of crippled and weak chicks. It was found that humidity significantly influenced egg weight loss during incubation; lower relative humidity resulted in increased egg weight loss. Humidity also significantly influenced the body weight of the chicks. In the group with the lowest humidity, the ratio of the chick body weight to the initial egg weight w

Key words: egg, emu, hatchability, humidity, incubation..

INTRODUCTION

The subclass Paleognathae represents a very old avian group, which includes the African ostrich, South American rhea, Australian and New Guinean cassowary, Australian emu, and the small kiwi of New Zealand. In Poland, since about the mid-1990s, much interest has grown in the farming of some species belonging to this group of birds, particularly ostriches and, to a lower extent, emus and rheas. At present, several hundred farms of ratite species operate in Poland, most of which are ostrich farms [4]. The importance of emu and rhea seem underestimated, although these birds are by many features very suitable for semi-intensive management on both small and large farms, as well as on agritourism farms [16].

One of the main reasons that impede the development of emu farming is the fact that hatchability of the species is poorer compared to other poultry species. This is also due to the fact that an incubation technique for the emu has not been fully developed and it is difficult to tell which incubation parameters, particularly those of thermal and humidity regime, presented by many authors, should be applied.

Minnaar and Minnaar [9] reported that the best hatching performance can be achieved if carried out under 24 to 35% of relative humidity. According to Stewart [14], on the other hand, humidity may reach as much as 40%. Majewska [6] achieved 70 to 83% hatchability from fertilised eggs at the 35% humidity maintained over the entire period of incubation. According to Brake and Rosseland [1] the optimum temperature for emus is about 36.0°C with about 33% relative humidity in high-air-flow incubators. Szczerbińska [15] carried out emu eggs incubation at 36.4°C and humidity 30% and achieved between 54% and 72% hatchability from fertilised eggs. This performance should be considered good if compared with that reported by Kinder [5], who obtained 36.6% hatchability. The literature, however, lacks comparative studies in which differentiated level of relative humidity applied during emu eggs incubation would be tested.

It seems reasonable, therefore, to undertake an experiment in order to determine the effect of various levels of humidity during incubation on hatchability performance in the emu.

MATERIALS AND METHODS

The eggs for the experiment were collected from 6-year-old emus kept on a private farm in the West Pomeranian Province of Poland. The flock of 20 emus was managed in the semi-intensive system. During the mating season, the birds were housed in a shed divided into fixed compartments with exits to the yard, also divided into compartments, each used by a pair of birds. The birds were fed on standard complete feeds ad libitum. The nutritional value of the feeds, both before and during the laying season, reflected the nutritional requirements of the species [8, 9, 11,12].

The eggs were collected daily, graded for size, weighed, and labelled for identification; the date of laying was recorded too. The eggs selected for incubation were of similar size and shape, were properly coloured, and had the shell intact. Due to low intensity of laying, the eggs were collected for two weeks, stored at 16°C and 70% humidity, and rotated by 180° once a day. Before placing in the incubator, the eggs were disinfected with formalin vapour for 30 minutes at 24°C. The incubation was carried out in cabinet incubators with separate setters and hatchers.

The hatchability was evaluated using eggs collected between February and April, which were divided into three groups in relation to humidity:

Group I – 20% (n = 76)
Group II – 25% (n = 53, lower number due to the incubator capacity)
Group III – 30% (n = 77)

According to the results of our previous incubation experiment, the temperature in both setting and hatching chambers was constant, 36.4°C [17]. Every week of the incubation, the eggs were weighed, to determine the weight loss, and candled, using a device with a night vision camera. The eggs were transferred to the hatcher on 48 day of incubation. The time of hatching was monitored (see film) and if it exceeded 24 hours, the chicks were assisted in leaving the shells. Body weight of one-day-old chicks was recorded in order to estimate its proportion to the egg weight. After completion of the incubation period, infertile eggs and the eggs with dead or unhatched embryos were opened; this allowed us to calculate the hatchability for set eggs and fertilised eggs as well as the percentage of dead or unhatched embryos. The results were processed statistically using the one-way ANOVA and Duncan test.

RESULTS AND DISCUSSION

In the group with the highest humidity (30%), the weight decreased gradually by less than 2% per week. The weight loss in the groups with lower humidity was slightly higher (more than 2% per week), so the loss rate measured on each weighing date was higher and differed significantly from that of the group III. The highest weight loss was recorded in the group I (15.3%) and it was by 1.2% higher that that in the group III. The mean daily weight loss in these groups was therefore 0.31 and 0.29% of the weight of the egg before setting (Table 1).

Besides the thermal and humidity regime, also the size and shape of the egg is what affects the weight loss. In our experiment, egg weight was similar in all groups and ranged between 670 and 685 g, while the shape index remained within 1.44-1.55, without significant differences between them. Also the thickness and porosity of the shell influences the weight loss rate; in order to eliminate differences resulting from these factors, the eggs from individual layers were evenly distributed among the groups. In optimal incubation conditions and with an appropriate egg selection, the loss in relation to the initial weight should remain within 13-17% [9]. According to Delfel and Rosseland [2] as well as Brake and Rosseland [1], the conditions of emu incubation are in their optimum if the eggs lose from 12 to 15% of their initial weight. In the previous studies [17], a constant, 30% humidity and varied temperature of incubation did not cause changes in the relative egg weight loss, which ranged fr om 13.8 to 13.9% and was significantly lower compared to the present experiment.

The egg fertilisation rate ranged from 81.1% (group II) to 88.1% (group I), and was very high as for this species of poultry, which demonstrates that males and females were properly mated (Table 2). Similar fertilisation rates, although in a flock of 4-year-old emus, were reported by Majewska [6]. The fertilisation in the emu depends primarily on the period of laying season and the system of mating. So far, the monogamous system has been applied on Polish farms and our previous observations show that an adequate mating of partners may be difficult. The birds do not always accept each other, often fight, and the male does not service the female. If the birds are allowed to mate freely during the first mating season, we can expect better fertilisation rates than in the case of pair mating [6, 7].

The highest hatchability of fertilised eggs was recorded in the groups I (82.1%) and II (83.7%), in which the humidity during incubation was maintained at, respectively, 20 and 25% (Table 2). The humidity elevated to 30% resulted in reduced hatchability performance, primarily due to increased rates of crippled and weak chicks. Stephenson [13] also observed an elevated percentage of very weak chicks and chicks with oedema if the incubation humidity was high (40 %). Excessive air humidity in the incubator impedes the gaseous exchange between the egg and its environment and waters down the yolk, while the excess of fluid hampers the embryo's moves [1, 9]. As a result, weak chicks hatch, often covered with jelly-like mass. Elevated humidity, however, facilitates the assimilation of shell calcium, so the chicks have well-formed skeletons [10]. Therefore, the upper limit of the optimum humidity range should rather be recommended. At 20% humidity, Stephenson [13] observed a high percentage of malpositioned embryos, which in most cases did not survive. In an environment of too low the humidity, excessive evaporation makes the yolk too dense for the embryo to fully consume the nutrients of the yolk. The literature lacks, however, comparative studies in which differentiated level of humidity would be applied, hence further discussion of this problem is difficult. According to Horbańczuk [3], in the ostrich, which is similar in biology to the emu, excessive humidity of the incubator result in so called “watery” incubation; the chicks show numerous swellings, especially on the neck and limbs. Embryos are commonly malpositioned in the egg, have unretracted yolk sac, need longer time to incubate and hatch, and often need assistance to hatch.

The percentage of dead embryos remained at a similar level in all the groups, being 13.6% on average. The highest numbers of crippled and weak chicks were recorded in the group III (8.9%), where the humidity was 30%, the lowest in the group II (2.3%), at 25% humidity.

The humidity during incubation did not significantly influence the duration of hatching; however, it took the shortest to hatch in the group III (10.2 hour) in the highest humidity (Table 3). The duration of incubation, on the other hand, significantly increased in the group I; however, no pattern was found in the distribution of this character, which impedes any discussion of these results. According to Minnaar and Minnaar [9], duration of emu eggs incubation may range from 46 to 56 days and depends primarily on the temperature. According to Majewska [6] and Szczerbińska [15], incubation took respectively 52 to 57 days and 52 to 54 days, and its duration was similar to those most commonly reported in the literature.

The highest, although non-significantly different, percentage of hatching remnants was found in the group of 30% humidity. During the experiment, 14 chicks were helped to hatch. The highest percentage of such cases was recorded in the group III (11.5%), whilst in the groups II and I, the rate was lower, respectively 8.3 and 9.1%. The body weights of the hatchlings were similar, which was related to similar egg weights in each group. It was found, however, that incubation humidity significantly influenced the relative chicks body weight, since in the group of the lowest humidity, the proportion of the chick to the initial egg weight was the lowest and significantly differed from those in the other groups. According to Minnaar and Minnaar [9], the weight of a healthy emu chick should represent about 2/3 of the initial weight of the set egg. These authors observed that the chicks of the relative weight lower than 61 % should be considered dehydrated, while those exceeding 69% as “over-hydrated ”, which is often indicated by oedema.

CONCLUSIONS

1. Humidity regime significantly influenced egg weight loss during incubation. Lower relative humidity resulted in increased egg weight loss during incubation.

2. The hatchability of fertilised eggs in the groups with 20 and 25% humidity in the incubator were by 5% higher compared with the group with 30% humidity.

3. The chick weight in relation to initial egg weight was the lowest in the group with the lowest humidity and differed significantly from the other groups.

The project was financed by the State Committee for Scientific Research, grant no. 5 P06E 042 19

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