MATERIALS AND METHODS

Foundation Stocks Management
A total number of 350 pullets and cockerels comprising two ecotypes namely dwarf and bare neck were purchased from villagers in the rural community of Sudan. The dwarf chicken which locally called betwil are mainly found in the Western Sudan in the area of Nuba mountain whereas, the bare neck home land is Southern Sudan. These birds were selected according to the phenotypic characteristics. The foundation stocks were intentionally established for breeding purposes with almost equal number of birds in each ecotype. On arrival to the poultry houses of the Faculty of Animal Production, University of Khartoum the birds were randomly distributed to individual breeding pens each 100x90x80 cm. Each cockerel was randomly assigned to mate with three pullets rotationally. The birds were treated against internal and external parasites and vaccinated against new castle disease. Formulated layer feed with 17.50% crude protein and 2750 (Kcal kg^-1) metabolizable energy and fresh water were provided continuously.

Broody Traits Measurement
The experiment lasted for 44 weeks with the first 4 weeks considered as adaptation period. On close observation the birds were classified into broody and non broody according to the characteristic signs of broodiness as described by Romanov et al. (2002). This include persisting nesting, turning and retrieval of egg, clucking, aggressiveness and defense of the nest from attempts for eggs removal. Therefore, hens are defined as broody if they exhibit broody behavior while nesting. The broody traits measured included broody cycle which calculated as the number of days for the complete broody process which commences by nesting on eggs laid and ends by the first egg laid in the next reproductive cycle. The intensity of broodiness was intimately observed for the betwil and bare neck ecotypes. To test the effect of maternity on broody cycle, two trials were conducted, in the first one hens were left to rear their naturally hatched chicks until the end of the reproductive cycle, while in the second trail the hens were immediately deprived from chicks rearing after hatching. On the other hand, the effect of eggs accumulation in the nest on the onset of broody behavior and egg production was studied by intentionally leaving eggs to accumulate in the nests throughout the production period and then by immediately collecting eggs from nests as they were laid during another production period.

Prolactin Hormone Measurement
Ninety blood samples were collected from randomly selected 10 hens (5 from each ecotype) to estimate the level of prolactin hormone and it's relationship with broodiness. Nine blood samples were taken from each hen (3 from each production, incubation and rearing period). The production period was represented by samples taken at first egg laid, egg laid at the middle of the clutch and the last egg laid; whereas the incubation period was represented by samples taken at the first incubation day, middle and end of incubation. On the other hand, the rearing period was represented by the samples taken at weekly interval. The onset of incubation period is detected by the exhibition of apparent signs of broodiness and the end of this stage is determined by the hatch of the first chick whereas the hen enters the rearing period.

The blood samples were collected from the major patagial vein using 3 mL needle. Each blood sample was centrifuged and plasma was harvested in Ependorf tubes (2 mL) and stored at 4°C for 50 days waiting for analysis. About 200 μL prolactin reagent was added into the prolactin coated tubes (0.5 mL) with 50 μL of plasma, then the tubes were shaken by plate shaker for 2 h at room temperature, then the fluid was decanted and blotted on an absorbent pad. Each tube was then washed twice with 2 mL distilled water. Finally, the radioactivity was counted with gamma counter for 1 min to calculate the level of prolactin micIU mL^-1.

Statistical Analysis
Statistical Package for Social Science (SPSS) software version 11.5 was employed for data analysis. For prolactin analysis, Steel et al. (1997) was used according to the following equation:

Where:

RESULTS AND DISCUSSION

Broodiness
On close observation the dwarf betwil ecotypes was found to exhibit apparent and intense broody behavior, being more aggressive towards moving objects, resist attempts for removing eggs from the nest and exhibit aloud characteristic cry compared to bare neck. The results indicated that 86.67% of the betwil hens were broody while the corresponding result for bare neck was 55.56%.

Table 1:	The effect of broodiness on feed intake in betwil and bare neck chicken ecotypes
Means with different superscripts within each ecotype are significantly different (p<0.01). BT: Betwil; BN: Bare neck

Table 2:	The influence of managerial practice on broody cycle and egg production rate in betwil and bare neck chicken ecotypes
Means with different superscripts within columns are significantly different (p<0.05). BT: Betwil; BN: Bare neck

Table 3:	The overall mean prolactin levels during production, incubation and rearing periods for both ecotypes
Means with different superscripts are significantly different (p<0.05)

Table 4:	Mean prolactin level during production, incubation and rearing period in betwil and bare neck ecotypes
**(p<0.01). BT: Betwil; BN: Bare neck

The broody cycles were found to be 65.52±0.9 and 64.61±1,03 days in betwil and bare neck, respectively. On the other, hand the broody cycle was significantly (p<0.05) reduced due to depriving hens from chicks rearing. This reduction attained 38 and 40% in betwil and bare neck, respectively. Table 1, shows the effect of broodiness on feed intake there was a significant (p<0.05) reduction in feed intake during broody period compared to that during production period in both ecotypes. This reduction represented 43 and 52% in betwil and bare neck, respectively. The onset of broodiness was substantially delayed by frequently collecting eggs from the nest, resulting in significant increase in egg production (Table 2).

Prolactin Hormone Status Associated with Broodiness

The prolactin secretion in all domesticated chicken has a major effect on maternal behavior through its effect on the ovary by inhibiting ovulation and inducing broody behavior. Table 3 and 4 showed the overall mean prolactin levels and prolactin levels for betwil and bare neck ecotypes at three different stages (egg production, incubation and rearing). The results showed significant difference (p<0.05) in prolactin levels during egg production, incubation and rearing periods. The average prolactin level (micIU micL^-1) was highest during the incubation period (66.06±3.76) and lowest during rearing period (26.81±3.87) (Fig. 1). The prolactin curve exhibited rising trend throughout the production period to reach the maximum level at week 5 (Fig. 2). These findings are in agreement with those reported by Lighton (2001), Hessling (2007) and El-Halawani (1980). The maximum prolactin level was reached at the 5th week in betwil and 4th week in bare neck ecotype during the incubation period and then declined steady to reach the lowest level for both ecotypes at 9th week during the rearing period (Fig. 2).

Fig. 1:	Mean levels of prolcatin in three periods in two chicken ecotypes

Fig. 2:	Prolactin levels during production, incubation and rearing periods. Weeks 1-3: Production period, Weeks 4-6: Incubation period and Weeks 7-9: Rearing period

The present results indicate a strong relationship between plasma prolactin level and the onset and maintainance of incubation behavior. This finding has also been emphasized by Reddy et al. (2006) when he used active immunization against cProlactin which resulted in increased egg production and decreased pause days. Generally the prolactin levels at different stages show significant difference (p<0.05) between the two ecotypes. Prolactin level was significantly higher in betwil than that in bare neck during incubation and rearing periods, whereas the reverse was true during egg production period, this may partially explain the strong broodiness which was observed in betwil compared to that in bare neck.