الفهرس 
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Abstract
This experiment was carried out at the Poultry Farm of Animal Production Department, Faculty of Agriculture, Minia University during the period from February to June 2003. This work was designed to study the effect of force molting on the productive and some blood parameters of By-line commercial hybrid strain.
A total number of 144 By-line hens at 75 weeks of age were used in this experiment. Birds were randomly classified equally into three groups (2 force molting treatments + control). Each group included forty-eight hens which was divided randomly into 4 replicates of twelve hens.
Birds were force-molted by fasting either for 7 days or for 10 days and the restriction of photoperiod to eight hours/day. Water was available at all times. After feed withdrawal period, the birds were given a crushed yellow com for three weeks and then fed the laying mash ration ad-libitum associated with the increase of photoperiod up to sixteen hours/day.
The traits studied were body weight (grams); hen day production; egg weight (gm); feed consumption (gm feed/hen/day); feed conversion (gm feed/gm egg mass); external and internal egg quality traits and some
blood parameters. .~
The data obtained could be summarized as follows:
1. Egg production during molt period:
1- when feed was withheld to initiate a forced molt, some eggs were laid for several days before egg production DROPped to zero, hens subjected to 7 days and 10 days fasting period reached to zero egg production by 6!h and 5!h day after onset of fasting period, respectively. The number of days out of egg production was 13 days and 28 days for 7 and 10 days, respectively. The 50% egg production reached at 37 and 40 days
SUMMARY AND CONCLUSION after onset of fasting phase with 7 and 10 days fasting period, respectively,
this means that the 7 days hens reached to 50% egg production three days earlier than 10 days.
2- Changes in body weight:
Initial and final body weight were not significantly different between treatments. At 5 days of fasting period the loss of body weight of both fasting periods was 17.91% and 17.58% with 7 days and 10 days, respectively, the differences between them were not significant.
At the end of fasting period, it was observed that the body weight decreased by 20.76% and 24.18% of their initial body weight, with 7 days and 10 days, respectively. The differences between both fasting periods are highly significant (P<O.OOI). from these results it could be observed that the loss in body weight of layers occured in almost linear relationship with time of fasting .
3. Hen-day production:
The overall average of hen-day production was 62.1, 67.92 and 68.73% for control, 7 days and 10 days, respectively. These results indicate that the highest value (68.73%) was recorded for the 10 days fasting period, followed by 7 days (67.92%) and the differences between them were not significant, while the lowest value of hen-day production (62.1 %) was obtained from the control group. This means that the hen-day production tended to increase with increasing the fasting period. The estimated increase was (9.37%) and (10.68%) for both 7 days and 10 days, respectively, when those compared with the control group.
2-The pooled average of hen-day production was 32.21%, 69.650/0, 77.790/0, 76.85%, 65.47%, 68.08% and 61.71 % at 1, 3, 5, 7, 9, 11 and 13 weeks of the laying period. from these results, it could be noticed that the pooled average of hen-day production increased gradually after the first
SUMMARY AND CONCLUSION week and reached to peak egg production at fifth week, then slightly
decreased with some fluctuations .
4. Egg weight:
The pooled average of egg weight was 62.95, 59.19 and 58.48 gm for control, 7 days and 10 days, respectively. The differences in the egg weight means between the control and both fasting periods were highly significant. Also, there were higWy significant differences between 7 days and 10 days fasting period. from these results, it could be noticed that the 10 days egg weight was the smallest, while the control egg weight was the heaviest and 7 days egg weight was intermediate between them
The egg weight in both fasting periods decreased with the advance of age after molt. It was also noticed that the egg weight was not improved by force molting
5. Feed consumption:
The overall average of feed consumption was 97.35, 93.21 and 96.06 gm for control, 7 days and 10 days, respectively. The differences between control and 10 days were not significant, while there were significant differences between 7 days and 10 days as well as control. These results indicate that the highest value (97.39 gm) was recorded in the control treatment, followed by 10 days (96.06 gm), while the lowest value of daily feed consumption (93.21 gm) was obtained from 7 days group.
2-Daily feed consumption during the thirteen weeks post-molt for each treatment, showed a slight decrease for 7 days and 10 days fasting period when compared to the control treatment. The reduction in feed consumption per day with both fasting periods may be attributed· to restricted feeding in the molting period, loss body weight increase during the hen year and less total of egg weight