الفهرس 
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Abstract
This study was carried out in the Poultry Research Farm, Faculty of Agriculture, Assiut University, Egypt. The study was designed to evaluate the efficacy of probiotics as affected by the presence of preservatives and storage periods (fresh, 2month, and 4month) of broiler diets on production performance, digestion, intestinal growth, and gut microbiota of broiler chickens from day 1 to 42. Therefore, a total number of 750 one-day broiler chicks (Ross) were understudy in three successive experiments (each of 250 chicks) at 2-month interval. The probiotic was consisted of one strain bacteria (Pediococcus acidilactici) at concentration of 109CFU/g. The preservatives (acidifiers) were organic acids; acetic, propionic, or benzoic.
In each experiment, two hundred and fifty one-day-old broiler chicks were randomly allocated into 5 treatments each of five 10- bird replicates. Treatments diets were: 1) Basal diet (control); 2) Basal diet + 2 grams of probiotics / kg of feed; 3) Basal diet + 2 grams of probiotics + 10 ml acetic acid / kg of feed; 4) Basal diet + 2 grams of probiotics + 10 ml of propionic acid / kg of feed; 5) Basal diet + 2 g probiotics + 10 ml benzoic acid / kg feed. Chicks were fed treatments diets (0-6 weeks). Chicks were fed a starter diet from 0 to 3 and a grower diet from 4 to 6 weeks of age.
The three experiments revealed the following results:
1.Live body weight
The birds of experiment 1 those received the fresh BD supplemented with probiotics plus benzoic acid had significantly heavier LBW from age of 2 weeks to age of 6 weeks, followed by those fed fresh BD+ probiotics+ propionic acid. The LBW of the birds received stored feed for 2 months (exp.2) or 4 months (exp.3) showed the same trend as those of (exp.1).
2. Body weight gain
The effect of treatments on BWG was coincided with the same results of LBW during the same periods. The birds of experiment 1 those received fresh BD supplemented with probiotics plus benzoic acid had significantly heavier BWG from age of 2 weeks to age of 6 weeks, followed by those fed fresh BD+ probiotics+ propionic acid. The BWG of the birds received stored feed for 2 months (exp.2) or 4 months (exp.3) showed the same trend as those of (exp.1).
3. Feed consumption (FC) and feed conversion ratio (FCR)
There were no significant difference in the feed consumption during the overall period of (0 - 6) weeks for any of the treatments, however during the fifth and sixth weeks, the treatments that received probiotics plus organic acids specially (T5) during the three experiments showed some increase in feed consumption. However, the feed conversion ratio for the overall period (0 - 6), the results revealed significant differences, hence the treatments that received probiotics alone or probiotics plus organic acids showed better FCR, especially (T5), which was the best compared to the control group.
4. Mortality, and economic efficiency
a. No mortalities occurred in Exp.1 and the birds were healthy. While during the second experiment, the mortality were 6 from the group that received probiotics alone (T2). Nevertheless, 14 mortalities were recorded during the third experiment, all of them were in the control group (T1).
b. The relative economic efficiency was better for all the treatments (BD+ probiotics or BD+ probiotics+ OA) compared with the control. The treatment received BD+ probiotics+ benzoic acid rewarded the highest REE.
5. Carcass traits
Eviscerated carcass weights were the highest in the treatments that received probiotics plus organic acids specially (T5) regardless of the storage period. Abdominal fat % was less in all probiotics plus OA treated groups specially (T5) compared to the control.
6. Blood serum hematology
Total proteins, albumin, and globulin were not affected by treatments and all values were within normal physiological range. For triglycerides and cholesterol, the results showed that addition of probiotics plus organic acids led to a decrease in cholesterol and triglycerides compared to the control group, however; all values were within normal physiological range. Enzyme activity: AST, ALT, and ALP showed significant differences as the value were higher when birds received 4- months stored feed compared with those received fresh or 2- months stored feed which may be attributed to exposure of birds of Exp.3 to heat stress.
7. Digestibility
Apparent digestibility coefficient were not affected by storage period except NFE which was higher for fresh feed. Moreover, the apparent digestibility coefficient was also significantly better for CP, EE, and NFE in all treatments (T1, T2, T3, T4, T5) compared with their control (T1).
8. Intestinal development
The results showed better villi height and crypt depth in the duodenum of the probiotics + benzoic acid (T5) group. Also, the treatment received probiotics + propionic acid (T4) significantly improved the ratio of villi height to (villi height/ crypt depth) in both the jejunum and ileum at 42 days of age compared with other treatments. Furthermore, probiotic only significantly improved crypt depth at 42 days of age, and the probiotic + benzoic acid significantly improved villi height and crypt depth in the duodenum at 42 days of age compared to the control group.
9. Enumeration of intestinal and feed bacterial count
a. Chicks received feed stored for 2 or 4 months resulted in decreasing the number of lactobacillus while increased the number of E. coli in the ileum compared to the chicks received fresh feed. However, contrary results were recorded in the cecum (higher number of Lactobacillus and low number of E. coli).
b. A pronounced decrease in the bacterial count of pure probiotics was proved due to increased feed storage periods. This number continued to decrease after storage to become (33%) after one month, (28%) after two months, (1.6%) after 3 months and then significantly to (0.8%) after 4 months.
5.1. GENERAL CONCLUSIONS
According to the summarized overall results, it can be concluded that:
a. Addition of probiotics at a dose of 2 g + 10 ml of acetic acid / kg of feed, the addition of probiotics at a dose of 2 g + 10 ml of propionic acid / kg of feed, or the addition of probiotics at a dose of 2 g + 10 ml of benzoic acid / kg of feed from the first day to the 42nd day of age were of beneficial effect on final body weight gain (6 weeks), BWG (0-6 weeks) and dressed carcass. Moreover, they resulted in increased villus height, villus depth, decreased E. coli count. and increased the number of lactobacilli at 42 days of age.
b. Addition of probiotics at 2 g/kg feed from day 1 to day 42 of age increased BWG (6 weeks), BWG (0-3 weeks), and BWG (0-6). They also improved the eviscerated and dressed carcass weights, and jejunum crypt depth at 42 days of age. Moreover, it decreased the ileal and cecal E. coli population at 42 days of age.
c. Beneficial effects of the tested supplements were proved, and were consistent; (on growth performance, carcass characteristics, villi histology, and intestinal microflora). Moreover, in general, synergistic effect was proved when mixing probiotics mixed with organic acids better than those obtained when using probiotics alone.
d. Addition of probiotics along with organic acids to feeds for long storing periods of up to 4 months may stimulate and increase the number of beneficial bacteria. Also, adding organic acids to poultry feed during periods of heat stress may alleviate the harmful effect of heat stress on birds.
e. It is more guaranteed in case of using probiotics to evaluate the actual number of bacteria in the commercial product and to calculate the required level of supplementation according to the actual concentration.
f. It is better to use probiotics in fresh form and may be at higher levels than usually recommended.
g. Probiotics preparation should be kept -till be used- under suitable conditions.
h. Also, it may be recommended that the addition of probiotics and organic acids, (especially benzoic acid) may be better applied in their protected form (coated) instead of the free form, to guarantee their efficiency degrades under storage conditions.