الفهرس 
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Abstract
The present study was carried out to evaluate the effects of probiotics in diets of growing calves on performance, blood metabolites and rumen metabolism parameters. Twelve Holstein calves (~151 kg ± 1.16) were divided into three groups of four animals according to their body weight and were reared for 3 months at Abdel Monaem Abdel Aziz Farm, Tanta Province, Egypt during the duration of the experiment. The calves were reared individually in clean well-ventilated boxes. A clean, fresh drinking water was provided ad libitum for all calves individually. All the calves in both control and experimental groups were offered diet contained roughage as chopped hay (1 Kg/ 100 Kg body weight) and concentrate (2 Kg/ 100 Kg body weight) separately to meet the requirements . Calves were fed concentrates twice daily (~2 kg/100 Kg body weight/d). On the next day morning, any residues were weighed. In the treatment groups. Probiotic was supplemented with concentrate mixture at the rate of 0.5 kg/ton feed (recommended levels) as well as at higher level of 1 kg/ton feed. The concentrate mixture contained 50, 30, 15, 3 and 2% for cotton seed cake, rice bran, wheat bran, lime stone and salt, respectively. Calves were weighed every 2 weeks until end of trial and body weight gains were determined. Moreover, the fecal consistency was scored (1 to 4) bi-weekly before feeding. Blood samples were collected every 4 weeks via jugular vein puncture. Blood was collected in 10 ml tubes containing potassium oxalate and sodium fluoride for glucose analysis and sodium heparin for plasma urea nitrogen (PUN) and β-Hydroxy Butyric acid (BHBA) analyses. The blood was centrifuged for 15 minutes at 3000 rpm, then plasma was collected and stored in deep freeze at -20 ºC until analyses. Every four weeks the rumen fluid was collected via stomach tube for analysis of ammonia nitrogen and VFA throughout the experimental period at 4 h post-feeding. Rumen fluid was analyzed for pH immediately and for further analysis, rumen fluid was stored frozen (-20° C). Ammonia nitrogen was determined by, while VFA concentration At beginning of the experiment, body weight of calves was averaged 151 kg body weight. The calves fed unsupplemented diet (control group) have lower significantly final body weight than experimental animals (Table 2). Average daily gain of all treated calves showed a significant difference from the control. The ADG of the calves in the control group (0 Pro) had the lowest value (54 kg) as compared to those in the supplemented groups 0.5 Pro (58.7 kg) and 1 Pro (64.8 kg). Supplementation of probiotics in diets of calves did not show any significant differences in the blood glucose, total protein and albumin in comparison to those fed unsupplemented diet. It was observed from the above table that 1 Pro and 0.5 Pro recorded the lowest values of blood glucose (74.2 mg/dl) and (70.7 mg/dl), respectively whilst the highest value was recorded in 0 Pro (78.4 mg/dl) but the difference observed was not statistically significant (P > 0.05). Addition of probiotics led to significant higher concentration of β-hydroxybutyrate in comparison to control group. In the current study, all pH values of rumen fluid were within the normal range and were not affected by probiotic addition. In this study, differences in the pH values of rumen fluid sampled from experimental calves were statistically insignificant. Total VFA of rumen fluid were significantly increased upon dietary supplementation with probiotic compared to unsupplemented group. No significant effects for ammonia-N were noted by feeding probiotic-supplemented diet compared to control group.