الفهرس 
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Abstract
This study was carried out at the Animal Production Department Experimental Farm, Faculty of Agriculture, Assiut university to determine the effect of zinc source either from organic or inorganic as well as a method of administration on animal performance, blood metabolites and carcass characteristics. The present work included two parts:
The First Part: Include four digestibility trials which were carried out using three adult rams for each trial to determine the digestion coefficients, nitrogen balance rumen liquor characteristics and total bacteria and total protozoa counts for all experimental diets. The experimental groups included the control group (G1) lambs were fed 60% of their requirements as a concentrate mixture and the rest of the requirements were covered from wheat straw which was given ad libitum. While, the other three tested groups were fed the same basal diet, supplemented with 20 mg Zn//head/day as Zinc Methionine (G2), or as Zinc Sulphate (G3) and
20 mg Zn//head/day as Zinc methionine (G4) by drench.
The Second Part: A Feeding trial was conducted to study the effect of zinc source and method of administration on feed intake, growth rate, feed conversion ratio, some serum constituents and carcass characteristics. Twenty healthy local male lambs (six months’ old with 26.5± 3.1 kg Bodyweight) were divided into four groups (five males each). The average initial weights were similar in all groups. Lambs were kept in individual pens. The experimental period lasted for
195 days and consisted of two periods, i.e. 15 days adjustment period followed by 180 days experimental period. Animals were weighed in two successive days every other week before morning feeding. Body weight was averaged to the nearest 0.1 kg. Blood samples were collected monthly from the jugular vein of each lamb. Three animals from each group were slaughtered at the end of the
experimental period when they reached the target slaughter weight of 50 kg and then carcass characteristics were evaluated. Also, meat samples were taken from the eye muscle piece (between 12 and 13th rib) was taken for proximate analysis according to AOAC (1987).
The results could be summarized as follows: I. Digestibility Trials
1- Nutrients digestibility
Supplemented Zn-methionine increased significantly (P>0.05) CF digestibility as compared with other groups. Also, treated rams fed diets contain ZnSO4 and Zn-Meth were higher (P>0.05) in CP digestibility as compared with control groups. However, no differences (P>0.05) were found among groups for DM, OM, EE, and NFE digestibility.
2- Rumen liquor characteristics:
Average ruminal pH values for ZnSo4 and Zn-Meth groups were significantly higher (P<0.05) than control and Zn-Meth.D (6.55 and 6.60 vs.
5.98 and 6.02, respectively).
Total VFA and NH3-N concentration in rumen fluids were not significantly affected by treatments.
3- Rumen Microbial counts
Supplement different sources of Zn to sheep rations increased significantly (P<0.05) total protozoal counts than the control group. However, the total bacterial counts were not affected by supplement Zn.
4- Nitrogen retained
The higher value of nitrogen retained was recorded in Zn-Meth group followed Zn-Meth.D and control groups. However, the group received ZnSO4 recorded the lowest value of N retained.
II. Performance Trial
1- Average daily gain and Feed conversion ratio
Lambs fed ZnSo4 and Zn-Meth with diets improved significantly (p<0.05) fed conversion ratio (g DM / g gain) as compared with control and Zn-Meth.D groups. The average daily gain (ADG) was significantly (P > 0.05) higher in Zn-Meth and ZnSo4 groups than Zn-Meth.D and control groups.
2- Feed Intake
The total DM intake did not differ significantly due to treatments.
3- Blood Serum Constituents
The serum total protein, albumin, globulin, glucose, triglycerides and total antioxidant capacity (TAC) were not affected by Zn sources supplementation or method of administration
The average value of cholesterol for lambs fed diets supplemented with different Zn treatments were significantly (P>0.05) higher than those fed control diet. The higher values of serum Zn were recorded in Zn-Meth (2.13±1.22) and Zn-Meth-D (2.08±0.15) groups followed by ZnSo4 (1.31±0.06). However, the lowest value was recorded in the control group (1.11±0.06).
4- Carcass characteristics and longissimus muscle analysis
There are no significant (P<0.05) differences in the hot carcass, dressing percentage, internal organs and carcass components between the control group and groups fed different sources of zinc.
However, the kidney fat and the pelt weight are significantly (P<0.05) higher in the group fed Zn-Meth than other zinc treatments and control group. Also, the hot
carcass, right and left sides’ weights tended to be higher in lambs fed different
sources of zinc as compared with the control group.
Supplement different source of zinc not significantly affected the longissimus muscle composition. However, a numerical difference was found in the fat content of longissimus muscle.
It could be concluded that:
1. Supplementation of 20 mg Zn /head/day either Zn-Meth or ZnSO4 to the basal ration of lambs contained 40 mg/Zn/kg DM improved daily gain and feed conversion ratio of growing lambs.
2. The addition of a different source of zinc especially Zn-Meth to the diets of lambs increased serum zinc and serum cholesterol concentrations.
3. The dressing percentage and carcass characteristics of lambs were not affected by zinc supplementation.
4. Zinc supplementation has a positive effect on fiber, protein digestibility and nitrogen retained.
5. Zinc supplementation increased protozoa population that may reflect its effect on nutrient digestibility
6. The method of administration for Zn-meth showed preference to the dietary vs. drench.
7. It is recommended to supplement Zn into sheep ration as a dietary organic source of zinc.