الفهرس 
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Abstract
The present study was carried out at Animal Production Department, Faculty of Agriculture, Tanta University in co-operation with Sakha Animal Production Research Station, belonging to the Animal Production Research Institute, Agricultural Research center, Ministry of Agriculture. A total of 30 Friesian cows were used in this study. The experimental cows aged 3.5-6 years and at 2nd and 3rd parity. All Friesian cows used in this study were early postpartum. The experimental animals were divided into three groups according to LBW, milk production, parity and age. The cows of the first group were fed a concentrated feed mixture and were considered as a control group. While the cows of the second groups were fed a concentrated feed mixture and supplementedinorganic Zinc 2.4 g per day each cow. Cows of the third groups were fed a concentrated feed mixture and supplemented organic Zinc 2.4 g per day each cow. Cows were free of any diseases with healthy appearance and they were housed in groups and were kept under semi-sheds. Throughout the experimental period, changes in live body weight were monthly recorded for each animal. Individual milk samples were obtained monthly to measure the content of milk. Blood samples were biweekly collected in clean test tubes via the jugular vein from all cows in each group. Concentration of total proteins and albumin urea-N, glucose and insulin in blood plasma were determined using commercial kits. The number and duration of estrous cycles were monitored from calving until conception. Average concentration of P4, P4 peak and interval to P4 peak during the estrous cycle was determined. Additionally, postpartum first ovulation, first estrus, and intervals post-treatment were • recorded, as well as the number of services per conception (NS/C), conception rate (CR%), and days open (DO). On day 60 post insemination, conception was achieved through rectal palpation. The main results of this study could be summarized as follows: 5.1. Changes in live body weight: The present results revealed that at 2 to 6 months of ages studied, LBWs of cows were insignificantly different, being almost the highest in cows fed on diets containing organic zinc (chelated, G3) as compared to those fed inorganic zinc (G2) and control diets 5.2. Milk yield: Effect of supplemented inorganic and organic trace minerals Zinc were significantly (P<0.05) increased average daily milk production during the 180 days of lactation compared to the control. In cows resaved organic trace minerals (chelated) in G3 significantly (P<0.05) increased average monthly milk production during 1, 3 and 4 monthly of lactation as compared to the control (G1) and inorganic groups. However, cows resaved inorganic and organic trace minerals (chelated) in G2 and G3 significantly (P<0.05) increased average monthly milk production during 2, 5 and 6 monthly of lactation, in term of actual milk yield by 11.58 and 14.74% as compared to the control. The results shown that organic trace minerals (chelated) in G2 significantly (P<0.05) increased total milk production during the 180 days of lactation compared to inorganic and control groups. However, cows resaved inorganic trace minerals in G2 were significantly increased compared to the control groups. It is of interest to note that inorganic and organic trace minerals treatment in G2 and G3 significantly (P<0.05) increased percentages of fat and protein as compared to G1 about by 5.55 and 3., respectively. But lactose and total solid percentages insignificantly increased in G2 and G3 than in G1 about by 3.22 and 2.97%, respectively. All treatments were no effect on fat, protein and total solid percentage. 5.3 Biochemical parameters in blood plasma: 5.3.1. Total proteins in blood plasma: In cows resaved 100% organic zinc (chelated) in G2 significantly (P<0.05) increased protein concentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) and inorganic (G2) groups. 5.3.2. Albumin concentration in blood plasma: The albumin concentration was affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on albumin concentration were not significant (P≥0.05). In cows resaved 100% organic zinc (chelated) in G2 significantly (P<0.05) increased protein concentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) and inorganic (G2) groups. 5.3.2. Globulin concentration in blood plasma: The globulinconcentration in blood plasma of cows was affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on globulinconcentration were not significant (P≥0.05). In cows resaved 100% organic zinc (chelated) in G2 significantly (P<0.05) increased protein concentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) and inorganic (G2) groups. 5.3.2. Glucose concentration in blood plasma: The albumin concentration was not affected significant by supplemented, lactation stage and interaction between treatments groups on albumin concentration in blood plasma of cowswere not significant (P≥0.05). In cows resaved 100% inorganic (G2) and organic zinc (chelated) in G3 increased glucoseconcentration during the 180 days of lactation, as compared to the control (G1). 5.3.2. Lipid concentration in blood plasma: The lipidconcentration in blood plasma of cowswas affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on albumin concentration were not significant (P≥0.05). In cows resaved 100% inorganic (G2) and organic zinc (chelated) in G3 significantly (P<0.01) decreased lipidconcentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) group. 5.3.2. Cholesterol concentration in blood plasma: The cholesterolconcentration in blood plasma of cowswas affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on albumin concentration were not significant (P≥0.05). In cows resaved 100% inorganic (G2) and organic zinc (chelated) in G3 significantly (P<0.05) decreased cholesterolconcentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) group. 5.3.2. Urea-N concentration in blood plasma: The urea-Nconcentration in blood plasma of cowswas affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on albumin concentration were not significant (P≥0.05). In cows resaved 100% inorganic (G2) and organic zinc (chelated) in G3 significantly (P<0.05) decreased urea-Nconcentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) group 5.3.2. Zinc concentration in blood plasma: The Zincconcentration in blood plasma of cows was affected significantly by dietary treatments (P<0.05), however, the effect of lactation stage and interaction between treatment group on albumin concentration were not significant (P≥0.05). In cows resaved inorganic (G2) and organic zinc (chelated) in G3 significantly (P<0.05) decreased Zinc concentration in blood plasma of cowsduring the 180 days of lactation, as compared to the control (G1) group. 5.3. Ovarian activity: Results showed that inorganic and organic zinc (chelated) treatment in G2 and G3 decreased (P<0.05) average number of estrus cases and ovulatory cycles per cow during the ovulatory cycles compared with the control group. On the other hand, the no statistical differences in average number of total ovulations, ovulatory cycle length during the ovulatory cycles were observed among experimental groups. Average Pg and Pg peak concentrations during the ovulatory cycles in G2 and G3 were significantly (P<0.05) increased as compared to G1. However, P4 level significantly (P<0.05) decreased prior to estrus incidence in G2 and G3 as compared to G1. But, interval to P4 peak during the ovulatory cycles among experimental groups was not significant (Table 14). Reproductive performance: The average of postpartum first estrus interval of cows is shown marked effect of dietary treatment, being significantly (P<0.05) shorter for cows’ organic zinc (chelated) supplemented than those the control group. However, the differences between organic zinc (chelated) and inorganic or inorganic and control groups were not significant. Results revealed significant (P<0.01) effect of dietary treatment on postpartum first service interval, being shorter for cows’ organic zinc (chelated) than those fed control diet. Also, postpartum first service interval was significantly (P<0.05) earlier in average of postpartum first estrus interval than in inorganic zinc group. This means earlier postpartum first service interval of cows resaved organic zinc (chelated) by about 8.2 and 29.2 days than those the inorganic zinc and control groups, respectively. Data showed that the service period length (SPL) in cows was affected significantly (P<0.01) by dietary treatment. As a result of conceiving most cows in organic zinc (chelated) group after the 1st service (60%), SP length was 10.83 day, being significantly (P<0.05) than the control and inorganic zinc groups. The corresponding SP was 21.8 and 17.7 days in control and inorganic zinc group, respectively (Table 15). These results indicated a good impact of feeding cows on diets supplemented with organic zinc (chelated) than with inorganic zinc on the service period length (10.83 vs. 17.7 days). On the other hand, feeding cows on inorganic zinc showed somewhat improvement in SP length as compared to the control animals (17.7 vs 21.8 days). These results indicated a good impact of feeding cows on diets supplemented with organic zinc (chelated) than those fed diets supplemented with inorganic zinc on number of services per conception (1.4 vs. 1.75). On the other hand, feeding cows on treatment group showed somewhat improvement in NS/C (1.4, 1.75 vs. 2.00 NS/C) as compared to the control animals. Cows fed organic zinc (chelated) significantly (P<0.05) showed the shortest DO (62.67 d), while DO for cows fed inorganic zinc and control diets were nearly similar, being 90.2 and 102.5 days, respectively. Conception rates (CR) at successive postpartum days of cows was higher significantly (P<0.05) 100% and 80% of cows in organic zinc (chelated) and inorganic zinc diet, respectively than 60% of cows in control group during this period.