Twenty lactating multifarious cows were divided into four groups, 5 in each. Cows in the 1st group (G1) were fed a control diet; while those in G2, G3 and G4 were fed the control diet supplemented with 0.19, 0.57 and 0.93 mg Co /kg diet on DM of concentrate feed mixture, respectively.This experiment aim to study to evaluate the effect of dietary cobalt (Co) supplementation at different levels on digestibility, milk production, some blood parameters of Friesian cows, growth performance of their offspring. and Economical efficiency.
Total and Average daily milk yield (TMY, ADMY) as well as composition of milk was individually recorded. Blood samples were individually taken pre-partum and 30 and 60 day-postpartum for determination of Co, Fe, Cu and Zn contents and total cholesterol (CHO), IgG and estradiol concentrations in blood serum. Postpartum first estrous interval (PPFEI), conception rate (CR) after artificial insemination, number of services per conception (NSC), and days open (DO) were recorded. After calving, live body weight (LBW) of calves was recorded and average daily gain (ADG) was calculated during the suckling period
Results indicated that, the rations supplemented with cobalt were high palatable in DM intake. Also, the digestibility's of all nutrients for the same rations were significantly (P<0.05) higher than those of control (CR). The feeding values as TDN appeared to the same trend of digestibility coefficients, with significantly (P<0.05) with DCP for tested ration to increase with no significant different. The ADMY for 35 lactation weeks was not affected significantly by dietary Co. ADMY and TMY were the highest (P<0.05) in G3 (11.76 and 4034.3 kg) with the longest (P<0.05) lactation period. Milk in G3 showed lower (P<0.05) fat content (4.90%) than in G1 (5.78%), G2 (5.63%) and G4 (5.67%) with the highest (P>0.05) protein and lactose contents (4.55 and 6.83%) as compared to other groups (4.44-4.50 and 6.65-6.75%), respectively. Prepartum Zn content increased (P<0.05) in G3 and G4 as compared to G1 and G2. The effect of Co on mineral contents and on CHO and IgG concentrations was not significant within 30 day-postpartum. Within 60 day-postpartum, Cu content and IgG concentrations decreased (P<0.05) in Co supplemented groups than in G1, while Fe decreased (P<0.05) only in G3. Cows in G3 showed the shortest (P<0.05) PPFEI (40 d) and DO (78.7 d) and decreased (P<0.05) NSC (2.5 serv.). CR within 120 day-postpartum was 80% in G1 and G3, and 60% in G2 and G4. LBW and ADG of calves were higher (P<0.05) in G2 and G3 than in G4 and G1. Dietary Cobalt Supplementation tended to higher economical efficiency and with improving in economical return. In conclusion, there was tendency of increasing milk production and improve reproductive performance of dairy cows fed diet supplemented with 0.57 mg/kg diet as well as improving LBW and weight gain of their offsprings from birth up to 16 wk of age.