الفهرس 
Composition of natural clays:
The role of clay minerals:Only 14 pages are availabe for public view
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Abstract
The present study was carried out at the Department of Animal Production, Faculty of Agriculture, Tanta University and Animal production Research Institute, Ministry of Agriculture. This study was conducted to evaluate the effect of feeding two levels of tafla clay to Friesian cows during late gestation and early postpartum period on their productive and reproductive performances. A total of 15 Friesian cows (2-4 lactations) at late gestation period (30 days prepartum) were used in this study. Animals were divided randomly into three groups, 5 animals in each. 1- G1: 5 cows were fed according to NRC (1988) requirements for dairy cows, diet was containing of concentrate feed mixture (CFM), berseem (Trifolium alexandrinum) (2nd cut) and rice straw (RS) as a control group. 2- G2: 5 Cows were fed the control ration with 1.5% of DMI /h/d from tafla clay. 3- G3: 5 Cows were fed the control ration with 3% of DMI /h/d from tafla clay. Digestibility trails were conducted at 60 days postpartum using three cows from each group. After 120 days postpartum, rumen liquor (RL) samples were collected individually from three animals in each group for three consecutive days, just before morning feeding and 2 hours post feeding. Blood samples were taken during the experimental period from 30 days prepartum in to 150 days postpartum from the jugular vein of three cows in each group into dry and clean test tubes. Blood plasma samples were analyzed for total proteins, albumin, cholesterol, glucose, triglycerides, urea and creatinine. Also, the activity of asprtate (AST), alanine (ALT) transaminases and alkaline phosphates (ALP) were determined. However, the globulin concentration was computed by subtraction of albumin from total protein concentration. The concentration of triiodothyronine (T3) and thyroxin (T4) hormones were estimated in blood plasma. Also, progesterone (P4) concentrations were estimated. During postpartum period, cows were milked twice daily at 5 a.m. and 5 p.m. and average daily and monthly milk yield were recorded. During postpartum period (150 days), all cows were observed for estrous activity twice daily and cows in heat were inseminated through the 12 h of estrus 17 detection. Animals were examined by rectal palpation for pregnancy after 60 days of insemination. After parturition, the dropped fetal membranes were weighted (FMW, kg), uterine involution (UI), uterine horns symmetries period (UHS, day) and uterine cervical closure (CC, day) were recorded. Also, the interval from calving to first detected estrus (day), service period length (day), number of services per conception, days open, gestation period and calving interval (day) were calculated. The results could be summarized as the following:- 1. Feed intake: Results showed that feed intake of CFM significantly increase (P≤0.05) in G2 and G3 compared to G1 by the percentage of 6.6 and 30% in G2 and G3, respectively. Also, there was significant increase in rice straw intake in G3 compared to G1 by 39.2% and in G2 by 30.5%, in the same order. Whereas, the average of berseem feed intake did not differ significantly (P≤0.05). 2. Digestibility coefficients and nutrient values: Results indicated significant (P≤0.05) increased in digestibility coefficients of CP and CF in G3 than those in both G1 and G2 (72.85 vs. 61.08 and 68.82% for CP and 65.04 vs. 52.56 and 62.97% for CF). The digestion coefficient of CP and CF were not significant between G1 and G2 or between G2 and G3. Digestibility coefficients of CF was significantly (P≤0.05) higher for cows in G3 than those in both G2 and G1 (69.55 vs. 63.69 and 53.16%), while the differences between G2 and G3 were not significant. There were no significant effects for experimental treatments on digestibility coefficients of DM, OM, EE and NFE. Data showed that the effect of dietary tafla clay addition on total digestible nutrients (TDN %) was not significant, while, the effect of tafla clay treatment was significantly on digestible crud protein (DCP %). The significant increase in digestible crude protein (DCP %) was associated with tafla clay treatment being the higher in G3 and G2 than in G1 (9.34 and 8.85 vs. 7.81%), also, there were significant differences (P≤0.05) between G1 and G3. However, the differences between G2 and G3 were not significant. On the other hand, there were insignificant differences of nutritive values as total digestible nutrients (TDN %). It was higher in cows of G3 and G2 than those in G1. The significant improvement in nutritive values 17 as DCP was associated with increasing the digestibility coefficients of CP. The observed improvement in TDN was related to the increase in digestion of OM, EE and CF was insignificant.