الفهرس 
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Abstract
This study was carried out in the Research Laboratory of the Physiology Department, Faculty of Veterinary Medicine (Moshtohor), Benha University, from the beginning of October, 2013 and lasted until the end of February of the next year (5 months).
The animal breed of the present study was Holstein- Friesian cows. Apparently healthy animals were collected from the private sector of animal production in Ismailia government. The work was done during a period extended from October to February with range average dry temperature (15.47 ± 1.84°C) and relative humidity of 82.75 ± 3.98%) which represent a cold season in egypt.
The aims of this study were to throw some lights on the effect of age, pregnancy (parity) and lactation on the following parameters: 1) the osmotic fragility of bovine erythrocytes, 2) the plasma cations concentrations of sodium (Na+), potassium (K+), magnesium (Mg++), total calcium (Ca++) and inorganic phosphorous (P), 3) the erythrocyte cations concentrations of sodium (Na+), potassium (K+) and magnesium (Mg++), 4) the percentage of phospholipids fractions in the bovine erythrocyte membrane.
Cows were grouped according to age and reproductive status (pregnant or lactating) as follows:
Group I (The immature calves after weaning age from 3-6 months).
Group II Uniparous cows means pregnant cows for the 1st time in their third trimester of pregnancy from (2-3 years of age).
Group III Lactating cows in the early period of the 1st lactation (2-3 years of age).
Group IV Multiparous cows means pregnant cows in the 2nd pregnancies (3-5 years of age).
Group V lactating cows in early lactation periods of the 2nd lactation (3-5 years of age).
Group VI multiparous cows means pregnant cows in their 3rd pregnancies above 5 years).
Group VII lactating cows in the 3rd lactation (above 5 years).
All pregnant groups were in the third trimester of pregnancy in the dry period 2 months prepatrum.
All lactating groups were in the early period of lactation 2 months postpartum.
The total number of cows which were used in this study was 105 cows as 15 cows for each group.
Blood samples were collected via jugular vein puncture into heparinized bot¬tles for obtaining whole blood samples for determination of osmotic fragility test of red blood cells, phospholipids’ fractions in the bovine erythrocyte membrane and erythrocyte cations concentration (sodium, potassium and magnesium), and the plasma samples for determination of plasma cations concentration (sodium, potassium, magnesium, total calcium and inorganic phosphorus).
The obtained results revealed that:
• At concentration of 0.4 and 0.5% of NaCl, the fragility was increased with advanced age. Moreover, the pregnant cows showed significant decrease in the fragility of erythrocytes as compared with the lactating ones.
• The highest significant value of plasma Na+ concentration had been established in young calves of 3-6 months age (151.24mmol/l), while aged cows showed the lowest significant values of Na+ concentration (131.34mmol/l). Moreover, the highest value of plasma potassium (PK+) concentration was non significant higher in cows above 5 years (6.00mmol/l) when compared with all of the other tested groups. In addition, the highest significant value of plasma magnesium (PMg++) concentration had been established in calves of 3-6 months age (1.87mmol/l), then decreased non significantly with aging. Regarding to calcium and phosphorus, there was gradual decrease in the plasma Calcium (Ca++) level as the age of cow progresses but the difference was statistically non significant. While, calves 3-6 months of age showed non significant lower plasma P level (5.56 mg/dl) than all of the other tested groups
• At different ages of this study, pregnant cows showed non significant decrease in plasma Na+ concentration (132.14mmol/l in pregnant cows 2-3 years of age) when compared with the lactating cows of the same age (141.32mmol/l in lactating cows 2-3 years of age). Moreover, the pregnant cows showed non significantly higher K+ concentration (5.51 mmol/l in pregnant cows 2-3 years of age) than lactating cows of the same age (4.66mmol/l in lactating cows 2-3 years of age). In addition, the pregnant cows showed non significant decrease in PMg++ concentration (1.24mmol/l in pregnant cows 2-3 years of age) comparing with the lactating cows of the same age (1.27mmol/l in lactating cows 2-3 years of age). In respect to plasma calcium and phosphorus, the pregnant cows showed significantly higher plasma Ca++ concentration (12.29 mg/dl in pregnant cows 2-3 years of age) than lactating cows of the same age (9.78 mg/dl in pregnant cows 2-3 years of age). While, pregnant cows showed non significantly lower plasma P concentration (5.32 mg/dl in pregnant cows 2-3 years of age) than lactating cows of the same age (6.95 mg/dl in pregnant cows 2-3 years of age).
• The erythrocyte sodium (ENa+) concentrations was lower significantly in calves 3- 6 months of age (84.33 mmol/l) than the older cows (2-3 years) (111.33mmol/l) and did not show any significant age variation in those between 2-3 years of age and aged cows. While, erythrocyte potassium (EK+) concentrations was higher non significantly in calves 3-6 months of age (57.66mmol/l) than the older cows (48.66mmol/l at 2-3 years, 31.27mmol/l at 3-5 years and 41.83mmol/l at aged cows). Moreover, the highest significant value of erythrocyte magnesium (EMg++) concentration had been observed in calves of 3-6 months age (1.99mmol/l) then decreased significantly with aging.
• At different ages of this study, pregnant cows showed non significant decrease in ENa+ concentration (101.33 mmol/l in pregnant cows 2-3 years of age) comparing with the lactating cows of the same age (111.33 mmol/l in lactating cows 2-3 years of age). Moreover, the pregnant cows showed non significant increase in EK+ concentration (48.66 mmol/l in pregnant cows 2-3 years of age) comparing with the lactating cows of the same age (42.04 mmol/l in lactating cows 2-3 years of age). Also, the pregnant cows showed non significant increase in EMg++ concentration (1.36 mmol/l in pregnant cows 2-3 years of age) comparing with the lactating cows of the same age (1.32 mmol/l in lactating cows 2-3 years of age).
• The results of the present study revealed that increasing age caused significant decrease in total phospholipids while lactating cows showed non significantly decrease in total phospholipids comparing with pregnant cows of the same age group.
• Age, pregnancy and lactation caused non significant changes in sphingomyelin and phosphatidylserine percentages. While, concerning to the phosphatidylcholine, calves of 3-6 months age and pregnant cows 2-3 years of age had the highest significant percentages (16.77% and 16.99% respectively) of phosphatidylcholine comparing with all the other groups. While, the calves of 3-6 months age and pregnant cows 2-3 years of age had the lowest significant percentages (24.65% and 25.21% respectively) of phosphatidylethanolamine comparing with all the other groups. Regarding to phosphatidylserine, the highest non significant phosphatidylserine percentage had been obtained in calves 3-6 months of age (23.99%) and pregnant cows 2-3 years of age (22.88%) when compared with all of the other tested groups.
• Regarding to the pregnancy and lactation, pregnant cows had non significant higher percentage of phosphatidylcholine (16.99% in pregnant cows 2-3 years of age) than lactating cows of the same age (15.74% in lactating cows 2-3 years of age). Moreover, pregnant cows had non significantly lower percentage of phosphatidylethanolamine (25.21% in pregnant cows 2-3 years of age) and phosphatidylserine (22.88% in pregnant cows 2-3 years of age) than lactating cows of the same age (25.62% phosphatidylethanolamine and 23.32% phosphatidylserine respectively) in lactating cows 2-3 years of age.
CONCLUSION:
The results of the present study indicated that measuring osmotic resistance of erythrocytes could be used as a determinant of oxidative stress in cows. Old age and lactation caused an increase in the osmotic fragility of bovine erythrocyte.
This study revealed that old ages and lactation decreased the osmotic resistance of bovine erythrocytes and caused distortion in percentages of phospholipids fractions in bovine erythrocyte membrane. Therefore, it is concluded that the maintenance of percentages phospholipids fractions of erythrocyte membrane is essential for retaining the normal lifespan of the cell.
It was concluded that because of specific requirement for different ages, there was differences between plasma profiles of cows with different ages, only young ages (till one year old) had requirement for growing therefore no deficiencies were observed, moreover many differences in plasma constituents were observed in the different age groups, however cows in age of reproduction had requirement for fetal growth or milk yielding so deficiencies in some plasma constituents were observed.
We can conclude from the present study that there is marked variation in mineral profile during the different ages, pregnancy and lactation as they perform various functions in these periods. Therefore these micronutrients must be supplemented through diet during gestation and lactation periods to satisfy the requirement of these physiological stages. Although cow can adapt to these marked changes in some important parameters during these physiological stages by different physiological homeostatic mechanisms.
Age, pregnancy and lactation caused some changes in the bovine erythrocyte biology constituted in some changes in percentage of phospholipids fractions and in erythrocyte cations concentration during different ages, pregnancy and lactation.
So we recommended that old and lactating cows should be supplemented by antioxidant to increase the resistance of erythrocytes and improve the productivity and health care during these critical periods.