Effects Of Parity And Lactation Stage On Peripheral Blood Leukocytes, Somatic Cells And Endogenous Enzyme Activity In Milk Of Dairy Cattle

The study was carried out to explore the effects of parity and lactation stage on peripheral blood leukocytes, somatic cells and endogenous enzyme activity in milk and milk composition in dairy cattle.The whole study incuded four experiments showen as follows:Experiment 1: Effect of parity on composition of peripheral leukocytes of the dairy cattleTwenty five Chinese Holstein dairy cattle with similar body weight and milk yield were selected as expremental animanls. The cattles were of five different parities(5 per parity) and in early lactation.Blood samples of tail vein were obtainend and analyzed by flow cytometry.Results showed that the proportion limit of MAC, PMN and LYM were 5.24% to 7.08%, 30.62% to 48.58% and 40.47% to 57.32%.With the increase in parity, MAC and LYM tended to be decreased and PMN tended to be increased without significant difference(p>0.05).Experiment 2: Effect of Parity on composition of Somatic cells of the dairy cattleTwenty five Chinese Holstein dairy cattle with similar body weight and milk yield were selected as expremental animanls. The cattles were of five different parities (5 per parity) and in early lactation. Milk samples were collected and detected by flow cytometry. Results showed that the somatic cells in milk are mainly MAC, PMN and LYM. The proportion limit of MAC, PMN and LYM were 11.47% to 39.70%, 8.07% to 23.00% and 23.60% to 71.97%.With the increase in parity,MAC, increased, between the first parity and fourth parity was significantly difference(p<0.05), PMN increased, at the fourth parity reached the highest value, LYM decreased,the fourth parity to the minimum value, between the first parity and fourth parity was extremely significantly difference (p<0.01).Experiment 3: Effect of parity and Stage of Lactation on conventional milk composition of the dairy cattleThirty Chinese Holstein dairy cattle with similar Lactation Stage, body weight and milk yield were selected as expremental animanls. The cattles were of six different parities (5 per parity). Milk samples were collected by 10 consecutive of lactation months, and detected by DHI. Results showed that with the increase in parity, milk fat, milk protein, MUN were not significantly affected(p>0.05), the total solids added to the trend, the lactose has decreased, extremely significantly difference(p<0.01), the SCC increased, significantly difference(p<0.05). With the changes in stage of Lactation, the milk fat in mid-lactation was higher, early lactation and late lactation were significantly lower difference(p<0.05).The milk protein in mid-lactation was lower, and early lactation was significantly difference(p<0.05), and late lactation was not significant affected(p>0.05) , but the tenth lactation month was extremely significantly difference(p<0.01). The lactose content was lowest in the late lactation and early lactation significantly difference(p<0.05), and mid-lactation was extremely significant difference(p<0.01). Total solids gradually increased to the highest in the early lactation, then gradually reduced in mid-lactation, and significant difference(p<0.05), in which the sixth, and ninth lactation month as compared with fourth lactation month was extremely significantly difference(p<0.01). MUN levels gradually increased in early lactation,then mid-lactation and late lactation decreased gradually,the early lactation was extremely significantly difference(p<0.01). SCC decreased in early lactation, mid-lactation gradually increased, especially in the seventh lactation month was extremely significantly difference(p<0.01), further decreased in late lactation.Experiment 4: Effect of Parity and Stage of Lactation on endogenous milk enzymes of the dairy cattleThirty Chinese Holstein dairy cattle with similar Lactation Stage, body weight and milk yield were selected as expremental animanls. The cattles were of six different parities(5 per parity). Milk samples were collected by 10 consecutive of lactation months. Results show that with the increase in parity, LPS reduced significantly difference(p<0.05), CAT and NAG tendency to increase was not significant difference(p>0.05), LP first increased and then gradually decreased steadily in the first and third parity was significantly difference(p<0.05); LDH increased, extremely significant difference(p<0.01). with the increase in lactation month, LPS with higher levels was in milk early lactation, with lower levels was in mid-lactation and late lactation, significant difference(p<0.05), and seventh lactation month was extremely significant difference(p<0.01), CAT was higher in early lactation and as compared with mid-lactation and late lactation significantly difference(p<0.05), LP in early lactation and late lactation was high, and the fifth, eighth lactation month was significantly difference(p<0.01), NAG reduced first, then increased high, second and third lactation month as compared with seventh lactation month was significant difference(p<0.05), LDH lower in early lactation, high in mid-lactation were significantly difference(p<0.01).