| Subclinical mastitis is one of the most common diseases in dairy cows. It not only influences milk production but also causes serious economic losses in the dairy industry. The occurrence of cow subclinical mastitis was investigated and the pathogens were then isolated and identified in dairy farms in Yangzhou area. Genetic polymorphisms in LAO gene and the5’-flanking region of IL-8gene were detected in Chinese Holstein cows by PCR-single strand conformation polymorphism (SSCP), PCR-restriction fragment length polymorphism (PCR-RFLP) analysis and sequencing methods, and their associations with milking traits and somatic cell score (SCS) were analyzed by the least squares linear model. The results showed:In experiment one, BMT (Beijing Mastitis Test) was used to test subclinical mastitis for8months from2009to2010in the Yangzhou University cattle farm in order to study the relationship between disease incidence and some factors such as parity, seasons, lactation months. The result showed:1. The head positive incidence of subclinical mastitis took up30.02%of totally2162 dairy cows, and the mammary positive incidence was14.48%of a total of8034.2. The incidence of subclinical mastitis increased greatly significantly (P<0.01) as the parity increased.3. The incidence of cow subclinical mastitis varied greatly significantly among different seasons (P<0.1), with a peak in September (46.23%).4. There was an increase trend of subclinical mastitis incidence on the whole when lactation months increased, and the lactation months index exerted a greatly significant effect on the incidence (P<0.01).In experiment two, main pathogens causing subclinical mastitis in310Holstein cows from four dairy cattle farms were isolated, cultured and identified with method of microbiology. The results showed:1. The head incidence of subclinical mastitis was44.84%(139out of310), and the mammary positive incidence was17.88%of totally1163mammary areas.2.322strains of bacteria were isolated from the208milk samples of cows with subclinical mastitis. Identification of these strains indicated three pathogens, Staphylococcus, Escherichia coli and Streptococcus, dominated in the cow population. Of all the strains,71strains were Staphylococcus (22.05%),95strains were Escherichia coli (29.50%), and156strains were Streptococcus (48.45%).3. Among the139cows with subclinical mastitis, the infection rate by one kind of pathogen was43.16%, including Streptococcus with31.65%. While the infection rate by two or more kinds of pathogens was54.68%, including mainly Escherichia coli and Streptococcus.In experiment three, genetic polymorphic investigation and its associations with milking traits and SCS revealed:1. A mutation site+84(A/G) of the3’-flanking region of LAO gene was detected, determining three genotypes, AA, AB and BB. AB genotype had greatly significantly higher test-day milk yield than AA (P<0.01),while AB and AA showed no significant difference from BB in test-day milk yield. Further more, no significant correlations of these genotypes were found with SCS(P>0.05)2. A mutation site-233(G/A) of the5’-flanking region of IL-8gene was detected, determining and three genotypes, CC, CD and DD. CD genotype had greatly significantly higher test-day milk yield than CC (P<0.01),and DD had significantly higher test-day milk yield than CC (P<0.05), while there was no significant differences between CD and DD in test-day milk yield (P>0.05). CD had greatly significantly higher lactose percentage than DD (P<0.01), CC had significantly higher lactose percentage than DD (P<0.05), while there was no significant differences between CD and CC in lactose percentage (P>0.05). Further more, no significant correlations of these genotypes were found with SCS (P>0.05)... |
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