Factors affecting aerobic plate count in the milk of Chinese Holstein cows in the lower reaches of the Yangtze River

Abstract:

[Background] With the increase of living standards and health awareness, quality and safety of milk are acquiring great concern. [Objective] To investigate aerobic plate count (APC) and total number of Coliform Group (TCG) in the milk of lactating Chinese Holstein cows from an intensive farm located in the lower reaches of the Yangtze River, China, by using different bacteriological methods. The causative factors of APC and TCG were also explored. [Methods] Taking the milk of Chinese Holstein cows as the research object, mastitis detection using mastitis rapid diagnostic agents, APC, TCG and the number of bacteria in the environment detection method with reference to national standards. The collected raw milk samples were subjected to routine isolation and identification of the bacteria, and the milk composition change data was collected. [Results] The results of multivariate analysis of variance showed that different lactation stages and different milk yields had significant (P<0.05) and significant (P<0.01) effects on the total number of colonies in Holstein cows? raw milk. Body condition score, milk yield, stage of lactation, parity and udder quarters had no significant effect (P>0.05) on TCG; APC and TCG measured in summer were significantly (P<0.01) higher than other seasons. Effect of the number of bacteria in different environment on APC and TCG were significant (P<0.05) above. With the increase of mastitis degree, APC and TCG in milk increased, with a significant difference in aerobic plate count for different degree of mastitis (P<0.01). Bacterial identification results in the majority of Staphylococcus and Bacillus infections and almost no Streptococcus infection. The change of the total number of colonies had no significant effect on the rate of milk protein (P>0.05), but had a significant effect on milk fat percentage (P<0.01). [Conclusion] Different physiological and pathological conditions of the randomly sampled lactating cows and the external feeding conditions and hygiene environment had different effects on APC and TCG in the raw milk. The milk fat percentage of raw milk was negatively correlated with the change in total number of bacteria.