Abstract: The purpose of this experiment was to explore the effects of adding active yeasts and their cultures on the lactation performance, feed intake, blood biochemical parameters and immunity of lactating Holstein cows in different lactation periods. The experiment used a two-factor completely randomized block test design. According to the principle of similar body weight and parity, 48 lactating dairy cows were divided into four groups, 12 in each group, 6 in pre-lactation and 6 in mid-lactation. The cow in the control group (CG group) was fed with the basic diet, and cows in the other three groups were fed with 0.075% LY yeast, 0.100% Se-enriched yeast (SY group) and 0.075% Se-enriched yeast and Lesfox yeast mixture (LY+SY group). The trial period of the study was 45 days, including 10 days of adaptation and 35 days of experiment. The results showed that: 1) Compared with the CG group and the other two experimental groups, the milk yield in SY group was significantly increased (P<0.05). 2) There was no significant difference in feeding intake among the four treatment groups (P>0.05). The feed utilization rate in SY group was significantly lower than that in LY group and LY+SY group at the early lactation stage (P<0.05), whereas there was no significant difference in feed utilization rate between different treatments at the middle lactation stage (P>0.05). 3) The level of blood amylase (AMY) in CG group was the highest at the early lactation stage, whereas the difference was not significant (P>0.05). The level of blood AMY and lactate dehydrogenase (LDH) in LY+SY group were significantly higher than those of other three groups at the middle lactation stage (P<0.05). There were no significant differences in blood immunoglobulins in all groups in the early lactation (P>0.05). However, the IgG content in LY+SY group was significantly higher than those in CG group and SY group in the middle lactation stage (P<0.05). In conclusion, the addition of active yeast and their culture in feed has a positive effect on improving immunity of dairy cows. This study provides a certain theoretical support and guiding significance for the feed formulation of dairy cows in the breeding industry.
Key words: active yeast; yeast culture; milk production performance; blood biochemical indicators; immunity