Effects of dietary yeast culture supplementation and different particle sized rations on milk yield and quality in dairy cows under heat stress

Objective: The study was aimed to investigate the effects of ration particle size and dietary supplementation of live yeast (Saccharomyces cerevisiae) on dry matter intake, milk yield and milk quality, apparent nutrient digestibility and ruminal fermantation parameters in dairy cattle under heat stress condition. Material and Methods: Four multiparus Holstein dairy cattle in midlactation were fed diets consisting 2 different particle size with (1g/day) or without live yeast (LY). Treatments were arranged in a 2 x 2 factorial within a 4 x 4 Latin square design. Results: Nutrient intake was similar when cow were fed diets containing live yeast. The diets containing low particle size increased DMI, OMI, NDFI and ADFI (p<0,001), however decreased peNDF intake (P<0,05) compared with diets containing high particle size. Milk production and milk fat percentage were similar when cows were fed all treatments. However, cows fed diets containing live yeast tended to produce more fat corrected milk (P=0,058). Cows fed low particle size had reduced milk crude protein percentage (P<0,05). None of the dietary treatments had any significant effect on apparent nutrient digestibility. Ruminal pH increased when cow fed diets containing LY (P<0,05). The ruminal total volatile fatty acid concentration and percentage of VFA were not significantly affected by ration particle size or LY. Conclusion: In the study, it was determined although reducing ration particle size increased DM intake under hot stress conditions, it had no effect on milk yield. Ration contaning LY did not affect the yield parameters statistically.