Replacing soybean meal with high-oil pumpkin seed cake in the diet of lactating Holstein dairy cows modulated rumen bacteria and milk fatty acid profile

This research aimed to investigate the effects of re-placing soybean meal with high-oil pumpkin seed cake (HOPSC) on ruminal fermentation, lactation perfor-mance, milk fatty acid, and ruminal bacterial commu-nity in Chinese dairy cows. Six multiparous Chinese Holstein cows at 105.50 +/- 5.24 d in milk (mean +/- standard deviation) and 36.63 +/- 0.74 kg/d of milk yield were randomly allocated, in a 3 x 3 Latin square design, to 3 dietary treatments in which HOPSC replaced soy-bean meal. Group 1 was the basal diet with no HOPSC (0HOPSC); group 2 was a 50% replacement of soybean meal with HOPSC and dried distillers grains with solubles (DDGS; 50HOPSC), and group 3 was a 100% replacement of soybean meal with HOPSC and DDGS (100HOPSC). We found no difference in the quantity of milk produced or milk composition among the 3 treat-ment groups. Feed efficiency tended to increase linearly as more HOPSC was consumed. In addition, rumen fer-mentation was not influenced when soybean meal was replaced with HOPSC and DDGS; the relative abun-dance of ruminal bacteria at the phylum and genus levels was altered. We also observed that as the level of HOPSC supplementation increased, the relative abun-dance of Firmicutes and Tenericutes linearly increased, whereas that of Bacteroidetes decreased. However, with increasing HOPSC supplementation, the relative abun-dance of Ruminococcus decreased linearly at the genus level in the rumen, and the relative abundance of Pre-votella showed a linear downward tendency. Changes in dietary composition and rumen bacteria had no significant effect on the fatty acid composition of milk. In conclusion, our results indicated that replacing soy - bean meal with a combination of HOPSC and DDGS can meet the nutritional needs of high-yielding dairy cows without adversely affecting milk yield and qual-ity; however, the composition of rumen bacteria could be modified. Further study is required to investigate the effects of long-term feeding of HOPSC on rumen fermentation and performance of dairy cows.