Maternal dietary protein levels during gestation and lactation affect post-weaning feed efficiency, nutrient digestibility, rumen fermentation, and microbiota in Qinchuan calvesMaternal dietary protein levels during gestation and lactation affect post-wea

This study evaluated the effects of maternal dietary protein levels from gestation through lactation on post-weaning feed efficiency, apparent nutrient digestibility, rumen fermentation, and rumen microbiota in Qinchuan calves. Eighteen mid-gestation cows were assigned to low (LCP = 8.08% CP), medium (MCP = 10.01% CP), or high (HCP = 12.04% CP) protein diets (n = 6 per group) from mid-gestation to weaning at 90 d. Calves were allowed to suckle freely from birth to 90 d and were then fed the same diet ad libitum from 90 to 180 d. Calves in the MCP group had higher body weight than those in the LCP and HCP groups at birth and 15 d (P < 0.05), whereas both MCP and HCP calves had greater body weight than LCP calves from 45 to 180 d (P < 0.05). During the post-weaning period, dry matter intake did not differ among treatments, but the feed-to-gain ratio was lower in the HCP group than in the LCP group (P < 0.05). Apparent nutrient digestibility was affected by maternal dietary protein level, with higher ADF and EE digestibility in the HCP group and higher CP digestibility in both MCP and HCP groups than in the LCP group (P < 0.05). At 90 d, ruminal ammonia nitrogen and valerate concentrations were higher in the MCP and HCP groups (P < 0.05). At 180 d, ruminal ammonia nitrogen, acetate, isobutyrate, and total volatile fatty acid concentrations were higher in the MCP and HCP groups than in the LCP group, while the HCP group also showed higher propionate concentration and a lower acetate-to-propionate ratio (P < 0.05). Maternal dietary protein level did not markedly alter the core rumen microbiota, but influenced microbial richness and the abundance of functionally relevant taxa. At 180 d, Prevotella was enriched in the MCP and HCP groups, and Succiniclasticum was enriched in the HCP group. These results indicate that maternal dietary protein level during gestation and lactation has lasting effects on post-weaning feed efficiency, nutrient digestibility, rumen fermentation, and microbial functional maturation in Qinchuan calves.