In the fight against global hunger, dairy milk plays an important part. Now, according to new research, there might be a way to make milk even more nutritious. Researchers previously discovered that even when fed the same diet, some cows make higher-protein milk than others. To find out why, they recently examined the microbiome of cows’ rumens. Multi-omics analysis showed that a large proportion of variations in milk protein yield, or MPY, could be traced to differences in rumen microbiota. A closer look revealed that cows producing high-protein milk hosted a high abundance of certain species of bacteria, including Prevotella, and lower abundances of methane-producing bacteria. This unique assembly of microbes could help cows increase their microbial protein synthesis and amino acid supply, improving their MPY. These findings could help clarify the microbiome- and host-dependent contributions to MPY and inform precision feeding and genetic strategies to increase milk quality and production.