Constraints on the utilization of cereal straw in lactating dairy cows: A review from the perspective of systems biology

Cereal straw, a human inedible crop byproduct, can be used as a roughage source in ruminants. However, the nutrition density and palatability are very low, limiting its efficient utilization in animal production. This review aims to systematically provide an overview of the limitations of cereal straws, which is crucial for developing new strategies to enhance the efficient use of cereal straws by lactating dairy cows. Evolutionary molecular biology makes it possible to comprehensively understand the limitations of using cereal straw as a roughage source in dairy cows by different techniques, e.g., multi-omics. Main constraints for utilization of cereal straw and stover in lactating dairy cows include low contents of easily fermented carbohydrates (pectin) and essential amino acids (Met, Phe, and branched-chain amino acids), high content of lignin and silica, and low nutrient digestibility. These cause insufficient supply of the precursors for milk synthesis and result in increased loss of nutrients in feces and urine. Several molecular mechanisms are revealed by multi-omics techniques, including changed amino acid and glucose metabolism, altered rumen microbial composition and function, and differential expression of miRNAs, mRNA, and protein in multi-organs that are associated with milk synthesis. These can be targets of approaches to improve the utilization of cereal straw by dairy cows. In addition, much attention should be given to the efficient countermeasures, including pretreatments by fibrolytic enzymes or steam explosion, dietary formulations such as supplement of pectin, methionine, and branched-chain amino acids, and feeding with other functional feedstuffs, which may improve the feeding and economic value of cereal straw for lactating dairy cows. The newly revealed functional genes (such as BAG3 in the rumen, PC in the liver, CSN1S2 in the mammary gland) and biomarkers (hippuric acid) as well as the integrative signaling and metabolic pathways (phenylalanine metabolism) related to the shortages of cereal straws could be used as nutritional or genetic regulatory targets to improve dairy cow production.