Integrative network analysis revealed molecular mechanisms of urine urea output in lactating dairy cows: Potential solutions to reduce environmental nitrate contamination

BACKGROUND

The enriched nitrogenous compounds in the dairy farms negatively affect the surrounding soil quality and air condition. The objective of this study is to investigate the transcriptomes of five key tissues involved in nitrogen metabolism and their changes under different diets to elucidate the molecular regulatory mechanisms of urine urea nitrogen (UUN) yield, one of the indicators of nitrogenous compound secretion of dairy cows.

RESULTS

Cows fed high quality forage-based diet had lower UUN content and UUN yield, compared to those fed low quality forage (crop byproducts) based diets. From the transcriptomes of rumen, duodenum, jejunum, liver and udder, key driver genes and their UUN yield-associated functional gene networks were identified. In addition, the functional networks and expression of key drivers in various tissues (such as S100A8, CA1 and BPIFA2C in the duodenum; A2ML1, HMGCS2 and S100A12 in the jejunum; CYP2B6 and GLYCAM1 in the liver; APOE in the udder) changed in the cows fed crop byproducts based diet, which might be the predominant molecules to drive the increase UUN yield in these cows.

CONCLUSION

The information suggested that gut, liver and udder play important roles in regulating UUN yield, which could regulate nitrogen excretion waste. These findings provide fundamental information on future nutritional intervention strategies to reduce the UUN yield from dairy cows fed human inedible crop byproducts, which is vital for a sustainable and environmentally friendly dairy industry.

A genome-wide association analysis for susceptibility of pigs to enterotoxigenic Escherichia coli F41

Enterotoxigenic Escherichia coli (ETEC) is a type of pathogenic bacteria that cause diarrhea in piglets through colonizing pig small intestine epithelial cells by their surface fimbriae. Different fimbriae type of ETEC including F4, F18, K99 and F41 have been isolated from diarrheal pigs. In this study, we performed a genome-wide association study to map the loci associated with the susceptibility of pigs to ETEC F41 using 39454 single nucleotide polymorphisms (SNPs) in 667 F2 pigs from a White Duroc×Erhualian F2 cross. The most significant SNP (ALGA0022658, P=5.59×10-13) located at 6.95 Mb on chromosome 4. ALGA0022658 was in high linkage disequilibrium (r 2>0.5) with surrounding SNPs that span a 1.21 Mb interval. Within this 1.21 Mb region, we investigated ZFAT as a positional candidate gene. We re-sequenced cDNA of ZFAT in four pigs with different susceptibility phenotypes, and identified seven coding variants. We genotyped these seven variants in 287 unrelated pigs from 15 diverse breeds that were measured with ETEC F41 susceptibility phenotype. Five variants showed nominal significant association (P<0.05) with ETEC F41 susceptibility phenotype in International commercial pigs. This study provided refined region associated with susceptibility of pigs to ETEC F41 than that reported previously. Further works are needed to uncover the underlying causal mutation(s).