LAUSR

Abstract This study was conducted to evaluate the effects of dietary supplementation of a fenugreek seed extract (SAP) as a source of saponins on dry matter intake, blood metabolites, apparent total tract nutrient digestibility, and whole blood transcriptome of Holstein dairy heifers. Eight heifers (BW = 477 ± 23.8 kg) were stratified by BW and then randomly assigned to one of two treatments in a cross-over design with two 35-d experimental periods and a 14-d wash-out between the two periods. The heifers were housed individually in eight dry lot pens. Each pen was equipped with one GrowSafe intake node. Treatments were 1) corn silage-based diet with no additive (CON) and 2) corn silage-based diet plus 2 g per hd per d of SAP. Dairy heifers fed supplemental SAP had higher (P ≤ 0.05) DMI and apparent total tract digestibility of dry matter, crude protein, and neutral detergent fiber compared to CON. Dairy heifers fed supplemental SAP had lower (P = 0.03) blood urea nitrogen and higher (P = 0.01) blood glucose concentration compared to CON. Pathway analysis via gene set enrichment analysis revealed increased (FDR ≤ 0.05) transcript levels for gene sets belonging to ISG15 antiviral mechanism, metabolism of proteins, citric acid cycle and respiratory electron transport, ATP synthesis by chemiosmotic coupling, and complex I biogenesis in dairy heifers fed supplemental SAP compared to CON. Decreased (FDR ≤ 0.05) transcript levels for gene sets associated with erythrocytes take up/release carbon dioxide, release/take up oxygen, and O2/CO2 exchange in erythrocytes were also observed with SAP supplemental group. Taken together, our results revealed that fenugreek seed extract can be used as an effective dietary supplement for dairy heifers to improve intake and digestibility, and alter the host transcriptome toward improved energy and amino acid metabolism, improved antiviral immune status, and reduced oxidative stress damage.