Mojtaba Daneshi ^1* Pawel P Borowicz ¹ Mara R Hirchert ¹ Yssi L Entzie ¹ Jessica G Syring ¹ Layla E King ² Kazi Sarjana Safain ¹ Muhammad Anas ¹ Lawrence P. Reynolds ¹ Alison K Ward ³ Carl Dahlen ¹ Matthew Crouse ⁴ Joel Caton ¹

• ¹ Department of Animal Sciences, North Dakota State University, Fargo, United States
• ² Department of Agriculture and Natural Resources, University of Minnesota Crookston, Crookston, MN, USA, Crookston, United States
• ³ Department of Veterinary Biomedical Sciences, University of Saskatchewan, Saskatoon, SK, Canada, Saskatoon, United States
• ⁴ United States Department of Agriculture, Agriculture Research Service, U.S. Meat Animal Research Center, Clay Center, NE, USA, Clay Center, United States

The objective of this study was to explore the impact of nutrient restriction and one-carbon metabolite (OCM) supplementation on the mRNA expression of antimicrobial peptides (AMP), including βdefensins and cathelicidins, in fetal and maternal lung, mammary gland, and small intestine. Twentynine crossbred Angus beef heifers were synchronized for estrus and artificially inseminated. They were then randomly assigned to one of four treatments in a 2 × 2 factorial design, with the main factors being nutritional plane [control (CON) vs. restricted feed intake (RES)] and OCM supplementation [without OCM (-OCM) or with OCM (+OCM)]. Heifers on the CON diet were fed to achieve an average daily gain of 0.45 kg/day. Heifers on the RES diet were fed to lose 0.23 kg/day. Targeted heifer gain and OCM treatments were applied from day 0 to 63 of gestation, after which all heifers were fed a common diet targeting a 0.45 kg/day gain until day 161 of gestation, at which time the heifers were slaughtered, and samples were collected. Quantitative real-time polymerase chain reaction (RT-qPCR) was performed to assess the expression levels of AMP in the collected tissues. Nutritional plane had no effect (p ≥ 0.24) on mRNA expression of AMP in either the fetus or dams. However, the mRNA expression of cathelicidin5 (CATHL5; p = 0.07) and bovine neutrophil β-defensin5 (BNBD5; p = 0.07) in the fetal lung and mammary gland, respectively, was lower in the +OCM groups compared to the -OCM groups. In the maternal small intestine, the expression of enteric β-defensin (EBD) was lower (p = 0.01) in the +OCM groups compared to the -OCM groups. Additionally, in the maternal lung, there was a tendency (p = 0.06) for an interaction in CATHL5 mRNA expression, with the RES +OCM group having greater expression compared to the CON + OCM (p = 0.07) and RES -OCM (p = 0.08) groups. Our findings suggest that while restricted maternal nutrition did not affect mRNA expression of AMP, OCM supplementation modulated AMP expression in both fetal and maternal tissues. Further research is needed to elucidate the mechanisms underlying OCM's impact on AMP expression.