Influence of endophyte-infected tall fescue seed consumed by pregnant heifers on uterine artery blood flow and offspring growth performance: investigating melatonin as a potential therapeutic

Lay Summary Previous studies have reported that cattle grazing toxic fescue during gestation have decreased uterine artery diameter and give birth to lighter calves with decreased growth performance. Cattle supplemented with melatonin during gestation have been found to have increased uterine artery blood flow and offspring growth performance. The objective of this study was to evaluate the influence of toxic fescue seed consumed by heifers during mid to late gestation on uterine artery blood flow parameters and postnatal offspring growth performance. As expected, toxic fescue seed consumption by pregnant heifers was associated with decreased uterine artery blood flow and offspring growth performance. While melatonin did not recover losses in uterine artery blood flow, it did recover over 60% of fescue-associated losses in offspring weaning and post-weaning body weights. To our knowledge, this is the first study to evaluate the use of melatonin supplementation in pregnant cattle as a therapeutic to rescue fescue-associated losses in uterine artery blood flow and offspring growth performance. Results support the potential use of melatonin supplementation in pregnant cattle to improve the growth rates of calves in the fescue belt.