Impacts of Toxic Fescue Seed Consumed by Pregnant Heifers on Maternal Blood Flow and Offspring Growth Parameters: Potential for Melatonin as a Therapeutic to Improve Offspring Growth

Abstract

The southeastern United States is home to endophyte-infected (E+), toxic, tall fescue grass. Consumption of E+ fescue by livestock has been linked to fescue toxicosis, a disease reported to cost the United States beef industry around $1 billion in annual losses. The primary objective of this dissertation was to evaluate the influence of pregnant cattle consuming E+ seed during gestation on uterine artery blood flow and growth performance of female offspring. The secondary objective was to investigate melatonin supplementation as a mitigation strategy for expected fescue-associated decreases in uterine artery blood flow and offspring growth performance. The study reported in chapter II investigates the influence of pregnant heifers consuming E+ seed with (M) or without (NM) melatonin supplementation during mid-late gestation on uterine artery hemodynamics, plasma prolactin (PRL) and melatonin (MEL) concentrations, as well as total antioxidant capacity (TAC). Body weight, total uterine artery blood flow (TBF), ipsilateral uterine artery blood flow (BF), ipsilateral uterine artery blood flow as a proportion of body weight (BF/BW), ipsilateral and contralateral uterine artery diameters, and PRL were decreased and ipsilateral uterine artery pulsatility index (PI) was increased in pregnant heifers consuming E+ seed relative to endophyte-free fescue (E-) seed. Concentration of MEL and TAC were increased for M heifers relative to NM heifers. The study reported in chapter III investigates the influence of pregnant heifers consuming E+ seed with M or NM during mid-late gestation on growth performance of female offspring. Gestation length, birth weight, 205-d weaning weight (205-d WW), and post-weaning weights were decreased in calves born to dams that consumed E+ relative to E- seed. Calf birth weight tended to be increased in calves born to M dams relative to NM dams. Calf 205-d WW was decreased in calves born to E+/NM dams relative to E-/NM, E-/M, and E+/M. Ultrasonic estimate of ribeye area (UREA) was decreased in calves born to E+/NM dams relative to E-/NM and E+/M. The study reported in chapter IV investigates the influence of pregnant heifers consuming E+ seed or E- seed during mid-late gestation on feedlot performance and carcass characteristics of female offspring. Dams consuming E+ seed during gestation produced calves with decreased pre-feedlot body weight (BW), UREA, UFAT, ultrasonic estimate of rump fat (URUMP), feedlot BW, hot carcass weight (HCW), back fat (FT), yield grade (YG), and income relative to offspring born to dams consuming E- seed. Percentage of retail product was increased in calves born to dams consuming E+ seed relative to E- seed perhaps due to increased fat trimming. In summary, consumption of E+ seed by pregnant heifers during mid-late gestation resulted in decreased uterine artery blood flow and offspring growth rates. Decreased growth rates were maintained through the feedlot stage and carcasses generated decreased income. Such losses could translate to a decreased return on investment for the producer and packer. However, melatonin supplementation to pregnant dams consuming E+ seed appeared to rescue fescue-associated losses in offspring weaning weight and ribeye area at weaning, indicating potential as a mitigation strategy