47 Influence of Melatonin Supplementation in Pregnant Cattle Consuming Endophyte-Infected Tall Fescue Seed on Offspring Performance

Abstract The objective was to evaluate growth performance and estimates of body composition in offspring of dams that consumed diets containing tall fescue seed with (E+) or without (E-) the toxic endophyte and with or without melatonin during mid-late gestation. Pregnant heifers (n = 57) artificially inseminated with sex-sorted semen (X chromosome-bearing sperm) from a single Angus sire were administered dietary treatments in a 2 x 2 factorial treatment arrangement (E- without melatonin, E-/NM; E- with melatonin, E-/M; E+ without melatonin, E+/NM; or E+ with melatonin, E+/M; melatonin dose: 100 µg/kg of BW) for a 70-d period between May and July starting at 160 ± 13 days of gestation to mimic ergot alkaloid concentrations in a grazing scenario. All diets contained corn gluten and molasses and were fed using SmartFeed Pro (C-Lock Inc.) controlled feeding units between 0900 and 1400 h daily. Cattle were removed from dietary treatments 39 ± 19 days before calving. Two replicates were housed separately in an open-air barn, each with a 1.2-ha paddock. before and following the 70-d treatment period, all cattle were maintained as a single group free from toxic fescue. Calves were weaned at 226 ± 19 d of age. Gestation length, calf birth weight, 205-day adjusted weaning weight (205-d WW), carcass ultrasonography measures (ribeye area, REA; REA/CWT; percent intramuscular fat, IMF; rib fat thickness, UFAT; rump fat thickness, URUMP), post-weaning weights (recorded every 28 days between weaning and 84 days post-weaning), and post-weaning ADG (between weaning and 84 days post-weaning) were evaluated in offspring (n = 44). Post-weaning calf weights were analyzed using the MIXED procedure of SAS specific for repeated measures with treatment and time as fixed effects and replicate as random. All other variables were analyzed using the MIXED procedure of SAS with treatment as a fixed effect and replicate as random with gestation length as a covariate for birth weight. Gestation length, birth weight, 205-d WW, and post-weaning calf weight were decreased (P < 0.04) in offspring of dams that consumed E+ relative to E- during gestation. Birth weight was increased (P = 0.02) in offspring of dams receiving melatonin relative to those without melatonin during gestation. The 205-d WW and REA were decreased in calves born to E+/NM dams relative to E-/NM, E-/M, and E+/M (P < 0.03). Post-weaning weight tended to be decreased in calves born to E+/NM dams relative to E-/NM, E-/M, and E+/M (P = 0.06). UFAT tended to be decreased (P = 0.06) in offspring of dams that consumed E+ relative to E- during gestation. There were no other effects of treatment, time or the interaction (P > 0.10). To our knowledge, these preliminary results are the first to evaluate the potential of melatonin as a therapeutic to recover performance losses in offspring born to pregnant cattle consuming toxic fescue.