Mycotoxins are harmful secondary fungal metabolites which contaminate a variety of feedstuffs worldwide and are detrimental to animal health and productivity. This study investigated the occurrence and contamination levels of mycotoxins in 2018 US corn silage and total mixed ration (TMR) samples. Corn silage harvested in 2018 as well as TMR samples submitted for analysis since January 2018 were screened via LC-MS/MS technique for the presence of 6 major mycotoxin groups: aflatoxins, type A trichothecenes, type B trichothecenes (B-Trich), fumonisins (FUM), zearalenone (ZEN) and ochratoxin A. Parameters of the main mycotoxins detected are presented (as-received) in Table 1. Corn silage contamination was compared with the prior harvest year using Kruskal-Wallis Test (Prism7, GraphPad, La Jolla, CA). Mean toxin count per sample has increased from 1.2 to 1.7 in 2018 corn silage versus 2017. The prevalence of B-Trich was comparable between years while the percentage of 2018 corn silage samples positive for ZEN was more than 2 times that of 2017 and FUM prevalence was more than 2.5 times that observed in 2017. Mean contamination levels (parts per billion, ppb) for B-Trich and ZEN in 2018 silage samples were significantly greater than 2017 toxin concentrations. Mycotoxin contamination was high in TMR with B-Trich detected in 95% of samples. ZEN and FUM were less frequently detected and at lower average concentrations in TMR samples. Preliminary 2018 corn silage survey results suggest increased contamination levels of B-Trich and ZEN, but consistent FUM contamination when compared with 2017 crop year samples. Although formulations of TMR vary widely across the US, B-Trich contamination was common in these complex rations. Table 1 (Abstr. 448).Fusarium toxin contamination in US corn silage and TMR samples

Parameter	Corn silage		TMR
2017	2018
N	208	76	236
Mean toxin count	1.2a	1.7b	1.4
B-Trich
Prevalence, %	85	83	95
Mean ± SEM, ppb	643a ±34	1162b ± 157	601 ± 25
ZEN
Prevalence, %	26	55	31
Mean ± SEM, ppb	202a ± 34	387b ± 70	176 ± 18
FUM
Prevalence, %	12	32	9
Mean ± SEM, ppb	612 ± 144	763 ± 267	443 ± 140

^a,bValues across rows are different P < 0.05.