Mycotoxin Survey of Common Bermudagrass in South-Central Florida

Common bermudagrass (Cynodon dactylon L.) is a warm-season perennial grass found across the southern United States. Evaluation of factors impacting production and reproductive performance of beef cow-calf pairs grazing pastures on a large ranch in south-central Florida led to the investigation of potential mycotoxin contamination in standing forages. Mycotoxins produced by molds infecting many grains and forages can compromise animal health and performance. Zearalenone (ZEN) is the mycotoxin frequently associated with reproduction-related effects due to its estrogenic activity. The distribution of mycotoxins in pastures at the farm was assessed between paddocks and over time. Samples were hand-plucked (25 to 30 samples per paddock) during four sampling periods with a total of 157 sampled paddocks over time. Activation Laboratories (Ancaster, Ontario, Canada) analyzed samples for 15 mycotoxins via liquid chromatography tandem mass spectrometry. Mycotoxin levels were reported on a dry basis in parts per billion (ppb; Table 1). Zearalenone was the predominant mycotoxin, detected in 61.1% of samples. Zearalenone prevalence was lower in May and August samples compared to March and January samples (P<0.05). The concentration of ZEN in positive samples also tended to be lower in August samples. The combination of low prevalence and low concentrations in August meant that the estimated average sample level (overall MCMC mean; Table 1) was lower than in January (P<0.05). Other mycotoxins detected included type A trichothecenes (T-2 or HT-2 toxin; 14.6%), type B trichothecenes (deoxynivalenol; 2.5%), sterigmatocystin (2.5%), and fumonisins (0.6%). Mycotoxins were detected in 62.4% of samples while 18.5% of samples tested positive for multiple mycotoxins. We conclude that additional sampling across a larger geographic region is needed to determine the wider significance of mycotoxins in common Bermudagrass.

Table 1. Summary of zearalenone results in pasture samples over time.

			Overall	Statistics on Positive Samples [ppb]
Month	Total Count	Percent Positive	Mean [ppb]*	Mean*	Median	90th Percentile	Maximum
Mar2016	56	78.6a	786a,b	1000a	270	3400	9490
May2016	62	51.6b	489a,b	946a	140	1850	10770
Aug2016	24	20.8b	27b	128a	80	270	270
Jan2017	15	100.0a	1936a	1936a	1110	5920	7930
Combined	157	61.1	664	1085	290	3420	10770

 

 

 

^a,bValues in the same column sharing a letter were not significantly different (95% confidence level). Percent positive tested with Chi-square and monthly means tested with Bayesian inference (10⁶iterations), R Version 3.3.2.

*Markov chain Monte Carlo methods used to estimate means of all samples within a month and of samples positive for ZEN within a month.