Author details:
1 Department of Animal and Poultry Science, University of Saskatchewan, Saskatoon, SK; 2 Agriculture and Agri-Food Canada, Lethbridge Research and Development Centre, Lethbridge, AB; 3 Agricultural Food and Nutritional Science, University of Alberta, Edmonton, AB; 4 Gowan’s Feed Consulting, Raymond, AB.
Abstract
With the rising impact of climate change on grain crops in North America, more wheat grain has failed to meet milling grade standards and has been diverted to animal feed. A common reason for rejection is infection with F. graminearum and C. purpurea, which produce deoxynivalenol (DON) and ergot alkaloids (EA), respectively. Current allowable limits in cattle for DON are 5 ppm in Canada, while EA limits are 2 to 3 ppm. The objectives of this study were to investigate the effects of high mycotoxin levels on ruminal fermentation, growth performance, and carcass characteristics of finishing steers. The primary mycotoxin assessed was DON (5 ppm and 10 ppm), but EA were also present in the same wheat at 2.1-4.3 ppm. Forty crossbred steers (8 cannulated) were housed in individual pens, blocked by weight, and randomly assigned to 1 of 4 treatments; control-low (0 ppm), control-high (0 ppm), MYC-low (5 ppm-DON; 2.1 ppm-EA), and MYC-high (10 ppm-DON; 4.2 ppm-EA). Wheat screenings were added to control diets so as to generate diets with a chemical composition that was similar to MYC diets. Steers were fed a finishing diet consisting of 88% dry rolled wheat based-concentrate and 12% barley silage on a dry matter basis for 112 days. Ammonia and volatile fatty acid concentrations in rumen fluid did not differ among treatments. Final body weight, dry matter intake (DMI), average daily gain (ADG) and gain to feed ratio (G:F) of steers fed MYC were reduced when compared to controls (P<0.01), with DMI for controls averaging 9.67-9.85 kg/d, MYC-low at 8.38 kg/d, and MYC-high at 6.29 kg/d. ADG for controls ranged between 1.90-1.92 kg/d, MYC-low at 1.36 kg/d and MYC-high at 0.84 kg/d. Hot carcass weight and fat cover were also reduced (P<0.01), but lean meat yield was increased in MYC steers (P<0.01). No differences were noted in carcass grades. In conclusion, a combination of DON and EA, negatively impacted growth performance and carcass traits of steers. These findings illustrate the importance of knowing what toxins are present in feed wheat for finishing cattle. Adjusting approved levels of mycotoxins when two or more are present may help avoid adverse impacts on growth performance of finishing feedlot cattle.
Keywords: beef cattle, wheat, mycotoxins, performance, DON, ergot.
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