Strategies to Enhance the Use of Wheat Grain in Feedlot Diets

Background

Wheat is used in feedlot diets when feed prices make it a favourable option. It is also more resistant to lodging, and higher energy than other cereal crops (similar to corn), but it does come with some drawbacks. Wheat is high in energy and low in fibre meaning it digests rapidly and can cause digestive disorders such as rumen acidosis, founder, liver abscesses and bloat which limit its use. Wheat can be fed safely if it is processed correctly but its kernel variability makes that difficult.   

Wheat is susceptible to ergot and mycotoxin contamination. Unlike humans and other livestock species, ruminants can be fed lesser amounts of DON mycotoxin contaminated feed making this feed source available at a cheaper price. Though ruminants are less susceptible to these toxins than monogastrics like swine and poultry, the impacts of mycotoxins on rumen microbiology and feed efficiency have not been studied very closely.

Objectives

• To define the impact of processing methods including dry-rolling, tempering and steam flaking on the feed value of wheat.  
• Design diets and make recommendations that capture the feed value of wheat without encountering the negative health consequences of clinical and subclinical acidosis 
• Assess if there is any detrimental impact of high levels of the mycotoxin, deoxynivalenol (DON) in wheat fed to feedlot cattle 

What They Did

Three studies were conducted.   

The first study used an in vitro laboratory technique to investigate the response of 55 wheat samples representing three types (soft, medium, hard) to three processing methods (grinding, dry- and temper-rolling). Wheat samples were characterized for chemical traits and classified for kernel hardness. In vitro gas production (GP) kinetics, fermentation characteristics and digestion at 6, 24 and 48 h of incubation were also measured.  

The second study examined the effect of feeding beef steers high protein (18% CP) or low protein (13% CP) wheat that had been either dry or temper rolled to a processing index (PI) of 75% ± 3%.  160 angus-cross steers were assigned to 16 feedlot pens to assess growth performance, feeding behaviour, and ruminal health. Steers were fed a backgrounding diet for 84 days (35% wheat grain, 60% barley silage, 5 % supplement) and then transitioned to a finishing diet (85 % wheat grain, 10%t barley silage, and 5% supplement) for 140 days.  

The final study used 40 Angus cross steers that were housed individually and fed one of four diets that either contained negligible levels (0 ppm) or a mixture of DON and ergot alkaloid (EA) mycotoxins at increasing levels (5.0 ppm DON, 2.1 ppm EA or 10 ppm DON, 4.1 ppm EA) over a 112-d finishing trial.

What They LEarned

When comparing all the wheat varieties, physical and chemical traits varied slightly, but kernel size and hardness was responsible for the variation in processing responses among wheat types.  

Processing like dry-rolling and grinding ended up producing more than the ideal number of fine particles, increasing the risk of digestive upsets. However, tempering was found to not only reduce the number of fine particles compared to the other processing strategies, but also moderated fermentation. With the high protein low starch wheat varieties, this meant steers were exposed to a low-ruminal pH (ruminal acidosis) for less time during the transition from backgrounding to finishing. This was not true for the wheat varieties that characteristically had lower protein.  

Ultimately, the team found that high-protein wheat worked best when fed to backgrounding steers by improving the feed efficiency during that time. The opposite was true for finishing feedlot steers who’s ADG was improved when offered the low-protein wheat varieties. 

The incidence of liver abscesses was not impacted by the type of wheat fed or how it was processed. Although, the liver abscesses observed in steers fed a high-protein variety were more severe as compared to those fed a low-protein wheat variety.   

Finally, it was no surprise that exposure to mycotoxins (DON and EA) resulted in negative performance in finishing steers. Mycotoxins increased white blood cell counts, adversely impacted liver function, and dramatically reduced feed intake. Despite having a higher digestibility of dry matter and protein, this was not enough to offset the mycotoxin mediated reduction in feed intake resulting in a substantial drop in ADG and feed efficiency. Feeding a diet that included mycotoxins did not impact the occurrence of liver abscesses. 

What It Means

This means that there are options when it comes to feeding wheat without the fear of negative outcomes. Tempering reduces fine particles and cases of acidosis which means producers can reap the benefits of a higher proportion of protein for backgrounding cattle as compared to other grains like barley and corn. Though, it is still important to always stay vigilant, the large distribution in kernel size means processing type/time may vary from case to case and variety to variety.  

While high-protein low-starch wheat works better in backgrounding diets and low-protein low-starch wheat is more ideal for finishing feedlot diets, wheat contaminated with EA is never a good idea. This body of work shines light on the need to feed test and the importance of proper grain processing when it comes to feeding cattle.