Estimating the TDN of Low Bushel Weight Oats

The value of all grains including oats is based on its energy (TDN) content. Unfortunately, there is no easy and inexpensive method to determine energy content of specific samples. "Average" predetermined values must be used. Over the years, people have attempted to correlate bushel weight (test weight) to energy content and animal performance. Research has shown though that there is a poor relationship between bushel weight and energy content of most grains. With barley and wheat, energy remains fairly constant with decreasing bushel weight to a certain point (43 and 52 lbs., respectively) and then begins to drop off at a linear rate (see Nutrition Update, November 1996). Very little information has been available on the relationship between the bushel weight and feeding value of oats, especially at very light bushel weights.

In order to provide this information, eleven samples of oats with varying bushel weights (21.7-33.5 lbs.) were provided by MCIC. The samples were submitted to Norwest Labs for proximate analysis which included %dry matter, crude protein, ash, acid detergent fibre, crude fibre, ether extract and nitrogen-free extract.

The TDN of the samples was calculated using both a Penn State equation (ADF only) and a Utah State equation (CP, NFE, EE, CF). There was no difference in the TDN values calculated from the two equations. This indicates that, for oats, ADF analysis alone is sufficient to estimate TDN. Table 1 shows the calculated TDN of the eleven samples and the TDN as a percent of the NRC TDN value for oats (77%).

Table 1. TDN of low bushel weight oats as determined by both proximate analysis and ADF











1 21.7 70.1 71.6 91.8
2 22.7 73.0 72.5 94.8
3 23.1 73.0 73.1 94.8
4 23.3 71.6 72.7 93.0
5 24.5 73.3 75.8 95.2
6 25.8 75.7 75.2 98.3
7 26.1 74.0 73.8 96.1
8 26.2 74.1 72.7 96.2
9 29.2 73.5 73.5 95.5
10 29.9 75.1 74.6 97.5
11 33.5 76.8 75.2 99.7

*TDN determined by proximate analysis divided by 77

(TDN value for oats from NRC, 1996) 



  • TDN values for oats with varying bushel weights can be calculated using ADF analysis.
  • Light weight oats (to 21.7 lbs./bu) have significant feeding value.
  • There appears to be a linear relationship between bushel weight and TDN in oats 
    Nutrition Update
    Volume 11 No.2, November 2000