Following is how you might approach using ammoniated wheat straw in a cow's diet. Use of ammoniated wheat straw in diets for first-calf cows and developing replacement heifers would be different from that suggested below.
The ammoniation process increases the digestibility of straw, the greatest benefit of ammoniation of crop residues, and our data seem to suggest that the straw takes on an energy value much like that of an average-quality grass hay. So you might use TDN content of 52 to 53%.
The crude protein, DIP, UIP question is a little more complicated. The 1996 NRC indicates that straw is 3.5% crude protein and of that 3.5% CP value, the DIP is 31%, and the UIP is 69%. Ammoniation does not change UIP, so 3.5% (normal straw) x 0.69 = 2.4% units UIP. Now we can use your analysis of the ammoniated straw, which indicated that it was 11% CP. So 11% - 2.4% (UIP) = 8.6% units (DIP). Now 8.6/11 x 100 = 78% DIP. So in the 1996 NRC model, you would need to change the DIP content to 78%, and the model will automatically change the UIP to 22% because %DIP + %UIP = 100.
Here are some rations using ammoniated straw in a lactation ration for 1150-lb cows for you to consider. One ration has 22 lb/hd/da ammoniated wheat straw and 7.5 lb/hd/da dry distillers grain. We assumed that the straw and distillers grain were both 90% DM. This is a pretty dry ration, and if you could get wet distillers grains, it would add some moisture (21 lb/hd/da wet distillers grain that is 35% dry, 65% moisture). It would be important to have plenty of bunk space (24" to 36") per cow so that all cows received their share of the distillers grain. I have never fed this ration and would be interested, if you use it, how it worked. You could use wet distillers grains but would need to feed more of it to account for the moisture. I would be more comfortable with a ration where the 22 lb/hd/da ammoniated wheat straw was 11 lb/hd/da ammoniated wheat straw and 11lb/hd/da brome hay, sorghum hay, or some other medium-quality hay or even alfalfa. If you do use alfalfa hay, you could substitute whole corn for the dry distillers grains.
