Discussion of Feed Composition and Analysis
1. Complete the blank column in the table below matching which chemical analysis is used to estimate each of the feed components.
|Feed Components ("Feed Fraction")||Chemical Analysis #||Chemical Analysis|
|Lipids||5||1. Oven Dry Matter (DM)|
|N-Containing Compounds||2||2. Kjeldahl N - Crude Protein (CP)|
|Cellulose||7 minus 8||3. Calculated as 100 - CP - EE - Ash - NDF|
|Water||1||4. Neutral Detergent Fiber (NDF)|
|Feed fraction that makes the cow chew||4||5. Ether Extract (EE)|
|Non-Fiber Carbohydrates||3||6. Muffle Furnace (ashing oven) (Ash)|
|Lignin||8||7. Acid Detergent Fiber (ADF)|
|Cellulose + Hemicellulose||4 minus 8||8. Acid Detergent Lignin (ADL)|
|Minerals (inorganic matter)||6|
2. Indicate which of the chemical analyses listed in the Table above are typically used in ration formulation and why?
When we will balance rations for dairy cows we will pay attention to the dietary concentration of the following chemical fractions:
- NDF: Total NDF in dairy cattle diet should range from 28% (peak lactation) to 40% or above (dry cows) of the ration dry matter. It is one of our indicators that there is enough "roughage" in the diet that will make the cow chew and thus deliver plenty of bicarbonate and phosphate buffer to the rumen (vial saliva) to help neutralize the volatile fatty acids produced by fermentation of the carbohydrates (NFC, cellulose and hemicellulose).
- NFC: In ration balancing we try try to keep the NFC from getting to high. An upper limit of 45% of the ration dry matter (peak lactation diet). In our typical midwest diet, the main component of the NFC is starch (from corn grain). More NFC means more readily available energy for rumen microbes to grow (good news), but also higher risk of rumen acidosis (bad news).
- Crude protein (N-containing compounds): As we will discuss later in the class, dietary N is profoundly transformed in the digestive tract of the cow. Crude Protein in a well-balanced ration of a high producing dairy does not have to be higher than 16.5% (dry matter basis), but the greater the inclusion of high quality alfalfa silage in the ration, the more difficult it is to keep dietary CP low. We want to keep CP low because any excess of N is lost as urinary urea-N, which is at the source of air and water pollution.
- Lipids: Total lipids should not be greater than 7% of dairy diets (dry matter basis). Lipids are concentrated form of energy, but they do not contribute to the synthesis of rumen microbes (a main source of amino acids to the cow). Too much lipids may have a negative effect on dry matter intake and fiber digestion (two really bad news!).