How To Choose Feeds Based on Nutrient Content

Given today’s high feed costs, cattle producers and feeders often dream about turning straw into alfalfa, and corn silage to corn.

 

Unfortunately, as much as we’d like that to happen, it won't.

Cattle can’t perform on straw like they would alfalfa, and corn silage is not an adequate replacement for good old-fashioned corn itself. They’re just not the same in terms of nutrition, plain and simple.

However, each pound of a feed is made up of a combination of the same general nutrients (carbohydrates, protein, vitamins, minerals, and water). Therefore, the feeding value, and by extension, the cost, should be directly proportional to the concentration and digestibility of the desired nutrient in each pound of feed.

 

 

Comparing Feed Content vs. Value

Comparing feeds based on their nutrient content is like comparing apples to apples. For example, a pound of alfalfa has more protein than a pound of straw. Thus, the feed value of alfalfa as a protein source is greater than straw.   

When evaluating feeds this winter (including supplements!), there are two factors to consider:

1) cost per pound of nutrient 
2) nutrient density: the amount of a nutrient in each pound of feed.

By looking at both factors, you can make decisions based on which feeds are the best buy, relative to their feeding value. Let’s continue comparing straw and alfalfa as an example of this. We’ll use crude protein as a measure of protein content and total digestible nutrients.

Before we start, note that TDN is a measure of energy content that represents the proportion of a feed that can be digested and utilized for energy.

  

Alfalfa vs. Straw

Because alfalfa has much higher crude protein than straw, alfalfa is cheaper per unit of protein than straw, even at almost 4 X the price (Table 1).

 

Table 1: Feeding Straw VS. Alfalfa
Feed	% Dry matter	$/ton	$/ton Dry matter	% Crude Protein	% TDN	$/lb.  of Crude Protein	$/lb.  of TDN
	A	B	C	D	E	F	G
Calculation	na	na	B/(A/100)	na	na	C/(2000*(D/100))	C/(2000*(F/100))
Straw	90	60	66.6	4.5	41	.74	.08
Alfalfa	90	180	200	18	60	.62	.16

At $60/ton and 41% TDN, straw may initially look like a better buy per unit of energy than alfalfa — $180/ ton and 60% TDN.

However, a cow can only eat so much straw!

This is where nutrient density comes into play.

Cows can generally eat between 1.8 and 2.25% of their body weight of forage (dry matter basis) each day depending on how digestible the fiber is. If a 1300 lb. cow can eat 26 lb. of straw (2% of body weight) she will be able to get 10.6 lb. (26 X .41) of TDN from straw and 15.6 lb. (26 x .60) of TDN from the alfalfa.  

Straw will not meet a 1300 lb. cow’s TDN requirement during late gestation, while most alfalfa will. However, some straw may be appropriate earlier in gestation or in combination with other more energy-dense feeds like alfalfa, grass hays, corn silage or grain and potato by-products.

 

The Importance of Dry Matter Content

When making comparisons between feeds, it’s crucial to pay attention to the proportion of the feed that is water, or in common language “dry matter content.”

For example: if corn silage is only about 33% dry matter, then 67% is water.

Compare that to alfalfa, which is generally about 90% dry matter.

Therefore the real price of $55/ton corn silage on a “dry matter basis” is $166.7/ton ($55/.33). This example demonstrates why it is so important to evaluate, and compare feeds on a dry matter basis.

Of course, there are a number of aspects to take into consideration when evaluating the content of your feed: labor, feed availability, and infrastructure requirements. But, by using your own prices and a feed analysis, you should be able to get a good idea what the most economical way to feed your cattle is.

Using this information will not turn straw into alfalfa or corn silage into corn, but it will allow you to make cost-conscious decisions that will help you feed your cattle at a price that’s right for you, all without sacrificing performance.