Beef Cow Winter Feed Utilization
In Ontario, most beef cows are fed a significant amount of conserved forage during winter. While extending the grazing season with stockpiled grass and annual forage crops has reduced the length of the feeding season on many farms, there is still a lot of baling and chopping done in preparation for winter! Harvesting, storing and delivering the herd's winter rations are major expenses, up to 50 % of the cost of keeping a cow. Even small improvements in the system can result in significant savings. After all of the effort and expense of creating the feed inventory, ensuring that it is being efficiently utilized by the animals is the critical last step.
Efficient feed utilization includes:
The better we understand how feed is being utilized, the more effectively we can manage the winter feeding program.
Feeds and Feed Terminology
Nutritionists use a variety of terms when talking about feeds and feeding. It's important to have a working knowledge of them in order to be able to use the information presented in lab analysis reports and animal requirement tables, as well general feeding management. A list of some of these terms and their meanings are presented in Table 1.
Table 1. Feeding Terms and Definitions
Good feeding management starts with an accurate prediction of how much of a particular feed the cows are expected to be consuming in a particular situation. In order to do this, the first thing we need to deal with is whether we are referring to feed intake and nutrient content on an As Fed basis (AF) or a Dry Matter basis (DM).
All feeds contain at least some moisture. But since nutrients such as energy, protein and minerals are only contained within the dry matter, the amount of nutrients the cow gets is solely determined by the amount of dry matter she consumes. The cow adjusts to the amount of moisture in the feed by regulating how much water she drinks - the higher the proportion of water in the feed, the less the cow drinks. In general, the maximum amount of forage a cow can consume is based on her capacity to intake dry matter, and is independent of moisture content.
Example Dry Matter Calculations
"Dry" bales of hay typically contain about 15% moisture and 85% dry matter, while wrapped baleage may contain around 45% moisture and 55% dry matter. Let's assume we weigh a 4 ft X 5 ft bale of dry hay and get a reading of 850 lbs this is the As Fed weight of the bale. So what does this information mean? Assuming the bale contains 85% DM
The amount of dry material in this bale is: 850lbs AF X 85% DM = 723 lbs of DM
The amount of moisture in the bale is: 850lbs AF X 15% moisture = 127 lbs of moisture
If this same forage had been baled "green" and wrapped up as a 4 ft X 5 ft bale of silage, its scale weight would be much greater, say 1300 lbs (it's As Fed weight). However, the actual amount of dry material would still be the same (723 lbs), and all of the extra weight would be from additional moisture. In this case:
The total amount of moisture in the silage bale would be:
1300 lbs AF - 723 lbs of DM = 577 lbs of moisture.
The % of dry matter in the silage bale would be:
723 lbs / 1300 lbs X 100% = 56% DM.
The % of moisture in the bale would be:
577 lbs / 1300 lbs X 100% = 44% moisture
Assuming the above hay and silage bales contain identical plant material (species, degree of maturity etc.), a cow's intake of dry matter would be quite similar regardless of whether she is fed the dry bale or the silage bale, although there may be a slight decrease in dry matter intake (DMI) over time for the ensiled feed. Of course, the total scale weight of feed consumed by the cows would be much greater when fed the baleage.
So if we want to measure the nutritional value of a feed, relate it to animal requirements, and be able to compare it to other feeds, it is essential that we deal with nutrient content on a DM basis. Likewise, if we want to evaluate the feed intake of animals in terms of nutrients supplied, we have to convert scale weights (as fed basis) to dry matter intake (DMI).
Feed Intake Estimates
Knowing the expected feed intake for a group of animals is an essential step in evaluating diets and feeding systems. Feed intake of beef cows is affected by a number of factors, including body size, body condition, physiological state (dry, lactating, pregnancy etc.) the palatability and digestibility of the feed, and the environmental temperature. Table 2 contains some useful guidelines for the forage dry matter intake capacity of beef cows as a % of their body weight.
Table 2. Forage Intake Capacity of Beef Cows1,2
1 Hibbard, C. A. and T. A. Thrift. 1992. J. Anim. Sci.
70:(Suppl. 2). (Abstr.).
Forage intake increases as quality increases. This is due to a combination of both increased palatability and improved digestibility of the better forage, which speeds up rate of passage through the digestive tract.
Let's look at the expected intake of a 1400 lb dry cow in good body condition being fed average quality hay on a free choice basis
DMI = 1400 lbs X 2.2% = 30.8 lbs of dry matter
Since this is on a dry matter basis, we have to convert to it to an as fed basis in order to relate it to the actual weight of hay being consumed. If this is the same hay we looked at earlier, it would contain 85% DM. So
As Fed weight = 30.8 lbs DM / 85%DM = 36.2 lbs of hay as fed
What would happen if we were feeding the same quality forage but it had been wrapped instead of dried down? The cow would still consume about the same amount of dry matter (30.8 lbs), but the actual weight of feed consume would be much higher.
As Fed weight = 30.8 lbs DM / 56% DM = 55 lbs of silage as fed
Other Factors Affecting Dry Matter Intake
For any specific feeding situation, environmental factors such as air temperature and yard condition can impact dry matter intake, in addition to animal class and forage quality. Some environmental adjustment factors are given in Table 3.
Table 3. Dry Matter Intake Adjustments for Environmental Factors1
1 NRC 1987. Adapted from Predicting Feed Intake of Food Producing Animals
Feed Intake vs. Feed Disappearance
When farmers talk about the amount they are feeding their cows, they are usually referring to the amount of forage offered and which disappears from the inventory. This will always be larger than what the cows are actually consuming. The difference is due to several factors, including:
It's important to have a good idea of how feed disappearance matches up with the expected intake of the cows. If the gap is too wide, after adjusting for typical wastage, there may be some issues with the feeding system that can be corrected in order to save feed and therefore money. If actual feed intake is significantly lower than anticipated, after accounting for wastage, there may be an issue with the quality of the forage. Table 4 has some guidelines for evaluating various levels of feed disappearance.
Table 4. Interpretation of the Difference between Observed Forage Disappearance and Predicted Intake1
1 forages fed to beef cows under typical on farm conditions
Here's an example of a feeding scenario:
What is the expected dry matter feed intake of these cows?
Basic cow dry matter intake:
DMI = Cow wt. X % DMI (per lb of cow wt.)
Adjustment for daily air temperature = 1.05
Cow DMI adjusted for environment:
DMI = 33 lbs X 1.05 X 1.00
What is the expected actual (as fed) amount of hay which would be consumed by these cows? We need to convert our estimated DM intake to an AF basis for the hay been offered.
As Fed Intake = DMI lbs / % DM in the hay
So we would expect each cow to consume about 41.3 lbs of hay per day. For the feeding group of 50 cows this would be:
41.3 lbs X 50 hd = 2065 lbs of hay
The group is being fed an average of 4.0 bales per day, with a very minimal amount left in the feeders. How does this feed disappearance match up with what is expected? Let's look at it on a per hd basis
Feed disappearance/hd = 4.0 bales X 600 lbs / 50 hd = 48 lbs/hd/day
We had estimated the hay disappearance for this group as 41.3 lbs/hd/d. The difference between disappearances estimated intake:
Difference = disappearance - estimated intake
On a percentage basis this would be:
Difference / estimated intake X 100%
This indicates that about 16% of the feed which is being offered is not actually being eaten by the cows. This falls under the Medium utilization category (Table 4), so there is likely significant room for improvement. It would be a good idea to closely observe the cows' feeding behavior and see how much hay is being pulled out of the feeder and lost on the ground, as well as how much forage is being left uneaten in the feeders. In trials, hay wastage when feeding round bales has been measured from 5% to 40%, with the higher range occurring when the bales are rolled out on the ground. You can compare the design of your feeders with those evaluated in a feed wastage trial
The Bottom Line
Examining the winter feed utilization of your cow herd is an excellent management tool. Comparing the amount of feed you are going through to what is expected for your situation gives you the information needed to evaluate the feeding system and take corrective action if needed. Since feed accounts for such a large portion of overall costs, it's important to ensure that "disappearance" matches up well with cow requirements.
1The Disappearing Act Efficiently Feeding Beef Cows
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