Evaluating Rations for Predicted Gain

Targeting an average daily gain (ADG) is an important aspect of beef cattle nutritional programs. For example, replacement beef heifers should gain approximately 1.5-1.8 pounds/day to achieve breeding weight standards by 13 - 15 months of age. Dietary corrections are made for frame type, body condition, breed make up, reproductive status, health status, muscling characteristics and other factors. Charts of nutrient requirements for beef cattle are available; the basis for these is the Nutrient Requirements of Beef Cattle, seventh revised edition, 2000. Embedded in ration balancing software are the sophisticated modeling formulae from this publication. One example of this kind of computer program is Cowbytes 4.6 from the Government of Alberta, Agriculture and Rural Development.

Ration balancing is an important management tool in achieving ADG targets, as deficiencies or imbalance in energy, protein, minerals and vitamins will hamper animal performance. Forages need to be analyzed for nutrient content as they may vary greatly in digestibility, fibre and protein content based on species composition and cutting date.

Nutritional tables may be utilized for standard grains and protein sources. Non-standard feed sources should be analyzed for nutrient content. Nutrient content of feeds sourced from commercial suppliers may be available upon request.

With this arsenal of nutrient information, how should one go about evaluating a diet for a specific gain target at best cost? The following example demonstrates steps taken to evaluate a diet:

Assumptions

Cattle factors:

  • 600 pound steer calf, exotic cross, expected to be backgrounded for 6 months
  • Body condition score of 3.5/5
  • Health status is good
  • Target average daily gain (ADG) is 2 pounds, based on frame type
  • No implants or ionophores

Feed factors:

  • Calf coming off pasture mid October
  • Mixed dry hay available free choice
  • Bale weight 800 pounds
  • Coarse rolled barley fed at 1% of body weight
  • Higher energy feed available as an option
  • Appropriate mineral fed free choice
  • Cobalt-Iodized salt fed free choice
  • Water quality is good and available in troughs
  • Ration balanced and costed with Cowbytes Beef Ration Balancer version 4.6
  • NEg=net energy gain
  • NEm=net energy maintenance

Housing and environmental factors:

  • Adequate bunk space for all cattle to eat at one time
  • Adequate number of bale feeders
  • Barn available and windbreak in drylot
  • Yard is scraped as required
  • Concrete yard

Table 1: Nutrient content of feeds, dry matter basis

Nutrient Dry Hay Barley Corn Grain Mineral
Dry Matter 86.5 88.5 89 99
Crude Protein 10.8 11.8 12  
NEm Mcal/LB .58 .92 .99  
NEg Mcal/LB .32 .62 .69  
Calcium .75 .07 .06 18
Phosphorus .2 .38 .34 18
Unit type/size Rnd bale 800 LB Tonne Tonne Bag 55 LB
Cost per unit $25 $315 $355 $28

Here is the output of the Cowbytes program for this scenario:

Ration Report-1

Cowbytes 4.6 AAFRD

Steer 600 pounds 1% BW barley
Nutrient(DM basis) Supplied Feed Only Recommended
DM Intake (lbs) 14.9 14.2
NEmTot (Mcal) 5.83 5.83
NEg (Mcal) 2.60 2.79
Protein (g) 766 768
Calcium (g) 40 31
Phos. (g) 20 17
Target Gain lb/day 2.00  
Predicted Gain lb/day 1.92  
Cost per lb gain $0.62  
Feed Conversion 7.7/1  

NEm is the net energy for maintenance in Mcal/kg or Mcal/lb of feed. Net energy (NE) is the metabolizable energy less the heat increment of feeding (heat lost during the digestive process). When formulating a diet, the NEm recommendation is met first. NEmTot (Net Energy Total for Maintenance) is the total energy needed to meet demands for NE maintenance, NE pregnancy, NE milk, NE cold stress, NE heat stress and NE activity. It is the accumulated energy to meet all NE requirements except growth. NEg is the net energy value of the feed for growth. The NEg supplied does not accumulate until the maintenance recommendation is met.

Photo of calf

Figure 1. Net energy needs for both maintenance and gain have to be met

A quick evaluation of the ration report 1 shown above reveals that the barley grain, which has 0.62 Mcal of NEg/LB and is fed at 1% of body weight along with mixed hay, meets the NEm requirements. Upon close scrutiny of the ration, however, it appears we are slightly low on our target ADG of 2.00 pounds. The Cowbytes program determined that while protein and NEm intake were adequate, NEg requirement was deficient. Increasing our grain source energy to 0.69 Mcal of NEg/LB from 0.62 Mcal NEg/LB fixed the problem. The following ration report 2 indicates the correction.

Ration Report-2

Cowbytes 4.6 AAFRD

Steer 600 pounds 1% BW corn grain
Nutrient (DM basis) Supplied Feed Only Recommended
DM Intake (lbs) 14.9 14.2
NEmTot (Mcal) 5.83 5.83
NEg (Mcal) 3.00 2.79
Protein (g) 767 768
Calcium (g) 38 31
Phos. (g) 19 17
 
Target Gain lb/day 2.00  
Predicted Gain lb/day 2.16  
Cost per lb gain $0.65  
Feed Conversion 6.8/1  

What about cost differences? The barley cost $315/tonne and the corn cost $355/tonne. That's a $40/tonne difference- can we justify this higher priced feed? We met our target gain with the more expensive feed, with a feed conversion of 6.8/1 and cost per pound of gain of $.65/LB. The barley ration gives us a feed conversion of 7.7/1 and cost per pound of gain of $.62/LB.

Results:

The cost per tonne of a feed reflects quality and performance aspects. A higher feed conversion ratio means more days on feed to achieve your performance targets. In our example, while the more expensive feed cost slightly more per pound of gain, ($.03/LB) the target gain was met with a lower feed conversion ratio. Evaluate your grain and feed purchases carefully for expected results instead of focusing on a price/tonne basis. Your beef cattle nutritionist may assist with these calculations.

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