Breedcow+ AE Calc
Step 2 - Complete the Breedcow+ AE Calc worksheet
Open the AE Calc sheet in Breedcow+. Note that data can only be entered in the cells with a yellow background.
The first step in setting up a herd model is to estimate the opening weights and weight gains for each class of livestock in the breeding herd. This allows the relative grazing pressure exerted by the various classes of livestock in the herd to be estimated.
In the Breedcow+ program, the relative grazing pressure exerted by each class of livestock is estimated by comparing each class to a standard measure, in this case one adult equivalent.
It is important that adult equivalent weightings are considered and included when building a herd model as most changes to the management of a herd will have some impact on the amount of feed consumed by at least one group of animals. Maintaining the same grazing pressure (or knowing the change in grazing pressure) in each management option explored underpins the validity of the comparisons between management options.
Changes in grazing pressure can arise through animals being heavier or lighter under the new strategy, or because they are sold sooner or later in the year, or perhaps because they are being supplemented and eat more as a consequence.
The AE Calc worksheet is used to define the average grazing pressure exerted by the herd being modelled. The worksheet requires users to:
- identify the starting weight and annual weight gain for all classes of livestock in the herd, except for mature cows and bulls which require just an average weight for the class for the year entered as the same opening and closing weight
- specify the month of peak calving and the month of sale of each livestock class
- specify the ages of sale cattle in months and their weights at sale
The calving peak month in AE Calc is used to match the various classes of cattle to their birthdays. In this way, deaths, weaning rates and variable costs can be applied from birthday to birthday for livestock classes, i.e. from 12-24 months, 24-36 months etc. Weaners are an exception, since they are rated from 5 months (when they cease to be rated as calves) until 12 months. The other exception is sale cattle, which are included in the model from their “birthday” until the expected average sale month and given a rating in adult equivalents representing only that part of the year.
Ensure that weights on growing cattle correspond to the ages at the start and end of the period selected. Mature cows and bulls held within the herd are mostly at a mature body size and weight and can use the same weight for the "lowest" and "highest" value in the AE Calc table, with this weight representing an average across the group throughout the year.
It is recommended that the "weight at sale" used in AE Calc is the weight of sale cattle in the paddock. The expected weight at sale or curfew weights can be entered later in the Prices worksheet by reducing the paddock sale weights transferred in from the AE Calc sheet by an estimated percentage weight loss.
If a breakeven analysis of potential male sale ages is to be run in the Breedcow+ program, or particular male or female sale ages compared, each potential sale class in the AECalc worksheet must have the expected sale month and sale weight entered, even if cattle are not currently sold at that age under the current management strategy. This applies particularly to weaner weight and likely sales month if the comparison to be run in Breedcow+ is of breeder and steer gross margin, since the price at which steers are ‘sold’ from breeders to growers helps determine relative profitability. If running a breakeven analysis of potential sale ages, include all sale month and weight data for each sale class.
The AE Calc example
Points to note:
- The standard weight of one adult equivalent has been set at 455 kilograms liveweight. This is a standard measure used by all of the examples provided. Therefore, although the AE reference weight can be changed if desired, it is recommended that the current value is retained for consistency.
- The peak calving month has been set at 11 (November). This is the typical peak month of calving for the case study property. The classes of livestock will be rated from birthday to birthday based on an average birthdate of November.
- The extra weighting for cows that wean a calf is retained at 0.35. This means that the total adult equivalent rating for the herd is increased by 0.35 for each calf weaned.
- The opening weight of weaners at approximately five months old is assessed as averaging 168 kilograms across both male and female weaners. (Note: the calves might not be weaned at five months though – this is just the age that Breedcowplus starts to count the grazing pressure applied by the young stock separately to their mothers). All weaners have an average closing weight of 234 kilograms at twelve months. This becomes an average opening weight of 229 and 234 kilograms for heifers and steers respectively, as the manager expects the steers to be 5 percent heavier than heifers at one year old. The total opening weight of yearling steers and heifers equals the total closing weight of all weaners as the herd is expected to produce 50 percent male and 50 percent female weaners on average.
- Retained heifers are expected to gain 171 kilograms liveweight each year for the two years they are held separate.
- The start weight for heifers at the start of 2 years old is the same as the end weight for heifers in the preceding age-group, but this does not always have to be the case (e.g. for heifers that lose weight before the end of the year).
- Breeder cows are expected to average 550 kilograms liveweight during the year. It makes no difference in the model whether the average weight or annual weight range of mature breeders is used as the average of the opening and closing values is used to calculate the rating.
- Steers are expected to have annual liveweight gains of 180 kilograms for each year that they are held (average paddock live weights of 419, 599 and 779 kilograms at the end of each year). All steers are currently sold between three and four years of age. This allows the option to consider the impact on herd structure, costs and profit of holding the steers for one additional year prior to sale.
- The adult equivalent rating for a three year old steer that gains 180 kilograms after starting the year at 599 kilograms liveweight is 1.51. Therefore in the herd model, a three year old steer gaining 180 kilograms over the year will exert nearly the same grazing pressure than a mature cow (AE rating 1.14) that produces a calf weighing 168 kilograms liveweight at five months of age (AE rating 0.35).
- All classes of cattle have been given a sale month and an expected average sale weight even though a number of the classes are not sold under the current management strategy. This has been done to facilitate the breakeven analysis to be undertaken later in the exercise and to ensure all classes are stock are counted in the valuation of livestock capital.
- The month of sale selected for most classes of cattle is February, May or June. These sale months are typical for this property.
- The sale weights shown in AE Calc are for the weight of the sale cattle as they leave the paddock. These can be modified in the Prices worksheet to reflect the actual sale weight achieved at the point of sale.
Once the various classes of weights have been collated in the AE Calc worksheet, the next step is to determine the expected sale weights and prices and add them in the Prices worksheet.