Adult equivalent

Adult equivalents in Breedcow+

Another key concept underpinning Breedcow+ analyses is that of adult equivalents. The calculation of the total adult equivalents for each modelled herd structure indicates the relative grazing pressure exerted by the herd structure and, if herds have similar total adult equivalents, a meaningful comparison of relative profitability can be made.

The main calculation of adult equivalents is based on the total number of cattle carried for the whole year in all classes. The number carried is calculated as the opening number plus purchases less sales less spays. Cattle recorded as sold or spayed are no longer in the “number carried” and have an adult equivalent rating attributed to them separately.

Adult equivalents in Dynama+

Adult Equivalents are calculated using the same process in all Breedcow and Dynama programs with Dynama+ allowing users to consider the impact of change on both cash flow and grazing pressure over time.

What are adult equivalents?

Most planning in grazing livestock enterprises requires that track be kept of how much feed is used or at least of the “stocking rate”. Thus the comparison of herd structures, turnoff strategies or gross margins is undertaken whilst observing self-imposed limits on how much stock the property can carry.

An immediate problem encountered in herd modelling is that all cattle are not the same size and do not eat the same amount of feed, e.g. weaners eat less than bullocks. Likewise a herd of 2,000 cattle comprising breeders turning off weaners will most likely not eat the same amount as a herd of 2,000 comprising fewer cows but turning off older steers.

To ensure that herds are compared on the basis of consuming the same amount of feed when making predictions of relative profitability, feed requirements are estimated for each class of cattle relative to an adult equivalent.

For the Breedcow+ program an adult equivalent is taken as a non-pregnant, non-lactating beast of average weight 455 kilograms (1,000 lbs) carried for 12 months.

Animals of average weight over the twelve months of more or less than 455 kilograms are rated in proportion to their average bodyweight over the period. Thus a beast growing from 450 kilograms to 600 kilograms (average 525 kilograms) would be rated at 1.15 adult equivalents for twelve months. (525 divided by 455 equals 1.15)

Animals carried for periods less than twelve months, e.g. sale cattle carried three months into the budget year, are rated on the period of time carried as a fraction of twelve months. A beast carried for three months and growing from 400 to 440 kilograms would be rated at 0.23 adult equivalents (average weight 420 divided by 455 multiplied by three and divided by twelve equals 0.23).

In the calculation of total adult equivalents in the herd model an additional allowance of 0.35 adult equivalents is made for each breeder that rears a calf. This allowance covers the extra nutritional requirements of pregnancy, lactation, and incidental forage consumption by the calf until age 5 months. This rating is placed on the calves themselves, effectively from conception to age five months, while their mothers are rated entirely on weight.

Five months is an arbitrary age beyond which the former “calves” are rated purely on weight. This age may bear no relationship to the age at which they are actually weaned.

The AECalc worksheet is used to calculate adult equivalent ratings, based on weights and months carried, for each group. Values for the AECalc worksheet in Dynama+ can be imported from an AECalc sheet in Breedcow+. The values for the first year in the Dynama+ AECalc sheet are automatically transferred to the remaining nine years but can be overwritten where weights or appetite change over time. This is important where a supplement feeding program is under consideration or being altered.

Adult equivalents and feeding supplements

There are some adult equivalent calculation issues that arise with cattle receiving feed supplements that may need to be considered if systems that provide supplements are to be compared to systems that do not.

The adult equivalent rating is used to represent comparative pasture consumption. Since phosphorus and non-protein nitrogen (e.g. urea) supplements work in part by increasing feed consumption, the potentially increased consumption of the supplemented herd may only be partly captured through the increased weight of supplemented cattle. One solution is to use a lower weight as the adult equivalent standard for supplemented cattle, thereby calculating higher adult equivalent ratings for them.

There may also be issues with energy supplements such as molasses if the adult equivalents are being supported in part by pasture and in part by the supplement. A possible solution is to increase the stocking rate limit by an amount equivalent to the feed value of the energy supplement.

These issues are especially important when assessing the economics of supplementation. Care needs to be taken when comparing supplemented herds with herds that are not supplemented to avoid overgrazing. Appetite and pasture consumption may vary by more than 30% for a breeding herd depending on the level and type of supplementation.

One solution is to initially calculate the AE rating for the herd that does not receive supplements and then reduce the AE rating for the herd that does receive supplements by (an initial) 30%. Once the expected benefits of the supplementation program have been implemented in the “with supplements” model the differences between the profit, cash flow and herd numbers in the two models can be compared.

Where a supplementation program is being implemented over time and some delay is expected in the impact on such things as conception and mortality rates, the two Dynama+ models (with and without supplementation) can be compared with Investan to identify the net benefit of the strategy over time.

If the supplementation strategy is profitable at a 30% reduction if AE’s, the strategy can be tested again at a 40% reduction to test the assumptions further. This is little available evidence to identify the actual impact of a supplementation regime on consumption in the paddock so some sensitivity testing is warranted.