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 Breedcowplus 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. Modelling herds where the feeding of supplements to some classes of cattle is undertaken may need to have the calculation of adult equivalents adjusted. This is especially so if the supplements (specifically phosphorus and non-protein nitrogen (e.g. urea)) work in part by increasing feed consumption and the comparison is of the pasture consumption of a herd that is supplemented and that of a herd that is not supplemented.

Therefore, when comparing herds with and without phosphorus or non-protein nitrogen (e.g. urea) supplementation, pasture consumption at a given weight will be greater for the supplemented animals at the same weight and may need to be taken into account in the allocation of adult equivalent ratings.

The increased consumption is likely to be only 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. Alternately the comparison may be between say 4,000 adult equivalents that are not supplemented with 3,600 adult equivalents supplemented, thus acknowledging that a supplemented adult equivalent represents more forage consumption. 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. These issues are especially important when assessing the economics of supplementation. Unfortunately, there is currently no scientific evidence to support how the adult equivalent ratings should be adjusted to cope with the impact of supplementation on increased intake, making the estimates of experienced livestock managers the best source of information available.