Average Daily Gain Calculator NZ
Two weights and the days between them give you the single most useful number in finishing stock: how much liveweight the mob is putting on each day. This works it out in both kilograms and grams a day, since cattle are usually talked about in the first and sheep and deer in the second, and then tells you how many days are left to a target weight at that rate. The daily gain figure is what turns a feeding decision into an arithmetic one. It tells you whether the pasture in front of them is doing anything, whether a mob is worth holding or better sold as stores, and whether a target date is realistic before you book anything against it. Two things worth keeping in mind. The number is an average across the whole period, so it hides everything that happened in between, and a long gap between weighings can average a good three weeks and a bad three weeks into something that looks steady when it was not. And the days to target figure assumes today's rate continues, which is the assumption most likely to break: gain falls away as feed quality drops, as covers tighten, and as animals get closer to mature weight.
Days to target assumes the current rate holds, which it usually will not: gain falls away as feed quality drops and as stock approach mature weight.
How it works
Average daily gain is the weight gained divided by the days it took. Grams a day is the same figure multiplied by a thousand, and gain a week is it multiplied by seven. Days to target is whatever weight remains between the current weight and the target, divided by the daily gain. If the mob is already at or above the target the calculator says so rather than returning a negative number of days, and if the mob has lost weight it reports the loss as a loss instead of quietly showing a target that will never arrive.
Weighing the same animals
The number is only as good as the two weights behind it. Weigh the same sample each time, at the same time of day and with a similar gut fill, because an animal weighed off a full paddock in the afternoon and the same animal weighed off the yards in the morning can differ by several percent without having changed at all. Over a short interval that difference can be larger than the gain you are trying to measure, which is how a mob doing perfectly well comes to look like it has stalled.
Worked example
Lambs weighed at 28 kilograms and again at 42 kilograms twelve weeks later have gained 14 kilograms in 84 days. That is 0.167 kilograms a day, or 167 grams a day, which is 1.17 kilograms a week. With a target of 45 kilograms there are 3 kilograms still to find, so at that rate the mob is 18 days away. If the run is heading into a dry February the honest expectation is longer than that, because 167 grams a day is what the last twelve weeks delivered and not a promise about the next three.
Related calculators
- Feed Conversion Ratio: what the gain cost in feed.
- Liveweight from Girth: getting the weights without scales.
- Kill Sheet: what the finished animal returned.
- Stock Units: the feed the mob is demanding meanwhile.