Hay by Body Weight: Flakes, Bales and a Whole Winter

A flake is not a unit, and neither is a bale

The tool asks for the weight of your flake and your bale because both vary by a factor of two in the real world. A small square bale runs 15 to 30 kg depending on the baler settings, the crop and how dry it was baled; the flakes inside it are simply the bale divided by however many slices the machine made, so a heavier bale gives heavier flakes and not more of them. Weigh three flakes off a fresh bale, take the average, and you have converted a guess into a measurement.

Round bales widen the problem rather than solving it. A large round bale is anywhere from 200 to 500 kg, loses weight to weather and waste at the feeder, and cannot be split into portions the way a square bale can. If you feed rounds, weigh one at delivery, divide the paddock consumption over a fortnight and work backwards to a per-horse figure; the daily calculation is still the same arithmetic, only the denominator is harder to establish.

Dry matter, not what comes off the scale

The percentages describe dry matter, and hay is about 85 to 90 per cent dry matter — so 10 kg of dry matter is 11 to 12 kg of hay as fed. For hay that difference is small enough that most yards ignore it. For haylage, which runs 55 to 70 per cent dry matter, ignoring it is a serious error: 10 kg of dry matter is 14 to 18 kg of haylage on the scale, and feeding 10 kg of haylage delivers little more than half the intended forage.

The other correction is grazing. A horse at pasture takes a substantial part of its forage from grass, and the hay figure is the balance rather than the total — which is why the same horse eats far less hay in June than in January without any change to its work. The calculation gives a total forage requirement; deciding how much of it the field is already supplying is a judgement made by looking at the field.

Buying a winter, not a week

The number that matters at the end of summer is the season total, and it is large. A single 500 kg horse at maintenance needs 1,800 kg of hay across a 180-day winter — ninety small square bales, or roughly five round bales. Three horses in a yard need two hundred and seventy squares, which is a barn, not a corner of one; and hay bought in September costs materially less than hay bought in February, when everyone else has run out.

Buy about ten per cent more than the calculation says. Hay is lost to waste at the feeder, to spoilage at the bottom of a stack, to a bale that turns out mouldy and to the days that are colder than the plan assumed — a horse's maintenance requirement rises measurably below its lower critical temperature. The margin is cheap in September and expensive in February, which is the whole argument for computing the season total before the season starts.

Frequently asked questions

How much hay does a 500 kg horse eat a day?

Ten kilograms of dry matter at maintenance, which is eleven to twelve kilograms of hay as fed. In flakes of 2.3 kg that is between four and five, and it should be spread across at least three feeds or a slow-feed net — a horse's stomach is small and secretes acid continuously, so long gaps without forage are the practical risk, not the daily total.

How do I weigh a horse without a weighbridge?

A weight tape around the girth gives a figure within about ten per cent, which on a 500 kg horse is fifty kilograms and a full kilogram of daily hay. The heart-girth and body-length formula does better: girth squared times length divided by a constant, with the constant depending on the type of horse. Either way the tape is worth using consistently — a trend measured the same way every month is more useful than a single accurate number.

Is 1.5 per cent safe for an overweight horse?

It is the usual floor and it should not be crossed without veterinary advice. Below about 1.5 per cent of body weight in forage a horse's gut function and behaviour both suffer, and prolonged restriction is associated with gastric ulceration and stereotypies. Weight loss in horses is managed by soaking hay to remove sugars, by using slow-feed nets to stretch the same quantity over more hours, and by exercise — not by dropping the quantity further.