Why a sudden swap upsets the hindgut
A horse does not digest hay by himself. The fibre is fermented by an enormous population of microbes in the hindgut, and that population is specialised — tuned over weeks to the particular mix of grasses, maturity and sugar levels in the hay it has been receiving. A new batch, even a good one from the next field over, arrives with a different profile: cut at a different stage, richer or stemmier, drier or leafier. Swap overnight and the existing microbes cannot process the new forage at full efficiency while their replacements multiply, and the horse shows you the gap — loose droppings, gassy discomfort, hay left uneaten, in the worst cases a colicky evening. Nothing was wrong with either hay. The change was simply faster than the biology.
The blending ladder
The remedy is to make the change in steps small enough for the microbes to follow. Start by filling nets and racks with about three-quarters old hay to a quarter new for a few days, mixing the two through each net rather than layering them, so every mouthful is a blend. Move to half and half for a few days, then three-quarters new, and only then feed the new batch on its own — roughly a week to ten days from first blend to full changeover. Horses with sensitive digestion, older horses, and any horse who has had digestive trouble before get the slower version: smaller steps, longer at each. Keep everything else constant during the changeover week so that if droppings do change, you know the hay is the variable.
Check the new bales before the first blend
Blending cannot rescue bad hay, so the inspection happens before any of it reaches a net. A good bale smells sweet and clean when opened; mustiness, visible mould, white or dark dust clouds on shaking, and a sour or tobacco-like smell all condemn it, and suspect bales go back or go on the bonfire, never into a blend in the hope of diluting them. Shake out a slice and look for weeds, thistles and litter, and note the texture — a much stemmier or much richer batch than the old one deserves the slowest ladder you have. Store the new stack under cover, off the ground, and use opened bales promptly.
When the old hay runs out early
Plans meet reality when the last old bale is gone before the ladder is climbed. If you are forced into a faster change, cushion it: feed the new hay in smaller, more frequent nets rather than two large ones, keep turnout and the rest of the routine steady, watch water intake and droppings closely for several days, and make sure every horse is actually eating the new forage rather than picking out a protest fast. Throughout any changeover, the horses to watch hardest are the ones who go quiet, leave feed, or pass very loose droppings — those signs earn a call to your vet rather than a wait-and-see. Because the ladder only works when everyone filling nets blends the same proportions on the same days, KinsLe's Care Teams carries the changeover as a dated sequence of duties in each horse's routine, so Monday's feeder and Thursday's feeder are climbing the same ladder.