The RSPCA has launched an emergency appeal to find foster homes for a "never ending tide" of abandoned young horses.
The charity said it was currently looking after nearly 600 horses and ponies which have suffered neglect and cruelty - a figure which has more than doubled since last year, with almost half of the animals involved being youngsters.
It has launched the "Stable Future" appeal to find fosterers able temporarily to look after some of the 270 animals which are too young to be ridden.
Sally Learoyd, the RSPCA's equine rehoming officer, said: "Over the past year we've seen a huge increase in the amount of horses being disowned or allowed to get into an appalling state because the trade in horses has collapsed."
She added: "I've heard of young horses being sold for £5 - less than the price of a bottle of wine. I've heard of horses being bought and sold in pubs and we've come across a case of someone keeping a horse on a tower block balcony and feeding it on kitchen scraps.
"We have a never-ending tide of young horses coming into our centres. Fostering our youngsters is a way that horse lovers can help us with this problem."
The recession, rising hay costs and irresponsible breeding are thought to be to blame for the rising number of horses being neglected and abandoned.
An RSPCA spokesman said: "We have found new homes for a record number of horses over the past year but we simply cannot keep up with the flood of animals which need our help because of terrible neglect and cruelty.
"We face a huge £3.2 million bill just to care for the influx of ponies and horses which does not include vet bills or prosecution costs.
"To help ease the crisis we are urging people to foster one of our youngsters until it is old enough to be prepared for work and we can find it a new home."
Learoyd added: "Fostering is a great way for people to have the enjoyment of being around youngsters whilst helping us out in the short-term.
"Just like teenagers, these young horses need experience of life, a day to day routine and a guiding hand. Being a fosterer is a really rewarding experience. You can see these youngsters' personalities change and develop as they grow."
The RSPCA has 594 horses and ponies in its care compared to about 290 in April last year - 266 are youngsters.
The charity has seen an increase in the number of equine convictions, calls about abandoned horses and the amount of welfare advice being given out by its inspectors.
It rehomed 240 horses last year - 50% more than the previous year.
The youngsters available for fostering are aged between one and three and all happy, healthy and handleable. They are microchipped, will have passports and tetanus vaccinations.
Foster carers must have experience handling horses, grazing and be able to take in a youngster for a minimum of six months. To apply log on to www.rspca.org.uk/stablefuture or call 0300 123 8,000 for an application form.