Please

At a minimum if they are being left outside for a good portion of the day at least an acre for a pony and 2 per horse

Normally 2 acres per horse for grazing purposes. It varies from state to state as far as the laws go, but 2 per is the norm.

You must have at LEAST 1 1/2 acres. Having at least 2 is better.

The actual law where l am is 1 acre per large animal. So 1 horse, 1 acre, etc.

You also have to check your own zoning area to see if there are any laws to follow as well so it does not just go by your state, it might go by your county.

The new law is 1,000 lbs per acre. That can mean one horse per acre, or two 500 lb ponies per acre.

Generally, in most places, its about 1 acre per pony and 2 per horse, at least. I'd recommend 2 or more per horse.

You should have no less than 1 acre per horse however if they are having to live outside feilds should be changed around every 4-5 months.

Most places r ''2 acres for the first horse & 1.5 acres for each after that. This does not include the area of the barn or arenas. It must be the grazing area''

This is what l found for a specific for PA
Whether or not it is been changed (source outdated?) u will need to contact ur town hall & see what they say.

''Lot Size Requirements - The minimum lot size
required for the zone in which the use is located must
be met. In addition, a minimum of one (1) acre of land,
exclusive of buildings & impervious surfaces, must
be provided for the first two (2) Animal Units which
are housed or pastured on the lot. One (1) additional
acre of land shall be provided for each additional
Animal Unit, beyond the two (2) permitted on the first
acre, which is to be housed or pastured on the lot.
Notwithstanding the acreage available for the domestic
livestock use, no more than eight (8) individual
animals shall be permitted, regardless of size, weight,
or species.
(The purpose of specifying a maximum number of
animals is twofold: for large animals such as horses, to
limit the scale & impact of the use and, in the case of
smaller animals such as chickens, ducks or pigs, to
minimize the potential for the transmission of diseases
to which such animals r susceptible. Other regulatory
options might include: (1) The total number of animals
permitted might vary, depending upon the density of
dwelling units permitted & other applicable
regulations of the zoning district. (2) Conceivably, the
maximum number of animals permitted could be
scaled according to the size of the animals.
The land designated as acreage for each Animal Unit
shall be used exclusively for the animal(s) of the
domestic livestock use proposed, & such open area
shall be maintained entirely in vegetative cover. Wood
lots & forested areas shall not be included in the
calculation of the open acreage required for an Animal
Unit(s). Further, domestic livestock shall be prohibited,
by fencing or other measures, from occupying or
grazing within wood lots & forested areas.''

http://lebcounty.org/lebanon/lib/lebanon/lccp_appiii_36_zoning_guidelines_for_permitting_domestic_livestock_uses.pdf