although artillery would take good care of their horses, it was not always possible during the war.
just a few observations on horses from an artillery standpoint:
Chickamauga was a battle with a large loss of horses. Due to the terrain, the artillery action was at very close quarters (at times exchanging canister between batteries). both sides lost a large number of horses, and many guns changed hand multiple times as the lines moved since they did not have enough horses to take the artillery with them when they had to retreat.
Capt. Goodspeed of 1st Ohio Battery A wrote "Horses wounded 15, and in consequence of not unharnessing for six days and the hardship they have undergone, I will lose 25 more horses"
Pvt James Walker of Battery A wrote "any amount of horses starved to death at the picket rope for want of food"
these losses were not due to neglect, but the realities of combat on the battlefield - the need for continuous
movement and the logistical problems of providing feed.
As far as feeding horses, I did some calculations and the logistics would be even difficult today.
From the field artillery manual regarding horses:
"The Daily allowance of oats, barley and corn is 12 pound;that of hay, 14 pounds."
One Battery would have 120 horses (for mounted. For horse artillery, add about 75 more)
Per Day for a battery:
Oats, barley and corn: 1440 Pounds
Hay: 1680
a modern square bale of hay weighs about 40 pounds.
a modern bag of grain 50 pounds
Per Battery
42 bales of hay
29 bags of feed
At Gettysburg there were approximately 65 union artillery batteries.
65 * 120 horses = 7,800 artillery horses
65 * 1440 Pounds of oats,barley and corn= 93,600 pounds/day
65 * 1680 pounds of hay= 109,200 pounds/day
in modern square bails: 109,200/40=2,730 bales of hay/day
modern bags of feed; 93,600/50= 1,872 bags of feed/day
plus add in water
plus, what goes in eventually comes out - don't know how many pounds come back out of the horse, but for that many horses, that's still a major problem to clean up.
The reality is that there is no way that could be provided. Living off the land was not possible (that many horses would have the ground stripped to dirt within days.)
as far as wounded horses, artillery drivers were issued pistols and a large knife. If a horse was wounded during a battle, it would be shot, and the harness cut away so they could keep going. the last thing they needed was a wounded horse thrashing around in the harness, possibly injuring the drivers or other horses. during battle, they had to keep moving. Not nice things to think about, but it was the reality of the war.