Once again, Bob has made an excellent point.As soon as Grant cleared the Wilderness area, he sent Sheridan and the cavalry off on a raid, so they start eating and wrecking the available forage in Virginia. The events that General Lee had worked so hard to avoid in 1863 were about to take place, if he could not expel the US army from Virginia.
He also sent back a large section of the artillery, and its horse teams, back to Washington, where they could sit at the end of the US railroad network, or be mustered out.
Both efforts were designed to do the same thing. Reduced the US demand for oats and hay, so that roads would not be jammed with wagons carrying horse food.
As @Rhea Cole points out, Grant not only decreased the mass of the horse herd supported by the army, but was working hard to control the points from which supplies had to be freighted, to Fredericksburg, White House, and City Point.
Sherman also pointed out in his memoirs that as the distance the horses and mules have to work increases, the forage demand increases at a more than linear rate, and eventually the army can do nothing but haul forage.
A round bale of hay weighs about 1,000 pounds. That is about 70 fourteen pound hay rations. Most everyone who lives in or near a rural area has seen round bales in fields in the last few weeks. An idea of the sheer cubic volume of the fodder that a battery with 125 horses for a month can be made by counting round bales stored in a field. That will open your eyes. Of course, there were no round bales during the CW & there was still the 12 pound ration of grain.
A bushel of shelled corn weighs 56 pounds which equals 4.5 rations. Next time you go to the store to buy dog food, wild bird seed etc. think on how many of those fifty pound bags the AoP went through every day. The sheer cubic volume is a measure of what it took to ship & deliver a day's ration of grain.
Depending on a number of factors, an army wagon normally carried about 3,000 of hay & grain rations. AoP fed 26 pound rations to about 30,000 horses a day which adds up to 780,000 pounds per day. That is 260 wagon loads or a convoy 2 1/2 miles long. Anyone who has ever baled hay or fed stock is asking, 'How the heck did they handle all that hay & grain?'
In order to handle the hay efficiently, they compressed it & bagged it. Hay & grain was shipped in burlap bags that US quartermasters were very insistent be returned. The collection, shipping & redistribution of those bags is one of those nuts & bolts things that made US logistics work.
it is no kind of exaggeration to state that without the manufacture & meticulous recycling of burlap bags the war could not have been won. The source of hemp, the material to make those bags, was Kentucky. Hemp was grown & twisted into twine in huge rope walks, one of which was owned by John Hunt Morgan. It was then twisted into ropes & woven into all kinds of products, including sails for ships.
By holding onto a Kentucky, the Union not only held onto the horse & mules, they also held onto the hemp that made feeding them possible.
Logistics, logistics, logistics... it is ever a source things to ponder.