Sheep manure has a high nitrogen content but lower ratio in the other macro-nutrients; however, its pellet size makes it a quick waste to compost. Horse manure takes longer and has similar content to cow manure but its larger size and the weed seeds the animal digests means it takes much longer to age and compost.

Ruminants are better at nutrient extraction than horses, and a usual benefit of that is destruction of seed. But the quality of manure in any case will be determined by what the inputs are. If the horse (s) are eating differently than your cattle, the manure will give your compost a potentially broader range of desired substances.