Yes there is a difference between cow and horse manures. It has to do with their stomachs and how it's digested. Cow is just fine to over cover a lawn and work into a vegetable garden soil. It is NOT good for roses unless it is WELL rotted. Burying it in the soil, particularly soil which doesn't drain, can easily lead to it souring and the plant rotting. NEVER bury garbage in a rose hole. Organics digest best where soil temps remain in at least the 70 F degree area; there is sufficient oxygen, moisture and available nitrogen to get the soil bacteria activated. Burying organic material under ground and introducing water generates methane. Many landfills are piped for methane so it can be used as a fuel. Our local hospital has been run mainly on the methane our landfill generates for years. Personally, I would remove the rose planted with cow manure, empty the planting hole and refill it with the clay and garden soil with no cow manure. If you can't obtain horse manure, then use whatever other organic mulch you have available...compost, ground redwood, ground fir, pine, etc. Oak leaves are great, pine straw can be used. Just keep the mulch away from the crown of the roses and out under the drip zone where the water falls off the plant when it rains. That's where the feeder roots will be most concentrated .
You should dig a hole the size of a five gallon nursery can, fill it with water, then time how long it takes for the water to drain out of it. A couple of hours should be fine. A day and longer spells trouble. Anything organic in standing water will quickly sour. That souring KILLS plants. Plant roots require oxygen. The "sour" is the growth of anaerobic bacteria, those which grow in the absence of oxygen.
