I have never been involved with horses, so I can't speak to what else you could grow with roses because I don't know what plants are toxic to horses.

I have grown albas in shaded areas. My experience with them is that they will still bloom as long as they get at least some sun during the day. They will not bloom their best. To get the hundreds or thousands of blossoms a big alba is capable of producing you need fertile soil, sufficient water, and full sun, but even with less than half a day of full sun if the alba is getting the water and nutrients it needs it will give you flowers.

My York Rose grew on the southeast side of my townhouse, spending a decent chunk of the morning in the dappled shade of a flowering cherry tree, and after mid-afternoon in the shade of the townhouse, but even so I got a nice display of flowers (& autumn hips) from its big, arching canes.

(Unfortunately it died during a freak winter we had a few years ago where the temps. stayed warm into January (into the 60's!!), and then suddenly became brutally cold in early Feb. :((( )

As a young man I lived with my parents in the Philadelphia area. There I grew Maiden's Blush on the west side of their house (where it was also shaded by tulip poplars). It also bloomed, although as I indicated, not as heavily as it would have in full sun.

I have two Madame Plantier albas, one in mostly shade and one in full sun. The one in the shade is not worth having at all. Blooms a little, but not worth the real estate. The one in full sun is a happy camper.

Here's a website that lists plants non-toxic to horses. I have no idea what would work in Zone 4, but I'd pass on the rose in the shade idea if I were you.

Here is a link that might be useful: Plant lists for toxicity to horses.

I, on the other hand, had a 'Mme. Plantier' growing in part shade, and it flowered splendidly. The Albas in general will take a good deal of shade and still grow and flower well, though, as York Rose says, not as well as when cultivated under ideal conditions.
Melissa

In my experience, it all depends on is it shade from deciduous trees and they get a lot of sun in winter/early spring or it is a shade from building or other permanent shade. Just summer shade is fine for many oncebloomers including Albas. They perform well for me in these conditions. Permanent shade year round is completely different matter. They need sun, I guess when they set their flower buds.
Olga

All of my Albas thrive in shade.
This is 'Alba Semi-plena' after 3 years on the North side of my house. It gets about 1 hour max of dappled sunlight in the evening, otherwise it's in full shade all day. The new growth reached the roof line this year. It also gets beautiful bright red hips in the fall. The horses will probably love those since they have a slight apple flavor. No need to ever spray, it's very clean all season. I bought it bareroot from Pickering Nursery in Canada.

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Most roses cannot stand competition from tree roots.

Thank you for all the responses and Brother Cadfael, thank you for the beautiful pictures. The shade is on the east side of a single story house, no trees, and there is probably four to five hours of sun in the morning.

I think the Albas will do very well there after reading your comments :)

I have used albas for trellises. Could you perhaps wind clematis vines through your alba bushes? Albas are very healthy; for me they suffered no ill effects at all from having morning glory vines draped over them through the summer.

I have several roses with only 4-5 hours of sun in the morning at most; one Königin von Dänemark, one Felicite Parmentier and three Souvenir du Dr Jamain. They grow and flower well. However I have a few albas in full sun all day and they are larger, denser plants in comparison.