Most "fruiting" mulberry trees/shrubs sold are grafted to ensure a flavorful fruiting variety (exactly the same genetically as the parent).
You could dig up the free seedlings and use them as rootstock.
Here is the list I have come up with for plant to use for chicken feed- please add to it if you can!
PLANTS FOR SOWING IN ROTATION
Sunflower, amaranth, corn, millet, buckwheat, chickpea, sorghum, wheat, oats, barley, clover
TREES and SHRUBS
peach,
banana (chop up the stems),
fig,
jaboticaba,
grumichama,
Brazilian cherry,
pears
Black Locust- Robinia
Honey locust (pods are high protien and tree is nitrogen fixing)
Cornus,
sorbus,
Nanking cherry
Sand Cherry
Siberian Pea Shrub- Carragana spp.
Apple
Plum
Raspberry
Mulberry (fruit is relatively high protien)
Sea Buckthorn
Apricot
rosa rugosa
Plums
Raspberries
Gooseberries
Saskatoon (Service berry)
Sea buck thorn
Sand cherry
persimmon, pawpaw, feijoa, strawberry guava, tamarillo, custard apple,
GREENS and/or SEEDS
dandelion (Taraxacum officinale)
plantain (Plantago spp.) (high in calcium for chickens)
chickweed
arrowroot,
New Zealand spinach syn. - Tetragonia tetragonoides,
nettles,
brassicas (radishes, mustards),
alfalfa,
clovers- Strawberry clover, Ladino Clover, White Dutch Clover, Red Strawberry Clover
chicory,
purslane
Buckwheat,
black oats,
Perennial Cereals
pumpkins,cucumber
squash
Sunflowers,
amaranth,
corn,
chard, cabbage, kale,
spinach, lettuce, broccoli...in fact any of the green leafy vegetables.
sesame, sunflower,
pigeon pea
Flax,
Birdsfoot Broadleaf Trefoil,
Red Cowpeas
Strawberries
Radishes
corn salad
lambs quarters
dock (Rumex spp.)
Vines
chayote,
passionfruit
grapes
peas
climbing spinach- Ceylon Spinach
Herbs
Bergamot
Clary sage
Nettles
Yarrow
Comfrey (limited portion of diet- liver toxin)
borage (self-reseeds freely)
Feverfew
Wormwood (Artemesia absinthe)
rue (Ruta graveolens)
POND PLANTS
Lemma