In a large bowl, dissolve yeast in warm water. Add squash, milk, eggs, butter, sugar and salt; mix well. Gradually add 3-1/2 cups flour; beat until smooth. Add enough remaining flour to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 6-8 minutes. Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch dough down. Shape into three loaves; place in greased 8x4-in. loaf pans. Cover and let rise until doubled, about 30 minutes.
Bake at 375° for 25-30 minutes or until tops are golden. Remove from pans to cool on wire racks.