I did notice a sprinkler head in one pic. Is there a way to irrigate? 

The sheep you have, how many? and how long do you keep them in each pasture? Sheep are very effective grazers,, they will eat grass right down to the dirt if given 1/2 a chance. Animals are p&$$ poor efficiency harvester's...  As a suggestion, short of irrigation,, fence off your pastures (according to the number of animals you have) so the sheep are on any one pasture no longer than maybe 10 days,or the majority of the grass is eaten down to 2-3 inches,, then move them to the next pasture, same routine next pasture, etc...

Cows eat only about 1/2 of what they walk all over, sheep are no better.. I did see some trails in the pastures.  You want to avoid that as much as possible. If they're walking they're not eating,but stomping down the grass instead. I know they need water,, but pasture wise,, it's better to bring the water to the animals instead of them walking to the water. When the grass is no more than 5-6 inches high move the sheep onto the pasture.  The picture everybody has in their minds of chest high grass and animals standing there eating away only makes for a nice picture.  Cows or sheep,etc.. like the nice young tender stuff not that nasty old tall grass. They just stick their heads down and eat the tender grass the rest gets stomped flat.

Idealy,,if you can sprinkle,, soon as the sheep are moved off a pasture even 12 hours of sprinkling would give your pasture a tremendous shot in the arm.  If possible 7-10 days grazing then 3-4 weeks for the pasture to recoup..

Pasture's are like underwear,, it's best if you change them frequently.

What is or isn't possible depends on your specific situation. But, this would be optium conditions.