I’ll take a bit of exception to the part of your statement implying that cattle are only eating prickly pear and mesquite beans- I drive all over West Texas (well, around and south of the I-20/I-10 line), and the grass is in fine shape wherever it grows. Been plenty of rain out here the last couple of years- I even see water in the Pecos river on a regular basis! :)
This time of year they prefer prickly pear and mesquite beans due to the high sugar content, later in the winter they will eat the pads themselves. I don’t drive through West TX I live in it and we’ve raised cattle on the same family ranch for over 100 years. But your right it has been a couple of good years and we’re up to 25 head a section from a low of 10 back in 2011 during the heavy drought. Most of the grass you see is either Buffalo or Bear grass and the cows only eat it when it sprouts in the early spring. These are weed ranches out here with much of what they eat having a higher protein content than your native grasses. That little Pecos river has turned into a full blown river a few times this month with the recent heavy rains. If you drive West on I-20 you drive right past our place, in fact you drive through it. We have 8 sections Nth of I-20 with the remaining 34 going back straight South. It start on the east side of Howard County and goes South into Glasscock County. Look south for Signal Peak just pass you pass Moss Lake road.