Couple of observations:
1) This young bull (that had been fed well) was turned out on 15 cows and has lost weight. He may have been standing in knee deep green grass but it does not have a lot of nutrients in it. Orange, TX average rainfall is 64.21 inches per year. A yearling bull needs a little help to keep up, especially as he sheds his teeth.
2). Our weather has been screwy. Big temperature swings. Animals that are stressed are more susceptible to sickness. I know that when running yearling stocker calves, when the day time and night time temperature spread is more than 30 degrees we doctor more animals.
There has been a good bit of good suggestions in this thread. If you are going to own cattle you need facilities to work them (I have worked too many cattle in a trailer because of a lack of facilities). You need to find and develop a good working relationship with a veterinarian in which you have confidence. Work with the vet to develop a herd health program tailored to your operation based on his/her observation of what is going on in the area. Learn about the forages in your area and when/if they need to be supplemented.