Bulls are typically either grossly over-fed or neglected. Overfeeding should be avoided for several reasons. The most recent to come to light is that overweight bulls have lowered sperm production. This is because a layer of fat will reportedly line the scrotum and insulate the testes. This raises the temperature, thereby retarding the development of viable sperm.
Another problem related to overfeeding is liver abscess. Actually, this isn't directly related to being overweight, but a product of sub-acute acidosis. This occurs most commonly with high-grain "growing" rations often fed by purebred breeders and/or centralized bull-test feeding facilities. Since we've discussed these other aspects of bull feeding previously, we'll restrict this column to winter feeding only.
Winter Feeding Is Simple With respect to mature bulls, winter feeding is rather simple. The feed requirements are essentially the same as for a dry cow. The only complication would be if you're fall calving and use bulls for breeding during the winter. In this case they may need additional energy (more on this later).
But for simply maintaining mature bulls, just feed them as you would dry cows. If we want to be technical we can say that bulls don't need as much vitamin A as dry cows, and need somewhat more grass or hay. However, as a practical matter, a protein/vitamin/mineral supplement designed for dry cows will maintain bulls quite nicely, and bulls will simply eat more of whatever grass or hay is provided to compensate for their needs.
Mature bulls need on the order of 24-30 lbs. of mediocre grass hay or dormant grass and, in most instances, 1-11/2 lbs. of a 38-45% crude protein supplement, along with about 15-18 grams of phosphorous and 25,000-28,000 IUs of vitamin A daily. Trace mineral requirements will depend on the area and soil type, but again they will be similar to the cows' requirement.
If we're talking replacement bulls (calves, yearlings or two-year olds) with growth requirements, then additional energy will be required. In that case, analysis of the grass or hay becomes more important in order to precisely determine how much additional supplementation is required.
Likewise, the climate must be considered when contemplating gain. For mild climates, usually 3-4 lbs. of an energy concentrate (in addition to protein) will be required for a bull calf to gain 1 lb./day through the winter. This assumes good-quality range grasses (such as grama grass) or hay. For low quality range grasses (such as tobosa, love grass, etc.) or mature hay, the amount of energy concentrate required can easily increase by 50%, and can double in the case of extremely coarse forage. Cold weather can increase energy concentrate requirement from 1-3 lbs., depending upon the severity.
Fall Calving Recommendations If you're fall calving (breeding during late winter), some energy supplementation of bulls may be desirable, though not obligatory. In the South, if there is green grass (or you are breeding on cereal pastures) energy supplementation would not be required. (Nor would protein, if the grass is green.)
In the North, bulls breeding on dormant grass would definitely benefit from energy supplementation, though failure to supplement energy would not result in a catastrophic problem. (Failure to supplement protein would seriously impede bull potency.) However, the question is academic since cows bred on dormant grass would definitely require energy supplementation, or conception will be markedly decreased (bulls running with the cows would obviously eat whatever supplement is given to the cows).
Caution should always be taken when feeding energy concentrates to valuable breeding stock. Specifically, care must be taken to ensure larger aggressive animals don't eat a disproportionate share, or that excessive amounts in general are not fed. This can create sub-acute acidosis, which in turn can create liver abscess.
Although it has not been proven conclusively, liver abscess could conceivably result in reduced longevity. On occasion, I've been called in on mysterious deaths of cows and bulls which, on necropsy, the veterinarian reported severe liver abscess. In reviewing the nutritional history of the animals, years previously, high-grain rations or supplements were fed.