Source: Alberta Agriculture and Forestry, http://www.agric.gov.ab.ca/
Winter is the time to properly feed bulls for the coming breeding season because bull fertility has a major impact in determining whether a cow will conceive and calve early or late in the calving season and influence calf weaning weight and uniformity. Because of the high (1:25 to 1:50) bull:cow ratio used for natural service, the fertility of the bull is much more important than in any individual cow. Fertility is 5 and 10 times more important than growth performance and product quality.
Nutrition is the main factor which influences their fertility so that they do not have impaired sex drive (libido) due to being either too fat or too thin. The target of the feeding program is to allow the bulls to reach a moderate body condition score of 3 to 3.5 at breeding time (see Table 1 ). To attain a body condition score of 3 to 3.5 involves knowing the rate of gain needed to achieve that score. Table 2 details target weights and daily gains necessary for growing bulls to achieve their full breeding potential.
Diet recommendations for growing yearling bulls are designed to result in a growth rate of 3.0 to 3.5 lbs per day. The following are targets to aim for when balancing rations:
- Dry matter (DM) intake – 2.7% of bodyweight at 500 lbs; 2.5 % of body weight at 1200 lb.
- Energy – % Total Digestible Nutrients (TDN) – 67.5% to 68.5% (DM basis).
- Crude Protein – 13.5 % to 14 % (DM basis).
- Calcium – 0.55% (DM basis)
- Phosphorous – 0.40% (DM basis).
- Calcium to Phosphorous ratio – within the range of 2:1 and 7:1
- Ensure that all trace minerals are adequate and vitamins A D & E are adequate.
Use a good quality alfalfa-grass hay or cereal silage and coarse ground or rolled barley or whole oats for feeding growing bulls. A protein supplement may be required or 2 to 3 lbs of feed peas, or lentils may be used to supplement protein. Feed an ionophore to improve feed efficiency and to reduce the potential of bloat occurring. Feeding the grain/supplement mixture in two equal portions each day is another practice to reduce the risk of bloat. The above growing ration recommendations should provide an excellent opportunity for development of the frame and muscle of growing bulls without fattening them.
Winter feeding bulls that are 2 or more years old at breeding should be geared to reach the optimum breeding condition when they are put with the cows. If you calve in January-February, supplementary winter feeding of thin bulls (score of 2 or less) for gains as in Table 2 may be necessary. On the other hand, if breeding to calve in April-May, it may be possible to winter feed the same bulls at nearer a maintenance level and depend on spring grass to bring up the condition by breeding time. Judgement on the exact level of winter feeding needed depends on the condition of the bull as he goes into the winter.
There is no advantage to shoot for high rates of gain in growing bulls by feeding large amounts of grain. Do not coerce growing bulls to attain their maximum mature weight by overfeeding. Bulls that attain a moderate body condition score at the target weight for age for their breed have fewer breeding problems than bulls that have been over-fed and thus are too fat for their weight.
Table 2. Target Weights and Daily Gains for Growing Bulls