The number of muscle cells in the adult boar is established at birth with postnatal muscle growth involving an increase in their size (hypertrophy). Hence, different feeding strategies or nutrient supplies to the young boar will not alter the number of muscle cells of the young animal nor will it affect what he transmits genetically. Because muscle is the largest body component in the growing boar, growth of muscle mass generally parallels the growth of the whole animal. Improvements in daily gain, feed efficiency, loin-eye area, and lower backfats occur when boars are provided the dietary protein concentration that meets their requirement.
The boar's retention in the herd is largely dependent on the size and the subsequent maintenance of its skeleton. This is largely influenced by genetics, but it is also dependent upon a sound nutritional program during the boar's developmental period. Structural soundness at sexual maturation is essential for optimum breeding performance and subsequent semen production. Grouping young boars during the pre-pubertal developmental period results in fewer feet and leg problems and has also been shown to improve sexual behavior.
Although bone structure is an inherited trait, adequate dietary macro- and micromineral concentrations must be provided for proper bone development. Boars have bones of a greater length and diameter than either gilts or barrows. An increased dietary calcium and phosphorous concentration is therefore necessary for the higher bone mass and bone-mineral content, both of which are essential in withstanding breeding stresses on the legs. An adequate dietary vitamin D concentration will ensure optimum absorption and utilization of calcium and phosphorus. However, an excessive amount of vitamin D may cause calcification of connective tissue and decalcification of bone tissue.
Sexual maturation in the boar is a gradual process, with sexual activity and sperm production starting at approximately four months of age. Testosterone concentration in the blood increases by five to seven months, with "sexual maturity" occurring at six to eight months of age. Semen collected as early as five months of age is at a low volume and contains a high proportion of immature and abnormal sperm. Therefore, the use of boars for breeding should not be initiated too early.
When feed is restricted to the boar prior to puberty, both growth rate and sexual maturity will be delayed without permanently damaging the testes. The seminiferous tubules in the testes, which are the origin of the sperm cells, however, will be reduced in diameter and size.
The practice of restricting boar feed intake during late development to maintain a lower breeding weight has several risks. If the intake of the nutrients is below the boar's requirement, semen quality and quantity may be affected, with bone structure and health compromised. This could result in poor reproductive performance and the premature culling of the animal. The diet must be fortified to supply the required nutrients (Table 13). Because weight, age, body condition, and collection frequency can affect the amount of feed that should be provided, feed intake recommendations are presented in Table 14.
| Table 13. Nutrient Recommendations for Boars (As-Fed Basis). | |||||
|---|---|---|---|---|---|
| Item | Development Phase | ||||
| Earlya | Middlea | Lateb | Matureb | ||
| Body weight, lb. | 50-120 | 120-200 | 200-300 | 300-600 | |
| Protein, % | 22 | 20 | 18 | 16 | |
| Amino acidsc | |||||
| Lysine, % | 1.2 | 1.1 | 1.0 | 0.85 | |
| Tryptophan, % | 0.24 | 0.22 | 0.19 | 0.17 | |
| Threonine, % | 0.86 | 0.79 | 0.68 | 0.58 | |
| Methionine + Cystine, % | 0.72 | 0.66 | 0.63 | 0.54 | |
| Macro-mineralsc | |||||
| Calcium, % | 0.95 | 0.85 | 0.80 | 0.90 | |
| Phosphorus (total), % | 0.75 | 0.65 | 0.75 | 0.80 | |
| Phosphorus (available), % | 0.49 | 0.40 | 0.49 | 0.50 | |
| Sodium, % | 0.12 | 0.12 | 0.20 | 0.20 | |
| Chloride, % | 0.08 | 0.08 | 0.16 | 0.16 | |
| (Salt, %) | 0.25 | 0.25 | 0.50 | 0.50 | |
| Trace-mineralsd | |||||
| Copper, ppm | 15 | 15 | 15 | 25 | |
| Iodine, ppm | 0.15 | 0.15 | 0.15 | 0.15 | |
| Iron, ppm | 100 | 75 | 75 | 100 | |
| Manganese, ppm | 10 | 10 | 10 | 20 | |
| Selenium, ppm | 0.3 | 0.3 | 0.3 | 0.3 | |
| Zinc, ppm | 150 | 100 | 100 | 150 | |
| Vitaminsd | |||||
| Vitamin A, IU/lb. | 2500 | 2000 | 2000 | 2500 | |
| Vitamin D, IU/lb. | 250 | 200 | 200 | 250 | |
| Vitamin E, IU/lb. | 30 | 30 | 30 | 30 | |
| Vitamin K, mg/lb. | 0.6 | 0.6 | 0.6 | 1.0 | |
| Biotin, mg/lb. | 0.10 | 0.10 | 0.10 | 0.10 | |
| Choline, g/lb. | 0.25 | 0.25 | 0.25 | 0.60 | |
| Niacin, mg/lb. | 15 | 12 | 12 | 15 | |
| Riboflavin, mg/lb. | 6 | 4.5 | 4.5 | 6 | |
| Pantothenic acid, mg/lb. | 10 | 7.5 | 7.5 | 10 | |
| Vitamin B12, µg/lb. | 15 | 15 | 15 | 20 | |
| a Assumes ad libitum feeding. b Assumes limit feeding. c Values reflect total dietary concentrations unless noted otherwise. d Values reflect the supplemental level to be added to the diet. | |||||
| Table 14. Feeding Guidelines for Boars. | ||||
|---|---|---|---|---|
| Body Wt. (lb.) | Pounds of Feed for Maintenancea | Target Gain/Day (lb.) | Pounds of Feed for Gainb | Total Feed/Day (lb.)cd |
| 300 | 3.42 | 1.2 | 1.50 | 4.9 |
| 350 | 3.78 | 1.1 | 1.38 | 5.2 |
| 400 | 4.14 | 1.0 | 1.25 | 5.4 |
| 450 | 4.47 | 0.9 | 1.13 | 5.6 |
| 500 | 4.80 | 0.8 | 1.00 | 5.8 |
| 550 | 5.11 | 0.7 | 0.88 | 6.0 |
| 600 | 5.42 | 0.6 | 0.75 | 6.2 |
| 650 | 5.71 | 0.5 | 0.63 | 6.3 |
| 700 | 6.00 | 0.4 | 0.50 | 6.5 |
| a Based on a corn/soybean meal diet. b Assumes 80% efficiency. c Add 0.25 lb. feed/ejaculate. d Add 0.1 lb. feed for each degree temperature below 68 degrees F. | ||||