Amino acids - Among the ten essential amino acids, the most likely to become limiting in low-protein (to avoid scours in antibiotic-free diets) nursery diets are lysine, methionine, threonine, tryptophan, isoleucine, and valine. Glutamine supplementation in early nursery diets may also be warranted on grounds of gut health (about 0.5% additional glutamine can help restore gut health following early weaning). Dietary specifications for essential amino acids are calculated based on a fixed lysine specification and the ideal protein profile. For the latter, most authorities would agree to lysine: methionine & cysteine:threonine:tryptophan ratios of 100:60:65:18.
A reduction of dietary crude protein is deemed beneficial for both the animal (better growth, less diarrhoea problems) and the environment (less nitrogen excretion). Indeed, pigs fed lowprotein diets (less than 21%) have been shown to be less prone to Escherichia coli infection. Low-protein diets have also been shown to reduce nitrogen excretion by 30%-50%, depending on original specifications, ingredient selection, and magnitude of reduction in dietary protein concentration. Crude protein should not be lowered more than 3-4 percentage units (that is, it should not be less than 17%) unless valine (now commercially available) and (or) isoleucine (not available) are added.
Lactose - Piglets love lactose. Indeed, research has shown that in the first couple weeks post-weaning their feed intake and growth increases linearly with dietary lactose concentration up to 50% (at which levels, lactose causes severe secretory diarrhoea!) In more practical terms, inclusion of 10%-20% dried whey in simple diets has consistently improved growth performance by at least 15%-30%. Several studies investigating minimum dietary lactose concentrations in weaned pigs suggest that dietary lactose concentrations can be rapidly lowered after the initial two weeks post-weaning, whereas for pigs over 12-15 kg body weight there are no real benefits from lactose.
Vitamins and minerals - For vitamins and minerals, including trace minerals, the recommendations of BSAS (2003) provide a practical compromise between levels recommended by manufacturers and those established under research conditions. Nevertheless, there are cases where these levels can be reduced or increased. For example, vitamin E is often included at levels up to 250 IU/kg because of (potential) health benefits, whereas recent research has clearly demonstrated that NRC (1998) levels are inadequate. From minerals, calcium is the least expensive nutrient and as such, many low-cost formulas tend to be over-fortified with it; some containing over 1% Ca. Calcium carbonate, however, has such a strong buffering activity that significantly lowers the acidity of the stomach and, thus, interferes with protein digestion. It is strongly recommended, therefore, that dietary calcium specifications do not exceed actual requirements and that calcium to phosphorus ratio be no more than 1.2:1.
Research has also revealed that piglets clearly benefit from additional sodium and chlorine in their feed. It is thus, recommended that starter diets for pigs less than 10 kg contain about 0.4% Na and at least as much Cl.