REDUCING LOSSES THROUGH DIET MODIFICATION – SWINE
Theo van Kempen, North Carolina State University, Raleigh, NC
Scope of problem:
The efficiency of nitrogen utilization under production conditions is approximately 30%
for wean to finish pig operations, and 25% for farrow to wean operations. An estimated
70% of nitrogen is excreted as urinary nitrogen, which is prone to ammonia emission.
The remainder is excreted in feces predominantly as undigested protein, endogenous
material, and bacterial biomass.
Nutritional means for improving the efficiency of nitrogen utilization:
 Feed waste: assuming 5% feed waste on average, 7% of waste N is derived from feed
waste. Feed waste should be reduced with proper management and feeder design.
 Maximizing apparent digestibility of feed: through selection of highly digestible/low
fiber feed ingredients, processing, and enzyme treatment the N digestibility in feeds
can be improved.
 Precision nutrition: through optimally matching the nutrient yield of the feed with the
nutritional requirement of the animal, substantial reductions in waste N are possible.
Example strategies are phase feeding, split sex feeding, and using a larger number of
feed ingredients including synthetic amino acids to reduce dietary excesses of amino
acids.
Feed formulations should be optimized from an environmental standpoint, thus taking
into consideration that the animal responds in a diminishing returns fashion to
increments in nutrients. Diets that are nutritionally sub-optimal may actually be
preferred economically and environmentally.
Feeds should be manufactured using appropriate quality control, thus after
quantifying the digestible amino acid content of feedstuffs and properly weighing and
mixing feed ingredients. Variation in feed quality is an important reason for waste N.
Nutritional means for reducing ammonia emission:
 Through following the above guidelines for reducing nitrogen excretion, ammonia
emission is reduced proportionally.
 Ammonia emission can be reduced through the addition of non-starch
polysaccharides. Fermentation of this leads to the conversion of ammonia to bacterial
protein and results in a lowering of excreta pH, both factors that lower ammonia
emission. Fiber, though, lowers nitrogen digestibility and may augment odor.
 Ammonia emission can be delayed through a reduction of excreta pH. Excreta pH is a
function of the acid-base balance of the feed and can also be lowered through the use
of feed additives such as benzoic, adipic, or phosphoric acid.
Bottom line:
Through nutrition, nitrogen excretion can be reduced 20 to >30% but under many
conditions this is only possible if an increase in production cost is acceptable. Reductions
in ammonia emission are easier to achieve, particularly through manipulation of excreta
pH but also through reductions in nitrogen excretion. Reductions of 30 to >50% are
possible.