Our understanding of the pigs nutritional needs

When I ended my 2 year Army enlistment and began graduate school 38 years ago swine nutritionists were just beginning to talk about lysine as a critical nutrient in swine diets as opposed to crude protein. The 1974 version of the University of Nebraska Swine Diet Suggestions extension circular still talked about crude protein requirements assume a corn/soybean meal basal diet.

I remember participating in extension meetings in Indiana where producers still thought that all diets needed to contain some meat and bone meal. The emphasis of many meetings at that time was to convince producers that diets formulated with soybean meal and dical were ok for growing pigs. While the HogCon 40 product from the local feed dealer provided for the pigs needs as known then, there were other options.

Fast forward to today’s nutrition discussions and we’re still talking about soybean meal. However, today’s discussion concerns the possibility of a limited supply next summer and options for SID or TID available amino acids and TTTD or STTD phosphorus.

We’ve come a long way in our understanding of the nutritional needs of pigs. When we combine the improved nutritional understanding with improved housing conditions (a fully slatted barn at 65F in the winter versus a Cargill floor in a snow storm), improved feeders and improved genetics we have the basis for today’s world class pig performance. This past fall I’ve seen quite a few data sets of grow-finish pigs growing faster than 2.0 lb/d. Even with ddgs in the diet, overall feed conversions continue to improve.

On the nutrition side, other than the relatively small world of swine nutritionists, how many producers really understand what we mean when we talk about SID Lysine or STTD Phosphorus requirements as the basis for our diet formulations?

Only a certain proportion of each nutrient in feed ingredients is digested and absorbed by the pig. For amino acids expressing the diet composition in terms of total amino acid content or total lysine doesn’t account for this difference in absorption.

Apparent ileal digestibility (AID) of amino acids is defined as the net disappearance of ingested amino acids. However, this doesn’t account for the amino acids that are lost from the digestive tract due to such things as tissue turnover, etc. Much of the industry now talks about standardized ileal digestibility (SID) for amino acids which is derived by correcting AID by an estimate of endogenous losses. The National Swine Nutrition Guide from the US Pork Center of Excellence and the 2012 National Research Council Nutrient Requirements of Swine both report the requirements for the specific amino acids on a SID basis.

We’ve known for years that the phosphorus in corn had a low availability for swine. This is because the majority of the phosphorus in corn is contained in phytic acid and the pig lacks the necessary enzyme to effectively cleave the chemical bonds of this compound. When we fed corn/soybean meal based diets we added a highly available form of phosphorus – generally dicalcium phosphate or meat and bone meal and talked about a total phosphorus requirement.

The 1995 edition of the Nebraska and South Dakota Swine Nutrition Guide was the first publication from these universities that used the term available phosphorus. This term was used to account for the variation in digestibility of phosphorus from various feed ingredients and the impact of the newly available phytase enzyme on this availability.

Just like was done with amino acids, the new NRC Nutrient Requirements of Swine now talks about standardized total tract digestestibility (STTD) as a more precise measure of the phosphorus needs of pigs while the National Swine Nutrition Guide uses the term digestible phosphorus.

Because we now have better estimates of the ‘real’ requirements we are expanding our range of feedstuffs for swine diets. Assuming we can get an estimate of the SID amino acid content and STTD phosphorus content of a proposed ingredient we now can formulate diets with an expectation of similar performance if formulated to the same standard. We have progressed a long ways in the past 40 years since I began my professional career in the swine industry – I wonder what the next 40 years will bring?

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