A recent research trial, reported in the Journal of Animal Science, evaluated how pigs housed in over-crowded conditions would respond to increased dietary amino acid levels.

Regularly measuring grow-finish feed intake allows producers to generate farm-specific feed intake curves. Abrupt changes in voluntary feed intake can alert producers to potential changes in herd health and/or negative weather effects.

If feed intake levels are lower than expected due to disease outbreaks, crowding or heat stress, some experts recommend increasing dietary amino acid concentration by using synthetic amino acids or protein sources. This increase is recommended to maintain minimum daily amino acid intake levels, which are thought to improve performance without hurting profitability.

"In our opinion, this concept has been insufficiently documented with appropriate research trials," says Michael S. Edmonds, vice president of swine nutrition with Kent Feeds, Inc., and lead researcher on this project.

Kent Feeds research staff designed trials in which pigs were provided with adequate square footage (from 4 to 8 sq. ft./pig in uncrowded conditions, compared to crowded pigs with less square footage (from 2.5 to 5.4 sq. ft. /pig). "Feed intake is reduced by crowding pigs, therefore, we were able to evaluate how pigs with acceptable and lower feed intakes due to crowding stress would respond to increasing the protein (amino acid) level in the diet," Edmonds explains.

Uncrowded grower pigs in the trial (between 40 to 120 lb.) received 4-5 sq. ft./pig compared to crowded grower pigs which had 2.5 to 3 sq. ft./pig. Space was increased as pigs grew. Pens of crowded or uncrowded pigs were fed either 15.7% (low), 18.2% (medium) or 20.7% (high) crude protein. Lysine levels were 0.98, 1.16, and 1.34% for the low, medium and high crude protein diets, respectively.

The diets were formulated by using corn and multiple protein sources, along with vitamins, minerals, amino acids and medication. PIC genetics were used. The pigs were housed in a mechanically ventilated, grower-finisher building with fully slotted floors at the Kent Research Farm. When slaughtered at 280 lb., these mixed-sex pigs had a fat-free lean index of approximately 49.5% with a last-rib backfat of about .95 in.

Average daily feed intakes, for both uncrowded and crowded grower pigs fed the different protein diets, are shown in Figure 1. Crowded pigs consumed roughly 6% less feed than uncrowded pigs.

Crowded pigs grew considerably slower than uncrowded pigs. (Figure 2). Growth rate improved similarly for the uncrowded and crowded pigs when fed the medium protein level compared to the low protein level.

"Note the uncrowded pigs had even greater growth rates from the high level of protein, whereas the crowded pigs did not respond," Edmonds states. "We found increasing the amino acid concentration for pigs with lower feed intakes (in order to retain minimum amino acid intakes per day) did not improve the growth rate as much for the crowded pigs versus uncrowded pigs."

Both the crowded and uncrowded pigs had improved feed efficiencies resulting from being fed the medium protein level (Figure 3). Only the uncrowded pigs continued to have improved feed efficiency when fed the highest level of protein.

The crowded pigs clearly did not have better gain and feed efficiency from being fed the diet with the highest level of protein.

Economic data are shown in Figure 4. Feed cost/lb. of gain was similar for the uncrowded and crowded pigs fed the low or medium protein levels. At the highest protein level fed, the uncrowded pigs had a lower cost/lb. of gain than crowded pigs.

A better economic tool for comparing profitability is net return (value of gain minus feed cost of gain), according to Edmonds. Because of the improved growth rate and lower cost/lb. of gain, the uncrowded pigs (at all dietary protein levels) had a net return advantage.

"Based on this research, we believe crowded pigs have a lower amino acid requirement when expressed as grams per day than the same genetic line that is uncrowded and has a higher feed intake and growth rate," Edmonds says. "Therefore, the amino acid requirements would be similar for crowded and uncrowded pigs when expressed as a percentage of the diet."

Researchers: Michael S. Edmonds, Bruce E. Arentson and Glen A Mente, Kent Feeds, Inc.