The effects of dietary protein concentration on compensatory growth in barrows and gilts

An experiment using 120 crossbred pigs (60 barrows and 60 gilts) was conducted to determine the effect of dietary protein concentration on the compensatory response in growth after a period of feed restriction. Thirty pigs were allowed ad libitum (AL) access to one of five corn-soybean meal diets (13.1 to 18.4% CP) from approximately 42 to 102 kg BW. Thirty additional pigs were restricted (R) to a maintenance amount of a 14.4% CP diet for 21 d, after which they were allotted to one of the five diets and allowed ad libitum access to feed until they reached 102 kg. Restricted pigs had lower ADFI, ADG, and ADG/ADFI (P < .05) than did AL pigs. During the postrestriction period, R pigs had higher ADFI and ADG (P < .001) and tended to be more efficient (P < .08) than AL pigs. Average backfat thickness was not different (P > .8) between AL and R pigs. Lean percentage (5% fat) was not affected (P > .5) by feeding regimen but increased linearly (P < .1) as protein level increased. Organ weights (expressed as a percentage of empty BW.75) were similar in AL and R pigs. However, kidney and stomach weights differed among protein levels (P < .01), as did liver weight (P < .06), with a linear increase (P < .02) in both kidney and liver weights to dietary protein level. Barrows had higher ADFI and ADG and greater average backfat thickness (P < .02) than gilts. Barrows had smaller LMA, a lower percentage of lean (P < .001), and higher average backfat (P < .005) than gilts. Liver weight was heavier (P < .02) and small intestine weight tended to be heavier (P < .07) for barrows than for gilts. Kidney, spleen, and lungs were heavier (P < .05) in gilts than in barrows. Livers from barrows tended to contain more protein (P < .06) and less fat (P < .05) than livers from gilts. These results indicate that a compensatory growth response occurred during relimentation, and that the effects of dietary protein concentration on growth rate and carcass measurements were similar in both AL and R pigs.