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 c onducted to determine the effect of dietary protein concentration on t he compensatory response in growth after a period of feed restriction. Thirty pigs were allowed ad libitum (AL) access to one of five corn-s oybean meal diets (13.1 to 18.4% CP) from approximately 42 to 102 kg B W. 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 reache d 102 kg. Restricted pigs had lower ADFI, ADG, and ADG/ADFI (P <.05) t han 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 feedi ng 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 p rotein levels (P <.01), as did liver weight (P <.06), with a linear in crease (P <.02) in both kidney and liver weights to dietary protein le vel. Barrows had higher ADFI and ADG and greater average backfat thick ness (P <.02) than gilts. Barrows had smaller LMA, a lower percentage of lean (P <.001), and higher average backfat (P <.005) than gilts. Li ver weight was heavier (P <.02) and small intestine weight tended to b e heavier (P <.07) for barrows than for gilts. Kidney, spleen, and lun gs were heavier CP <.05) in gilts than in barrows. Livers from barrows tended to contain more protein(P <.06) and less fat(P <.05) than live rs from gilts. These results indicate that a compensatory growth respo nse occurred during realimentation, and that the effects of dietary pr otein concentration on growth rate and carcass measurements were simil ar in both AL and R pigs.