Document Type

Dissertation - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

First Advisor

George W. Libal


Two experiments were conducted to determine the lean growth potential of finisher pigs as affected by dietary nutrient level and lean growth indicators determined during the grower phase. Lean gain (with 5% fat) was computed using the NPPC (1991) equation in order to sort contemporary pigs into high (HLG) and low (LLG) lean gain types by the NPPC formula. Plasma urea nitrogen concentration (PUN) was also used as a criterion to sort pigs into HLG and LLG types based on the principle of an inverse relationship between PUN concentration and lean gain per day (LGPD; Exp. 2 only). Only pigs with at least one standard deviation (±) from the mean LGPD or PUN utilized as HLG and LLG, or low (LPUN) and high (HPUN) concentration for the finisher phase. Pigs with less than one standard deviation from the mean LGPD or PUN concentration were discarded. Experiment 1 included two trials with a combined total of 220 grower pigs from which 68 pigs were sorted for HLG, LLG and medium lean gain (MLG). The objectives of this experiment were 1) to determine the efficacy of sorting contemporary pigs into groups based on HLG and LLG potential determined during the grower phase by a combination of weight change and composition of growth determined by the NPPC formula; and 2) to evaluate the effect of pig gender and dietary protein level on the lean growth performance and carcass characteristics of these selected groups between 60 to 100 kg live weight. In Trial 1, pigs sorted for high lean gain gained faster (P = .02) and had less 10th rib fat depth (FAT; P = .08) during the finisher phase. Type of lean gain had no effect (P > .10) on lean gain per day (LGPD) or on other carcass measurements during the finisher phase. Barrows gained faster (P = .02) than gilts, however, there were no gender differences (P > .10) for LGPD or carcass characteristics. Average daily gain was greater (P = .08) for pigs fed high protein (HP); however, protein level had no effect (P > .10) on other pig performance. In the second trial, type of lean growth determined during the grower phase affected LGPD during the finisher phase with HLG pigs having greater LGPD (P = .004) than LLG pigs. Medium lean gain (MLG) pigs consumed more feed (P = .07) than HLG or LLG pigs. High lean gain pigs had larger LEA (P = .0001) than MLG or LLG pigs. In Trial 2, barrows fed either HP or LP during the finisher phase gained faster (P = .03) than gilts fed LP. Gilts fed HP had greater LGPD (P = .02) and greater G/F (P =.007) than gilts fed LP. Barrows consumed more feed (P = .0002), gained faster (P = .001), had greater FAT (P = .0001), lower G/F (P = .03) and smaller longissimus muscle area (LEA; P = .0002) than gilts. Pigs fed HP had greater LGPD, larger LEA (P = .07), and higher PUN concentration (P = .0001). However, the level of protein in the diet had no effect (P > .10) on other pig performance. Objectives of the second experiment were I) to determine the efficacy of sorting contemporary pigs into groups based on HLG and LLG types by the methods described for Experiment 1 or based on LPUN and HPUN; and 2) to evaluate the effect of pig gender and dietary energy level on LGPD and PUN during the grower phase. The second experiment involved 160 pigs from which pigs were independently sorted for LGPD by the NPPC formula or by PUN concentration during the grower period. These pigs (49 by each selection criterion) were evaluated for lean growth during the finisher period. During the grower phase, gilts gained faster (P = .04), had greater LGPD (P = .009), greater G/F (P = .05), and larger LEA (P = .03) than barrows. Feed intake, FAT, and PUN concentration were not affected (P > .10) by pig gender. Pigs fed high energy (HE) level had greater G/F (P = .004) and lower PUN concentration (P = .05) than pigs fed low energy (LE) level. However, dietary energy level had no effect (P > .10) on LGPD, ADFI, or FAT depth during the grower phase. Gilts fed LE during the grower phase had larger LEA (P = .006) than gilts fed HE or barrows fed either HE or LE. In the finisher phase all traits measured except HCW were affected by the type of lean gain potential for pigs sorted by the NPPC formula. Pigs sorted as HLG during the grower phase exhibited greater lean gain during the finisher phase than those sorted for LLG. Gender differences existed for all performance and carcass traits except for HCW. For pigs sorted by formula, LLG barrows had greater FAT and smaller LEA (P = .07) than either LLG or HLG gilts or HLG barrows. There were no other interactions (P > .10). High lean gain gilts had the least FAT (P =.07) compared to all others. Pigs sorted for LPUN or HPUN during the grower phase had high lean and low lean gain, respectively, during the finisher phase. Pigs sorted for LPUN had greater LGPD (P = .007), less FAT (P = .02), less backfat depth (BF) (P = .002), and larger LEA (P = .05).

Library of Congress Subject Headings

Swine -- Growth
Swine -- Feeding and feeds




South Dakota State University



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In Copyright