Tratamiento

Before initiation of this experiment, animal care and experimental protocols were

approved by the University of Missouri Animal Care and Use Committee. Then, a study

involving 64 crossbred (Monsanto genetics) pigs with an initial body weight of 31 ± 1.8

kg was designed to evaluate four dietary treatments (Table 2.1) consisting of a corn-

soybean meal diet and three additional diets containing 15, 30, or 45% DDGS. Diets were

fed to growing-finishing pigs from 31 ± 1.8 kg to 120 ± 3.1 kg body weight in three

phases. Diets were formulated to contain 0.83, 0.70, and 0.58% true ileal digestible (TID)

lysine during the three phases of the study with diet changes made at 60 and 93 kg body

weights, respectively. Diets and water were provided on an ad libitum basis.

The DDGS source (Table 2.2) was supplied by Archer Daniel Midland (Decatur,

IL) and replaced corn and soybean meal. In order to maintain constant TID levels of

lysine and tryptophan, up to 0.22% L-lysine HCl (0.17% L-lysine) and 0.04% L-

tryptophan were added to the diets in each phase. Pigs were randomly allotted to

treatments in a randomized complete block design (RCBD) with a total of four

replications of four pigs per pen with sexes being penned separately. Pens were the

Growth Performance

To evaluate performance of the pigs, average daily gain (ADG), average daily

feed intake (ADFI) and feed to gain ratio (F:G) were determined at periodic intervals and

at the end of each phase. Growth performance traits were terminated on a replication

basis when the pigs in the control pen (Diet 1) of a given replication reached the target

weight of 120 kg. Pens within a replication that did not reach 120 kg were continued on

their respective diets until they reached the target weight. Thus, growth performance

traits were summarized on a constant time basis while carcass data on a constant weight

basis.

Harvest and carcass quality

At the end of the experiment, pigs were humanely harvested using standard U.S.

pork industry practices and USDA/FSIS inspection criteria. After slaughter, hot carcass

weight (HCW) was recorded and carcasses were chilled at 2ºC for 24 h. At 24 h after

slaughter, 10th rib back fat (TRBF), last rib back fat (LRBF), dressing percentage (DP)

and loin eye area (LEA) were determined on the left side of the carcass. Carcass fat free

lean (CFFL) was calculated following the NPPC (2000) equation. Furthermore,

longissimus muscle objective color (L*, a* and b*) was measured using a Minolta

Chroma Meter CR-410 (Minolta Camera Co., Osaka, Japan).

Moreover, by using the method described by Rentfrow et al. (2003), vertical and

horizontal belly firmness was determined. After removal from the right side of the

carcass, spareribs, cartilage and leaf fat were removed and bellies were squared. Next,

bellies were placed, skin side-up, on a polyvinyl chloride (PVC) pipe mounted

measured relative to the grid matrix where a vertical belly flex of zero meant the belly

was completely parallel to the floor and completely stiff while a horizontal belly flex of

six meant that the belly flexed to a point where there was approximately 15 cm between

the ends of the squared belly. Thus, a lower horizontal and a higher vertical flex indicated

a softer, more flexible belly.

Fat sample collection and fatty acid procedure

Fat samples from belly, jowl, and subcutaneous (SUB-Q), and a longissimus

muscle sample (LMS) were collected from carcasses on the day after slaughter to

determination of fatty acid profile and IV. Belly fat was removed posterior to the sternum

and anterior to the teat line on the left side of the carcass. Jowl samples were collected on

the anterior tip of the jowl at the site of head removal. Subcutaneous fat was collected at

the 10th rib while LMS was collected from the longissimus muscle exposed between the

10th and 11th rib. After collection, samples were frozen at -10ºC until analysis was

performed.

The methodology utilized for fatty acid determination was an adaptation of the

methods used by Folch et al. (1957) and Morrison and Smith (1964). At the moment of

the analysis, approximately 100 mg of adipose tissue (or 1 g of muscle) was placed in

glass tube and 5 mL of a solution of chloroform:methanol (CHCL3:CH3OH, 2:1, v/v) was

added to the tube in order to extract lipids. Sample was filtered through a sintered glass

filter funnel fitted with a Whatman 2.4 cm GF/C filter and a solution of 0.74% KCl was

added to the tube at a volume of 8 mL. Sample was allowed to sit for 2 h to separate the

was then, transferred to a glass tube and evaporated to dryness with nitrogen gas in a

heated water bath at 70ºC.

A 1 mL solution of 0.5 N KOH in MeOH was added to the sample and the tube

was placed in a water bath at 70 °C for 10 min. A 1 mL solution of 14% boron trifluoride

(BF3) in MeOH was added to the tube which was flushed with nitrogen, loosely capped

and placed in a water bath at 70 °C for 30 min. After 30 min, sample was cooled to room

temperature and 2 mL of HPLC grade hexane and 2 mL of saturated NaCl was added to

the tube. Next, the upper layer was removed and placed in a glass tube with

approximately 800 mg of Na2SO4 in order to remove moisture from the sample.

Following this, 2 mL of hexane was added to the tube with saturated NaCl and once

more, the upper layer was removed and placed in the same tube with Na2SO4.

The liquid portion was then transferred to a scintillation vial which was placed in

a water bath at 70 °C and the sample was evaporated with nitrogen. A Varian 3,800 gas

chromatographer (Varian, Pala Alto, CA) was used to analyze fatty acid methyl esters;

samples were injected onto a fused silica capillary column (SPTM – 2,560; 100 m x 0.25

mm x 0.2 µm film thickness; Supelco, Bellefonte, PA). The temperature of the injector

and of the flame-ionization detector was held constant at 240ºC and 260ºC, respectively.

Helium was used as the carrier gas at a constant pressure of 37 psi and the oven was

operated at 140ºC for 5 min (temperature programmed 2.5ºC/min to 240ºC and held for

16 min). Fatty acids were normalized which means that the area of each peak was

represented as a percentage of the total area. Iodine value was determined based on the

equation described by AOCS (1998): IV = (0.95 × C16:1) + (0.86 × C18:1n9) + (1.732 ×

(PUFA) and saturated (SFA) fatty acids was calculated using the equation: [(C18:2n6c) +

(C18:3n3)]/[(C14:0) + (C16:0) + (C18:0)].

Statistical Analysis

All performance and carcass data were analyzed using the GLM procedure of

SAS (SAS Inst., Cary, NC) with pen as the experimental unit. Orthogonal contrasts were

analyzed for linear and quadratic responses. Furthermore, correlation analysis among fat

depots for the variable IV was performed by using PROC CORR procedure of SAS. An

alpha level of 5% was considered significant.

RESULTS AND DISCUSSION