IMPROVING BACON QUALITY IN LEAN GENOTYPE SWINE:

 EFFECTS OF DIETARY FAT AND SUPPLEMENTAL CLA

 

L. Averette Gatlin, M.T. See, J. Odle, and D.K. Larick

 

Summary 

Nutrition, genetics, management and pork processing techniques influence belly quality.  Slicing of pork bellies for bacon can be hindered if the belly is thin or has soft fat composition.  Combining extreme leanness in the pig with diets composed of cereal grains and supplemented with soft fat that is often high in polyunsaturated fatty acids (PUFA) in order to maximize grow-finish performance and efficiency can result in soft fat composition.  Tallow has a lower linoleic acid content compared to higher IV fats (ex. choice white grease) which can improve fat firmness.  Other researchers have recently shown that conjugated linoleic acid (CLA) has similar effects on pork fat quality.

 

Our data show that tallow and conjugated linoleic acid will significantly reduce the iodine value (IV) of belly fat and have an additive effect when supplemented together.  This combination can enhance the value of tallow as a fat source.  We did not detect any negative effects of tallow or CLA supplementation on growth, feed intake, feed efficiency or carcass quality.  Both tallow and CLA addition increased the saturation of belly fat and when supplemented together resulted in a reduction of the IV to 62.

 

Introduction  

Significant increases in belly firmness and positive improvements in belly fatty acid composition have been measured in pigs fed saturated fats (Averette et al., 1999).  Tallow (IV = 40) is a saturated fat source that has been shown to reduce linoleic acid content of adipose tissue when fed to pigs.  Supplementation of unsaturated fat sources such as sunflower oil leads to extremely high amounts of linoleic acid in backfat samples (Viljoen and Ras, 1991).  Similar results were obtained in bacon samples when pigs are fed diets containing extruded full-fat soybeans (FFS) (Leszczynski et al, 1992).

 

Recently, researchers have also shown significant improvements in belly firmness when swine diets were supplemented with conjugated linoleic acid (CLA) (Theil et al., 1998; Eggert et al., 1999a, b, c) without negatively impacting ADG or feed conversion.  Therefore, we tested the hypothesis that supplementation of a more saturated fat source (tallow; IV = 47) and CLA combined would improve belly quality to a greater degree than CLA combined with a more unsaturated fat source (yellow grease; IV = 83).     

 

Materials and Methods

Live animal care and measurements:  144 gilts (avg. wt. 49.3 kg) of a lean genotype were randomly assigned to one of six treatments according to a 2 x 3 factorial design (24 pigs per treatment; 3 pigs/pen).  Treatments (Table 1) included two sources of supplemental fat, a zero supplemental fat control, and two sources of linoleic acid.  The yellow grease and tallow had iodine values of 82.8 and 47.2, respectively (Table 2).  Dietary treatments were initiated after a 1 wk acclimation period.  Animals received ad libitum access to their respective diet and to water for 6 wk until they reached an average slaughter weight of 250 lbs.  Pigs were weighed prior to initiation of treatments and then every two weeks until slaughter.  Feed consumption was recorded throughout the study.

 

Carcass measurements:  Hot carcass weight was determined on-line.  Carcasses were chilled for 24 h at which time a 2.5 cm chop was removed between the 9^th and 10^th ribs.  After allowing a minimum of 20 minutes bloom time, each chop was evaluated for color, ultimate pH, drip loss and temperature.  Backfat depth and longissimus muscle depths were measured using acetate tracing of the loin chop.  The longissimus muscle chop was measured in triplicate (middle, medial and lateral) and mean values were calculated for color lightness (L*), redness (a*) and yellowness (b*) using a Minolta Chromameter 200 (Minolta, Ramsey, NJ).  A visual color score was also determined on a scale from 1 to 6 (1 = pale, 6 = very dark) using plastic Japanese color standards. Fat samples were removed from the shoulder end of the belly of each pig for fatty acid analysis.

 

Statistical Analysis:  Data were analyzed using the GLM procedure of SAS (SAS, Cary, NC).  Least squares treatment means were obtained assuming fixed models that included the effects of block, fat source, linoleic acid source and fat source x linoleic acid source.  The degrees of freedom (df) were partitioned into contrasts for the effects of supplemental fat source and supplemental fat level.

 

Table 1. Diet composition

 

 

Table 2. Fatty acid composition of supplemental fats

 

 

Results and Discussion

Performance: Feed consumption was not affected by fat supplementation or addition of CLA to the diets (P < 0.10) and averaged 2.26 kg/d (Table 3).  Average daily gain during the 47 d experiment was improved by 4% supplemental fat (P < 0.09), but not affected by CLA consumption.  Efficiency of gain was improved by supplemental fat (P < 0.01) with animals consuming 4% added fat diets gaining an additional 0.02 kg/kg feed.

 

Table 3. Average daily gain, feed intake and feed efficiency of pigs consuming 0% or 4% supplemental fat combined with linoleic acid (LA) or conjugated linoleic acid (CLA)

 

 

Pork Quality: Backfat depth, longissimus muscle area, ultimate pH, and color were not affected by supplemental fat or CLA (Table 4; P > 0.10).  Water holding capacity (WHC) of longissimus chops was improved by 17.6% with 4% supplemental fat.  This may result in improved shelf life of pork products.  Longissimus muscle (LM) pH from pigs fed 4% tallow was 2.5% greater at 45 min post-slaughter (P < 0.04).  However, supplemental tallow did not affect ultimate pH at 24 h.  Subjective marbling score was 18.8% greater in LM chops from pigs fed CLA (P < 0.01).  Others have shown similar results with increases of 11.3% with CLA supplementation (Dugan et al., 1997). An 18.0 g increase in lean (per kg of loin wet wt.) and a 2.77 g increase in intramuscular fat was associated with the increase in marbling score (Dugan and Aalhus, 1999).

 

Table 4. Pork quality

 

 

Fatty acid analysis: Conjugated linoleic acid supplementation increased the percentages of C14:0, C18:0 and C18:1trans and reduced the percentage of C18:1cis and C20:1cis (P < 0.001) in belly fat samples (Table 5).  The percentage of linoleic acid was 12.5% greater in pigs consuming 4% yellow grease (P < 0.001).  Both the 9c, 11t and the 10t, 12c isomers of CLA were increased in belly fat from animals fed CLA, and that increase was even greater when 4% supplemental fat was fed (fat source x linoleic acid interaction, P < 0.001).  Linoleic acid concentration in belly fat was also increased with supplementation of 4% yellow grease (P < 0.01).  Other data collected in our lab have shown a linear decrease (P < 0.05) in C18:2 content and IV of carcass fat as dietary tallow level increased (Averette et al., 1999).  Monounsaturates were reduced in belly fat from pigs consuming CLA (P < 0.001).  The total percentage of polyunsaturates was increased with 4% supplemental fat (P < 0.01), especially in those animals consuming yellow grease (P < 0.01).  CLA supplementation reduced the ratio of monounsaturates to polyunsaturates (MUFA/PUFA ratio) (2.50 vs 2.30, P < 0.001).  Most importantly, both fat and CLA affected iodine value.  Addition of CLA reduced belly fat IV by 6.6% (P < 0.001) and the IV of fat from animals consuming tallow and CLA combined was 62.0.

 

Table 5. Fatty acid profile of belly fat samples