J. Anim. Sci. 2004. 82:2937-2944
© 2004 American Society of Animal Science
Effects of rancidity and free fatty acids in choice white grease on growth performance and nutrient digestibility in weanling pigs1
J. M. DeRouchey,
J. D. Hancock2,
R. H. Hines,
C. A. Maloney,
D. J. Lee,
H. Cao,
D. W. Dean and
J. S. Park
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-0201
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Abstract
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Two experiments were conducted to determine the effects of rancidity and FFA in choice white grease (CWG) on growth performance and nutrient digestibility in nursery pigs. In Exp. 1, 150 crossbred pigs (average initial BW of 6.8 kg and average initial age of 21 d) were used. Treatments (as-fed basis) were a corn-soybean meal-based control with no added fat, 6% CWG, and 6% CWG heated at 80°C, with oxygen gas bubbled through it at 849 mL/min for 5, 7, 9, or 11 d. Peroxide value for the CWG increased as oxidative exposure was increased from 0 to 7 d (i.e., peroxide values of 1, 40, and 105 mEq/kg for d 0, 5, and 7, respectively), but decreased to 1 mEq/kg as the hydroperoxides decomposed after 9 and 11 d of oxidation. Pigs fed the control diet (no added fat) had the same (P = 0.91) overall ADG (d 0 to 35) but lower G:F (P < 0.04) than pigs fed diets with added fat. As for the effects of fat quality, ADG (linear effect, P < 0.01) and ADFI (linear effect, P < 0.001) decreased as the fat was made more rancid. However, there were no changes in digestibility of fatty acids as the rancidity of the fat was increased (P = 0.16), suggesting that the negative effects of rancidity were from decreased food intake and not decreased nutrient utilization. In Exp. 2, 125 crossbred pigs (average initial BW of 6.2 kg and average initial age of 21 d) were used to determine the effects of FFA in CWG on the growth performance and nutrient digestibility in nursery pigs. Treatments (as-fed basis) were a corn-soybean meal-based control with no added fat, 6% CWG, and 6% CWG that had been treated with 872, 1,752 or 2,248 lipase units/g of fat. The FFA concentrations in the CWG were increased from 2% with no lipase added to 18, 35, and 53% as lipase additions were increased. Pigs fed the control diet (no added fat) had the same (P = 0.30) overall ADG (d 0 to 33) but lower G:F (P < 0.01) than pigs fed diets with added fat. There were no effects of FFA concentration on ADG (P = 0.18), and ADFI increased (linear effect, P < 0.04) as FFA concentration in the CWG increased. Fatty acid digestibility was not affected (P = 0.17) by FFA in the diet. In conclusion, our data suggest that as fat is oxidized (especially to peroxide values greater than 40 mEq/kg), ADG and ADFI in nursery pigs will decrease; however, FFA concentrations of at least 53% do not adversely affect utilization of CWG in nursery pigs.
Key Words: Fat Quality • Free Fatty Acids • Pigs • Rancidity
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Introduction
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Fat is added to swine diets to improve rate and/or efficiency of gain (Stahly and Cromwell, 1979
; Cera et al., 1988; Pettigrew and Moser, 1991). To further identify and define the beneficial effects of fat on growth performance, attempts have been made to define fat quality. However, those research efforts have focused mainly on the effects of essential fatty acids (Cunnane, 1984), unsaturated:saturated fatty acid ratios (Powles et al., 1995), and fatty acid chain lengths (Hamilton and McDonald, 1969). Few studies address the effects of rancidity and FFA concentrations on pig performance. Experiments with rats (Andrews et al., 1960) and broilers (Cabel et al., 1988) showed decreased growth performance, whereas data from experiments with turkeys (Leeson et al., 1997) and finishing pigs (Lewis et al., 1976) indicated no affects of increased rancidity of dietary fat on growth performance. Additional conflicting opinions about the effects of fat quality on animal growth results from the use of commercial fat blends of unknown sources and backgrounds to generate data concerning the effects of FFA (Wiseman and Cole, 1987). Thus, our objective was to determine the effects of rancidity and FFA in a defined source of CWG on growth performance and nutrient digestibility in weanling pigs.
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Materials and Methods
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Animal care and use for the experiments reported herein were in accordance with the Guide for the Care and Use of Agricultural Animals in Agricultural Research and Teaching (FASS, 1999).
Experiment 1
One hundred fifty (Line 326 boars x C 22 sows, PIC, Franklin, KY) piglets, with an average initial BW of 6.8 kg and an average initial age of 21 d, were used in a 35-d growth assay to determine the effects of rancidity in choice white grease (CWG) on growth performance and nutrient digestibility. The pigs were weaned, blocked by BW, and allotted to pens based on sex and ancestry. There were five pigs per pen and five pens per treatment. The diets (Table 1) were formulated to 1.7% lysine for d 0 to 7, 1.55% lysine for d 7 to 21, and 1.4% lysine for d 21 to 35 and to meet or exceed all nutrient concentrations suggested by the NRC (1998). Treatment diets were a corn-soybean meal-based control with no added fat, 6% CWG (Darling Int., Inc., Coldwater, MI), and 6% CWG (as-fed basis) subjected to heating in the presence of oxygen gas for varying lengths of time. To create rancidity, the CWG was added to metal barrels (145 kg of CWG/208-L barrel) equipped with heaters. The fat was heated to 80°C with oxygen gas bubbled through it for 5, 7, 9, or 11 d. The flow rate of the gas was 849 mL/min through a 6.4-mm-diameter hose with multiple punctures to ensure even distribution of oxygen gas throughout the CWG. On d 5, half the CWG was removed from one barrel, and the rest of the fat was heated and oxidized for an additional 2 d to create the 7-d treatment. On d 9, half the CWG was removed from the second barrel, and the remainder of the fat was heated and oxidized for an additional 2 d to create the 11-d treatment. The CWG treatments were stabilized with 1 g of an antioxidant (Rendox AT 20 Liquid, Kemin Industries, Inc., Des Moines, IA)/kg of fat. The fat treatments were stored in a cool room (10°C) to prevent further development of rancidity. Fat samples were collected and analyzed for peroxides, p-anisidine, FFA, moisture, impurities, unsaponifiable matter, and iodine value using AOAC (1990) procedures.
The pigs were housed in an environmentally controlled building with 1.2- x 1.5-m pens with woven wire flooring. Room temperature was maintained at 32, 29, 27, and 24°C for d 0 to 7, 7 to 14, 14 to 21, and 21 to 35, respectively. Each pen had a self-feeder and nipple waterer to allow ad libitum consumption of feed and water. Pigs and feeders were weighed on d 7, 21, and 35 to allow calculation of ADG, ADFI, and G:F. Chromic oxide was included in the diets for d 7 to 21 (as an indigestible marker), and on d 20, fecal samples were collected from four pigs per pen by rectal massage. Feed and feces were analyzed for concentrations of Cr (Williams et al., 1962), DM, GE, ether extract (AOAC, 1990), and N (FP-2000, Leco Corp., St. Joseph, MO). Fatty acid concentrations in the fat, feed, and feces were determined with GLC (Sukhija and Palmquist, 1988). Calculations of apparent digestibilities of DM, N, GE, ether extract, and fatty acids were done using the index ratio procedure, with Cr2O3 used as the marker.
Statistical analyses were conducted using the GLM procedure of SAS (SAS Inst., Inc., Cary, NC), with pen as the experimental unit. Polynomial regression (Peterson, 1985) was used to determine shape of the response (linear and quadratic) to increased rancidity in the CWG.
Experiment 2
One hundred twenty-five (lines 326 boars x C 22 sows, PIC, Franklin, KY) piglets, with an average initial BW of 6.2 kg and average initial age of 21 d, were used in a 33-d growth assay to determine the effects of FFA in CWG on growth performance and nutrient digestibility. The pigs were weaned, blocked by BW, and allotted to pens based on sex and ancestry. There were five pigs per pen and five pens per treatment. The diets (Table 1
) were formulated to 1.7% lysine for d 0 to 5, 1.55% lysine for d 5 to 19, and 1.4% lysine for d 19 to 33 and to meet or exceed all nutrient concentrations suggested by the NRC (1998). Treatment diets were a corn-soybean meal-based control with no added fat, 6% CWG (Darling Int., Inc.), and 6% CWG (as-fed basis) that had been heated to 35°C and treated with 872, 1,752, or 2,248 lipase units (Validase Fungal Lipase 8000, Valley Research Inc., South Bend, IN)/g of fat. For the lipase treatments, 73 kg of CWG was placed in three barrels (208 L capacity), mixed with water (1.3:1 water:CWG), and lipase was added. The mixture was agitated with a rotating propeller for 12 h and allowed to settle for 24 h for separation of the fat and water. The fat was collected and stabilized, stored, and analyzed as in Exp. 1.
The pigs were housed in the same environmentally controlled nursery room used for Exp. 1. Management of the room and pigs was the same as in Exp. 1, but the pigs and feeders were weighed on d 5, 19, and 33 in this experiment. Chromic oxide was included in the diets as an indigestible marker from d 5 to 19, and on d 18, fecal samples were collected from four pigs per pen by rectal massage. Fat, feed, and fecal analyses were the same as described for Exp. 1.
Statistical analyses were performed using the GLM procedure of SAS, with pen as the experimental unit. Polynomial regression (Peterson, 1985) was used to determine shape (linear and quadratic) of the response to increased FFA in the CWG.
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Results and Discussion
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Experiment 1
Analyses of the CWG (Table 2) indicated that thermal and oxidative exposure increased peroxide value (a measure of hydroperoxide concentration) of the fat until d 7 (i.e., 105 mEq/kg). Then, hydroperoxides decreased to a level similar to that of the untreated fat with 9 and 11 d of oxidative exposure. Hydroperoxides result from the loss of hydrogen and addition of oxygen to replace a double bond in the carbon skeleton of a fatty acid. A hydroxyl group then attaches to the oxygen at the broken double bond, and a hydroperoxide is formed (Frankel, 1998). Hydroperoxides will decompose into secondary products of aldehydes, carbonyls, ketones, alcohols, acids, esters, hydrocarbons, lactones, and substituted furans when exposed to prolonged autoxidation (Frankel, 1998). Hydroperoxides are odorless, but these decomposition products create a "rancid" aroma. Also, the breakdown of hydroperoxides produces free radicals that are readily reactive with other fatty acids to accelerate the initial oxidation reaction (Enser, 1984). Thus, peroxide values of fats or oils are useful to characterize fat quality only for samples that are oxidized to low levels (e.g., 50 to 100 mEq/kg) and may be misleading when used to characterize quality of fats exposed to extreme oxidative stress.
To better elucidate degredation of the fat, a p-anisidine assay was used to determine the aldehyde content of the CWG (Table 2). Like peroxides, p-anisidine values increased until d 7. Thereafter, p-anisidine values decreased, but to a lesser extent than peroxide values. Therefore, p-anisidine values, like peroxide values, proved unreliable as indicators of the degree of rancidity for fats exposed to extreme oxidative challenge.
No differences in moisture, insoluble impurities, or unsaponifiable matter were observed as the fat became more rancid (Table 2). However, iodine number and the unsaturated:saturated fatty acid ratio decreased with increasing rancidity, indicating a change in fatty acid composition. In particular, the percentage of C18:1 and C18:2 decreased with oxidative challenge, indicating that these fatty acids were especially affected by the oxidative process. Similar results were reported by Yoshida and Kajimoto (1989) when soybean oil was oxidized by blowing dry air at 40°C for 40 d onto the oil. In that experiment, peroxide values were 359 mEq/kg and the unsaturated:saturated ratio was significantly lower (C18:1 was converted to C16:0) compared with fresh soybean oil.
For d 0 to 7 and 7 to 21 of the growth assay, adding fat did not affect (P = 0.13) ADG or G:F compared with the control diet with no added fat (Table 3). These results agree with those of Li et al. (1990) and Jones et al. (1992), who reported no positive response from adding fat to piglet diets for the first 2 wk after weaning. However, for d 21 to 35 of our experiment, ADFI was lower (P < 0.001) and G:F was greater (P < 0.03) for pigs fed the diets with added fat vs. the control. Also, fat addition to nursery diets improved (P < 0.04) overall efficiency of growth (i.e., d 0 to 35) compared with the control.
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Table 3. Effects of rancidity on growth performance and digestibility of nutrients in nursery pigs (Exp. 1; as-fed intake)a
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For d 0 to 7 of the growth assay, ADG, ADFI, and G:F were not affected (P = 0.15) by increased thermal and oxidative exposure of the CWG. However, for d 7 to 21, ADG (linear effect, P < 0.003) and ADFI (linear effect, P < 0.01) were decreased as rancidity of the added fat was increased. Also, overall (d 0 to 35) ADG (linear effect, P < 0.01) and ADFI (linear effect, P < 0.001) decreased as the added fat had more thermal and oxidative exposure. These effects occurred primarily for fat treatments with more than 5 d of thermal and oxidative exposure (i.e., peroxide values >40 mEq/kg). Other researchers have reported decreased growth performance when animals were fed fat with high peroxide values. Behniwal et al. (1993) observed lower ADG and G:F when rats were fed peanut oil (10% of their diet) with a peroxide value of 90 mEq/kg. Kimura et al. (1984) reported that rats fed oxidized soybean oil (peroxide values of 490 and 580 mEq/kg) had decreased ADG and ADFI and developed diarrhea. In contrast, Lewis et al. (1976) heated soybean oil over a gas burner for 2 to 4 h (peroxide value of 5.4 mEq/kg) and observed no harmful effect of feeding that fat as 4 or 8% of the diets for finishing pigs. L’Estrange et al. (1967) reported no negative effects in nursery pigs when fed diets with oxidized meat meal as 10% of the formulation. Thus, there seems to be a threshold for rancidity above which feed intake and rate of growth are decreased.
No differences in apparent digestibility of DM, N, or GE (P = 0.30) were observed among pigs fed the control and the fat added treatments. Jones et al. (1992) reported greater digestibility of N and GE when fat was added to diets for weanling pigs compared with a nonfat control. Asplund et al. (1960) reported greater digestibility of N with fat inclusion in the diet. They suggested that increased digestibility of N was related to longer transit time through the intestines when fat was added to the diets; however, the data from our experiment do not support those proposed effects of fat on improved digestibility of other nutrients.
Digestibilites of total fat, long-chain unsaturated fatty acids, and long-chain saturated fatty acids were greater (P < 0.001) for the fat added treatments compared with the control (Table 3). Frobish et al. (1970) also reported greater digestibility of fat in diets with added fat compared with a no-added-fat control, and this was most likely caused by endogenous losses (that are not accounted for with apparent digestibility determinations) contributing a high proportion of the lipids excreted in feces of pigs fed a diet with little fat.
When fat was subjected to the initial degrees of thermal and oxidative challenge, there was a tendency for decreased digestibility of nutrients, but the trend was reversed with the greatest extent of oxidative exposure (hence the quadratic effect of oxidative exposure on digestibility of DM, P < 0.04). Likewise, digestibility of total fat and/or fatty acids was not affected (P = 0.23) by subjecting the fat to oxidative stress. Thus, our results support the argument of Aw et al. (1992), who suggested that chylomicrons within the lymphatic system are adept in the transport of lipid peroxides. Also, oxidized lipid metabolites formed after the consumption of thermally oxidized oils were found to increase the rancidity in blood plasma of chickens (Sheely et al., 1994), thus suggesting, as did our data, that oxidation of fatty acids does not prevent their digestion and absorption.
These findings are in sharp contrast to those of Andrews et al. (1960), who reported little to no digestion and absorption of fatty acids having peroxides. In addition to the potential negative effects of peroxides themselves on fat digestibility, the digestibility of unsaturated fatty acids is greater than that of saturated fatty acids (Sewell and Miller, 1965; Li et al., 1990). Powles et al. (1995) observed decreased DE in fat with a decreased unsaturated:saturated ratio in young pigs. Borgstrom (1967) proposed that saturation of fatty acids decreases micelle formation and therefore decreased absorption of fatty acids from the lumen of the small intestine. In our experiment, as the fat became more rancid, the percentage of the fatty acids that were saturated was increased but there was no consistent decrease in fatty acid digestibility. Thus, the negative effects we observed on growth rate suggest that rancidity of fat in the diets of young pigs is a serious consideration, but the effect seemed to result from decreased food intake and not from decreased nutrient digestibility and/or utilization.
Experiment 2
Chemical analyses of the CWG used in this experiment indicated a greater percentage of FFA as lipase additions were increased (Table 4). The peroxide and p-anisidine values were low and remained unchanged regardless of the presence of FFA. Also, fatty acid composition, iodine value, and unsaturated:saturated fatty acid ratios were unchanged by enzyme hydrolysis of triglycerides. However, moisture, and therefore the total of moisture, insoluble impurities, and unsaponifiable matter (MIU) percents increased as FFA were increased. Lipase hydrolysis occurs at the 
-positions of a triglyceride to yield 2-monoacylglycerol and two fatty acids (Frankel, 1998), and these products of triglyceride hydrolysis are more soluble in water. Hence, less separation of the CWG and water was achieved as the concentration of FFA increased and more water was retained.
As for pig growth and feed intake, no differences were observed for d 0 to 5 (P = 0.30) and d 5 to 19 (P = 0.11) among the fat-added treatments and no-added-fat control (Table 5); however, for d 19 to 33 and overall (d 0 to 33), G:F was increased with the fat-added treatments (P < 0.01). These results are in agreement with those of Exp. 1, where adding fat improved efficiency of gain in the latter portions of the nursery phase.
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Table 5. Effects of free fatty acid concentration on growth performance and digestibility of nutrients in nursery pigs (Exp. 2; as-fed intake)a
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For the fat-added diets, ADG and G:F were not affected (P = 0.24) from d 0 to 5 and from d 5 to 19 regardless of concentration of FFA. For d 19 to 33 and overall (d 0 to 33), there was a trend for G:F to decrease as FFA concentrations increased to 35%, but then to increase as FFA concentrations were increased further to 53% (quadratic effects, P < 0.09). Thus, there seemed to be no negative effects of high concentrations of FFA on rate or efficiency of gain and, indeed, overall ADFI was increased (linear effect, P < 0.04) with increased amounts of FFA in the diet.
As in Exp. 1, digestibility of total fat, long-chain unsaturated fatty acids, and long-chain saturated fatty acids were greater (P < 0.001) for the fat-added treatments compared with the control. But, there were no differences (P = 0.14) for digestibility of DM, GE, total fat, long-chain fatty acids, and medium-chain fatty acids among pigs fed the various fat-added treatments. These results are in contrast with the data of Powles et al. (1995) in swine and Wiseman and Salvador (1991) in broilers, where apparent DE of fats decreased with increased FFA. However, some of that decrease was likely related to oxidative damage of the FFA, and not simply to the fact that they were not esterified with glycerol.
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Implications
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Rancidity in choice white grease must be monitored to ensure maximal performance in nursery pigs. However, the use of peroxide value and p-anisidine tests to detect rancidity can be misleading, depending on how much thermal and oxidative exposure the fat has undergone. Our data suggest that a peroxide value up to 40 mEq/ kg and a p-anisidine value of 10.6 or less will not result in decreased growth performance in nursery pigs if hydroperoxides have not already begun the degradation process. In addition, as much as 53% free fatty acids in choice white grease did not adversely affect piglet performance. Thus, our experiments indicate that rancidity should be of concern when purchasing choice white grease for use in diets for piglets; however, the concentration of free fatty acids that were not damaged or rancid did not affect fat utilization and therefore is not a suitable measure of quality.
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Footnotes
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1 Contribution No. 03-133-J from the Kansas Agric. Exp. Stn., Manhattan 66506. 
2 Correspondence: 244 Weber Hall (phone: 785-532-1230; fax: 785-532-7059; e-mail: jhancock{at}oznet.ksu.edu).
Received for publication January 23, 2004.
Accepted for publication May 17, 2004.
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Abstract
Introduction
