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Journal of Animal Science - Animal Nutrition

Effects of dietary lipid sources on performance and apparent total tract digestibility of lipids and energy when fed to nursery pigs1

 

This article in JAS

  1. Vol. 92 No. 2, p. 627-636
     
    Received: Mar 17, 2013
    Accepted: Dec 05, 2013
    Published: November 24, 2014


    2 Corresponding author(s): eric_vanheugten@ncsu.edu
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doi:10.2527/jas.2013-6488
  1. S. M. Mendoza and
  2. E. van Heugten 2
  1. Department of Animal Science, North Carolina State University, Raleigh 27695

Abstract

Acidulated fats and oils are by-products of the fat-refining industry. They contain high levels of FFA and are 10% to 20% less expensive than refined fats and oils. Two studies were designed to measure the effects of dietary lipid sources low or high in FFA on growth performance and apparent total tract digestibility (ATTD) of lipids and GE in nursery pigs. In Exp. 1, 189 pigs at 14 d postweaning (BW of 9.32 ± 0.11 kg) were used for 21 d with 9 replicate pens per treatment and 3 pigs per pen. Dietary treatments consisted of a control diet without added lipids and 6 diets with 6% inclusion of lipids. Four lipid sources were combined to create the dietary treatments with 2 levels of FFA (0.40% or 54.0%) and 3 degrees of fat saturation (iodine value [IV] = 77, 100, or 123) in a 2 × 3 factorial arrangement. Lipid sources were soybean oil (0.3% FFA and IV = 129.4), soybean-cottonseed acid oil blend (70.5% FFA and IV = 112.9), choice white grease (0.6% FFA and IV = 74.8), and choice white acid grease (56.0% FFA and IV = 79.0). Addition of lipid sources decreased ADFI (810 vs. 872 g/d; P = 0.018) and improved G:F (716 vs. 646 g/kg; P < 0.001). Diets high in FFA tended (P = 0.08) to improve final BW (21.35 vs. 21.01 kg) and ADG (576 vs. 560 g/d). Lipid-supplemented diets had greater ATTD of lipids than control diets (67.4% vs. 29.7%; P < 0.001). Apparent total tract digestibility of lipids was greater in diets with low FFA (69.9% vs. 64.9%; P < 0.001) and decreased linearly with increasing IV (73.2%, 69.1%, and 67.2%). For GE, ATTD was greater in diets with low FFA (83.1% vs. 80.9%; P = 0.001). In Exp. 2, 252 pigs at 7 d postweaning (BW of 7.0 ± 0.2 kg) were used for 28 d with 9 replicate pens per treatment and 4 pigs per pen. Diets included a control diet without added lipids and 6 treatments with 2.5%, 5.0%, or 7.5% of lipids from either poultry fat (1.9% FFA) or acidulated poultry fat (37.8% FFA) in a 2 × 3 factorial arrangement. Addition of lipids increased (P < 0.001) final BW (19.9 vs. 18.4 kg) and ADG (460 vs. 405 g/d) regardless of source. Fat increased (P < 0.001) ADFI when added at 2.5% and then decreased ADFI with each further increment (663, 740, 681, and 653 g for 0%, 2.5%, 5.0%, and 7.5% fat, respectively). Inclusion of lipids linearly (P < 0.001) improved G:F (615, 615, 688, and 692 g/kg for 0%, 2.5%, 5.0%, and 7.5% fat, respectively) and ATTD of lipids (17.8%, 50.2%, 71.0%, and 77.3% for 0, 2.5, 5.0, and 7.5% fat, respectively) and GE (76.1%, 76.4%, 83.3%, and 84.4% for 0%, 2.5%, 5.0%, and 7.5% fat, respectively). Acidulated lipids resulted in similar performance compared with refined lipids and could be economical alternatives to more expensive lipid sources.



INTRODUCTION

Acidulated fats and oils are by-products of the fat-refining industry. The purpose of refining is to remove nontriglyceride molecules. During the neutralization step, caustic soda is added to the crude oil and reacts with FFA, resulting in soap stock and fats and oils with low impurities. Soap stock is then acidulated by the addition of sulfuric acid, which again releases FFA, and this product is referred to as acidulated fat (Levin and Swearingen, 1953). Acidulated fats and oils are high in FFA content and are approximately 10% to 20% less expensive than refined fats and oils.

Lipid composition and configuration can greatly influence intestinal lipid absorption by affecting micelle formation, especially chain length, position of fatty acids on the glycerol backbone, FFA content, and degree of saturation (Freeman, 1984). Commonly used indicators of the dietary energetic value of lipids in pigs are the presence of FFA and the degree of saturation of the fatty acids (NRC, 2012). Increasing FFA concentration in lipids causes a progressive reduction in their energy value (Wiseman et al., 1991; Powles et al., 1993; Jørgensen and Fernández, 2000). Fats of animal origin have a greater content of saturated fats and have lower digestibility and energy value than oils of vegetable origin (Cera et al., 1988a; Jørgensen et al., 1992; Øverland et al., 1994; Wiseman et al., 1990).

The effects of FFA content of supplemental lipids on performance of pigs have not been extensively studied, and the experiments conducted have produced conflicting results (Bayley and Lewis, 1965; Frobish et al., 1970; Hillcoat and Annison, 1974; Swiss and Bayley, 1976). More recently, DeRouchey et al. (2004) reported no impact of FFA on pig performance, which indicates that fats with high FFA content, such as acidulated lipids, may be used in diets of nursery pigs without reducing performance. Thus, the objective of the present studies was to measure the dietary effect of FFA, saturation, and level of lipid inclusion on growth performance and ATTD of lipids and GE in nursery pigs.


MATERIALS AND METHODS

Animal use protocols were approved by the North Carolina State University Institutional Animal Care and Use Committee.

Experiment 1

This experiment was conducted using 189 crossbred pigs ([Landrace × Yorkshire] × [Hampshire × Duroc]), with an average initial BW of 9.32 ± 0.11 kg. Pigs were weaned at approximately 21 d of age and fed a common diet (Renaissance Nutrition Inc., Roaring Spring, PA) for 14 d to adjust pigs to solid feed, followed by treatment diets for 21 d. Pigs were blocked by BW and sex and assigned to 1 of 7 dietary treatments. Litter mates were distributed across treatments and avoided in the same pen. Pigs were placed into a temperature-controlled raised-deck nursery at the Swine Educational Unit (Raleigh, NC) and housed in 63 pens and 3 pigs per pen (0.91 × 1.52 m) with 9 replicate pens per treatment. Two farrowing groups, 2 wk apart, were used for this experiment to obtain sufficient numbers of pigs for this study. The first group represented blocks 1 to 4, and the second group represented blocks 5 to 9. Pigs were allowed ad libitum access to feed and water throughout the experiment. Each pen had 2 nipple water drinkers and a double-space feeder.

Feed was manufactured at the North Carolina State University Feed Mill Educational Unit. Two corn-soybean meal base mixes were formulated to meet or exceed all nutrient concentrations suggested by NRC (1998) and contained 3.76 g standardized ileal digestible Lys/Mcal ME. The first base mix was divided into 6 portions, to which lipid sources were added to generate the final dietary treatments. The second base mix served as the negative control diet. The purpose of this process was to ensure that diets within lipid supplemented treatments were identical in composition. Additionally, diets contained 0.5% of titanium dioxide as indigestible marker to calculate apparent total tract digestibility (ATTD) of lipids and GE. Four sources of lipids (Divers Processing Co. Inc., Portsmouth, VA) were combined to create 6 diets in a 2 × 3 factorial arrangement with 2 levels of FFA (low or high FFA concentrations of 0.4% and 54.0% on an as-fed basis, respectively) and 3 degrees of lipid saturation (low, medium, or high with iodine values [IV] of 77, 100, and 123, respectively). Lipids were supplemented at 6%, and a negative control diet without added lipids was included in the design (Table 1). Lipid sources consisted of soybean oil (SO; 0.3% FFA and IV = 129.4), soybean-cottonseed acid oil blend (SAO; 70.5% FFA and IV = 112.9), choice white grease (CWG; 0.6% FFA and IV = 74.8), and choice white acid grease (CWAG; 56.0% FFA and IV = 79.0; Table 2). The CWAG was obtained from the refining process of the original CWG that was used in the present study. Lipid sources were included in diets at the following proportions: diet 1, 100% CWG; diet 2, 95% CWAG and 5% CWG; diet 3, 50% SO and 50% CWG; diet 4, 38% SAO, 12% SO, 48% CWAG, and 2% CWG; diet 5, 100% SO; and diet 6, 76% SAO and 24% SO (Table 3). Diets were fed in meal form.


View Full Table | Close Full ViewTable 1.

Composition of the experimental diets for Exp. 1 and Exp. 2, as-fed basis1

 
Item Exp. 12
Exp. 23
0% Lipids 6% Lipids 0% Lipids 2.5% Lipids 5.0% Lipids 7.5% Lipids
Ingredient, %
    Corn, yellow dent 65.31 55.02 66.56 62.47 58.44 53.97
    Soybean meal, 47.5% CP 30.23 34.5 29.34 30.90 32.41 34.35
    Lipids 0 6 0 2.5 5.0 7.5
    l-Lys·HCl 0.37 0.38 0.35 0.36 0.37 0.38
    dl-Met 0.14 0.18 0.12 0.14 0.16 0.18
    l-Thr 0.14 0.15 0.12 0.13 0.14 0.15
    Monocalcium phosphate, 21% P 1.55 1.53 1.35 1.35 1.34 1.34
    Limestone 1.09 1.07 0.99 0.98 0.97 0.96
    Salt 0.4 0.4 0.4 0.4 0.4 0.4
    Copper sulfate, 25.2% Cu 0.08 0.08 0.08 0.08 0.08 0.08
    Vitamin premix4 0.04 0.04 0.04 0.04 0.04 0.04
    Trace mineral premix5 0.15 0.15 0.15 0.15 0.15 0.15
    Titanium dioxide6 0.5 0.5 0.5 0.5 0.5 0.5
Analyzed composition, %
    Ether extract 2.68 7.27 2.78 4.87 6.94 9.61
    Titanium dioxide6 0.40 0.51 0.42 0.46 0.50 0.43
1Diets were formulated to meet or exceed NRC (1998) requirements.
2Lipid sources were soybean oil (0.3% FFA and iodine value [IV] = 129.4), soybean–cottonseed acid oil blend (70.5% FFA and IV = 112.9), choice white grease (0.6% FFA and IV = 74.8), and choice white acid grease (56.0% FFA and IV = 79.0) and were included in diets 1 to 6 in different ratios.
3Lipid sources were poultry fat and acidulated poultry fat.
4Supplied per kilogram of complete diet: 8,227 IU of vitamin A, 1,172 IU of vitamin D3 as D-activated animal sterol, 47.0 IU of vitamin E, 0.03 mg of vitamin B12, 5.8 mg of riboflavin, 35.2 mg of niacin, 23.5 mg of d-pantothenic acid as calcium pantothenate, 3.8 mg of vitamin K as menadione dimethylpyrimidinol bisulfate, 1.7 mg of folic acid, and 0.23 mg of d-biotin.
5Supplied per kilogram of complete diet: 16.5 mg Cu as CuSO4, 0.30 mg I as ethylenediamine dihydriodide, 165 mg Fe as FeSO4, 40 mg Mn as MnSO4, 0.30 mg Se as Na2SeO3, and 165 mg Zn as ZnO.
6Titanium dioxide was used as an indigestible maker.

View Full Table | Close Full ViewTable 2.

Chemical composition of experimental lipid sources, as-fed basis

 
Item Exp. 1
Exp. 2
Soy oil Soy acid oil CWG1 CWG acid Poultry fat Acidulated poultry fat
Moisture,2 % 0.4 0.6 0.2 10.4 0.4 1.2
Insoluble impurities,3 % 0 0 0 0.26 0 0
Unsaponifiable matter,4 % 0.54 2.6 0.37 1.8 1.3 2.2
Free fatty acids,5 % 0.3 70.5 0.6 56.0 1.9 37.8
Iodine value6 112.9 129.4 74.8 79.0 85.8 85.5
Anisidine value7 12.4 5.8 0 15.3 0 10.1
Peroxide value, mEq/kg
    Initial8 33.6 1.8 1.8 7.0 0.1 0.1
    4 h AOM9 103.6 1.0 2.6 4.0 0.1 0.1
    24 h AOM9 543.0 2.0 6.6 1.4 0.1 0.4
1Choice white grease.
2Method Ca2a-45 (AOCS, 2009).
3Method Ca3a-46 (AOCS, 2011a).
4Method 933.08 (AOAC, 1933).
5Method 940.28 (AOAC, 1940).
6Method 920.159 (AOAC, 1920).
7Method Cd18-90 (AOCS, 2011b).
8Method 969.33 (AOAC, 1969).
9AOM, active oxygen method (IUPAC, 1979).

View Full Table | Close Full ViewTable 3.

Percentage contribution of experimental lipid sources to supplemental lipids for the dietary treatments, Exp. 11

 
Treatment FFA,% IV Percentage of inclusion
Soy oil Soy acid oil CWG2 CWG acid
1 0.6 74.8 100
2 54 78.8 5 95
3 0.4 102.1 50 50
4 54 97.8 12 38 2 48
5 0.3 129.4 100
6 54 116.8 24 76
1Lipid sources were combined to create 6 diets in a 2 × 3 factorial arrangement with 2 levels of FFA (low or high) and 3 degrees of lipid saturation (low, medium, or high iodine value [IV]).
2Choice white grease.

Experiment 2

This experiment was conducted using 252 crossbred pigs ([Landrace × Yorkshire] × [Hampshire × Duroc]) with an average initial BW of 7.04 ± 0.20 kg. Pigs were weaned at approximately 21 d of age and fed a common diet (Renaissance Nutrition Inc.) for 7 d to allow pigs to adjust to solid feed. Piglets were used for 28 d in a growth performance study to determine the effects of source of lipids and level of inclusion of supplemental lipids on growth performance and ATTD of lipids and GE. Pigs were blocked by BW and sex and assigned to 1 of 7 dietary treatments in a 2 × 3 factorial arrangement plus a negative control. Litter mates were avoided in the same pen. Factors consisted of lipid source (Divers Processing Co. Inc.; poultry fat [PF]: 1.9% FFA and IV = 85.8 and acidulated poultry fat [APF]: 37.8% FFA and IV = 85.5) and lipid level (2.5%, 5.0%, and 7.5%). A negative control diet without supplemental lipids was included in the experimental design. Pigs were placed at the Swine Educational Unit (Raleigh, NC) at 4 pigs per pen using a total of 63 pens with 9 replicate pens per treatment. Two farrowing groups, 2 wk apart, were used for this experiment. The first group represented blocks 1 to 5, and the second group represented blocks 6 to 9.

Feed was manufactured at the North Carolina State University Feed Mill Educational Unit. Four corn-soybean meal base mixes were formulated to meet or exceed all nutrient concentrations suggested by NRC (1998) and contained 3.65 g standardized ileal digestible (SID) Lys/Mcal ME (Table 1). Thus, these base mixes were formulated with increasing amounts of soybean meal and synthetic AA as levels of supplemental lipids increased (0%, 2.5%, 5.0%, and 7.5%) to maintain a constant SID Lys/Mcal ME ratio between diets. The first base mix served as the negative control diet without added lipids. Base mix 2 was divided into 2 equal portions, and PF was added to 1 portion at 2.5%, whereas APF was added to the second portion at 2.5%. The same procedure was repeated for the 5.0% and 7.5% lipid inclusion rates. This procedure of diet manufacturing ensured diets were close to identical within lipid level. All dietary treatments contained 0.5% of titanium dioxide as an indigestible marker to calculate ATTD of lipids and GE, and diets were fed in meal form.

Measurements

In each experiment, pig BW and feed disappearance were measured weekly. Feed disappearance was calculated from the feed offered minus feed refusal. At the end of the study, fresh fecal samples were collected from at least 2 pigs per pen after defecation during 3 consecutive days and frozen in plastic bags at -20°C for subsequent analyses. Feed and fecal samples were prepared for analyses by drying for 4 d at 55°C. Feed was ground using a Thomas-Wiley laboratory mill (Thomas Scientific, Swedesboro, NJ) through a 1-mm mesh screen, and the fecal samples were ground using a kitchen blender (Oster, Sunbeam Products Inc., Jarden Corporation, New York, NY).

Chemical Analyses

Lipid sources were analyzed by a commercial laboratory (New Jersey Feed Laboratory Inc., Trenton, NJ) for moisture (AOCS, 2009), insoluble impurities (AOCS, 2011a), unsaponifiable matter (AOAC,1933), FFA content (AOAC, 1940), IV (AOAC, 1920), anisidine value (AOCS, 2011b), initial peroxide value (AOAC, 1969), and 4 and 20 h peroxide value by the active oxygen method (AOM; IUPAC, 1979).

Concentrations of titanium dioxide in the diets and in the fecal samples were determined according to Myers et al. (2004) with a minor modification. The modification consisted of the addition of 50 μL of stabilized 30% hydrogen peroxide into all wells of the microwell plate 30 min before reading to ensure the orange color of the reaction. Concentrations were determined relative to a standard curve at 410 nm using a microplate reader (Synergy HT Multi-detection; Bio-Teck Instruments Inc., Winooski, VT).

Lipid content of feed and fecal samples were measured by ether extraction after acid hydrolysis with HCl (AOCS, 2004) using an XT15 fat extractor and HCl hydrolysis system (ANKOM Technology, Macedon, NY). The gross energy of diets and feces was determined by dynamic bomb calorimetry (C5000 Calorimetric System, IKA, Wilmington, NC), calibrated using benzoic acid. Apparent total tract digestibility of lipids and GE was calculated using the index ratio procedure (Adeola, 2001) as follows:

Statistical Analyses

For both experiments statistical analysis was performed using the GLM procedure of SAS (SAS Inst. Inc., Cary, NC) with the pen as the experimental unit. In Exp. 1, the model included block (BW), FFA content, IV, and the FFA × IV interaction. Initial BW was used as a covariate, given that it differed between treatments. Orthogonal contrast comparisons were conducted to determine linear and quadratic effects of IV and to compare the negative control with lipid-added diets. In Exp. 2, the model included block (BW), source, lipid level, and the source × lipid level interaction. Orthogonal contrasts were used to determine linear and quadratic effects of lipid level and to compare the negative control with lipid-added diets. For Exp. 2, a second model was included to determine if there was an interaction between farrowing group and dietary treatments. The model included farrowing group, lipid source, lipid level, and their interactions. Least squares means were reported, and differences were considered statistically significant at P ≤ 0.05 and were considered tendencies when 0.05 < P ≤ 0.10.


RESULTS AND Discussion

Experiment 1

The composition of the lipid sources used was within expectations for moisture, insoluble impurities, unsaponifiable matter, FFA concentration, and IV (Table 2). However, the anisidine value of SO and CWG acid grease and the peroxide value at 0, 4, and 24 h AOM for SO were greater than expected.

The addition of lipids to the diet did not affect final BW or ADG compared to pigs fed diet without supplemental lipids (Table 4). As expected, pigs fed diets containing supplemental lipids consumed less feed (P = 0.018), compensating for the greater energy density of the fat- or oil-supplemented diets. Lipid addition improved feed efficiency (P < 0.001) and ATTD of lipids (P < 0.001); conversely, no effect was observed for ATTD of GE compared to the negative control.


View Full Table | Close Full ViewTable 4.

Effects of FFA concentration and iodine value (IV) of supplemental lipids (6%) on growth performance and apparent total tract digestibility of lipids and GE in nursery pigs in Exp. 11

 
Item No lipid control 0.4% FFA
54% FFA
IV
IV
P-value
74.8 102.1 129.4 78.8 97.8 116.8 SEM Fat2 IV FFA
BW, kg
    Initial 9.33 9.30 9.30 9.26 9.34 9.34 9.34 0.03
    d 73 12.36 12.64 12.44 12.39 12.94 12.59 12.46 0.18 0.239 0.144 0.279
    d 14 16.23 16.73 16.34 16.41 16.99 16.90 16.87 0.28 0.122 0.684 0.104
    d 21 21.01 21.45 21.07 20.62 21.35 21.91 21.69 0.40 0.363 0.678 0.079
ADG, kg
    d 0 to 73 0.439 0.479 0.451 0.443 0.522 0.473 0.454 0.026 0.239 0.144 0.279
    d 8 to 14 0.554 0.584 0.557 0.575 0.578 0.616 0.629 0.030 0.313 0.792 0.218
    d 15 to 21 0.697 0.689 0.695 0.646 0.639 0.731 0.704 0.029 0.798 0.206 0.485
    d 0 to 21 0.560 0.581 0.563 0.541 0.576 0.603 0.592 0.019 0.363 0.678 0.079
ADFI, kg (as-fed basis)
    d 0 to 7 0.667 0.628 0.593 0.616 0.636 0.610 0.600 0.024 0.044 0.402 0.925
    d 8 to 14 0.867 0.797 0.784 0.779 0.848 0.845 0.803 0.032 0.081 0.640 0.147
    d 15 to 214,5 1.082 1.020 1.033 0.909 0.955 1.090 1.042 0.040 0.085 0.101 0.215
    d 0 to 21 0.872 0.815 0.803 0.768 0.813 0.849 0.815 0.025 0.018 0.368 0.159
G:F
    d 0 to 7 0.660 0.765 0.757 0.728 0.821 0.777 0.755 0.033 0.003 0.315 0.225
    d 8 to 144,6 0.638 0.736 0.713 0.735 0.685 0.728 0.785 0.020 <0.001 0.054 0.773
    d 15 to 21 0.645 0.675 0.671 0.688 0.665 0.672 0.678 0.019 0.102 0.765 0.749
    d 0 to 21 0.646 0.716 0.706 0.715 0.711 0.715 0.732 0.011 <0.001 0.484 0.409
Apparent total tract digestibility,%
    Lipids6,7 29.7 73.2 69.4 67.2 64.1 66.0 64.7 0.9 <0.001 0.002 <0.001
    GE 81.7 83.2 83.4 82.6 80.3 81.4 81.1 0.7 0.690 0.644 <0.001
1Pigs were allowed an adjustment period of 14 d after weaning before initiation of the study. Values represent least squares means of 9 pens with 3 pigs per pen. Initial body weight was used as a covariate.
2Probability values for the effect of lipid supplementation (6% added lipids vs. no added lipids diet).
3Linear effect of IV (P = 0.06).
4Interaction (P = 0.06).
5Quadratic effect of IV (P = 0.035).
6Linear effect of IV (P ≤ 0.022).
7Interaction (P < 0.001).

During the first week of the study, BW and ADG linearly (P = 0.06) decreased when IV increased (Table 4). During wk 3, a tendency for an interaction (P = 0.062) was observed for ADFI. When diets were low in FFA, pigs consumed less feed at the highest level of unsaturation (diet containing 100% SO). In contrast, when diets were high in FFA, the lowest ADFI was found when diets were the most saturated (diet containing 95% CWAG and 5% CWG). An interaction (P < 0.001) was also observed for ATTD of lipids. Digestibility decreased linearly with increasing IV when the FFA concentrations was low, but when the FFA concentration was high, digestibility was unaffected by IV. Low-FFA diets were composed exclusively of SO and CWG. The greatest lipid digestibility was 73.2% for 100% CWG, compared to 69.1% for 50% CWG and 50% SO and 67.2% for 100% SO.

Diets with high FFA tended (P = 0.08) to improve BW and ADG (Table 4). Apparent total tract digestibility of lipids (P < 0.001) and GE (P < 0.001) were greater for diets containing low FFA than diets containing high FFA.

Experiment 2

During wk 3 and 4 and overall, ADG increased linearly (P ≤ 0.01), resulting in a linear increase in final BW (P < 0.01) with increasing levels of lipids regardless of lipid source (Table 5). This increase was most prominent after the first increment of lipid supplementation (2.5%) with little improvement in ADG with subsequent levels. Feed intake decreased linearly (P < 0.001) with increasing levels of supplemental lipids during wk 1 of the study. During wk 2, 3, and 4 and overall, ADFI increased with the addition of 2.5% fat and then decreased (quadratic, P < 0.05) with each further increment regardless of source. Feed efficiency responded linearly (P < 0.001) during wk 3 and 4 and overall and quadratically (P < 0.05) during wk 3 and overall, with lipid supplementation showing the greatest G:F at 5.0% and 7.5% supplemental lipids. Apparent total tract digestibility of lipids (linear, P < 0.001) and GE (linear and quadratic, P < 0.001 and 0.01, respectively) increased with increasing level of lipids regardless of lipid source.


View Full Table | Close Full ViewTable 5.

Effects of lipid source and level of supplemental lipids on growth performance and apparent total tract digestibility of lipids and GE in nursery pigs in Exp. 21

 
Item No lipid control Lipid source
Poultry fat, %
Acidulated poultry fat, %
P-value2
2.5 5.0 7.5 2.5 5.0 7.5 SEM Level Source Interaction
BW, kg
    Initial 7.07 7.03 7.06 7.17 7.05 7.05 7.04 0.05 0.428 0.401 0.370
    d 7 8.35 8.27 8.51 8.39 8.45 8.49 8.04 0.16 0.244 0.625 0.309
    d 14 11.06 11.44 11.49 11.60 11.50 11.43 10.86 0.29 0.673 0.302 0.377
    d 213 14.60 15.51 15.46 15.80 15.34 15.66 14.70 0.29 0.575 0.149 0.091
    d 284 18.39 20.03 20.05 20.18 19.89 20.23 19.30 0.35 0.539 0.342 0.321
ADG, kg
    d 0 to 7 0.184 0.178 0.206 0.174 0.203 0.204 0.141 0.021 0.075 0.810 0.425
    d 8 to 14 0.387 0.452 0.425 0.456 0.435 0.419 0.403 0.033 0.816 0.363 0.798
    d 15 to 214 0.491 0.583 0.561 0.607 0.549 0.629 0.548 0.029 0.586 0.791 0.090
    d 22 to 284 0.542 0.645 0.655 0.626 0.643 0.653 0.658 0.021 0.831 0.611 0.668
    d 0 to 284 0.405 0.464 0.464 0.465 0.459 0.470 0.437 0.012 0.441 0.406 0.411
ADFI, kg (as-fed basis)
    d 0 to 75 0.354 0.377 0.350 0.294 0.397 0.348 0.291 0.016 <0.001 0.709 0.740
    d 8 to 146 0.583 0.667 0.623 0.586 0.671 0.593 0.580 0.028 0.021 0.644 0.855
    d 15 to 217 0.789 0.861 0.804 0.799 0.890 0.818 0.781 0.043 0.001 0.476 0.590
    d 22 to 286 0.938 1.019 0.969 0.943 1.046 0.967 0.956 0.031 0.009 0.752 0.961
    d 0 to 287 0.663 0.731 0.684 0.656 0.749 0.678 0.650 0.022 <0.001 0.708 1.000
G:F
    d 0 to 7 0.517 0.467 0.574 0.567 0.507 0.578 0.469 0.056 0.314 0.675 0.483
    d 8 to 14 0.664 0.678 0.696 0.776 0.642 0.686 0.697 0.042 0.247 0.259 0.758
    d 15 to 215,6 0.620 0.619 0.701 0.756 0.617 0.762 0.711 0.028 0.000 0.807 0.196
    d 22 to 285 0.583 0.624 0.680 0.666 0.618 0.679 0.693 0.025 0.043 0.768 0.772
    d 0 to 285,7 0.615 0.616 0.681 0.708 0.614 0.695 0.677 0.015 <0.001 0.587 0.357
Apparent total tract digestibility,%
    Lipids5 17.8 49.8 71.8 78.7 50.6 70.2 75.8 1.6 <0.001 0.333 0.470
    GE5,7 76.1 76.3 83.2 84.8 76.6 83.6 84.0 1.0 <0.001 0.935 0.789
1Pigs were allowed an adjustment period of 7 d after weaning before initiation of the study. Values represent least squares means of 9 pens with 4 pigs per pen.
2Probability values represent statistical analysis of data excluding the no-lipid control diet and represents the main effects and interaction effects of the 2 × 3 factorial with 2 sources of lipids and 3 inclusion levels (2.5%, 5.0%, and 7.5%).
3Linear effect of level of lipid (0%, 2.5%, 5.0%, or 7.5%) inclusion (P < 0.10).
4Linear effect of level of lipid (0%, 2.5%, 5.0%, or 7.5%) inclusion (P ≤ 0.01).
5Linear effect of level of lipid (0%, 2.5%, 5.0%, or 7.5%) inclusion (P < 0.001).
6Quadratic effect of level of lipid (0%, 2.5%, 5.0%, or 7.5%) inclusion (P < 0.05).
7Quadratic effect of level of lipid (0%, 2.5%, 5.0%, or 7.5%) inclusion (P < 0.01).

Mortality in Exp. 2 was 2.7%, and occurred primarily in pigs of the first farrowing group (5 out of 140 pigs died in this group). Two pigs were fed the 2.5% APF diet, 2 pigs were fed the 5.0% APF diet, and 1 pig was fed the 7.5% APF treatment; 1 pig from each APF treatment died in the first week, 1 pig in the 2.5% APF group died in wk 4, and 1 pig fed 5% APF died in wk 3. For the second farrowing group of pigs, a total of 2 out of 112 pigs died. One pig was fed 5.0% PF, and 1 pig was fed the negative control; both pigs died in week 3. To account for death losses, data were reanalyzed considering group of pigs in the model. In addition, death losses were included in the calculation of total daily gain, feed intake, and feed efficiency. Specifically, we calculated an adjusted weight gain per pen to account for any death losses that occurred as the difference between final BW of pigs in the pen minus initial BW of pigs in the pen. Adjusted G:F was calculated from the total gain of pigs per pen divided by the total feed intake of pigs in the pen. We observed a tendency for an interaction between group of pigs and source of lipids for adjusted gain (P = 0.06) and adjusted G:F (P = 0.006; data not shown). For group 1, adjusted gain was superior when pigs were fed PF compared to APF (51.3 vs. 43.9 kg/pen; P = 0.02); conversely, for group 2, the difference was not statistically significant (50.7 vs. 51.7 kg/pen for PF and APF, respectively; P = 0.8). Adjusted G:F was greater for group 1 when PF was included in the diet (0.679 vs. 0.597; P = 0.002); however, differences between fat sources were not statistically significant for group 2 (0.638 vs. 0.662 for PF and APF, respectively; P = 0.37).

The addition of lipid sources to nursery pig diets has been shown to primarily reduce feed intake, resulting in an improvement in feed efficiency (Pettigrew and Moser, 1991); however, the effect on BW gain has not been consistent (Øverland and Sundstøl, 1995; Tokach et al., 1995). In our 2 experiments, the use of supplemental lipids improved feed efficiency, being more evident during the last weeks of the studies. In Exp. 1, the improvement in G:F was driven mainly by a reduction in ADFI, which is in agreement with the results obtained by Lewis et al. (1980) and Li et al. (1990). In their experiments, nursery pigs fed a diet with 5% lipid inclusion, using a mixture of vegetable oils and lard, had decreased feed intake and improved feed efficiency compared to pigs fed diets without added lipids. In contrast, in Exp. 2 of the current study, the improvement in G:F was due to a combination of increased ADG with lipid supplementation and reduced feed intake at lipid levels above 2.5%. The improvement in ADG with lipid supplementation was greatest at 2.5% supplemental lipid, which coincided with an increased ADFI in pigs fed 2.5% added lipids compared to pigs fed the negative control diet. We suggest that supplementation of lipids at the low level may have improved palatability of the diet because of reduced dustiness of mash diets, subsequently improving feed intake and daily gain. Similarly, Leibbrandt et al. (1975) reported that pigs, given a choice, preferred lipid-supplemented diets compared to diets without added lipids. Tokach et al. (1995) did not report any differences in ADFI when nursery pigs were fed diets containing 3%, 6%, or 9% soy oil.

During wk 3, there was a reduction in feed intake when the diet was low in FFA and saturation, specifically the dietary treatment with the lipid source consisting of 100% SO; the same feed intake reduction was observed for the high-FFA and high-saturation treatments, specifically the dietary treatment with 95% CWAG. Cera et al. (1988a) fed lard, tallow, or corn oil to nursery pigs and did not report any difference in performance related to the level of saturation of the lipid sources. The low feed intake observed in pigs fed diets with high levels of SO and CWAG in the present study could be related to their greater level of rancidity compared to the other sources (Table 2). Rancid dietary lipids can reduce ADFI in nursery pigs (DeRouchey et al., 2004).

The results of Exp. 1 showed that pigs fed high-FFA diets had superior BW and ADG compared to those fed low-FFA diets. Low-FFA dietary treatments were prepared with SO and CWG. The SO used in Exp. 1 was a food grade refined, bleached, and deodorized soybean oil (refined to remove most impurities or nontriglyceride materials) and was not stabilized with antioxidants. Peroxide values of SO increased from 33, 100, and 543 meq/kg for initial, 4, and 20 h, respectively (Table 2). Additionally, the p-anisidine value was 12.4. The peroxide value measures primary products of lipid peroxidation, and p-anisidine measures secondary peroxidation products. Consequently, a linear increase in PV indicates that lipids can be further peroxidized, and the p-anisidine values provide a more reliable judgment of the oxidative status of the lipids. However, these values characterize the lipids in a specific instant and may not represent potential changes over time. Thus, our data indicate that the SO used was susceptible to lipid peroxidation. Feeding peroxidized lipids has demonstrated to reduce growth in rats (Kimura et al., 1984), chickens (Cabel et al., 1988; Sheehy et al., 1994; Dibner et al., 1996a,b), and pigs (DeRouchey et al., 2004). It may also increase the need to detoxify peroxidation products by the pig (Shurson et al., 2012), causing oxidative stress because of accumulation of reactive oxygen substances. Dibner and Knight (2008) stated that oxidative stress in the gastrointestinal system is associated with loss of barrier function. Failure of the intestinal barrier can increase bacteria translocation (Walker and Sanderson, 1992) and subsequently increase protein degradation (Waggoner et al., 2009) and reduce feed intake (Elsasser et al., 1995; Steiger et al., 1999). Figure 1 shows the relation of calculated initial PV (the percentage of lipid source included in the dietary treatment times the initial PV of the source) and ADG. Average daily gain was reduced when initial PV increased.

Figure 1.
Figure 1.

Relationship (R2 = 0.68) between initial peroxide value of supplemental lipids and ADG (Exp. 1, d 0 to 21). Treatments (Trt) consisted of the following proportions of lipid sources in the 6% supplemental dietary lipids: Trt 1, 100% choice white grease (CWG); Trt 2, 95% choice white acid grease (CWAG) and 5% CWG; Trt 3, 50% soybean oil (SO) and 50% CWG; Trt 4, 38% soybean-cottonseed acid oil blend (SAO), 12% SO, 48% CWAG, and 2% CWG; Trt 5, 100% SO; and Trt 6, 76% SAO and 24% SO.

 

In Exp. 2, there was no difference in final BW and ADG between PF and APF. Nevertheless, when including death losses in the calculations of growth performance data, pigs fed diets supplemented with APF had lower BW gain and feed efficiency for the first group of pigs but not the second farrowing group. It is not clear why we experienced greater death losses uniquely in pigs fed APF dietary treatments for the first group. Necropsy results did not reveal potential causes that could be attributed to dietary treatments. Leibbrandt et al. (1975) reported that lard improved G:F, in contrast to hydrolyzed fat in weanling pigs. Conversely, DeRouchey et al. (2004) did not find adverse effects on weanling pig performance when feeding CWG (hydrolyzed by lipase) with up to 53% FFA. Thacker et al. (1994) showed no difference in performance of broilers when fed wheat-soybean meal diets with 8% of acidulated fatty acids containing 57% FFA compared with diets containing 8% tallow.

In both experiments, inclusion of lipid sources to the diets greatly improved ATTD of lipids. Xing et al. (2004) used chromium oxide at 0.1% as an indigestible marker for the estimation and reported an ATTD of lipids of 36% for diets with no supplemental lipids. Bayley and Lewis (1965) and Dove (1995) used total collection and reported 28% and 29% apparent fecal lipid digestibility for diets without added lipids fed to nursery pigs. Digestibility of lipids and GE in the present study gradually improved with each further increment of lipid inclusion. Similarly, Eusebio et al. (1965) found that ATTD of lipids increased with increasing dietary lipid levels. These observations are likely a consequence of the change in the relative proportion of endogenous lipid excretions relative to total lipids, rather than a result of more efficient lipid digestion. In addition, the greater ATTD of lipids in the present study for lipid-supplemented diets may be related in part to a reduction of food passage, resulting in a more complete absorption of nutrients (Mateos et al., 1982), and to the fact that young pigs can use extracted lipids better than lipids originating from plant-based ingredients (Adams and Jensen, 1984; Kil et al., 2010).

Unexpectedly, ATTD of lipids decreased linearly when saturation level decreased for low-FFA diets (100% CWG, 50:50 CWG and SO, and 100% SO). Many studies have demonstrated that unsaturated lipids are more digestible than saturated lipids (Sewell and Miller, 1965; Carlson and Bayley, 1968; Hamilton and McDonald, 1969; Stahly, 1984; Cera et al., 1988b; Wiseman et al., 1990; Jørgensen et al., 1992; Øverland et al., 1994; NRC, 2012). We propose that this observation may be primarily related to the oxidative stability of SO. Libby (2006) reported that inflammatory responses affecting organs such as the liver, kidneys, and lungs are activated when lipid peroxidation products are absorbed in the gut and can damage the small intestinal structure (Dibner et al., 1996a,b). Thus, our data indicate lipid peroxidation of SO may have decreased ATTD of lipids and growth performance.

Wiseman et al. (1991), Powles et al. (1993), and Jørgensen and Fernández (2000) reported that increased FFA concentration in supplemental lipids caused a progressive reduction in the DE value of the lipids. This is in agreement with Exp. 1. Conversely, no differences in ATTD of lipids and GE were reported for PF and APF. DeRouchey et al. (2004) used CWG in nursery pig diets containing up to 53.0% FFA and did not observe a decrease in fat and GE digestibility.

Results from Exp. 1 and Exp. 2 indicated that lipid sources high in FFA (54% and 35%, respectively) can be used in diets of nursery pigs without reducing pig performance. The experiments were not designed to specifically assess the effect of rancidity of lipids on pig performance. However, the results indicated that rancidity of lipid sources may need to be considered closely when selecting lipid sources for inclusion in diets for pigs. Acidulated fats and oils seem to be an attractive alternative for more expensive lipid sources. Nonetheless, mortality reported for Exp. 2 indicates that management factors may affect the response of nursery pigs to acidulated poultry fat. Clearly, the utilization of acidulated lipids in swine diets needs to be studied in commercial facilities while considering death losses and viability of pigs to verify in practice their economical advantage.

 

References

Footnotes


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