Subsequent response to early diet cholesterol and feed restriction in swine

NUTRITION RESEARCH, Vol. 11, pp. 461-469,1991 0271-5317/91 $3.00 + .00 Printed in the USA. Copyright (c) 1991 Pergamon Press plc. All rights reserved.

SUBSEQUENT RESPONSE TO EARLY DIET CHOLESTEROL AND FEED RESTRICTION IN SWINE Wilson G. Pond, Ph.D.1 and Harry J. Mersmann, Ph.D.1

U.S. Department of Agriculture, Agricultural Research Service Roman L. Hruska U.S. Meat Animal Research Center P. O. Box 166, Clay Center, NE 68933

ABSTRACT

Three four-way cross (Chester White x Landrace x Large White x Yorkshire) female pigs from each of twelve litters were used. One pig from each trio remained with its primiparous dam and its other littermates to age 28 d. Two pigs from each trio were removed to individual boxes at age 24 to 36 h and fed liquid sow-milk substitute containing low cholesterol (14 rag/100 g) or high cholesterol (151 rag/100 g) to age 28 d. All pigs were weaned to a dry diet containing 182 mg cholesterol/100 g to age 12 wk and 115 mg cholesterol/100 g from age 12 wk to 20 wk. Carcass measurements and organ weights were recorded at slaughter (20 wk) and liver was analyzed for cholesterol. Body weights were recorded weekly to 28 d and bi-weekly thereafter; serum total cholesterol was determined on d 1, 28, 56, 84, 112 and 136. Sow-reared (SR) pigs were heavier (P<0.01) at age 28 d than sow-milk substitute-reared pigs and the difference persisted to age 20 wk. Weights of trimmed Boston butt, picnic, loin and ham and of liver, heart, spleen, kidneys, except brain, were reduced (P <0.0D proportionately in sow-milk substltute-reared compared with SR pigs, but HC and LC were similar to each other. Serum cholesterol of LC pigs was less than that of HC and SR pigs by d 28 (77, 171 and 145 rag/100 mL, respectively, P < 0.01). Serum cholesterol response curves over time and peak concentration were less for LC than HC and SR (LC < HC < SR, P < 0.01). Peak concentration was reached later in LC than in HC and SR pigs (91, 70 and 70 d, respectively, P < 0.01). Liver cholesterol concentration was unaffected by early cholesterol deprivation (LC vs HC) or by reduced growth due to early weaning to liquid diets. It is concluded that dietary cholesterol deprivation of pigs during the first 4 wk of postnatal life reduced the serum cholesterol response to a high cholesterol diet fed from age 4 wk to 20 wk, but had no effect on concentrations of cholesterol in liver at age 20 wk. KEY WORDS: Pigs, serum cholesterol, liver cholesterol, liquid diets, artificial rearing, growth.) 1 Present address: USDA-ARS Children's Nutrition Research Center, 1100 Bates Street, Houston, TX 77030.

461

462

W.G. POND and H.J. MERSMANN INTRODUCTION

Conflicting results have been reported concerning the effect of cholesterol ingestion in neonatal life on cholesterol metabolism in later life. Some have reported a smaller increase in plasma (or serum) cholesterol in rats and pigs in response to a dietary cholesterol challenge following ingestion of a high cholesterol diet compared with ingestion of a diet containing no cholesterol (i, 2, 3). Others have failed to show such a response in rats (4,5,6),gerbils (7) and adult (age 6 to 8 yr) baboons (8).There is evidence for differences in serum cholesterol, lipoprotein cholesterol and apoprotein concentrations and in cholesterol metabolism in juvenile baboons following breast versus formula feeding (9,10). Baboons breast fed during infancy had lower high density lipoprotein cholesterol concentrations and lower cholesterol production rate at age 6 to 8 yr than did those fed formula {8). In humans, a higher serum cholesterol was observed in 1 year-old (11) and 7 to 12 year-old (12) children who had been breast-fed or fed a cow's milk formula compared to children who had been fed a low-cholesterol formula. F o m a n et al. (13) reported no difference in serum cholesterol of 8-year-old children fed low versus high cholesterol in infancy. The present experiment was designed to determine the effect of cholesterol deprivation in suckling pigs on plasma and liver cholesterol concentrations in later life. The effect of handfeeding four times daily a liquid sow-milk substitute (with or without added cholesterol) at a restricted level of total daily nutrient intake on subsequent serum and liver cholesterol concentration and on body growth and carcass traits was also determined. MATERIALS

AND

METHODS

Three four-way cross (Chester White x Landrace x Large White x Yorkshire) female pigs from each of twelve litters were used. One pig from each trio remained with its primiparous d a m and its other littermates to age 28 d. T w o pigs from each litterwere removed at age 24 to 36 h and placed in individual plywood boxes (approximately 50 x 60 c m floor area) equipped with overhead heat lamps to maintain ambient temperature at 36 to 40~ Liquid sow-milk substitute (Table 1) was provided four times daily from plastic feed dishes that were removed and washed immediately after each feeding (usually all feed was consumed within 5 rain). One of the pigs received the liquid diet with high-cholesterol content (HC), and the other pig received the lowcholesterol (LC) liquid diet. A m o u n t of feed offered was gradually increased each day (daily dry matter intake of approximately 5 % of body weight) except when the onset of poorly formed or light colored feces was observed, in which case upward adjustment of feed allowance was delayed one or~more days. Beginning at d 26, dry feed of the same composition used for the liquid formulas Was sprinkled onto the liquid diet as fed to enhance the transition to dr~ feed. O n d 28, liquM feeding was discontinued and pigs were fed exclusively dry diets ad libitum. O n d 29, littermate trios were placed together in concrete slatted-floor pens in an environmentally controlled nursery building (22 _+ 2~ 12 h light, 12 h dark cycle) and fed the dry high cholesterol diet (Table 1) ad libitum. At age 12 w k pigs were moved in groups of 5 to 7 to concrete slatted-floor pens in an environmentally controlled growing-finishing building (20 __. 2~ 1 2 h light, 12 h dark cycle) and fed ad libitum to age 20 w k a corn-soybean meal-based diet containing 1 0 % tallow and 4 % dried egg yolk ~Table 1).

Body weight of individual pigs was recorded on d 1, 7, 14, 21, 28, 56, 84, 112, and at slaughter at wk 20. Feed consumption of individuals was recorded during the liquid feeding period (d 1 to 28). Feed consumption of groups was recorded from d 29 to slaughter, but group composition prbcluded analysis of diet or litter effects on feed consumed. Blood was sampled from the anterior vena cava of each pig on d 1, 28, 56, 84, i12, and 136 for determination of serum cholesterol (14). All pigs were electrically stunned and exsanguinated at age 20 wk. Carcass weight, carcass length {anterior edge of first rib to pubic bone), weights of trimmed (visible external fat removed) wholesale cuts {Boston butt, picnic, loin, h~im) and of heart, spleen, liver, kidneys, cerebrum and cerebellum were recorded. Subcutaneous backfat depth was measured on the longitudinally split carcass at the first rib, last rib and last lumbar vertebra and cross-sectional area of the Ion-

RESPONSE TO DIETARY CHOLESTEROL

463

TABLE 1 Composition of Diets. 0 to 4 wk Low High Cholesterol Cholesterol (liquid)* (liquid)* Dried skim milk Dried whole milk Corn Oil Dried egg yolk Tallow Casein Corn Soybean Meal Dicalcium p h o s p h a t e Limestone Iodized salt Vitamin premix Choline chloride Trace mineral premix TOTAL

84.2 -15.0 --------

12 to 20 wk High Cholesterol (dry)

30.0 56.2 -4.0 7.0 2.0 -----

0.2 0.2 0.4 100.0

0.2 0.2 0.4 100.0

0.2 0.2 0,4 100.0

---4.0 10.0 -61.9 20.0 2.4 0.5 0.4 0.2 0.2 0.4 100.0

28.4 15.7 14.1

28.9 15.6 151.1

26.3 22.6 182.7

15.1 13.0 114.7

-

-

37.0 56.2 -4.0 -2.0 -----

4 to 12 wk Low Cholesterol (dry)

-

-

-

-

Calculated analysis, dry basis: Protein, %~ Fat, %# Cholesterol, mg/100gw

* Dry m i x t u r e diluted with water (4 parts water to 1 p a r t dry mixture) a n d mixed in Waring Blender. Values used: corn oil, 0; dried skim milk, 33.7; dried whole milk, 25.4; dried egg yolk, 6.0; soybean meal, 44.6; corn, 9.6; crude casein, 85%. # Values used: corn oil, 100; dried skim milk, 0.8; dried whole milk, 26.6; tallow, 100; soybean meal, 1.4: corn, 3.8; dried egg yolk, 10.0; crude casein, 0%. w Values used: corn oil, 0; dried skim milk, 16.7; dried whole milk, 117; dried egg yolk, 2,630; tallow, 95; crude casein, 0 rag/200 g. Sources: NRC (29); Feeley et al. (30); Wilson et al. (31)

gissimus muscle was m e a s u r e d planimetrically from an acetate paper tracing of t h e 1 0 t h - l l t h rib interface. Subcutaneous fat {boundaries delineated by line t h r o u g h spinal process to skin and perpendicular line on plane of v e n t r a l edge of longissimus muscle to skin) m e a s u r e d planimetrically was recorded from a n acetate paper tracing of t h e 10th-11th rib interface. A sample of liver {cut from tip of lobe a t t a c h e d to gall bladder) from 27 pigs (nine litters of t h r e e littermates) was frozen a t -20~ and later analyzed for cholesterol concentration (15). Data for s e r u m cholesterol were plotted in concentration (mg/100 mL) a t each sampling t i m e and t h e area u n d e r the curve derived from t h e plot, the peak concentration, and the m e a n day a t which t h e peak was reached were recorded for each animal. Body weight, feed c o n s u m p t i o n (d 1 to 28), carcass and organ weight and liver cholesterol data were subjected to analysis of variance using the SAS general linear model (16) procedure with diet and litter as main effects. Carcass traits were adjusted to a c o n s t a n t carcass weight by covariate analysis (16). S e r u m cholesterol data were analyzed by split-plot analysis of variance (16). The individual a n i m a l was t h e experimental unit for all traits. Differences in m e a n values for each trait were considered to be statistically significant a t P < 0.05.

W.G. POND and H.J. MERSMANN

464

RESULTS

Daily body weight gain from d 1 to d 28 was less (P < 0.01) in pigs fed liquid sow-milk substitute than in sow-reared pigs (81, 87 and 213 g/d in low cholesterol, LC; high cholesterol, HC and sow-reared, SR, pigs, respectively} (Table 2). Liquid feed consumption was almost identical in TABLE 2 Daily Weight Gain {g) of Pigs Fed High or Low Cholesterol in Early Life {Age 1 to 28 Days}.

Time Day 1 to 28 Day 29 to 136

High cholesterol n = 12

Diet Low cholesterol n = 12

Sowreared n = 11

SD

Probability

87* 701

81" 707

213 ~ 754

21 56

0.01 0.10

* ~ Means in the same row without a common superscript differ significantly, P < 0.01. HC and LC pigs from 1 to 28 d. The greater weight gain of SR than of HC and LC pigs to 28 d suggests greater dry matter IDM) intake in SR than in other pigs, but no attempt was made to measure intake of SR pigs. Daily gain from d 29 to d 136 tended to be less (P < 0.104) in LC and HC than in SR pigs (701,707 and 754 g, respectively). Absolute values for carcass weight (48.0, 48.1, 56.6 kg, SD 3.7), carcass length [69.2, 69.4, 72.3 cm, standard deviation (SD) 2.1|; weights of trimmed Boston butt i2.2, 2.0, 2.4 kg, SD 0.2), picnic {2.0, 2.1, 2.3 kg, SD 0.2}, loin ~4.4, 4.3, 5.2 kg, SD 0.4) and ham {4.5, 4.4, 5.1 kg, SD 0.3); weight of belly (5.1, 5.2, 6.1 kg, SD 0.6} iP < 0.01); and cross-sectional area of longissimus muscle (23.6, 23.1, 26.4 cm2, SD 2.7) (P < 0.03} and of fat {18.8, 19.2, 22.7 sq. cm, SD 3.6) {P < 0.05) at the 10th-llth rib interface were greater in SR than in HC and LC pigs. However, when adjusted for differences in carcass weight, effects of diet were removed except for trimmed loin and h a m which remained greater in SR than in HC and LC pigs. Absolute weights of liver, kidneys, cerebrum and cerebellum were Unaffected by diet fed during early life, but heart and spleen were heavier in SR than in HC and LC pigs at slaughter {P < 0.01). Relative weights of liver {P < 0.01) and cerebellum {P < 0.05}, but not of other organs, were larger in HC and LC than in. SR pigs {Table 3). Serum cholesterol concentration was similar in all groups at d 1 (62.1, 58.0 and 63.1 +_ 13.9 mg/100 mL for HC, LC and SR, respectively}, but by d 28 LC pigs had lower serum cholesterol (P < 0.01) than did HC and S R pigs {76.8, 171.4 and 144.5 ___ 22.7 mg/100 mL for LC, HC and SR, respectively}. Serum cholesterol response curves over time, peak concentration, and day at which concentration reached a peak are summarized in Table 4. Area under the response curve from d 1 to 136 and from d 28 to 136 was less (P < 0.01) for LC than for HC and was less for HC than for SR pigs. Likewise, peak cholesterol concentration was less for LC than for HC and SR pigs (LC < HC < SR, P < 0.01). Peak concentration of plasma cholesterol occurred 21 d later in LC than in HC and SR pigs ~P < 0.01; 91, 70 and 70 d for LC, HC and SR, respectively). Liver cholesterol concentration was unaffected by early cholesterol deprivation or by feeding a liquid sow-milk substitute (cholesterol content of 300 rag/liter) that supported a body weight (BW) gain less than half of that of sow-reared littermates (cholesterol content of sow milk is about 200 to 500 mg/liter, ref. 17) when fed four times daily in limited amounts during the 28-d liquid feeding period (Table 5).

465

RESPONSE TO DIETARY CHOLESTEROL

TABLE 3 Organ Weights of Pigs Fed High or Low Cholesterol in Early Life (Age 1 to 28 Days).

Organ Liver, g Percent BW Heart, g Percent BW Spleen, g 9Percent BW Kidneys, g Percent BW Cerebrum, g Percent BW Cerebellum, g Percent BW *t #

High cholesterol n--- 12

Diet Low cholesterol n - - 12

1,085.1 1.59" 214.3" 0.31 85.5* 0.12 220.6 0.33 59.2 0.088 9.76 0.0145"

1,061.6 1.54" 212.4" 0.31 90.1" 0.13 209.9 0.30 59.6 0.087 9.70 0.0142"

Sowreared n - - 11 1,089.6 1.37t 236.9 0.30 106.0~ 0.13 227.3 0.29 62.3 0.079 9.87 0.0125 ~

SD

74.3 0.127 17.5 0.026 10.3 0.015 41.7 0.095 4.9 0.010 0.80 0.002

Probability Diet Litter

NS# <0.01 <0.01 NS <0.01 NS NS NS NS NS NS <0.04

< 0.01 NS <0.01 NS <0.01 NS NS NS NS NS < 0.01 <0.01

Means in the same row without a common superscript differ significantly. Not significant.

TABLE 4 Serum Cholesterol Response From Day 1 to 136 or Day 28 to 136 in Pigs Fed High or Low Cholesterol (Age 1 to 28 Days).

Trait Area under curve Serum cholesterol conc (rag/100 mL) x time, d 1 to 136 Serum cholesterol conc (mg/100 mL) x time, d 28 to 136 Peak cholesterol conc, rag/100 mL Day of peak cholesterol conc

High cholesterol n ~ 12

Low cholesterol n -- 12

Sowreared n = 11

SD

Probability Diet Litter

19,393"

15,704

20,721//

1,502

<0.01 <0.01

16,124"

13,816

17,814//

1,207

<0.01 <0.01

177.2"

144.9

194.4//

16.0

<0.01 <0.01

70*

91

70*

14.6

<0.01

NSw

*~f// Means in the same row without a common superscript differ significantly. w Not significant. DISCUSSION The effect of dietary cholesterol in the early life of the pig on subsequent cholesterol metabolism and tissue accretion is relevant to pork composition and human nutrition. The observed effect of dietary cholesterol deprivation in early life on serum cholesterol concentration during a cholesterol challenge in later life has important implications in human nutrition. There is extensive documentation that the pig is a useful model animal for studies of human cholesterol metabolism and heart disease (24, 25, 26) and for nutritional studies related to cholesterol metabolism

W.G. POND and H.J. MERSMANN

466

TABLE 5 Weight and Cholesterol Content of Liver of Pigs Fed High or Low Cholesterol in Early Life (Age I to 28 Days).

Trait Weight, g Cholesterol, mg/100 g Cholesterol, total, mg *

High cholesterol n--9

Low cholesterol n--9

1,074 295 3,179

1,064 287 3,068

Sowreared n=9 1,096 320 3,444

SD

Probability

77.1 42.5 548

NS* NS NS

Not significant.

(27). Reiser et al. (3) suggested that ingestion of cholesterol by human infants might be important for later adequate utilization and metabolism of dietary cholesterol. Exposure of rabbits to cholesterol in early life is associated with persistent changes in aorta. These changes might increase aortic response to subsequent cholesterol challenge (18). The results of the present experiment with pigs suggest that serum cholesterol concentration during the postweaning period is affected by early dietary cholesterol restriction, in the absence of evidence for an effect of this early restriction on cholesterol concentration of liver later in the growing period. However, our results in pigs are the opposite of those of Reiser and Sidelman (2) in that dietary cholesterol was directly related to serum cholesterol in pigs, but inversely related in rats. Limited evidence {19,20,21,22,23) shows that cholesterol content of perk can be altered by diet. Concentrations of tissue cholesterol, except for liver, were not determined in the present experiment. However, the different response of serum cholesterol to early dietary cholesterol suggests the possibility of a difference in muscle and adipose tissue cholesterol concentration. If a relationship exists, it is not necessarily a positive one, since Baldner-Shank et al. (23) observed an inverse relationship between plasma and tissue cholesterol in pigs fed soybean oil or tallow. There is altered cholesterol metabolism {lower cholesterol production rate, reduced mass of the rapidly exchanging cholesterol compartment and lower neutral steroid excretion rates) in breast-fed baboons compared with formula-fed baboons at age 6 to 8 years in the absence of differences in serum cholesterol or lipoprotein concentrations (8). This indicates that primary long term effects of breast or formula feeding in the baboon are likely mediated through programming of the regulation of liver cholesterol metabolism. There were no effects of diet on concentration of cholesterol in liver in the present experiment even though pigs fed the low cholesterol diet as neonates had persistently lower serum cholesterol later in life compared with sow-reared pigs and those fed high cholesterol diets. Further work is needed in pigs to describe the adaptations in cholesterol synthesis, transport and metabolism in response to early ingestion of cholesterol and the kinetics of cholesterol homeostasis and to determine the basis for the apparent species difference between the baboon (8) and pig in long term serum cholesterol concentration. The persistent BW deficit of pigs fed liquid sow-milk substitute in limited amounts to age 28 d compared with sow-reared pigs up to age 20 wk, despite ad libitum consumption of an adequate high cholesterol diet after age 28 d, occurred in the absence of any observed effect on liver cholesterol concentration. The failure to show a compensatory growth response suggests that restricted growth imposed in neonatal pigs agrees with the lack of a compensatory response in overall BW gain in pigs restricted beginning at 17 kg BW (age 6 to 8 wk) and refed after 21 d of restriction (28). Specific organs, i.e., liver, kidney, gastrointestinal tract, may show compensatory growth in the absence of observable compensation at the whole animal level (28). In the present experiment, any such compensation by the liver in restricted pigs apparently was not associated with a permanent change in the processing of dietary lipids and cholesterol by the liver with respect to liver cholesterol deposition.

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467

ACKNOWLEDGMENTS The authors are grateful to Ted Acton, Wayne Peshek, Jenell Dague and associates for animal care and feeding; Pat Roiman and associates for diet preparation; Sandy Cummins for serum cholesterol measurement and statistical analyses; Dave Kohmetscher and associates for animal slaughter and carcass measurements; and Sherry Hansen, Norma Hayley and Rosalyn Schoppa for technical assistance in manuscript preparation. Finally, we thank E. R. Klein, J. D. Eastman and C. Fedrick for their skilled editorial assistance. This work is supported in part by the USDA/ARS, Roman L. Hruska, U.S. Meat Animal Research Center, Clay Center, NE and the Children's Nutrition Research Center, Department of Pediatrics, Bayior College of Medicine and Texas Children's Hospital, Houston, TX. This project has been funded in part with federal funds from the U.S. Department of Agriculture, Agricultural Research Service under Cooperative Agreement number 58-7MOZ-1-001. The contents of this publication do not necessarily reflect the views or policies of the U.S. Department of Agriculture, nor does mention of trade names, commercial products, or organizations imply endorsement by the U.S. Government. REFERENCES

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Accepted for Publication January 21, 1991