Plasma Lipoproteins in Neonatal, Preruminant, and Weaned Calf

Plasma Lipoproteins in Neonatal, Preruminant, and Weaned Calf K. J. JENKINS, G. G R I F F I T H , and J.K.G. K R A M E R Animal Research Centre, 1 Research Branch Agriculture Canada Ottawa, Ontario, K1A 0C6 Canada INTRODUCTION

ABSTRACT

This study compared plasma lipoprotein fraction profiles and lipid composition in the calf at 3 d, 3 wk, and 12 wk (weaned). For all ages the major plasma lipoprotein fraction was high density lipoproteins (52 to 73%), followed by very high density lipoproteins (10 to 22%), low density lipoproteins (13 to 18%), and chylomicrons plus very low density lipoproteins (5 to 9%). Most plasma lipid was cholesterol esters (41 to 49%) and phosphatidylcholine (21 to 29%). Most cholesterol esters (66 to 81%) and phosphatidylcholine (68 to 80%) were in high density lipoproteins; free fatty acids (83 to 96%) and lysophosphatidylcholine (75 to 85%) in very high density lipoproteins; and triglycerides (93 to 98%) in the remaining lipoprotein fractions. Of the three ages studied, 3-dold calves had comparatively low plasma total lipids, high density lipoproteins, cholesterol esters, phosphatidylcholine, and linoleic acid in all lipid classes; they had relatively high plasma very high density lipoproteins, triglycerides, free fatty acids, phosphatidylethanolamine, and 20:3 n-9 fatty acid (indicative of essential fatty acids deficiency). Lipoprotein classes and lipid composition were similar at wk 3 and 12. Comparison of fatty acid profiles for phosphatidylcholine with those for lysophosphatidylcholine and cholesterol esters indicated plasma lecithin-cholesterol acyltransferase was active in calves at all three ages studied.

Plasma lipoproteins are lipid-protein complexes that function in the stabilization and vascular transport of lipids as well as in the exchange of lipids between tissues (2). Five main groups of lipoproteins have been defined (2) according to the density range that permits their isolation during ultracentrifugation: chylomicrons, very low density lipoproteins (VLDL), low density lipoproteins (LDL), high density lipoproteins (HDL), and very high density lipoproteins (VHDL). Bovine plasma contains small amounts of chylomicrons and VLDL, and these two fractions usually are combined (3). Chylomicrons and VLDL are characterized by their high triglyceride (TG) content. The LDL and HDL fractions are the principal carriers of phospholipids and cholesterol esters (CE), and VHDL contains the complexes of plasma proteins and free fatty acids (FFA), as well as lysophosphatidylcholine (LPC). The VHDL fraction plays an important role in promoting lipoprotein lipase (LL) and lecithin: cholesterol acyltransferase (LCAT) activities (5). Most studies on bovine lipoproteins have been on pregnant or lactating animals (2, 3) and relatively few on the preruminant calf (1, 11). Lascelles and Wadsworth (11) investigated the origin of lipoproteins in the lymph of newborn calves, and Bauchart and Levieux (1) studied the composition of the major classes of lipoproteins in calves at 3 wk of age. This study was to determine the effect of calf development, from 3 d postpartum through the preruminant and early weaning stages, on plasma lipoprotein classes and their lipid composition. MATERIALS AND METHODS Calves and Diets

Received March 2, 1988. Accepted May 26, 1988. 1Contribution Number 1529. 1988 J Dairy Sci 71:3003-3012

Three Holstein heifers were obtained at birth from the Animal Research Centre dairy cattle 3003

3004

JENKINS ET AL.

TABLE 1. Fatty acid composition of milk and colostrum fed to calves. I Fatty acids 2

Herd milk

Milk at 2 d postpartum

4:0 6:0 8:0 10:0 12:0 t4:0 16:0 18:0 16:1 18:1 18:2 18:3

3.3 1.2 1.0 2.9 4.1 14.2 30.6 7.2 2.1 22.5 2.5 .4

2.6 1.2 .9 2.5 3.7 14.0 30.5 6.9 2.2 24.0 2.6 .4

n-7 n-9 n-6 n-3

1 Relative abundance of fatty acids in weight percent with minor fatty acids not included. Milk was a single composite sample from dairy herd; milk at 2 d postpartum was a composite of three samples. 2Number of carbon atoms: number of double bonds, n-x, where n is the chain length of the fatty acid and x is the number of carbon atoms from the last double bond to the terminal methyl end.

n u t r i t i o n herd and raised to obtain samples o f b l o o d plasma at 3 d, 3 wk, and 12 wk of age. Calves were allowed to suckle their dams for 3 d after birth. Samples o f 2d p o s t p a r t u m milk

TABLE 2. Composition of starter-grower ration. Ingredient (%) Rolled barley Flaked corn Soybean meal (49% CP) Wheat bran Dehydrated alfalfa meal (17% CP) CP content, % DM Molasses Trace-mineralized salt 2 Limestone Dicalcium phosphate

37.4 24.9 20.0 5.0 5.0 17.3 5.0 1.5 .7 .5

1Added to 1 tonne of above mixture: 4.5 × 106 IU stabilized vitamin A, 7.2 × l0 s IU stabilized vitamin D, and 4.5 X 104 IU stabilized vitamin E. ~Composed of (%): CuSO4-SH20, .1; ZnSO4, 1.0; MnSO 4 -H 2 O, .5 ; Na 2 SO4, 17.0; cobalt-iodized salt, 75.4 (contained 99.0% NaC1, 40 ppm cobalt, 70 ppm iodine; Canadian Salt Company, Mississauga, Ont.); MgO, 6.0. Journal of Dairy Science Vol. 71, No. 11, 1988

were taken f r o m the three cows and subjected to fatty acid analyses (Table 1). A f t e r 3 d of age, calves were fed whole milk twice daily (each meal at 5% b o d y weight) to 6 wk of age, weaned abruptly, and fed starter-grower ration (Table 2) for an additional 6 wk. The calves appeared in g o o d health t h r o u g h o u t the experiment. Blood Samples

Jugular blood was o b t a i n e d f r o m the calves in the morning following an overnight fast, after t h e y had received the d a m ' s milk for 3 d, and again w h e n t h e y were 3wk and 12 w k of age. Blood was centrifuged at 5000 × g for 15 rain, and the plasma was r e m o v e d and stored no longer than 1 d at 5°C b e f o r e being ultracentrifuged for lipoprotein class separation. Isolation of Lipoprotein Fractions

The procedures used for separating lipoproreins were essentially those of Wendlandt and Davis (21). All centrifugations were performed with a Beckman t y p e 30 r o t o r (Beckman Instruments, Fullerton, CA) in a Beckman L-2 ultracentrifuge at 100,000 × g and 5°C. Samples were adjusted to desired densities with sodium chloride and potassium b r o m i d e solutions, as described by Havel et al. (8). F o u r lipoprotein fractions were isolated using the density intervals c o m m o n l y used for ruminants (3, 13): c h y l o m i c r o n s plus V L D L , density < 1 . 0 0 6 g/ml; LDL, density 1.006 to 1.063 g/ml; HDL, density 1.063 to 1.21 g/ml; and V H D L , density >1.21 g/ml. Because of the small a m o u n t s o f c h y l o m i c r o n s and V L D L , t h e y were c o m b i n e d to f o r m the first fraction. The V H D L fraction usually is o m i t t e d in analyses for lipid c o m p o s i t i o n ; apparently this study presents the first c o m p l e t e data for V H D L in calf plasma. Lipid Analyses

All analytical procedures for lipids in lipoproteins, plasma, milk, and colostrum were as by Jenkins et al. (10). These included lipid extraction m e t h o d s , lipid class separation and quantitation by the latroscan m e t h o d (The Iatroscan TH-10 Analyzer, Mark II; Technical Marketing Associates Ltd., Mississauga, Ontario, Canada), and f a t t y acids analysis by TLC separation of lipid classes, transesterification with an-

LIPOPROTEINS IN DEVELOPING CALF hydrous methanol-HC1, and determination of fatty acid methyl esters by gas chromatography. Total blood lipids were determined by extraction of 1.0 ml of plasma by methods described by Jenkins et al. (10) and quantitation by the Iatroscan method using methylheptadecanoate as internal standard. Statistics

Data were analyzed statistically by analysis of variance and Duncan's rnultiple range test using 5% probability (19). RESULTS A N D DISCUSSION Plasma Total Lipids, Lipoprotein Profile

The plasma of 3-d calves contained a low concentration of total lipids (106.5 mg/100 ml; Table 3) relative to the older calves and to published data for adults [300 to 400 rag/100 ml (4)] but was typical for newborn ruminants. Christie (3) reported average values (mg/100 ml plasma) of 110 for calves, 60 for lambs, and 68 for goats. Forte et al. (7) found only 44 mg lipid/100 ml plasma for the fetal calf. By 3 wk, plasma total lipids rose to 193 mg/ 100 mI and slightly higher to 238 rag/100 ml for the weaned calf at 12 wk (Table 3). Others have also observed a rapid rise in plasma

3005

lipids in calves (4) and lambs (18) several weeks after birth and have attributed this to the high intake of dietary fat provided by colostrum and milk. Plasma lipids in the young ruminant tend to be relatively constant after weaning (4). The main lipoprotein (Table 3) in the 3-d calves was HDL (51.6% of total lipoproteins), followed by VHDL (21.7%), LDL (18.0%), and a small amount of chylomicrons plus VLDL (8.7%). Forte et al. (7) reported that LDL is the major lipoprotein in fetal calf plasma until the onset of suckling when there is an immediate shift to HDL as the predominant class. This contrasts with the human, where there is a shift from HDL to LDL after birth (7). At both 3 and 12 wk HDL increased (52 to 72%) and other lipoprotein fractions decreased (Table 3). Bauchart and Levieux (1) found a similarly high proportion of HDL for 3-wk-old Friesian calves. High density lipoprotein also represents over 70% of the plasma lipoproteins in lactating dairy cows (21), adult sheep (13), and beef animals (6). Thus, it appears that HDL expresses its predominance as a plasma lipid carrier virtually throughout the life of the ruminant animal. Plasma from calves of all ages studies contained a low concentration of chylomicrons plus VLDL (Table 3), which is a characteristic feature of ruminants (3, 14, 21). The low con-

TABLE 3. Effect of calf age on total plasma lipids and lipoprotein profile. 1 Lipids and lipoproteins 2 Total lipid, rag/100 ml plasma Chylomicrons plus VLDL LDL HDL VHDL

3d

Calf age3 3 wk

12 w k

SE

106.5c

193.3 b

23 7.7a

10.1

5.1 b 12.6 b 72.8a 9.5b

.9 1.6 4.0 1.5

8.7 a 18.0a 51.6 21,7 a

(% by weight) 5.4b 13.1 b 71.8 a 9.7b

a'b'CMeans in the same row with different superscript letters differ (P<.05). 1Average of three calves for each age group. 2Chylomicrons plus very low density lipoproteins (VLDL), density <1.006 g/ml; low density lipoproteins (LDL), density 1.O06 to 1.063 g/ml; high density lipoproteins (HDL), density 1.063 to 1.21 g/ml; very high density lipoproteins (VHDL), density >1.21 g/ml. 3Calves 3 d postpartum fed colostrum and early milk only; 3 wk postpartum fed colostrum and early milk first 3 d and whole milk next 18 d; 12 wk fed as for 3 wk but weaned from milk at 6 wk and fed dry diet for additional 6 wk. Journal of Dairy Science Vol. 71, No. 11, 1988

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JENKINS ET AL.

centration of these lipoproteins has been attributed to continuous absorption of small amounts of lipid from the gastrointestinal tract and to extensive lipolysis of these lipoproteins in the lymph (1, 2). Lipid Classes in Lipoprotein Fractions

For all calf ages, the major lipid classes in plasma (Table 4, lipoprotein fractions combined) were CE (41 to 49%) and phosphatidylcholine (PC; 21 to 29%), with smaller amounts of other phospholipids, TG, and FFA. The main change in lipid class profile, from 3 d to 3 wk, was an increase in CE and PC, and lowered TG, F F A and phosphatidylethanolamine (PE). Data were similar for wk 3 and 12. Lipid class profiles for each of the lipoprotein fractions (Table 4) showed that, for all calf ages, chylomicron plus VLDL contained mostly CE, TG, and PC with TG reduced and PC increased at wk 3 and 12. In LDL, both CE and unesterifled cholesterol (C) were present, as well as TG, PC, and other phospholipids, notably PE in the newborn. This lipoprotein fraction had an appreciable effect on increasing the proportions of CE and PC in plasma lipids of the older animals, as well as lowering TG and PE. The lipid class profiles for HDL were similar for all calf ages and contained mostly CE and PC, as found by Bauchart and Levieux (1) for calves at 3 wk of age. The VHDL showed marked reduction in FFA and LPC and increased PC during calf development. Calculations for the amounts of each lipid class showed that about 66% of the plasma CE and PC were carried in the HDL at 3 d and 80% at wk 3 and 12. At all ages studied, virtually all of the TG in plasma of calves was located in the chylomicrons plus VLDL and in LDL fractions, and F F A was located in VHDL. There are numerous reports for most animals showing that the chylomicrons, VLDL, and LDL fractions are the main transporters of TG (2, 5). Similarly, plasma F F A are albumin-bound in

2Number of atoms: number of double bonds; n-x where n is the chain length of the fatty acid and x is the number of carbon atoms from the last double bond to the terminal methyl end.

Journal of Dairy Science Vol. 71, No. i I, 1988

VHDL and in this manner are transported as a source of energy from adipose tissue to sites of utilization (2). In ruminants, FFA appears to be the only lipid in maternal plasma made available to the fetus (15). Our relatively high plasma F F A concentration of 9.1% for 3-d calves agrees closely with a 9.6% value found in another study (4) and indicates that F F A is an important source of energy for the newborn calf as well as presumably for the fetus. Fatty Acids in Major Lipid Classes

The fatty acid compositions of some of the principal lipid classes in lipoprotein fractions are in Tables 5 and 6. Triglycerides

The fatty acid composition of TG in the chylomicrons plus VLDL fractions was similar for 3 d and 3 wk calves (Table 5) and resembled the fatty acids in their diet of perinatal milk or herd milk (Table 1). There were high concentrations of 16:0 and 18:1, as found by (1) for 3-wk-old Friesian calves, but lower 14:0 and no short-chain fatty acids in milk and colostrum that are metabolized rapidly (20). The TG of our ruminating animals at 12 wk contained lower 16:0, 18:1 n-9, 2 and higher 18:0 and 18:2 n-6, than the preruminants, in agreement with a report by Christie (3). Some of these differences result from extensive microbial conversion of 18:1 n-9 to 18:0 in the functioning rumen (12) and from highly selective retention (15) of 18:2 n-6. Phosphatidylcholine, Lysophosphatidylcholine, and Cholesterol Esters

For all lipoprotein fractions, the PC of 3-d calves contained much less 18:2 n-6 than PC for the older animals (Table 6). Relatively low concentrations of PC 18:2 n-6 were in the chylomicrons plus VLDL, and LDL fractions. These low values are to be expected for fetal and newborn calves as most of the 18:2 n-6 in maternal plasma is in the CE and PC, which cannot traverse the placenta (17). High 18:2 n-6 in plasma CE and PC of adults results from hydrolysis of chylomicron TG (containing food 18:2 n-6), preferential utilization of released 18:2 n-6 in the synthesis of PC, and subsequent redirection to CE (18). Very little 18:2 n-6 finds its way

T A B L E 4. Principal classes o f lipids in b l o o d p l a s m a l i p o p r o t e i n s of calves at v a r i o u s ages.*

Lipoproteins fraction =

Calf age 3

CE

C

TG

FFA

L i p i d classes 4 PC

LPC

PE

SP

PI + PS

( w e i g h t %)

e" O

C h y l o m i c r o n s plus VLDL

3 d 3 wk 12wk SE

44.5 43.3 42.1 1.9

LDL

3.d 3 wk 12 w k SE

26.6 b 41.3 a 36.9 a 2.0

10.6 b 13.5 a 12.4 ab .9

HDL

3 d 3 wk 12 w k SE

52.1 52.7 53.8 2.2

5.2 6.7 6.2 .6

.4 .3 .2 .1

VHDL

3 d 3 wk 12 w k SE

24.2 ab 23.2 b 27.5 a 1.3

3.5 2.9 4.7 .8

0 0 0 .. .

3 d 3 wk 12 w k SE

40.8 b 48.9 a 48.7 a 2.3

5.4 6.8 6.7 .6

8.1 a 2.7 c 4.0 b .3

Fractions combined

2.0 2.2 2.4 .3

T o t a l lipids in f r a c t i o n (mg/lO0 ml plasma)

32.8 a 24.8 b 31.6 a 1.5

2.3 a 2.1 ab 1.3 b .3

18.4 c 27.6 a 22.6 b .9

0 0 0 .

0 0 0

26.0 a 10.8 c 17.1 b 1.2

.1 .1 .1 .. .

9.9 b 19.7 a 19.8 a 2.5

.3 .3 .3 .. .

.3 .3 .2 .1

27.7 30.8 31.3 1.7

.5 .4 .4 .I

.

40.2 a 24.9 b 10.5 c 2.7

15.7 b 14.7 b 27.0 a 1.3

5.3 b 21.6 a 19.4 a 2.7

9.1 a 2.5 b 1.2 c .3

21.2 b 27.9 a 29.0 a 2.0

1.3 b 2.1 a 2.0 a .2

.

.

.

0 0 0 .

.

.

.

0 0 0 .

.

9.2 10.5 12.1 1.6

.

21.3 a 7.5 b 7.0 b 1.0

4.6 6.4 6.1 .8

.6 a .4 b .3 b .1

19.2 b 25.4 a 30.0 a 1.9

7.0 a 3.4 b 3.2 b .8

5.7 4.4 4.0 .7

1.1 1.0 .7 .2

6.7 8.7 7.3 1.1

3.3 2.5 2.8 .5

1.1 ab 1.5 a .8 b .2

23.1 18.8 22.3 1.7

8.8 a 4.1 b 3.9 b .9

4.5 4.2 4.0 .6

.8 a .8 a .5 b .1

106.5 c 193.3 b 237.7 a 10.1

55.0 c 138.6 b 173.3 a 5.1

O ,q m Z t7 tO

a'b'CMeans in the s a m e c o l u m n w i t h d i f f e r e n t s u p e r s c r i p t l e t t e r s w i t h i n f r a c t i o n s differ (P<.05). 1 Average of three calves for each age g r o u p . < o

Z .o

0o

00

= C h y l o m i c r o n s plus v e r y l o w d e n s i t y l i p o p r o t e i n s ( V L D L ) , d e n s i t y < 1 . 0 0 5 g / m l ; l o w d e n s i t y l i p o p r o t e i n s (LDL), d e n s i t y 1.006 to 1.063 g / m l ; high d e n s i t y lipop r o t e i n s (HDL), d e n s i t y 1.063 to 1.21 g / m l ; v e r y high d e n s i t y l i p o p r o t e i n s (VHDL), d e n s i t y > 1 . 2 1 g/ml. 3 Calves 3 d p o s t p a r t u m fed c o l o s t r u m a n d e a r l y m i l k o n l y ; 3 w k p o s t p a r t u m fed c o l o s t r u m a n d early m i l k first 3 d and w h o l e m i l k n e x t 18 d; 12 w k p o s t p a r t u m , fed as for 3 w k b u t w e a n e d f r o m m i l k at 6 w k a n d fed dry d i e t for 6 wk. 4 Lipid classes: C E , c h o l e s t e r o l esters; C, c h o l e s t e r o l ; TG, t r i g l y c e r i d e s (also c o n t a i n e d small a m o u n t s of m o n o g l y c e r i d e s a n d d i g l y c e r i d e s for c h y l o m i c r o n plus V L D L f r a c t i o n o n l y ) ; FFA, free f a t t y acids; PC, p h o s p h a t i d y l c h o l i n e ; LPC, l y s o p h o s p h a t i d y l c h o l i n e ; PE, p h o s p h a t i d y l e t h a n o l a m i n e ; SP, s p h i n g o m y e l i n ; PI, phosp h a t i d y l i n o s i t o l ; PS, p h o s p h a t i d y l s e r i n e .

O

e-

T A B L E 5. F a t t y a c i d c o m p o s i t i o n o f c h o l e s t e r o l esters in p l a s m a l i p o p r o t e i n f r a c t i o n s , a n d o f t r i g l y c e r i d e s in c h y l o m i c r o n s p l u s v e r y l o w d e n s i t y l i p o p r o t e i n s , as a f f e c t e d b y c a l f age. 1

00

O

Fatty acids 4

~7 Lipoprotein fraction2

Calf age 3

14:0

16:0

16:1 n-7

18:0

18:1 n-9

18:2 n-6

18:3 n-3

20:3 n-9

20:4 n-6

20:3 20:4

.3 .3 .4 .1

.20 .13 .15 .05

2; 2 2 PUFA

W Triglycerides Chylomicrons plus VLDL

3 d 3 wk 12 w k SE

5.1 6.3 6.1 .7

34.8 a 32.4 a 24.0 b 1.4

2.6 a 1.6 b 1.2 b .3

11.2 b 12.9 b 25.6 a 1.0

30.8 a 27.0 b 22.0 c 1.2

Chylomicrons plus VLDL

3 d 3 wk 12 w k SE

4.1 2.7 b 2.7 b .3

31.1 a 13.3 b 13.1 b 1.2

3.2 a 3.1 a 2.3 b .2

13.0 a 2.1 c 7.7 b .9

Cholesterol 15.0 a 10.3 b 8.4 b 1.3

esters 15.8 b 52.3 a 50.1 a 4.7

1.2 b 3.9 a 3.8 a .3

0 0 0 . . . .

1.1 b 2.5 a 1.9 a b 3

... ... ... . ..

LDL

3 d 3 wk 12 wk SE

5.4 4.2 3.9 .6

36.8 a 20.6 b 18.5 b 2.7

3.1 a 2.8 a b 2.0 b .3

7.9 b 4.2 c 12.4 a 1.0

22.4 a 16.4 b 12.6 b 1.5

10.4 b 35.5 a 33.2 a 3.8

.9 b 2.5 a 2.7 a .4

.04 .03 .03 . . . .

1.2 1.7 .3 3

... ... . . . . . .

HDL

3d 3 wk 12 w k SE

2.5 2.6 1.9 .3

17.1 a 11.8 b 8.3 c 1.0

5.7 a 3.5 b 2.9 b .4

.9 a .5 b .6 b •1

18.1 a 8.5 b 6.7 b 1.1

37.2 b 57.8 a 63.8 a 3.4

3.1 b 3.8 ab 4.9 a .5

.09 .02 .03 . . . .

3.2 2.2 2.3 4

... ... ... .. .

VHDL

3 d 3 wk 12 w k SE

2.2 2.8 2.3 .4

15.9 a 13.2 b 10.1 c .7

7.0 a 4.3 b 4.0 b .5

.8 b 2.4 a 1.8 a b .4

16.1 a 8.5 b 8.1 b 1•1

40.9 b 52.9 a 58.6 a 2.3

3.9 4.0 4.9 .4

.09 .02 .02 . . . .

4.2 a 2.5 b 2.6 b 4

... ... .. . .. .

2.9 b 3.3 b 4.8 a .5

.4 .4 .6 .1

.06 .04 .06 .01

.15 .11 .34 .09

. •

.

Z

.r"

•

•

•

°

a ' b ' C M e a n s in t h e s a m e c o l u m n w i t h d i f f e r e n t s u p e r s c r i p t l e t t e r s w i t h i n f r a c t i o n s d i f f e r ( P < . 0 5 ) . 1 A v e r a g e o f t h r e e calves f o r e a c h age g r o u p . R e l a t i v e a b u n d a n c e o f t h e m a j o r f a t t y a c i d s in w e i g h t p e r c e n t • 2 C h y l o m i c r o n s p l u s v e r y l o w d e n s i t y l i p o p r o t e i n s ( V L D L ) , d e n s i t y < 1 . 0 0 5 g / m l ; l o w d e n s i t y l i p o p r o t e i n s ( L D L ) , d e n s i t y 1 . 0 0 6 t o 1 . 0 6 3 g / m l ; h i g h d e n s i t y lipop r o t e i n s ( H D L ) , d e n s i t y 1 . 0 6 3 t o 1.21 g / m l ; v e r y h i g h d e n s i t y l i p o p r o t e i n s ( V H D L ) , d e n s i t y > 1 . 2 1 g / m l . 3 Calves 3 d p o s t p a r t u m f e d c o l o s t r u m a n d e a r l y m i l k o n l y ; 3 w k p o s t p a r t u m f e d c o l o s t r u m a n d e a r l y m i l k f i r s t 3 d a n d w h o l e m i l k n e x t 1 8 d; 1 2 w k p o s t p a r t u m , f e d as f o r 3 w k b u t w e a n e d f r o m m i l k a t 6 w k a n d f e d d r y d i e t f o r 6 w k . 4 N u m b e r o f ~carbon a t o m s : n u m b e r o f d o u b l e b o n d s ; n-x, w h e r e n is t h e c h a i n l e n g t h o f t h e f a t t y a c i d a n d x is t h e n u m b e r o f c a r b o n a t o m s f r o m t h e l a s t d o u b l e b o n d t o t h e t e r m i n a l m e t h y l e n d ; ~; 2 2 P U F A = p o l y u n s a t u r a t e d f a t t y acids•

LIPOPROTE1NS IN DEVELOPING CALF into TG, which would be lost as a source of energy (18). The PC in chylomicrons plus VLDL and in LDL fractions of the 3-d-old calves (Table 6) also contained elevated 20:3 n-9 and ratio of 20:3 n-9 to 20:4 n-6 in excess of .4, two factors associated with development of essential fatty acid (EFA) deficiency in nonruminants (17). As in a previous study (9), calves with these deficiency indicators had no external signs of E F A deficiency, suggesting that these indicators are not applicable for the young calf. In adult ruminants, plasma LCAT has an important role in the catalytic transfer of 2position acyl group of PC to the 3-hydroxy group of cholesterol (14, 15), forming CE and LPC in the process. The LCAT system acts primarily on PC in the HDL fraction (3). Our data on fatty acid composition of PC and CE in HDL, and of LPC in VHDL (Tables 5, 6), indicate that LCAT is also active in the young calves we studied (3 d, 3 wk, 12 wk). For example, bovine plasma PC contains mostly 16:0 and 18:0 in the sn-1 position and 18:1 n-9, 18:2 n-6, 18:3 n-3, and 20:4 n-6 in the sn-2 position (3). (The term "sn" is "stereospecific numbering", used to show the position of a group attached to glycerol.) We would then expect that LCAT activity would result in higher 16:0 and 18:0 (from sn-1) and lower concentrations of the above unsaturated fatty acids (from sn-2) in LPC than PC. This occurred in each instance with most differences significant at 5%. Similarly, LCAT activity should produce lower 16:0 and 18:0 and higher proportions of the unsaturated fatty acids in CE (HDL) and PC (HDL). These differences were found in our data, except for 18:1 n-9 and 20:4 n-6, which possibly were reutilized in the acytation of LPC to PC. We found very high concentrations of 18:2 n-6 in CE (HDL), as did Bauchart and Levieux (1) for calves at 3 wk of age, which concur with observations of Noble and coworkers (15, 16) that LCAT in adult bovine plasma discriminates heavily in favor of transferring 18:2 n-6 from PC to CE. Linolenic acid (18:3 n-3) also was high in the CE fraction of several lipoprotein fractions and 20:4 n-6 high both in CE and PC of HDL and VHDL. Because CE and PC are the major plasma lipids and contain high contents of EFA, they represent an appreciable mobile store of E F A for ruminants.

3009

Free Fatty Acids

Plasma F F A , located in VHDL, function as a readily available source of energy (14). Plasma albumin provides the means for F F A solubilization and transport. The F F A content of FHDL represents a composite of effects including lipolysis of TG during absorption, in liver cells, and in extrahepatic tissues. In addition, there is liberation of F F A from PC by LCAT (5). Oleic acid (18:1 n-9) generally is the main component of F F A . This was the case with our data for all ages of calves. Oleic acid and the EFA in our F F A may have been derived in part from LCAT activity. Palmitic acid (16:0), which is bound tightly b y bovine albumin, also was a major component (18 to 22%). As our calves grew older, 18:1 n-9 and 16:0 in F F A decreased and 18:0 and the EFA increased, in agreement with observations by Noble et al. (18) for growing lambs. CONCLUSIONS

At birth the calf has low concentrations of plasma lipids and these concentrations remain relatively low at 3 d, despite high fat colostrum feeding, because of extensive buildup of fat in adipose tissues (15). Free fatty acids bound to albumin in VHDL are elevated in the rapidly developing newborn, and with the dietary short-chain fatty acids, make an important contribution as readily available sources of energy (14). As the calf grows, much of the dietary TG is converted either to adipose TG or the liberated fatty acids utilized for synthesis of lipoprotein PC and PE. By 3 wk, much of the increase in total plasma lipids has been derived from increased PC and CE, and of HDL carrying these lipids. Synthesis and turnover of plasma lipoproteins do not appear to change appreciably after rumen development, and ]ipoprotein profile and lipid composition remain similar as the ruminant animal grows to maturity (3). The maternal blood is able to transfer very little E F A to the bovine fetus, and at birth there is a low store of EFA. Therefore, it is important that 18:2 n-6 and 18:3 n-3 are present in the liquid diet of the newborn ruminant to improve E F A status. Fortunately, the young as well as the mature ruminant selectively incorporates absorbed E F A into plasma PC rather than into TG, which subsequently would Journal of Dairy Science Vol. 71, No. 11, 1988

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infectious diseases (15). Providing E F A to the y o u n g calf m a y be of practical benefit under c o n d i t i o n s o f high infection and under conditions of stress from high environmental temperatures (15).

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REFERENCES

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1 Bauchart, D., and D. Levieux. 1985. Lipoprot~ines plasmatiques du veau pr~ruminant. Reprod. Nutr. Dev. 25:243. 2 Chapman, M. J., and P. Forgez. 1985. Lipid transport systems: some recent aspects in swine, cattle and trout during development• Reprod. Nutr. Dev. 25:217. 3 Christie, W. W. 1981. The composition, structure and function of lipids in the tissues of ruminant animals. Lipid metabolism in ruminant animals. W. W. Christie, ed. Pergamon Press, Oxford, UK. 4 Christie, W. W. 1981. The effects of diet and other factors on the lipid composition of ruminant tissues and milk. Lipid metabolism in ruminant animals. W. W. Christie, ed. Pergamon Press, Oxford, UK. 5 Coleman, R. 1973. Phospholipids and the hepatoportal system. Form and function ofphospholipids. G. B. Ansell, J. N. Hawthorne, and R.M.C. Dawson, ed. Elsevier Sci. Publ. Co., Amsterdam, Neth. 6 Dryden, F. D., J. A. Marchello, G. H. Adams, and W. H. Hale. 1971. Bovine serum lipids. II. Lipoprotein quantitative and qualitative composition as influenced by added animal fat diets. J. Anim. Sci. 32:1016. 7 Forte, T. M., J. J. Bell-Quint, and F. Cheng. 1981. Lipoproteins of fetal and newborn calves and adult steer: a study of developmental changes. Lipids 16:240. 8 Havel, R. J., H. A. Eder, and J. H. Bragdon. 1955. The distribution and chemical composition of uhracentrifugally separated lipoproteins in human serum. J. Clin. Invest. 34:1345.

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9 Jenkins, K. J., and J.K.G. Kramer. 1986. Influence of low linoleic and linolenic acids in milk replacer on calf performance and lipids in blood plasma, heart, and liver. J. Dairy Sci. 6 9 : 1 3 7 ¢ . 10 Jenkins, K. J., J.K.G. Kramer, F. D. Sauer, and D. B. E m m o n s . 1985. Influence of triglycerides and free fatty acids in milk replacers on calf performance, blood plasma and adipose lipids. J. Dairy Sci. 68:669. 11 Lascelles, A. K., and J. C. Wadsworth. 1971. The origin of lipoprotein in the intestinal and hepatic l y m p h of unsuckled new-born calves. J. Physiol. 214:443. 12 Leat, W.M.F. 1966. F a t t y acid composition of the plasma lipids of newborn and maternal ruminants. Biochem. J. 98:598. 13 Leat, W.M.F., F.O.T. Kubasek, and N. Buttress. 1976. Plasma lipoproteins of lambs and sheep. Q. J. Exp. Physiol. 61:193. 14 Noble, R. C. 1978. Digestion, absorption, and transport of lipids in r u m i n a n t animals. Prog. Lipid Res. 17:55. 15 Noble, R. C. 1981. Lipid metabolism in the neonatal ruminant. Lipid metabolism in r u m i n a n t

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animals. W. W. Christie, ed. Pergamon Press, Oxford, UK. Noble, R. C., M. L. Crouchman, and J. H. Moore. 1975. Synthesis of cholesterol esters in the plasma and liver of sheep. Lipids 10:790. Noble, R. C., J. H. Shand. J. T. Drummond, and J. H. Moore. 1978. Protected polyunsaturated fatty acid in the diet of the ewe and the essential fatty acid status of the neonatal lamb. J. Nutr. 108:1868. Noble, R. C., W. Steele, and J. H. Moore. 1971. Diet and the fatty acids in the plasma of Iambs during the first eight days after birth. Lipids 6:26. Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill Book Co., Inc., New York, NY. Toullec, R., and C. M. Mathieu. 1969. Utilisation digestive des maiteres grasses et de leurs principaux acides gras par le veau pr~ruminant a l'engrais. Influence sur la composition corporelle. Ann. Biol. Anita. Biochim. Biopbys. 9 : 139. Wendtlandt, R. M., and C. L. Davis. 1973. Characterization of bovine serum lipoproteins. J. Dairy Sci. 56:337.