Feeding Cholesterol and Tallow to Young Calves

Feeding Cholesterol and Tallow to Young Calves T. R. W R E N N , J. B I T M A N , S. K A H L 1 , J. R. W E Y A N T , and D. L. W O O D Nutrient Utilization Laboratory Animal Physiology and Genetics Institute Agricultural Research, Science and Education Administration U,S. Department of Agriculture Beltsville Agricultural Research Center Beltsville, M D 20705 ABSTRACT

plasma when fed dietary cholesterol, but liver fat and cholesterol composition increase greatly and rapidly (4, 5). In both the rat and rabbit these increases in lipid appear to be synergistic with much greater increases with both added dietary cholesterol and fat than with either alone. In guinea pigs, Green et al. (9) have suggested that liver storage of cholesterol is an important homeostatic mechanism. The objective of our experiment was to determine whether tallow feeding is beneficial to calf growth and whether feeding cholesterol stimulates lipid absorption in calves. A preliminary report was presented (24).

Four groups of eight 4 wk-old Holstein bull calves were fed calf starter diets containing either no additive (control) or added ingredients: 1% cholesterol, 5% tallow, or 1% cholesterol plus 5% tallow. Body weight and size were reduced, and average daily gain was lowered by added 5% tallow. The added dietary tallow and cholesterol increased lipids and cholesterol of plasma by 35 to 40%. The increased intake of fat due to feeding tallow caused both increased fat metabolism and fat excretion as based on chromic oxide estimates of digestibility. Fat digestibility was lowest in animals receiving cholesterol with no added tallow. Organ weights and composition of meat at slaughter at 21 wk of age were not different.

EXPERIMENTAL PROCEDURE

INTRODUCTION

Unprecedented increases in cost of customary feed ingredients with high energy have led to incorporation of animal fat in cattle feeds. Feeding calves tallow has been largely successful whether fed in liquid diets (12) or formulated with calf starter (13). Jacobson et al. (12) found significantly higher weight gains in calves fed lard or tallow supplemented with cholesterol (1.4%, dry weight). We demonstrated that dietary cholesterol stimulates lipid absorption in rabbits (3), increasing both cholesterol and total lipids in blood plasma 20 to 40 and 10 to 20 times, respectively. In contrast to the rabbit, the rat shows little change in cholesterol and lipids of

Received November 8, 1978. a Akademia Rolnicza, Instytut Stosowanej, Fizjologii Zwierzat, 30-059 Krakow, AI. Micklewicza, 24/28 Poland. 1979 J Dairy Sci 62:746-753

Thirty-two Holstein bull calves were raised to 4 wk of age on whole milk fed from open pails twice daily at 8% of body weight per day. In addition, calves were given access to calf grain starter. At 28 days, the milk fed was reduced by .25 kg/day until the calves were weaned completely (44 to 46 days of age). They were tethered with collar and chain and bedded on wood shavings kept to the rear to minimize consumption of the shavings. At 4 wk of age calves were assigned in a complete randomized block design, 2 x 2 factorial, to four dietary treatments fed daily at 2.8% of body weight until 21 wk of age. These feeds were: 1) ground calf starter concentrate (control), 2) the starter plus 1% added cholesterol, 3) starter plus 5% stabilized tallow, and 4) starter plus 1% cholesterol and 5% tallow. The diets (Table 1) were designed to be isonitrogenous by varying the amount of soybean oil meal, but no attempt was made to provide similar caloric value. Chromic oxide marker was included to aid in estimates of ration digestibility. Each calf was supplemented with 30 g/day of mineral-vitamin mixture. No roughage was fed.

746

CHOLESTEROL AND TALLOW FED TO CALVES

747

TABLE 1. Ingredient composition of calf starter mixtures.

Ingredient

Control

1% Cholesterol

Cracked corn Soybean oil meal, 44% Wheat bran Whole oats Linseed meal Tallow Alfalfa meal Molasses, blackstrap Cholesterol Meat scrap Salt, iodized Chromic oxide marker Vitamin A

34.2 14.6 14.6 14.6 9.8

33.7 14.9 14.5 14.5 9.6

5% Tallow

1% Cholesterol and 5% tallow

31.2 17.0 13.4 13.4 8.9 5.0 4.5 4.5

30.5 17.9 13.1 13.1 8.7 5.0 4.3 4.3 1.0 .9 .9 .4 .02

(%)

4.9 4.9 1.0 1.0 .3 .02

Records were kept of health of the calves. Blood was sampled biweekly by jugular venipuncture at times midway between feedings. Feces for analysis were obtained by compositing four consecutive a.m. and p.m. grab samples. The calves were weighed every week, and height at withers and heart girth were determined biweekly. At 21 wk o f age they were slaughtered, and the weights of various organs and dressing percent were measured. One-half of each carcass was boned, ground, and sampled for determinations of moisture, lipid, cholesterol, and crude protein. Fatty acid composition was determined on blood plasma and fat from the ground carcass after extraction with chloroform-methanol (2:1) by the method of Storry and Millard (21).

4.8 4.8 1.0 1.0 1.0 .2 .02

.9 .9 .4 .02

Fatty acids of feed concentrates were determined after chloroform extraction in the Goldfisch apparatus. Methyl esters of the lipids were formed in sealed vials by the procedure of Christopherson and Glass (7). Esters were analyzed by programmed (65 to 180 C) gas liquid chromatography on 15% EGSS-X on Gas-Chrom P (100/200 mesh--Applied Science Laboratories, State College, PA) in a .6-cm × 183-cm glass column on a model 7620 HewlettPackard gas chromatograph. Peak areas were measured with an electronic integrator. Peak identities and quantitative accuracy were determined from known standards for each fatty acid. Fatty acid percentages (wt %) were determined by dividing individual peak areas by total chromatographic peak areas. Cholesterol

TABLE 2. Water, fat, crude protein, sterol, and computed digestible energy composition of calf feeds.

Component

Control

1% Cholesterol

5% Tallow

1% Cholesterol and 5% tallow

Dry matter (DM) % Fat, as % of DM Crude protein (determined) as % of DM Sterols, g/kg of DM Digestible energy (from tables (15)), Mcal/kg of DM

88.5 3.1

88.8 3.7

89.4 7.4

89.7 8.7

19.6 .8

19.8 6.6

21.6 .6

23.7 7.7

3.55

3.60

3.77

3.82

Journal of Dairy Science Vol. 62, No. 5, 1979

748

WRENN ET AL.

TABLE 3. Fatty acid composition of fat in starter feeds.

Fatty acid

Control

1% Cholesterol

C14:0 C16:0 C16:1 C18:0 C18:1 C18:2 C18:3 Others

.2 14.3 .1 2.8 23.3 50.0 9.5 . .

.2 14.2 .2 2.7 22.2 51.4 9.1 . .

5% Tallow

1% Cholesterol and 5% tallow

2.5 23.9 2.6 12.4 35.9 18.5 4.3

2.2 24.5 3.0 11.5 35.0 16.6 5.6 1.6

(%)

.

.

.

.

of plasma was measured by the colorimetric procedure of Pearson et al. (16) after acetoneethanol extraction by the m e t h o d of Sobel and Mayer (19). Feeds were oven-dried, and feces samples were freeze-dried. The fat content of feeds and feces was determined gravimetrically after chloroform (feeds) or ether (feces) extraction with the Goldfisch fat extraction apparatus. Feed concentrates were ground finely with a water cooled micro-mill before extraction. Total lipid of blood plasma was determined as described by Postma and Stroes (17). Crude protein of feeds and ground carcass was estimated by the Kjeldahl method. Ration digestibility was estimated by the chromic oxide marker technique at ages 60, 90, 120, and 150 days. Vitamin E of plasma was determined by the ~, 0?-dipyridyl reaction as described by Quaife et al. (18). Blood hemoglobin analysis was by the cyanmethemoglobin absorbance method. Hematocrit was measured by micro-capillary centrifuge and reader. Thyroxine (T4) and 3, 5, 3'-triiodothyronine (T3) concentrations in plasma were measured in duplicate by specific double-antibody radioimmunoassay, as in (14). Statistical comparisons were by two-factor analysis of variance (20). The feed analyses are in Table 2. Slightly more dry matter was in the feeds with added tallow. The fat, as percent of dry matter, ranged from 3.1 for the control feed to 8.7 for the feed containing both cholesterol and tallow. Crude proteins were similar for feeds without tallow, and higher for feeds with tallow. The calories provided by the different feeds as determined from National Research Council tables (15) was greatest for the calf starters Journal of Dairy Science Voi. 62, No. 5, 1979

.

.

.

.

containing tallow. Table 3 shows that the addition of tallow markedly changed the fatty acid composition of the dietary fats with increases in percentages of saturated fats C14:0 to C18:0 and decreases in C18 unsaturated fatty acids. This was expected since tallow is composed largely of saturated fats. RESULTS AND DISCUSSION

The intakes of concentrate and gains in body weight for the calves during the experimental period (age 4 to 21 wk) are in Table 4. Differences for intakes of dry matter of digestible energy were not significant, and only minimal amounts of feed refusals were encountered. Slightly smaller amounts of feed were consumed by the calves fed tallow, both as dry matter and as calories. Tallow significantly lowered average daily gain which was only .850 and .747 kg/day for calves receiving 5% tallow and 5% tallow plus 1% cholesterol as compared to .902 and .914 kg/day for control and 1% cholesterol calves not fed tallow. Differences in measurements of body size were similar. Daily gain per kg dry matter did not differ significantly among the groups, but when daily gain was computed per Meal of digestible energy consumed, significantly lower gains were caused by inclusion of cholesterol or tallow. In calves fed cholesterol and tallow, the interaction of these dietary components significantly lowered heart girth. Height at withers was reduced in calves fed tallow. Our work agrees with that of Johnson et al. (13), who found no appreciable differences in consumption of starter by calves fed various amounts of tallow.

CHOLESTEROL AND TALLOW FED TO CALVES

749

TABLE 4. Intake of diet components, body weight gains, and body size measurements of calves fed various starters.

Dry matter (DM) intake, kg/day Digestible energy (DE) intake, Mcal/day Average daily gain, kg Gain/kg DM, kg Gain/Mcal DE, kg Heart girth at 20 wk, m Withers height at 20 wk, m

Control

1% Cholesterol

5% Tallow

1% Cholesterol and 5% tallow

Significant anovaa

2.25

2.42

2.21

2.04

....

7.98

8,71

8.34

7.81

....

.902 .421 .114

.914 .377 .108

.850 .383 .102

.747 .376 .092

1.152

1.187

1.151

1.112

.966

.982

.956

.939

T .... C,T C XT T

aLetters indicate significant main effects (P<.05) from feeding cholesterol (C), tallow (T), or interaction of cholesterol and tallow (C × T).

Weekly changes in mean body weights during the experiment are in Figure 1. The bulls fed the 1% cholesterol diet grew best and those on cholesterol plus tallow grew least. Other workers have found growth of calves fed tallow satisfactory (12, 13), but their results contrast with ours which indicate reduced gain with tallow diets. The significant response in weight gains due to supplementation by cholesterol reported by Jacohson et al. (12) with liquid diets was not demonstrable with our starter formulations. Several investigations have dealt extensively with feeding supplemental tallow or lard to young calves. These have been fed as liquid milk replacer diets (1, 2, 12) or as starter concentrate (13). In experiments at Iowa (11, 12, 22, 23), supplemental feeding of cholesterol to calves has been studied. The chief impetus to the present experiment was the finding by Jacobson et al. (12) that gains in body weight were enhanced in Holstein bull calves fed supplemental cholesterol in liquid diets that simulated milk feeding with 3.5% lard or tallow as the dietary fat. The increased rates of gain were accompanied by much higher cholesterol in plasma. Jacobson et al. (12) nearly doubled cholesterol concentration in plasma from about 150 mg/100 ml plasma to about 250 mg/100 ml with cholesterol fed as 1.4% of dry ingredi-

ents. Their experience also showed that feeding both lard and tallow elevated cholesterol of blood more than did soybean oil. When cholesterol was fed in doses between 25 and 250 mg/kg body weight to calves on whole milk, Jacobson et al. (11) found that cholesterol of plasma increased over 4 wk from initial 100 to 125 rag/100 ml to 150 for those supplemented with the low dose and to about 250 for all higher doses (100 to 250 mg/kg body weight).

BODY W E I G H T

IBC

,..=C

160

..-"~-r

140

..,'

12C kg

w.""

.y."°"

I/.

/

10C

/~¢.-

•

SC

....j:'~ 6C

A'"~'~"~

.

'

40 .i

4

i

I

6

I

I

8

i

I

10

i

i

12 AGE,

i

l 14

i

J 16

J

I 18

i

I 20

I

22

WEEKS

Figure 1. Weekly mean body weights of calves fed control (0), 1% cholesterol (C), 5% tallow (T), and 1% cholesterol plus 5% tallow (CT) diets. Journal of Dairy Science Vol. 62, No. 5, 1979

750

WRENN ET AL. PLASMA

cholesterol

110

CHOLESTEROL

_

plus

,,.~ ....

tallow

mg

9¢

"/I~%.

per

".~

~'

cholelterol

7C 100m|

5C ,~l

i

|

• 4

6

S

/

I

10 AGE,

16

20

waeks

Figure 2. Mean biweekly total lipids of plasma of calves fed control and various lipid diets.

The same workers also reported (11, 23) that the elevated cholesterol of plasma resulting from cholesterol supplementation of whole milk was depressed when the calves also were fed calf starter• Calves fed supplemental cholesterol (250 mg/kg b o d y weight daily) while on a milk diet had much higher cholesterol in plasma than either calves fed the same amount of cholesterol while on a milk and grain diet or calves fed the cholesterol while on a grain only diet (23). The low cholesterol in plasma of calves on the grain only diet was thought to be the result of the combined effect of depressed efficiency of absorption and ruminal degradation of the cholesterol. The low cholesterol in plasma of calves on the milk and grain diet was thought to be due at least partially to the lower amount of fat in the diet. Our total lipids in plasma (Figure 2) were in proportion to amounts of lipids in the diets. They were highest in calves fed both cholesterol and tallow and, not surprisingly, lowest in calves fed control starter only. Significant elevations in lipids of plasma were caused by

PLASMA

both cholesterol and tallow, but there was no interaction of these• Plasma cholesterol (Figure 3) was elevated significantly by the addition of 1% dietary cholesterol or 5% tallow, thus clearly reflecting the fat composition of the diets. The cholesterol in plasma we measured initially at 4-wk (75 to 105 mg/100 ml) is similar to that for young calves fed whole milk. Carroll et al. (6) describe cholesterol in plasma of young Holstein bull calves rising sharply from about 20 mg/lO0 ml at birth to 75 to 1OO mg/100 ml between 2 and 5 wk. Weaning at 5 wk reduced cholesterol concentration to about 50 mg/100 ml. Their post-weaning concentrations were similar to those of our control calves• In contrast to the decline in cholesterol in plasma in our control and cholesterol-fed calves, the calves fed diets containing fat maintained the initially high cholesterol. The curves for total lipids (Figure 2) and for cholesterol (Figure 3) in the plasma of calves are strikingly similar, with the cholesterol accounting for less than half of the concentration of total lipids in plasma. Assimilation of fat by the calves was examined by estimating excretion of fecal fat at 60, 90, 120, and 150 days of age. The graphs of Figure 4 show the relationship of fecal fat excreted to fat ingested. In each graph the mean fat intakes of a calf group were plotted at these intervals of time to obtain the top line. Amounts of fat excreted, shown in the middle of each graph, were determined by fecal analysis computed by the chromic oxide dye technique for estimation of fecal quantity excreted• The shaded area represents average amounts of fat metabolized (intake minus excretion), and the clear area indicates average amounts o f fat passing through to be excreted in feces. The 1%

LIPIDS

26C mg

choles~eeo~

pluJ

tallow

~'~'~'" ~240

220

180 100ml

[

j

Excreted

~200

per

~

-"'~'~....."-"

~.~*L~!....;.*!

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

~160

40

14G

60

% DIG=

~0

12o

age, days

48 CONTROL

AGE,

weeks

Figure 3. Biweekly mean cholesterol of plasma of calves fed control and various lipid diets. Journal of Dairy Science Vol. 62, No. 5, 1979

Iso

oge, days

o

ii I% CHOLESTEROL

oge, days 45

5% T A L L O W

o

aga, doy~

o

5e I% CHOLESTEROL PLUS 5 % r A t t o w

Figure 4. Intake, assimilation, and excretion of fats in calves fed control and various lipid diets (% DIG. = apparent % digestibility of fat).

CHOLESTEROL AND TALLOW FED TO CALVES

751

TABLE 5. Comparison of various physiological measures in the blood of calves fed control and lipid diets (20 wk old).

Vitamin E in plasma, ug/ml Hemoglobin, g/100 ml Hematocrit, % Triiodothyronine (T 3), ng/ml plasma Thyroxine (T 4 ), ng/ml plasma

Control

1% Cholesterol

5% Tallow

.34

.18

.46

12.0 33.0 1.429 66

12.0 33.7 1.560 64

11.7 32.4 1.486 57

1% Cholesterol and 5% tallow

.43 12.1 34.2 i .494 60

Significant anova a

T .... .... .... ....

aLetter indicates significant main effect (/'<.05) from feeding tallow (T).

cholesterol diet (3.7% fat by analysis, Table 2) severely reduced apparent fat digestibility when it was fed without tallow, but feeding cholesterol together with 5% tallow (8.7% fat by analysis) resulted in increased fat digestibility. It may be that added cholesterol only stimulates digestibility of fats when high amounts of fats are fed. The apparent percent digestibilities are under each graph in Figure 4. These are means of values computed at 60, 90, 120, and 150 days of age. Other physiological variables measured in the blood of calves the week just preceding slaughter are in Table 5, Vitamin E was elevated significantly in calves fed tallow. We have observed similar elevations in plasma tocopherols of rabbits (3) and cows (25) when added fat was fed. Added dietary fat, whether of

vegetable or animal origin, seems to increase circulating tocopherols and to be correlated with the lipid in plasma. In an experiment in which safflower oil and Vitamin E were fed to lactating Cows (8), much more Vitamin E was transferred to milk than in control cows fed the same amount of Vitamin E but no added oil. Hemoglobin and hematocrit (Table 5) were normal for calves o f this age and did n o t differ with treatment. Grice et al. (10) have compared the hematologic effects of feeding cholesterol and fats in rats, chickens, rabbits, and guinea pigs and reported reductions in hematocrit in male rabbits, chickens, and guinea pigs. They obtained no differences in rats. Anemia o f this kind was not encountered in the calves of our experiment. Thyroid hormones, thyroxine (T4) and

TABLE 6. Liver weight, lipid, and cholesterol, and heart and testes weights of calves slaughtered at 21 wk.

Liver weight, g/kg live weight Liver lipid, % of wet weight Liver cholesterol, total mg/g wet tissue Heart weight, g/kg live weight Testes weight, g/kg live weight

Control

1% Cholesterol

5% Tallow

1% Cholesterol and 5% tallow

18.7

18.4

19.0

16.7

3.65

3.98

3.98

3,95

2.47

2.53

2.48

2,76

5.0

4.7

4.5

5,0

.54

.57

.60

Significant anova

,52

Journal of Dairy Science Vol. 62, No. 5, 1979

752

WRENN ET AL.

TABLE 7. Carcass analysis.

Control Dressed weight, kg Dressing percent Moisture, % Lipid, dry matter Total cholesterol mg/100 g dry matter Crude protein % of dry matter

1% Cholesterol

5% Tallow

1% Cholesterol and 5% tallow

82.6 52.3 72.1 8.4

88.7 53.7 71.4 8.7

82.0 52.7 71.5 8.7

76.1 52.6 72.6 6.9

241.1

258.9

245.2

284.2

74.5

74.0

73.9

76.4

3,5,3'-triiodothyronine (T3), were measured since the concentrations sometimes are correlated with differences in growth rate (14). The T4 was lowest in the blood plasma of animals receiving tallow, the same calves that also showed significantly lower daily gains. The T4, however, did not differ significantly. Liver weights, total cholesterol of liver, and total lipid concentrations of liver are in Table 6. Also shown are other data at slaughter. There were no significant differences in weight, cholesterol, or total lipid of liver, nor in heart or testes weights. Carcass analysis is in Table 7. Dressed weights and dressing percent did not differ significantly. The boned and ground veal was similar in percentages of moisture and lipid, in cholesterol concentration, and in crude protein, regardless of the diet. Failure to show increases in carcass lipid in those calves fed tallow is n o t easily understood, especially since both concentration of blood lipid (Figure 2) and estimated metabolized fat (Figure 4) were greater for calves fed tallow than for other calves. Unfor-

Significant anova

tunately, visceral fat depots were not measured. Omental and perirenal fat may have increased in calves fed the high fat diets. Another possibility is that the tallow-fed groups expended more energy, but there was no evidence of this. The various diets produced no differences in fatty acid composition of fat or blood plasma or of meat. Table 8 shows the percentage of major fatty acids of plasma of control calves at 4 and 20 wk of age and of fat from the ground half-carcasses of the control calves. Inclusion of cholesterol or tallow or both in calf starter diets was not beneficial for calf growth. The calves fed cholesterol were n o t able to utilize additional energy for growth and did not show any greater feed efficiency with either the 4% fat in the control diet or the 9% fat (Table 2) in the cholesterol-tallow diet. Cholesterol feeding did stimulate an increase in lipid absorption as evidenced by higher lipids and cholesterol in the circulation. There was no increase in liver storage of cholesterol or lipid in contrast to the marked hepatic accumulation in the rat, rabbit, and guinea pig. Since

TABLE 8. Major fatty acid composition of fat from blood plasma and ground meat. All values are for control calves since other diet groups did not differ from controls.

Age of calves Blood plasma Meat fat

4 wk 20 wk 21 wk

14:0

16:0

1.7

17.9 13.4 22.2

2.5

Journal of Dairy Science Vol. 62, No. 5, 1979

Fatty acid, weight % 18:0 18:1 14.4 19.1 24.2

19.0 10.4 42.7

18:2 36.6 49.2 8.2

CHOLESTEROL AND TALLOW FED TO CALVES t h e s e species are n o n r u m i n a n t s , this d i f f e r e n c e in lipid a c c u m u l a t i o n m a y result f r o m g r e a t e r relative a b s o r p t i o n in t h e m o n o g a s t r i c intestinal tract. This d i f f e r e n c e also m i g h t arise because o f greater d e g r a d a t i o n and utilization o f d i e t a r y lipids in t h e r u m e n , t h e r e b y providing a smaller n u t r i e n t p o o l for a b s o r p t i o n in t h e i n t e s t i n e o f the ruminants. ACKNOWLEDGMENTS

T h e a u t h o r s are grateful for t h e assistance o f A. M. De R o c c o , J. E. Faltynski, B. S. Folz, R. Fritz, T. W. Klema, L. P. Rosamilia, Jr., a n d L. L. Strozinski.

REFERENCES

1 Adams, R. S., T. W. Gullickson, J. E. Gander, and J. H. Sautter. 1959. Some effects of feeding various filled milks to dairy calves. I. Physical condition and weight gains, with special reference to low-fat rations. J. Dairy Sci. 42:1552. 2 Barr, G. W., S. R. Martin, M. L. Kakade, R. D. Jahn, and F. M. Crane. 1976. Influence of fat level and sources in milk replacer on calf performance and health. Page 91 in Progr. Amer. Dairy Sci. Ass. Ann. Mtg. (Abstr.) 3 Bitman, J., J. Weyant, D. L. Wood, and T. R. Wrenn. 1976. Vitamin E, cholesterol, and lipids during atherogenesis in rabbits. Lipids 11:449. 4 Bitman, J., J. R. Weyant, D. L. Wood, and T. R. Wrenn. 1977. Stimulation of lipid absorption in young rats by cholesterol: Early time changes. J. Amer. Oil Chem. Soc. 54:140 (Abstr.) 5 Bitman, J., J. R. Weyant, and T. R. Wrenn. 1978. Effect of cholesterol and fat on pentobarbital sleeping time of rats. Fed. Proe. 37: 321. 6 Carroll, K. K., R.M.G. Hami/ton, and G. K. Macleod. 1973. Plasma cholesterol levels in suckling and weaned calves, lambs, pigs, and colts. Lipids 8:635. 7 Christopherson, S. W., and R. L. Glass. 1969. Preparation of milk fat methyl esters by alcoholysis in an essentially nonalcoholic solution. J. Dairy Sci. 52:1289. 8 Goering, H. K., C. H. Gordon, T. R. Wrenn, Joel Bitman, R. L. King, and F. W. Douglas, Jr. 1976. Effect of feeding protected safflower oil on yield, composition, flavor, and oxidative stability of milk. J. Dairy Sci. 59:416. 9 Green, M. H., M. Crim, M. Traber, and R. Ostwald. 1976. Cholesterol turnover and tissue distribution in the guinea pig in response to dietary cholesterol. Lipids 106:515.

753

10 Grice, H. C., Z. Z. Zawidzka, and J. L. Beare. 1966. Comparative pathologic and hematologic effects in various species fed cholesterol and fats. Can. J. Comp. Med. Vet. Sci. 30:42. 11 Jacobson, N. L., M. Richard, and P. J. Berger. 1973. Depression of plasma cholesterol in calves by supplementing a high cholesterol liquid diet with dry feed. J. Nutr. 103:1533. 12 Jacobson, N. L., M. Richard, P. J. Berger, and J. P. Kluge. 1974. Comparative effects of tallow, lard and soybean oil, with and without supplemental cholesterol, on growth, tissue cholesterol and other responses of calves. J. Nutr. 104:573. 13 Johnson, D., K. L. Dolge, J. E. Rosseau, Jr., R. Teichman, H. D. Eaton, G. Beall, and L. A. Moore. 1956. Effect of addition of inedible tallow to a calf starter fed to Holstein calves. J. Dairy Sci. 39:1268. 14 Kahl, S., J. Bitman, and T. S. Rumsey. 1978. Effect of synovex-S on growth rate and plasma thyroid hormone concentrations in beef cattle. J. Anita. Sci. 46:232. 15 National Research Council. 1971. Nutrient requirements of dairy cattle. 4th ed. Nat. Acad. Sci. Publ. ISBN 0-309-0196-8. 16 Pearson, S., S. Tern, and T. H. McGavack. 1953. Rapid accurate method for the determination of total cholesterol in serum. Anal. Chem. 25:813. 17 Postma, T., and J.A.P. Stroes. 1968. Lipid screening in clinical chemistry. Clin. Chem. Acta 22:569. 18 Quaife, M. L., N. S. Scrimshaw, and O. H. Lowrey. 1949. A micromethod for assay of total tocopherols in blood serum. J. Biol. Chem. 180:1229. 19 Sobel, A. E., and A. M. Mayer. 1945. Improvements in the Schoenheimer-Sperry method for the determination of free cholesterol. J. Biol. Chem. 157:255. 20 Steel, R.G.D., and J. H. Torrie. 1960. Principles and procedures of statistics. McGraw-Hill Book Co., Inc. New York, NY. 21 Storry, J. E., and D. Millard. 1965. The determination of steam-volatile fatty acids in rumen liquor, blood plasma and milk fat. J. Sci. Food Agr. 16:417. 22 Wiggers, K. D., N. L. Jaeobson, and R. Getty. 1971. Experimental atherosclerosis in the young bovine. Atherosclerosis 14:379. 23 Wiggers, K. D., N. L. Jacobson, R. Getty, and M. Richard. 1973. Mode of cholesterol ingestion and atherosclerosis in the young bovine. Atherosclerosis 17:281. 24 Wrenn, T. R., J. Bitman, S. Kahl, J. R. Weyant, and D. L. Wood. 1977. Cholesterol and tallow fed to young calves. Page 72 in Prog. Amer. Dairy Sci. Ass. Ann. Mtg. (Abstr.) 25 Wrenn, T. R., J. R. Weyant, D. L. Wood, and J. Bitrnan. 1976. Increasing polyunsaturation of milk fats by feeding formaldehyde protected sunflowersoybean supplement. J. Dairy Sci. 59:627.

Journal of Dairy Science Vol. 62, No. 5, 1979