Metabolic Effects of Feeding Protected Tallow to Dairy Cows1

Metabolic Effects of Feeding Protected Tallow to Dairy Cows 1 D. S. KRONFELD, S. OONOGHUE, J. M. N A Y L O R , K. JOHNSON, and C. A. BRADLEY Department of Clinical Studies School of Veterinary Medicine University of Pennsylvania Kennett Square 19348 and Damon Medical Laboratory Trevose, PA 19047 ABSTRACT

to hydrolytic digestion in the intestine, was developed to alter the composition of fat in beef, lamb, and milk for the benefit of heart risk patients who wish to include them in their diet (12). We have postulated that feeding protected fat should be beneficial to the health and productivity of cows when incorporated into most contemporary rations.(8, 9). Fat need not be polyunsaturated for this purpose. The inclusion of much protein and soluble carbohydrate in the ration yields a plethora of amino acids and propionic acid, i.e., glucogenic nutrients. These promote synthesis of glucose in the liver and availability of glucose to the mammary gland. Mammary uptake of glucose appears to be a major determinant of the rate of milk secretion (3); thus, it creates a demand for lipogenic nutrients (8, 9). If insufficient levels of these are supplied directly from the diet, then milk fat content is depressed or b o d y fat is mobilized. The latter option leads to ketosis, other postcalving complaints (5), and poor reproductive efficiency (6). The present experiments test if the provision of protected tallow will lower ketone bodies in blood and improve the metabolic efficiency of lactation. These potential benefits of feeding protected fat should be exhibited during the rising and peak phases of lactation, perhaps for the first 3 or 4 mo (9). The experiment reported was extended beyond 4 mo because of a subsidiary interest in subsequent health and performance of cows fed protected tallow for a full lactation (21).

Twelve Holstein cows were matched into pairs after 7 days lactation. Each was fed 1 kg of grain concentrate per 3 kg milk and corn silage free choice. At 2 wk, one cow from each pair was maintained on this diet and the other was fed a protected tallow product mixed with the grain concentrate, 1 to 2, providing 25% of metabolizable energy as fat. For 14 wk, milk fat production was 12.4% higher and efficiency of utilization of metabolizable energy for lactation was 8.0 to 13.6% higher in tallow-fed cows. These had higher concentrations of glucose in plasma and cholesterol in serum and lower concentrations of acetoacetate and b e t a h y d r o x y b u t y r a t e in plasma. At 16 wk, cows were fed in two groups, the concentrate to milk ratio was 1:4 and silage intake 41 kg/day. Digestible protein was reduced from 118 g/kg dry matter to only 80 g/kg. Milk production declined rapidly, so that duration of lactation averaged only 163 days in both groups. Protected tallow conferred metabolic advantages during the first 16 wk of lactation. Its influence on the duration of lactation requires further study in cows fed adequate protein. INTRODUCTION

Polyunsaturated fat, protected against fermentative digestion in the rumen but susceptible

MATERIALS A N D METHODS

Received June 6, 1977. 1Supported in part by the Fats and Proteins Research Foundation, Des Plaines, IL. The protected tallow was donated by Alta Lipids, Boise, ID. 1980 J Dairy Sci 63:545-552

Milk production of 12 Holstein cows was measured for 7 days, then they were matched into pairs and assigned to two groups by coin toss. (In the past, we have tried to match cows

545

546

KRONFELD ET AL.

on their performances in the previous lactation. Twelve individual stanchions are available, so we have selected six pairs and assigned cows to two groups by coin toss. The results usually have been c o n f o u n d e d because 1 or 2 cows o u t o f 12 have p e r f o r m e d differently f r o m one lactation to the next. So we decided to m a t c h cows into pairs on their p e r f o r m a n c e at the start o f the lactation under observation.) The first observations on blood and milk were in the 2nd wk; t h e n p r o t e c t e d tallow (HE, Alta Lipids Ltd., Boise, ID) was i n t r o d u c e d into the feed o f group B while group A r e m a i n e d as controls. The cows were fed corn silage and a grain c o n c e n t r a t e or a 2:1 m i x t u r e of this with p r o t e c t e d tallow. These feedstuffs were subj e c t e d to p r o x i m a t e analysis (Table 1). The concentrate was f o r m u l a t e d by Penn field Corporation (R. G. Peacock) f r o m wheat, corn, and soy bean meal to s u p p l e m e n t the corn silage according to r e c o m m e n d a t i o n s (1). It was provided as a meal which m i x e d readily with p r o t e c t e d tallow so that the m i x t u r e was n o t sorted by cows. The cows were k e p t in individual stanchions for 16 wk, then m o v e d into an adjacent area in two groups. In the stanchions, feed intakes were measured individually. Concentrate was provided at 1:3 of milk for a b o u t an h o u r after milking. A n y remainder was r e m o v e d and weighed. Corn silage then was placed in feeder boxes and c o n s u m e d ad libitum with weighbacks of a b o u t 5% of material offered. After the cows shifted to group feeding, c o n c e n t r a t e was provided in a single trough at 1 to 4 of average milk production. It was c o n s u m e d entirely within an hour. The silage was provided to the group at an average o f 41 kg per cow. Once a m o n t h cows were weighed a b o u t 1100 h. Tail b l o o d samples were taken at a b o u t the same time on a different day. Milk samples were taken in the evening and the following morning, then c o m b i n e d p r o p o r t i o n a t e l y . Milk was assayed for fat (4) and protein (16). Blood plasma was analyzed for glucose (2), betah y d r o x y b u t y r a t e (20), acetoacetate (19), and free fatty acids (5). Serum samples also were assayed for cholesterol, urea, uric acid, bilirubin, calcium, magnesium, protein, albumin, lactic dehydrogenase, alkaline phosphate, and glutamic-oxalacetic transaminase on an SMA-12 a u t o m a t e d analyzer (Technicon, Inc.). Statistical analysis was primarily t w o - w a y Journal of Dairy Science Vol. 63, No. 4, 1980

TABLE 1. Composition of corn silage, grain concentrate, and 2:1 mixture of grain concentrate and protected tallow (HE, Alta Lipids). a

Nutrients b

Silage

Grain

HE mixture

Moisture Protein Fat Fiber, acid detergent Ash N-free extract Energy c Gross d Digestiblee Metabolizable f

74 6.7 3.0 31.1 4.5 51,7

12 24.5 3.3 11.3 9.1 51.8

11 24.3 14.5 9.4 6.2 43.7

4.16 3.04 2.65

4.38 3,41 3.00

4.59 3.66

3.24

aMean of two assays by Merkle Laboratory, Forage Testing Service of the Pennsylvania State University. bNutrients expressed as percent of dry matter (except moisture). CEnergy expressed as Mcal/kg dry matter. dGross energy calculated with factors of 5.8, 9.3, and 4.2 Mcal/kg of protein, fat and carbohydrate, respectively. eDigestible energy calculated with efficiency factors from digestibility study on two heifers (11). fMetabolizable energy (ME) calculated from digestible energy (DE) by regression ofMoe et al. (12): ME = .96 DE -- .27.

analysis of variance for two diets, five t i m e periods (6 to 26 wk) with six cows per group for the first 3 periods, t h e n five for the 4th and f o u r for the 5th. The BMDP2V program for analysis o f variance and covariance ( U C L A Health Sciences C o m p u t i n g F a c i l i t y ) a d j u s t e d for covariance at the 2rid wk and allowed for data missing due to the decrease in n u m b e r of cows in the last 2 periods. Handling of missing data follows principles described by Sokal and R o h l f (14). No diet-time interaction was significant, so variances calculated for diet or time were c o m p a r e d to residual variation. Significances o f differences a m o n g the five time periods were tested b y the T u k e y w-procedure (14). RESULTS A N D DISCUSSION

There were no significant differences b e t w e e n groups A and B at 2 wk when all cows were fed

FEEDING PROTECTED TALLOW

547

m i l k i n g o p e r a t i o n w h e n yield fell b e l o w 9 k g / d a y . Cows in g r o u p A were r e m o v e d a f t e r 17 t o 36 wk, in g r o u p 13 a f t e r 22 to 36 wk. Mean d u r a t i o n o f l a c t a t i o n was t h e s a m e 163 days in b o t h groups, T h r e e f a c t o r s w h i c h could h a v e c o n t r i b u t e d t o t h e s h o r t d u r a t i o n o f l a c t a t i o n have b e e n m e n t i o n e d already. A n o t h e r possible f a c t o r was t h e exclusive use o f corn silage as a r o u g h a g e . This was d e c i d e d u p o n for c o n v e n i e n c e in t h e i n d i v i d u a l feeding e x p e r i m e n t w h i c h lasted o n l y 16 wk. T h e r a t i o n s h o u l d have i n c l u d e d s o m e grass or l e g u m e r o u g h a g e t o s u s t a i n cows for a w h o l e l a c t a t i o n , b e c a u s e c o r n silage a l o n e has b e e n associated w i t h h e a l t h p r o b l e m s (e.g., 15, 17). O u r cows also m a y have b e c o m e d e f i c i e n t in p r o t e i n . T h e r e were n o d i f f e r e n c e s b e t w e e n g r o u p s or w i t h t i m e in b o d y w e i g h t ( T a b l e 2). T h e a p p a r e n t increase in g r o u p B f r o m 22 to 26 w k was d u e to r e m o v a l of t w o light cows. Also, t h e r e were n o d i f f e r e n c e s b e t w e e n g r o u p s in f o o d i n t a k e , w i t h t h e e x c e p t i o n o f fat (Table 2). Digestible f a t a c c o u n t e d for 25.6 +- .4% of i n t a k e o f m e t a b o l i z a b l e e n e r g y (ME) in g r o u p B

t h e grain c o n c e n t r a t e . T h e process o f selecting cows i n t o pairs a n d t h e n assigning r a n d o m l y i n t o g r o u p s a p p e a r s to have b e e n effective. Only o n e cow (group A) s u f f e r e d a serious illness, mastiffs, w h i c h t o o k a w e e k to c o n t r o l . Services per c o n c e p t i o n were 2.2 + .4 a n d 2.8 +.6 ( m e a n + SE) in g r o u p s A a n d B. T h e interval of calving to c o n c e p t i o n was t h e same in b o t h groups, 119 -+ 19 a n d 118 + 17 days. T h e cows received a serious s e t - b a c k d u r i n g t h e 1 7 t h w k a f t e r t h e s h i f t t o g r o u p feeding. Part o f this was p r o b a b l y associated w i t h t h e a b r u p t c h a n g e f r o m u n t h r e a t e n e d to c o m p e t i t i v e feeding. Also, cows were b e g i n n i n g to gain excessive w e i g h t w h e n fed silage free choice, so silage i n t a k e was r e s t r i c t e d at this t i m e to less t h a n f o r m e r average c o n s u m p t i o n , a n d t h e rate o f c o n c e n t r a t e o f f e r e d was c h a n g e d f r o m 1 : 3 to 1:4. These r e s t r i c t i o n s e x a c e r b a t e d c o m p e t i t i o n a m o n g cows for c o m m u n a l feed. D u r i n g this week, a h e a t wave s t r u c k t h e d i s t r i c t a n d depressed m i l k p r o d u c t i o n generally. Despite these disturbances, no diet-time interactions f r o m 6 to 26 w k were significant. Individual cows were r e m o v e d f r o m t h e

TABLE 2. Body weights and daily intakes of silage, concentrate, digestible protein, and digestible fat in cows fed grain concentrate (group A) or grain-tallow mixture (group B) after 2 wk. Body weight Time a

Silage

A

B

A

2

564 b 32

577 34

6

566 39

10

Concentrate

Dig. protein

B

A

B

A

B

28.6 5.8

27.0 c 4.5

8.9 1.7

9.3 c 1.2

1820

568 41

32.6 3.0

31.8 d 4.3

8.5 1.2

8.4 .8

566 44

588 52

33.9 3.4

32.8 d 3.5

8.4 1.2

16

590 45

598 54

42.6 4.5

42.2 e 6.4

22

588 50

596 53

40.9

26

585

637 52

40.9

(Weeks)

B

1872

405

402

1791

1874

426

1239

8.3 c 1.4

1787

1866

433

1234

5.6 1.6

5.6 d .9

1393

1462

435

979

40.9

4.8

3.9

1239

1134

405

766

40.9

4.5

3.6

1187

1079

398

730

(kg)

26

Dig. fat A (g)

~Veeks of observation. Protected tallow was introduced after 2nd wk. Cows moved to group feeding after 16 wk. bMean (above) and standard deviation (below). c'd'eMeans which have different superscripts are significantly different in time (P<.05). fDigestibility coefficients were determined in an associated study (11). Journal of Dairy Science Vol. 63, No. 4, 1980

548

KRONFELD ET AL.

and 9.1 ~ .3% of ME in group A from 4 to 16 wk (Tables 1 and 2). As milk production declined, so did the amount of concentrate offered and consumed. This was associated with a voluntary intake of more silage up to 16 wk (Table 2); then silage intake was restricted. Up to this point, intake of digestible protein was adequate, averaging 118 g/kg dry matter, but it subsequently averaged only 80 g/kg in both groups. The NRC recommendations (1) are 114 and 105 g/kg for cows producing 20 to 30 kg milk and less than 20 kg, respectively. Protein insufficiency probably contributed to the short lactations, but it was not manifested as anorexia, in blood contents of protein or urea, or in milk protein. Total milk production was 4127 + 557 and 4230 -+ 561 kg in groups A and B for average lactation periods of only 163 days in both groups. Daily milk yield declined at rates of about .50 and .51 kg/wk in A and B, respectively, for 16 wk (Table 3). Milk fat content was .41 £ .07% higher in B up to 26 wk (P<.025). Milk protein content changed significantly with time; an initial fall was followed by an increase

which persisted until 26 wk (Table 3), perhaps longer. Both milk protein and milk fat were correlated negatively with milk yield (r -- - . 9 0 and - . 6 0 ) . Problems inherent in the estimation of metabolic efficiency o f lactation have been elaborated elsewhere (9) and are exemplified here. Low and high estimates of partial efficiencies have been generated (Table 4). Intake of metabolizable energy has been estimated high with data based on our digestibility experiments (Table 1) and low with estimates based on Merkle Laboratory TDN and the assumption of 3.6 Meal ME/kg TDN. Maintenance requirement has been estimated on the high side by the current assumption of the National Research Council (1) and on the low side by a value reported by Tyrell and Moe (18) for a corn silage diet like that used here but presented by those authors with the reservation that it could be anomalously low. Metabolizable energy above maintenance has been adjusted for changes in body weight, assuming the same value for body weight increasing or decreasing (11). Thus, comparisons with low or high

TABLE 3. Milk production and contents of fat and protein. Milk Time

Cows

A

(Weeks)

Fat B

A

Protein B

(kg) ~

A

B

(%)

2

12

29.0a 6.0

28,2 4.7

3,37 ,60

3.30 .72

2.50 .25

2.73

6

12

25.7 3.4

26.0 b 3.8

3.28 ,44

3.57 .85

2.44 .29

2.34 b .32

10

12

24,5 5,4

26,1 b 4.1

3.52 .26

3.78

2.68

2.68 c

.35

.22

.16

.19

16

12

21,6 6,4

20.6 c 3.5

3.43 .22

4.05 .38

2.82 .24

2.84 c .18

22

8

19.4 4.1

13.8 d 4.8

3,45 .60

3.80 .80

3,10 .19

3.44 b .28

26

6

18.2 .8

16.8 c 4.3

3.62 .21

4.15 1.13

3,11 .42

3.51 d .26

22.52

21.67 4.02

3.44 e .37

3.84 f .64

2.77

2.86 .24

6--26

4.80

.26

aMeans (above) and standard deviations (below), b'c'dsignificant changes with time are shown by different superscripts; milk yield, P<,001; milk protein, P<.05. e'fsignificant difference between controls (A) and tallow fed cows (B) in milk fat from 6 to 26 wk, P<.025. Journal of Dairy Science Vol. 63, No. 4, 1980

FEEDING PROTECTED TALLOW

549

TABLE 4. Two estimates (lower and upper) of metabolic efficiency of lactation. Intake of metab, energy, Mcal ME B Time

Mcal ME above maintenance c

Adjust for /x W: ME for milk d

Net energy of milke

Efficiency %

A

B

A

B

A

B

A

B

A

13

Lower 6 10 16

44.93 45.57 44.18

46.13 46.54 45.25

34.02 34.67 32.93

35.19 35.31 33.88

34.02 31.12 33.21

31.06 33.84 33.05

17.45 17.31 15.04

18.52 19.21 15.80

51.3 55.6 45.3

59.6 56.8 47.8

Upper 6 10 16

40.20 40.69 38.65

40.07 40.39 38.81

25.46 25.59 23.45

25.29 25.22 23.45

25.46 22.05 23.73

21.16 23.'15 22.62

17.45 17.31 15.04

18.52 19.21 15.80

68.5 78.5 63.4

87.5 80.9 69.8

(Weeks)

aWeeks of duration of study; duration of tallow feeding is 2 weeks less. bCalculated from mean intakes (Table 2) and lower and upper alternate estimates of metabolizable energy (Table 1). CMetabolizable energy above maintenance calculated from mean body weights (Table 2) and equation, M = aWkg .75 kcal ME/day, where a is 94 for lower estimate of efficiency, from Tyrell and Moe (13), or 127 for upper estimate, from the 1971 NRC recommendations (1). dMetabolizable energy above maintenance is adjusted for change in body weight, 6.2 Mcal/kg (11). eNet energy milk = 304.8 + 114.4 F kcal/kg milk, where F is fat content, %.

estimates of partial efficiencies are consistent w i t h the prediction t h a t feeding p r o t e c t e d tallow should increase the partial efficiency of lactation (9). The peak efficiency of 87% in group B at 6 wk (Table 4) reaches the theoretical m a x i m u m calculated f r o m biochemical equations when 22% of metabolizable energy is supplied as long chain f a t t y acids (9). Glucose c o n c e n t r a t i o n in plasma increased at 22 and 26 wk (Table 5). It was significantly higher in group 13 than in A f r o m 6 to 26 wk (Table 5). Free fatty acids in plasma changed significantly but unsystematically with time. B e t a h y d r o x y b u t y r a t e and acetoacetate in plasma were significantly lower in cows fed tallow (Table 5). The acetoacetate c o n c e n t r a t i o n averaged 5.6% o f b e t a h y d r o x y b u t y r a t e , and the correlation b e t w e e n these two variables was huge (r = .99). Glucose c o n c e n t r a t i o n in plasma (G, mg/dl) correlated significantly with m a n y variables: Plasma b e t a h y d r o x y b u t y r a t e , mg/dl = 43.2 - .528 G, r = --.74, P<.01 Plasma acetoacetate, rag/all = 2.67 - .033 G, r = --.77, P<.01

Milk yield, k g / d a y = 81.0 - .987 G, r = --.87, P < . 0 0 1 Milk protein, % = .080 G -- 1.91, r = .91, P < . 0 0 1 Milk fat, % = 1.19 + .041 G, r = .61, P<.01 There are two alternative physiological hypotheses to explain the elevation o f plasma glucose in cows fed p r o t e c t e d tallow. One is that extra utilization of fat spares the utilization o f glucose. The other is that the protein c o m p o nent of the p r o t e c t e d tallow p r o d u c t stimulates glucose synthesis. Glucose c o n c e n t r a t i o n o f plasma was correlated negatively, however, with dietary protein (r = - . 7 8 ) . E x p e r i m e n t s with radioactive glucose could decide this p o i n t (10). The negative correlation b e t w e e n milk yield and plasma glucose is a r e m i n d e r that the availability of glucose to the udder and the m a m m a r y u p t a k e of glucose m a y be dissociated f r o m the c o n c e n t r a t i o n o f glucose in plasma (3). This also emphasizes the need for more penetrative m e t a b o l i c studies (e.g., 3, 10). Journal of Dairy Science Vol. 63, No. 4, 1980

550

KRONFELD ET AL.

TABLE 5. Concentrations (mg/dl) of glucose, betahydroxybutyrate (BHB), acetoacetate (ACA), and free fatty acids (FFA) in plasma. Glucose Time

BHB

ACA

FFA

A

B

A

B

A

B

A

B

2

55.5 a 5.7

57.6 3.4

13.3 4.9

12.5 1.4

. . . . . .

5.4 .9

5.8 1.4

6

54.5 3.6

57.1 b 3.6

16.2 6.0

8.7 1.0

. . . . . .

g.9 1.7

13.7 b 5.8

10

53.6 3.6

58.5 b 3.1

15.6 4.2

10.6 1.9

,89 .32

.52 .09

10.4 3.0

9.3 b 2.4

16

58.4 4.1

59.7 c 1.4

15.8 9.9

12.6 5.6

.91 .67

.70 .32

6.6 4.3

7.8 c 1.4

22

62.8 4.3

67.4 c 3.8

12.1 4.6

8,2 4.0

.68 ,32

.45 .25

6.4 1.9

6.0 c 1.3

26

61.5 3.4

65.5 b 3.1

9.4 3.4

7.4 1.4

,52 .20

.43 .12

1.6 1.4

1.7 d

57.39 e 3.82

60.72 f 3.04

13.77 e 6.50

7.77 f

,79 e .46

.53 f .22

7.43 2.89

8.55 3.20

(Weeks)

6--26

3.40

.8

aMeans (above) and standard deviations (below). bcd .... >lgmncant changes with time are shown by different superscripts; P<.001 for both glucose and FFA. ef Slgmficant differences between controls (A) and tallow fed cows (B) for glucose (P<.001) and BHB (P<.005) from 6 to 26 wk and for ACA (P<.05) from 10 to 26 wk.

The remarkable correlation between acetoa c e t a t e a n d b e t a h y d r o x y b u t y r a t e is a r e f l e c t i o n n o t o n l y o f t h e i r close m e t a b o l i c e q u i l i b r i u m , b u r also o f t h e s u s t a i n e d h e a l t h o f t h e s e cows, for t h e ratio t e n d s t o w a r d a h i g h e r f r a c t i o n o f k e t o n e b o d i e s in t h e f o r m o f a c e t o a c e t a t e in c o w s w i t h clinical k e t o s i s . T h e lack o f s i g n i f i c a n t c o r r e l a t i o n b e t w e e n a c e t o a c e t a t e or betah y d r o x y b u t y r a t e a n d t h e free f a t t y acids fails t o s u p p o r t t h e s t e p s in t h e g l u c o g e n i c / l i p o g e n i c t h e o r y w h i c h relate to f a t m o b i l i z a t i o n a n d h e p a t i c k e t o g e n e s i s (9). In a s u b s e q u e n t s t u d y , c o n c e n t r a t i o n s o f g l y c e r o l in p l a s m a b u t n o t free f a t t y acids w e r e l o w e r in t a l l o w fed cows t h a n in c o n t r o l s ( u n p u b l i s h e d d a t a ) , so m e a s u r e m e n t o f free f a t t y acids m a y i n c l u d e s o m e derived f r o m t h e digestive t r a c t as well as b o d y s t o r e s in c o w s fed p r o t e c t e d tallow. Feeding protected tallow elevated the c h o l e s t e r o l c o n c e n t r a t i o n in s e r u m ( T a b l e 6). There were no significant differences a m o n g the r e m a i n i n g variables m e a s u r e d in b l o o d ( T a b l e 7). T h e c a l c i u m a n d p h o s p h o r u s d a t a s h o w t h a t Journal of Dairy Science Vol. 63, No. 4, 1980

TABLE 6. Cholesterol concentrations (mg/dl) in serum in cows fed protected tallow (B) and controls (A).

Time

Concentrations

Number of cows

A

12

164 a

B

(Weeks) 8

156 10

12

108 22

223 21

22

12

170 15

229 17

26

8

156

224

2

6

16 6-26

143 18

23 225 b

20

aMeans (above) and standard deviations (below). bcumulative means of A and B from 6 to 26 wk were different (P<.025).

FEEDING PROTECTED TALLOW TABLE 7. Concentrations of metabolites in serum of 12 cows.

Variable

Number of observations

Triglycerides, mg/dl Total protein, g/dl Albumin, g/dl Urea, rng/dl Uric acid, mg/dl Bilirubin, mg/dl Calcium, mg/dl Magnesium, mg/dl Phosphorus, mg/dl LDH, units b AP, units b GOT, units b

27 51 51 51 51 51 51 12 27 51 27 27

Mean

SDa

17.2 6.7 6.55 1.50 3.48 1.57 17.1 13.9 .92 .37 .17 .09 8.66 1.09 1.75 .10 5.53 1.82 78.1 368 49 18 147 14

aThere were no significant differences associated with diet, week of observation, or interaction. bLactic dehydrogenase, alkaline phosphatase, and glutamic-oxalacetic transaminase expressed in international units.

t h e i n t e r r e l a t e d h o m e o s t a s i s o f these s u b s t a n c e s was m a i n t a i n e d in cows f e d tallow. T h e albu-. rain, bilirubin, a n d uric acid c o n c e n t r a t i o n s , t o g e t h e r w i t h SAP a n d SGOT, reflect liver f u n c t i o n and suggest t h a t this was n o t i m p a i r e d b y feeding tallow. Similarly, t h e urea c o n c e n t r a t i o n s are c o n s i s t e n t w i t h n o r m a l f u n c t i o n o f t h e k i d n e y s in cows fed p r o t e c t e d tallow. Cows fed a p r o t e c t e d oil seed s u p p l e m e n t have h a d s h o r t e n e d l a c t a t i o n s (21). T h e s e o b s e r v a t i o n s were c o m p a r e d to p r e v i o u s lactat i o n s b e c a u s e t h e r e were n o c o n c u r r e n t c o n t r o l s , a n d it was c o n c l u d e d t h a t feeding t h e p r o t e c t e d oil was r e s p o n s i b l e for t h e early cessation o f l a c t a t i o n . T h e p r e s e n t s t u d y e m p l o y e d conc u r r e n t c o n t r o l s , and t h e p o o r p e r f o r m a n c e of c o n t r o l s as well as t h e t r e a t e d cows d u r i n g t h e declining p h a s e o f l a c t a t i o n suggests t h a t feeding t h e p r o t e c t e d fat was n o t a m a j o r f a c t o r c o n t r i b u t i n g t o t h e s h o r t e n i n g o f l a c t a t i o n in our study. Poor persistence of lactation may have b e e n partially d u e to p r o t e i n i n s u f f i c i e n c y f r o m 16 w k o n w a r d s , even t h o u g h t h e cows m a n i f e s t e d n o n e of t h e o t h e r t y p i c a l signs o f p r o t e i n insufficiency. We c o n c l u d e t h a t feeding p r o t e c t e d t a l l o w d u r i n g t h e rising a n d peak phases o f l a c t a t i o n e x e r t e d beneficial effects o n b l o o d m e t a b o l i t e s and metabolic efficiency of lactation. Feeding p r o t e c t e d fat or oil d u r i n g t h e declining phase

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