- Email: [email protected]
Lipid Supplementation of Dairy Cow Diets
Lipid Supplementation of Dairy Cow Diets w. STEELE The Hannah Research Institute Ayr KA6 5HL, Scotland
ABSTRACT
In experiments (5) where energy density of the ration of dairy cows was raised by including high-starch concentrates, both total weight of food eaten as well as energy intake were increased. Further increases of energy density by fat inclusion, however, reduced total food intake. Although it was possible to calculate the substitution effect of high-starch concentrate on forage intake, it was impossible to do so for fat alone as amounts of concentrates were reduced for each incremental increase of fat. Thus, to measure the direct effect of fat on forage intake, I added two lipids directly to grass at a fixed percent at ensiling. Effects of these diets on intake characteristics and performance of dairy cows then were measured. Because there have been no reports to show upper lipid intake by cows, another experiment ascertained how two methods of adding oil to the ration affected maximum voluntary intake of oil and subsequently animal health and performance.
Two aspects of lipid supplementation of dairy cow diets have been examined. Forage intake of cows was measured when lipids were ensiled with ryegrass. Intake of dry matter from silage was reduced by 2.77 and 1.66 kg/kg when tallow and groundnut oil were additives. Animals receiving groundnut oil ingested more energy, produced more milk, but secreted less fat than those receiving tallow supplement. In a second experiment, maximum voluntary intake of oil by cows in first lactation was 2.5 kg/day of free groundnut oil and 2.2 kg groundnut oil as crushed seeds. All animals developed hypocalcemia and hypomagnesemia. Increasing recommended calcium and magnesium in the diet by 50% prevented recurrence of symptoms. Multiparous cows and heifers in first lactation receiving extra minerals then had maximum voluntary intakes of 1.8 kg free groundnut oil and 1.5 kg/day as groundnut oil in crushed seeds. Milk fat secretion was reduced on free oil diets compared to those containing crushed seeds. Direct addition of lipid to diets of only forage are not practical for increasing milk production. Further, high oil supplementation of diets for dairy cows must be accompanied by increased calcium and magnesium.
MATERIALS AND METHODS Experiment 1
INTRODUCTION
Fats and oils are becoming increasingly important inclusions in diets for dairy cows (10). One of the main reasons for increasing the lipid content of diets is to raise energy density, and if weight of food eaten remains contant, energy intake must increase.
Received November 7, 1983. 1984 J Dairy Sci 67:1716--1724
Animals and Diets. Four Ayrshire cows with an average weight of 495 kg and in their 4th wk of lactation at the start of the trial were in Experiment 1. The experimental design was a 4 x 4 Latin square. Experimental periods lasted 4 wk, and changes of ration were abrupt. All results were analyzed statistically by methods outlined by Snedecor and Cochran (11). Four silages were prepared from an $23 perennial ryegrass sward. One of the silages was made when D (digestible organic matter in dry matter (DM)) was estimated to be 70, which is equivalent to a metabolizable energy (ME) content of 10.5 MJ/kg DM (8). This silage was made without addition of lipid. The other three silages were prepared from the grass when it was judged to have matured to 65 D (9.75 MJ ME/ kg DM). One of these three silages was made without lipid addition while the other two had
1716
LIPID SUPPLEMENTATION OF DAIRY COW DIETS
1717
either tallow or groundnut oil added at 1.85% of the fresh weight. This addition was calculated to increase the energy content of these two sitages to that of the 70 D silages. The tallow was Megalac 95 (supplied by the Volac Company) and the groundnut oil was the normal commercial grade containing .02% by weight butylated hydroxytoluene as an antioxidant. All four silages were conserved by addition of formic acid. Cows were fed individually and each cow received fresh silage three times daily for ad libitum consumption in such a way that refusals were about 10% of the amount offered. Refusals were removed three times per day, weighed, and analyzed. Digestion coefficients of certain dietary components were measured by my incorporating chromic oxide (Cr2 O3) into the silage, and on each of the last 10 days of every period, 500-g samples of feces were collected at 12-h intervals, bulked, weighed, and analyzed. Chemical Analyses. Amounts of Cr203 in food, refusals, and feces were measured by the method of Stevenson and De Langen (17). Dry matter contents of silages were determined by a toluene distillation method (6), and other determinations on food and feces were as before (12).
ber 3.8 and average weight 490 kg were in Experiment 2. All animals were in their 2nd wk of lactation at the start of the experiment. The forage portion of their diet consisted of 5 kg DM/day of either good quality ryegrass silage (70 D) or ryegrass hay (61 D). Two concentrate mixtures were given with the two forages, thus making four treatments. The two concentrates differed only in their method of oil incorporation. In one, oil was in intracellular form from crushed groundnuts. In the other, it was incorporated as free oil, thereby being in extracellular form. Oil intake was .5 kg/day in the 1st wk and thereafter at the start of each subsequent week was increased by .5 kg/day. The two concentrates were prepared by my combining the desired proportion of mixture A (Table 1) with either mixture B or C to give the required intake of oil when the animals were receiving 8.5 kg/day of concentrate. The experimental design was a 4 × 3 randomized block, and statistical analyses were by the methods outlined by Snedecor and Cochran (11). Chemical Analyses. Chemical analyses of foods, milks, and bloods were as in (12).
Experiment 2
Experiment 1
Animals and Diets. Four Ayrshire heifers in first lactations, average weight 475 kg, and 8 Ayrshire cows with an average lactational num-
R ESU LTS A N D DISCUSSION
Intake of DM was greater (P<.001) with high-quality than with medium-quality silage (Table 2) and confirms other findings (4). Addi-
TABLE 1. Composition (kg/ton) of basal mixture to make up concentrates in Experiment 2. High-oil mixtures
Constituent
Low-oil mixture A
Barley Starch Sugar-beet pulp Decorticated extracted groundnut meal Crushed groundnuts Groundnut oil Molasses Minerals
200 330 200 200 . . . .. 50 20
Oil in extracellular form B . . . . 280 330
.
.
.
. 295 65 30
Oil in intracellular form C . .
. .
. .
. . 280 35 590 " 65 30
Journal of Dairy Science Vol. 67, No. 8, 1984
17i 8
STEELE
TABLE 2. Food dry matter (DM) and metabolizable energy (ME) intakes in cows given silage alone or with supplements of tallow or groundnut oil.
Highquality
DM intake, kg/day Silage Tallow Groundnut oil Total
silage, no supplement
No supplement
13.0
11.5
Medium-quality silage + + GroundTallow nut oil
SE a
10.4
.23
10.47
.63 11.03
.23
2.28
2.32
.051
5.78 2.77 .072 112.5 10.8
6.20 1.66 .043 120.2 10.9
9.9
.57 13.0
DM intake, % liveweight Added fatty acids intake, g/kg liveweight"Ts Replacement rate, kg silage/kg added fat Replacement rate, kg silage/MJ added fat ME intake, MJ/day ME, MJ/kg DM
11.5
2.71
2.50
136.7 10.5
114.5 10.0
2.20
astandard error of difference between treatment means.
t i o n s o f lipid t o silage d e p r e s s e d i n t a k e s o f b o t h forage a n d t o t a l DM. W h e n i n t a k e s were calculated o n an energy basis, h o w e v e r , a d d i t i o n o f g r o u n d n u t oil increased ( P < . 0 5 ) e n e r g y i n t a k e w h e r e a s a d d e d t a l l o w did n o t c h a n g e it compared to the medium-quality unsupplemented silage. N e i t h e r t a l l o w n o r oil increased e n e r g y i n t a k ~ to t h a t o f t h e h i g h - q u a l i t y silage diet. Because o f d i f f e r e n c e s in DM intakes, cows ingested m o r e ( P < . 0 1 ) lipid o n g r o u n d n u t oil t h a n o n t a l l o w diets ( T a b l e 2). T h e r e p l a c e m e n t rate o f lipid o n silage int a k e was greater w i t h t a l l o w t h a n w i t h g r o u n d -
n u t oil ( T a b l e 2). In t u r n , b o t h were m u c h m o r e p o t e n t i n h i b i t o r s (average 5.75 times) o f silage i n t a k e as c o m p a r e d w i t h high-starch conc e n t r a t e s (5). W h e n t h e c o m p a r i s o n is o n an energy basis, average d i f f e r e n c e in s u b s t i t u t i o n rate b e t w e e n starch a n d lipid s u p p l e m e n t s is r e d u c e d f r o m 5.75 t o 2.82. The most probable reason for the difference in s u b s t i t u t i o n effect b e t w e e n tallow a n d g r o u n d n u t oil is t h a t t a l l o w a d d i t i o n r e d u c e d digestion of fat-free organic m a t t e r (OM) t o m o r e t h a n g r o u n d n u t oil ( T a b l e 3). Similarly, r e d u c e d OM digestibility also w o u l d explain t h e
TABLE 3. Digestibility coefficients (%) of dietary components in cows given silage with or without lipid supplements.
Dietary constituent
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
Organic matter in dry matter Organic matter Fat-free organic matter
70.4 74.8 74.5
66.5 70.9 70.5
63.0 67.0 66.5
65.0 69.2 66.8
1.04 1.13 1.16
Medium-quality silage
aStandard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
LIPID SUPPLEMENTATION OF DAIRY COW DIETS
1719
TABLE 4. Digestibility coefficient (%) of lipid components in diets of cows given silage with or without lipid supplements.
Lipid component Total fatty acids C~6 fatty acids C~s fatty acids Added fatty acids Added C16 fatty acids Added C~8 fatty acids
Highquality silage, no addition
No. addition
+ Tallow
91.7 86.8 94.5
88.8 84.6 93.0
72.4
Medium-quality silage
79.8
68.0 66.3 78.1 58.9
+ Groundnut oil
SE a
76.4 80.9 74.6 71.7 76.5 68.5
1.44 1.04 1.61 1.38 1.18 2.25
astandard error of difference between treatment means.
lower i n t a k e of m e d i u m - q u a l i t y u n s u p p l e m e n t e d c o m p a r e d to h i g h - q u a l i t y u n s u p p l e m e n t e d silage. U n f o r t u n a t e l y , results are n o t available t o s h o w if t h e r e was a d e p r e s s i o n o f t h e digestion c o e f f i c i e n t o f t h e diet w h e n highs t a r c h c o n c e n t r a t e s were given in (5). In sheep, h o w e v e r , a d d i t i o n o f b a r l e y to silage diets reduces OM digestion in t h e r u m e n (18).
A c t u a l a n d p r e d i c t e d D for t h e high- a n d m e d i u m - q u a l i t y silages were in close a g r e e m e n t ( T a b l e 3). A l t h o u g h D of t h e silages w i t h a d d e d lipid were less t h a n f o r t h e h i g h - q u a l i t y silage, t h e e n e r g y d e n s i t y o f t h e l a t t e r was less t h a n t h o s e w i t h a d d e d lipid (Table 2). F a t t y acids in t h e h i g h - q u a l i t y silage were m o r e digested ( P > . 0 5 ) t h a n t h o s e in t h e
TABLE 5. Milk yield and composition, and efficiency of conversion of metabolizable energy (ME) surplus to maintenance to milk in cows given silage with or without lipid supplements.
Parameter Milk yield, kg/day Milk composition, % Fat Protein Lactose Yield of components, g/day Fat Protein Lactose Energy output in milk, MJ/day Efficiency No allowance for liveweight change Allowance for liveweight change a
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
14.8
15.2
14.0
15.4
.52
4.31 2.89 4.85 638 429 719
Medium-quality silage
3.85 2.86 4.79
627 380 660
585 433 729
47
45.4 .50 .57
4.48 2.70 4.71
.64 .48
3.60 2.86 4.74 554 437 733
44.6 .64 .44
.112 .O26 .05I 11.6 14.3 30.2
44.2 .57 .57
1.23 .029 .031
Standard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
1720
STEELE
TABLE 6. Fatty acid yields (g/day) in the milk of cows given diets of silage with and without lipid supplements.
Fatty acids
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
C4to C~4 C16 C18 Tot~ fatty acids
148 232 187 600
122 187 212 548
89 188 290 595
77 130 294 521
2.0 7.0 6.7 10.9
Medium-quality silage
aStandard error of difference between treatment means.
m e d i u m - q u a l i t y silage (Table 4) and p r o b a b l y result f r o m the lipid in the m o r e mature grass being less accessible to digestion because of a higher lignin c o n t e n t in the m o r e mature herbage. The digestion coefficients for fatty acids in added lipids (Table 4) are lower than those for sheep (13). Poor dispersion of lipid in the diet was not the cause, because 91% of the fecal lipid of the cows was 18:0. This d e m o n s t r a t e s efficient hydrogenation, which is a good indicator of the dietary lipid being dispersed well (13). A much more likely e x p l a n a t i o n of the difference is that intake of lipid by the cows, when expressed per kilogram m e t a b o l i c b o d y weight (Table 2), was a p p r o x i m a t e l y three times that for the sheep (13). Thus, the digestive capacity of the cows for lipid m a y have been approaching saturation at the intake in Table 2. There were no significant (P>.05) differences in yield of milk or milk energy b e t w e e n
diets (Table 5). Yield and c o n t e n t of milk fat were higher (P<.O1) on the g o o d c o m p a r e d to the m e d i u m - q u a l i t y u n s u p p l e m e n t e d silage diet. A d d i t i o n of tallow to the ration increased (P<.01) and that of g r o u n d n u t oil decreased (P<.05) yield and c o n t e n t o f milk fat. More milk fat was p r o d u c e d f r o m the highquality c o m p a r e d to the m e d i u m - q u a l i t y uns u p p l e m e n t e d silage diet as a result of a greater o u t p u t of shorter chain f a t t y acids in the milk (Table 6). This was the result of greater intake of silage that would provide a greater o u t p u t of acetate in the r u m e n which in t u r n would be used to enhance de novo synthesis of shortchain milk fatty acids (9). The reduction of milk fat secretion f r o m the g r o u n d n u t oil compared to the tallow diet was f r o m r e d u c t i o n of de novo synthesized f a t t y acids (Table 6). It is likely that the cause of this difference has its origin in changes of r u m e n f e r m e n t a t i o n between the t w o dietary regimens. F o r example, unsaturated fatty acid n o t only increases the
TABLE 7. Liveweight and liveweight changes in cows given silage with and without lipid supplements.
Liveweight, kg Liveweight change, kg/day
Highquality silage, no addition
Medium-quality silage No addition
+ Tallow
+ Groundnut oil
SE a
478 +.31
460 -.70
459 -.86
477 -.04
2.7 .160
astandard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
LIPID SUPPLEMENTATIONOF DAIRY COW DIETS ratio of propionate to acetate but also reduces total volatile fatty acids concentration in the rumen as compared to saturated fatty acids such as those in tallow (15). The 18:1 + 18:2 content of the groundnut oil was 80% whereas that in tallow was only 34%. Efficiency of transfer of energy surplus to m~i~ntenance and liveweight change into milk is in Table 5. The ME intakes were calculated from digestibilities in Tables 3 and 4, and energies of liveweight changes (Table 7) were calculated as in (8). When no allowances are made for changes of tiveweight, the mediumquality silage with no additive and the tallow diets were used more efficiently for milk production than the other two diets. When allowances are made for liveweight changes, then efficiencies of transfer for the dietary energy into milk are reversed. Thus, when the cows were losing weight, food energy was used less efficiently for milk production than when they were gaining weight.
1721
o
= o
o
~
Za
~
Experiment 2
Cows in first lactation were the first group to receive the experimental diets, and voluntary intakes of groundnut oil quickly increased to 2.5 and 2.2 kg/day, respectively, for free oil and crushed groundnut diets (Table 8). During the 6th wk all four animals developed clinical symptoms of hypocalcemia. Blood samples were taken, and analyses confirmed that animals were suffering from hypocalcemia. Further tests showed that blood magnesium was also low. The animals then were given Ca and Mg therapy, and their dietary concentrations increased by 50% from the recommended (1) 50 to 75 g/day for Ca and from 25 to 37.5 g/day for Mg. The Ca and Mg in blood of the animals returned to normal within 5 days of treatment. However, the maximum amount of oil that the cows now would consume was 1.8 kg oil on the free oil diet and 1.5 kg oil/day on the crushed groundnut diet (Table 8). Heifers in first lactation already had developed hypocalcemia before the other two groups of animals were given experimental rations. Thus, the multiparous cows received 50% extra Ca and Mg above recommended (1) in their diets from the beginning of the treatment period. Intakes of oil by these two groups of animals increased over 5 wk to a maximum of
~o
2 0
~"0
e, o
0
0
o
Journal of Dairy Science Vol. 67, No. 8, 1984
1722
STEELE
TABLE 9. Concentrations (mM/liter) of calcium, magnesium, and 3-hydroxybutyrate in blood serum and of glucose in blood of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage
Hay
Blood parameter
Concentration
Crushed groundnuts
Groundnut oil
Crushed groundnuts
Groundnut oil
Calcium
Highest Lowest Mean
3.03 2.03 2.46
2.70 2.23 2.42
2.70 2.16 2.36
2.56 1.87 2.30
.089 .095 .044
1.21 .59 .87
.059 .070 .054
1.63 .27 .70
.596 .054 .269
3.17 1.76 2.40
.233 .245 .226
SE a
(Normal range b 2.0-3.0) Magnesium
Highest Lowest Mean
1.14 .89 1.01
1.15 .78 1.00
1.05 .58 .88
(Normal range .65--1.23) 13-Hydroxybutyrate
Highest Lowest Mean
1.73 .27 .97
3.03 .36 1.24
2.35 .29 1.03
(Normal range .13--.33) Glucose
Highest Lowest Mean
3.13 2.50 2.85
3.43 2.47 2.93
2.93 2.10 2.50
(Normal range 2 . 0 - 3 . 0 ) astandard error of difference between treatment means. bReference (7).
TABLE 10. Milk yield and composition of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage
Parameter Milk yield, kg/day Milk composition, % Fat Solids-not-fat Yield of components, g/day Fat Solids-not-fat
Crushed groundnuts 20.8
3.48 9.08
720 1890
Hay Groundnut oil 21.4
2.91 8.78
623 1878
astandard error of difference between treatment means. Journal o f Dairy Science Vol. 67, No. 8, 1984
Crushed groundnuts 21.4
3.74 8.84
800 1895
Groundnut oil
SE a
20.0
.73
3.61 8.78
720 1760
.123 .075
37.5 74.3
LIPID SUPPLEMENTATIONOF DAIRY COW DIETS
1723
TABLE 11. Fatty acid yields (g/day) in the milk of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage Fatty acids C4to C14
C16 C18
Hay
Crushed groundnuts
Groundnut oil
Crushed groundnuts
Groundnut oil
SEa
122 173 379
103 151 316
125 191 439
113 175 372
4.4 6.1 7.7
astandard error of difference between treatment means.
1.8 kg and 1.5 kg/day for the free oil and crushed groundnut treatments (Table 8). Attempts to increase their intake further by increasing the oil content of their diet or by offering more concentrates of a lower oil content resulted in refusals of concentrates. There were no differences (P>.05) in oil intake of animals between silage and hay-based diets. The Ca and Mg in blood of cows were maintained (Table 9) within the normal range (7) when the basal ration consisted of silage but not when it consisted of hay. It was surprising to find that animals in first lactation developed hypocalcemia as it is not found normally before third lactation (3). One possibility for low availability of Ca and Mg might be that indigestible soaps were formed on the high-fat diets (13). However, this cannot be confirmed at present as fecal losses were not determined. Further research thus is needed to define optimum Ca and Mg in the diet with different lipid intakes. Also, more experimental work is needed to explain why animals develop hypocalcemia and hypomagnesemia on highlipid diets. f3-Hydroxybutrate in the blood of the cows was elevated throughout the experimental period (Table 9), and only on few occasions did they fall within the normal range (7). There were no significant effects of diet on blood glucose concentrations (Table 9), and all contents fell within the normal range (7). There is normally an inverse relationship between glucose and /3-hydroxybutyrate in the blood (2). This was examined in the cows, and although not significant (P>.05), the regression of blood glucose on/3-hydroxybutyrate was
y = .031x + 2.56
The lack of an inverse relationship suggests that cows were in positive energy balance and that elevated /3-hydroxybutyrate in blood resulted from large amounts of dietary fatty acids being oxidized for energy and not to any pathological condition. This seems reasonable as none of the animals developed clinical symptoms of ketosis in spite of the high fl-hydroxybutyrate at certain times. There were no significant differences (P>.05) in milk yield or solids-not-fat among diets (Table 10). Significantly less (P<.05) milk fat was produced, however, from silage than from hay diets. Also, less milk fat was secreted (P<.05) when free-oil diets were compared with crushed seeds. Fatty acid analysis of the milk fat (Table 11) showed that these reductions were loss of both fatty acids that are synthesized within the udder and those that are taken up preformed from the blood (9). It is reasonable that silage diets that contain less fiber than hay-based diets would interact with high-oil to increase propionate production in the rumen (14). Further, extracellular oil compared to intracellular oil in the diet will increase propionate in the rumen (16). This increased output of propionate will increase glucose with a concomitant increase of insulin, thereby redirecting fat synthesis towards adipose tissues and away from mammary tissue (19). These changes would explain the reduction of milk fat secretion on silage compared to hay and also on free oil compared to crushed groundnut diets. Journal of Dairy Science Vol. 67, No. 8, 1984
1724
STEELE
Direct additions of lipids to diets of only f o r a g e are n o t p r a c t i c a l f o r i n c r e a s i n g m i l k p r o d u c t i o n . F u r t h e r , h i g h oil s u p p l e m e n t a t i o n o f diets for dairy cows must be accompanied by i n c r e a s e d C a a n d Mg.
10 tl 12
REFERENCES
1 Agricultural Research Council. 1980. The nutrient requirements of ruminant livestock. Agric. Res. Counc., London. 2 Bergman, E. N. 1973. Glucose metabolism in ruminants as related to hypocalcemia and ketosis. Cornetl Vet. 63:341. 3 Braithwaite, G. D. 1976. Calcium and p h o s p h o r u s metabolism in r u m i n a n t s with special reference to parturient paresis. J. Dairy Res. 43:501. 4 Castle, M. E., and J. N. Watson. 1973. Silage and milk production. A comparison between wilted grass silages m a d e with and w i t h o u t formic acid. J. Br. Grassl. Soc. 28:73. 5 Clapperton, J. L., and W. Steele. 1983. Effects of concentrates with beef tallow on food intake and milk production of cows fed grass silage. J. Dairy Sci. 66:1032. 6 Dewar, W. A., and P. McDonald. 1961. Determinations of dry m a t t e r of silage by distillation with toluene. J. Sci. Food Agric. 12:790. 7 Doxey, D. L. 1977. SI Units: T h e new m e t h o d of recording laboratory results for diagnostic purposes. Vet. Rec. 100:555. 8 Ministry of Agriculture, Fisheries and Food. 1975. Energy allowances and feeding s y s t e m s for ruminants. MAFF Bull. 33. Her Majesty's Stationery Office, London. 9 Moore, J. H., and W. W. Christie. 1979. Lipid metabolism in the m a m m a r y gland of r u m i n a n t
Journal of Dairy Science Vol. 67, No. 8, 1984
13
14
15
16
17
18
19
animals. Page 366 in Progress in lipid research. Vol. 17. R. T. Holman, ed. Pergamon Press, Oxford. Palmquist, D. L., and T. C. Jenkins. 1980. Fat in lactation rations: Review. J. Dairy Sci. 63:1. Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. Iowa State Univ. Press, Ames. Steele, W. 1980. The effects of soya-bean oil and type of forage in the diet on plasma lipid composition of sheep. Br. J. Nutr. 44:333. Steele, W. 1983. Intestinal absorption of fatty acids, and blood lipid composition in sheep. J. Dairy Sci. 66:520. Steele, W., and J. H. Moore. 1968. Further studies on the effect of dietary cottonseed oil on milk-fat secretion in the cow. J. Dairy Res. 35:343. Steele, W., and J. H. Moore. 1968. The effect of m o n o - u n s a t u r a t e d and saturated fatty acids in the diet on milk fat secretion in the cow. J. Dairy Res. 35:353. Steele, W., R. C. Noble, and J. H. Moore. 1971. T h e effects of 2 m e t h o d s of incorporating soyabean oil into the diet on milk yield and composition in the cow. J. Dairy Res. 38:43. Stevenson, A. E., and H. De Langen. 1960. Measurement of feed intake by grazing cattle and sheep. VII. Modified wet digestion m e t h o d for determinations of chromic oxide in faeces. N.Z. J. Agric. Res. 3:314. Thomas, P. C., N. C. Kelly, D. G. Chamberlain, and M. K. Wait. 1980. The nutritive value o f silages. Digestion of organic matter, gross energy and carbohydrate constituents in the rumen and intestines of sheep receiving diets o f grass silage or grass silage and barley. Br. J. Nutr. 43:481. Vernon, R. G. 1980. Lipid metabolism in the adipose tissue of r u m i n a n t animals. Page 92 in Progress in lipid research. Vol. 19. R. T. Holman, ed. Pergamon Press, Oxford.
ABSTRACT
In experiments (5) where energy density of the ration of dairy cows was raised by including high-starch concentrates, both total weight of food eaten as well as energy intake were increased. Further increases of energy density by fat inclusion, however, reduced total food intake. Although it was possible to calculate the substitution effect of high-starch concentrate on forage intake, it was impossible to do so for fat alone as amounts of concentrates were reduced for each incremental increase of fat. Thus, to measure the direct effect of fat on forage intake, I added two lipids directly to grass at a fixed percent at ensiling. Effects of these diets on intake characteristics and performance of dairy cows then were measured. Because there have been no reports to show upper lipid intake by cows, another experiment ascertained how two methods of adding oil to the ration affected maximum voluntary intake of oil and subsequently animal health and performance.
Two aspects of lipid supplementation of dairy cow diets have been examined. Forage intake of cows was measured when lipids were ensiled with ryegrass. Intake of dry matter from silage was reduced by 2.77 and 1.66 kg/kg when tallow and groundnut oil were additives. Animals receiving groundnut oil ingested more energy, produced more milk, but secreted less fat than those receiving tallow supplement. In a second experiment, maximum voluntary intake of oil by cows in first lactation was 2.5 kg/day of free groundnut oil and 2.2 kg groundnut oil as crushed seeds. All animals developed hypocalcemia and hypomagnesemia. Increasing recommended calcium and magnesium in the diet by 50% prevented recurrence of symptoms. Multiparous cows and heifers in first lactation receiving extra minerals then had maximum voluntary intakes of 1.8 kg free groundnut oil and 1.5 kg/day as groundnut oil in crushed seeds. Milk fat secretion was reduced on free oil diets compared to those containing crushed seeds. Direct addition of lipid to diets of only forage are not practical for increasing milk production. Further, high oil supplementation of diets for dairy cows must be accompanied by increased calcium and magnesium.
MATERIALS AND METHODS Experiment 1
INTRODUCTION
Fats and oils are becoming increasingly important inclusions in diets for dairy cows (10). One of the main reasons for increasing the lipid content of diets is to raise energy density, and if weight of food eaten remains contant, energy intake must increase.
Received November 7, 1983. 1984 J Dairy Sci 67:1716--1724
Animals and Diets. Four Ayrshire cows with an average weight of 495 kg and in their 4th wk of lactation at the start of the trial were in Experiment 1. The experimental design was a 4 x 4 Latin square. Experimental periods lasted 4 wk, and changes of ration were abrupt. All results were analyzed statistically by methods outlined by Snedecor and Cochran (11). Four silages were prepared from an $23 perennial ryegrass sward. One of the silages was made when D (digestible organic matter in dry matter (DM)) was estimated to be 70, which is equivalent to a metabolizable energy (ME) content of 10.5 MJ/kg DM (8). This silage was made without addition of lipid. The other three silages were prepared from the grass when it was judged to have matured to 65 D (9.75 MJ ME/ kg DM). One of these three silages was made without lipid addition while the other two had
1716
LIPID SUPPLEMENTATION OF DAIRY COW DIETS
1717
either tallow or groundnut oil added at 1.85% of the fresh weight. This addition was calculated to increase the energy content of these two sitages to that of the 70 D silages. The tallow was Megalac 95 (supplied by the Volac Company) and the groundnut oil was the normal commercial grade containing .02% by weight butylated hydroxytoluene as an antioxidant. All four silages were conserved by addition of formic acid. Cows were fed individually and each cow received fresh silage three times daily for ad libitum consumption in such a way that refusals were about 10% of the amount offered. Refusals were removed three times per day, weighed, and analyzed. Digestion coefficients of certain dietary components were measured by my incorporating chromic oxide (Cr2 O3) into the silage, and on each of the last 10 days of every period, 500-g samples of feces were collected at 12-h intervals, bulked, weighed, and analyzed. Chemical Analyses. Amounts of Cr203 in food, refusals, and feces were measured by the method of Stevenson and De Langen (17). Dry matter contents of silages were determined by a toluene distillation method (6), and other determinations on food and feces were as before (12).
ber 3.8 and average weight 490 kg were in Experiment 2. All animals were in their 2nd wk of lactation at the start of the experiment. The forage portion of their diet consisted of 5 kg DM/day of either good quality ryegrass silage (70 D) or ryegrass hay (61 D). Two concentrate mixtures were given with the two forages, thus making four treatments. The two concentrates differed only in their method of oil incorporation. In one, oil was in intracellular form from crushed groundnuts. In the other, it was incorporated as free oil, thereby being in extracellular form. Oil intake was .5 kg/day in the 1st wk and thereafter at the start of each subsequent week was increased by .5 kg/day. The two concentrates were prepared by my combining the desired proportion of mixture A (Table 1) with either mixture B or C to give the required intake of oil when the animals were receiving 8.5 kg/day of concentrate. The experimental design was a 4 × 3 randomized block, and statistical analyses were by the methods outlined by Snedecor and Cochran (11). Chemical Analyses. Chemical analyses of foods, milks, and bloods were as in (12).
Experiment 2
Experiment 1
Animals and Diets. Four Ayrshire heifers in first lactations, average weight 475 kg, and 8 Ayrshire cows with an average lactational num-
R ESU LTS A N D DISCUSSION
Intake of DM was greater (P<.001) with high-quality than with medium-quality silage (Table 2) and confirms other findings (4). Addi-
TABLE 1. Composition (kg/ton) of basal mixture to make up concentrates in Experiment 2. High-oil mixtures
Constituent
Low-oil mixture A
Barley Starch Sugar-beet pulp Decorticated extracted groundnut meal Crushed groundnuts Groundnut oil Molasses Minerals
200 330 200 200 . . . .. 50 20
Oil in extracellular form B . . . . 280 330
.
.
.
. 295 65 30
Oil in intracellular form C . .
. .
. .
. . 280 35 590 " 65 30
Journal of Dairy Science Vol. 67, No. 8, 1984
17i 8
STEELE
TABLE 2. Food dry matter (DM) and metabolizable energy (ME) intakes in cows given silage alone or with supplements of tallow or groundnut oil.
Highquality
DM intake, kg/day Silage Tallow Groundnut oil Total
silage, no supplement
No supplement
13.0
11.5
Medium-quality silage + + GroundTallow nut oil
SE a
10.4
.23
10.47
.63 11.03
.23
2.28
2.32
.051
5.78 2.77 .072 112.5 10.8
6.20 1.66 .043 120.2 10.9
9.9
.57 13.0
DM intake, % liveweight Added fatty acids intake, g/kg liveweight"Ts Replacement rate, kg silage/kg added fat Replacement rate, kg silage/MJ added fat ME intake, MJ/day ME, MJ/kg DM
11.5
2.71
2.50
136.7 10.5
114.5 10.0
2.20
astandard error of difference between treatment means.
t i o n s o f lipid t o silage d e p r e s s e d i n t a k e s o f b o t h forage a n d t o t a l DM. W h e n i n t a k e s were calculated o n an energy basis, h o w e v e r , a d d i t i o n o f g r o u n d n u t oil increased ( P < . 0 5 ) e n e r g y i n t a k e w h e r e a s a d d e d t a l l o w did n o t c h a n g e it compared to the medium-quality unsupplemented silage. N e i t h e r t a l l o w n o r oil increased e n e r g y i n t a k ~ to t h a t o f t h e h i g h - q u a l i t y silage diet. Because o f d i f f e r e n c e s in DM intakes, cows ingested m o r e ( P < . 0 1 ) lipid o n g r o u n d n u t oil t h a n o n t a l l o w diets ( T a b l e 2). T h e r e p l a c e m e n t rate o f lipid o n silage int a k e was greater w i t h t a l l o w t h a n w i t h g r o u n d -
n u t oil ( T a b l e 2). In t u r n , b o t h were m u c h m o r e p o t e n t i n h i b i t o r s (average 5.75 times) o f silage i n t a k e as c o m p a r e d w i t h high-starch conc e n t r a t e s (5). W h e n t h e c o m p a r i s o n is o n an energy basis, average d i f f e r e n c e in s u b s t i t u t i o n rate b e t w e e n starch a n d lipid s u p p l e m e n t s is r e d u c e d f r o m 5.75 t o 2.82. The most probable reason for the difference in s u b s t i t u t i o n effect b e t w e e n tallow a n d g r o u n d n u t oil is t h a t t a l l o w a d d i t i o n r e d u c e d digestion of fat-free organic m a t t e r (OM) t o m o r e t h a n g r o u n d n u t oil ( T a b l e 3). Similarly, r e d u c e d OM digestibility also w o u l d explain t h e
TABLE 3. Digestibility coefficients (%) of dietary components in cows given silage with or without lipid supplements.
Dietary constituent
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
Organic matter in dry matter Organic matter Fat-free organic matter
70.4 74.8 74.5
66.5 70.9 70.5
63.0 67.0 66.5
65.0 69.2 66.8
1.04 1.13 1.16
Medium-quality silage
aStandard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
LIPID SUPPLEMENTATION OF DAIRY COW DIETS
1719
TABLE 4. Digestibility coefficient (%) of lipid components in diets of cows given silage with or without lipid supplements.
Lipid component Total fatty acids C~6 fatty acids C~s fatty acids Added fatty acids Added C16 fatty acids Added C~8 fatty acids
Highquality silage, no addition
No. addition
+ Tallow
91.7 86.8 94.5
88.8 84.6 93.0
72.4
Medium-quality silage
79.8
68.0 66.3 78.1 58.9
+ Groundnut oil
SE a
76.4 80.9 74.6 71.7 76.5 68.5
1.44 1.04 1.61 1.38 1.18 2.25
astandard error of difference between treatment means.
lower i n t a k e of m e d i u m - q u a l i t y u n s u p p l e m e n t e d c o m p a r e d to h i g h - q u a l i t y u n s u p p l e m e n t e d silage. U n f o r t u n a t e l y , results are n o t available t o s h o w if t h e r e was a d e p r e s s i o n o f t h e digestion c o e f f i c i e n t o f t h e diet w h e n highs t a r c h c o n c e n t r a t e s were given in (5). In sheep, h o w e v e r , a d d i t i o n o f b a r l e y to silage diets reduces OM digestion in t h e r u m e n (18).
A c t u a l a n d p r e d i c t e d D for t h e high- a n d m e d i u m - q u a l i t y silages were in close a g r e e m e n t ( T a b l e 3). A l t h o u g h D of t h e silages w i t h a d d e d lipid were less t h a n f o r t h e h i g h - q u a l i t y silage, t h e e n e r g y d e n s i t y o f t h e l a t t e r was less t h a n t h o s e w i t h a d d e d lipid (Table 2). F a t t y acids in t h e h i g h - q u a l i t y silage were m o r e digested ( P > . 0 5 ) t h a n t h o s e in t h e
TABLE 5. Milk yield and composition, and efficiency of conversion of metabolizable energy (ME) surplus to maintenance to milk in cows given silage with or without lipid supplements.
Parameter Milk yield, kg/day Milk composition, % Fat Protein Lactose Yield of components, g/day Fat Protein Lactose Energy output in milk, MJ/day Efficiency No allowance for liveweight change Allowance for liveweight change a
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
14.8
15.2
14.0
15.4
.52
4.31 2.89 4.85 638 429 719
Medium-quality silage
3.85 2.86 4.79
627 380 660
585 433 729
47
45.4 .50 .57
4.48 2.70 4.71
.64 .48
3.60 2.86 4.74 554 437 733
44.6 .64 .44
.112 .O26 .05I 11.6 14.3 30.2
44.2 .57 .57
1.23 .029 .031
Standard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
1720
STEELE
TABLE 6. Fatty acid yields (g/day) in the milk of cows given diets of silage with and without lipid supplements.
Fatty acids
Highquality silage, no addition
No addition
+ Tallow
+ Groundnut oil
SE a
C4to C~4 C16 C18 Tot~ fatty acids
148 232 187 600
122 187 212 548
89 188 290 595
77 130 294 521
2.0 7.0 6.7 10.9
Medium-quality silage
aStandard error of difference between treatment means.
m e d i u m - q u a l i t y silage (Table 4) and p r o b a b l y result f r o m the lipid in the m o r e mature grass being less accessible to digestion because of a higher lignin c o n t e n t in the m o r e mature herbage. The digestion coefficients for fatty acids in added lipids (Table 4) are lower than those for sheep (13). Poor dispersion of lipid in the diet was not the cause, because 91% of the fecal lipid of the cows was 18:0. This d e m o n s t r a t e s efficient hydrogenation, which is a good indicator of the dietary lipid being dispersed well (13). A much more likely e x p l a n a t i o n of the difference is that intake of lipid by the cows, when expressed per kilogram m e t a b o l i c b o d y weight (Table 2), was a p p r o x i m a t e l y three times that for the sheep (13). Thus, the digestive capacity of the cows for lipid m a y have been approaching saturation at the intake in Table 2. There were no significant (P>.05) differences in yield of milk or milk energy b e t w e e n
diets (Table 5). Yield and c o n t e n t of milk fat were higher (P<.O1) on the g o o d c o m p a r e d to the m e d i u m - q u a l i t y u n s u p p l e m e n t e d silage diet. A d d i t i o n of tallow to the ration increased (P<.01) and that of g r o u n d n u t oil decreased (P<.05) yield and c o n t e n t o f milk fat. More milk fat was p r o d u c e d f r o m the highquality c o m p a r e d to the m e d i u m - q u a l i t y uns u p p l e m e n t e d silage diet as a result of a greater o u t p u t of shorter chain f a t t y acids in the milk (Table 6). This was the result of greater intake of silage that would provide a greater o u t p u t of acetate in the r u m e n which in t u r n would be used to enhance de novo synthesis of shortchain milk fatty acids (9). The reduction of milk fat secretion f r o m the g r o u n d n u t oil compared to the tallow diet was f r o m r e d u c t i o n of de novo synthesized f a t t y acids (Table 6). It is likely that the cause of this difference has its origin in changes of r u m e n f e r m e n t a t i o n between the t w o dietary regimens. F o r example, unsaturated fatty acid n o t only increases the
TABLE 7. Liveweight and liveweight changes in cows given silage with and without lipid supplements.
Liveweight, kg Liveweight change, kg/day
Highquality silage, no addition
Medium-quality silage No addition
+ Tallow
+ Groundnut oil
SE a
478 +.31
460 -.70
459 -.86
477 -.04
2.7 .160
astandard error of difference between treatment means. Journal of Dairy Science Vol. 67, No. 8, 1984
LIPID SUPPLEMENTATIONOF DAIRY COW DIETS ratio of propionate to acetate but also reduces total volatile fatty acids concentration in the rumen as compared to saturated fatty acids such as those in tallow (15). The 18:1 + 18:2 content of the groundnut oil was 80% whereas that in tallow was only 34%. Efficiency of transfer of energy surplus to m~i~ntenance and liveweight change into milk is in Table 5. The ME intakes were calculated from digestibilities in Tables 3 and 4, and energies of liveweight changes (Table 7) were calculated as in (8). When no allowances are made for changes of tiveweight, the mediumquality silage with no additive and the tallow diets were used more efficiently for milk production than the other two diets. When allowances are made for liveweight changes, then efficiencies of transfer for the dietary energy into milk are reversed. Thus, when the cows were losing weight, food energy was used less efficiently for milk production than when they were gaining weight.
1721
o
= o
o
~
Za
~
Experiment 2
Cows in first lactation were the first group to receive the experimental diets, and voluntary intakes of groundnut oil quickly increased to 2.5 and 2.2 kg/day, respectively, for free oil and crushed groundnut diets (Table 8). During the 6th wk all four animals developed clinical symptoms of hypocalcemia. Blood samples were taken, and analyses confirmed that animals were suffering from hypocalcemia. Further tests showed that blood magnesium was also low. The animals then were given Ca and Mg therapy, and their dietary concentrations increased by 50% from the recommended (1) 50 to 75 g/day for Ca and from 25 to 37.5 g/day for Mg. The Ca and Mg in blood of the animals returned to normal within 5 days of treatment. However, the maximum amount of oil that the cows now would consume was 1.8 kg oil on the free oil diet and 1.5 kg oil/day on the crushed groundnut diet (Table 8). Heifers in first lactation already had developed hypocalcemia before the other two groups of animals were given experimental rations. Thus, the multiparous cows received 50% extra Ca and Mg above recommended (1) in their diets from the beginning of the treatment period. Intakes of oil by these two groups of animals increased over 5 wk to a maximum of
~o
2 0
~"0
e, o
0
0
o
Journal of Dairy Science Vol. 67, No. 8, 1984
1722
STEELE
TABLE 9. Concentrations (mM/liter) of calcium, magnesium, and 3-hydroxybutyrate in blood serum and of glucose in blood of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage
Hay
Blood parameter
Concentration
Crushed groundnuts
Groundnut oil
Crushed groundnuts
Groundnut oil
Calcium
Highest Lowest Mean
3.03 2.03 2.46
2.70 2.23 2.42
2.70 2.16 2.36
2.56 1.87 2.30
.089 .095 .044
1.21 .59 .87
.059 .070 .054
1.63 .27 .70
.596 .054 .269
3.17 1.76 2.40
.233 .245 .226
SE a
(Normal range b 2.0-3.0) Magnesium
Highest Lowest Mean
1.14 .89 1.01
1.15 .78 1.00
1.05 .58 .88
(Normal range .65--1.23) 13-Hydroxybutyrate
Highest Lowest Mean
1.73 .27 .97
3.03 .36 1.24
2.35 .29 1.03
(Normal range .13--.33) Glucose
Highest Lowest Mean
3.13 2.50 2.85
3.43 2.47 2.93
2.93 2.10 2.50
(Normal range 2 . 0 - 3 . 0 ) astandard error of difference between treatment means. bReference (7).
TABLE 10. Milk yield and composition of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage
Parameter Milk yield, kg/day Milk composition, % Fat Solids-not-fat Yield of components, g/day Fat Solids-not-fat
Crushed groundnuts 20.8
3.48 9.08
720 1890
Hay Groundnut oil 21.4
2.91 8.78
623 1878
astandard error of difference between treatment means. Journal o f Dairy Science Vol. 67, No. 8, 1984
Crushed groundnuts 21.4
3.74 8.84
800 1895
Groundnut oil
SE a
20.0
.73
3.61 8.78
720 1760
.123 .075
37.5 74.3
LIPID SUPPLEMENTATIONOF DAIRY COW DIETS
1723
TABLE 11. Fatty acid yields (g/day) in the milk of cows given diets of hay or grass silage supplemented with concentrates containing groundnut oil either as a direct addition or as crushed groundnuts. Silage Fatty acids C4to C14
C16 C18
Hay
Crushed groundnuts
Groundnut oil
Crushed groundnuts
Groundnut oil
SEa
122 173 379
103 151 316
125 191 439
113 175 372
4.4 6.1 7.7
astandard error of difference between treatment means.
1.8 kg and 1.5 kg/day for the free oil and crushed groundnut treatments (Table 8). Attempts to increase their intake further by increasing the oil content of their diet or by offering more concentrates of a lower oil content resulted in refusals of concentrates. There were no differences (P>.05) in oil intake of animals between silage and hay-based diets. The Ca and Mg in blood of cows were maintained (Table 9) within the normal range (7) when the basal ration consisted of silage but not when it consisted of hay. It was surprising to find that animals in first lactation developed hypocalcemia as it is not found normally before third lactation (3). One possibility for low availability of Ca and Mg might be that indigestible soaps were formed on the high-fat diets (13). However, this cannot be confirmed at present as fecal losses were not determined. Further research thus is needed to define optimum Ca and Mg in the diet with different lipid intakes. Also, more experimental work is needed to explain why animals develop hypocalcemia and hypomagnesemia on highlipid diets. f3-Hydroxybutrate in the blood of the cows was elevated throughout the experimental period (Table 9), and only on few occasions did they fall within the normal range (7). There were no significant effects of diet on blood glucose concentrations (Table 9), and all contents fell within the normal range (7). There is normally an inverse relationship between glucose and /3-hydroxybutyrate in the blood (2). This was examined in the cows, and although not significant (P>.05), the regression of blood glucose on/3-hydroxybutyrate was
y = .031x + 2.56
The lack of an inverse relationship suggests that cows were in positive energy balance and that elevated /3-hydroxybutyrate in blood resulted from large amounts of dietary fatty acids being oxidized for energy and not to any pathological condition. This seems reasonable as none of the animals developed clinical symptoms of ketosis in spite of the high fl-hydroxybutyrate at certain times. There were no significant differences (P>.05) in milk yield or solids-not-fat among diets (Table 10). Significantly less (P<.05) milk fat was produced, however, from silage than from hay diets. Also, less milk fat was secreted (P<.05) when free-oil diets were compared with crushed seeds. Fatty acid analysis of the milk fat (Table 11) showed that these reductions were loss of both fatty acids that are synthesized within the udder and those that are taken up preformed from the blood (9). It is reasonable that silage diets that contain less fiber than hay-based diets would interact with high-oil to increase propionate production in the rumen (14). Further, extracellular oil compared to intracellular oil in the diet will increase propionate in the rumen (16). This increased output of propionate will increase glucose with a concomitant increase of insulin, thereby redirecting fat synthesis towards adipose tissues and away from mammary tissue (19). These changes would explain the reduction of milk fat secretion on silage compared to hay and also on free oil compared to crushed groundnut diets. Journal of Dairy Science Vol. 67, No. 8, 1984
1724
STEELE
Direct additions of lipids to diets of only f o r a g e are n o t p r a c t i c a l f o r i n c r e a s i n g m i l k p r o d u c t i o n . F u r t h e r , h i g h oil s u p p l e m e n t a t i o n o f diets for dairy cows must be accompanied by i n c r e a s e d C a a n d Mg.
10 tl 12
REFERENCES
1 Agricultural Research Council. 1980. The nutrient requirements of ruminant livestock. Agric. Res. Counc., London. 2 Bergman, E. N. 1973. Glucose metabolism in ruminants as related to hypocalcemia and ketosis. Cornetl Vet. 63:341. 3 Braithwaite, G. D. 1976. Calcium and p h o s p h o r u s metabolism in r u m i n a n t s with special reference to parturient paresis. J. Dairy Res. 43:501. 4 Castle, M. E., and J. N. Watson. 1973. Silage and milk production. A comparison between wilted grass silages m a d e with and w i t h o u t formic acid. J. Br. Grassl. Soc. 28:73. 5 Clapperton, J. L., and W. Steele. 1983. Effects of concentrates with beef tallow on food intake and milk production of cows fed grass silage. J. Dairy Sci. 66:1032. 6 Dewar, W. A., and P. McDonald. 1961. Determinations of dry m a t t e r of silage by distillation with toluene. J. Sci. Food Agric. 12:790. 7 Doxey, D. L. 1977. SI Units: T h e new m e t h o d of recording laboratory results for diagnostic purposes. Vet. Rec. 100:555. 8 Ministry of Agriculture, Fisheries and Food. 1975. Energy allowances and feeding s y s t e m s for ruminants. MAFF Bull. 33. Her Majesty's Stationery Office, London. 9 Moore, J. H., and W. W. Christie. 1979. Lipid metabolism in the m a m m a r y gland of r u m i n a n t
Journal of Dairy Science Vol. 67, No. 8, 1984
13
14
15
16
17
18
19
animals. Page 366 in Progress in lipid research. Vol. 17. R. T. Holman, ed. Pergamon Press, Oxford. Palmquist, D. L., and T. C. Jenkins. 1980. Fat in lactation rations: Review. J. Dairy Sci. 63:1. Snedecor, G. W., and W. G. Cochran. 1967. Statistical methods. Iowa State Univ. Press, Ames. Steele, W. 1980. The effects of soya-bean oil and type of forage in the diet on plasma lipid composition of sheep. Br. J. Nutr. 44:333. Steele, W. 1983. Intestinal absorption of fatty acids, and blood lipid composition in sheep. J. Dairy Sci. 66:520. Steele, W., and J. H. Moore. 1968. Further studies on the effect of dietary cottonseed oil on milk-fat secretion in the cow. J. Dairy Res. 35:343. Steele, W., and J. H. Moore. 1968. The effect of m o n o - u n s a t u r a t e d and saturated fatty acids in the diet on milk fat secretion in the cow. J. Dairy Res. 35:353. Steele, W., R. C. Noble, and J. H. Moore. 1971. T h e effects of 2 m e t h o d s of incorporating soyabean oil into the diet on milk yield and composition in the cow. J. Dairy Res. 38:43. Stevenson, A. E., and H. De Langen. 1960. Measurement of feed intake by grazing cattle and sheep. VII. Modified wet digestion m e t h o d for determinations of chromic oxide in faeces. N.Z. J. Agric. Res. 3:314. Thomas, P. C., N. C. Kelly, D. G. Chamberlain, and M. K. Wait. 1980. The nutritive value o f silages. Digestion of organic matter, gross energy and carbohydrate constituents in the rumen and intestines of sheep receiving diets o f grass silage or grass silage and barley. Br. J. Nutr. 43:481. Vernon, R. G. 1980. Lipid metabolism in the adipose tissue of r u m i n a n t animals. Page 92 in Progress in lipid research. Vol. 19. R. T. Holman, ed. Pergamon Press, Oxford.