J . Sci. Food Agric. 1980, 31, 368-374

The Yield, Fatty Acid Composition and Physical Properties of Milk Fat Obtained by Feeding Soya Oil to Dairy Cows

William Banks, John L. Clapperton, Morag E. Kelly, Agnes G. Wilson and Roba-t J. M. Crawfordo

Hunndi Researcli Iiisfitufe, A)Y KA6 5HL and 11 Departtirent 08 Dnirj' Tecliiiologj~, West of Scoflund A~ricrilfrtrc~l College, Ayr K A 6 5HW

(Mrrtiriscript received 10 SeptetnLw 1979)

The presence in the bovine mammary gland of a desaturase specific for the conversion of stearic to oleic acid allows the manipulation of the physical properties of milk fat by varying the dietary intake of c16 and CIH fatty acids. In particular, feeding the dairy cow an oil with a high C1ti:Cni ratio should allow the proportion of milk fat that is liquid at 5 'C to be increased, with a consequent improvement in the low-temperature spreadability of butter. In this paper, the effect of feeding concentrate rations contain- ing (a) soya oil as the free oil and as cracked soya beans; (b) various levels of soya oil, the ration being offered twiceor 24-times daily, on the thermal properties of the milk fat and on the yield of milk constitiients is examined in detail. Feeding ratios containing free soya oil greatly increased the proportion of milk fat liquid at 5 C, whereas cracked soya oil gave only slight increases. Proportion and yield of milk fat were decreased by feeding soya oil twice daily but were increased by continuous feeding.

1. Introduction

The response of the fatty acid composition of milk fat to feeding the dairy cow various dietary oils is now understood in broad detail (for a review, see Moore and Steelel). We are currently developing this work in order to producc milk fats of specific physical and rheological properties. In particular, we wish to identify a dietary treatment that will yield a butter having improved spreadability a t refrigeration temperature.

The rheological properties of a fat are controlled by the proportions of solid and liquid material a t a given temperature, which in turn are related to the fatty acid composition and structure of the triglycerides. An increase in the relative amount of acids of high melting point (m.p.) increases the proportion of solid material at a given temperature. Conversely, an increase in the amount of acids of low m.p. decreases the proportion of solid material a t that temperature. In essence, therefore, the objective of increasing the spreadability of butter a t low temperature demands that the pro- portion in the milk fat of fatty acids of low n1.p. should be increased.

This increase can be accomplished by manipulating the content of unsaturated CIR acids. The proportion of 18:2 and 18:3 i n milk fat can be greatly increased by feeding a suitable vegetable oil in a form in which it is protected against rumen activity,2 but this method is somewhat expensive. An alternative approach, adopted here, is to make use of the desaturase system3 of the mammary gland, which is specific for the conversion of stearic acid (18:O) to oleic acid (18: 1 cis). Thus by feeding the cow a n oil relatively rich in CLH acids, such as soya oil (> 85n,; CIH), hydrogenation in the rumen provides 18:O and the increased supply of this acid to the mammary gland results in an elevated 18 : I cis content in the milk fat.

However, the inclusion of unsaturated vegetable oil in the diet can affect ruminal performance, with consequent adverse effects on milk composition. In particular, the proportion and yield of

0022-5142jSOj04OcM368 SO2.00 $1 1980 Society of Chemical Industry

368

Effect of feeding concentrates on milk fat 369

milk fat can be markedly diminished.1~4 Obviously, if dietary manipulation of the type proposed here were to be adopted on the farm-scale, it would be necessary economically to produce milk fat of the desired properties with the minimum loss in terms of yield. We present here, therefore, details on animal performance as well as on the changes in milk fat composition and properties brought about by the supplementation of hay-based diets with soya oil. Three experiments are reported, namely (a) a comparison between feeding soya oil in the free form and as the unextracted, cracked bean; (b) the effect of different levels of free soya oil fed in two meals daily; and (c) the effect of different levels of free soya oil fed continuously, i.e. 24 meals daily.

2. Experimental 2.1. Animals For each experiment, four Ayrshire heifers in their second month of lactation were selected.

2.2. Experimental plan Three 4 x 4 Latin squares, with the final period being repeated, were used, as described previously.5 Each feeding period was 21 days in duration, so that a complete experiment required 15 weeks. Statistical analysis of the results were carried out using the methods detailed by Cocliran and Cox.6

2.3. Oils Soya oil, cracked soya beans and edible tallow were obtained from the Clyde Oil Extraction Co Ltd, Glasgow. The fatty acid composition of the free soya oil was the same as that of the oil in the cracked beans.

2.4. Diets The basal ration for all three experiments consisted of hay (5 .5 kg day-'), and niolassed sugar beet pulp (2.7 kg day-1). In addition, each animal received a concentrate mixture. The compositions and levels of feeding of the four concentrate mixtures are shown in Table 1 . The amount of concentrate fed was adjusted weekly on the basis of the milk yield during the preceding week. Rations were changed abruptly a t the end of each experimental period.

Table I . Compositions (g 100 g-l) of the concentrate mixture offered to the cows

Experiment (a) Experiment (b) Experiment (c) - ~ .~

Low Low 5 % 77; l o g Low 57; 7 % 10% tallow, Soya High Soya fat, soya soya soya fat, soya soya soya control oil tallow beans control oil oil oil control oil oil oil

Barley 77.3 67.0 67.0 67.0 86 78 74 79 82 74 Soya meal 17.9 23.0 23.0 - 12 15 17 19 16 19 Mineralsivitarnins 2 . 0 2 . 0 2 . 0 2 .0 2 2 2 2 2 2

5 Soya oil - 5.0 - - - 5 7 10 - Soya beans - - - Tallow 2 .8 3 .0 8 .0 3 .0 - - - - - - Rate of feeding

- - - - - 28.0 -

(hg kg-'milk) 0.118 0.36 0.36 0.36 0.40 0.38 0.37 0.35 0.40 0.38

70 63 21 25 2 2 7 10

0.36 0.34

In experiments (a) and (b) the concentrate mixture and the sugar beet pulp were fed in two equal amounts a t 07.00 h and at 15.30 h ; hay was offered at 12.00 h and at 17.00 h. In experiment (c), the concentrate mixture was fed 24-times daily, using the automatic feeders described by Minson and C ~ w p e r , ~ hay and sugar beet pulp were provided at 08.00 h, 12.00 h and 17.00 h. There were no significant food refusals.

370 W. Banks et al.

2.5. Sampling and analysis In each experiment, samples were taken from six successive milkings on days 12-14 and 19-21, bulked according to yield over the 3 day period, and analysed as described p r e v i o u ~ l y . ~ ~ ~

2.6. Butter Milk was collected and stored at 4’C during days 19-21 of each feeding period. Cream was then separated, standardised to 30 7; fat, pasteurised and stored overnight a t 4°C prior to churning at 13°C. The time of churning varied with the milk fat, but lay in the range 25-120 min. After chilling for at least 25 min, the butter was worked by hand for the minimum period required to remove free water and then stored at 4’C for 48 h. Subsequently, it was transferred to a deep freeze.

For technical reasons, butter could not be made during experiment (c). At a later stage, the low fat, control and the 10% soya o i l diets were fed to two groups of cows for 4 weeks, using the con- tinuous feeders, and butter was made in weeks 3 and 4. The fatty acid composition of this milk fat was found to be, within experimental error, the same as that recorded for the corresponding treatments in the changeocer design experiment.

2.7. Differential scanning calorimetry Butter samples were melted, washed with hot water to remove salts and protein and dried in VNCUO

at 50°C. The individual samples resulting from each dietary treatment within a given experiment were then bulked. The method (of thermal analysis used in this work has been described previo~isly.~

3. Results and discussion

The experimental design was such that residual effects may be accurately estimated and added to the direct effects to give the permanent effects, i.e. the values t o be expected if the treatment were applied continuously rather than in a changeover design. However, in all three experiments the residual effects were negligibly small and therefore only the direct effects are reported here.

Within each experiment, differences are related in the statistical sense to the control treatment. In experiment (a), tallow (2.8:;) was added to the ration because the small quantity of fatty acids otherwise present in the control diet may have limited milk p r o d ~ c t i o n . ~ The high level of dietary tallow provided the same proportion of fat as did the soya oil and cracked soya bean treatments, thus allowing identification of effects arising from the specific composition of the oil. Tallow was chosen for these treatments bel:ause it has little effect on the yield of milk or of milk fat.loS1l The quantities of fatty acids in the control treatments in experiments (b) and (c) were sufficient not to limit milk production.

3.1. Mean proportions and yields of milk fat and solids-not-fat (SNF) The mean proportions and yiellds of milk fat and S N F resulting from the various dietary treatments are shown in Table 2. In all three experiments, the inclusion of dietary oil did not materially affect the proportion or yield of the !3NF fraction. However, the proportions and yields of milk fat were found to be dependent on the method of inclusion of the soya oil, the amount of the oil and the frequency of feeding of the ration. Thus whereas free soya oil caused a decrease in the proportion and yield of milk fat, the same amount of oil given in the form of soya beans occasioned a slight increase in both parameters. Feeding various levels of the free oil twice daily decreased both milk fat percentage and yield, the extent of the decrease in milk fat content being greatest a t the lowest level of oil inclusion. By contrast, continuous feeding of the same amounts of free oil increased the proportion and yield of milk fiit.

3.2. Fatty acid composition of the milk fat Mean fatty acid compositions of the milk fats produced by the various dietary treatments are shown in Table 3. In agreement with previous work, the proportion of acids of short and intermediate chain-length synthesised within the niammary gland (i.e. 6:0-14: 1) decreased as a result of including

Erect of feeding concentrates on milk fat 371

Table 2. Mean proportions (g 100 g-l) and yields (kg day-1) of milk fat and solids-not-fat (SNF) resulting from various dietary treatments

Proportion Milk fat SNF

Yicld Milk fat SNF

Experiment (a)

Low tallow, Soya High Soya control oil tallow beans

4.12 3.47 4.14 4.37 8.6.3 8.63 8.56 8 .61

0 .62 0.54 0.63 0.67 1.31) 1.33 1.29 1.31

Experiment (b), twice daily feeding

_ _ Low 5:; 77: 10% fat. soya soya soya

control oil oil oil

4.30 3.56' 3.72' 4.01* 8.54 8.50 8.42 8.62

0.61 0.51* 0.51* 0.56' 1.29 1.25 1 . 1 7 1.25

Experiment (c). continuous feeding

Low 5 % 7:; 10% fat, soya soya soya

control oil oil oil

3.97 4.18 4.33* 4.23 8.76 8.75 8.65 8.72

0.44 0 . 4 6 0.51* 0.49* 0.99 0.97 1.03 1.02

*Statistically significant (P< 0.05) different from the control value.

Table 3. Mean fatty acid compositions (g 100 8-1) of the milk fats produced by the various dietary treatments

Experiment (b), twice daily Experiment (c), continuous Experiment (a) feeding feeding

- .~ _ _ - ~ _ _ _ _ _ _ ~ ~ - Low Low 5 % 7:: 107; Low 57; 77: lo;.;

tallow, Soya High Soya fat, soya soya soya fat, soya soya soya control oil tallow beans control oil oil oil control oil oil oil

S(6 :0 -14 :1 ) 23.5 14.8* 17.3; 17.9* 26.4 19.2* 16.7; 14.6* 25.2 19.1* 15.5" 13.1* 16:0+16:1 35.8 28.4; 35.7 31.5* 43.4 30.0; 27.7; 26.2* 40.0 28.9* 24.5* 22.5* 1 8 : O 10.8 16.0* 13 .2 16.8; 7 . 7 15.1; 16.0; 18.8* 9 . 7 16.8* 20.9* 22 .1* 18 : l total 27.0 37.0* 31.2; 30.0 19.2 31.2* 35.1; 35.7* 22.7 31.7* 35.4" 38.0"

18 : 1 ci.\ 24.8 31.0' 27.8 27.1 17.4 25.9* 28.7' 29.4* 20.6 27.6" 30.8' 32.3* l 8 : l t row 2 . 2 6.0* 3.4* 2 .9 1.8 5.3* 6.4" 6.3" 2 . 1 4.1" 4.6' 5.7*

1 8 : 2 + 2 .9 3.8; 2 .6 3 . 8 * 3 . 3 4 .5* 4.5; 4 .7* 2 . 4 3.5* 3 .6* 4 .3 *

* Statistically significantly ( P i 0.05) different from the control value. I 8 : 2 + = I8 : 2 and higher fatty acids.

long-chain fatty acids in the diet of the cow (4:O is omitted from the tabulated values because i t alone of the short chain fatty acids showed no response to dietary treatment). Moreover, the decrease in proportion of these acids became greater as the amount of oil in the diet increased. A similar situation is observed in the case of the c16 acids, only the high tallow diet failing to produce a statistically significant (P<O.O5) decrease in the proportion of this group of acids. The fatty acid profile obtained on feeding cracked soya beans was quite different from that observed on feeding an equivalent amount of free oil, in agreement with earlier work,12 although in that case the com- parison was to some extent confounded because the free oil treatment induced the so-called low fat milk syndrome.4~13 In experiments (b) and (c), the proportions of the Cis acids increased with increasing dietary intake of the soya oil. In these two experiments, the patterns of fatty acids pro- duced by twice daily and continuous feeding were similar, but the former mode of feeding tended to produce a slightly higher proportion of c16 acids and a slightly lower proportion of 18 :O.

The proportion of total 18: l present as the trans isomer was 8-11 7; in the case of the low fat, control diets and those containing soya beans or tallow, 16-18% in the case of diets containing free soya oil fed twice daily and 13-15"/, when the oil was fed continuously. It is perhaps surprising that this stable intermediate in the ruminal hydrogenation process should be so little dependent on

312 W. Banks ct al.

the amount of dietary oil or the frequency a t which it is offered. The constancy in both the relative proportion of 18 : 1 trans and in the level of the polyunsaturated acids may indicate that the differ- ences in milk fat output due to the frequency and amount of oil fed d o not originate in the rumen.

3.3. Thermal analysis of the milk fats Representative thermograms of the various milk fats are shown in Figure I . The melting profiles of the milk fats obtained from all three control (low fat) diets were very similar in appearance and hence only one curve is reproduced here. Free soya oil in experiment (a) and the 5 :,< and 7 levels in experiment (b) also produced milk fats having virtually identical melting profiles and hence only one curve [from experiment (ail is shown in Figure I .

The main characteristic of the thermogram of the milk fats derived from the control diets is a single continuous melting spectrum, with three partially resolved peaks at 8, 19 and 34°C. The fatty

--L - - ! € 0 IF, 3 2

Te7:ce:o'are :"C:

I

Figure 1. Melting thermograms of anhydrous butterfats from cows olTered (a), low fat, control diet; (b), soya beans; (c), soya oil (5-7%); (d), soya oil (lo;;), continuous feeding; (e ) , soya oil (lo",;), twice daily feeding; and (f), high tallow, control.

Effect of feeding concentrates on milk fat 313

acid compositions of the milk fats from the control diets differ quite appreciably in all the major groups of acids save that synthesised in the mammary gland, i.e. C(6: 0-14: 1). This group might therefore be the dominant factor in determining the characteristic form of the thermogram, which is common to the control milk fats.

Addition of appreciable quantities of fatty acids to the diet yields milk fats having a melting gap, i.e. two quite distinct melting ranges are produced. With free soya oil, this gap is apparent a t 21- 22T, whereas the oil in the form of cracked beans produced a melting gap at 26"C, as did the inclusion of tallow in the diet. Indeed, the melting curves obtained by feeding cracked soya beans and tallow are very similar in appearance.

Low and intermediate amounts of dietary soya oil yield a milk fat in which it is possible to identify three poorly resolved peaks in the low melting region, i.e. a t temperatures below the melting gap. With 10% soya oil, however, this low melting region is characterised by a single broad peak.

The proportion of the various milk fats that are liquid a t 5"C, calculated from the melting curves shown in Figure 1, are recorded in Table 4. The calculationg assumes a constant heat of melting over the entire temperature range, a n assumption that may not be valid.14 Nevertheless, the relative values for the content of liquid fat are of interest.

Table 4. Proportion of milk fat that is liquid at refrigeration temperature (5°C)

Diet from which milk fat IS derived ~ .

Soya oil (10 %)

Low tallow, Soya oil Fed Fed control High tallow (5-7"/,) Soya beans twice daily continuously

Liquid at 5°C (e3 18 28 35 23 40 38

All the oil-rich diets increased the proportion of the milk fat that was liquid at 5°C. Free soya oil was much more effective in this respect than was the same amount of oil in the form of soya beans (35 :(, liquid fat compared with 23 5:). Indeed, even a n equivalent amount of tallow was more effective in increasing the liquid fat content than was the soya bean treatment. Dietary soya oil a t the 10;; level, fed either twice daily or continuously, increased the liquid fat content a t 5°C to cn 4014. This value is in good agreement with that recorded in previous work.9

4. Conclusions

These experiments show that the thermal properties of butterfat can be controlled by suitable manipulation of the diet of the dairy cow. In particular, the proportion of milk fat that is liquid at 5'C can be greatly increased by the inclusion of free soya oil in the ration, whereas only a slight increase in this proportion is achieved by feeding cracked soya beans. It is unfortunate that the beans produce such a poor response in terms of the thermal properties of the milk fat, since this dietary supplement has little effect on the proportion or yield of milk fat, whereas free soya oil fed twice daily tends t o decrease both proportion and yield. However, by feeding the free oil in a number of small meals throughout the day, the desired changes in the melting profile of the milk fat can be achieved, with the added benefit of an increase in the yield of milk fat. Implicit in this conclusion is the assumption that the yield of milk fat is not decreased in going from twice daily to continuous feeding. Whilst the present work cannot comment on the validity of the assumption, previous results15 indicate that the yield of milk fat is unaffected by the frequency of feeding of low fat, control diets similar to those used in this work. The growing use on dairy farms of electronically-

374 W. Banks et PI.

controlled food dispensers, allowing frequent ~ C C C S S to concentrate rations, might allow advantage to be taken of the results presented here.

Acknowledgements The authors thank Dr D. Reid and Miss E. Macdaid for statistical analyses and MI. J. N. Watson and the byre staff for looking after the animals.

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Moore. J. H . ; Sleek, W. Dietary fat and milk Pat secretion i n the cow. Pror. Nurr. Sur. 1968, 27, 66-70. Scott, T. W . ; Cook, L. J . ; Fcrguson, K . A.; McDonald. I . W . ; Buchanan. R. A , ; Loftus Hills, G . Production of polyunsaturated milk rat in domestic ruminants. Aiisrr. J. Sci. 1970, 32, 291-293. Bickerstaffe. R . ; Annison, E. F. The denaturation of stearic acid by mammary gland tissue of the lactating goat and sow. Biorhem. J. 1068, 108, 47-48. Steele, W . ; Noble, R. C.; Moore, J . H . The effects of two methods of incorporating soya bean oil into the diet on milk yield and composition in the cow. J. Duir.LB Hes. 1971, 38, 42--48. Banks. W . ; Clapperton, J. l..; Ferrie, M . E.: Wilson, A. G. E l k t of feeding fat to dairy cows receiving a rat-deficient basal diet. I. Milk yield and composition. J . Dr1ir.v Rcs. 1976, 43, 213-218. Cochran. W. G.; Cox, C. M. E.~pprritrim/al Designs John Wiley & Sons Ltd. New York, 2nd edn, 1957. Minson. D. J . ; Cowper. J. L. Diurnal variations in the excretion of faeces and urine by sheep fed once daily o r a t hourly intervals. Brit. J. Nurr. 1966, 20, 757 764. Banks, W . ; Clapperton, J . I..; Ferrie, %I. E. EfTect of feeding fat to dairy cows receiving a fat-deficient basal diet. 11. Fatty acid composition of the milk fat. J. Duiry Rrs. 1976, 43, 219-227. Banks, W.; Clapperton. J. L . ; Ferrie, M. E. The physical properties of milk fats of different chemical composi- tions. J . Suc. Doirl, Tec,hno/. 1976. 2Y, 86 YO. Macleod, (3. K . ; Wood, A. S . ; Yao, Y. T. Influence of dietary fat on rumen fatty acids, plasma lipid and milk fat cornposition in the cow. J. Doir.v Sci. 1972, 55, 446-453. Storry, J. E.; Hall, A . J . ; Johnson. V. W. The effects of increasing amounts of dietary tallow on milk fat secretion in the cow. J. Doir.v Rrr. 1973, 40, 293-299. Steele, W. ; Noble, R. C.; Moore, .I. H. The effects ofdietary soya bean oil on milk fdt composition in the cow. J. DoirLz Res. 1971, 38, 49-56 Davis, C. L. ; Brown, R. E. ILow-fat milk syndrome. Ph.vsiu/ogy u/’ Digc’rtiori und Mo/aBu/irnr iti rlrc Rirnrincrnr (Phillipson, A. T.. Ed) Oriel Press Ltd. Sewcastle upon Tyne, 1970, pp. 545 565. Norris, R . ; Gray, 1. K . : McDowell. A . K . R . : Dolby. K . M. The chemical composition and physical properties of fractions of milk fat obtained by a comniercial fractionation process. J , Doir-v RPS. 1971, 38, 179-191. Thomas, 1’. C:.; Kelly, M. E. The efTect o f frequency of feeding on milk secretion in the Ayrshire cow. J. Dairi, Res. 1976, 43, 1-7.