Animal Feed Science and Technology, 7 (1982) 135--140 135 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

USE OF FISH PROTEIN HYDROLYSATE IN MILK REPLACERS

E.R. ORSKOV, H.S. SOLIMAN and C.F.S. CLARK

Rowe t t Research Institute, Bucksburn, Aberdeen AB2 9SB (Gt. Britain)

(Received 29 April 1981; accepted for publication 16 September 1981)

ABSTRACT

~rskov, E.R., Soliman, H.S. and Clark, C.F.S., 1982. Use of fish protein hydrolysate in milk replacers. Anita. Feed Sci. Technol., 7: 135--140.

Fish protein hydrolysate (FPH) has been used as the sole source of protein in milk replacers for lambs in several experiments. In comparison with casein, diets containing FPH gave slightly inferior growth rates during the first 2 weeks of a 5-week rearing period. The lower growth rate was generally compensated for in the following 3 weeks so that overall growth rate and food utilization were similar with milk replacers containing casein or FPH. Diets based on FPH, lard and hydrolysed starch were found to give results similar to a milk replacer based on casein, butterfat and lactose. The use of fat fish to provide both the source of fat and protein has received some attention and needs to be further investigated.

INTRODUCTION

The use of skimmed milk powder as the main ingredient in milk replacers for lambs and calves is justified as long as there is a surplus available which is not required for human nutrition. In the long term, however, the production of skimmed milk powder and but ter as an economic proposition is likely to be very doubtful if the skimmed milk powder is to be used for lambs and calves. The processing cost of what is effectively the exchange of butter fat for cheaper sources of fat in milk replacers is so high that this system can only survive with considerable government support, either to producers of the milk or to feed manufacturers using the skimmed milk powder in milk replacers. In the long term we need to explore the use of non-milk consti tuents to replace skimmed milk completely.

Unlike the functioning ruminant, which can be fed on a large variety of feeds of varying quality because of the action of the rumen micro-organisms, the young new born ruminant (which has only a rudimentary rumen) has to rely on liquid food passing directly to the true stomach for digestion in the small intestine. The range of digestive enzymes secreted by the young ruminant therefore determines the extent to which it is possible to diverge

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from the composition of the milk from the dam, and also the way in which such milk replacers have to be prepared.

In a series of experiments at the Rowet t Institute an a t tempt has been made to solve some of the problems in using non-milk constituents, partly in collaboration with Dr Mackie of the Torry Research Station. Concentra- tion has been mainly on the replacement of protein and most emphasis here is given to this constituent. However, a brief comment on the replacement of fat and lactose is necessary, as undigested fat and carbohydrate can interfere with protein digestion.

Replacement o f milk fat with vegetable and/or animal fat

Many of the technical problems involved in the incorporation of fat into milk replacers have been solved. The importance of a small globule size, and a homogeneous and stable distribution of the fat globules, is well recognized (Raven and Robinson, 1958). There is evidence to suggest that an inefficient digestion of the fat (caused for instance by large fat globules and aggregation of globules) can interfere with protein digestion (Ternouth et al., 1975). However, it is also possible that an inefficient digestion of protein can inter- fere with digestion of fat. The consequences are, that the more milk protein that is replaced by animal or vegetable protein which does not clot, the greater the need for accuracy and competence in the physical preparation of milk replacers (homogenization and emulsification etc.).

Replacement o f milk lactose with other sources o f carbohydrate

Lactose The enzyme lactase is obviously most abundant in the intestine of the

new-born and while it may be uneconomic to produce skimmed milk powder, whey products containing lactose are likely to be available for use in milk replacers for a long time (as by-products from the production of cheese).

Sucrose There is no sucrase activity in the small intestine of new-born ruminants

and therefore the amount of sucrose that can be used in milk replacers is extremely small and limited to the amount that can be digested through microbial activity in the hind gut (Mayes and q)rskov, 1974).

Glucose Since hydrolysis of lactose leads to one mole of glucose and one of

galactose it is no surprise that glucose can be used to replace lactose in milk replacers (Walker, 1959; Mathieu and de Tugny, 1965).

Starch Small amounts of amylase are secreted into the intestine of new-born

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ruminants, and maltase is found in the intestinal brush borders (Dollar and Porter, 1957). The use of raw starch has never been successful, however, since only a little appeared to be hydrolysed in the small intestine, in col- laboration with Roquet te Fr~res of Lille, France, we have examined the use of partially hydrolysed wheat or maize starch (Protamyl 110) (Soliman et al., 1979). Protamyl 110 contains about 13% glucose, 29% of raw starch, 4% of sorbitol and 56% of di- and oligosaccharides of varying chain length. This product is used largely for veal calves in France. The results of using Protamyl 110 as complete replacement of milk lactose were excellent, and it was even used to replace a large proportion of the fat with no deleterious effect on animal performance.

It is thus possible to replace milk lactose complete with other sources of carbohydrate, such as glucose or partially hydrolysed starch.

Replacement of milk protein with other sources of protein

Of all the milk constituents the replacement of casein has p roved to be the most difficult. This is largely due to casein forming a clot in the abomasum (owing to the action of the enzyme, rennin), and also to the spectrum of proteases which at birth is uniquely suited to the hydrolysis of milk proteins. The ability of milk protein to form a clot effectively delays the rate of passage of the protein (and fat trapped in the clot) to the small intestine, so that even with twice daily feeding, the passage of digesta is almost continuous. In the replacement of milk protein therefore, two possibilities were pursued: first, to increase the frequency of feeding, and secondly, to ensure that the protein used was partly digested externally. Several attempts were made to use partial- ly hydrolysed single cell protein (Toprina) but with little success (Soliman, 1977). However, the use of undried and later dried fish protein hydrolysate (FPH) was successful and has so far been the only source of protein with which it has been possible to completely replace milk protein without drastic reduction in animal performance (Soliman et al., 1979). In two experiments FPH gave results similar to casein when it was used as the only source of pro- tein for the rearing of lambs. Casein appeared to be slightly superior during the first 2 weeks, but the lambs compensated during the final 3 weeks so that the overall growth rates were similar over the 5-week rearing period. The results from one of these experiments are given in Table I. Food utilization and digestibility were essentially similar for all the diets, although milk consti- tuents were progressively replaced. It should be pointed out also that the measurements of digestibility were made after the rearing period and may not have represented digestibility during the early part of the trial.

In all the trials with lambs an automatic feeding device was used to feed the lambs on small quantities in 8 meals/day to ensure that ideal conditions were achieved. On the other hand, preliminary trials of feeding with FPH to calves did not show a difference between two and four feeds per day (Dods- worth et al., 1977).

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TABLE I

Food utilization by lambs of diets based on FPH, lard and starch*

Protein source: Casein Casein Casein FPH Carbohydrate source: Lactose Protamyl Protamyl Protamyl Fat source: Butter oil Butter oil Lard and Lard and

coconut coconut

Live weight gain (g/day) Weeks 2--3 151 167 Weeks 4--6 197 196 Overall 177 183

Food conversion (kg DM/kg gain) 1.02

Digestibility (%) of: Fat 98.9 98.3 Starch -- 99.8 Protein 96.4 94.9

128 112 175 218 154 170

1.06 1.08 1.00

98.2 97.7 99.8 99.9 94.4 93.6

*From Soliman et al., 1979.

From the above discussion it seems possible with lambs (see Table I) to replace milk constituents altogether, at least from 1 week of age. It should be pointed out again that the experience so far indicates that a greater use of non-milk constituents places a greater demand on the technical skills needed for the manufacture of the substitutes. There is probably also a greater demand for adequate housing and good husbandry.

While the use of starch hydrolysates may not be of great commercial interest as long as whey materials are available, the production of whey powder is energy demanding since whey contains only about 3% dry matter and the remaining 97% has to be evaporated. FPH also has to be dried in order to enable it to be safely transported. It would seem possible, at least theoretically, to combine the two processes by carrying out the hydrolysis of the fish waste in liquid whey.

To take this development further, we have, in collaboration with Dr Mackie, obtained FPH derived from hydrolysis of fat fish unsuitable for human consumption. The dry matter contained 49% fat. It was made into a milk replacer for which the fish provided all the fat. The whole FPH fractions containing the high level of fat were homogenised and emulsifiers added. The final milk replacers contained 42% fat, 35% protein and 20% hydrolysed starch.

In an experiment, three 2-month-old lambs fitted with cannulae in the terminal ileum were used to measure the digestibility of diets in the small intestine (Table II). The digestibility coefficients are similar to those which could be expected from whole milk diets, the digestibility of the fat being particularly high. The results of the trial are preliminary and no performance data are available. Even so, the results are interesting and suggest exciting

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TABLE II

The effect of feeding lambs on an artificial milk diet based on fatty fish and starch on digestion in the small intestine

Dry Organic Protein Fat Starch matter matter

Intake (g/day) 219 214 81 104 40 Passing into large

intestine (g/day) 28 24 8 4 3 Digestibility in small

intestine (%) 87.2 88.8 90.2 96.2 92.5

possibil i t ies in s impl i fy ing the p r o c e d u r e s fo r mak ing mi lk subs t i tu tes . I t leaves o p e n the poss ibi l i ty o f h y d r o l y s i n g the f a t t y fish in l iquid whey which cou ld t hen be spray-dr ied and used d i rec t ly as a mi lk subs t i tu te .

CONCLUSION

There are re la t ively few p r o b l e m s in replacing fa t and c a r b o h y d r a t e in mi lk replacers p r ov i ded the p r e p a r a t i o n o f tl~e mater ia l is adequa te . The on ly p ro te in source which so far has been successful ly used as c o m p l e t e replace- m e n t fo r mi lk p r o t e i n has been FPH, which in e x p e r i m e n t s wi th l ambs has given f o o d u t i l i za t ion and live weigh t gains s imilar t o casein. Use o f fa t fish to p rov ide b o t h the fa t and the p ro t e i n in mi lk replacers holds p romise bu t needs t o be fu r t he r e x p l o r e d in feeding trials.

REFERENCES

Dodsworth, T.L., Owen, J.B., Mackie, I.M., Ritchie, A. and q)rskov, E.R., 1977. Fish protein hydrolysate as a substitute for milk protein in calf feeding. Anim. Prod., 25: 19--26.

Dollar, A.M. and Porter, J.W.G., 1957. Utilization of carbohydrates by the young calf. Nature, 179: 1299--1300.

Mathieu, C.M. and de Tugny, H., 1965. Digestion et utilisation des aliments par le veau pr4}ruminant ~ l'engrais. 2. Remplacement des mati~res grasses du lait par du glucose. Ann. Biol. Anim. Biochim. Biophys., 5: 21--39.

Mayes, R.W. and {~rskov, E.R., 1974. The utilization of gelled maize starch in the small intestine of sheep. Br. J. Nutr., 32: 143--153.

Raven, A.M. and Robinson, K.L., 1958. Studies on the nutrition of the young calf. Br. J. Nutr., 12: 469--482.

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Soliman, H.S., ~}rskov, E.R., Atkinson, T. and Smart, R.I., 1979. Utilization of partially hydrolysed starch milk replacers by new born lambs. J. Agric. Sci., 92: 343--349.

Soliman, H.S., ~rskov, E.R. and Mackie, I.M., 1979. Utilization of fish protein hydro- lysates in milk substitutes for lambs. J. Agric. Sci., 93: 37--46.

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Ternouth, J.H., Roy, J.H.B., Thompson, S.Y., Toothill, J., Gillies, C.M. and Edwards- Webb, J.D., 1975. Concurrent studies of the flow of digestion in the duodenum and of exocrine pancreatic secretion of calves. 3. Further studies on the addit ion of fat to skim milk and the use of non-milk proteins in milk substitute diets. Br. J. Nutr., 33: 181--196.

Walker, D.M., 1959. The development of the digestive system of the young animal. 4. Proteolytic enzyme development in the young lamb. J. Agric. Sci., 53: 381--386.