Rev. sci. tech. Off. int. Epiz., 1989, 8 (2), 551-566.

Applications of probiotics to animal husbandry J. TOURNUT *

Summary: The microbial equilibrium of the intestinal flora reflects, and also is responsible for, a harmonious digestive function, and thus a satisfactory state of health of the individual. One attempts to obtain this equilibrium by dosing the animal with certain microbial strains, called probiotics.

In order to explain the value of probiotics and to define the rules governing their administration, the author points out that intestinal colonisation is established mostly during the early postnatal period, and that the indigenous, permanent flora varies with feeding, husbandry conditions and gastro-intestinal diseases, the latter being governed by immune protection of the digestive tract during the first three weeks of life.

To limit such variations it is necessary to know when to use probiotics, and for what purpose. During the neonatal period, the indication is therapeutic, but usage is confined to prophylaxis by distributing high doses as soon as possible after birth. The other indication is promotion of growth by regular administration over a long period. The mode of administration may be as a liquid, paste, or mixture with feed. An equilibrium in a newborn mammal may be achieved through the dam by administering probiotics for 15 days before parturition, in order to modify the gut contents of the dam.

In each case it is necessary to examine the possibility that the vehicle used might have an adverse effect on viability of the bacteria, for adequate numbers are essential to obtain the desired result.

Good results have been obtained in pigs, rabbits and calves. The results are less convincing in poultry. However, rigorous experimental procedure is always necessary to evaluate a result.

K E Y W O R D S : Applications - Digestive system - Digestive system diseases -Enteritis - Growth promoters - Intestinal flora - Newborn animals - Probiotics.

The term "probiotic" was proposed in 1974 by Parker (20) to describe live micro­organisms whose action was the opposite of antibiotics ("pro" versus "anti") . Probiotics promote an equilibrium of micro-organisms in any medium, but particularly in the intestinal flora. For Parker (21), the process may be extended to ecological niches in soil, when a grain seed coated with favourable bacteria could be planted in a hostile soil. A similar action could take place in glaciers and oceans. It is consequently a universal problem, and any microbial balance achieved would improve physiological phenomena in any medium (gut, soil, sea) by a chain reaction.

In this paper, we limit ourselves to the digestive tract of animals, excluding substances which are not micro-organisms, in particular enzymes (which legislators

* Ecole Nat ionale Vétérinaire de Toulouse , Chemin des Capelles, F-31076 Toulouse Cedex, France .

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have placed in the same category). As far as we know, there has been no exhaustive study of substances in which just enzymes are the active constituent.

Before proceeding further, it should be recalled that in 1983 Freter (7) pointed out that the results of using probiotics as growth promoters are reported in the literature as positive or negative in equal proportions, and that the same can be said of studies of antibiotics for the same purpose. Nevertheless, it is known to be very difficult to forego the latter growth factors in animal husbandry.

The use of probiotics is in its infancy, and parameters for assessing their efficacy have not been defined with precision. However, existing assessments should not be rejected, for it is important to develop substances which leave no residues in products for human consumption, when the number of antibiotics permitted is being reduced.

Applications of probiotics in animal husbandry will be discussed under the headings:

— Why use probiotics?

- When to use them ?

- How to use them, and in what doses ? What precautions have to be taken ?

— Results.

W H Y USE PROBIOTICS?

Any change in the "equilibrium" of the digestive flora may result in an intestinal or nutritional disorder, leading to irregularity in growth. To know when and how to use probiotics, it is necessary to understand the way in which the gut flora develops and the main factors responsible for variations in the flora.

The intestinal flora and colonisation of the intestine

Mammals and birds are born with a sterile digestive tract. This protective phenomenon makes it possible to rear axenic animals, which harbour no micro­organism, without recourse to laboratory procedures. Such animals are useful for studying the role of certain bacterial species or strains. The appearance of an intestinal flora depends essentially on the environment and on the physiological characteristics of each species (2, 4, 8, 25, 26, 27, 33).

These characteristics influence the equilibrium of the flora, as in the case of facultative anaerobic bacteria. Lactobacilli and enterococci are dominant in rats and mice (4, 8) as well as in piglets (4, 33). In rabbits, strict anaerobes become dominant from the start of colonisation (8). A comparison of healthy and ill piglets has shown that the overall ratio of coli bacteria to enterococci provides a good indication of the flora equilibrium (38).

The flora and digestive system diseases during the neonatal period

The neonatal period is characterised by a dominance of intestinal diseases in all species. For example, a Belgian survey (13) showed that 6.5% of calves born alive

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died during the first month of life, and 95% of the deaths were due to intestinal infections. The situation is similar in other species.

Diseases during the neonatal period are dominated by imbalance of the intestinal flora.

Most of these intestinal infections, whether primary or secondary, are caused by the group of Escherichia coli bacteria, which exert their pathogenic effect more readily after the intestinal mucosa has been damaged by other micro-organisms, such as rotavirus or Coronavirus (14). Examination of the intestinal flora, by simple diagnostic procedures (33), during such diseases reveals changes in the ratio of E. coli bacteria to enterococci, and of E. coli to sulphite-reducing bacteria.

The pathogenic bacteria are invariably dominant. However, this dominance can be discovered only by examining an animal which has died or been killed recently (within six hours of death). In any diagnostic examination, bacterial counts reveal a major difference from the normal counts per gram of intestinal contents. A considerable increase in E. coli populations (108 or 109), enterococci (106) and sulphite-reducing bacteria (109) is evidence of incipient putrefaction, and is therefore impossible to interpret. On the other hand, a considerable fall in these numbers indicates the presence of another pathogen not tested for. This occurs in calves with acute intestinal salmonellosis, in which 109 Salmonella/g is accompanied by 102 E. coli, 101 enterococci and 101 sulphite-reducers.

The intestinal microflora has been estimated to consist of 10 1 4 bacteria, with little variation above or below this rate (11).

During the neonatal period, another factor involved in digestive tract infections is the immune protection of the digestive tract.

Immune protection of the digestive tract during the neonatal period

A review of this subject is necessary in order to highlight the difficulties and failures, which are different in mammals and birds.

Mammals

The importance of colostral immunity to the newborn animal is recognised for all species. The animal is born with a sterile digestive tract, colonisation of which depends on the environment. Colostrum ingested during the first 4-5 days of life provides protection, in principle, against digestive tract infections. This protection is provided only if the colostrum is adequate in quality and quantity.

Immune protection in mammals begins with the process of intestinal immunity. Augmentation of the titre of mammary antibodies is not such a simple matter as it may appear to be. There is considerable variation in the antibody titre available to newborn animals (such as calves and piglets). Consequently, it is possible for neonatal infections to appear as early as 24 or 48 hours after birth if protection is inadequate, and this period extends up to 3 weeks of age, when local immunity commences (22).

Birds

Different phenomena operate in birds because their physiology is different (27). Immune protection of the young bird depends on the mother, but it is more effective, being concentrated in the egg yolk supplied to the intestine during incubation and

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the first few days of life. Yolk discharges its antibodies directly and regularly into the intestinal lumen. This assures protection of the young bird against common infections (which have immunised the mother) during the first four days after hatching. Naturally-occurring infections and losses usually commence after the fourth day (23, 27).

This epidemiological feature demonstrates the link between the disease and imbalance of the flora, having been under control (and not expressed) during the first four days. The situation after the fourth day is different, for protection disappears between then and about the 21st day (31), when local intestinal immunity begins to operate (22). During the period of 4-21 days, protection against intestinal bacterial infections depends exclusively upon an equilibrium of the flora. Every means must be used to maintain this equilibrium.

The digestive flora and feeding

The results of studies of the relationship between feeding and the gut flora of normal, holoxenic animals in good health are difficult to interpret. By contrast, pathological situations are easier to interpret. The most typical example in veterinary medicine is enterotoxaemia in sheep and goats (3). Increasing the energy content of the ration by feeding larger amounts of cereals or by allowing the animal to graze young pasture, rich in legumes, has an inevitable consequence. Enterotoxaemia, provoked by an increase in the number of Clostridium perfringens, leads to death of the animal.

When the proportion of cereals in the ration is increased, ruminai protozoa disappear because of a fall in pH towards 5.5 (9). Streptococci increase until the pH reaches 4.45, when their place is taken by lactobacilli, leading to ruminai acidosis. This phenomenon is well known and is taken into account in the feeding of ruminants. In both cases there is a direct link between feeding and the gastro-intestinal flora.

As far as weaning is concerned, it is known that early weaning creates digestive problems, particularly in piglets (15). The diet must not be changed abruptly or radically, and a transitional period is necessary, allowed for in feeding techniques for the period after weaning, in order to avert irregularity in growth and enteritis of nutritional or infectious origin.

Axenic animals are used in order to study the mode of action of feeding on the digestive tract flora (6). In young piglets fed milk substitute, E. coli is part of the dominant flora. If these E. coli are transferred to two mice fed differently, with one receiving milk and the other a normal diet, there is evidence of a permissive barrier effect against E. coli in the mouse fed normally, due to an inhibitory factor present in the diet.

The variability of the digestive tract flora at each change of diet thus deserves to be emphasised.

The digestive flora in relation to husbandry conditions, including exposure to stressors

The effects of husbandry conditions and stress have been studied in the author's laboratory, using hares and rabbits (1), and pigs (32, 35).

As already mentioned, strict anaerobes form the dominant gut flora of rabbits (4, 8), but E. coli is rare or absent in rabbits kept in cages having a wire floor. When

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such rabbits are placed in floor pens with or without litter, E. coli appears in their caecal, colonic and faecal flora within 21 days, without the diet having been changed.

Inversely, rabbits kept in floor pens with litter, shedding E. coli in their droppings, lose E. coli from their intestines or from their droppings 15-20 days after being placed in wire-floored cages or pens.

This is worth examining in detail because it throws light on aetiological factors in the enteritis of newborn hares kept in wire-floored cages or pens. This disease can be accompanied by a mortality rate of 50-70% of hares reared in captivity, and it is caused by strict anaerobes belonging to the genus Clostridium (5). The animals can be kept alive by daily administration of antibiotics, but the condition recurs once treatment stops.

Observation of the mating behaviour of male and female hares in cages shows that 2-4 days after parturition the male mates the female, after sending away the sucking young by biting them, so that the female can adopt a mating posture. The male may chase the young if they have been unable to find shelter at the back of the cage.

These events suggest a simple prophylactic procedure, which involves placing the couple in a floor pen of 4 m 2 surface area, at least 15 days before parturition, in order to establish a more balanced intestinal flora. The space provided permits the young to flee, avoiding the severe stress of being bitten. This technique has protected some 95% of young hares from enteritis (1).

Among pigs, two types of stress have been studied: restraint in a harness (32), and restraint in a metabolism cage (35). Following restraint in a harness there was a significant increase in the total flora of bacteria other than strict anaerobes, and in the total flora of strict anaerobes and E. coli in the ileum, colon and caecum. This flora did not diminish much, except after oral administration of meprobamate, and it was not influenced by intramuscular injection of a neuroplegic agent (which has a direct action on nerve endings in the intestinal mucosa).

Another experimental model, conducted in a metabolism cage, provides a better picture of conditions on the farm. The same procedures were followed, starting with the ileum and colon, and including counts of E. coli, enterococci, sulphite-reducing bacteria and also the body weight of the animal before being caged. At the end of the experiment, which lasted for 8 days for the study of chemical substances and 15 days following administration of micro-organisms, intestinal weight was measured. The animals were killed under general anaesthesia by exsanguination. These experiments demonstrated a beneficial effect on flora equilibrium of anti-infective agents, neuroplegic agents and certain probiotics (Lactobacillus acidophilus, Streptococcus faecium and Bacillus subtilis; unpublished results).

At the end of this chapter the following conclusions may be drawn. The intestinal flora undergoes variation: between species; during the neonatal period in a given species, depending on the environment; due to feeding, particularly after a radical change; due to husbandry conditions and stress. These phenomena explain the variability of results and counts made on members of a group of animals reared together.

Finally, during the neonatal period, effective protection lasts no more than 0-4 days, a period corresponding to the secretion of colostrum by mammals, and

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absorption of yolk by birds. Immune protection does not commence until the third week, with antibodies formed in the intestinal mucosa.

An intestinal equilibrium is thus necessary to avert intestinal infections and also disorders of growth, and this fact explains the current interest in probiotics.

W H E N TO USE PROBIOTICS, A N D FOR W H A T PURPOSE?

Probiotics are used in order to obtain satisfactory equilibrium in the intestinal flora. This equilibrium affects growth and development of the animal, influences its

nutritional requirements, affects the morphology of the digestive tract, changes substances of endogenous and exogenous origin present within the gut lumen, and plays a role in the multiplication of bacteria, whether they are pathogenic or not (24). These are the primary indications for using probiotics. We shall not discuss here the phenomenon of bacterial antagonism, which is dealt with by other authors.

A probiotic has a therapeutic indication or a growth-promoting indication, according to the nature of the imbalance of the flora.

Therapeutic indication

The indication for a probiotic is therapeutic if experiments on axenic animals have demonstrated a preventive or curative barrier effect, depending on whether it acts before or after the introduction of pathogenic bacteria. The effect is drastic if the pathogen is eliminated before it has multiplied, or permissive if the pathogen persists in small, undetectable numbers, as in a healthy carrier. Under clinical conditions, with specified probiotics at specified dosages, no curative effect has been demonstrated. Any effect can only be preventive.

The principal prophylactic indication is bacterial infection of newborn animals. During this period of intestinal colonisation, the role of probiotics is fulfilled if

high doses (109 daily) are given for at least 3-5 consecutive days, starting immediately after birth. A single daily administration is preferable to divided doses. The maintenance of a large number of bacteria belonging to the probiotic family should be tested (for biomass effect) during the five-day colonisation period.

Another proposed therapeutic indication is diarrhoea in young animals, particularly that associated with weaning of piglets. The proponents (and the farmers) confuse softening of faeces with intestinal disease, and may confuse the qualitative and quantitative changes in the flora in response to the change in diet with intervention of a pathogen. The efficacy of the doses used (106/g of feed) is more likely to favour flora imbalance than to affect disease caused by a pathogen.

Indication as a growth promoter

For this purpose a probiotic is given in a minimum effective dosage of approximately 106-107/g of feed, but it has to be adjusted for a particular commercial preparation by examining the dose-effect curve.

In addition, daily administration has to last for at least 1-2 months before a result can be achieved. It is important for the probiotic agent to persist within the gut lumen

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in sufficient numbers in order to obtain a buffering effect on variations associated with feeding and husbandry conditions.

HOW ARE PROBIOTICS ADMINISTERED?

They are administered directly or indirectly.

Direct administration

This mode of administration has been proposed for piglets (31) and calves (34), using a suspension of the probiotic in Ringer's solution, injected into the mouth of the newborn animal by using a syringe. This technique is impractical, and so remains an experimental procedure. On the other hand, the firms Pioneer (of Des Moines, Iowa, USA) and Lactiferm SF68 (Lugano, Switzerland) have developed a paste which is easy to give to young animals. Tests of the keeping quality of the strain within the paste have shown that it remains at the stated level for 2 months when stored at +4°C.

Indirect administration

The various procedures for indirect administration are:

In liquid form

A probiotic can be administered in drinking water or a drinking device for birds, and in milk for calves. In either case the product is administered in an amount of fluid which will be absorbed entirely and rapidly, in order to avoid contamination by pathogenic bacteria (23). In the case of milk reconstituted from a milk replacer, a temperature above 40° C must be avoided if the stated dose of revitalised bacteria is to be given.

In feed

A probiotic may be administered in feed after mixing with a meal or incorporation in granules. Streptococci, lactobacilli and particularly sporulated bacteria can be mixed with meal, because they lose no activity when kept for 2-6 months (at 20°C). However, viability should be tested, because the moisture content of meal is about 13%, while that of freeze-dried bacteria is about 3%. Under certain conditions non-sporulated bacteria could multiply and lose their activity. A guaranteed storage life is necessary.

Mixture in granules is ruled out for the present in the case of unsporulated bacteria, because of the moistness of the temperature and pressure used. In the case of spores, their resistance should be tested by placing them for 10 minutes in water heated to 80°C. This test has been chosen by the National Fraud Laboratory at Rennes, France (M. Michard, unpublished information).

Another technique is to coat the surface of the granules after manufacture. This is attractive in theory, but neither this technique nor the coating of bacterial strains has been applied.

Strict controls are required to ensure that the necessary number of revitalised bacteria is present, for this governs the dose of probiotic administered.

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A rather special distribution procedure is to administer the probiotic to the dam, before and after parturition, and until weaning. At the time of parturition the dam will have a balanced gut flora, and will pass it on to her offspring, eventually providing the young with a certain quantity of probiotic (10, 28).

Probiotics may thus be administered orally in different doses, according to the result required (therapy or growth promotion), and for a period which ranges from 3 to 7 days for therapy and 30-90 days for growth promotion.

Bacteria used as probiotics

The bacteria may be classified as follows:

- Spore-forming aerobes of the genus Bacillus:

a) Bacillus cereus, variety toyoi (also known as B. toyoi; present in Toyocerin ®) b) B. cereus var. caron (Paciflor ®) c) B. coagulans (Lactobacillus sporogenes) d) B. subtilis (B. natto). - Strictly aerobic spore-formers of the genus Clostridium:

Clostridum butyricum.

— Bacilli which produce lactic acid:

a) Bifidobacterium thermophilum, B. pseudolongum b) Lactobacillus acidophilus, L. salivarius, L. helveticus c) Enterococcus (Streptococcus) faecalis, Enterococcus (Streptococcus) faecium. — Yeast: Saccharomyces cerevisiae.

Note that certain complex floras were used with good results against infection of chicks with Salmonella gallinarum-pullorum (16), but these strains have been lost.

RESULTS

Results obtained depend on whether the probiotics are used for therapy or for growth promotion.

THERAPEUTIC PROBIOTICS

These have been investigated mainly in piglets and calves. The trials reported below are taken from the literature, and the number within round brackets refers to the list of references.

Trial on piglets

Lactobacillus acidophilus ( 6x l0 9 ) and Enterococcus faecium (6XlO 9) were administered orally by using a syringe, once daily for three days, to newborn piglets of primiparous sows.

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The results of treatment, compared with untreated piglets also born of primiparous sows, are given in Table I, and they show a distinct difference.

T A B L E I

Trial on piglets (31)

Treated group Control group

Number of piglets 259 254 Mortality rate at 35 days (%) 6.94 16.88 % piglets with diarrhoea 0 50 Mean daily gain (grams) 160 140

Trials on calves

In calves, the same product was given in the same way from birth, but for five consecutive days. The results, shown in Table II, demonstrate a clear effect.

T A B L E II

Trials on calves (30)

Treated group Control group no. % no. %

Number of calves 950 453 Days of treatment 5 0

Cases of diarrhoea 187 19.6 292 64 Mortality 5 0.05 19 4.2

In another trial, treatment commenced between 5 and 15 days after birth and lasted for 5 days. The probiotic Streptococcus faecium was administered in milk powder at 10 1 0 bacteria per g of powder (200 g powder to a litre of water, one litre daily per calf). The results are equally encouraging (Table III).

T A B L E III

Trial on calves (30)

Treated group Control group no. % no. %

Number of calves 117 117 Cases of diarrhoea 2 2 7 6 Mortality 0 1 Weight increment after 30 days 120 100

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In a third trial, between 200 and 500 g of milk powder (depending on age) were given daily from 10 to 50 days of age. The powder contained Bacillus toyoi at 1010

per g. The efficacy of this treatment is shown in Table IV.

T A B L E I V

Trial on calves (10)

Treated group Control group no. % no. %

Number of calves 52 52

Days of administration 40 0

Cases of diarrhoea 1 1.8 9 17

Mortality 0 2

Weight increment 120 100

Treatment seems to have given good results, whether it started at birth or after five days of age. However, it must be pointed out, at least in the trials reported here, that the prognosis of the diseases involved was not very grave.

PROBIOTICS AS GROWTH FACTORS

Trials on pigs

1. Unweaned piglets, administration of probiotic to the sow

Among primiparous sows synchronised for farrowing, the probiotic was mixed with the sow's feed, the daily ration being 4-6 kg. Lactobacillus acidophilus (6 x 109) and Enterococcus faecium (6 x 109) were given from 15 days before farrowing to 21 days afterwards. The results are encouraging (Table V).

T A B L E V

Probiotic given to sows (29)

Treated group Control group

Number of sows 120 120 Number of piglets born 1 032 1 045 Number of piglets weaned 920 708 Mortali ty ( %) 11.2 32.2 Weight at weaning (kg) 7.3 6.4

Most reports refer to the use of sporulated bacteria of the B. cereus type.

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Table VI summarises two trials of Bacillus toyoi (from reports supplied by G. Chomette, responsible for the registration of Toyocerin in France). Sows were each given 4-5 kg of feed daily, from the 10th day before farrowing until the time of weaning, containing 2 x 106 of probiotic per g of feed.

T A B L E V I

Trials with Bacillus toyoi given to sows

Trial 1

Groups treated control

Ti

Gi treated

ial 2

•oups control

Number of litters 22 26 30 30

Piglets born alive total mean litter size

214 248 9.68 9.53

298 9.9

288 9.6

Total losses no . %

30 49 14.01 19.75

21 7

22 7.6

Diarrhoea cases treated (°/t>) 0 8.67 5 14

The probiotic Bacillus cereus var. caron (in Paciflor) has also been tested, and the results are given in Table VII. Sows were given 106 Paciflor organisms per g of feed once daily, starting 10 days before farrowing and ending at weaning. The sows received 4-6 kg of feed a day.

T A B L E V I I

Trial with Baci l lus cereus viven tn sows (17)

Groups control treated

Number of sows 28 30

No . piglets born per sow: total 11.1 11 P 0.05 born alive 10.1 10.5 P = 0.07 no . weaned 8.2 9.3 P 0.05 % stillborn 8.8 4.05 P = 0.07

% losses: born alive 16.6 11.8 P > 0.05

% losses: total born 24.2 15.3 P 0.05

Mean weaning weight of litter 63.8 70 P = 0.15

Mean weaning weight of piglets 7.79 7.6 P 0.05

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2. Weaned piglets

In a trial of Toyocerin (Bacillus toyoi; report provided by G. Chomette) the results were quite striking for mean daily weight gain, the favourable effect amounting to between 5 and 20% (mean 9.2%). Germination of the spores, studied by Hendrickes et al. (personal communication), was 50-70% in the ileum and 80-95% in the rectum; it took place at pH 5 to 9.

In the case of Bacillus cereus in Paciflor (18), the effect was noticeable mainly in the feed conversion ratio, but also in carcass grading, which improved the net profit.

A review of the literature, summarised in Table VIII, demonstrates the value of probiotics in fattening pigs. Nevertheless, it seems to us that the effect is most pronounced between weaning and 50-60 kg weight.

T A B L E V I I I

Trials of probiotics on piglets at the start of fattening (Pollmann, 1985)

% of control Piglets group ( + or - )

Authors Probiotics no. Age Daily Feed

(weeks) gain conv.

Mixture of 32 3 - 2 . 9 - 2 . 0 Holden (1976) Lactobacillus spp. 288 4 - 2 . 7 - 1 . 4 Mahan and Newland (1976)

( " P r o b i o s " ) 144 5 - 8 . 5 + 3.3 Cline et al. (1976) 100 3 + 10.8 + 7.2 Baird (1977) 192 3 + 4.5 + 7.2 Pol lmann et al. (1980) 224 3 + 9.7 + 21.4 Pol lmann et al. (1980)

72 3 + 8.0 + 3.3

Lactobacillus 155 3 + 7.5 _ England (1975) 72 3 + 11.0 + 1.5 Pol lmann et al. (1980)

Bacillus subtilis 330 3 - 4 . 4 + 0.7 Pol lmann et al. (1980) 96 4 + 1.5 + 0.5 Peo (1984)

542 4 + 4.6 + 0.6 Trot ter (1984)

Trials on calves

Probiotics have a variable effect in calves fed milk substitute.

In the case of Lactobacillus, the results have been:

- either favourable (36), as shown in Table IX; - or less favourable (36), as shown in Table X.

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T A B L E I X

Comparative evaluation of the results obtained with antibiotic or Lactobacillus (Blanchet, 1986)

Control 1 *

Control 2 **

Lactobacillus groups Control 1 *

Control 2 **

with antibiotics

without antibiotics

Groups Compared with

I II I

III IV I II

V I

VI II

Carcass weight (%) 100 + 1 - 2 + 3 . 5 - 4 . 5 + 1 . 5 - 2 . 5 + 4 - 5 + 2 - 3

Growth (%) 100 + 2 - 3 + 5 - 6 + 2 . 5 - 3 . 5 + 6 - 7 + 3 - 4

Consumpt ion (%) 100 - 1 - - 2 - 3 - - 4 - 1.5 - - 2 . 5 -- 4 - - 5 - 2 - - 3

* neither antibiotic nor Lactobacillus ** antibiotics given

T A B L E X

Summary of trials with probiotics in calves (after McCormick, 1984)

Experimental Duration Mean Health Bacteria conditions (days) daily gain

(% of controls)

aspect Authors

Lactobacillus Day-old calves 42 NS NS Ellinger et al. acidophilus (1978)

Lactobacillus sp. freeze-dried Young beef bulls,

200 kg Transpor ted 650 km 28 + 22 Hutcheson et al.

(1980) Transpor ted 18 km 28 NS Hutcheson et al.

(1980) Lactobacillus sp .

freeze-dried Young beef bulls • 28 NS Kiesling et al. (1982)

Lactobacillus sp . freeze-dried Young beef bulls 209 NS Kiesling et al.

(1982) Freeze-dried Calves at weaning 35 - 1.77 Kiesling and

Lofgreen (1981) Inactivated Calves at weaning 35 + 7 Kiesling and

Lofgreen (1981)

NS: not significant

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In the case of Bacillus cereus var. toyoi (report supplied by G. Chomette), a study of the effect of giving this probiotic to calves at weights of 70-100 or 140 kg showed that the best result (in terms of weight gain and feed conversion) was obtained with a dose rate of 106 per ml of milk (daily administration of 10-15 litres).

Mean daily weight gain

Feed consumption

Controls Treated calves

100 103.9 or 105.6

100 96.8 or 95

Yeasts

Numerous favourable results have been claimed for yeasts, mostly in trials on young beef cattle. Interpretation of the results is difficult (12).

Trials on rabbits

Bacillus cereus (Paciflor) seems to improve the growth of rabbits by 6.3%, with a fall in feed consumption by 6% (19).

Trials on poultry

Results obtained in chicks, laying hens and turkeys (36) are difficult to interpret, because they are often contradictory.

In conclusion, it must be pointed out that the results available are often meagre, seldom comparable one with another, often omitting the most important parameters, such as the bacterial count of the feed.

CONCLUSIONS

Our own observations with different probiotics, used therapeutically or as growth factors, confirm the positive results obtained by others.

Nevertheless, there is a current fashion to develop miracle products in response to the trend away from products which leave residues in human food. It is therefore necessary to be rigorous in accepting such solutions. This rigour should be provided by international regulations which establish experimental conditions, particularly for formal testing of safety and efficacy.

But we should not automatically reject what may prove to be a trump card for livestock farming. In the words of Alexis Carrel, "science should be on guard constantly against trickery and credulity, but it is the task of science never to reject facts just because they seem to be extraordinary, and because they cannot be explained".

* * *

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