3. small Anim. Pract. (1973) 14, 391-397.

Preweaning mortality in specific pathogen free kittens

C A R O L I N E Y O U N G

Medical Research Council, Laboratory Animals Centre, Carshalton, Surrey.

A B S T R A C T

The incidence, causes and age distribution of preweaning deaths in a specific pathogen free (SPF) cat colony are described. The age distribution of kitten mortality is compared with that in one other SPF and four conventionally housed colonies. Almost all preweaning deaths in the SPF colonies occurred within the first week of life. The only infectious agent considered to be a cause of death was Escherichia coli. I t is suggested that in the selection of breeding stock the mothering ability of the dam is of particular importance.

I N T R O D U C T I O N

In recent years several strictly barrier-maintained specific pathogen free (SPF) cat colonies have been established to produce healthy animals for use in research. At present, there is little published information on the reproductive performance and mortality of animals in these colonies, except for that of Festing & Bleby (1970), who have investigated the breeding performance in the Laboratory Animals Centre SPF cat colony. A survey of some feline viral infections carried out by Povey & Johnson (1971) includes the examination post mortem of a group of kittens from both private and commercial conventionally housed colonies and an analysis of the probable causes of death, but there are no records of the kitten mortality rates within these colonies.

In this paper an attempt is made to analyse in detail the incidence, causes and age distribution of kitten preweaning deaths in the Laboratory Animals Centre SPF cat colony, and where possible to compare the results with those in one other barrier maintained colony and several conventionally housed colonies.

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392 C A R O L I N E Y O U N G

M A T E R I A L S A N D M E T H O D S

The SPF cat colony The colony is housed in a brick building ventilated by air filtered under positive

pressure. The building is completely sealed, except for sterilizing entry locks, and run on a barrier system designed to prevent the entry of pathogens. The building is described in detail by Dinsley (1963) and Blackmore (1972).

In 1963, colonies of SPF mice and rats were established in the building by the introduction of germfree animals artificially contaminated with a lactobacillus, Escherichia coli and an enterococcus. Later, a guinea-pig colony was established by hysterectomy and handrearing techniques, and a pair of gnotobiotic rabbits monocontaminated with Bacillus subtilis was introduced as the breeding nucleus of a rabbit colony.

The cat colony was established in 1967. Kittens were obtained by sterile hysterectomy techniques, passed into the SPF building and handreared as de- scribed by Bleby & Lacey (1969). They were not artificially contaminated with any bacteria, so that their commensal flora was acquired from the species already in the building or from the staff. In 1969, the cat rooms were partitioned off from the rest of the building, and the SPF cat colony became a self-contained unit.

The methods of husbandry, nutrition and management are described by Bleby & Lacey (1969) and Festing & Bleby (1970) and, apart from the strict barrier maintenance, are similar to those practised in conventionally housed colonies.

Regular microbiological screening of the colony is carried out to ensure that no feline pathogens have gained access. Faecal samples from the cats are examined each week for evidence of parasites and salmonella or shigella species. One animal is culled approximately every 2 months for detailed examination post mortem and extensive microbiological and parasitological tests, including serological examinations for evidence of viral infections and toxoplasmosis. Any cat which dies or is culled because of disease is similarly examined. The results of these regular examinations suggest that the colony is free of known feline viruses, mycoplasmata and pathogenic bacteria, although Pasteurella pneumotropica has been isolated from the upper respiratory tract of some animals.

Post mortem examinations Kittens which died or were killed in extremis were examined as soon as possible

and subjected to a normal diagnostic autopsy procedure. Bacteriological cultures and material for histological examination were taken when it was considered that these would aid diagnosis. Cultures were made on blood agar and MacConkey agar plates and incubated aerobically. Paraffin sections for microscopic examina- tion were stained with haematoxylin and eosin.

Criteria for inclusion in the survey The few kittens which were not submitted for examination post mortem have

P R E W E A N I N G MORTALITY I N S P F KITTENS 393

been included in the results for completeness, and the cause of death has been determined where possible from the observations made by the animal technicians and detailed on the record card.

R E S U L T S

During the period under review, 1967-1971, fifty-six queens produced 633 full-term kittens. The total number of litters was 183, with an average of 3-5 kittens per litter. Total preweaning losses were ninety-five, ninety-four of which occurred within the first week of life, giving a preweaning mortality of 14.8%.

The causes of death were analysed and grouped under six headings, as shown in Table I. Determination of the primary cause of death in certain instances- such as a deformed kitten which had been chewed-was difficult, and the case was grouped under the most probable heading.

TABLE 1. Causes of death

% of total deaths

Maternal neglect 18 19.0

Congenital deformity 18 19.0

Undetermined, stillborn 20 21.0 Undetermined, born alive 17 18.0

Total 95 100.0

Cannibalism 12 12.5

Coliform infection 10 10.5

Maternal neglect Eighteen kittens, including thirteen from seven complete litters, were considered

to have died as a result of maternal neglect. When examined post mortem, the majority were found to have an empty stomach and a .full bladder, but were otherwise apparently normal. The presence of a full bladder suggested that micturition had not been stimulated by maternal licking of the perineum. These findings were frequently supported by a history of apparently normal viable kittens being ignored.by their dams.

Cannibalism Technicians’ observations were as important as post mortem findings when

categorizing deaths under this heading, as it is always difficult to be certain whether a kitten has been cannibalized by its mother or whether it has been chewed after death. One apparently normal 2-day-old kitten was found chewed, and no detailed examination post mortem was possible. As its three litter mates were reared normally, it is questionable whether it was killed by the mother or

394 C A R O L I N E Y O U N G

died from some other cause and was then eaten. This death was classified a ‘cause undetermined’.

Twelve kittens were apparently killed by their dam. Ten were kittens from thi same cat who killed her complete sixth, seventh and eighth litters. Prior to this she had produced twenty-three kittens, reared twenty, and had not cannibalize( the three that died. There is no explanation for the change in this cat’s behaviour A second dam killed both kittens of her first litter.

Congenital deformity Eighteen kittens were found to have congenital deformities, as listed in Table 2 Three stillborn kittens from the same litter were found to have congenita

deformities. I n one kitten, the stomach, small intestine and colon were absent in the second the oesophagus was absent, and the third kitten had a deformec cranium. Two other kittens in the litter were normal. This was the dam’s fourtl litter, and she produced no abnormal kittens in previous or subsequent litters In three other kittens, two of them litter mates, there was a complete absenci of both the small and large intestine, with the stomach and rectum ending blindly Another kitten with similar intestinal abnormalities also had an abnormal heart with very small ventricles and a cystic dilation of the right auricle. This anima survived for 2 days.

Two newborn kittens which were culled because they were deformed, bu were not sent to the laboratory for examination, have been included in thi section.

TABLE 2. Congenital deformities

Absence of part of digestive tract Cardiac defect Absence of part of digestive tract and also cardiac defect Cranial deformity Umbilical hernia Non-patient urethra Deformity of hind legs Deformity of thorax Unknown

Total

6 2 1 3 1 1 1 1 2

18

Colifrm infection Escherichia coli was considered to be the primary cause of death in ten cases. (1) Pneumonia. E. coli was isolated in pure culture from the lungs of three kittens

Histological examination of the lungs revealed an acute pneumonia characterize( by marked pulmonary oedema. Large numbers of erythrocytes were present ii the alveoli, and numerous bacilli were also seen.

P R E W E A N I N G M O R T A L I T Y I N S P F K I T T E N S 395

(2) Septicaemia. E. coli was isolated in pure culture from the liver of seven kittens; the latter were assumed to have died of a septicaemia associated with this organism.

The E. coli were not serotyped, so it is not known whether the same strain of organism was isolated in all cases.

Undetermined-still born Twenty kittens which were either born dead or died immediately after birth

were found to have totally atelectatic lungs and were classified as stillborn. This group includes a singleton kitten born 9 days after the expected date of parturition.

Undetermined-born alive The seventeen kittens placed in this category had expanded lungs, distinguishing

them from those classified as stillborn. Included here is the only kitten in this series which survived for more than 5 days. Death occurred at 5 weeks, but the cause was not determined.

The time of survival of the other sixteen kittens ranged from a few hours to 4 days. In four kittens, milk clots were found in the stomach, indicating that they had suckled. In six others, the stomachs were empty, suggesting either an inability to suckle or possible maternal neglect. One animal was reported to have been crushed by the dam, and another was found chewed, but it could not be determined whether this was the cause of, or had occurred after, death.

D I S C U S S I O N

The results were compared with records from four conventionally housed cat colonies of varying disease status, and also with a limited survey of kitten mortality in the Bristol University Veterinary School SPF cat colony (Povey, 1971), which was founded from breeding stock supplied from the Laboratory Animals Centre SPF colony. The results of these surveys are summarized 'in Table 3. No figures were available for a direct comparison of preweaning mortality with the Bristol Veterinary School SPF colony. Preweaning losses in the conventional colonies ranged from 13.7% in an outdoor colony (Stara & Bermann, 1967) to 23% in a colony maintained under semi-external conditions (Quinn & Pearson, 1968). A precise comparison of surveys was not possible, as they did not all include such details as the number of stillbirths and causes of death. Nevertheless, a difference was found in the age distribution of preweaning deaths when SPF and conventional colonies were compared.

In the Laboratory Animals Centre SPF colony 99% of the preweaning losses occurred within the first week, and in the SPF colony at the Bristol University Veterinary School 90% of the preweaning losses occurred over the first 10 days (Povey, 1971). In contrast, in papers describing conventionally housed colonies,

396 C A R O L I N E YOUNG

Quinn & Pearson (1968) and Rutty & Smith (1967) commented on the occur- rence of upper respiratory tract infections and recorded 82.6% and 83.3% of preweaning losses respectively occurring within the first week. 62.8% of the preweaning losses were within the first week in the outdoor colony described by Stara & Berman (1967). Lamotte & Short (1966) mentioned that kitten deaths were caused by feline panleucopaenia as well as upper respiratory tract infections and recorded only 59.8 % of preweaning losses in the first week of life. See Table 3. The proportion of kitten losses occurring during the first week of life therefore appears to be related to the incidence of infectious disease within a particular colony.

TABLE 3. Comparison of kitten mortality in six cat colonies

Total Colony kittens born

Present Survey (SPF) 633 Bristol Vet. College (SPF) Povey (1971) -

Quinn & Pearson (1968) 667

Lamotte & Short (1966) 3060 Stara & Berman (1967) 176

Rutty & Smith (1967) 775

% of preweaning Total Preweaning deaths in

weaned mortality % week

538 14.7 98.8 - - 76,7< 5 days

90.0 < 10 days 514 23.0 82.6 635 (82%) 18.0 83.3

1543 16.7 59.8 - 13.7 62.8

In addition to showing the age distribution of kitten deaths in an SPF colony, this survey records a low incidence of deaths (9.5 %) due to infectious agents, and all were considered to be caused by the same bacterial species. Escherichia coli was isolated from all ten kittens thought to have died from coliform infection and, in the absence of feline viruses, mycoplasmata and bacteria known to be pathogenic to cats, it was presumably the primary pathogen. I t is perhaps surprising that other indigenous organisms in the SPF building, such as coagulase- positive staphylococci and Pseudomonas pyocyanea, which have been associated with disease in other species in the colony (Blackmore & Francis, 1970), were not involved. I t is unfortunate that the E. c d i isolated were not serotyped to investigate whether they were of human or animal origin and whether the same serotype was involved in every case. I n their survey of feline viral infection in Britain, Povey & Johnson (1971) considered that respiratory disease was the cause of death in 50.3% of 149 kittens examined, and state that the viral isolation rate from kittens under 2 weeks of age was notably poor. The majority of deaths from respiratory disease occurring in the first 2 weeks of life were characterized by pulmonary oedema, a finding in the three cases of primary E. coli pneumonia recorded here.

P R E W E A N I N G MORTALITY IN SPF KITTENS 397

It would appear that the exclusion of major feline pathogens from an SPF cat colony virtually eliminates the occurrence of kitten deaths after the first week of life, but at the same time it highlights losses due to other factors which might be obscured by endemic disease in a conventional colony. A high proportion of deaths, 31.5 %, including those caused by maternal neglect and cannibalism, could be attributed to the dam. This emphasizes the need to select future breeding stock for mothering ability. Up to the present this has not been possible, because of the demands made on the colony to supply foundation stock for other new SPF colonies.

The results of this survey show that by maintaining cats under strict specific pathogen free conditions preweaning mortality after the first week of life can be virtually eliminated, and also indicate the need to select dams carefully for mothering ability.

ACKNOWLEDGMENTS

I would like to thank Dr D. K. Blackmore and Dr M. F. W. Festing for advice and help in the preparation of this paper.

R E F E R E N C E S BLACKMORE, D.K. (1972) Lab. Anim. 6,257-271. BLACKMORE, D.K. & FRANCIS, R.A. (1970) J . comb. Path. Ther. 80,645. BLEBY, J. & LACEY, A. (1969) 3. small Anim. Pract. 10,237. DINSLEY, M. (1963) Lab. Anim. Cent. coll. Pap. 12, 47. FESTING, M.F.W. & BLEBY, J. (1970) J . small Anim. Pract. 11, 533. LAMOTTE, JOAN H.L. & SHORT, D. J. (1966) J . Znrt. Anim. Tech. 17, 85. POVEY, R.C. (1971) Personal communication. POVEY, R.C. &JOHNSON, R.H. (1971) 3. small Anim. Pract. 12, 233. QUINN, E.H. & PEARSON, A.E.G. (1968) J. Znrt. Anim. Tech. 19, 85. RUTTY, D.A. & SMITH, G.K.A. (1967) Lab. Anim. 1 , 11. STARA, J.F. & BERMAN, E. (1967) Lab. Anim. Care 17, 81.