M. Bush, L. Phillips, R. Montali, E. Dierenfeld, S. Hakala, K. Traylor-Holzer, G. Binczik and R. Tilson
After a typical gestation of 103–104 days, ranging from 102 to 106 days from conception, tiger cubs are born. As a general rule of thumb, the day of parturition can be estimated by taking the last day of observed copulations and adding 104 days. All tigers typically show a 1:1 sex ratio at birth. Data on 652 litters and 1,654 newborn Siberian tigers extracted from the International Tiger Studbooks (Seifert and Muller 1985) show an overall sex ratio (males to females) of 0.962 (Mlikovsky 1985). Of 217 Siberian tigers born as part of the Tiger SSP in the last ten years, a 1.3:1 sex ratio was observed. Siberian tiger cubs weigh about 1.3 kg at birth regardless of sex, and grow about 100 g per day. The other subspecies will show slightly lighter weights in all categories. Adult body weights will show greater variance among the subspecies and between the sexes, males being 10-20% heavier. Historically, the neonatal mortality rate for captive tiger cubs within the first year was about 40%; it has improved to about 35% (data from the AZA Tiger SSP).
(S. Hakala and K. Traylor-Holzer)
A behavioral analysis of time-lapse videotape of five tiger birth sequences at the Minnesota Zoo (13 hours before to 13 hours after parturition) revealed the following information. The time interval between the first and last birth ranged from 2-4 hours. In the 13 hours following the first birth, the females spent an average of 36% of their time nursing the cubs or with the cubs resting in a nursing position, although this figure varied widely among the females (11-58%). The females spent about 24% of the time grooming the cubs (range = 15-37%) and majority of the remaining time resting within 0.5m of the cubs (21%). Although the females had access to an adjacent holding enclosure, they spent 98-100% of their time in the approximately 3m x 3m maternity den.
Similar observations at the Minnesota Zoo documented the behavior of a wild-caught female Siberian tiger and her first litter (four cubs) through 14 weeks of age. This female spent about 60% of her time resting with at least one cub in a nursing position through the first seven weeks, after which nursing decreased. The cubs began eating solid food by 13 weeks of age and were completely weaned as of week 17. The cubs began grooming each other at nine weeks and self grooming at 12 weeks. Social play was noted at five weeks and increased with age.
These observations may be specific to the behavioral patterns and "personalities" of these individual tigers, but they are an attempt to quantify information which is rarely documented to this extent. They may be used as guidelines to which the behavior of other females with varying levels of maternal experience and with varying litter sizes can be compared.
When cubs are born London and Stuttgart offer the following comments that will help avoid the need to hand-rear cubs: "Newborn cubs can be observed using a video if desired, but 24-hour direct observation is likely to be disturbing for the female and therefore detrimental to the well-being of the cubs. There should be no interference with a female and cubs in the early stages (0-28 days), as with many carnivores this has caused the death, or necessity for hand-rearing, of cubs. Cleaning should not take place in the cubbing area until the youngsters are moving out of the birth den on their own volition; again, such disturbance is likely to be detrimental. Staff cannot be certain that the mother will not harm the cubs until they are at least three weeks old.
If examination of cubs at an early stage is deemed necessary, the hands of the keepers and veterinarians, and all equipment used, should be covered in scent from used bedding before contact with the cubs, and noise should be kept to an absolute minimum. Before returning the mother to them, the cubs themselves should also be thoroughly covered with scent from used bedding to remove human odors."
Although the opportunity to cross-foster cubs from one female mother to another will probably not occur at most zoos, it has been demonstrated to be a viable option and is recommended over removing the cubs and hand-rearing them. At the Minnesota Zoo two females gave birth within the same week. One female (# 732) gave birth to four cubs (SB#'s 5464-67); the other female (# 5069) gave birth to two cubs (SB# 5475 and 5476). The cumulative growth curves for the four cubs immediately were below the standard curve so one cub (the heaviest of the four to allow him to compete with the larger cubs of the other female) was transferred on day 27 to female 2003. The transfer was accomplished by shifting mother 2003 temporarily into an adjacent enclosure, moving the new cub in with the other two cubs, and covering the new cub with excrement from the mother. The mother was immediately reintroduced to the cubs. She went straight to the new cub, smelled it, and licked it clean. Within minutes she was nursing all three cubs. The cub prospered, as did the smaller litter of three left with mother #732 (Fig. 1) (R. Taylor and R. Tilson, unpublished data).
Fig. 1. Growth rates of two litters of tiger cubs during a cross-fostering attempt.
(M. Bush, L. Phillips and R. Montali)
[Editors' note: Whether to hand-rear or not hand-rear tiger cubs is controversial and one of the most polarized issues in tiger husbandry.]
The Tiger SSP believes cubs should be raised by their mother for four reasons: 1) she does a better job; 2) the cub usually grows up to be better adjusted behaviorally; 3) it makes a great exhibit; and 4) it saves considerable staff time and reduces management constraints. When this is not possible due to maternal neglect or health reasons the cubs should be hand-raised. The cubs should remain with the mother long enough to receive colostrum.
The Arnhem Zoo objects to hand-raising any rejected cubs. The exception is genetically important cubs, and attempts should be made to determine the cause of the mother's neglect in order to improve the situation for the next litter. Furthermore, Arnhem Zoo believes that unless the mother is highly valuable genetically, she should not have anymore litters. London Zoo believes valuable females should be given several chances to improve maternal behavior.
When cubs are removed they should receive a complete physical examination, weighed, the umbilicus checked for infection, blood collected for baseline values, and given a prophylactic antibiotic (penicillin).
There are numerous protocols for handraising tigers (Hoff 1960, Husain 1966, Theobald 1970, Kloss and Lang 1976, Hughes 1977, Richardson 1988, and see Dierenfeld below) using various products and techniques. The AAZK Hand-Rearing Protocol is another good source. Certain guidelines are important, initially the cubs should receive 5% dextrose for the first two feedings and then started on milk replacer. The choice of milk replacer for tigers seems to be Esbilac or KMR (Borden, Inc., Hampshire, IL 60140). London Zoo uses Cimicat (Hoeschst). We suggest adding the enzyme lactase to the milk to break down the lactose and have noted fewer problems with gastrointestinal upsets. The cub should be kept hungry the first day or two and then the diet increased in volume to about 10% of body weight/24 hr. Initially the cub is fed by stomach tube to minimize the risk of inhalation pneumonia, but also to assess residual stomach content by aspiration prior to the next meal. When started on the bottle the first liquid should be 5% dextrose to minimize lung damage if inhalation occurs. The cub is held in a normal sternal feeding position when taking the bottle. When the cub is taking 5% dextrose well with no coughing, milk can be started. The concentration of the formula is started at 6% and elevated to 12, 15 and 18% as the cub grows to meet the energy requirement without overfilling the stomach. The cub should be receiving the 18% formula at 4-6 weeks of age.
The cubs should be stimulated to urinate and defecate after each feeding by massaging the ano-genital area with cotton moistened with warm water. If diarrhea occurs, the formula should be diluted with an oral electrolyte solution and total volume decreased by 20-40% for 8-12 hrs. A stool culture prior to antibiotic therapy should be obtained to check for pathogenic bacteria. If diarrhea is severe and persistent, all oral intake should be stopped for 12-18 hrs and the cub supported with subcutaneous fluids, and then started on oral electrolytes followed by dilute formula and returned to normal feeding over the next 12-24 hrs.
Many hand-raised tigers develop hair loss at 6-8 weeks of age (Kloss and Lang 1976), possibly due to some deficiency in the diet. The addition of liver homogenate to the diet has been helpful in preventing and correcting this alopecia. Weaning the cubs to solid food also usually enhances hair coat, growth, and general appearance. This should begin at 5-8 weeks.
"Hand-raised cubs, especially those being hand-raised alone, should be reared in a rich and varied environment. The most successful procedure appears to be rearing the cub in a home environment with access to large domestic dogs. Hand-raising in an isolated zoo nursery environment may result in severe behavioral inadequacies. Where home environment rearing is not possible, the cub should be provided with a non-human companion, e.g., domestic dog. Under no circumstances should a cub be hand-raised alone in an isolated nursery setting."
(from J. Mellen)
Hand-raised cubs should be weighed regularly to monitor weight gain and calculate necessary food intake. A growth chart of these animals can be compared to other published charts (Hemmer 1979, Binczik et al. 1987). Iron supplements are needed for young growing tigers to prevent anemia. Although many milk replacers have iron added, an additional supplement is beneficial. Iron deficiency is not uncommon in mother-reared cubs that have no exposure to dirt. Iron dextran injections to the cubs may be required in these cases (see Growth Curve for Siberian Tiger Cubs ).
Vaccination against feline viral diseases with a trivalent killed product (Fel-O-Vax, Fort Dodge Labs., Fort Dodge, IA 50501) at the recommended dose should be given at 10-12 weeks, 16 weeks, six months and one year of age. In collections where female tigers have very high titers due to repeated vaccination, passive immunity transferred to the cub can be high enough to delay active immunity induced by the vaccine. This is why additional vaccinations are recommended. Fecal examinations of mother and cubs should be performed monthly. If hookworms have been a problem in the collection, then the cubs should be prophylactically treated at 6-8 weeks of age.
A number of collections have successfully introduced the male to the mother and cubs; ages of introduction vary up to about four months old. The temperament of the adult tigers, and their attitudes to each other, are of great importance in evaluating the advisability of this approach, but in general problems are rare. It should be borne in mind that male tigers have been observed interacting with their offspring in the wild (London Zoo).
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