Rhino Husbandry Manual
Greater One Horned Rhinoceros
Reproduction
Greater-One Horned Rhino Reproductive Age
According to the North American Regional Studbook for greater one-horned rhinos (Cseplo, 2023) that contains data on 229 births, the youngest greater one-horned rhino to give birth was just four years old, which means she conceived at two years eight months. The oldest greater one-horned rhino to give birth was 31 years 4.5 months. The oldest female to become pregnant as a first time dam was 24 years old. The youngest male greater one-horned rhino to sire a calf was four years eight months (at time of conception) and the oldest to sire a calf was 41 years 6 months (at time of conception). In general, greater one-horned rhinos can potentially reproduce between the ages of three and 30 (females) and five and 40 (males) if they are maintained in good health. Although fertility tends to decline in nulliparous females as they age, the oldest dam at first reproduction was 24 years and the oldest sire at first reproduction was 30, suggesting that a few greater one-horned rhinos can breed for the first time fairly late in life. However, only two female greater one-horned rhinos successfully reproduced for the first time after they exceeded the age of 18, suggesting that most females need to conceive before they reach the age of 16.5 or they are unlikely to ever reproduce.
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Seasonal Changes in Physiology or Behavior Associated with Reproduction and Management Implications
The mature female greater one-horned rhinoceros will breed throughout the year. Based on year-long fecal hormone metabolite analyses (Schwarzenberger et al., 2000) and urine hormone metabolite analyses paired with serial ultrasound exams (Stoops et al., 2004), it appears the female greater one-horned rhino is consistently exhibiting reproductive cycles throughout the year, and hormone concentrations associated with the cycles do not differ by season. There is evidence that females may become acyclic, at least behaviorally, when no male is present. There could also be a case for some females in colder climates becoming seasonally acyclic over the winter. More work needs to be done. (Cseplo,2023) Although some of these cycles are anovulatory, data are insufficient to determine if anovulation is seasonally influenced (Stoops et al., 2004) and documentation of anovulatory cycles during all seasons of the year would argue against a seasonal association (Stoops, unpublished data). Similarly, male greater one-horned rhinos will mate with females throughout the year. Furthermore, ejaculate sperm concentration is high and semen quality good when collected by electroejaculation throughout the year, and no seasonal influences on either of these characteristics or serum testosterone concentrations have been reported (Stoops et al., 2010).
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Reproductive Cycle
The female greater one-horned rhinoceros is a spontaneous ovulator with a somewhat variable cycle length. Although most reports are in agreement that the average cycle length for a greater one-horned rhino is approximately 43 days, the range (36-61 days) is greater than that typically observed in other rhino species making the greater one-horned rhino’s estrus somewhat more difficult to predict (Kassam and Lasley, 1981; Kasman et al., 1986; Hodges and Green, 1989; Schwarzenberger et al., 2000; Stoops et al., 2004). Most of the variation appears to be in the length of the luteal phase since the follicular phase is fairly consistent at about 14 days, which is a much longer follicular phase than those observed in other rhino species (Stoops et al., 2004). The greater one-horned rhino also differs from other rhinos by the size of follicle produced prior to ovulation. The greater one-horned rhino’s preovulatory follicle is the largest reported for any mammalian species and measures about 12 cm in diameter. Its pattern of growth also is unusual in that it reaches maximum size many days before ovulation instead of just prior to ovulation (Stoops et al., 2004).
Peak Breeding Season for Greater One-Horned Rhinos in North America
The distribution of births by month for greater-one horned rhinos is shown in Figure 4.1 for the greater one-horned rhino births reported in the 2024 regional studbook (Cseplo, 2024) Figure 4.2 shows the months of conception for greater-one horned rhinos based on an approximate gestation of 480 days. Based on these data, it is clear that greater one-horned rhinos are fertile and conceive throughout the year. The trend towards more fertile matings during the interval from March to September is almost certainly management related since temperate zoos are more likely to pair their rhinos for mating during months with good weather.
Table 4.1 Number of greater one horned calves born per month (2024 GOH AZA Studbook; Cseplo)
Table 4.2 Number of fertile greater one horned rhino matings by month (2024 GOH AZA Studbook; Cseplo)
Introductions
Changing social groupings of rhinos through the introduction of additional individuals to an established individual, pair or group is a process requiring care and planning. Rhino species vary widely in social structure, and rhinos periodically vary their grouping patterns in the wild according to factors such as reproduction and the rearing of young. Social groupings in captivity, therefore, should also vary according to species, as well as to the circumstances within each institution. Rhinos may be very protective of their individual boundaries, but proper introduction procedures can minimize injury from conflict and aggression. The following section outlines general considerations for any rhino introduction and provides systematic descriptions of aggression, procedural recommendations, and descriptions of potential species-specific introduction types. Factors that must be considered in any introduction include individual animal personalities, staff experience and confidence level, and enclosure type (i.e., indoor/outdoor, public/off-exhibit, relatively small/large). Barrier types and temperature should also be considered. Introductions often result in aggression, and it should be noted that rhinos of both sexes have been the aggressors. Territorial defense is often limited to ritualized confrontations, in which two rhinos advance toward each other but stop nose-to-nose and engage in a staring contest to gauge each other’s size and strength. Also as part of this ritual, the two individuals may touch horns, back apart and wipe their horns on the ground (Nowak, 1991). More intensive conflicts involve head-on charges and inflicting injuries by horning or ramming. In general, behaviors that have been noted during rhino introductions are listed in Table 4.3. It is important to note that what is often perceived as serious or dangerous aggression between rhinos is, in fact, normal behavior requiring no intervention of any kind. Along with increased size and thick skin comes decreased vulnerability compared with many other animals. Table 4.4 lists a descriptive hierarchy of aggression levels in rhinos.
Table 4.3. Behaviors noted during rhino introductions (Fouraker and Wagener, 1996).
Non-aggressive Behaviors Ritualized Confrontations Potential Stress-Related Aggressive Behaviors
Follow Head sweep Pacing Charge/chase
Touch/rub/lick Face-to-face stare Running (excessive) Open-mouth threat
Anal or genital Space-maintenance and Sparring
investigation threat vocalizations Goring
(excessive)
Diarrhea
Head Bob
In some cases, aggression may proceed to a point at which management should intervene to prevent serious injury. Rhino managers should allow some aggression during an introduction but be prepared to intervene in the event that aggression threatens the lives of one or more rhinos. Protocols for intervening may vary across institutions, but in general, careful consideration should be given to intervening in an introduction before aggression reaches Level 5 (Table 4.4). Stopping an introduction at a level prior to this will not lessen aggression during a subsequent introduction attempt. Animals that are allowed to “settle their differences” will establish some territorial boundaries and will usually not engage in serious aggression again, with the exception of a male attempting to approach an estrous female. In sum, moderate aggression is commonplace in any rhino introduction; sparring and fighting will occur and result in minor injuries (cutaneous wounds). However, in most cases, aggression levels prior to Level 5 may be allowed to continue using the discretion of management. The introduction process requires much planning and cooperation among rhino managers. Table 4.5 outlines recommended steps for rhino introductions. Familiarization through visual, olfactory and tactile contact should be permitted if at all possible prior to a full-scale introduction. If the facility permits, this may be accomplished by first placing individuals in the same barn or in nearby outdoor lots, or by providing olfactory clues such as urine, feces or skin rubbings from the animal being introduced. As the animals acclimate, managers may move them to adjacent barred stalls or fenced outdoor yards. These barriers prevent confrontations leading to serious injury but allow acclimation and familiarization prior to introduction.
Table 4.4. Levels of aggression in rhinos (Fouraker and Wagener, 1996).
Level of Aggression Definition
1 Rhinos are charging each other but do not make physical contact.
2 Rhinos are charging each other with physical contact resulting in some cuts and scrapes to the facial area.
3 Rhinos are charging each other with physical contact resulting in cuts and scrapes to the facial area and body.
4 Charging and/or pursuit proceeds to the point that one or both rhinos are knocked down at least once. Scrapes and cuts are deeper and more numerous.
5 Aggression and pursuit proceed to the point that one or both rhinos have subcutaneous wounds or arterial blood flow.
It should be noted that one animal might break away from the confrontation and attempt to escape. The aggressor often will pursue and begin horn-prodding the underbelly of the escapee as the two run around the enclosure. Often a rear leg is hooked and held aloft while pursuit continues. If the escapee does not stop and resume a defensive posture, the animals might continue until heat or exhaustion becomes a critical factor. Aggression at this point is more serious.
The actual introduction should be attempted in the largest available enclosure. Enclosures should be large enough to allow ample space for shading, mock-fighting, aggression and defense. Prior to an attempted introduction, water pools in an outdoor enclosure should be filled with substrate to prevent injury in the event of serious aggression. The enclosure should contain visual barriers such as brush or earth piles or boulders (“run-arounds”), which give rhinos places to hide without becoming cornered or trapped. These features lessen overt aggression if a rhino is able to escape the sight-line of another. An enclosure should not contain dead ends in which an individual may become trapped by an aggressor. The enclosure should allow for the use of high-pressure fire hoses, CO2 fire extinguishers and/or vehicles to aid in separating individuals.
Animal personality and disposition should always be considered in introductions. A subordinate animal should be introduced to a more dominant animal in an enclosure familiar to the subordinate. Male greater one-horned rhinos should be introduced only during the female’s estrous period. Appropriate personnel for first-time introductions include the primary animal manager, a vet with immobilization equipment, and the curator and keepers most familiar with rhinos. Other staff may be needed at critical points around the enclosure’s perimeter so that the animals may be observed at all times in case separation becomes necessary. It should be noted that if a barn is opened and used to separate individuals, only one individual should be allowed inside the barn, and it must not be trapped inside by an aggressor. Because of the relatively more aggressive, territorial nature of greater one-horned rhinos, introductions should be attempted only for breeding purposes (one male to one female). With the exception of very large facilities, individual rhinos should be held separately in all other situations.
Table 4.5. Steps in the introduction process.
Step Description
1 Animals in the same barn or multiple outdoor lots should have olfactory and auditory exposure to each other. If the animals are not housed near each other (i.e., enclosures on opposite sides of the zoo, etc.), they should be moved to the same exhibit area.
2 Animals should be given visual contact with each other in addition to the above sensory modalities. Animals may be shifted within a barn or in adjacent outdoor lots. If at any point during this process the animals display symptoms associated with stress (e.g., pacing, diarrhea, excessive vocalizations) for more than 2-3 hours, the introduction should return to the previous step.
3 If animals are not already positioned adjacent to each other, they should be moved closer together (e.g., to adjacent stalls or adjacent outdoor enclosures).
4 The actual introduction (full tactile exposure) should take place in the largest enclosure available and follow guidelines stated in this chapter. Preferably, the enclosure should be familiar to the least dominant animal and include ample “run-arounds”.
5 Within institutions in which rhinos can be left together 24 hours per day, they should be separated during the first several nights or until they show only minor aggression.
Introduction of a Male to a Female for Breeding Purposes
Introductions should occur only for breeding purposes and when the female is in estrous (see Table 4.6 for behaviors associated with estrous). The introduction should take place in the largest area available. Some females display strong, attention-seeking, estrous behavior whereas others are far more subtle, even resembling male avoidance in some stages. If two adjoining yards are opened to create a larger introduction area, the female should be placed in the yard she is most familiar with first and allowed to acclimate. After she is acclimated to the yard, the male should be introduced to her. As stated in the general introduction protocols, if the facility allows, preliminary visual and tactile contact may increase the likelihood of mating success. If intervention is required because of aggression between the rhinos, the introduction should cease and be attempted at a later date. If possible, the female should be kept from entering a barn if the individuals cannot be separated in the outdoor enclosure. In all likelihood, the male will follow her into the barn, and the chances of serious injury will increase. Because the introduction should occur during estrus, and introduction may be required at any time of the day or night. Bulls detect the onset of estrous 3 – 7 days before the behavioral estrous of the female starts. Once the female enters estrus, the males will be restless; they will not eat well, will frequently spray urine and are very eager to be near the female. The female does not show any interest at all at this stage. Signs of behavioral estrous in the female are also restlessness, lack of appetite, frequent squirting of urine / marking and repetitive whistling sounds (EAZA; 2015). The rhinos should be monitored and separated following breeding.
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Table 4.6. General reproductive behaviors observed during estrous and courtship (Fouraker and Wagener, 1996)
Female Behaviors Male Behaviors
Vocalizations* Vocalizations
Urine squirt/spray* Frequent urination; urine spray
Urogenital changes (e.g., vulva swelling) Erection
Vulva “winking” Genital inspection of female
Vaginal discharge* Flehmen response
Aggression toward male** Charge/chase female
Maintains proximity to male Maintains proximity to female
Nuzzles male’s belly and/or genitals Follows female
Stands for male Chin-rest
Inappetance Mounts female
*Estrous behaviors in the absence of a male are often difficult to distinguish. In general, increased activity, agitation, vocalizations, spray-squirting urine, and vaginal discharge have been cited. As the female approaches peak estrus, these behaviors usually increase in frequency. Some females have been reported to successfully breed without exhibiting any overt behavioral signs of estrus
**Minimal aggression with females with strong estrous behavior but some aggression noted in females that show subtle signs. (Cseplo, 2023)
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Reintroduction of a Post-partum Female (Without Calf) to a Male
An introduction of a post-partum female to a male for breeding should occur only during the female’s estrous period. It may be advisable to wait until after the first post-partum estrous cycle. The calf should not be introduced with the female when she is introduced to the male; therefore, the calf should be trained to be separated from the female to allow for the introduction of a male (see Calf Development, this chapter). It is possible to keep a calf with dam and bull in large areas that favor sight breaks. Females will adopt a "tuck" behavior with their calves in areas of high visual exclusion when in estrous. There have also been successful pairings in large areas where the "tucking" behavior is not adopted. If facilities are unable to keep a calf safely with the breeding pair then training or tranquillizers can be used to facilitate a temporary separation.
Pregnancy and Parturition
Table 4.7 lists behaviors associated with pregnancy and impending birth. In all species, there may be a mucus discharge, noticeable weight gain or increase in girth size, as well as increased frequencies of defecation and urination throughout gestation. The onset of birth often takes place at night or in the early morning and may last one to three hours. Parturition usually lasts ten to 12 hours from breaking of the water, though first-time mothers may take longer to calve. The presentation of a calf is generally head-first, although rear feet presentations do occur and may take longer than head-first births, but usually deliver without assistance. Capabilities for monitoring births remotely through closed-circuit television or other means are advisable.
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Table 4.7. Physiological and behavioral indicators of impending parturition.
30 Days Prior to Birth 2 Weeks Prior to Birth 24 to 48 Hours Prior to Birth
Increase in teat size Nipples enlarge Udders increase dramatically in size
Beginnings of milk production Nipples develop wax Inappetance
Milk may be expended with pressure on the teats Vulva swelling occurs Becomes irritable and aggressive to stimuli, including staff
Female may prolapse Mucus plug forms
vaginally when defecating Increased vulva dilation
Increased restlessness, lies down often
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Calf Development
A single calf is generally the rule. Few data are available on birth weights, but in general, calves weigh 65 to 81 kg at birth (144-178 lb; n=9). Immediately following birth, the newborn calf is usually cleaned by its mother and stands for the first time within 30 minutes to five hours of birth. A newborn calf may require a substrate that allows traction to help steady itself. Suitable materials may include sand, gravel, straw, hay or rubber matting. In all cases, both the dam and calf should be monitored closely to prevent ingestion of the substrate. A calf should begin nursing within one to two hours of standing (though in a single case, a calf removed from its dam for medical intervention nursed 16 hr post-birth). The dam will nurse her calf while standing or lying on her side.
Infants less than two months old may nurse hourly, while older calves nurse at intervals of about 2.5 hours. Few data are available on nursing durations and frequencies, but it has been reported that as the calf ages and grows stronger, nursing will usually increase in duration but decrease in frequency. It has been reported that calves may gain up to 4.54 kg (10 lb) per day for the first ten days. The first defecation has been reported at two to ten days of age (n=2). Calves may nurse for up to two years, although they have been observed first sampling solid food at less than one week to one month of age. Calves may be offered supplemental feedings of milk if the dam is believed to be a poor milk producer or the calf is not gaining weight (see Nutrition chapter). Infant rhinos have been successfully pulled from their mothers because of rejection, medical issues related to the mother or infant, or from a failure to nurse. Otherwise, it should be noted that weaning for management purposes can be accomplished if necessary at six months, but one year is preferable. One attempt to use a surrogate mother was unsuccessful; however, hand-reared infants have been assimilated into existing groups and have shown reproductive success. Keeping the calf with the dam even longer helps to facilitate social learning. Male calves are usually weaned by the dam at an earlier age than female calves. If the facility is able to run multiple female greater one-horned rhinos together, the cow and calf should not be introduced to the others for approximately four months following birth. Calves generally do not have peers to play with, though they are generally very curious and often chase and mock-fight with their dams or occasionally keepers. Non-aggressive sexual behaviors may be exhibited at as early as 18 months of age in males. In general, the long-term social effects of removing rhino calves from dams should be investigated. For all species, weaning or permanent separation of the calf except for medical reasons should not occur before one year of age. A calf can, however, be temporarily separated from its mother at as early as one month of age for short periods of time (e.g., re-breeding of dam). Generally, the procedure is to separate the calf for short periods of time (e.g., 15-20 minutes during cleaning) and gradually increase the separation time. If a dam is not going to be re-bred, her calf may remain with her until it reaches sexual maturity (at approximately 4.5-5 yr of age). It should be noted that available data indicate that nursing does not inhibit conception. The first calf may be forced away before parturition of the second calf as the dam seeks to isolate herself.
Reproductive Monitoring and its Use in Timing Introductions for Mating
Although institutions with very large greater one-horned rhino enclosures have been very successful in breeding the species by simply allowing the bull to run with the cows much of the year and minimizing any intervention by animal care staff, most zoos do not have this luxury. For smaller facilities and more aggressive pairs, reproductive monitoring is extremely useful in timing introductions. This is especially true for the females that fail to exhibit behavioral estrus. Although estrous behaviors (including urine spraying, pacing, anorexia, vocalizations) can be very flamboyant in this species, some females, during some or all cycles, fail to exhibit any signs of estrous.
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Fortunately, greater one-horned rhinos produce very high concentrations of estrogen metabolites in their urine during their follicular phase, thereby providing an ideal non-invasive reproductive monitoring tool. Once a female’s baseline urinary estrogen concentration is determined, the start of the follicular phase can be identified accurately as the first day urinary estrogen rises above baseline, and estrus can be predicted to occur approximately 12 days later (Stoops et al., 2004). Although ultrasonography can be useful in confirming that a dominant or preovulatory follicle is present, it cannot be used alone to accurately determine the day of estrus. In contrast, ultrasonography is essential to confirm ovulation after mating since anovulatory cycles often are associated with hormone profiles that appear identical to those of ovulatory cycles (Stoops et al., 2004).
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Several hormones and their metabolites have been employed for monitoring reproductive activity in the greater one-horned rhinoceros (Table 4.8). Estrogen metabolites excreted by the greater one-horned rhino accurately reflect reproductive status, whereas in the other rhino species, only progesterone metabolite monitoring has proven useful for tracking ovarian activity.
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Table 4.8. Reproductive hormones monitored in the greater one-horned rhinoceros.*
Sample Estrogen Progesterone Testosterone LH Other
Urine f2,1,5 f3,2,5 f5
Feces f4 f4 f4
Serum m6
Saliva f7 f7
**f= female; m= male
*Table adapted from Roth, 2006.
1 Kassam and Lasley, 1981; 2Kasman et al., 1986; 3Hodges and Green, 1989; 4Schwarzenberber et al., 2000;
5 Stoops et al., 2004; 6Stoops et al., 2010; 7Gomez et al., 2004
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Pregnancy Detection and Loss
Early pregnancy in the greater one-horned rhino has been diagnosed 18 days after ovulation using ultrasonography to identify the embryonic vesicle within the uterine lumen (Stoops et al., 2007). However, early diagnosis by ultrasound can be challenging in this species because portions of the uterine horns drop out of view to a depth that the ultrasound is incapable of penetrating. Therefore, early diagnosis by ultrasound examination is not always possible. However, urinary and fecal progestin metabolites can be used to confirm pregnancy after three months of gestation because concentrations exceed those measured during the luteal phase (1 Kassam and Lasley, 1981; 2Kasman et al., 1986; 3Hodges and Green, 1989; 4Schwarzenberber et al., 2000; 5 Stoops et al., 2004; 6Stoops et al., 2010; 7Gomez et al., 2004). Throughout gestation, images of the fetus, fluid or membranes may be obtained via trans-abdominal ultrasound examinations, but due to the size and thickness of the greater one-horned rhino’s skin, not every exam yields good quality images (Stoops, pers. comm.). Early embryonic loss has now been documented in the greater one-horned rhino (Stoops et al., 2007), just as it has been documented in all other captive rhino species. Unfortunately, this species appears to be especially prone to miscarrying or producing stillborn offspring. That number seems to have decreased considerable given the advances of captive management.(Cseplo;2024)
Published percentage as of 3/15/2016 (n=30): 17.4%
Possible stillbirth percentage since (n=1): 2.0%
Although such occurrences are more common in primiparous cows, many proven dams also fail to produce viable calves in subsequent pregnancies (Kock and Garnier, 1993; Pluhacek et al., 2007).
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Reproductive Technologies (Semen Collection, Artificial Insemination, etc.)
Semen collection by electroejaculation has proven very successful for collecting good quality greater one-horned rhino ejaculates (Roth et al., 2005; Stoops et al., 2010) and effective cryopreservation protocols have been established (Stoops et al., 2010). Post-thaw functionality of these samples has been proven by the production of multiple pregnancies following their use in artificial insemination procedures (Stoops et al., 2007). In the past, semen was collected by manual stimulation (Schaffer et al., 1990), but subsequent attempts to collect good ejaculates by manual stimulation in any rhino species have largely failed. Artificial insemination (AI) techniques have also been established for this species. AI can be conducted either manually with customized insemination tubing that is guided by hand into and through the tortuous cervix or by using a standard flexible colonoscope that is inserted through the cervix with tubing in the instrument port for the insemination (Stoops et al., 2007). Method of choice depends upon the individual rhino’s tolerance of vaginal manipulations. Neither in vitro fertilization nor embryo transfer have been attempted in this species and would be considered highly experimental. However, ovaries obtained post-mortem could provide a source of oocytes for initiating some preliminary research on these higher-tech applications.
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Fertility Assessment
Male fertility assessments should include: 1) an ultrasound examination of the testicles to evaluate tissue consistency and size, 2) electroejaculation to confirm sperm production, and 3) serum testosterone analysis. It is important to note that a positive result from electroejaculation is very meaningful, but a negative result should not be used alone to diagnose a male with infertility because electroejaculation is not always successful in producing good quality semen samples, even when conducted on proven bulls. Female rhinos should be examined by rectal ultrasound to determine if any masses or cysts exist in the vagina or uterus. These types of pathologies appear to be very prevalent in older rhinos of this species and some masses grow to be life-threatening (Montali et al., 1982; Kock and Garnier, 1993). Ultrasonography can also be used to determine if the ovaries are active, however any fertility assessment should include non-invasive urinary estrogen metabolite analysis, which is more informative for assessing ovarian activity than a single ultrasound exam of the ovaries. Given the relatively long and sometimes variable reproductive cycle of this species, samples should be collected and evaluated for at least three months.
Genome Resource Banking
A greater one-horned rhino sperm bank already exists at the Cincinnati Zoo’s Center for Conservation and Research of Endangered Wildlife (Stoops et al., 2010). Samples include both electroejaculated semen and sperm rescued from the epididymis of testicles recovered postmortem. Many zoos have participated in this collaborative effort to collect and bank semen from male greater one-horned rhinos. An effort was made to target the most genetically valuable males in the North American population. Some of this semen is currently being used for AI procedures, but some will be stored long term. Samples include at least one male that is deceased without ever siring offspring. Fibroblast cell lines from many greater one-horned rhinos are banked in San Diego Zoo’s Frozen Zoo. Oocytes and embryos have not yet been banked and additional research is necessary before such efforts will be fruitful.
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Challenges
Breeding greater one-horned rhinos in captivity can be quite successful if the enclosure space is large or the pair is behaviorally compatible. However, there continue to be problems at many zoos with incompatible pairs. In addition, females often experience an estrus without exhibiting any behavioral changes so animal care staff have a difficult time determining when the rhinos should be paired for breeding. Urinary estrogen metabolite monitoring offers a means of overcoming these challenges, but sample collection requires diligent commitment and is easier to achieve in some facilities than in others. Artificial insemination is another option that has proven successful for overcoming the challenge of trying to breed behaviorally incompatible pairs.