Chapter Eight

Bat milk varies in composition, not only among species (Jenness and Studier, 1976), but also during the course of lactation (Kunz, pers. comm.). TABLE 5 summarizes data on the composition of bat milk from the limited number of species which have been studied. Unfortunately, formulas currently available for handraising infant animals do not approximate the nutrient composition of bat milks, and therefore choices selected for rearing various species have been determined through trial and error. The nutrient composition of milk replacers commonly used in handrearing bat pups is summarized in TABLE 6.

The nutrient components of milk replacers vary enough to affect growth rates. In order to evaluate a pup's growth, weigh it each morning before its first meal. Growth curves of various bat species are shown in FIGURES 63 through 75, and approximate stages of development are summarized in TABLE 7. If an individual infant fails to gain weight on the prescribed formula, it may become necessary to increase the fat content. This should be done conservatively because over-supplementing the diet causes diarrhea. Add heavy whipping cream in 1/2-ml increments to about 25 ml of prepared milk replacer. TABLE 8 summarizes feeding regimes for selected species.

Fig. 63.  Growth curves for six handraised, straw- colored fruit bats, Eidolon helvum (data courtesy of Harmony Frazier-Taylor, Woodland Park Zoo, Seattle, WA).	Fig. 64.  Growth curve for a single mother-reared, grey- headed flying fox, Pteropus poliocephalus (plotted from data presented in George, 1990).	Fig. 65.  Growth curves for two handraised Rodriques fruit bats.  Pteropus rodricensis (after Young, 1987).	Fig. 66.  Growth curve for a single handraised Insular flying fox, Pteropus tonganus (plotted from data presented in Rohrer, no date).

Fig. 67.  Growth curve for handraised Egyptian fruit bats, Rousettus aegyptiacus (white symbols, after Larrow, 1988; black symbols, data courtesy of Diane Devison, Metropolitan Toronto Zoo, Toronto, Ont.).	Fig. 68.  Growth curve for a single handraised Jamaican fruit bat, Artibeus jamaicensis (plotted from data presented in Kahn, no date).	Fig. 69.  Growth curve for captive-reared short-tailed fruit bats (after Kleiman and Davis, 1979).	Fig. 70.  Average growth curve for sheath-tailed bats, Taphozous georgianus (after Jolly, 1990).

Fig. 71.  Average growth curve for pallid bats, Antrozous pallidus (redrawn from data prsented in Kunz, 1987).	Fig. 72.  Average growth curve for big brown bats, Eptesicus fuscus (after Burnett and Kunz, 1982 and Davis, et al., 1968).	Fig. 73.  Average growth curve for the cave bat, Myotis velifer (after Kunz, 1973).

Fig. 74.  Average growth curve for pipistrelle bats, Pipistrellus pipistrellus (after Kunz, 1987).	Fig. 75.  Growth curve for one mother-reared and two handraised common vampire bats, Desmodus rotundus (from Jenness and Studier, 1976 and Barnard and Sachs, 1992).

The shelf-life of milk powders can be extended if they are kept in the freezer. Mixed formulas must be refrigerated. Discard unused portions of mixed formula after 24 hrs. When mixing a milk formula as directed by the manufacturer, avoid adding supplements such as syrups or vitamins because they may cause diarrhea, and lead to serious dehydration. However, when commercial milk replacers are diluted with heavy whipping cream, it may become necessary to add very small amounts (e.g., 1 or 2 drops per 100 ml) of vitamins and minerals.

Bats have been fed milk, with varying degrees of success, using paintbrushes, eyedroppers or syringes. Appropriately sized, modified feeding and urethral catheters (FIG. 76) can be attached to syringes to serve as substitute teats when feeding flying foxes, or for dropping milk accurately to the mouths of very small pups. Most pups lose weight or remain stable until they learn how to take formula from the substitute teat.

Figure 76.  Milk can be delivered more accurately to the mouths of small pups by attaching catheters to syringes;  A) feeding catheter;  B) tom cat catheter.

Before feeding pups, warm the formula in a hot water bath (FIG. 77). Check for the desired temperature by placing a drop or two on the inside of the wrist, as one would do when feeding a human infant. Feed a pup on its belly or side, with its head lower than its feet (FIG. 78), to prevent it from aspirating fluids into its lungs.

Figure 77.  A convenient method for warming a pup's formula is shown here.

Figure 78.  The proper feeding technique for feeding a baby bat.  Note how the pup is tilted slightly downward to prevent it from aspirating formula into its lungs.  Also, excess formula can drip off the hand instead of pooling under the animal (photo courtesy of Forest Park Nature Center, Peoria Heights, IL).

The presence or absence of lactase in various species has not been determined. To reduce or avoid potential problems with lactose-intolerance, it may be advisable to add Lactaid® (FIG. 79), or a similar product, to the formula.

Figure 79.  Adding lactase to milk reduces the possibility of lactose-related dietary disorders.  Although most bats do not require such treatment, the presence or absence of lactase in various species could not be confirmed.

Maintaining adequate hydration is one of the most important factors in rearing bat pups. Experience has shown that many species dehydrate when offered oral electrolytes in combination with milk. Such solutions should neither be used when feeding bats a milk diet, nor as a substitute for water when mixing milk formulas. Clinically dehydrated pups being fed a milk diet should have fluids replaced by subcutaneous injections (FIG. 80; also see Chapter 9, FIG. 93). Dosages are listed in Chapter 9, TABLE 13.

Figure 80.  It is best to give small bats subcutaneous injections on the dorsum.  The arrow points to the small bubbles of lactated Ringer's solution under the pups' skin (photo courtesy of Lynda Moore, Jonesboro, GA).

It may be necessary to medicate pups with metoclopramide hydrochloride (Reglan®) syrup 5 to 10 days into the handraising period. Pups of some species, in particular vampire bats (Desmodus rotundus), sometimes red bats (Lasiurus borealis) and eastern pipistrelles (Pipistrellus subflavus), bloat until they adjust to the milk replacer. Mix 1 drop of Reglan® with 4 drops of tap or distilled water. Add 2 drops of this mixture to 1 ml of milk formula at every meal for 4 to 6 days.

INSECTIVOROUS BATS
In temperate regions of the United States and Europe, bats give birth primarily from May through July. Neonates are born with milk teeth (FIG. 2, Chapter 1) which allow them to cling to their mothers' teats. These teeth are useless for eating insects, so food should consist of a prepared milk diet. Powdered Esbilac® (FIG. 81) and Unilact®, mixed as directed on the label, have been used successfully to handraise insectivorous bats.  [WARNING!  SEE ALERT AT END OF CHAPTER]

Figure 81.  Esbilac® WAS the milk replacer of choice.  See ALERT at the end of this chapter for an explanation and what other milk replacers should be used. WARNING!  Do NOT use this product!

Pups should be warmed before they are fed. This can be accomplished by holding them gently in the palm of the hand. Insectivorous pups require frequent feedings (approximately every 2-3 hrs.). Feed approximately 0.05 cc per gram of body weight. If they reject food at 2-hr. feeding intervals, or if formula is still present in their stomachs (this is easily seen through the skin on the ventral surface), feed approximately every 3 hrs., or adjust the feeding schedule as necessary. Feed pups weighing 4 g or less at least one time during the night. For pups weighing over 4 g, feedings should begin around 6 A.M. (0600 hrs.) and can be discontinued at about 11 P.M. (2300 hrs.) to midnight (2400 hrs.).

Infant bats will accept milk readily, a drop at a time, from the palm of the hand or directly from an eye-dropper or syringe (FIG. 78). Avoid the use of nursing bottles, as these can cause fatal colic (Barnard, 1988). Before feeding a pup, wash hands thoroughly to prevent contaminating any formula that pups may lick from the palm of the hand. After each feeding, wet a cotton swab with lukewarm water and massage the pup's anus (FIG. 82) to stimulate defecation, although they may not defecate after every meal. Normal stools are firm and black. It is not unusual, however, for pups to have cream-colored stools for a day or two until they adjust to the milk replacer.

Figure 82.   A cotton swab makes an excellent tool for massaging a pup's anus to stimulate defecation.  Suckling bats, however, may not defecate after every meal (photo courtesy of Gregory C. Greer, Marietta, GA).

Most insectivorous pups are ready to be weaned at about 3 to 4 weeks of age (TABLE 9). This is also the age when they are ready to fly (they do not have to be taught; it is instinctive). Also, milk teeth have been replaced by permanent teeth, and the infant is ready to receive chitin in its diet. Chitin constitutes insect exoskeletons and is important to the bat for the continued formation of firm stools. To wean bats onto mealworms, cut off the insect's head and squeeze its viscera into the pups mouth as one would squeeze a tube of toothpaste. Whenever bats are willing, allow them to chew on the chitinous exoskeletons of the mealworms to strengthen their jaws.

To teach a juvenile to associate food with a dish, feed it over one containing mealworms. To avoid unnecessary bites, and to condition a weanling to feed from a hard surface, always feed it from the end of a blunt forceps, not the fingers. After the bat has eaten all it desires, offer it a few drops of fresh water. After the bat feeds regularly on whole mealworms (about 10 to 40 or more, depending on the species) with their heads intact, it should be housed and fed as an adult (see Chapter 5, ENVIRONMENT AND HOUSING FOR ADULT BATS and Chapter 7, FEEDING ADULT BATS).

It is not known why some species fail to thrive on milk replacer. For example, red bats (Lasiurus borealis) and eastern pipistrelles (Pipistrellus subflavus) bloat and/or dehydrate when fed exclusively milk formula. This problem is sometimes overcome by offering these pups milk replacer once a day and a blended mealworm diet (TABLE 10) for the remaining meals.

Special attention must be paid to the roosting habit of lasiurine bats because it directly affects their hygiene. These infants will soil themselves if they are not allowed to hang from a thin rough branch, or mesh on a cage top (FIG. 83). Within a day or two, the soiled fur loses its insulating properties and the pup dies. When any pup becomes soiled, clean its fur immediately with a warm, damp item such as a swab stick, gauze pad or cloth handkerchief.

Figure 83.  Many species hang freely from horizontal surfaces.  If not provided an appropriate perch, such as a tree branch or the mesh of cage tops, they will soil themselves with urine and feces.  This type of perch is critical to the well-being of infant red bats (photo courtesy of Barbara Schmidt French, Austin, TX).

FRUGIVOROUS BATS
Good Start® milk replacer appears to be the most satisfactory product for handraising small fruit bat species, including the Egyptian flying fox (Rousettus aegyptiacus). Heavy whipping cream must be added to these milk replacers (as described above). In Australia, flying foxes are routinely handraised on Wombaroo® diet (for availability, see APPENDIX I). In the United States, several species of flying foxes have been handraised on equal parts of canned evaporated milk and nectar (Frazier-Taylor, pers. comm.; Moore, pers. comm.; Rohrer, no date). The nectar can be prepared by boiling together 1/4 cup each banana, melon, papaya, peeled grapes and apple with 1 cup of water. Dietary supplements may have to be added to this diet. Feedings can be decreased slowly when the pup shows less interest in eating formula. This occurs naturally as it receives increased amounts of solids in its diet. Avoid feeding soybean-based milks to flying foxes (Luckhoff, pers. comm.) as these have not been successful.

Unlike insectivorous bats, flying fox pups nurse best when offered milk through a nipple. Nipples can be mounted on glass bottles or syringes. Jamaican fruit bats (Artibeus jamaicensis) also have been fed milk replacer using latex nipples. Nipples can be handmade (Swieca and Dunn, 1988) or purchased (see APPENDIX I for availability).

Pups of small frugivorous bat species should be fed every two hours, beginning approximately at 6 A.M. (0600 hrs.) and ending at midnight (2400 hrs.). The number of feedings should be decreased gradually to five in twenty-four hours. Small flying foxes (e.g., Rousettus spp.) should be fed in the same manner as other fruit bats, but the large flying foxes (e.g., Pteropus spp.) can be fed a total of four to five feedings in a day. As discussed in Chapter 7, FEEDING ADULT BATS, also avoid feeding fruit bat pups citrus juices (Luckhoff, pers. comm.; George, 1990).

Young flying foxes may contract aspiration pneumonia if they are torpid during feeding (George, 1990; Williams and George, 1984). It is essential that these animals be warm at the time they are fed. Until pups are about 3 weeks old, exercise them after each feeding by extending their wings gently.

Ages at which fruit bats can be weaned vary considerably (TABLE 9). The best technique is to introduce them to pureed fruits (especially apples) between milk feedings. Williams and George (1984) reported that the grey-headed flying fox (Pteropus poliocephalus) loses weight when apples are removed from the diet. As the pups grow, begin dicing the fruits, and sprinkle the fruit daily with approximately 10 g of powdered formula. Continue to feed these pups a variety of diced fruits until they are old enough to be housed and fed as adults.

SANGUIVOROUS BATS
Common vampire bat (Desmodus rotundus) pups should be fed with a syringe (FIG. 84); allow them to lick, not suck, from it. These bats do not digest their food as rapidly as many other species. For the first week of life they should be fed every three hours, commencing at 6 A.M. (0600 hrs.) and ending at midnight (2400 hrs.). The milk diet for these pups is listed in TABLE 11. The amount of water suggested should be reduced from 75 ml to 60 ml when the pup reaches 6 weeks of age. Individuals vary in the amount of formula they will consume, and the reader should consult TABLE 7 for specific feeding regimes.

Table 11 VAMPIRE BAT MILK-REPLACER FORMULA Yields approximately 13% solids, 7.5% fat, 4.1% protein and 2.3% carbohydrate. MIX FRESH DAILY Multi-Milk™ powder* (FIG. 86) . . . . . . . . . . . . . . . . . 10 g Dextrose powder (FIG. 87) . . . . . . . . . . . . . . . . . . . . . 2 g Tap or distilled water . . . . . . . . . . . . . . . . . . . . . . . . 75 ml Avitron® multivitamins (FIG. 57, Chapt. 7) . . . . 2 drops (0.10 ml) Drops Avimin® multiminerals (FIG. 58, Chapt. 7) . . .4 drops (0.20 ml) * Multi-milk™ does not dissolve instantly in water; therefore, push the lumps through a tea strainer. Figure 86.  Multi-milk™ has been used successfully to handraise vampire bat pups.  It is likely that Zoologic 33/40® may also be suitable.  Regardless of the milk replacer used, however, vampire bat pups must be treated for bloat approximately 5 to 10 days into the handrearing period. Figure 87.  When using Multi-milk™ to handraise bats, add dextrose to increase the carbohydrate content of the milk replacer (TABLE 11 above.)    Figure 84.  A 3-week old vampire bat.  Such pups should be trained to lap, not suck, formula from a syringe.  Note that the pup is unrestrained.  These animals imprint strongly on the hand that feeds them, and they will not stray far away from it.  Attempts to restrain a vampire bat pup may provoke a bite (photo courtesy of Dany Nieves, Decatur, GA).

It is not known if Desmodus rotundus requires feces in its diet in order to establish the appropriate intestinal flora for the digestion of blood. Barnard and Sachs (1992) handraised two infant vampire bats, and they felt it was necessary to add a vampire-bat-feces "cocktail" to the milk formula. The "cocktail" can be prepared by mixing together 1 pellet of fresh, adult vampire bat feces with 0.4 ml of tap or distilled water. When the bats are between the ages of one week and three months, add 0.1 ml of this mixture to the formula for one feeding twice weekly; between three and five months of age, add 0.2 ml to the formula for one feeding once a week. Discontinue the feces cocktails after 5 months of age.

Vampire pups are weaned by decreasing their intake of milk replacer while increasing the volume of blood, over a period of nine months. Because vampire bats will not eat clotted blood, it must be either citrated or defibrinated at the time it is collected. Blood is naturally palatable to vampire bats, and they may refuse the milk replacer by the time they reach the age of two or three weeks. This problem is easily solved by flavoring the formula with 1 part blood to 10 parts of milk replacer. For approximate ages of pups, and blood to milk replacer ratios, see TABLE 12.

When a vampire pup reaches the age of 13 weeks, it should be taught to eat from a dish (FIG. 85). I prefer using a 1½-in. (3.8 cm) glass culture dish. Occasionally, frozen (citrated or defibrinated) blood coagulates when mixed with milk. If this occurs, fill the dish several times during the feeding session or use fresh (citrated or defibrinated) blood. At about 18 to 21 weeks of age, the two feedings (see TABLE 12) should be split, with one dish containing a mixture of milk replacer and blood, and the other pure blood. Leave the dish of pure blood in the pup's cage for about 6 to 8 hours to encourage it to feed on its own. Until a pup learns to self-feed, handfeed (FIG. 85) the milk/blood mixture because it spoils rapidly.

Figure 85. Vampire bat at 3 months of age learning to feed from a dish (photo courtesy of Dany Nieves, Decatur, GA).

Do not remove milk from Desmodus pup diets until they are 24 weeks of age (TABLE 12). Joermann (1988) reported that mother-reared juveniles in captivity often die at 16 to 20 weeks of age. I have also observed this problem within my colony. Workers, therefore, should handfeed milk replacer to orphaned young during this critical period.

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