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.