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The following exchange provides a wealth of information for opossum owners:

Beverly Rosas of Project Wildlife wrote:

Dear Rosalyn:

Got your e-mail address from Geoff at Perfect Pets, Inc., U.S. Distributor of Wombaroo products. I am a volunteer with Project Wildlife, a non-profit wildlife rehabilitation organization in San Diego, California. We have recently been testing the Wombaroo Possum Milk Replacer on our neonate Virginia Opossums. We are using the >0.8 mid to late lactation formula for animals ranging in weight from approximately 25-35 grams up to 100 or so grams. We like the formula so far (as do the opossums), but I have a few questions for you, if you don't mind:

    1. The package directions for mixing call for weighing the powder formula. I understand that this is the most accurate method, but, for our volunteers, we need to simplify directions; a volume to volume method works best. I note that in your literature, you state that one level standard tablespoon dispenses about 10 g of powder. Our measurements disagree. We have concluded that a level 1/4 cup loosely packed equals approximately 22 g, and 1/4 Cup equals 4 tablespoons. Are the standard measures the same in Australia and the U.S.?

    2. Also, based on the Wombaroo package mixing directions, the ratio of powder to water is 1:1.4. Using 1/4 Cup as a base measurement, for ease of mixing instructions, we have figured as a formula: 1/4 Cup powder to 1/3 Cup water; the ratio of powder to water is, therefore, 1:1.333. Do you see any problems with this?

    3. The package directions say to add pre-boiled warm water, then fill to the remaining desired volume with warm water. What is the purpose of boiling the water first? What is the purpose of adding the water in two phases? Can't we just simplify and add the desired total volume of warm water at one time? Is city tap water okay or do you recommend distilled water?

    4. We notice that the powder seems to settle out of the prepared formula after a short period of time. Is there any solution to that? Once the babies are lapping on their own, a dish of formula is left out for them for stretches of several hours at a time.

    5. When the Wombaroo product is mixed according to package directions, the energy provided per ml = 3D 1.3 kcal/ml. The mixing directions that we have described above would provide even less. Our Virginia opossum milk, at its peak (11 weeks), provides 2.3 kcals/ml. Do we need to feed more often, or is it possible to increase the concentration of the formula? From the literature, the concentrations of Virginia opossum milk are as follows (mid-late lactation)-- total solids: 29.8, protein: 11.0, fat: 13.5, carbs: 4.3.

    6. About the Impact Colostrum Supplement: for marsupials, you recommend feeding for up to 5 days when the animal is first brought in. My understanding is that marsupials' milk provides colostrum throughout 1actation. Am I wrong? Is there a reason that 5 days was chosen vs. throughout the [entire] period of time the marsupials are on formula? In marsupials, at what age are the immunoglobulins in the colostrum no longer absorbed? Is it useful in juveniles or adults for anything other than intestinal infections? How useful is it for that, particularly in the neonates? We see a lot of Clostridia infections in them.

    7. Do marsupial young produce lactose equal to that occurring in eutharian neonates, apparently because the cleavage of the galactose-rich oligo-and poly-saccharides produces a lactose unit that must be further digested, even though marsupial milk in its natural form contains only traces of lactose?

Well, that's it for now. I appreciate your time in answering any of these questions,

Beverly Rosas
Co-Leader, Opossum Team
PROJECT WILDLIFE
San Diego, California, U.S.A.



Roslyn Richst of WOMBAROO answered:

Dear Beverly Rosas

    1. In Australia, 1 cup = 3D 12 tablespoons. In your email, 1 cup = 3D 16 tablespoons. (1/4 cup = 3D 4 tablespoons). Assuming both cups have the same capacity, then your tablespoon is smaller than the size of ours. The measures are obviously not the same. This is the reason we prefer users of our product to follow our directions so confusion over weights and volumes is avoided. Could your carers not make up 1 litre of milk as directed and freeze it in ice cube trays?

    2. I'm unsure how you worked the ratio of powder to water to be 1:1.4.

    We do not provide an amount of water to add. We say to MAKE UP TO 1 LITRE with water. We did the following calculation using your measure of 1 cup =3D 88g of powder (1/4 cup =3D 22g of powder) and assumed that 1 cup =3D 283ml of water. We estimate that when making 1 litre of milk the 250g of powder requires about 800ml of water. This translates into 2.84 cups of powder (250 = B8 88) and 2.83 cups of water (800 = B8 283). This gives a ratio of about 1:1. So, to make the required concentration of milk, add BC cup of powder (22g) to 1/8 cup (35ml) of preboiled warm water, mix to a paste, then add the other (1/8 35ml) cup of warm preboiled water. How does this sound?

    3. The inference is that all water used to prepare milk be preboiled.

    We recommended using preboiled water to prepare any milk because town water may be heavily chlorinated and the safety of any water supply cannot be guaranteed. Town water is fine if boiled. There is no need to use distilled water. Preboiling water greatly reduces the chance of microbial contamination. We recommend using sterilised utensils to prepare milk and that prepared milk be either refrigerated or frozen.

    Mixing the powder with half the required amount of water forms a light paste which when stirred thoroughly wets the lipid phase allowing it to emulsify with the rest of the powder.

    4. If you prepare the milk as outlined above, then the product should be more stable. We are concerned that prepared milk is left at room temperature for several hours. This action will undoubtedly negate much of the hygiene practiced in preparing the milk. You mention that you see a lot of Clostridia infections in the Opossums. The practice of leaving milk exposed to contamination, particularly faecal contamination, could be an excellent source of Clostridia.

    5. Our published energy value of 5.6kJ/ml or 1.3Cal/ml is metabolisable energy. This is equivalent to gross energy of 6.1kJ/ml or 1.5Cal/ml.

    Using the standard values of 25kJ/g for protein, 37kJ/g for fat and 17kJ/g for carbohydrate, a gross energy value for opossum milk of 8.5kJ/ml or 2.0Cal/ml us produced. As you are feeding the animals ad lib, they will drink sufficient milk each day to satisfy their energy requirements. Since both the Wombaroo and [natural] opossum milk have similar protein to energy values, 13.4mg/kJ for Wombaroo and 12.9mg/kJ for opossum milk, the daily protein requirements will also be satisfied.

    6. Marsupials do not produce colostral milk. Yes, immunoglobulins are probably present in the milk up to the time when intestinal closure occurs to the galacto-oligosaccharides (See below). The reason why we suggest using Impact Colostrum Supplement for only 5 days is purely because of cost. Like you, most wildlife carers are volunteers so the additional cost of continually feeding Impact throughout lactation could prove to be prohibitive.

    We have many reports from carers who have had success feeding Impact to furless joeys with what they call "failure to thrive" syndrome. The cause of this problem is largely unknown as little pathology is ever done on these animals. One suspects the problem is microbial since they get results feeding Impact. There is also evidence that colostrum produces nonspecific immuno-stimulation in several species of adult animals. This probably accounts for the increased use of colostrum preparations as nutritional supplements by people. Whether a similar effect occurs in marsupials is not known. We don't know if Impact is effective against Clostridia species.

    7. Pouched young marsupials have high intestinal lactase activity whilst the concentration of galacto-oligo saccharides in the milk is high. Once this concentration falls, about the time that the joey is emerging from the pouch, then lactase activity falls to the low level normally found in adults. Marsupials digest milk carbohydrate in a fundamentally different way to eutherians. In eutherians, milk lactose is the main carbohydrate and lactase is localised in the brush border membrane of the epithelial cells (enterocytes) that line the intestine. It acts on lactose in the lumen of the intestine cleaving (hydrolysing) it to its component sugars, galactose and glucose. Both galactose and glucose are then actively transported into the enterocytes. In marsupial milk, galacto-oligo saccharides are the main carbohydrate and lactase resides within the enterocytes and, along with other carbohydrate-digesting enzymes, is associated with cell organelles called lysosomes. The galacto-oligo saccharides in marsupial milk must first enter the enterocyte before the lactase can act on them. Large molecules (macromolecules) such as these are absorbed across the cell membrane by a process known as pinocytosis (cell drinking). Once inside the cell, they are then hydrolysed to their component sugars. The limiting factor for these reactions is the rate of pinocytosis or the speed at which the oligosaccarides enter the cell. Marsupials can tolerate small amounts of lactose in milk. However when they are fed eutherian milk formulae that contains high levels of lactose, diarrhoea is usually induced by the undigested lactose that remains in the gut.

Please contact us if we can be of further help.

Regards,
Roslyn Richst

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