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Introduction
Due to the fact that snakes typically eat whole prey, no matter what species of snake you keep (with the obvious exception of Gerarda prevostiana which bites its prey into more manageable mouthfuls) the questions of what the best prey items are, how to feed them and when to change them, all weigh heavily on our minds.
Within the world of snakes there are various highly evolved digestive and metabolic systems. The two systems that the majority of keepers come into contact with are those belonging to Boidae and Colubridae. The Boidae system has evolved to cope with elongated fasting periods and has developed the ability to change various internal organs throughout the feeding and digestive process allowing for an ambush predator lifestyle that can take large prey items with minimal problems. The rat snake however has gone the other way and has evolved to cope with short periods of fasting and a rapid metabolism allowing the animal to take smaller items in order to maintain a foraging lifestyle.

This article has been written to achieve coverage of 2 main areas involved in rat snake prey choice and feeding methods:

1) To provide a single source for the important information relating to prey items specifically for the feeding of rat snakes. This will correspond with the article written by Lou Reading that can be found HERE and show the nutritional values of common prey items as well as some of the less common items. As such data on larger (i.e. guinea pigs and mature rabbits) and more specialist (i.e. geckos and amphibians) prey items have been omitted.

2) To illustrate the pros and cons of several feeding methods in order for you to make an informed choice on the best ways to go about feeding your rat snakes.

With these areas covered you will be better able to decide for yourself how you feel you should proceed with the feeding aspect of rat snake husbandry. The most important notion to take away from this article is that while i have tried to cover different areas within each section from an impartial view my own views and opinions may shine through. This is an error on my part as there is no simple answer to how we should proceed. As keepers we must choose the path that works for us and the animals in our charge – no matter how strange it may appear or how far from the normal procedures it lies.

1.
When looking at prey selection it can be as easy as allowing your mind to wander to the thought of eating the same food, prepared in the same way, at every meal. It is not an appealing thought for us and yet this is what we offer to many captive snakes. Even lizards are offered an array of prey items as a standard.

It is apparent through the results of current captive propagation standards that a rodent diet is sufficient to maintain a healthy snake within a captive collection. Often it is stated that day old chicks are worthless in terms of nutritional value. Do we really know and understand what the standard diets are composed of though?

The following tables show just that:

Table 1. Proximate composition and energy content of whole prey on a dry matter (DM) basis. Values expressed as weighted means or as raw data when "n " was not stated.
 
Prey species n DM
%
Crude Protein
%
Crude Fat
%
Ash
%
Gross energy
kcal/g
Notes
Guinea pig
Cavia porcellus
  29.1 51.2 34.7 14.1 5.95 Neonatal males
Guinea pig
Cavia porcellus
  31.3 51.4 46.1 9.2 6.99ª Males, 10 week
Hamster
Mesocricetus auratus
    49.8 34.7 7.5 5.98 Juvenile
Mouse, domestic
Mus domesticus
287 19.1 64.2 17.0 9.7 4.87ª Neonatal, <3 g
Mouse, domestic
Mus domesticus
292 18.2 44.2 30.1 8.5 6.65ª Juvenile, 3-10 g
Mouse, domestic
Mus domesticus
108 32.7 55.8 23.6 11.8 5.25ª Adult or >10 g
Rabbit, domestic
Oryctolagus cuniculus
  15.4 72.1 13.0 14.9 5.06 Neonatal
Rat
Rattus norvegicus
5 20.8 57.9 23.7 12.2 5.30ª Neonatal, <10 g
Rat
Rattus norvegicus
5 30.0 56.1 27.5 14.8 5.55ª Juvenile, 10-50 g
Rat
Rattus norvegicus
51 33.9 61.8 32.6 9.8 6.37ª Adult or >50 g
Squirrel, grey
Epicurus carolinensis
  33.3 62.4 18.4 11.6 5.54  
Chicken
Gallus gallus
66 25.6 64.9 22.4 6.4 5.80 One-day-old
Quail, Japanese
Coturnix coturnix
18 34.6 71.5 31.9 9.9c 6.79ª  
 
ª Calculated by adding the product of % crude protein x 5.43 kcal/g to the product of % crude fat x 9.11 kcal/g.29
b Not analysed.
c Fat-free basis.
d Ash-free basis.


Table 2. Mineral content of whole prey on a dry matter (DM) basis. Values expressed as weighted means or as raw data when "n " was not stated.
Prey species n Ca
%
P
%
Mg
%
Na
%
K
%
Cu
mg/kg
Fe mg/kg Zn
mg/kg
Mn
mg/kg

Notes

Guinea pig
Cavia porcellus
6 3.02 N/A 0.7 N/A N/A 5.6 56.4 46.4 6.6 Males, 10 week
Hamster
Mesocricetus auratus
6 2.51 2.03 0.12 0.46 0.88 12.0 237.0 94.0 45.0 Juvenile
Mouse, domestic
Mus domesticus
5 1.17 N/A 0.11 N/A N/A 19.2 181.3 82.5 0.2 Neonatal, <3 g
Mouse, domestic
Mus domesticus
5 1.47 N/A 0.09 N/A N/A 13.4 153.6 75.4 13.1 Juvenile, 3-10 g
Mouse, domestic
Mus domesticus
78 2.98 1.72 0.16 N/A N/A 6.7 137.9 67.5 7.7 Adult or >10 g
Rat
Rattus norvegicus
5 1.85 N/A 0.14 N/A N/A 60.6 275.8 113.6 6.2 Neonatal, <10 g
Rat
Rattus norvegicus
10 2.07 N/A 0.12 N/A N/A 11.3 133.2 81.9 2.6 Juvenile, 10-50 g
Rat
Rattus norvegicus
49 2.62 1.48 0.08 N/A N/A 6.3 148.0 62.1 11.0 Adult or >50 g
Chicken
Gallus gallus
66 1.69 1.22 0.05 0.71 0.80 5.2 119.5 97.4 3.9 One-day-old
Quail, Japanese
Coturnix coturnix
18 3.43 N/A 0.06 N/A N/A 2.6 74.9 53.0 6.4  
 

ª All mineral values for this prey species were calculated from equation given in reference.
b Not analysed.

Key to minerals:

Ca - calcium Na - sodium Fe - iron P - phosphorus K - potassium Zn - zinc Mg - magnesium Cu - copper Mn - manganese


The tables above clearly show that differing prey items comprise of different levels of nutrients. It therefore stands to reason that repetitive feeding of a single prey item throughout the course of a predators life will lead to a build up of that nutrient within the animal.

Using an adult mouse as an example here (as they are the most common rat snake food found on the market throughout the world today) and comparing to a rat of roughly the same weight we can see that feeding 10 mice will lead to the predator taking on 77 mg/kg of manganese where as feeding 10 rats will lead to the predator taking on 26 mg/kg of manganese.

Varying prey sources enables us to minimise the excessive build up of any set factor and provide a more evenly balanced diet plan.

Unfortunately the above tables are lacking in certain areas and many prey options are omitted. It is also unclear as to the origins of each test subject so some may have been frozen for undetermined periods of time. It is however still useful in many areas and shows, for example, that day old chicks are not as worthless as many would lead you to believe.
2.
While prey choice poses a large enough question to be answered we also need to look at the various methods of feeding the chosen item. The method used is largely based on the type of prey item used. The three main types to start with are:
  • Live.
  • Pre-killed.
  • Defrosted frozen.
 
LIVE
This is still a popular prey type for feeding throughout Europe and especially the USA where it is the most common method. Despite popular belief it IS legal in the UK to use this method, under strict conditions. These conditions are set out within the Protection of animals act 1911 and the Animal Welfare Act (AWA). Unfortunately they are open to interpretation so further, written, guidance from your local government is required in order to fully comply with the law.
The main benefits of using this type are:
  • Fresh: You can not get a fresher prey item than a live item.
  • Readily taken: Often snakes which struggle to feed regularly on other prey types will feed on live prey items with little to no hesitation.
The main disadvantage of using this type are:
  • Supervision: To ensure the prey item doesn't suffer any more than is absolutely necessary the enclosure occupants must be supervised at all times. A failed attack by the predator may lead to an injured prey item which may need to be euthanased as soon as possible.
  • Fighting: The desire to survive is an instinct that can be found in all life. As such the prey item may inflict injuries on the predator and surprisingly these injuries may be severe or even lethal.
Fighting between prey and predator can lead to some horrific injuries. The threat of this can be reduced by choosing a none aggressive prey species or by stunning the prey item.
Rodents are equipped with large teeth, these have been known to cause significant predator injuries. In order to solve this problem we need to look at the feeding habits of the prey items. For example guinea pigs are an ideal prey to be fed live as they are unable to bite in any other direction than downwards therefore reducing the field of danger for the predator.
Stunning the prey item is another option open to live feeding keepers. While the prey is still as fresh as possible it is dazed and unaware of the impending threat to its life and as such is usually unaware or incapable of defending itself. This can be induced by banging the prey item on the head, not a pretty method but often it is the safest in this area. As noted previously UK residents are subject to differing laws from residents of other countries. As such, the method described above may contravene the UK AWA. Further, written, advice should be sought from local government representatives in order to ensure full compliance of the law.# When converting food from live to defrost feeding, this is a step used to get the animal more accepting of the following type.
 
PRE-KILLED
This is often the most preferred method by many keepers throughout the world offering the best of both the other options.
The main benefits of using this type are:
  • Fresh: The prey is incredibly fresh and suffers no protein denaturation.
  • Gut loaded: Many keepers who feed this way keep there own breeder stock which can be fed with set diets to create gut loaded prey items to boost certain attributes.
  • Danger removed: This method is as safe as defrost feeding as a dead prey item offers no resistance.
The main disadvantages of using this type are:
  • Prey killing: When using this method the keepers themselves have to kill the prey item. Some may not wish to do this or be unable to do so in a manner that is quick and painless for the prey item
  • Space and time: When breeding your own prey items you need to devote large areas and time to the production of these items.
The problem of euthanizing prey items is often a major factor for people when deciding on whether to use this type or not. There are several ways to ensure a swift death in the prey item that can vary in stress levels for the keeper but still provide a stress free death for the prey item. The first method most commonly used is cervical dislocation. This method is usually done by holding the throat and base of the tail of the prey and firmly pulling apart. On larger prey items (i.e. mature rats) a significant amount of strength is required. This method is not for the feint hearted.
The second method, more commonly used by commercial ventures is to utilise an inert gas such as carbon dioxide (Co2). In this method a low concentration of the gas is entered into a chamber containing the prey items which then peacefully go to sleep. This is then followed by an increase in the Co2 which causes the animal to die while asleep. Although approved and accepted by Home Office Regulations in the UK this latter method is NOT advised for pre-weaned animals as many are capable of extremely long periods without oxygen due to a “smother reflex” that has developed in nesting animals.
 
DEFROSTED FROZEN
This is the most common method used in the UK and is growing in popularity throughout the rest of the world.
The main benefits of using this type are:
  • Easy storage: Keepers are able to store large quantities of prey items in a freezer without having large volumes of space devoted to breeding racks.
  • No fighting: As the prey item is dead there is no fighting back. This means that this method is completely safe for the snake.
The main disadvantages of using this type are:
  • Not natural: Many European keepers note that a wild animal will never encounter a freshly defrosted prey item in the wild. This is actually irrelevant at best. We are not providing a replica of the wild environment so the question of “why do so here?” presents itself.
  • No guarantees: There are no guarantees that every snake (especially wild caught animals) will take to eating defrosted prey straight away. Some work may be needed to persuade the animal to start eating this type. There is often a thought that certain animals will never take defrosted food, this can usually be proven incorrect though through the examples that UK reptile keepers represent.
  • Protein denaturation: The freezing process does detract from certain nutritional qualities over a set period of time.
One of the biggest problems noted by advocates of other methods is protein denaturation. The concern is that frozen food items are lacking in proteins that can be found in live or pre-killed prey items. While this is true there are several ways we can ensure that the protein lost in the freezing process is overcome. When an item is frozen the protein denaturation occurs at a steady rate over the course of approx 15 weeks. From this point on there will be no further significant changes (shown on tests of frozen samples up to 4 years later).
 
In short, as keepers, we have 15 weeks to use a prey item from the point it is frozen before it reaches a base rate. Later, more specific, tests will be carried out to establish exactly how costly the freezing process is in terms of prey items.
 
As we have no reliable way of identifying the exact date the prey item was frozen it is worth noting that in order to obtain the best prey item we should feed prey items as soon as possible. This may indeed defeat the object of purchasing frozen prey items in the first place as for many keepers this form of food is chosen because of the ability to buy in bulk and store over a longer period. It is my suggestion that in order to achieve a workable solution to this problem the keeper only buys enough for a 5 week period. Depending on the size of the collection, this should allow a reasonable sized order with the supplier and still allow for the best quality food available to the snake/s involved.
 
Now we have identified the available prey types we can look at the methods involved. Standard feeding methods are all based around two simple practices. The prey item is either offered to the snake on forceps, tweezers etc. OR it is placed within the enclosure for the snake to find once the keeper has withdrawn. More complex methods utilised for the attempted feeding of non feeding rat snakes can be found in an article by Frankley Delores Some Tips and Tricks for Non-Feeding Ratsnakes
 
Rarely do keepers think that the way in which the prey item is presented can achieve differing results. As already noted, the digestive system of a rat snake has evolved to work quickly. This means that they do not have the time to digest certain parts of a prey item, nor do they have the time to fully utilise a standard prey item. We can improve on this in several ways, below is one of these.
A simple series of cuts into a prey item can maximise digestion and enable a snake to better utilise the nutrients a single prey item can give. A pair of cuts along the spine and a single cut piercing the chest cavity of a prey item can result in a significant growth increase when compared to an uncut prey feeding snake.
 
This method of presentation can be used to great effect in hatchling and younger snakes as well as those that are generally underweight or undergoing rehabilitation after an illness or injury as less energy is needed. CUTS MUST NOT BE CARRIED OUT ON LIVE PREY ITEMS.
 
Although I have only outlined one presentation method above you can see that in order to progress further with general presentation techniques we need to start looking at the way our snakes utilise the prey items they receive. In a time when basic husbandry techniques have been established and technology is pushing on our ability to provide accurate environments we should now be able to look further at the more commonly ignored aspects of husbandry.
 
To summarise, with the information enclosed in this article and the further reading that can be found in the reference list you should now be able to make an educated and informed decision on your feeding schedules rather than just following older methods because that is what others do or because this is simply the way you have always done it.

DOCUMENTS REFERENCED:
1. NUTRIENT COMPOSITION OF WHOLE VERTEBRATE PREY (EXCLUDING FISH) FED IN ZOOS Ellen S. Dierenfeld, PhD - Heather L. Alcorn, BS - Krista L. Jacobsen, MS
2. CUTTING MICE BEFORE FEEDING http://www.cornsnakes.com/forums/showthread.php?t=25837 Connie Hurley
3. THE INFLUENCE OF CIRCADIAN RYTHMS ON PRE- AND POST-PRANDIAL METABOLISM IN THE SNAKE LAMPROPHIS FULIGINOSUS J.H. Roe, W.A. Hopkins, J.W. Snodgrass, J.D. Congdon
4. ADAPTIVE REGULATION OF DIGESTIVE PERFORMANCE IN THE GENUS PYTHON Brian D. Ott and Stephen M. Secor
5. STUDIES ON PROTEIN DENATURATION IN FROZEN FISH. II R.M.Love, J.I.M.Ironside
This site has information on the following genera of Ratsnakes ... Spilotes, Spalerosophis, Ptyas, Zamenis, Elaphe, Rhinechis, Senticolis, Pseudelaphe, Pantherophis, Bogertophis, Orthriophis, Gonyosoma, Oreocryptophis, Oocatochus, Euprepiophis, Coelognathus, Archelaphe