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Laudanum in lettuce – fact or fiction?

Ah!, the much maligned lettuce!  Lettuce has had a bad reputation amongst rabbit keepers for this and a number of reasons not actually related to the nutrient levels it contains.

First of all, let’s get the laudanum thing straight. – Lettuce does not contain laudanum. Edible lettuce does contain a chemical called lactucin which is a component of lactucarian. Lactucarian is the milky fluid found in some species of lettuce and occurs in much larger amounts in wild lettuce, Lactuca virosa.

Lactucarium has sedative and analgesic effects. It creates a sense of mild euphoria. The milky exudate resembles that of opium and it can also be reduced to a thick substance which can be smoked in the same way as opium. As a result of which it acquired the name ‘lettuce opium’.

Edible lettuce, Lactuca sativa, does not even contain lactucarium although it does contain lactucin which is in lactucarium.

When is lettuce is to blame and when not?

The real reasons lettuce has such a bad reputation are many and varied.  Firstly it is not a food that many rabbit breeders feed to their stock so young rabbits are likely to suffer digestive upset if fed any more than just a little lettuce, but that also applies to any green food they are not already accustomed to.  Baby rabbits in new homes are also subject to stress and may be infected with coccidiosis if the breeder does not use anti-coccidiostats, both stress and coccidiosis can cause diarrhoea in baby rabbits.  It is recommended that baby rabbits be fed on the diet they are familiar with when first in their new home and only then should they be weaned slowly and gradually onto a new food.

Lettuce is normally kept in the fridge. Any food fed straight from the fridge is likely to cause tummy upsets whatever the age of the animal.   Wet leaves whether they are wet lettuce or wet grass/herbs in the run, can cause bloat.  Feeding wet lettuce also makes it vulnerable to going slimy if not eaten straight away. In addition, lettuce, especially iceberg type lettuce, has a higher water content and lower fibre content than tougher, dark green, herbs and vegetable leaves.

When and where to feed lettuce to rabbits and guinea pigs

Small amounts of watery lettuce can be used as a source of water during hot weather.  Do not consider lettuce fed in this way to be of any food value..  One of the reasons lettuce has such a bad name is that feasting on a lot of lettuce is bloating.

Dark green leafy lettuce fed at room temperature in the summer months as a mixed salad with other herbage, fed in moderate amounts, can be considered a valuable and safe food provided the rabbit or guinea pig has access at all times to fresh water and ad lib good quality hay to provide essential long fibre.

You should make sure your salad is balanced for calcium and phosphorous.  Clover and alfalfa are rich in calcium and also have a high Ca:P ratio so mixing fresh or dried clover or alfalfa will help balance out the leaves with less good Ca:P ratios.

Nutritional value of lettuce varieties

Green leafy lettuce has a good Ca:P ratio and many leaf varieties contain more calcium and less phosphorous than broccoli.

Loose leaf lettuce, (var. crispa) contains 68mg calcium and 25mg phosphorous per 100gm giving it in fact an overly high Ca:P ratio.  Compare that to Broccoli which contains 44mg calcium and 87 mg phosphorous per 100gm.  It does not contain very much vitamin C however, only 14mg – 22mg/100gm compared to, for example, broccoli.

Cos or Romaine lettuce contains more vitamin C at 22-24mg/100gm but the Ca:P ratio is possibly inverse with 36mg calcium and 45mg phosphorous per 100gm according to one source although another has the Calcium at 44mg and Phosphorous at 35mg/100gm

Iceberg lettuce has an poor Ca:P ratio with only 16-22mg Calcium and 23-26mg Phosphorous per 100gm and the lowest vitamin C level of all the lettuces at 8.1mg/100gm.

Little Butterhead or Cabbage lettuce also has a low level of vitamin C, just higher than iceberg at 9mg/100gm.  The Ca:P ratio is good though with 35-52mg Calcium and 26-39 mg Phosphorous per 100gm.

Water and Fibre Content

All lettuces are around 94-95% moisture, cucumber is 96% moisture with dandelion leaves 85% and broccoli 89%.  Fresh coriander (cilantro) is 92% moisture and fresh parsley 88%.  The main difference is in the fibre content.  Lettuces are between 0.7% and 1% fibre, herbs, broccoli and cabbage between 2% and 3.3%.  Young grass is 3% fibre and 80% moisture by way of comparison.