'Toxic Lettuce' Hysteria - a discussion
‘Toxic Lettuce’ Hysteria ....
The substance commonly referred to as being a risk when feeding lettuce is Lactucarium. Lactucarium is a milky fluid found in the whole lettuce plant and contains both Lactucin and Lactucopicrin. It occurs in high amounts in wild/bitter lettuce, Lactuca virosa and although it's not strictly 'toxic', gross overdoses are reputed to lead to cardiac arrest in humans (Chiej. R. Encyclopaedia of Medicinal Plants. MacDonald 1984, Launert. E. Edible and Medicinal Plants. Hamlyn 1981).
It is known as lettuce opium because of its supposed sedative and analgesic properties. Concentrations of lactucarium are low in young plants and most concentrated when the plant comes into flower (Bown. D. Encyclopaedia of Herbs and their Uses. Dorling Kindersley, London). However, edible lettuces; Lactuca sativa, and this grouping includes ALL of the edible lettuces, contain very low levels of this compound. The reason for this is that lactucarium is very bitter and this undesirable trait; along with the substance that causes it, has been bred out of our table lettuces through selective breeding.
Whilst all lettuces possess some of this narcotic like juice, Bitter Lettuce / Lactuca virosa has the most, with the others in the following order: Prickly Lettuce / L. serriola, L. altissima, Wild Lettuce of America / L. Canadensis, with Garden Lettuce / L. sativa, being the lowest.
In my eyes the biggest risk from feeding lettuce to rabbits; in addition to its low nutritive value, is the high water to fibre ratio which of course, can lead to diarrhoea and poopy butt. The odd lettuce leaf given as a rare treat as part of a mixed rabbit salad which is high in nutritious and fibrous herbs and weeds is not going to harm your rabbit. However we do need to keep in mind that all lettuce plants - both domesticated and especially wild ones, have the potential to cause a measure of sedation if fed to rabbits (in small amounts of course) and that being sedated can potentially put them at risk of injury or predation.
Copyright - Westley's World, 2021
Some General Nutritional Information
Iceberg, Green leaf & Red Leaf lettuce have a very low fibre:water ratio - 1.2gms, 1.3gms & 0.9gms/100gms respecively, which can cause Poppy Butt. Other lettuces - Cos/Romaine are marginally higher - both with 2.1gms/100gms, and can be fed, but this doesn't mean they should be fed in large quantities. Green leafy weeds and herbs are a much better option both for your rabbit nutritionally, and for its gut health
Here’s a comparison of the nutritive value of some common lettuces -
Iceberg lettuce: Per 100gms - Fibre: 1.2 gms, Vitamin A: 0, Folate: 29UG, Potassium: 141mg, Magnesium: 7mg, Phosphorus: 20mg, Calcium: 18mg, Water: 95.6gms
Butter lettuce: Fibre: 1.8 gms, Vitamin A: 166μg, Folate: 73μg, Potassium: 238mg, Magnesium: 13mg, Phosphorus: 33mg, Calcium: 35mg, Water: 95.6g.
Romaine/Cos lettuce: Fibre 2.1 gms, Vitamin A: 436μg, Folate 136μg Potassium: 247mg, Magnesium 14mg, Phosphorus 30mg, Calcium: 33 mg, Water 94.6g
Green Leaf: Fibre: 1.3gms, Vitamin A: 370μg, Folate: 38μg, Potassium: 194mg, Magnesium: 13mg, Phosphorus: 29mg, Calcium: 36mg, Water 95g
Red Leaf: Fibre: 0.9gms, Vitamin A: 375μg, Folate: 36μg, Potassium: 187mg, Magnesium: 12mg, Phosphorus: 28mg, Calcium: 33mg, Water: 95.6g.
Source -
Lettuce
Further Reading -
Botanical.com - A Modern Herbal - Lettuce, Wild
Henrietta's Herbal Homepage - Lactuca / Lettuce
Plants For a Future Database - Lactuca virosa