Can rabbits eat the leaves and bark from cherry, peach, apricot, almond, and plum trees?

There is a lot of contradicting information out there about plants in the stone fruit family (Prunus spp.) and whether or not the leaves, bark, and flowers of these species are safe for rabbits and rodents due to the 'cyanide' present in the seed and vegetation. You'll find some people saying yes, some people saying no, some people saying yes but be cautious.

bunloaf decided to look into the research surrounding stone fruit and other plants with these types of concerns, and have determined that yes, twigs, flowers, and leaves from these plants are safe in moderation for rabbits and rodents.

Many plants contain protective toxins, called phytotoxins, in various parts of their biology, some of which are more potent than others, or only affect certain predator species.

One common type of phytotoxin are cyanogenic glycosides, which is the reason why they say don't eat apple seeds (in large amounts). With Prunus species specifically (cherry, plum, peach, nectarine, apricot, and almond), there is amygdalin, which is contained solely within the seed, and prunasin, which is in the vegetative parts, such as the leaf, flower, and bark.

Amygdalin and prunasin, among other types of cyanogenic glycocides, are known to cause poisoning in pregastric fermenters, which include ruminants like cattle, sheep, and goats, as well as some hindgut fermenters that primarily digest in the colon, like horses and humans, after consuming significant amounts of these phytotoxins.

The higher pH (6 – 7 pH) in the stomach or rumen of these species also contributes to the breakdown, or hydrolysis, of these phytotoxins into hydrogen cyanide (HCN), also called cyanide gas or prussic acid, and the specific microflora within the gastrointestinal system contain enzymes (like β-glucosidase) which easily facilitate this breakdown with the presence of water, or after recent water intake. β-glucosidase in particular is very successful at breaking down cyanogenic glycocides into hydrogen cyanide in a stomach or rumen in the pH range of 6.5 – 7.

This aids in why poisoning is more prevalent with equine and ruminant species on pasture. Low intake amounts of these cyanogenic glycocides are naturally detoxified in the body, breaking down into thiocyanate (SCN) and expelled through urine, breath, and sweat. But if they eat copious amounts of the vegetation and their body is not used to these types of plants, the excess thiocyanate (SCN) absorbs into the bloodstream, causing illness or death.

Many things can affect the level or potency of cyanogenic glycocides in plants, including weather, temperature, and age of vegetation growth. Even the diet of the animal can contribute to the susceptibility, by increasing or lowering the gastro pH levels, having tolerance due to exposure, antibiotic use, or recent water intake.

For example, bovids on grain-heavy diets have lower gastro pH than those on pasture. Cyanogenic plants used as fodder (like sorghum, cassava, or species in the Lotus genus) have been shown to have lesser amounts of glycocides when the fodder is dried as a hay, versus when it is fed fresh.

Most rodents and rabbits, however, have lower gastro pH levels (1 – 2 pH), and, being hindgut fermenters that primarily digest in the cecum, do not have the same level of enzymes (β-glucosidase) there that easily facilitate the hydrolysis of cyanogenic glycocides into HCN.

Laboratory tests on rats, for example, show that up to 200mg of amygdalin given every day for five months, an amount far more excessive than could be consumed through causal foraging, showed only moderately toxic effects, mostly on growth of offspring, with thiocyanate being efficiently excreted through urine, signifying the body had successfully detoxified the hydrolyzed cyanide from the amygdalin.

Wild rabbit and rodent populations globally have been observed consuming shoots and new growth as well as flowers of species in the Prunus genus, with no known reports of death or illness due to casual consumption of this, or other vegetation containing cyanogenic glycocides.

With decades of observations from companion caregivers, nominally domestic rabbits, chinchillas, degus, rats, and guinea pigs, forage consisting of twigs, bark, leaves, fruit, and flowers of Prunus species are therefore safe in moderate amounts, in addition to being medicinal, providing enrichment, and considered highly palatable as well.

The seeds of these plants and other species with cyanognic glycocides (like apples) however, should not be offered, due to the concentrated amounts of amygdalin within them. If a rabbit or rodent eats a seed, it is not likely to cause significant harm one-off, but contact your experienced exotic vet if it does happen, and take proactive steps to avoid any consumption of the seeds in the future.

Due to hamsters being pregastric fermenters, caution should be taken, and we recommend checking with well-known and well-educated online hamster husbandry communities to see what has been observed with these companions over the years, with regard to forage from Prunus species.

TIPS: HOW TO SELECT SAFE FORAGE

While it is important to collect forage safely as a general rule, there are some actions to take when offering edible plants that contain cyanogenic properties in one or some of its parts.

⦿ Do not select leaves, or branches with leaves, that are wilted or frostbitten

⦿ Do not feed seeds, kernels, or pits of fruit that contain cyanogenic glycosides

⦿ Do not offer unripe fruit as a treat

⦿ Do not feet the roots of cyanogenic plants, regardless of growth stage

⦿ Do not select vegetation grown during drought conditions

⦿ Sun-drying vegetation can reduce the level of these properties, but it varies depending on the plant, the method of drying, the amount within the vegetation to start, and, in some plants, drying can increase the level

TYPES OF CYANOGENIC GLYCOCIDES

As of 2021, there are 112 known cyanogenic glycocides found in over 2500 different plants.¹

There are dozens of derivatives and compounds within each glycocide. For example, a mixture of prunasin and sambunigrin becomes the prulaurasin compound, and prunasin methacrylate is a derivitive of prunasin, found in Centaurea microcarpa.

Some examples of commonly found types are:

amygdalin – found in the seed/kernel of stone fruits (Prunus spp.), apple/crabapple fruit and seeds (Malus spp.), the fruit of jetbead (Rhodotypos scandens)

dhurrin – found in the leaves of sorghum (Sorghum vulgare), leaves and roots of taro/cocoyam (Colocasia esculenta, Xanthosoma spp.)²

eucalyptosin – found in eucalyptus (Eucalyptus spp)

linamarin – found in cassava root and shoots (Manihot esculenta), flax seed (Linum usitatissimum), Passiflora pendens

linustatin – found in flax seed (Linum usitatissimum), Passiflora pendens

lotaustralin – found in Passiflora pendens, austral trefoil (Lotus australis), bird's foot trefoil (Lotus corniculatus), lima beans (Phaseolus lunatus), white clover (Trifolium repens), cassava root (Manihot esculent)

neolinustatin – found in flax seed (Linum usitatissimum), rubber tree (Hevea spp.), Passiflora pendens

prulaurasin – found in cherry laurel (Prunus lauracerasus), black cherry (Prunus serotina),

prunasin – found in the vegetation of stone fruit trees (Prunus spp.), shiso (Perilla frutescens)³

sambunigrin – found in elder (Sambucus nigra)

taxiphyllin – found in the young shoots of bamboo (Bambusa arundinacea)

triglochinin – found in the leaves of giant taro (Alocasia macrorrhizos), arrowgrass (Triglochin spp.) bellflowers (Campanula spp.)

Yulvianti M, Zidorn C. Chemical Diversity of Plant Cyanogenic Glycosides: An Overview of Reported Natural Products. Molecules. 2021 Jan 30;26(3):719. doi: 10.3390/molecules26030719. PMID: 33573160; PMCID: PMC7866531.

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SOURCE

K. Nyirenda, Kumbukani. 2021. ‘Toxicity Potential of Cyanogenic Glycosides in Edible Plants’. Medical Toxicology. IntechOpen. doi:10.5772/intechopen.91408.

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Akatsuka, Ryota & Ito, Michiho. (2022). Content and distribution of prunasin in Perilla frutescens. Journal of Natural Medicines. 77. doi: 10.1007/s11418-022-01654-x.

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