Zylkène and alpha-casozepine. Tested in cats, barely in dogs

Before a move, before New Year's Eve, before a vet visit: ask about a supplement for days like these and Zylkène is the name you hear most. Behind it is a single ingredient, and with this one it pays to tell the species apart.

What is in the capsule

Zylkène contains alpha-casozepine, a peptide from cow's milk protein. It forms when casein is broken down with the enzyme trypsin, which is why the label says casein hydrolysate. Apart from that, the capsule holds only processing aids and its gelatine shell. It can be opened and mixed into food.

Because it is milk protein, one caution applies: if your animal reacts to cow's milk, ask your vet first.

In cats: one solid trial

For cats there is a multicentre, randomised, double-blind, placebo-controlled trial (Beata and colleagues, 2007). 34 cats received 15 mg per kilogram per day for 56 days, and their behaviour scores came out clearly better than on placebo. That is one trial, not a dozen, but it has the design you would want. So for cats we grade the evidence as "some evidence" and calculate with exactly that amount.

A higher amount was not tested. The 15 mg per kilogram is the figure that was tested, not an invitation to give more.

In dogs: the same amount, much weaker evidence

For dogs the maker gives the same amount per kilogram, and we use 15 mg per kilogram for dogs too. The evidence is a different matter: a knowledge summary in Veterinary Evidence concludes that there is no evidence of a short-term effect and only weak, low-quality evidence of a longer-term one. For dogs, alpha-casozepine is therefore listed here as "traditional use".

So a product can reach the reference in a dog and still stand on a thin basis. We show the two separately, so that a reached amount never looks stronger than the evidence is. What else there is for dogs is in the guide to calm in dogs.

Which strength suits which weight

Zylkène comes in three capsule sizes, all at the same amount per kilogram:

• 75 mg for cats and small dogs: one capsule per 5 kg.
• 225 mg for dogs of 10 to 30 kg: one capsule per 15 kg.
• 450 mg for large dogs: one capsule per 30 kg.

A 30 kg dog on one large capsule gets the same 15 mg per kilogram as a 5 kg cat on a small one. Because it is one formula in three strengths, we file it as one product family: in the recommendation, Zylkène fills at most one of the three slots, so the same formula never takes the top three places.

What comes first

A supplement does not replace preparation: a quiet place to retreat to, getting used to the carrier, and time often help more in unfamiliar situations than any capsule. If your animal behaves differently for days, the cause belongs with a vet. Supplements are not medicines.