Copper, sweet iron or rubber: what does the mouthpiece material do?

Wikipedia's article on bit mouthpieces says the metal or synthetic used may determine how much a horse salivates or otherwise tolerates a bit, and that a horse with a moist mouth is considered more relaxed and responsive. That idea runs through most of what makers say below.

We will be plain about the evidence as we go. The claims about copper and sweet iron rest on makers, reference works and rider experience. In what we read for this page, we did not find a controlled study that tests whether either one increases salivation. Here is the short version.

Equisearch says it doesn't flake or rust. Nickel plating, by contrast, can flake with wear and leave rough patches that can injure the lips and tongue. Wikipedia lists stainless steel and nickel alloys together as generally not rusting and having a neutral effect on salivation.

JP Korsteel's page says a plain stainless mouthpiece suits a horse that wants steady contact, and describes the heavier weight of its 19 mm solid eggbutt as quieter in the mouth. That is the maker's description of intent. Happy Mouth, for example, pairs its polymer mouthpiece with stainless steel cheeks, so the material choice is often a mouthpiece question, not a whole-bit question.

Korsteel says the copper in its roller dee ring snaffle encourages salivation and discourages the horse from taking hold of the bit. Turn-Two says copper encourages salivation and a soft mouth. JP Korsteel's copper links are described as encouraging salivation and acceptance. Equisearch says copper helps some dry-mouthed horses salivate and become more responsive.

Two cautions. First, 'copper' on a listing can mean several things. On our bits, the mouthpiece material filter lists copper, stainless steel with a copper inlay, sweet iron with copper and copper alloy, among others. A 2019 Swiss study of 103 horse bits using X-ray fluorescence found that copper and zinc were the key elements that defined its alloy groups, so a coppery color alone does not tell you what the bit is made of. Read the product name.

Second, Equisearch warns that copper tends to pit, so check the surface for sharp edges now and then. Happy Mouth's copper roller styles add a center roller of 99.9 percent pure copper, according to the maker.

Two listings show the range. The Korsteel Copper & Steel Roller Jointed Dee Ring Snaffle Bit alternates copper and stainless steel rollers on a single joint, and the JP Korsteel Stainless Steel Copper Oval Link Eggbutt Snaffle Bit has copper links. Both appear under 'copper' in a shopper's eyes, but they are different bits, which is why the product name is the thing to read.

• Stainless steel with copper inlay: a steel mouthpiece with copper set into it.
• Sweet iron with copper: sweet iron combined with copper.
• Copper alloy: an alloy, not pure copper; the Bern study found copper and zinc defined its alloy groups.

A 2019 study by Bern University of Applied Sciences researchers, published in Pferdeheilkunde Equine Medicine, describes sweet iron bits as a current trend for that reason. Equisearch is more cautious: it says sweet iron encourages salivation and softer response, and adds that whether the metal actually tastes sweet to a horse is unknown.

The same Bern study looked at safety. It analyzed 103 bits by X-ray fluorescence and ran a 90-day field test comparing 10 sweet iron bits with 9 conventional metal bits. The iron content did not change significantly in either group, and both groups lost a small amount of weight to wear: 0.28 g on average for conventional bits and 0.2 g for sweet iron. The authors concluded there was no reason to expect a toxic release of iron into the horse's mouth. That is a small test of one group of bits over three months, and it did not test the saliva claim.

Blue steel is related. JP Korsteel's page says the finish on its blue steel jointed eggbutt works much like a copper mouth, with a taste most horses accept. Turn-Two uses sweet iron on its working gags and lifters. Both are maker descriptions.

Equisearch says vulcanized rubber, a hard rubber coating baked onto the mouthpiece, is stronger and less prone to flaking than non-vulcanized, is warmer on the bars of the mouth and the tongue, and that some horses prefer the softer feel. It describes the polymer used in Happy Mouth bits as a soft, flexible high-tech plastic with an apple scent to help bit-shy horses accept it. Wikipedia adds that rubber bits are generally thicker than metal bits.

Korsteel describes its solid rubber mouth as warm, soft and ideal for young horses, and JP Korsteel's rubber mouth jointed dee is described as good for young horses or inexperienced riders. Those are the makers' pitches, and the bit's thickness, shape and cheek matter alongside the material.

Check thickness and wear. The notes on our Happy Mouth page say polymer is softer than metal, so a horse that chews can mark it, and suggest checking the mouthpiece after the first rides and replacing it when you see a tear. A thick mouthpiece takes up more room, so it is worth rechecking against his mouth. Horse & Hound's expert calls 20 mm very generous and says it is more common on rubber and mullen mouths, and our JP Korsteel page suggests a thinner mouthpiece for a very thick tongue or a low palate.

Equisearch says that finding the right material is often trial and error, and that what works for one horse may not work for another. Wikipedia's bit mouthpiece article makes the broader point that a heavy-handed rider can make even a bit labeled mild uncomfortable, and a skilled, light rider can use a much stronger mouthpiece without distressing the horse.

In other words, the metal sits beside the mouthpiece shape, the thickness, the width, the cheek and the rider. The quote below is a rider describing the whole list. If your horse fusses and the bit fits, have your vet or equine dentist check his mouth before you try another material.

Our pages on width and cheek come first: What size bit does my horse need? and Loose ring, eggbutt or D-ring. Change one thing at a time, ride a few sessions, and give it a fair trial.

For show riders, the rule book may limit the material. USEF dressage rule DR121 says a snaffle mouthpiece must be metal, flexible rubber or synthetic material. A metal mouthpiece may carry a rubber or plastic covering as made by the manufacturer, but you can't modify a bit by adding latex or other material, and leather or leather-covered bits are prohibited. The model-by-model check is in Is this bit legal for dressage?.

Look over any bit you own. Run a thumb along the mouthpiece for rough patches, pits and burrs. Equisearch flags flaking nickel and pitted copper, and the notes on our Happy Mouth page say to look for tears in polymer. Anything that catches your thumb should not go in his mouth. Our bits can be filtered by mouthpiece material when you want to compare.