Karen Goodchild, OK Doe K Dairy and Therapy Goats
"Bettering the Breed” – a phrase we all hear, but what does that mean to you as a breeder? Does this mean not registering certain offspring and selling unregistered, removing from your breeding program, taking to the sale barn, or making tacos?
There is a dirty, little secret in the dairy goat world that no one wants to discuss - teat abnormalities or hyperthelia. Teat abnormalities include supernumerary, fused, bifurcal, double orifice, or leaking orifices. Supernumerary teats can be found behind the main teat or attached to it. They are generally shorter and have thinner walls. Some may have their own mammary gland.
Supernumerary teats (SNT) are highly heritable and one of the most common abnormalities in dairy animals. SNT can have an orifice or be a blind teat. Some breeders often cut them off when an animal is young so no one is the wiser, but it can still pass on to progeny.
There is one study that indicates intrauterine hormones may play a role in SNT formation. A study of pigs shows the number of teats is partially determined by the number of males in a litter.
Both American Dairy Goat Association and American Goat Society identifies teat defects as a Very Serious to Disqualifying trait.
ADGA Linear Appraisal Chair confirmed teats are not checked during appraisal; AGS verified their classifiers check for teat abnormalities, and they are more likely to catch the tell-tale signs of removal due to having more time than in a showring. Judges from both registries check to ensure there are two teats, but due to the time in the show ring it is not apt to be closely inspected.
While boer goats have a high incidence of teat abnormalities, it is not regarded to the same degree as the defect of dairy goat registries.
A SNT study in Brazil indicated a 27 percent incidence out of 131 dairy goats in one study, proving it is a fairly common trait. The only way to effectively eradicate this trait is to cull it from your herd.
“My impression is that teat abnormalities are genetically linked but exact genes may not have not been found,” Dr. Roger Merkel of Langston University said. “On the weeping teat study, heritability was not very high. On supernumerary teats in Holstein, the heritability was higher and there is more information on specific genes responsible.”
While a supernumerary or double orifice teats are not usually a disqualification in does, one has to ask if this is a trait to be associated with your herd name. Sure, extra teats can be removed – quite often successfully – but at what cost to your herd and your reputation?
A prominent dairy cattle producer once commented, “It’s okay to have it in your dairy parlor, but not in the showring.” The issue arises when selling kids. Do you share the questionable dairy parlor issues to potential customers?
One anonymous member wrote they purchased a doe that had milk leaking from an area above/in front of the left teat when overly full or when pressure was applied to the area. An exam found a small opening in the udder with what appeared to be a burn mark. The original breeder confirmed the doe was born with a supernumerary teat that had been nipped off and cauterized.
The pro’s of keeping offspring with a SNT is that some have claimed these animals produce more milk. Additionally, it may be able to be used to graft in the event of a main teat injury.
The con is that it will keep reoccurring in your herd due to heritability, they can make milking difficult, and there is a higher potential for mastitis due to more openings for bacteria to enter the udder. If the SNT is removed, there is a chance it has its own milk gland that will then not be able to be emptied.
Research shows that boer goats in South Africa have a lower incidence of SNT due to their strict culling protocol. “The Boer breeders in South Africa are pretty stringent in culling does with supernumerary teats as a defect,” Merkel said. “Breeders in the US have not been as stringent, perhaps because of the high price of initial imported animals and their offspring.”
In a 2012 cattle study, four loci were identified in 2,467 progeny-tested bulls that were genotyped and their daughters evaluated for heritability phenotype. A 2014 study of 1,097 Holstein bulls pinpointed chromosome 20 for SNT expression during a genome-wide study of the breed. It is still unclear if this trait in cattle is purely oligogenic or polygenic, but research points to a combination.
A 2000 study of Simmental cattle made up of “537 unrelated animals and 614 members of 27 paternal half-sib families with known phenotype of each sire. The frequency of hyperthelia (SNT) was 58% in unrelated animals, 51% in families with unaffected sire, and 73% in families with affected sires.”
The few cattle studies show a heritability difference between breeds. Very little research has been conducted on dairy goats specifically.
Author Parvathi K. Basrur in his study titled Congenital Abnormalities of the Goat verified some breeds have a higher predisposition to certain malformations. He cited “common polygenic disorders including udder problems in does and gynecomastia in bucks are more difficult to eradicate because the mutant genes responsible for these traits generally do not declare themselves until inbreeding brings together a critical concentration of liability genes to create a crisis.” In short, know your lines. This is particular daunting considering the Nigerian Dwarf breed is still in its infant stage in tracking certain breed phenotypes.
France has studied the SNT phenotype for over 15 years in the country’s appraisal program. A study in 2012 involving Alpine and Saanen showed 4 percent of the animals were not allowed to be in the elite breeding program due to supernumerary teats.
The French study of 32,908 Alpine and 23,217 Saanen found .40 and .44 heritability of this binary trait. Further, a daughter genome-wide study was conducted of 1,185 Alpine AI-sired by 11 bucks and 810 Saanen AI-sired by 9 bucks. Seventeen regions in 10 chromosomes were found, although no major gene was identified, suggesting a polygenetic component.
It is unclear how prevalent this trait is among all dairy goat breeds. While Nigerians at one time in the U.S. had an open herd book, a 2014 Nigeria-based study showed this trait expressed in original WAD goats with a 17 percent incidence in a herd of 18 does.
We have to ask ourselves, as breeders, if we don’t want this trait in the showring, why would we allow it in our herd? If it a phenotype selection, is it ethical to fool people in the showring? That is an answer each breeder must decide for themselves and their own herd management.
One member suggested that if a doe with this fault is sold with papers and it is disclosed to the new buyer, there is no guarantee it won’t be resold and the information withheld. This could cause a new owner to question the original herd’s management practices.
Several members shared their stories that hormones during pregnancy may play a part. Pregnancy hormones has caused some member’s does to grow extra teats that were not visible at birth or prior to pregnancy.
One member suggested an environmental cause of dewormer during one season when it was prevalent in a particular herd, although a reputable goat vet has dismissed this citing “correlation does not mean causation.” Another member confirmed in her herd that the incidence was not based on any particular dewormer, such as Valbazen.
A well-known standard breeder vet suggested to keep accurate records. This vet sells her supernumerary animals to a dairy as unregistered animals rather than keep them in her herd. Tracking breedings can help eliminate it in your herd, pinpoint potential issues, and help make future breeding decisions.
There are rumors that this trait is “unlucky” and sometime appears, while research has shown polygenetic markers and highly heritability. Members wrote in that it can happen with an outcross or linebreeding; that it only happens once or repeatedly; that it can appear to be environmental and not always genetic; that pregnancy hormones can encourage development. Unfortunately, until more research is undertaken, we are left making our own ethical herd decisions.
Teat Defects are covered on Page 145 and 146 in the ADGA Guidebook; AGS has similar defect language.
May 2022 ANDDA Newsletter