Written with contributions by Kelly Froehlich, former Assistant Professor & SDSU Extension Sheep and Goat Specialist.
The approximate age of a sheep can be determined by their 8 lower incisors. Knowing how to “mouth sheep” is a valuable tool to verify age when purchasing or culling ewes. From one to four years of age, sheep will replace “baby teeth” with permanent teeth. Beyond four years old, age can be estimated by incisor gaping and damage. Erosion of both incisors and molars is inevitable with aging, but proactively monitoring flock dental condition can promote overall flock productivity.
How to Mouth a Sheep
From birth to approximately 1 year of age, lambs have impermanent incisors called “milk teeth.” From 12 to 18 months of age, the first set of permanent incisors erupt. Each year until the sheep is 4 years old, a pair of permanent incisors erupt, starting from the center teeth and going backwards (see our Mouthing Sheep for Age resource for some visual examples).
When a sheep has four permanent incisors, and the teeth have little to no wear, nor are they broken, they are considered a “solid mouth” sheep. As the sheep ages and continues wearing down their teeth, ewes that have broken, short, or missing teeth are known as “broken mouthed.” These sheep tend to be older than 5 years of age and need feedstuffs that have smaller particle size and are easier to chew. Severely broken or worn teeth lead to difficulty eating and, ultimately, decreased lamb, wool, and milk production. A sheep may have the appearance of a 'broken mouth' while incisors are erupting, but it’s important to recognize if the tooth is truly broken or beginning to protrude from the gumline. A true broken mouth has other indications of wear, gapping, damage, and other signs around all the teeth rather than 1 to 2 teeth.
Causes and Effects of Tooth Wear
As the initial step of digestion, teeth play an integral role in animal health. Tooth wear negatively impacts the longevity of sheep. The incisors are the easiest to evaluate, but sheep also have 24 molars (6 top pairs and 6 bottom pairs) that influence productivity. Several factors contribute to tooth damage. As animals graze, they also ingest abrasive particles, causing tooth shortening and damage over time.
- Abrasive Particles: Plant structure constituents called, silica phytoliths (in Greek, phyto means “plant” and liths means “stones”), have been suggested to contribute to dental wear. However, larger soil particles likely have a greater influence on tooth damage, especially for flocks grazing on sandy soils.
- Jaw Structure: Sheep with a shortened (referred to as “parrot mouthed”) or extended (referred to as “monkey mouthed”) mandible have incorrect jaw alignment. This can lead to increased difficulty eating, as well as increased tooth damage. Jaw abnormalities are a simple culling factor.
Dentition problems cause decreased feed inefficiency due to difficulty consuming feed and adequately breaking down feed particles. Animals with broken or short incisors may struggle to bite forage when grazing and will not consume enough feed. Ruminants are highly efficient convertors of forage to protein, due, in part, to their ability to decrease feed particle size multiple times through rumination. If their molars are worn or damaged, the animal can’t adequately break down particle size for easier access by rumen microbes. This leads to decreased wool and lamb production. In severe cases, broken-mouthed animals rapidly decrease in body condition and potentially starve. If you notice a poorly conditioned ewe, there may be a number of causes, but an easy starting place to look is checking its tooth integrity.
In Summary
Mouthing is a valuable tool for making culling decisions or identifying age when purchasing sheep. Dental problems lead to long-term loss of production and decreased animal lifespan. Print out the barn reference as a chute-side tool when evaluating and aging your flock.
