Wear in sheep's teeth

Abstract

1025 SummaryExcessive wear of incisor teeth of sheep grazing high-fertility (European) pastures occurs in various parts of New Zealand.Chemical analyses were made of enamels and dentines separated from teeth of 5-year-old ewes bred on farms of different types in various areas. Estimations of calcium, phosphorus, carbonate, sodium, magnesium, nitrogen, citrate, and 19 micro-elements disclosed no differences.There were, however, significant differences in fluorine contents.Fluorine contents (whole teeth) varied from 28 to 320 p.p.m., the higher amounts being associated with teeth from ewes on pastures topdressed with phosphatic manures, which contain about 1% fluorine.The composition of the apatite "bone salt", (Ca3(P04),)n(CaCO,J),,, varied but slightly, the average values of n for enamel and dentine being 5.2 and 3.5 respectively.Variations in tooth quality (as judged by relative extent of wear) could not be correlated with differences in chemical composition. The average composition, incidentally, is remarkably similar to that recorded for human teeth.These results support the earlier theory that substances in the rapidly growing leaves of high-yielding grasses and clovers soften the teeth of sheep grazing them either by dissolving or chelating their inorganic constituents, or by other types of attack with enzymes. These destructive processes would probably be further increased by the abrasive action of fibre in the grasses.

An evaluation of the effects of incisor dentition and of age on the performance of lactating ewes and their lambs

“…Effects of incisor dentition on the production of milk and its components were not pronounced, in confirmation of the early work of Barnicoat (1957). This may well reflect the buffering of the effect on milk production by the mobilization of body reserves of both energy and minerals (Gunn, 1969;Sykes et al, 1974a and b).…”

Pasture management trials on unploughable hill country at te Awa

“…Similarly, in spring there is a tendency for spelled pastures to rush up to seed-head and thus reduce leaf growth. It is of interest to record that Barnicoat (1957) working on wear in sheep's teeth at Te Awa, showed statistically significant results in favour of rotationally grazed ewes compared with set-stocked ewes.…”

The tooth to pad relationship in sheep - some mechanical considerations

“…Barnicoat (1957) described the tooth to pad relationship preferred in this country thus: "the incisors in a normal sheep's jaw should align themselves with the upper pad and there should be no perceptible ridge between it and the front edges of the teeth". In many parts of the country this ideal has proved sound.…”

“…Many sheep are culled because of dental defects (Barnicoat 1957). Observations show that sheep when grazing hold the grass between the lower incisors and the upper dental pad, tugging and breaking it over the incisal edge by a sudden movement of the head.…”

“…4 can be stable, and some young sheep with "overshot" jaws show this type of pad to pad contact as a developmental abnormality (Hitchin type 3). (Overshot and undershot foIl ow the convention of Barnicoat (1957): "Incisor teeth projecting forward of their normal position are described as overshot, those meeting the top pad behind this position as undershot".) If pad to pad contact cannot be achieved when the tips of the incisors clear the upper dental pad the unstable position shown in Fig.…”