Notes on the incidence of the Foot Louse (Linognathus pedalis) of Sheep as observed in the Narrabri Pastures Protection District.
During routine inspections of sheep for external parasites, which in this district are almost solely the Biting Lice (Bovicola ovis), it was noted that one of the sheep in the mob carried a light infestation with L. pedalis. Observations made on this mob led to further infestations being detected.
In the pamphlet issued by the N.S.W. Dept. of Agriculture on lice and sheep L. pedalis is said to be very similar to Haematopinus ovillus but that L. pedalis infests the legs below the wool in the coarse, short hair. It is relatively shorter than the body louse but otherwise closely resembles it. The colour is a light blue-grey and it is found with the head imbedded in the skin and the distended abdomen protruding. On account of the colour in light infestations it is difficult to find in sheep with dark skin on the legs or where there is dry mud on the feet. The fact that the hair will not part like the wool is an added difficulty.
Large numbers of eggs are laid which are sometimes found before the lice in particularly light infestations but epithelial debris is not to be mistaken for eggs.
Usually sheep show no signs of being affected such as rubbing or scratching at the affected parts. At odd times however, sheep have been seen to bite at their feet but this is not known to be a definite sign of infestation. In more heavily affected cases the wool often appears to be rubbed or bitten on the leg.
It might be expected, it seems, that English breeds and their crosses are more heavily and frequently infested.
No case of heavy infestation such as is described in text books has been observed. There has been no severe matting together of the hair with nits and only one case was infestation found on the testicles, and then it was only two or three. In no case has the parasite been found higher than the hock or knee.
The usual type of infestation which has been observed was 5 to 20 lice on each or one foot immediately above, between, or just below the dewclaws. A casual glance will not serve to find this type of infestation.
For a period it was found that almost every mob examined. As a result of our investigation, it is considered that an odd sheep in every mob carries at least a very light infestation, which on account of the slowness of spread from sheep to sheep and the harmless nature of the parasite, does not become obvious.
A consideration of the individual infestations encountered will serve to show what may be expected in the examination of flocks.
Case No. 1.—There were 1000 young sheep in this mob which was composed of two mobs which were each 70-75 per cent. infested. One portion of the mob had been dipped four days prior to inspection, in no sheep did it extend to the hock or knee. The whole mob were dipped again following which the infestation was found to be still present. A concurrent B. ovis infestation was satisfactorily dealt with in the previously undipped portion of the mob.
No. 2.—In this mob (1300 fat lambs for slaughter), three were found to be infested in twelve examined. Only an odd nit and two two or three lice were seen on each.
No. 3.—A light infestation—about 25 per cent. of the mob—had been overlooked by an inspector, who searched but failed to find any lice in the sheep.
No. 4.—About 5O per cent. of this mob were found to be infested but owing to the muddy condition of the feet the number affected was probably greater than was found. Seven mobs had then been examined of which four were found to he affected.
No. 5.—Fifty per cent. of this mob was affected.
No. 6.—Three were examined, two of which were found to be infested. There were 700 in the mob and their feet were very muddy.
No. 7.—This mob of a thousand had been dipped and though the ewe portion was quite free the merino rams were relatively severely infested. The affected area did not extend more than 2 inches above the dewclaws in any case.
No. 8.—In this lot (800 fat lambs being forwarded for slaughter), one sheep in three was found to carry a very light infestation.
No. 9.—Thirty per cent. of this lot (aged wethers were relatively severely infested.
No. 10.—Thirty per cent. of this mob (a small lot of fats), were lightly infested.
No. 11.—This mob had been dipped satisfactorily for B. ovis about a week prior to inspection. They retained a very light infestation with L. pedalis.
No. 12.—Every sheep examined in this mob of 1800 was found to be infested. In a second mob of 1900 from the same property 50 per cent. of the sheep were lightly infested.
No. 13.—Two sheep were examined out of this mob and found to be lightly infested.
No. 14.—On this property all the sheep had been dipped for B. ovis infestation following which all the merino sheep examined were found to be free. All of the Border Leicesters were carrying a few L. pedalis.
No. 15.—In this mob three or four lice were found around the dewclaws of all the examined but no infestation could be found on merinos.
No. 16.—In these sheep, inspected during crutching, about 75 per cent. of the Merino ewes were found to be infested; some heavily. All the Border Leicester rams which were running with the ewes were heavily infested about the feet.
No. 17.—No live L. pedalis but a few dead ones were found in these sheep which had been dipped on account of B. ovis infestation. The dip had been used for some mobs prior to the mob being dipped and an extra packet of dip had been added without extra water. It is probable that the dip was much stronger than is normally used during the last few years in the North-West.
Thanks are due to Mr. Blumer, District Veterinary Officer for the North for permission to use the information collected in the preparation of this article. He informs me in official correspondence that he has personally observed L. pedalis in odd sheep in the Tamworth, Armidale, Inverell and Glen Innes districts, and that in each instance the infestation was heavy involving the scrotum and the legs.
1. Infestation with Foot Louse of sheep has been found to be prevalent in the North-West to a degree previously not suspected. 2. The infestation is usually very light, occurring in the region of the dewclaws and examination has been found difficult on account of mud, the colour of the skin and the fact that the hair will not part easily.
3. The degree of infestation commonly observed gives rise to no clinical symptoms and is apparently not detrimental to the sheep.
4. A note is made on cases of infestation encountered.
5. A note is made of the towns from which infested sheep have come into the district and it is assumed that the distribution of the parasite corresponds.
6. Dipping solutions in the usual strengths do not seem to be effective against the louse.
During routine inspections at Manilla ram sales it was found that sheep were infested in all studs with the exception of two. The towns the affected studs came from were Deniliquin, Narrandera, Willow Tree, Upper Manilla, Gunnedah, Gulargambone, Narrabri, Jerilderie, Barraba, Conargo, Widgiewa Siding, Inverell. The infestations were generally very light. Every English sheep examined was infested.
In the Narrabri district infested sheep have been found which had recently been at, or whose home holdings were situated at Walgett, Bellata, Merah North, Burren Junction, Tamworth, Wee Waa, Coonamble, Baan Baa. From this it will be seen that the incidence is widespread throughout the North-West.
Enquiry also revealed that there have been odd sheep severely affected over the last three or four years. During this time there has been no effort to control the parasite, and it is consequently assumed that it has spread as much as it ever will in normal seasons.
I am indebted to Mr. Hugh Gordon for referring to the available literature on the subject. He assures me that little has been written on the incidence of the parasite other than the recording of heavy infestations. Sheep were examined at the Master Institute and were found to be infested. Large numbers of the lice were dead and all seemed to be "sick." The feet of these sheep were wet at the time of inspection and each day they are wet when the pens are cleaned out. It is considered that moist conditions do not favour this parasite and that the high incidence observed may be in part or entirely due to the prolonged dry conditions which have been experienced.