Effect of lice eradication on grain defects

LIGHT FLECKS AND SPOTS were described and precisely defined for the first time by Webster & Bugby (1990). These investigators defined light flecks and spots as small areas of grain loss up to 3mm in diameter that are seen on dyed crust bovine leather and associated the damage with the presence of lice. Both biting lice (Damalinia (Bovicola) bovis (Linnaeus 1758)) and sucking lice (Linognathus vituli (Linnaeus 1758)) caused light flecks and spots, but biting lice seemed to be the most important. Treatment with insecticides decreased the occurrence of damage significantly (Bugby et al 1990, Webster & Bugby 1990). Similar damage has also been described by other authors and associated with various ectoparasite species (Everett et al 1977, Rotz et al 1983, George et al 1986). The occurrence of light flecks and spots on Norwegian cattle hides was estimated for the first time in 1991 by tanners from all Nordic countries. Based on a commercial evaluation and classification, the tanners found lice related damage on 50-55% of the Norwegian hides (Dørum, personal communication). The damage was present on 75.8% of the hides before treatment in the present investigation (Nafstad & Grønstøl a). This evaluation was based on a more detailed examination of the hides and is not directly comparable with the tanners' report. Eradication as a control strategy of ectoparasites in domestic animals is described and assessed in general by Hiepe (1986). In the present study, a clinical evaluation of an eradication programme was undertaken together with the investigation of the hides. The results of the clinical evaluations indicated that eradication can be an appropriate control strategy for lice in cattle (Nafstad & Grønstøl b). The aim of this paper was to compare the leather quality and the occurrence of light flecks and spots on cattle hides before and after the eradication of lice. Materials and methods Design A prospective cohort study was performed in 33 dairy herds during a period of two and a half years with animals leaving or entering the herds at any time. Hides from all animals slaughtered in the 33 herds from January 1, 1994, to June 30, 1996, were collected and examined after tanning for ectoparasite related damage. Twenty-eight of the herds were treated to eradicate lice in the second third of 1994. Five herds took part in a pilot study and were treated to eradicate lice in December 1993. Hides from these five herds were only included in the 'after eradication' group. Herds, animals and hides The herds were selected by the District Veterinary Officers in Akershus and Østfold. Selection criteria and ectoparasite status were described previously (Nafstad & Grønstøl b). The herd size varied from eight to 50 dairy cows. In total, 1,032 hides were collected during the whole investigation period, 368 from the period before eradication and 664 from the period after eradication. The mean number of hides from each herd was 13.1 before treatment with a variation from two to 21. The mean number from each herd after treatment was 20.2 with a variation from seven to 51. Examination of the hides The tanning procedure and examination of the hides were described previously (Nafstad & Grønstøl a). Light flecks and spots were defined as areas of grain loss up to 3mm in diameter seen on dyed crust leather (Bugby et al 1990, Webster & Bugby 1990). The evaluation was based on the number of identifiable flecks/spots and was performed according to the following scale: Score 0 - no damage Score 1 - slight damage, with 1-2 light flecks or spots per 100cm Score 2 - some damage, with 3-5 light flecks or spots per 100cm Score 3 - severe damage, more than 5 light flecks or spots per 100cm Statistical methods Eight registrations from each hide were used to derive two parameters. The maximum score was defined as the highest single registration on each hide and the sum score was defined as the sum of the eight registrations on each hide. If only one half of a hide was available, a duplicate result from the available half of the hide was used in the statistical analyses. The Statistical Analysis System (SAS 1996) was used for data processing and statistical analysis. Spearman's rank correlation was used for testing changes with time after eradication. Otherwise, statistical hypothesis testing was carried out by use of the t-test. The statistical testing was based on the frequency of hides without damage (maximum score 0) or the average of the sum scores for the groups. Results Effect of eradication The frequency of cattle hides without light flecks and spots increased from 24.2% before the eradication of lice to 61.6% after eradication. The average sum score of the hides in the group decreased from 3.52 before eradication to 1.46 after eradication. The general effects of the eradication of lice are presented in table 1; the results from the subgroup of hides from animals born after the eradication of lice are shown in table 1b. There were no significant differences between this subgroup and the group of hides from all animals slaughtered after eradication. An increasing proportion of the hides came from reinfected herds as the observation period progressed and 53% of the hides from animals born after eradication came from reinfected herds. There were no significant differences between hides from reinfected herds and hides from herds that remained free of lice. The eradication both decreased the proportion of hides with damages and the extent of damage on affected hides. The average sum score of affected hides decreased from 4.64 before eradication to 3.80 after eradication (p<0.01). The quality of the hides from the herds in the pilot study did not differ from the quality of the hides in the main group after treatment. 61% of the 199 hides that were collected from the herds in the pilot group were free of light flecks and spots. Effect of eradication in various anatomical regions Following the eradication of lice, there were significant reductions in frequency of light flecks and spots in all anatomical regions examined on the cattle hides (table 2). Accordingly, the frequency of hides without damage increased in all anatomical regions. The neck and shoulders were the region with the highest incidence of damage before treatment. This region also showed the largest change in the prevalence of light flecks and spots after treatment. Change with time after eradication The change in the frequencies of damage during the whole period after eradication is shown in table 3. The frequencies of hides without damage increased significantly in periods I-III. The percentage of hides from reinfected herds increased noticeably with time after eradication up to 53.8% in period IV. Hides from period I (2-136 days after eradication) are classified in more detail according to time after eradication in table 3b. The frequency of hides without damage increased significantly during the periods 1-3. The difference between period 3 and 4 was not statistically significant. Seasonal effects The seasonal variation in hide damage after the eradication of lice is presented in table 4. There was no significantly seasonal variation in the frequency of light flecks and spots after treatment. Discussion Systematic treatment for the eradication of lice decreased the frequency of hides with light flecks and spots from 75.8% to 38.4%. The extent of damage on affected hides also decreased significantly. This investigation confirms the importance of lice for the development of light flecks and spots on cattle hides and supports the observations of Bugby et al (1990) and Webster & Bugby (1990), who were the first to suggest lice as the main cause of light flecks and spots on cattle leather. The frequencies of hides with light flecks and spots decreased in all anatomical regions after the eradication of lice. The distribution of damage before treatment corresponded with the distribution of lice on the animals (Chalmers & Charleston 1980, DeVaney et al 1988). The difference in the presence of damage in regions of the hide before and after treatment was most marked in the neck and shoulder region, which is the major predilection site of cattle lice. For the whole period after eradication, 38% of the hides were still affected by light flecks and spots. The period with highest frequency of hides without damage was 326 to 477 days after eradication. The frequency of hides without damage subsequently decreased, probably due to the proportion of hides from reinfected herds. Given the design of the study, it was not possible to estimate an exact time of reinfection. However, the lice population in the reinfected herds was much lower after reinfection than before eradication. Because of these findings, it was decided to include the hides from all herds even after the reinfection. The frequency of hides with light flecks and spots from animals born after eradication was similar to the frequency from animals born before eradication, about 35%. These results indicate that light flecks and spots may have causes other than lice and suggest that while the hide damage is closely associated with lice, it is not specific for lice. According to the results of the present study, 40-45% of the light flecks and spots seemed to have causes other than lice under Norwegian conditions. George et al (1986) suggested that Psoroptes ovis (Herning 1838) infestations in cattle may cause light flecks and spots, but this ectoparasite does not occur in Norway. Everett et al (1977) found that damage similar to light flecks and spots was caused by various tick species, but could identify no evidence of hide damage caused by short nosed sucking lice (Haematopinus eurysternus, Denny 1842), flies or mosquitoes. Under Norwegian conditions, Ixodes ricinus (Linneaus 1758), is the only present tick. However, this tick was not included in the present investigation because only two herds were localised in areas where this tick usually occurs. The distribution of the damage on hides also differed from the expected distribution of damage caused by ticks. Recent research by the BLC has suggested that the stable fly (Stomoxys calcitrans, Linnaeus 1758) may be a cause of light flecks and spots (Bugby personal communication). This fly may also be a cause of hide damage under Norwegian conditions, but so far this has not been confirmed. It should be noted that the treatment in the present study may have a temporary effect on the fly population in the herds. However, stable fly may be a cause of the persistence of light flecks and spots on hides after the eradication of lice. The frequency of hides without light flecks and spots increased significantly from the first period after eradication and the highest frequency was present in period III, 326-477 days after treatment. This result is consistent with the suggestion that the healing period for injuries induced by lice was more than 12 months (Christensson et al 1994). However, findings in the present study also indicate that most of the healing occurs much faster. The frequency of hides without damage increased to more than 60% during the first three-to-four months after treatment. This observation was possibly confounded by the increasing proportion of hides from reinfected herds over the period of the present study. The investigation by Bugby et al (1990) showed very slight damage on the leather nine weeks after treatment. These authors suggested, however, that hides from animals which had been infested with lice could never be used for top quality aniline leather. More research is needed to determine more precisely the duration of the healing period following injuries induced by lice. Before treatment, the frequency of hides with light flecks and spots varied significantly during the year. The variations were consistent with lice as a main cause and the frequency of hide damage varied according to the changes in the lice population during the year (Nafstad & Grønstøl a). The demonstration in the present study that this seasonal variation is eliminated following the eradication of lice, emphasises the importance of lice for the development of light flecks and spots on cattle hides.