While six species of lice are known to affect Australian cattle, biting lice (Bovicola bovis) and two species of sucking lice; Haematopinus eurysternus (the short nosed sucking louse) and Linognathus vituli (the long nosed sucking louse) are most common in southern Australian beef herds (Smeal 1995). Cattle lice usually do not cause a production loss (Cummins and Tweedle 1977, Scharff 1962). However, they cause irritation and affected cattle may damage infrastructure and their hides (Coles et al 2003).
Occasionally however, individual members of a herd with heavy lice burdens are encountered. These are sometimes referred to as ‘louse carriers’ and are highly susceptible to increasing lice populations under favourable conditions and may act as a reservoir of lice in the herd (Smeal 1995). They may be susceptible because they lack immune competence. This is a case of a ‘lice carrier’ heifer with normal selenium and pestivirus status.
In July 2017 the owner of a mob of 70 rising two year old Angus heifers noticed that a single heifer had lost weight over the last three weeks. The other heifers were in good body condition (average live weight estimated at 400 kg). The mob was examined on the 11 July 2017.
This mob had been previously examined in August 2016. Selenium deficiency was diagnosed and the cattle were treated with long acting selenium (Selovin LA containing selenium as barium selenate 50 mg/ml, dose 2.0 ml/100 kg, Bayer Australia), vaccinated with clostridial 5 in 1 and drenched with albendazole (Valbazen broad spectrum mini-dose cattle drench, albendazole 112.5 mg/ml, dose 3 ml/45 kg, Zoetis). At that time this heifer was noticed to be unusually thin but responded to treatment.
The mob was last treated for lice, with moxidectin pour on (Cattleguard Pour-On moxidectin 5g/L, dose 1ml/10kg, Zoetis Australia) and vaccinated with 5 in 1 on 6 January 2017.
A two year old Angus heifer (August Sep 2015 drop), one of 70, was noticed to be in poorer condition than its cohorts. The heifer had submandibular oedema, pale mucous membranes, tachycardia with heart sounds unusually audible on RHS, evidence of diarrhoea on the tail and breech and a heavy lice infestation over the entire body.
Samples of lice and hair were submitted for laboratory examination. Eight lice were examined microscopically. Shed lice skins and a large number of eggs on the hair indicated an extreme infestation.
The sample was desiccated and the lice were identified based on their size and conformation despite poor presentation. The sample contained the long-nosed cattle louse, Linognathus vituli, which was present as adults and two nymphs. The sample did not contain any adult / nymph short-nosed sucking lice, Haematopinus eurysternus, tubercle-bearing louse, Solenopotes capillatus or cattle biting louse Bovicola bovis.
|PROT-RTS||65-85 g/L||58 L|
|HB||8.0-15.0 g/dL||5.0 L|
|MCHC||30-35 g/dL||28 L|
|MCH||14-20 pg||8 L|
|WBC||4.0-12.0 109 /L||3.8 L|
Haematology shows a moderate microcytic, hypochromatic anaemia, with a mild leukopenia due to a moderate lymphopenia (1.52 109 g/L, normal 2.5 to 7.5 10 9 g/L). Biochemistry shows a mild hypoproteinemia characterised by hypoglobulinemia (25.7 g/L, normal is 30-45 g/L). Of interest, the albumin level was normal (31.4 g/L). There is a mild elevation in pepsinogen (6 U/L, normal is 1-5 U/L). The glutathione peroxidase level was high at 641 U/gHb (normal 40-300 U g/Hb).The results suggest chronic anaemia, presumably due to ectoparasites.
A hair sample was negative for pestivirus antigen. A faecal sample from this heifer had a strongyle count of 80 epg and was negative for fluke eggs. However, a bulk blood sample of 5 cohorts was strongly positive for liver fluke with an S/P ratio of 231.
Cattle producers and agricultural extension staff have long debated the merits of treating cattle for lice (Kettle 1974). Undernourished cattle, particularly in the winter, are regarded as most susceptible. However, randomized, replicated trials have shown that the routine treatment of cattle for lice is unlikely to be economic, at least in terms of production loss (Kettle 1974, Cummins and Tweedle 1977, Cummins and Graham 1982). Cummins and Tweedle (1977) found that undernourished cattle had higher lice burdens than their better fed cohorts, but they found that while the plane of nutrition influenced the lice score in untreated cattle, the lice score did not influence growth rate.
One of us (BW) has occasionally seen individual heavily infested cattle. Scharff (1962) cited a case of a single heavily infested Hereford steer that became anaemic and, in his opinion, would have died in the absence of lice control. He used rancher surveys and cattle buyer records and examined the hides of recently slaughtered cattle to estimate that 1-2% of Montana cattle were heavily infested with lice.
This ‘lice carrier’ heifer was anaemic presumably from the heavy sucking lice infestation. Two common causes of immune suppression, selenium deficiency and pestivirus infection, were ruled out as contributing to her susceptibility to biting lice infestation.
Even on properties that don’t routinely treat cattle for lice, ‘carrier cattle’ should be treated and preferably culled from the herd.