Revised methodology for a blood-clotting response test for identification of warfarin-resistant Norway rats (Rattus norvegicus)

A blood-clotting response test for warfarin resistance in Norway rats ( Rattus norvegicus ) was developed by our laboratory in the late 1970s, based on knowledge of biochemical mechanisms available at that time. That test used warfarin, its the free base which is not watersoluble, and vitamin K₁ 2,3-epoxide as an antidote for warfarin-resistant rats only. We have modified the above test to use a water-soluble salt of vitamin K₃ (1 mg kgg⁻¹ body weight), which is an antidote in a wider range of warfarin-resistant rat strains than vitamin K₁ 2,3- epoxide, and a water-soluble salt of warfarin (5.4 mg kg⁻¹ body weight). Sodium warfarin and vitamin K₃ are administered by oral gavage, and the blood-clotting response measured 24 h later. In a series of validation tests there were no significant differences between results obtained by either method. The new method, however, uses materials which are commercially available, and eliminates the possibility of misclassifying warfarin-resistant rats as susceptible because vitamin K₁ 2,3-epoxide was not an antidote in those strains. We also present evidence that measuring blood-clotting response to feeding on a vitamin K-free diet for 4 days is not a reliable method for determining the genotype of warfarin-resistant rats.     

Morphological, cytological and ecological discrimination of Bromus rigidus from Bromus diandrus

Morphological characters of different populations of brome found in the northern wheatbelt of Western Australia (Geraldton) pointed to the presence of Bromus diandrus and another taxon, most likely B. rigidus. This was later confirmed by the counts of somatic chromosomes made from root meristems of seedlings from different accessions. This is the first report of B. rigidus from Western Australia, and observations so far suggest that it is a serious weed of crops on the sandplains of the northern wheat-belt. The accessions of B. diandrus exhibited a much faster loss of seed dormancy than B. rigidus. Such short duration of seed dormancy coupled with rapid germination of non-dormant seeds of B. diandrus is likely to render it both more prone to premature germination following summer rainfall events and more susceptible to pre-sowing cultural and herbicide treatments following break of the season. Bromus rigidus appears to be well adapted to the Mediterranean climate of the northern wheat-belt of Western Australia, and is more likely to demonstrate seed carryover from one season to the next, thus making it a more troublesome weed.     

Silage and milk production: a comparison between grass silages of different chop lengths and digestibilities

Four grass silages of two chop lengths and two D-values were made from S23 perennial ryegrass, and compared in a feeding experiment with lactating cows and in an eating-behaviour study with non-lactating cows. The median chop lengths were 11·6 and 11·5 mm in the short silages and 18·2 and 19·5 mm in the medium silages. Chop length had negligible effects on D-value and on pH with values of 3·81 and 3·94 on the short and medium silages respectively.
Silage DM intakes were higher on the short than on the medium-chop silages in both experiments except where the high D-value silage was supplemented with concentrates. Milk yields were not affected significantly by chop length with daily values of 19·3 and 19·7 kg per cow on the short and medium treatments respectively with the high D-value silage, and 18·2 and 18·3 kg per cow with the low D-value silage. Chop length had only small and non-significant effects on milk composition.
Eating times expressed as min per kg DM were significantly lower on the short than on the medium-chop silages.
It is concluded that the small differences between the short- and the medium-chop silages were of no economic importance.     

Management of land and livestock contaminated with polychlorinated biphenyls

Investigations were conducted on several small neighbouring beef cattle and sheep farms that were found to be contaminated with polychlorinated biphenyls (PCBs). The residues detected contained about 62% w/w chlorine and soil concentrations ranged from 0.35 to 1.9 mg/kg. Beef cattle and sheep grazing the contaminated land had PCB concentrations in their fat of 0.3 to 1.7 mg/kg and 0.19 to 0.45 mg/kg, respectively. The concentration of PCBs in the caudal fat of cattle was 0.3 to 2 times the concentration of PCBs in the land they were grazing and was positively related to stocking rates. PCBs were present in milk fat from cattle at about the same concentration as in caudal fat, and lactation appeared to contribute to decontamination. Wool grease from sheep contained about 1 to 2 times the concentration of PCBs in subcutaneous fat. Calves of contaminated cows also became contaminated. The half-life for decontamination of PCBs in a group of 8 young female beef cattle was calculated at 13 months. PCBs were detected in pasture samples at concentrations ranging from less than 0.01 mg/kg to 0.12 mg/kg. However, PCBs were not detected in any sample of hay cut from these paddocks. In 4 sheep fed a sole ration of this hay, traces of PCBs were detected in their fat following 89 days of feeding. Grazing livestock for meat production on land contaminated with PCBs is not recommended because livestock readily acquire residues, and PCBs persist in soil and livestock for long periods. Grazing sheep for wool production on land contaminated with PCBs may be an option.