Impact of antibiotics on fluorescent Pseudomonas group and Bacillus cereus group isolated from soils exposed to effluent or waste from conventional and organic pig farming.

AIMS: To determine if antibiotics associated with conventional pig farming have a direct role in altering the populations of key soil micro-organisms isolated from piggery environments with and without exposure to antibiotics. METHODS AND RESULTS: Fluorescent Pseudomonas sp. and the Bacillus cereus group from soils adjacent to four conventional piggeries (use of antibiotics) exposed to effluent (via irrigation) and two organic piggeries (non-use of antibiotics) were assessed against nine relevant antibiotics using disc diffusion. The focus of the study was not to determine antibiotic resistance (or sensitivity) of isolates based on the manufacturer-defined sensitive break point, instead this point was used as the interpretation point to compare the populations (i.e. farm/organism combination) for the antibiotics tested. Each population was statistically analysed to determine whether the mean diameters were significantly above this selected interpretation point. Bacterial species from both environments did not show a distinct population pattern linked to the antibiotics. CONCLUSIONS: Antibiotics associated with conventional pig farming do not have a direct role in altering the environmental populations of Pseudomonas and Bacillus sp. when assessed by population shifts. SIGNIFICANCE AND IMPACT OF THE STUDY: This study confirms that an understanding of the resident soil microbiota, as compared to the transient bacteria of pig origin, is important in addressing the impact of antibiotic usage on the food-chain as a consequence of effluent re-use in, and around, pig farms.

Methods to determine resistance to anthelmintics when continuing larval development occurs.

The in vivo faecal egg count reduction test (FECRT) is the most commonly used test to detect anthelmintic resistance (AR) in gastrointestinal nematodes (GIN) of ruminants in pasture based systems. However, there are several variations on the method, some more appropriate than others in specific circumstances. While in some cases labour and time can be saved by just collecting post-drench faecal worm egg counts (FEC) of treatment groups with controls, or pre- and post-drench FEC of a treatment group with no controls, there are circumstances when pre- and post-drench FEC of an untreated control group as well as from the treatment groups are necessary. Computer simulation techniques were used to determine the most appropriate of several methods for calculating AR when there is continuing larval development during the testing period, as often occurs when anthelmintic treatments against genera of GIN with high biotic potential or high re-infection rates, such as Haemonchus contortus of sheep and Cooperia punctata of cattle, are less than 100% efficacious. Three field FECRT experimental designs were investigated: (I) post-drench FEC of treatment and controls groups, (II) pre- and post-drench FEC of a treatment group only and (III) pre- and post-drench FEC of treatment and control groups. To investigate the performance of methods of indicating AR for each of these designs, simulated animal FEC were generated from negative binominal distributions with subsequent sampling from the binomial distributions to account for drench effect, with varying parameters for worm burden, larval development and drench resistance. Calculations of percent reductions and confidence limits were based on those of the Standing Committee for Agriculture (SCA) guidelines. For the two field methods with pre-drench FEC, confidence limits were also determined from cumulative inverse Beta distributions of FEC, for eggs per gram (epg) and the number of eggs counted at detection levels of 50 and 25. Two rules for determining AR: (1) %reduction (%R)<95% and lower confidence limit <90%; and (2) upper confidence limit <95%, were also assessed. For each combination of worm burden, larval development and drench resistance parameters, 1000 simulations were run to determine the number of times the theoretical percent reduction fell within the estimated confidence limits and the number of times resistance would have been declared. When continuing larval development occurs during the testing period of the FECRT, the simulations showed AR should be calculated from pre- and post-drench worm egg counts of an untreated control group as well as from the treatment group. If the widely used resistance rule 1 is used to assess resistance, rule 2 should also be applied, especially when %R is in the range 90 to 95% and resistance is suspected.

In vitro infection of sheep lice (Bovicola ovis Schrank) by Steinernematid and Heterorhabditid nematodes.

Control of sheep lice with conventional pesticides can be compromised by difficulty in contacting lice in the dense water repellent fleeces of sheep, particularly when sheep have not been recently shorn. Entomopathogenic nematodes (ENs) are motile and are able to actively seek out insect hosts. They have particular advantages for the control of pests in cryptic habitats, such as the fleeces of sheep and avoid many of the problems frequently associated with chemical controls. This study investigated whether ENs were able infect and kill Bovicola ovis and compared the effectiveness of different species at different temperatures and when applied to wool. Four species of nematodes, Steinernema carpocapsae, Steinernema riobrave, Steinernema feltiae and Heterorhabditis bacteriophora were tested. All were shown to infect and kill lice in Petri dish assays at 30°C. At 35°C, the percent infection for S. carpocapsae and S. riobrave was significantly higher than for the other two species and percent infection by S. feltiae was significantly greater than for H. bacteriophora (P<0.05). At 37°C the percent mortality induced by S. riobrave was significantly greater than for S. carpocapsae (P<0.05). All species were able to locate and infect lice in wool when formulated in water with 8% Tween 80. In wool assays the percent lice infected with nematodes was significantly greater for S. riobrave than H. bacteriophora at 25°C, but there were no other differences between species (P=0.05). S. carpocapsae, S. riobrave and S. feltiae caused significantly higher lice mortality than H. bacteriophora at both 25 and 35°C in wool assays, but mortality induced by the three steinernematid species did not differ significantly (P>0.05). It is concluded that of the ENs studied S. riobrave is likely to be most effective against B. ovis when applied to live sheep because of its greater tolerance to high temperatures and 'cruiser' foraging strategy.

Reduced efficacy of macrocyclic lactone treatments in controlling gastrointestinal nematode infections of weaner dairy calves in subtropical eastern Australia.

Faecal Egg Count Reduction Tests (FECRTs) for macrocyclic lactone (ML) and levamisole (LEV) drenches were conducted on two dairy farms in the subtropical, summer rainfall region of eastern Australia to determine if anthelmintic failure contributed to severe gastrointestinal nematode infections observed in weaner calves. Subtropical Cooperia spp. were the dominant nematodes on both farms although significant numbers of Haemonchus placei were also present on Farm 2. On Farm 1, moxidectin pour-on (MXD) drenched at 0.5mg kg(-1) liveweight (LW) reduced the overall Cooperia burden by 82% (95% confidence limits, 37-95%) at day 7 post-drench. As worm burdens increased rapidly in younger animals in the control group (n=4), levamisole was used as a salvage drench and these calves withdrawn from the trial on animal welfare grounds after sample collection at day 7. Levamisole (LEV) dosed at 6.8mg kg(-1)LW reduced the worm burden in these calves by 100%, 7 days after drenching. On Farm 2, MXD given at 0.5mg kg(-1)LW reduced the faecal worm egg count of cooperioids at day 8 by 96% (71-99%), ivermectin oral (IVM) at 0.2mg kg(-1)LW by 1.6% (-224 to 70%) and LEV oral at 7.1mg kg(-1)LW by 100%. For H. placei the reductions were 98% (85-99.7%) for MXD, 0.7% (-226 to 70%) for IVM and 100% for LEV. This is the first report in Australia of the failure of macrocyclic lactone treatments to control subtropical Cooperia spp. and suspected failure to control H. placei in cattle.

Effect of genetic merit and concentrate feeding on reproduction of grazing dairy cows in a subtropical environment.

This study was conducted to determine the effects of genetic merit for milk production and concentrate feeding on the intervals to the onset of postpartum cyclic ovarian activity, first insemination, and establishment of pregnancy. Other factors considered included biochemical measures of energy balance, liveweight, and measures of production. A farmlet study was conducted with two lines of cattle that differed in Australian Breeding Value by 735 L milk and 47 kg of fat plus protein that were fed 300 or 2000 kg of concentrate per cow per year in a subtropical grazing system based on ryegrass, clover, and kikuyu pasture. Milk yield was higher in cows fed 2000 kg of concentrate per cow per year (23.6 L/d) than those fed 300 kg/cow per year (18.2 L/d), and cows of medium genetic merit (19.6 L/d) produced less milk than those of high genetic merit (22.2 L/d). Plasma glucose concentration was lower in the cows of high genetic merit (3.11 mmol/L), than in the cows of medium genetic merit (3.39 mmol/L). The cumulative probabilities of ovulation, insemination, and establishment of pregnancy by any day postpartum were determined by a Weibull distribution. Medium genetic merit cows in winter were more likely to ovulate by any day postpartum than in summer and more likely than high genetic merit cows in either summer or winter. The cumulative probability of insemination was lower in primipara than multipara and in summer than in winter. Primiparous cattle had a lower cumulative probability of pregnancy by any day postpartum.

The significance of leptospiral titres associated with bovine abortion.

To investigate relationships between serological titres to 2 serovars, pomona (L. pomona) and hardjo (L. hardjo), of Leptospira interrogans and abortions, log linear and logit models were fitted to herd and individual cow data from cattle serologically negative for brucellosis. Serological titres to both serovars were significantly related to abortions in individual cows, with L. pomona having a stronger relationship than L. hardjo. L. hardjo was not significant when herd data were analysed. Differences between dairy and beef cattle in the serological titres found to both L. pomona and L. hardjo were detected when data sets of all cattle or cattle with no history of abortion were analysed. The beef/dairy differences may be due to different management practices and/or to different geographical distributions of both serovars and populations of beef and dairy cattle. If there are no cattle in a herd with a reciprocal titre of 3000 or greater for L. pomona, it is unlikely that L. pomona is associated with the abortion problem. There was no specific L. hardjo titre which separated high and low probabilities that the serum came from a cow or herd with an abortion history.