Neale R. Towers

Uptake of palytoxin‐like compounds by shellfish fed Ostreopsis siamensis (Dinophyceae)

Abstract Greenshell™ mussels (Perna canaliculus Gmelin), scallops (Pecten novaezealandiae Reeve), and Pacific oysters (Crassostrea gigas Thunberg) were fed with a New Zealand strain of mass cultured Ostreopsis siamensis Schmidt (for 27 and 84 h and with 1.5 × 106 or 8.6 × 106 cells, respectively) under laboratory conditions. The microalgal cells contained 0.3 pg palytoxin equivalents cell–1 (as determined by the haemolysis neutralisation assay (HNA) of Bignami (1993)) and extracts of these cells were toxic to mice after intraperitoneal injection. No palytoxin‐like material was detected either in the hepatopancreas or the muscle and roe of mussels fed O. siamensis. Oysters contained detectable amounts of toxin in hepatopancreas muscle, and roe while higher concentrations were present in the hepatopancreas of scallops. Extracts of control shellfish (tested biotoxin free and not fed O. siamensis) were toxic to mice, and there was no definitive evidence that feeding shellfish with O. siamensis at the levels employed in the present experiment increased the toxicity of shellfish tissue extracts to mice.

Polyclonal antibodies to domoic acid, and their use in immunoassays for domoic acid in sea water and shellfish.

Ovine antibodies raised against conjugates linked through the secondary amino group of domoic acid (1) were used, together with activated-ester-derived conjugates of domoic acid (DA) as the plate coater, to develop a robust indirect competitive enzyme-linked immunosorbent assay (cELISA) for DA in shellfish and seawater. The ELISA was used to analyze shellfish samples for DA, and was compatible with several extraction procedures. The ELISA had a detection limit below 0.01 ng ml(-1), a limit of quantitation (LOQ) of 0.15 ng ml(-1) and a working range of 0.15-15 ng ml(-1) DA. The LOQ is equivalent to 38 ng g(-1) DA in shellfish flesh, assuming a 250-fold dilution during extraction. This is more than 500 times lower than the maximum permitted level (20 microg g(-1) flesh). The ELISA is designed for use alongside regulatory analyses, and, following formal validation, should be available for pre-screening of regulatory shellfish flesh samples. The ELISA was also shown to be appropriate for analysis of DA in algal cultures and in samples of seawater, and thus has the potential to provide early warning of developing algal blooms.

Selection for or against facial eczema susceptibility in Romney sheep, as monitored by serum concentrations of a liver enzyme

Abstract Genetic selection for or against susceptibility to facial eczema (FE) was begun in Romney sheep in 1975, with the establishment of a resistant (R) selection flock, a susceptible (S) selection flock, and later a control (C) flock. For all but the initial years, rams were identified by performance testing with a sporidesmin challenge, ranking them on relative elevation of the liver enzyme, gamma glutamyltransferase (GGT) measured in serum. A different dose rate of sporidesmin was used for performance testing in the R and the S flocks, with a balanced half of the C‐flock animals being tested at each dose rate; in some years R‐flock animals showing no elevation of GGT were re‐dosed later at an even higher rate. Mixed‐model methodology was used to determine responses to selection, expressing results as a breeding value for logeGGT. Analyses took account of one dose rate used in the R flock and in half of the C flock, and a second (lower) dose rate used in the remainder of the C flock and in the S floc...

Isoptaquiloside and caudatoside, illudane-type sesquiterpene glucosides from Pteridium aquilinum var. caudatum

Ptaquiloside and two new illudane-type sesquiterpene glycosides were isolated from Pteridium aquilinum var. caudatum. One- and two-dimensional NMR analyses revealed the new glucosides to be isoptaquiloside and caudatoside. Four pterosins, A, B, K and Z, were also isolated from a base-acid treated extract.

Inheritance of resistance to facial eczema: a review of research findings from sheep and cattle in New Zealand

Abstract Facial eczema (FE) is a costly problem to New Zealand pastoral agriculture, and has a detrimental impact on animal wellbeing. Incidence and severity of the disease can be reduced by grazing management and zinc prophylaxis. An additional strategy is to breed animals that are genetically resistant to intoxication with sporidesmin, the causative mycotoxin. This review summarises research findings on the inheritance of resistance of animals to FE, including evidence of among- and within-breed genetic variation, direct and correlated responses to selection, and identification of genetic markers and candidate genes for FE resistance.

Responses achieved in Romney flocks selected for or against susceptibility to facial eczema, 1975–87

Abstract Genetic selection foror against resistance to the mycotoxicosis, facial eczema (FE), was begun in a Romney flock in 1975. Randomly selected ewes were mated with rams which had been previously identified by progeny testing as resistant (R) or susceptible (S) to FE. In subsequent years (until 1982), the same ewes and their daughters were again mated within flock to progeny-tested rams. From 1983 until 1987, performance testing was substituted for progeny testing. The most resistant R rams and most susceptible S rams by performance test were then used for mating in their respective flocks. Over these 5 years, young rams bred in the trial were performance-tested using a challenge with sporidesmin, the mycotoxin which causes FE. The severity of the liver damage induced was assessed by measuring plasma gamma-glutamyltransferase (GGT) activity. In 1982, two further flocks were established from a common Romney source as demonstration flocks; they were managed together with the R and S flocks. Six years o...

Antioxidants in blood from sheep lines divergently selected for facial eczema resistance

Abstract Romney sheep have been evaluated for resistance to facial eczema (FE) using a process which involves challenge with the FE toxin, sporidesmin, and they have been bred in selection lines for increased resistance (R) or susceptibility (S) to FE. There is evidence that sporidesmin exerts its toxic effects by generating reactive oxygen species, and protection can be afforded by a number of antioxidants and antioxidant enzymes. Our objective was to summarise three separate experiments to determine whether the R and S lines differed in antioxidant mechanisms, in search of a non‐invasive genetic marker. Lines were compared for the activities of four enzymes in blood in Experiment 1, superoxide dismutase (SOD), catalase (CAT), glu‐tathione peroxidase (GPX), and glutathione reduct‐ase (GR), and for the concentration of the tri‐peptide thiol, glutathione (GSH). SOD, CAT, and GSH were also recorded in Experiment 2, and GPX alone in Experiment 3. Heritabilities were estimated for SOD, CAT, and GSH. SOD activity was lower and CAT activity was higher in the R than in the S line (P < 0.01 for both enzymes). GPX activity was higher in the R than in the S line in Experiment 1 (P = 0.002) and Experiment 3 (P = 0.06), whilst neither GR activity nor GSH concentration differed significantly between lines. Heritability estimates for SOD, CAT, and GSH were 0.19 ± 0.11, 0.63 ± 0.14, and 0.34 ± 0.14, respectively. It is concluded that selection for divergence in sensitivity to sporidesmin in sheep may have been successful partly because of correlated responses in activities of three antioxidant enzymes (SOD, CAT, and GPX), capable of scavenging reactive oxygen species. However, the divergence between resistant and susceptible sheep in blood antioxidant activity was not large enough to be a reliable indicator of individual FE resistance.

Development of immunodiagnostic field tests for the detection of the mycotoxin, sporidesmin A

Three rapid immunoassays—immunofiltration, immunochromatography and dipstick—were developed for the detection of sporidesmin A, the mycotoxin responsible for facial eczema’, a disease which causes liver injury and photosensitization of livestock in New Zealand. Each assay format exhibited particular advantages and disadvantages with regard to assay sensitivity, working range and ease of use. The immunofiltration assay proved to be suitable for the detection of sporidesmin A in pasture due to its sensitivity and its potential to be used outside a laboratory environment. Semi‐quantitative scores of spiked pasture samples using the immunofiltration assay were in good agreement with the amount of sporidesmin A added to the samples.

A note on the genetics of resistance or susceptibility to ryegrass staggers in sheep

Abstract A flock of mainly Romney × Coopworth ewes was established to test sires for genetic differences in resistance to ryegrass staggers (RGS). This disease is a neurotoxic condition caused by ingestion of endophyte‐infected perennial ryegrass containing the mycotoxin, lolitrem B. Lambs, 18‐month males and females, and ewes of all ages were scored from January to March each year for RGS (0 or 1; 0 = no staggers), while grazing toxic pastures during natural outbreaks of RGS. Over 6 years (the autumns of 1988–93) and over all stock classes scored, age‐group means for RGS ranged from 0 to 0.16. A breeding value for RGS was calculated for each animal, incorporating data from all years and all age groups, provided that the mean year x age group score was at least 0.04. RGS data were also recorded on another Romney flock managed at the same site over the same time period. The heritability of RGS score over both flocks was 0.07 ± 0.02 and the repeatability over years was 0.24 ± 0.04. In March 1993, 170 ewes w...

Food quality on the farm: Immunological detection of mycotoxins in New Zealand pastoral agriculture

Mycotoxin research throughout the world focuses primarily on the problems associated with stored grains, legumes and the commodities produced from these feed stocks. While contaminated grains and legumes represent a direct threat of major importance to both human and animal consumers, they are not the only source of mycotoxins important to the agricultural sector. Grazing animals are exposed to mycotoxins produced by fungi resident in the pastures they graze, thus, in pastoral agricultural systems, a different spectrum of mycotoxicoses takes prominence. The analysis of toxins from herbage samples by conventional means (such as liquid chromatography and high‐pressure liquid chromatography) is often difficult, slow and expensive. Consequently, we have developed immunoassays which permit analysis of simple extracts and allow the rapid quantification of mycotoxins in large numbers of herbage samples. We detail enzyme‐linked immunosorbent assays using both polyclonal and monoclonal antibodies for the measureme...