NASA's Satellite Laser Ranging Systems for the 21st Century.

For over 40 years, NASA's global network of satellite laser ranging (SLR) stations has provided a significant percentage of the global orbital data used to define the International Terrestrial Reference Frame (ITRF). The current NASA legacy network is reaching its end-of-life and a new generation of systems must be ready to take its place. Scientific demands of sub-millimeter precision ranging and the ever-increasing number of tracking targets give aggressive performance requirements to this new generation of systems. Using lessons learned from the legacy systems and the successful development of a prototype station, a new network of SLR stations, called the Space Geodesy Satellite Laser Ranging (SGSLR) systems, is being developed. These will be the state-of-the-art SLR component of NASA's Space Geodesy Project (SGP). Each of SGSLR's nine subsystems has been designed to produce a robust, kilohertz laser ranging system with 24/7 operational capability and with minimal human intervention. SGSLR's data must support the aggressive goals of the Global Geodetic Observing System (GGOS), which are 1 millimeter (mm) position accuracy and 0.1 mm per year stability of the ITRF. This paper will describe the major requirements and accompanying design of the new SGSLR systems, how the systems will be tested, and the expected system performance.

Changes in plasma enzyme activities and other blood components in response to acute and chronic liver damage in cattle.

Three calves were dosed orally with carbon tetrachloride at 0.05, 0.1 or 0.3 ml/kg body-weight. Plasma enzyme activities, clotting times, bilirubin concentrations and bromsulphthalein elimination times increased. These changes are associated with damage to the liver and are discussed in relation to the clinical syndrome. Three groups of seven calves were infected weekly with 10, 50 or 100 Fasciola hepatica metacercariae for 12 consecutive weeks. Maximum glutamate dehydrogenase and gamma glutamyltransferase activities in the plasma were greater with the larger infecting doses but there was no change in plasma clotting times.

Effect on calves of barley naturally contaminated with ochratoxin A and groundnut meal contaminated with low concentrations of aflatoxin B1.

Four groups of six 12-week-old male Friesian calves were fed diets containing 390 to 540 microgram ochratoxin A per kg, 320 to 500 microgram ochratoxin A plus 12 to 13 microgram aflatoxin B1 per kg, 10 to 13 microgram aflatoxin B1 per kg, or a control diet containing neither toxin. At the end of the 87-day experiment there was no evidence of kidney or liver damage in any group of animals as judged by serial plasma and urine enzyme assays, haematological examinations including the assay of blood coagulation factors, gross appearance at autopsy or histopathological assessment at the light microscopic level. Nor was there any significant alteration in serum IgA, IgM, IgG1 and IgG2 levels or in titres to environmental bacterial and viral antigens. Trace amounts of ochratoxin A were detected in kidneys of five out of the 12 calves exposed to this toxin but all 12 kidneys contained residues of the metabolite ochratoxin alpha (less than 5 to 10 microgram/kg). Traces of aflatoxin B1 and M1 were detected in the liver of one of the 12 calves exposed to aflatoxin B1 but nine kidneys contained the metabolite aflatoxin M1 (less than 0.01 to 0.03 microgram/kg). There was no evidence of interaction between the two toxins.

Aflatoxin B1 in dairy concentrates and other animal feedstuffs.

Over a period of 13 years 740 samples of various animal feedstuffs were analysed for the presence of aflatoxin B1. Nearly 500 were suspected of causing disease in farm animals but aflatoxin B1 could be detected in only 13.6 per cent of them. Groundnut meal samples nearly always contained the toxin but compounded feeds were contaminated to a varying extent. In particular, none could be detected in 62 poultry feeds. Where mycotoxicosis was suspected in dairy cattle, aflatoxin B1 was present at levels of more than 30 micrograms per kg in about 27 per cent of associated feed samples. In other dairy feeds (178 samples) this level of contamination was present in only about 9 per cent of samples. Concentrations of aflatoxin B1 likely to produce toxic effects (100 micrograms per kg and above) were present in about 4 per cent of suspect dairy concentrates but in 1 per cent or less of others. Contamination of dairy concentrates with aflatoxin B1 is usually at such a level that cows probably excrete the toxic metabolite aflatoxin M1 in milk at very low concentrations of 0.1 micrograms per litre or less.

The biological selenium status of livestock in Britain as indicated by sheep erythrocyte glutathione peroxidase activity.

The reliability of erythrocyte glutathione peroxidase activity as an indicator of selenium status in livestock is discussed. Based on this measurement, a survey is described of the biological selenium status of sheep on each of 329 farms in Britain. Results showed that 47 per cent of these farms were probably unable to provide grazing livestock with sufficient selenium to maintain blood levels greater than 0.075 microgram per ml. Increased selenium deficiency from the increasing use of home grown feeds as a major constituent of livestock rations may be causally related to the increase of white muscle disease and other selenium responsive diseases in Britain.

Some observations on "paralytic myoglobinuria" of cattle in Britain.

Characteristics of 44 outbreaks of "paralytic myoglobinuria" in yearling cattle reported to veterinary investigation centres during 1974 and 1975 are described. The clinical syndrome and associated nutrition and management of cattle are discussed in the light of present knowledge of this disease with particular reference to the diagnostic and epidemiological value of plasma creatine phosphokinase and blood glutathione peroxidase activities.

Investigation of suspected cases of mycotoxicosis in farm animals in Britain.

Mycotoxins were detected in 13 out of 131 feed samples examined over two years. Screening of feeds associated with cases of suspected mycotoxicosis occurring in farm animals over a further 12 month period showed that most incidents occurred during the winter and involved mainly cattle and pigs fed concentrates. A haemorrhagic syndrome in cattle and abortions in sows were most frequently connected with mouldy food. One or more known toxins (the aflatoxins, ochratoxin A, sterigmatocystin and zearalenone) were detected in three out of 65 cases and a wide variety of fungi were isolated. Toxicity to experimental animals was demonstrated in four out of 22 samples.

Border disease: a sequential study of surviving lambs and an assessment of its effect on profitability.

Pregnant Dorset horn gimmers inoculated with a non-cytopathic strain of the border disease virus produced "hairy shaker" lambs that were individually affected to a varying degree. Surviving lambs were observed for a period of up to 20 weeks when neurological signs were seen to gradually disappear. During this time live virus was isolated from a wide variety of sites in nearly all of the infected lambs. The infected animals grew at a significantly slower rate compared with the controls, particularly during the first 15 weeks. Several morphological defects are described the most consistent being the decreased weight of the central nervous system. By 20 weeks body-weights were about 20 per cent lower and carcase quality scores were reduced. An assessment is made of the economic losses attributable to BD taking into consideration carcase quality at 20 weeks and the perinatal losses.

Feed associated haemorrhagic disorder in pigs accompanied by pancreatic lesions.

The introduction of a new batch of feed to 400 pigs aged five to eight weeks resulted in 38 deaths and further morbidity associated with multiple haemorrhages. Signs abated within two days of withdrawal of the feed. Widespread haemorrhages were present in many tissues including the pancreas. Additional pancreatic lesions comprised focal necrosis, atrophy and fibrosis of exocrine tissue. The condition was reproduced experimentally in pigs and vitamin K protected mice against the injurious effects of the feed. The cause was not determined but it is speculated that more than one toxic factor and an imbalance of nutritional factors may have been present in the diet.

The failure of trichothecene mycotoxins and whole cultures of Fusarium tricinctum to cause experimental haemorrhagic syndromes in calves and pigs.

Piglets and calves were dosed orally with pure diacetoxyscirpenol (DAS) and T-2 toxin, crude extracts of Fusarium tricinctum containing T-2 toxin, and whole cultures of F tricinctum containing T-2 toxin at a constant daily rate of 0.1 mg toxin per kg body-weight (piglets) or 0.2 mg toxin per kg body-weight (calves). The treatment continued for periods of seven to 78 days but it failed to induce clinical haemorrhagic syndromes. Increasing the dose of F tricinctum culture five-fold for eight days following 78 days at the lower dose was equally ineffective. The lack of an effect by daily intakes of toxin that could have been ingested with naturally contaminated feedstuffs suggests that DAS, T-2 toxin and other metabolites of F tricinctum probably have little or no part to play in the aetiology of feed associated haemorrhagic disease.

Biochemical indicators of liver injury in calves with experimental fascioliasis.

Twenty calves were infected with 1000 metacercariae of Fasciola hepatica, the activities of 10 enzymes in plasma or serum were assayed and concentrations in serum of proteins, urea and bilirubin were determined. These values were compared with control data obtained from 14 uninfected calves. Aspartate aminotransferase, lactate dehydrogenase, sorbitol dehydrogenase, glutamate dehydrogenase, ornithine carbamoyl transferase and gamma-glutamyl transpeptidase activities increased in infected calves. Total serum protein increased, albumin decreased, globulin increased and the albumin/globulin ratio was decreased in infected calves. Plasma alanine aminotransferase, leucine aminopeptidase, alkaline phosphatase and cholinesterase activities and serum concentration of urea and bilirubin were unaffected. It was concluded that glutamate dehydrogenase and gamma-glutamyl transpeptidase were the most sensitive indicators of liver cell damage in fascioliasis.

Bovine virus diarrhoea-mucosal disease virus: pathogenicity for the fetal calf following maternal infection.

Fifteen pregnant, bovine virus diarrhoea-mucosal disease (BVD-MD) antibody-free Jersey heifers were infected experimentally with a mixture of 10 cytopathic strains of BVD-MD virus isolated from cattle in Britain. Each cow was inoculated intramuscularly on gestation day 100 with a high or a low dose of virus grown in primary calf testis tissue cultures. None of the cows showed clinical signs of illness following exposure, but all had seroconverted within six weeks. Six fetuses, including one set of twins, died in utero following infection. Of these five were aborted between days 136 and 154; the sixth one was mummified and still retained at day 300. The remaining 10 fetuses survived to term, but all showed evidence of intrauterine growth retardation with or without gross malformation and/or dysmyelination of the central nervous system. Three were clinically affected with congenital nervous disease. Of the 10 liveborn fetuses, two had specific serum antibodies to BVD-MD. Non-cytopathic BVD-MD virus was recovered from all of the remaining eight. When non-immune cows become infected with BVD-MD virus in mid gestation: transplacental infection of the fetus will probably result; apart from the risk of fetal death, with or without abortion, there is a high probability of fetal mal-development which may not always be clinically obvious; the immunological competence of the fetus may be impaired; congenital infection is likely in a substantial proportion of liveborn calves. About one in 16 bovine fetuses in British herds are estimated to be at risk from BVD-MD virus infection.