Progress in national control and assurance programs for ovine Johne's disease in Australia

Since the detection of ovine Johne's disease in Australia in 1980, 578 flocks have been diagnosed as infected, with 442 of these still infected. The disease was initially believed to be confined to the central tablelands area of NSW, but has subsequently been shown to be more widely distributed. Sheep strains of M. paratuberculosis are known to infect sheep and goats in south-eastern Australia. Although sheep strains have recently been identified in some cattle in Australia, epidemiological evidence to date supports the distinction between ovine Johne's disease, caused by sheep strains in sheep and goats, and bovine Johne's disease, caused by cattle strains in cattle, goats and alpaca, as a basis for control and eradication strategies. Four national initiatives to control and better understand OJD are outlined. The Australian Johne's Disease Market Assurance Program for sheep was launched in May 1997. By December 1998, 548 flocks had achieved an assessed negative status. Three flocks assigned a flock status have subsequently been found to be infected. National standards for State control of Johne's disease through zoning, movement controls and procedures in infected and suspect flocks have also been developed. In addition, a $40.1 m National Ovine Johne's Disease Control and Evaluation Program was agreed to in August 1998, and is currently being implemented. It is jointly funded by National and State industries, and Commonwealth and State governments. Its objectives are to deliver, through research and surveillance, a solid basis for a future decision on the most appropriate course for dealing with OJD and to maintain control of OJD nationally.     

Progress in national control and assurance programs for bovine Johne's disease in Australia

Cattle strains of Mycobacterium paratuberculosis are known to infect cattle, goats and alpaca in southeastern Australia, where there are also significant numbers of farmed deer. Although sheep strains have recently been identified in some cattle in Australia, epidemiological evidence to date supports the distinction (between bovine Johne's disease (JD), caused by cattle strains in cattle, goats and alpaca, and ovine JD, caused by sheep strains in sheep and goats) for the purposes of control and assurance programs. The National Johne's Disease Control Program is coordinated by the Australian Animal Health Council, working with the livestock industries and with the Commonwealth, state and territory governments. The council also brokers industry and government funding for the program. The National Johne's Disease Market Assurance Program for Cattle was launched in 1996 as the first of a suite of voluntary national market assurance programs (MAPs) to assess and certify herds as negative for JD. By December 1998, over 550 herds had achieved an assessed negative status. A MAP was also launched for alpaca in 1998 and a program for goats should be finalized in early 1999. National standards for state control of JD through zoning, movement controls and procedures in infected and suspect herds have also been developed. The paper covers factors affecting development and implementation, uptake of and improvements to national control and assurance programs for bovine JD in Australia.     

Cystic fibrosis locus defined by a genetically linked polymorphic DNA marker

A polymorphic DNA marker has been found genetically linked, in a set of 39 human families, to an autosomal recessive gene that causes cystic fibrosis (CF), a disease affecting one in 2000 Caucasian children. The DNA marker (called D0CRI-917) is also linked to the PON locus, which by independent evidence is linked to the CF locus. The best estimates of the genetic distances are 5 centimorgans between the DNA marker and PON and 15 centimorgans between the DNA marker and the CF locus, meaning that the location of the disease gene has been narrowed to about 1 percent of the human genome (about 30 million base pairs). Although the data are consistent with the interpretation that a single locus causes cystic fibrosis, the possibility of genetic heterogeneity remains. The discovery of a linked DNA polymorphism is the first step in molecular analysis of the CF gene and its causative role in the disease.     

Renal lesions in cattle fed sodium hydroxide-treated barley

Ten 14-week-old calves were fed a diet containing 87.5% NaOH-treated barley, and killed after 29, 65, 75, 117, 140, 179, 314, 338, and 408 days. Eight control calves were fed a diet in which untreated rolled barley was substituted for alkali-treated grain. Calves receiving NaOH-treated barley became polyuric with urine pH ranging from 9.0 to 9.5, and had significantly raised plasma creatinine levels on day 29. Other clinical findings were normal, and there were no other significant alterations in blood. At necropsy, bilateral renal lesions consisted of white cortical foci, medullary stippling, and the presence of uroliths in the renal papillae and calyces. Microscopic changes included tubular dilatation, atrophy, necrosis, and mineralization, interstitial fibrosis with mononuclear cell invasion and consequent glomerular changes. It appeared that glomerular and interstitial changes were secondary to primary tubular damage. No abnormalities were detected in control calves. Feeding of NaOH-treated barley can result in nephrotoxicosis in cattle.     

Antibody avidity in Yorkshire pigs of high and low immune response groups.

Avidity indices of antibody to hen egg-white lysozyme (HEWL) were measured by chaotropic ion (SCN-) elution enzyme-linked immunosorbent assay (ELISA) in pigs grouped as high, control or low for various immune and innate resistance-related traits. The avidity index was the molar concentration of SCN- required to reduce by 50% the ELISA optical density value for a given serum. The index was independent of the amount of antibody. Eight- to ten-week-old Yorkshire pigs were immunized with HEWL and serum antibody measured by ELISA as one of five traits used to assign them to high, low or control response groups. Serum antibody avidity for HEWL was evaluated on Day 14 and Day 30 after primary (Day 0) and secondary (Day 14) immunization. The effects of response group, gender, litter, serum IgG concentration and anti-HEWL antibody on avidity were determined using a linear model. Antibody avidity indices varied amongst individuals. Mean avidity indices for sera collected on Days 14 and 30 were 0.61 +/- 0.43 and 1.22 +/- 0.56, with maximum indices of 2.64 and 2.86 respectively. Avidity of secondary response antibody was significantly higher (P less than or equal to 0.05). Pigs of the high response group had significantly higher secondary antibody avidity than those of the control (P less than or equal to 0.08) and low groups (P less than or equal to 0.01). Avidity index was positively correlated with antibody to HEWL on Days 14 and 30 but not to preimmunization serum IgG concentration or to other measured traits.     

Effect of culling on selection response using phenotypic selection or best linear unbiased prediction of breeding values in small, closed herds of swine.

Records from 7,200 separate closed herds with either 12 or 25 sows that were mated to either four or eight boars per year were simulated by computer. Effects of selection method, herd size, and contemporary group variability on average genetic change, genetic variance, and inbreeding over 10 yr of selection were analyzed for traits with heritabilities of .1, .3, and .6. Selection of replacement animals was on individual phenotype or BLUP of breeding value using a reduced animal model. For both of these selection methods, two culling schemes were imposed: 1) based only on involuntary culling because of losses due to conception rate and age and 2) when an available replacement animal was projected to be superior to an existing breeding animal in the herd in addition to the involuntary culling. The contemporary group standard deviation was set at either .1 or .5 of a phenotypic standard deviation. Selection with BLUP gave 72, 36, and 12% more genetic improvement for heritabilities of .1, .3, and .6, respectively, than selection on individual phenotype after 10 yr. However, inbreeding increased 20 to 52% more rapidly and there was a decrease in genetic variance. Culling based on Scheme 2 increased genetic improvement over Scheme 1 by about 75% with coincident increases in inbreeding level and decreases in genetic variance. The largest changes in inbreeding and genetic variance were associated with culling on BLUP. Culling when a superior animal was available with individual phenotype had little effect on inbreeding and genetic variance. Use of four boars rather than eight boars and 25 rather than 12 sows per herd increased genetic response. Use of four boars also increased inbreeding and decreased genetic variance. Genetic variance was higher in herds with 25 sows, but the size of the sow herd had little effect on inbreeding. Contemporary group variation influenced only the genetic response of individual phenotypic selection with culling.     

Genetic comparison of ovine and bovine pestiviruses

Viral RNA oligonucleotide fingerprinting was used to compare genetic relationship among pestiviruses originating from ovine or bovine host species. Ovine pestiviruses, including reference border disease virus and 2 border disease isolates originating from natural pestivirus infections of sheep, appeared to have a more distant genetic relationship among themselves than with certain bovine pestiviruses. A closer genetic relatedness was evident between border disease virus and 3 noncytopathic bovine pestiviruses, including Draper bovine viral diarrhea virus (BVDV), a BVDV isolate that originated from aborted bovine fetuses, and a virus that was isolated from the serum of a calf that had a chronic BVDV infection. Four noncytopathic bovine viruses, including Draper BVDV and 3 field isolates, were closely related. Reference Oregon C24V BVDV, a cytopathic virus, was closely related to only 1 of the 7 noncytopathic viruses in this study.     

The effects of androgens and gonadotropins on testicular development in the prepubertal rat.

Treatment of male rat pups from five to 34 days of age with dihydrotestosterone or 5 alpha-androstane-3 alpha, 17 beta-diol, resulted in reduced testicular size at 35 days of age. This appeared to be due to decreased tubular diameters and reduced spermatocyte numbers, especially late pachytene cells in stages X to XIII. In rat pups treated with dihydrotestosterone or 5 alpha-androstane-3 alpha, 17 beta-diol, treatment with luteinizing hormone resulted in some restoration of tubular diameter and spermatocyte numbers. In 5 alpha-androstane-3 alpha, 17 beta-diol treated rat pups partial restoration of testes size resulted from follicle-stimulating hormone treatment, but tubular diameter and spermatocyte numbers were depressed. Single serum samples collected at 35 days of age were analysed for luteinizing and follicle-stimulating hormone concentrations. These data indicated that the effects of administered androgens were due primarily to depression of circulating gonadotropin concentrations but a direct inhibition at the level of the testis could not be ruled out.     

Laparoscopy in zoological medicine.

The technique of laparoscopy was adapted and utilized in zoological medicine for various mammals, birds, and reptiles for reproductive and diagnostic studies as well as clinically related research. It was concluded that since anesthesia was routinely required for most manipulative procedures in zoo animals, and since laparoscopy adds little additional risk, the use of this technique provides an additional diagnostic aid when indicated. Laparoscopy was found to be effective for evaluating reproductive status, particularly ovarian anatomy and function, direct visual biopsy of internal organs, sex determination in selected birds, and as a surgical means of fertility control.     

Plant growth substance action on lecithin and lecithin/cholesterol vesicles

The adsorption of some plant growth regulating compounds onto lecithin and equimolar lecithin/cholesterol vesicles and the effect of these substances on the rate of chloride/nitrate and sodium/potassium ion exchange across the vesicular membranes have been examined. On comparing the binding of 2,4-D, 2,6-D, 2,4,5-T and IAA to lecithin vesicles in solution at various pH values it is found that the unionised form of these acids is bound very much more strongly than the ionised form. Compounds having relatively low oil/water partition coefficients such as 2,4-D, 2,6-D and 2,4,5-T are adsorbed onto vesicles, from solutions containing equimolar equilibrium concentrations of the unionised molecules, to markedly different extents (depending on the structure of the lipophilic portion of these molecules). Where the oil/water partition coefficient is higher, as for 2,4-dichlorophenol and 2-(2,4-dichlorophenoxy)ethanol, binding to vesicles may also arise due to non-specific solution within the hydrocarbon region of the lipid bilayers. The affinity of these compounds for lecithin has also been assessed by noting the extent to which the inclusion of lecithin in the oil phase increases the oil/water partition coefficient. This has shown that affinity for lecithin depends on the structure of both the lipophilic and hydrophilic portions of the molecule. Only the unionised form of the compounds examined had any large effect on ion flux across the vesicle membranes. Significant increases in the rate of chloride/nitrate exchange were obtained on introducing quite high concentrations (0.015 to 1.5 mM) of the compounds 2,4-D, 2,6-D, 2,4,5-T, IAA, and 2,4-dichlorophenol, but not 2,4-dichlorophenoxyethanol, to suspensions of lecithin vesicles. Similar flux increases were observed with lecithin/cholesterol vesicles except that more pronounced effects on flux were obtained on adding 2,4-dichlorophenol and 2,4-dichlorophenoxyethanol. In contrast 2,4-D, 2,6-D, 2,4-dichlorophenol and IAA had no significant effect on the rate of Na⁺/K⁺ ion exchange across lecithin vesicles although increases were observed with equimolar lecithin/cholesterol vesicles. Interpretations of these phenomena are suggested and their relevance to plant growth substance effects at the plasmalemma membrane discussed.