Herd management practices and the transmission of Johne's disease within infected dairy herds in Victoria, Australia.

A retrospective cohort study involving 137 dairy herds randomly selected from all 390 participating in the Victorian Test and Control Program for bovine Johne's disease was undertaken to gain insight into the relationships between calf rearing practices and the occurrence of bovine Johne's disease on infected dairy farms. Each study farm was visited between July 2005 and January 2006 and a structured survey examining herd management and calf rearing practices was completed. The resultant data, along with information from annual herd testing for Johne's disease and records of clinical Johne's disease diagnosed in the herd, from May 1990 to March 2008, were analysed. Factors associated with time to the birth of the animal that was the first home-bred clinical case of Johne's disease or ELISA positive animal born after the second annual whole herd test in the herd were investigated using survival analysis methods. The publicly-subsidised Test and Control Program commenced in 1996. On the 1st of July 2003 the program was modified with more rigorous and externally audited calf rearing requirements introduced for all participants. The more stringent calf rearing requirements introduced in July 2003 appear to have translated into significantly reduced disease transmission within the infected study herds.

Effect of compliance with recommended calf-rearing practices on control of bovine Johne's disease.

OBJECTIVE: To assess the degree of compliance with recommended management procedures for the control of bovine Johne's disease and study the relationship between aspects of calf management and testing/disease outcomes in the herds. PROCEDURE: Fifty-four south Gippsland dairy herds participating in the Victorian bovine Johne's disease test and control program were visited between July and November 2002 and an audit of calf rearing practices was conducted. The results of testing completed under the program were analysed for each of the herds. Twenty seven management factors were examined for a relationship with the presence of clinical cases of Johne's disease or cattle with positive ELISA test results that were born after the completion of the second whole herd test. Logistic regression was used to examine the strength of relationships between the management practices and the frequency with which new cases of Johne's disease arose. RESULTS AND CONCULSIONS: Calves were removed from their dams within 12 hours of birth in only 17 (31.5%) of the herds. However, in all but one herd the calves were removed within 24 hours of birth. In 42 herds (77.8%) calf rearing facilities were adequately separated from adult cattle and the faeces from adult cattle. In 41 herds (75.9%) calves up to the age of 12 months were grazed on paddocks that were free of manure or effluent from adult cattle. However, in only 10 (18.5%) of the herds were all three of these calf management practices applied. Feeding whole milk containing antibiotic residues, or providing water for calves from birth, were found to have statistically significant associations with an increased occurrence of cases of bovine Johne's disease in the study herds. The practice of allowing cows to calve in a paddock was found to be associated with reduced occurrence of bovine Johne's disease. These associations were still found after analysis that included herd size, the number of clinical cases that had occurred in the herds before the start of testing, the number of animals with positive ELISA tests that were detected at the first test and the number of years of participation in the test and cull program. Early separation of newborn calves from cows and grazing calves under 12 months of age in areas free of adult cattle were not found to be protective against Johne's disease.

The skeletodental adaptations in deep bite correction.

The purpose of this study was to analyze the skeletal and dental changes produced by orthodontic correction of a deep bite. A comparison was made between the adolescents' and the adults' responses in an attempt to observe any differences that accounted for increased stability in a growing patient. Records on 30 patients were analyzed before and after treatment. These patients were divided into two equal groups on the basis of their stage of maturational development. The group of "growers" had an average age of 12.2 years, and the group of "nongrowers" averaged 26.7 years in age. All represented nonextraction cases with an excessive overbite before treatment. Deep bite was corrected by leveling with conventional continuous arch wires. Cervical headgear, Class II, or vertical elastics were used when indicated. On the average, the molars were extruded 4.7 mm in the grower's group. However, the mandibular plane angles did not change during treatment. This finding can be attributed to the greater amount of posterior mandibular development that was observed in growing patients. Even with minimal extrusion of the molars (1.3 mm on average), the adults did not maintain the original mandibular plane angle.

The relationship between bite depth and incisor angular change.

A geometric, two-dimensional model was developed, which estimates the effect of changing incisal angular position to the effective bite depth. Because of the constant lengths of incisors whose long axes can be viewed as the sides of a triangle, it is possible to calculate the amount of their overlap as a function of changing angle. Additionally, a distinction is made between controlled and uncontrolled tipping, defined in respect to their centers of rotation. It is suggested that an average of 0.1 to 0.2 millimeter change in overbite occurs for every degree of incisal angular change.