Individual Animal Level Research Articles

An individual-animal-level prospective study of risk factors associated with the occurrence of lameness in the Michigan (USA) equine population

Abstract A prospective cohort study of lameness in Michigan equids was conducted using the Michigan Equine Monitoring System (MEMS) Phase-II data base. MEMS Phase II was an equine healthmonitoring study of 138 randomly-selected Michigan equine operations. Management and individual-animal health-related data were collected on operations for two consecutive 12-month periods. New cases of lameness were reported in 7.2% (284/3925) of the equids monitored during the 2-year study period. A multivariable logistic-binomial regression model for distinguishable data was developed to evaluate risk factors associated with the occurrence of lameness at the individual-animal level. Equids on larger operations were associated with a decreased risk of experiencing lameness (2nd Quartile (Q):Relative Risk (RR) = 0.42; 95% Confidence Interval (CO: 0.25-0.72, 3rd Q: RR = 0.58; 95% CI: 0.35-0.95, and 4th Q: RR = 0.44; 95% CI: 0.19-1.02). Equids participating in racing were at increased risk of experiencing lameness (RR = 1.75; 95% CI: 1.03-2.99). Equids participating in showing also tended to be at increased risk of experiencing lameness (RR = 1.44; 95% CI: 0.95-2.20). Increasing exercise intensity, or the number of days exercised per days available to exercise, was also associated with an increase in the risk of experiencing lameness (Low intensity: RR = 2.32; 95% CI: 1.54-3.51 and High intensity RR = 2.48; 95% CI: 1.58-3.90).

Unbiased stereological estimation of the total number of synapses in a brain region.

Modern stereological methods have been used to make unbiased estimates of the total number of synapses in the striatum radiatum of the hippocampal CA1 region of five rabbits. The approach used involved a two stage analysis and is generally applicable to all parts of the nervous system. During the first stage of the analysis, the reference volume was estimated by point counting, at the light microscope level, according to the Cavalieri principle. During the second stage, the numerical density of synapses was estimated with dissectors at the electron microscopic level. The total number of synapses was calculated as the product of the numerical density and the volume of the region. The sampling with points and dissectors was carried out in all three dimensions of the entire CA1 region in a manner that ensured that all parts of the region and all synapses within it had equal probabilities of being sampled. An analysis of the precision of the estimate of total synapse number has been performed in terms of the variances of volume and synaptic numerical density at different levels of sampling, i.e. at the level of points, sections, individual animals and group of animals. Detailed descriptions of the procedures used to estimate the total number of synapses, evaluate the precision of the estimates, and optimize the sampling scheme are provided.

Aggregate risk study of exposure to endophyte-infected (Acremonium coenophialum) tall fescue as a risk factor for laminitis in horses

SUMMARY Loline and ergot alkaloids found in endophyte-infected (Acremonium coenophialum) tall fescue (eitf) cause vasoconstriction of equine vessels in vitro. An aggregate risk study was used to evaluate the association between horses exposed to eitf and development of laminitis. Veterinary teaching hospitals participating in the Veterinary Medical Data Base were grouped by whether equine accessions were likely to have been at high, moderate, or low risk for exposure to eitf. From 1980-1990, there were 185,781 accessions, of which 5,536 had diagnosis of laminitis. Proportion of equine accessions with laminitis reported by veterinary teaching hospitals for high, moderate, and low risks, were 3.41, 3.04, and 2.00 cases/100 accessions, respectively (P < 0.0001). Comparison of the proportion of accessions with laminitis in the high- and moderate-risk groups with that in the low-risk group revealed significant differences between risk groups over all months (P = 0.063) and differences from month to month within risk groups (P = 0.0001). If the difference among risk groups is attributed entirely to exposure to eitf, the population-attributable risk is 7 cases/1,000 admissions, or 15% of all admissions for laminitis at veterinary teaching hospitals in our data base. Preliminary data support an association between horses exposed to eitf and increased risk of laminitis; however, studies at the individual animal level are indicated to confirm this hypothesis.

Highly Aggregated Simulation Models

The process of aggregation of mathematical models and simulation is qualitatively described. Models are conceptually viewed as hierarchical structures. Aggregation results when state-variables and parameters of a model at one level are grouped and replaced by indices at a higher level as the domain of the model becomes broader. Conceptual clarity and computational feasibility of large and complex models stem from judicious use of aggregation. Properties of a system may emerge as a result of moving from lower to higher levels of organization. Quantitative genetic theory and methods often stem from an aggregation process. Several potential applications of models that are aggregated more highly than the level of individual animals and that require expertise in quantitative genetics and livestock production are identified and justified.