Individual Animal Model Research Articles

Estimation of genetic trend in a selected population with and without the use of a control population.

Data from a selection experiment conducted with sheep at Massey University, New Zealand, were analyzed to obtain an evaluation of selection response. Selection was for heavy 14-mo greasy fleece weight. Approximately seven generations of selection were represented in the data. Three estimates of genetic superiority of the selected line to the control line were obtained. All three estimates were obtained from a mixed model evaluation using the individual animal model for predicting breeding values from own and relatives' records. The estimators were 1) deviation of selected line predicted yearly phenotypes from control line predicted yearly phenotypes, 2) deviation of the predicted yearly phenotype for the selected line from the year estimate in the control line and 3) the mean yearly breeding value from the analysis of the selected line only. The realized heritability using the first approach was .20. However, the control line was found to have a slight positive drift; hence, this estimate was biased downward. Using Approach 2, accounting for drift, the realized heritability was .23. The same realized heritability, .23, was obtained from an analysis of the selected line ignoring the control (Approach 3), when a prior heritability of .30 was assumed for the mixed model evaluation. The estimate of genetic trend from predicted breeding values in the latter approach is, however, quite dependent on the assumed heritability.

Experimental renal disease due to schistosomiasis

Although there is a marked variability in the development of renal lesions among individual animal models of schistosomal infections, much has been learned about the mechanisms leading to renal injury. The lesions in S. mansoni and S. japonicum infections correspond quite closely to the immune complex type of lesions, with complement involvement. The main antigens involved seem to be polysacharides of worm-gut origin, but participation of other antigens (including soluble egg antigens) cannot be excluded. Many observations testify to the localization of immune complexes, preformed in circulation, but the possibility that antigens, filtered through glomeruli, deposit incapillary walls first and bind with corresponding antibodies later on should be considered also. Deoxyribonucleic acids also may play a role in the pathogenesis. The perpetuation of the lesions is probably due to constant supply of antigens. In some models, renal pathology was related to the dose of infection, but in others there was no relation to worm burden. Renal pathology in S. haematobium infections is different, being related to the lower urinary tract, with obstructive lesions causing pyelonephritis and hydronephrosis.