Genetic parameters of test day milk yields of Holstein cows

Data were obtained from 17,968 records from 2,130 first lactations of Holstein cows calving between 1988 and 1991. The subjects were daughters of 136 sires monitored by Brazilian Breeders Association, Animal Science Institute, Department of Agriculture, a branch of the State of São Paulo. Data were divided into 10 subsets based on the number of days in milk yield. Test day milk yields (M1 to M10) and 305-day milk yield (M305) were the traits studied. These traits were adjusted for several environmental effects: class of cow age at calving, interval from calving to first test day, and herd-year-season. Restricted maximum likelihood estimates of (co)variance components were obtained from one and two-traits analysis under a sire model. Estimates of heritabilities for M ranged from 0.04 to 0.32. The highest values were found in the second half of lactation (M5 to M7). Heritability estimate for M305 was 0.32. Genetic correlations between individual test days and M305 ranged from 0.78 to 1.00. Results suggested that test day milk yields, mainly in mid-lactation, can be used instead of 305-day milk yield in genetic evaluations, because estimates of these two-trait heritabilities are nearly alike. Moreover, early selection can reduce generation intervals.<br>No presente estudo foram utilizados 17.968 registros de produção de leite, referentes a 2130 primeiras lactações de vacas da raça Holandesa, paridas nos anos de 1988 a 1991, filhas de 136 touros e controladas pela Associação Brasileira de Criadores (ABC). Os dados foram distribuídos em dez sub-arquivos de acordo com o número do controle (M1 a M10). As características estudadas foram: produção de leite no dia do controle (M) e produção aos 305 dias de lactação (M305), as quais foram ajustadas para os seguintes fatores de variação: idade da vaca ao parto em classes, intervalo parto-primeiro controle e subclasses de rebanho-ano-estação de parto. Os componentes de (co)variância foram obtidos a partir de análises com duas características utilizando-se o método REML, sob um modelo de touro. As estimativas de herdabilidade para as M variaram de 0,04 a 0,32 sendo os maiores valores encontrados na segunda fase da lactação (M5 a M7), enquanto que para a M305 este valor foi 0,32. As correlações genéticas entre as M e a M305 variaram de 0,78 a 1,00. Os resultados sugerem que as M podem ser utilizadas em substituição à M305 nas avaliações genéticas dos animais, visto que as herdabilidades no meio da lactação foram semelhantes à encontrada para a M305. Além disso, a seleção antecipada pode levar a uma redução no intervalo de gerações

Magnetic resonance imaging in clinically isolated lesions of the brain stem

Twenty-seven patients with an isolated brain stem syndrome, thought to be due to demyelination, were examined by magnetic resonance imaging (MRI). A brain stem lesion was identified in 25, and clinically silent lesions outside the brain stem were demonstrated in 20. MRI was more sensitive than evoked potentials in detecting brain stem and other lesions. The scan findings were compared with those in 23 patients with multiple sclerosis, who had chronic brain stem dysfunction, with particular reference to the distribution of abnormalities and the MRI characteristics of the lesions. The relaxation times, T1 and T2, of the lesions were measured by MRI. These values were seen to fall in serial studies of acute lesions, but remained unchanged in the chronic lesions. MRI may therefore allow the age of lesions to be assessed