RESUMEN
Taiep (tremor, ataxia, immobility, epilepsy, paralysis) mutants show a significant increase in myelin thickness from 10 to 30 days of age but then demonstrate a decrease in myelin thickness from 1 to 6 months. The severity of the demyelination in the optic nerve suggests that visual deficits may exist in the taiep mutants. Animals were trained on a discrimination task, in which responses to a light stimulus (the SD period) were reinforced on a fixed ratio (FR)-1 schedule, and responses in the absence of the light stimulus (the SΔ period) were not reinforced. Following training, the light intensity presented during the SD period was gradually reduced between sessions until -6.0 candela/m2 was reached. Both groups of animals - taiep mutants and control Sprague Dawley rats - successfully recognized and responded in the presence of the stimulus near perfectly by the final day of training, suggesting that taiep mutants demonstrated normal learning, at least under this paradigm. Despite the severe demyelination of the taiep optic nerve, no visual deficits were detected as both groups of animals performed similarly as the light intensity decreased. Though the myelin loss of the optic nerve may have negatively affected signal transduction, this did not result in an increase in visual threshold.
RESUMEN
System A provided 7.26 kg concentrate per cow daily blended and group fed with silage in 125 total and 97 selected 305-day lactations. System B provided concentrate hand-fed according to each cow's daily production (1 kg concentrate/3.25 kg milk) separate from group-fed silage in 112 total and 75 selected 305-day lactations. The 305-day records excluded those containing more than 150 days open. Both groups had, when available, 2.27 kg hay/cow daily or limited and equal grazing. Combined refusals, 5 to 10% of concentrate-silage blend in A and 5 to 10% of silage in B, plus fresh silage and 2.27 kg concentrate/cow daily constituted the common dry cow ration. Milk, milk fat percentage, and 4% fat-corrected milk, respectively, were 6,475 kg, 3.80%, and 6,270 kg in A and 6,899 kg, 3.69%, and 6,566 kg in B in the total lactations and 5,900 kg, 3.78%, and 5,686 kg in A and 6,098 kg, 3.70%, and 5,818 kg in B in the selected 305-day lactations. Percentages of solids-not-fat and protein in the milk were similar between A and B. Excluding grazing inputs, fat-corrected milk per total digestible nutrients per total lactation was 1.73 kg in both systems. Days open, days in milk, mean Wisconsin Mastitis Test score, body weight, net weight change, days to peak daily milk yield, days to minimum body weight, and minimum body weight were not different between systems in either the total or the selected 305-day lactations. Involuntary culling and culling for low production terminated 18 and 17% of the lactations started on Systems A and B.