Periodic rotational crosses. II. Optimizing breed and heterosis use

Choice of the optimal number and sequence of breeds in a periodic cross was determined by comparing the trade-off between increased utilization of breed differences and decreased utilization of heterosis. It was shown that the change in mean efficiency resulting from adding the next best breed to the best conventional n-breed rotation is always less than the change in efficiency predicted from the increase in heterosis. Periodic rotations were generally optimized by decreasing the proportion of poorer performing breeds in the rotation. However, efficiency of periodic rotations can exceed that of the better breed even when the difference in additive breed effects for efficiency is almost twice the effect of heterosis on efficiency. The periodic rotation that was optimal also tended to have the lowest inter-generational variance. It was suggested that inter-generational variances of component traits, which are not necessarily minimized when crosses are selected on a combined efficiency trait, can be considered by including inter-generational variance in an index or by introducing maximum thresholds.     

Clinical features and treatment of renal tubular acidosis in two horses

Two horses were admitted separately for evaluation and treatment of profound hyperchloremic metabolic acidosis without azotemia. One, an 11-year-old Quarter Horse mare, had been depressed and ataxic for 2 days. The other, a 2-year-old Quarter Horse colt, had a 6-week history of depression, anorexia, and weight loss. Both horses responded to fluid and electrolyte therapy, but required daily oral administration of sodium bicarbonate for maintenance. In each case, the diagnosis was renal tubular acidosis.     

The effects of selenium, housing and management on the incidence of pneumonia in housed calves

The occurrence and incidence of pneumonia in housed calves were not related to the selenium status of the herd as measured by blood glutathione peroxidase activity nor were they affected by selenium treatment of calves during the neonatal period. Pneumonia was related more closely to herd size and building design.     

Evaluation of the Krupin-Denver valve implant in normotensive and glaucomatous beagles

The Krupin-Denver valve was implanted unilaterally in 2 normotensive and in 6 glaucomatous Beagles. The fellow eye of each dog had an external trabeculectomy. Before and after surgery, all dogs were evaluated serially by gonioscopy, biomicroscopy, tonometry, and tonography. The valve implant remained patent in 2 normotensive and in 2 glaucomatous Beagles throughout the 12 months of observation. Valve function was lost in 4 glaucomatous Beagles 4 to 6 weeks (3 dogs) and 6 months (1 dog) after implantation. Light microscopic and scanning electron microscopic evaluations of early loss of implant function revealed occlusion of the lumen and/or valve mechanism by inflammatory debris and cells. The late loss of valve function was related to chronic inflammatory response and fibrosis about the valve mechanism and tubing within the sclera.     

The development of eimerian infections during the first eight months of life in unweaned beef calves in a dry tropical region of Australia

The development of coccidial infections in 21 free-ranging, unweaned beef calves from birth to 8 months was investigated by examining faecal samples for oocysts. Most calves commenced shedding oocysts within a month of birth, and had shed all nine species identified by 3-4 months. Oocysts were shed by three calves as young as 12 and 13 days. The oocysts species shed earliest, and the commonest thereafter, were Eimeria bovis, E. ellipsoidalis and E. zuernii. Although several oocyst counts between 5.0 X 10(3) and 114.0 X 10(3)g-1 of faeces of these potentially pathogenic species were recorded there was no clinical disease. Some calves shed oocysts approximately four times more frequently than others, and individual species counts greater than or equal to 5.0 X 10(3)g-1 were confined to 10 of the calves. Intermittent oocyst shedding continued throughout the study with a similar distribution of oocyst species from all calves.     

Morphological changes in the pineal body of domestic swine (Sus scrofa domesticus) depending on light]

The cerebral epiphysis of twelve gilts, aged 6.5 months, was histologically, histochemically, and histometrically tested, after the animals had been kept permanently under artificial light, 100 lux, or in darkness, interrupted twice a day by two hours of lighting, over ten weeks altogether. The parenchymal cells of the epiphyses of the animals kept in darkness changed clearly from those of the other group with constant exposure to light. Changes in the darkness animals included significant enlargement of the cell nuclear volume by 33 per cent, increase in nucleoli count as well as increases of lipids and ribonucleic acid in cytoplasm.