Availability of solid feed and growth rates of pre-weaned mice of different litter size.

The effects of litter size and availability of solid feed before weaning on the growth mice were studied. Pups of small litters (n = 3) grew significantly faster than mice of large litters (n = 10), the mean difference at weaning being about 3 g. The difference in body mass persisted after weaning; at the age of 98 d the mean difference was about 5 g. Availability of solid feed to pre-weaned mice significantly stimulated mass gain of litters consisting of 10 but not of 3 pups. Body masses of the dams during the suckling period were markedly influenced by litter size: Mice with 10 pups had increased body masses when compared with mice having 3 young. By the time of weaning, body masses of mothers with larger or small litters had become similar again just as they were immediately after parturition.

[The effect of ivermectin on Psoroptes ear mange in rabbits]. / Effect van ivermectine op Psoroptes-oorschurft bij konijnen.

Ivermectin administered to rabbits in drinking water (3 ml of drenching liquid (0.08% w/v ivermectin) per litre of drinking water) for one of five days, gave rise to blood levels persisting on several days and were measured by the death of mosquitoes following a meal of blood from these animals. In practice ivermectin (3 ml/l) was administered to 98 rabbits on a rabbit-meat farm for 24 hours. This treatment was repeated within a fortnight. The degree of ear mange was determined by the amount of incrustation. Within three weeks after treatment was initiated, all animals were free of crusts. Incrustation gradually recurred during the following weeks. After 161 days, approximately ten per cent of the animals showed some incrustation again. Treatment with ivermectin once every six months is advised to suppress ear mange.

Elimination of murine viral pathogens from the caecal contents of mice by anaerobic preparation.

The aim of this study was to investigate methods to eliminate pathogenic viral agents while preserving the 'normalizing' properties of the gut microflora of mice. Mouse hepatitis virus A59 (MHV), Reo 3 virus and Theiler GD VII virus were added to the caecal contents of 'normal' mice and following dilution, with or without subsequent culturing, given to germ-free mice. Four weeks later antibody titres against these and other viruses were determined. MHV and Theiler CD VII virus survived dilution but were eliminated during culturing. Reo-virus survived the 10(-1) dilution-culture step. All dilutions and dilution-cultures of caecal contents resulted in 'normalization' in germ-free recipients of the relative caecal weight, percentage faecal fusiform-shaped bacteria, faecal bile acids and colonization of small intestine by segmented filamentous bacteria.

Hardness of diet pellets and its influence on growth of pre-weaned and weaned mice.

The hardness of 3 commercial diet pellets for laboratory rats and mice was studied. Hardness was measured as the force (kp) required to crush a diet pellet. Between-batch variation, expressed as coefficient of variation, ranged between 12 and 70%. In one type of diet hardness of the pellets varied between 4 and 50 kp. Hardness did not change during storage for a period of 8 weeks. To investigate the effect of hardness on growth performance of young mice experimental diets were prepared with identical ingredient composition but with hardness of either 15 or 45 kp. Female mice provided with hard pellets (45 kp) were not able to raise their litters. Feeding the experimental diet as 15 kp pellets resulted in a slightly retarded growth when compared with the experimental diet in the form of meal. Weaned mice were fed with the experimental diet in 4 different forms: meal, 15 kp, 45-kp and ground 45-kp pellets. Male mice, unlike females, fed the 45-kp diet grew slower than their counterparts fed the other diet forms. It is concluded that batches of extremely hard pellets may be occasionally delivered, and that such diets have undesirable effects on performance of young mice.

The influence of stress and cheese-whey on intestinal parameters in mice.

In a mouse model the effects of environmental stress on gastrointestinal parameters and the effects of cheese-whey on the changes induced by stress were studied. Mice were subjected to overcrowding, lack of bedding, overcrowding together with lack of bedding, continuous light, and housing at 30 degrees C. The influence of stress on relative caecal weight, faecal enterobacteriaceae, colonisation resistance (CR), filamentous segmented bacteria in the small intestine, fusiform bacteria in the faeces, and concentration of faecal bile acids was studied. Stress had no influence on relative caecal weight, faecal enterobacteriaceae, and faecal bile acids. Stress did decrease colonisation resistance, presence of segmented filamentous bacteria in the small intestine, and fusiform bacteria in the faeces. Cheese-whey had no positive effect on the microbiological disturbances caused by stress. The number of filamentous segmented bacteria in the small intestine and fusiforms in the faeces decreased by giving cheese-whey.

Hardness of diet pellets and growth of pre-weaned mice: separation of direct effects on the young and indirect effects mediated by the lactating females.

The effect of pellet hardness on growth of pre-weaned mice was studied with the use of a specially constructed cage so that lactating females and their young could be fed separately. Diet pellets with identical ingredient composition but hardness of either 20 or 40 kp were prepared. Growth of the young not supplemented with feed was markedly depressed by the feeding of the 40-kp diet to the mothers, when compared with the 20-kp diet. If the young of mothers fed the 40-kp diet had free access to diet pellets with hardness of either 20 or 40 kp, their growth performance improved. When the breeding females were fed the 20-kp diet, feed supplementation of the young did not affect their body weight. This study suggests that the observed effect of diet pellet hardness on body weight of pre-weaned mice is mediated in part through the mothers. Free access to feed was found to stimulate growth of pre-weaned mice only if the mothers were fed extremely hard diet pellets.

Diethyl pyrocarbonate: a chemical probe for DNA cruciforms.

Two palindromic DNA sequences were analyzed with respect to their chemical reactivities with diethyl pyrocarbonate. In negatively supercoiled plasmid templates enhanced N7 carbethoxylation was found with individual purines located in presumptive single-stranded loops of DNA cruciform structures. No enhanced reactivity at these positions was observed in linear, relaxed or low superhelical density plasmids. Hyperreactivity was found over a narrow region only, indicating that stable cruciforms contain loops of minimal size. No enhanced chemical reactivity was found with the four-way junction at the base of cruciforms. Diethyl pyrocarbonate has proved a sensitive structural probe for the analysis, with single nucleotide resolution, of DNA cruciform structures.