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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 microflora of the gastro-intestinal tract of dystrophic BIO 8262 Nij Syrian hamsters and Kun:Sh Syrian hamsters as controls was investigated by means of culturing techniques and scanning electron microscopy. The oesophagus, forestomach, stomach, small intestine, coecum and faeces were assessed for the presence of Enterobacteriaceae, Staphylococci, Lactobacilli, Streptococci, Clostridia, Bacteroides and yeasts. The normal hamsters showed low levels of yeasts in the oesophagus, forestomach and stomach; yeasts were not present in the other compartments. Relatively low levels of Staphylococci and Enterobacteriaceae were found in all gut segments; also Bacteroides was found in low levels in the upper part of the gut. The other groups of bacteria showed relatively high levels in all segments. In dystrophic BIO 8262 Nij hamsters no Enterobacteriaceae and yeasts have been detected in the gut. Scanning electron microscopy showed no difference in adhesion between both hamsters strains.

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.

Hysterectomy-derived germ-free (GF) rabbits were given strictly anaerobic microflora obtained from the caecum of an antibiotic-decontaminated conventional rabbit. One group was given the caecal flora diluted in doe's milk. The second group received caecal flora without doe's milk and administration of the flora was repeated when the animals were given pelleted diet. Body weight and intestinal parameters determined in the two groups of rabbits were compared with values in rabbits conventionally raised with the doe. In GF rabbits given caecal flora, the values for most intestinal parameters were similar to values recorded in conventional animals. However colonization resistance to Escherichia coli was limited in GF rabbits given caecal flora diluted in doe's milk and severely impaired in GF rabbits given caecal flora without doe's milk, although relative caecal weight was normal. It is concluded that enteric microfloras should be preferably incorporated in doe's milk when dosed to GF rabbits to obtain acceptable gastrointestinal "normalization".

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.