Effects of reproduction in sheep on the rate of cell division and nucleic acid content of the ruminal mucosa

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Abstract
The weight of the ruminal mucosa of breeding Blackface ewes and its total DNA and RNA content rose after parturition to reach a peak at 45 days post partum. There were no constant significant changes with time in the concentration of the nucleic acids.It was found that there was a positive correlation between the amount of food eaten during the final week of life and the weight of the ruminal mucosa and the length of ruminal papillae. The mitotic index of the ruminal epithelial cells was very variable but most of the higher values occurred between 7 and 80 days post partum. The mitotic index could not be correlated with the amount of food eaten in the week before slaughter, but high values were not recorded when the food intake of lactating ewes was restricted to that of non-breeding controls. It is suggested that the most likely explanation for these findings is that in the ruminal epithelium of lactating ewes fed to appetite, oell division occurred in waves or bursts.Hyperkeratosis of the ruminal epithelium occurred in pregnant and control animals but regressed during lactation and reappeared in the post-weaning period. The inverse relationship between the hyperkeratosis and the rate of cell division is of great interest when considering the aetiology of ruminal disease.