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The effects of the addition of yeast on in vitro roughage degradability and methane production were investigated in order to clarify the effects of yeast on the rumen microbes and to establish methods of rumen manipulation. Three roughages (whole crop corn, rice straw and Italian ryegrass) were incubated for 3, 6, 12 and 24 h with or without dried beer yeast following the method described by Tilley and Terry. Using the same method, these roughages were incubated with or without yeast extract, albumin or purified DNA. In vitro methane production was measured with or without dried beer yeast at 12 and 24 h. The degradability of yeast was found to be 57 and 80% at 12 and 24 h, respectively. The rate of degradation of fraction b was 6.16%/h. There was a significant increase in roughage degradability at 6 h (p<0.05), 12 h (p<0.05) and 24 h (p<0.01) by dried yeast addition. The degradability of all three roughages was higher in the samples treated with yeast extract than in the no addition samples except in the case of rice straw incubated for 12 h. Nevertheless, the magnitude of increment was smaller with the addition of yeast extract than without the addition of yeast. With the addition of purified DNA, there were significant increases in roughage degradability at 6 h (p<0.01), 12 h (p<0.01) and 24 h (p<0.05); however, higher degradability values were detected in the samples to which albumin was added, particularly at 6 h. If the degradability values of the no addition samples with those of samples containing yeast, yeast extract, DNA and albumin were compared, the largest difference was found in the samples to which yeast was added, although it is worth noting that higher values were observed in the yeast extract samples than in the DNA or albumin samples, with the exception of the case of rice straw incubated for 24 h. Methane production was significantly increased at both 12 and 24 h incubation. The increment of roughage degradation and methane production brought about by the addition of dried beer yeast to the samples was thought to be due to the activation of rumen microbes. Water soluble fraction of yeast also seemed to play a role in ruminal microbe activation. The increment of degradability is thought to be partially due to the addition of crude protein or nucleic acid but it is expected that other factors play a greater role. And those factors may responsible for the different effects of individual yeast on ruminal microbes.

The physiological role of GH secretion on growth retardation remains to be elucidated especially in patients with β-thalassemia. In the present study, we investigated IGF-1 circulating levels as well as GH release following GHRH alone or combined with some inhibitors of somatostatin: pyridostigmine and arginine. In thalassemic patients lower IGF-1 circulating levels appear to be negatively correlated with both aspartate aminotransferase and alanine aminotransferase as well as with ferritin circulating levels indicating a probable role of hepatic hemosiderosis in IGF-1 production. The authors however suggest that reduced IGF-1 secretion is not the main cause of growth retardation since this would have elicited an enhanced response of GHRH in the presence of a normal hypothalamic pituitary axis. In contrast, they noticed that GH response to GHRH when expressed as area under the curve was lower in thalassemic patients compared to controls. The combination of GHRH with either pyridostigmine or arginine induced a GH secretion in thalassemics which was comparable to that of controls. The results of this study lead to conclude that the alteration of GH secretion is due, in such patients, to an increased somatostatin activity.