WOOL PRODUCTION AND BLOOD-SUPPLY TO SKIN AND OTHER TISSUES IN SHEEP

Quantitative measurements of blood flow (BF) to skin and several other tissues were made using radioactive microspheres in conscious sheep. The sheep were from established flocks that had been selectively bred for greater (Fleece plus) or lesser (Fleece minus) wool production. The BF rate per unit area of wool-bearing skin was significantly greater in the Fleece plus (n = 9) than in the Fleece minus (n = 6) group, but the correlation between skin BF and the wool growth rate in individual animals was modest (r = .581). There was a strong, positive correlation (r = .813) between wool production and pineal BF. Other tissues that exhibited significant BF differences between the two groups included adrenal glands and fat, which were greater in Fleece plus sheep, and thyroid glands, reticulum, rumen, and extremity skin (non-wool-bearing), which were lesser in Fleece plus sheep. Our major conclusions are that 1) when the positive correlation between skin BF and wool production is considered together with computer model predictions of the relative importance of all factors determining wool growth, skin BF emerges as a significant, although minor, factor; 2) because skin BF is statistically correlated with wool production, it could be a useful indicator to be measured to predict wool production capacity, certainly in different groups and possibly in individual sheep; and 3) because the pineal gland is known to be involved in cyclic changes in growth of hair and wool, our positive correlation between pineal activity (as indicated by capillary BF) and wool production could be indicative of an enhancement of wool production by the pineal gland (such as via melatonin).