Blood flow through arteriovenous anastomoses and its thermal function in the laying hen.

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Abstract
Total (arteriovenous anastomoses + capillary) blood flow (tbf) and capillary blood flow (cbf) distribution were determined by 52 and 15 .mu.m microspheres, respectively, in body organs of 6 unanesthetized laying hens, exposed to thermoneutral air temperatures. Statistically significant differences between tbf and cbf were only found in the unfeathered metatarsal skin, comb and wattles. The cbf constituted 22, 42 and 45% of tbf, respectively, indicating significant arteriovenous anastomoses (ava) blood flow. Differences between tbf and cbf were small in the 2 larger ovarian follicles and digestive tract and were negligible in reproductive tract, liver and kidney. Microspheres of different size were injected into the external ischiadic artery in order to examine the vasomotor responses of leg tissues in 21 hens kept in thermoneutral, cold or hot conditions. In cold, thermoneutral and hot conditions 1, 16 and 35% of whole leg blood flow, respectively, passed through ava. Only cbf was present in bone and muscle in either treatment; cold and heat reduced it in bones and cold increased it in muscles. Arteriovenus anastomoses blood flow appeared mostly in unfeathered skin; it constituted 17, 53 and 83% of tbf to this tissue in cold, thermoneutral and hot conditions, while tbf increased from 1.4 to 14% and 30% of whole leg blood flow, respectively. Blood flow to feathered skin decreased during heat and cold.