Blood flow distribution during artificially induced respiratory hypocapnic alkalosis in the fowl.

In birds, hyperthermia is normally associated with panting and progressive respiratory alkalosis. The effect of respiratory alkalosis on capillary blood flow distribution was examined by artificially hyperventilating normothermic fowls, thereby dissociating it of the normally occurring concomitant hyperthermia. In contrast with mammals, in which hyperventilation associated with hypocapnia reduced blood flow to the brain, uterus and other organs, in the hen blood flow distribution in most organs remained unaltered. This indicates that the potential change in acid-base balance which develops in the hyperthermic birds during panting is not likely to affect the regulation of blood flow. The comb and wattles were the only affected organs, in which capillary blood flow diminished to about 45% of normal values. This reduction did not prevent a vasodilatation in those organs in hyperthermic fowls, though it probably limited its full expression.

Responses of the reproductive vascular system during the egg-formation cycle of unanaesthetised laying hens.

1. Vascular adjustments to the process of egg formation were examined in the unanaesthetised laying hen, by the radioactive microspheres method. 2. Three- to four-fold increases in blood flow were found in segments surrounding the egg during its passage along the oviduct, possibly due to an enhanced metabolic activity in the muscle layer of the oviduct. 3. Shell-gland blood flow was minimal in the absence of an egg and increased gradually to a maximum (5-fold) about 5 h after entrance of the egg into the shell gland. This parallels the rate of calcification of the egg shell. 4. Changes in blood flow in the ovarian follicles and other parts of the oviduct were small while the egg was in the shell gland. This might be typical for the reproductive system of the fowl, which undergoes little structural alteration during egg formation.

Heat stress effects on capillary blood flow and its redistribution in the laying hen.

The effect of heat stress on capillary blood flow (CBF) distribution was examined in laying hens, using 15 micron microspheres, by determining CBF before and after elevating body temperature by 1-2 degrees C. No changes was evident in unfeathered metatarsal skin, although its temperature increased by 7 degrees C. Breast skin CBF change was 3.5 times larger than that of back skin. Comb CBF increase was larger than in wattles. CBF in upper respiratory tract increased proportionally to increment in respiratory frequency. Digestive system CBF was reduced by hyperthermia: the effect was pronounced in its upper organs (46% of normal) and decreased along the tract. CBF increased 4-fold in an expiratory abdominal muscle, a smaller rise occurred in a pectoral muscle and no change in a leg muscle. CBF in the tibia fell to 64% of normal. In the reproductive system, CBF fell to 58% of control level in the uterus, to 70-80% in the larger ovarian follicles and infundibulum with no significant changes in magnum and isthmus. Cerebral CBF increased during hyperthermia. Heat stress significantly reduced CBF to inner body organs, with marked differences between systems as well as within systems. Changes were more pronounced on 2 degrees C hyperthermia than on 1 degree C hyperthermia.

Effect of diurnal or nocturnal heat stress on egg formation.

1. Mature laying hens were subjected to ambient temperatures sufficient to maintain body temperature of 43 degrees C for periods of 6 to 7 h during the day (eight periods) or the night (five periods). This did not reduce total daily food consumption. 2. The effect of heat stress during the day was mostly on egg-shell quality, being adverse and significant. During the night heat stress caused a significant decrease in egg production, its effect during the day was less marked in this respect. 3. Heat stress thus seems mostly to affect the early stages of shell formation, while its effect on egg production seems to depend on the time at which it occurs in relation to ovulation. 4. These results suggest that egg production is directly affected by heat stress; prolonged heat stress probably also acts indirectly, by suppression of food intake.