Changes in erythrocyte levels and the mean corpuscular haemoglobin concentration in hens during the laying cycle

1. 1. The percentage volume of erythrocytes (EV) in the blood of each of ten hens has been measured at frequent intervals during the physiological laying cycle. Statistically significant changes took place as follows: a rise during the 10 days preceding the final oviposition, a continued rise for the subsequent 20 days or so, then a progressive fall commencing about 30 days before recommencement of lay; this drop was pronounced during the onser of lay itself. 2. 2. The possible influence of endogenous oestrogenization on the changes is briefly indicated. 3. 3. Evidence is presented to indicate the dangers in this field of making deductions from isolated measurements on a population of hens. 4. 4. Statistically significant changes in the Mean Corpuscular Haemoglobin Concentration (MCHC) took place during the physiological cycle associated with laying, pausing from lay, laying once more. The MCHC was high at the commencement of lay and gradually fell to a minimum during thelast 10 days of lay and may or may not have fallen during the subsequent 10 days. Then it rose to a maximum which was reached just before or just after laying recommences. No satisfactory explanation for these changes can be offered at present. 5. 5. Changes in the MCHC did not follow the trends of simultaneous changes in EV. 6. 6. A simple modification of the alkaline haematin method which will reliably determine haemoglobin in nucleated erythrocytes is described. The lipaemic plasma of the laying hen does not interfere.