Characterization of different hematological responses during molts induced by zinc or fasting

Single Comb White Leghorn hens were induced to molt by complete fasting for 11 days (FAST) or feeding a layer ration that contained 20,000 ppm zinc as zinc oxide for 11 days (ZINC). In both cases hens lost approximately 30% of their initial body weight. A control (CON) group was maintained. At 4, 8, 12, 18, and 42 days after initiation of the treatments, total erythrocyte numbers (TRBC), percent packed cell volume (PCV), mean corpuscular volume, hemoglobin (Hb), mean corpuscular hemoglobin (MCHb), and mean corpuscular hemoglobin concentration (MCHC) were determined. Erythrocytes were characterized as reticulocytes, intermediate Stage VII erythrocytes, or mature Stage VIII erythrocytes. The FAST hens exhibited significantly increased PCV through 18 days, which was not exhibited by ZINC hens. The FAST treatment increased TRBC on Days 8 and 12 and decreased TRBC on Day 42 while ZINC decreased TRBC on Day 4 and increased TRBC on Day 12. The FAST hens exhibited decreased Hb on Day 42, as reproduction resumed. Both ZINC and FAST hens exhibited decreased MCHb and MCHC on Day 12. Percentages of reticulocytes were decreased at Day 4 by FAST and increased at Days 8 and 18 by ZINC. Stage VII erythrocytes were decreased on Days 4 and 12 in FAST hens whereas ZINC hens exhibited a decrease on Day 4 and an increase on Days 8 and 18. Concomitantly, FAST hens exhibited an increase in Stage VIII erythrocytes on Days 4 and 12, whereas an increase on Day 4 and decreases on Days 8 and 18 were observed in ZINC hens.