Dissertation

The effect of breeder hen age on reproductive characteristics and subsequent embryo and hatchling development and growth of turkeys and Pekin ducks

Applegate, Todd Jay

1999

Overview

To gain insight into how the age of the hen affects selected reproductive characteristics and subsequent embryonic and posthatching development, experiments were conducted to study: (1) hormonal and initial egg production characteristics as influenced by hen age and age at photostimulation; (2) changes in egg component distribution associated growth; with hen age; (3) effects of hen age on yolk sac lipid mobilization and embryonic growth; (4) hen age effects on post-hatch metabolic homeostasis and intestinal development. Reproductive experiments were conducted with the commercial turkey, whereas embryonic and posthatching experiments were conducted with both the commercial turkey and Pekin duckling as experimental subjects. The results of our initial research demonstrated that embryos from young hens developed more slowly than embryos from older hens during the last week of incubation. We hypothesized that these developmental differences are in part due to a proportional increase in yolk mass in eggs from older hens which allows for a greater mass transfer of yolk lipid to the embryo during the last week of incubation. Hypothetically, developmental differences during incubation may be related to problems that occur during the acclimation period after hatchlings come from very young hens. In testing this hypothesis, a metabolic challenge was imposed and intestinal development were measured in hatchlings from different hen production ages. The metabolic challenge was tested with a glucose tolerance assay and intestinal development was evaluated by measuring gross intestinal growth (weight and length) during the first week after hatching. Poults and ducklings from young hens remained hyperglycemic longer when given a glucose challenge, suggesting an early impairment in gluocse regulation. Hen production age did not consistently influence poult or duckling weight or length measures of the small intestine after hatching. As weight and length measures are relatively gross measures, final experiments studied the relationship between hen age, poult villus growth and enterocyte proliferation and migration during the first week after hatching. Enterocyte migration was determined after the labeling of proliferating enterocytes with a thymidine analog, bromodeoxyuridine (BrdU), and subsequent immunostaining for BrdU. Poults from the older hens had significantly longer villi and BrdU labeled enterocyte height at hatch, but not after placement. Even though intestinal. villi may have been more developed in Poults from the older hens at hatch, post-hatching growth of the intestinal system or the poult was not affected. Age-related changes in enterocyte proliferation support the theory that changes in enterocyte function occur due to an accumulation of cells rather than to enterocyte turnover rates. In a final study, comparisons were made between the duckling and turkey poult to determine if rates of small intestine development contributed to marked growth differences between the two species during the first week after hatching. By 7 days of age, the duckling's jejunum and ileum were 3.7X heavier, 1.6X longer, and 2.3X more dense (g/cm) and villi were 2.4X longer than in the turkey poult. This phenomenal growth difference aided the duckling in achieving a body weight nearly twice that of the poult during this initial 7 day growth period.

• Publisher: ProQuest Dissertations & Theses
• Subject: Anatomy & physiology / Animal sciences / Animals / Livestock / Physiology / Veterinary services
• ISBN: 9780599317338, 0599317337