An African penguin, Spheniscus demersus, that did not molt for four years

(from P. Schaller, Steinhart Aquarium)

 

Proceeeding Association of Avian Veterinarians 1993 pp 127-134

This is an OCR scan of my copy. It may contain scan translation errors. If you are interested in it, read an original copy.

PHARMACOLOGICAL INDUCTION OF MOLT AND GONADAL
INVOLUTION IN BIRDS


Ron Hines DVM PhD*,
P. E. Kolattukuty PhD**
Pat Sharkey. BS*'
*Sea World of Texas
10500 Sea World Drive, San Antonio. TX 78251 USA
**Ohio State University Biotechnology Center
Columbus. Ohio 43210 USA

ABSTRACT

A group of estrogenic, progestational and gonadotrophic hormone agonists successfully induce molt in a number of bird species. These compounds have clinical use in inducing new feather formation in display birds whose normal reproductive and moll cues are not adequately met. They also offer promise in the rehabilitation of oil-damaged waterfowl plumage and as humane husbandry alternative in the poultry industry. Effective doses their influence on behavior; blood chemistry and other parameters are reviewed.

Gonadal involution and subsequent molt are hormonally initiated processes. They are linked to circadian (daily) period, in all species of birds with defined annual rhythms. These rhythms involve a pineal gland “clock and calendar” entrained (set) by changes in the length of the day.1,2 . Since birds cannot molt and successfully raise their young, molt always occurs just prior to or after a rise in circulating sex steroids associated with gonadal activity 3,4 . In many species, including galliformes, anseriformes and penguins, molt is also associated with a transient rise in blood thyroxine levels. Beyond this, the factors Initialing annual molt in birds remain unknown.

Gallinaceous or chicken-like birds molt subsequent to each egg-laying cycle. In these birds, any factor which causes involution of the ovary will initiate molt. Starvation (-35% b.w.), light deprivation, tamoxifen (40mg/kg IM)5 , toxic levels of thyroxine (I ppm in feed or 0.1-0.2 mg/kg IM SID 14). oral copper or zinc, will all induce molt. Recently, several synthesized GnRH-agonist analogues have also been found effective in inducing molt in chicks through a mechanism that -shuts off pituitary GnRH production causing gonadal involution.

Anseriforme or duck-like birds have a more complex molting pattern. In many, post-nuptial gonadal involution results in an "eclipse" molt during which males assume female feather coloration and broodiness. In mallards, IM injection of l mg/kg estradiol benzoate In olive oil for 12 days precipitates molt.

Addition of l mg/kg of I thyroxine hastens the molt, but l-thyroxine alone - even at much higher doses - is ineffective. 6

The Sphenisciformes order of birds, the penguins, have unique physical and physiological characteristics. Antarctic and sub-Antarctic penguins exist in harsh natural environments where the timing of annual cycles of molt and reproduction are limited to short annual period of temperate weather and plentiful food supply. Antarctic and sub-Antarctic penguins are also post-nuptial fasting molters , that is, they molt after they have laid, incubated and fledged their chicks. During molt, wild penguins loose their ability to feed. In order to rapidly move through this stressful fasting period and re-enter the water, they have developed a climax or "catastrophic molt" in which their entire plumage is replaced during a 2-3 week period. Prior to molt, the birds eat ravenously and increase their body weight


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50 to 100%. Their skin becomes highly edematous as new leathers push out the old. When the process is complete, 30-60% of their pre-molt mass has been lost. Climax molt is an extremely stressful process. Penguins that return lo sea at less than 70% of their pre-molt weight rarely survive7. This is also the time when stress-related disease mortality such as aspergillosis is high in zoological collections.

In zoological displays, penguins often show signs of free-running or imprecisely set "clocks". They do not show the close group synchrony of reproduction and molt observed in the wild. Chinstrap Penguins in particular, rarely undergo normal breeding and molt cycles in captivity. With time, feather quality deteriorates and ozonization systems bleach and harden the feathers. In these situations, pharmacological induction of molt is desirable.

In zoo waterfowl exposed to natural light, molt abnormalities arc uncommon. In wild duck populations exposed to heavy hydrocarbon oil spills, feather quality rarely returns to normal. In these situations pharmacological induction of new feathers may also be desirable.

Egg producers currently rely on a combination of food and light deprivation to molt chickens for a second season of egg production. Pharmacological induction of moll offers them a more humane alternative.

MATHRIALS AND METHODS

A group of 28 four-year-old Chinstrap Penguins, Pygoscelis antarctica, which had not molted in 4 years, formed the basis of this study. In addition, two Rock Hopper Penguins Eudyptes crestatus, Two Gentoo Penguins, Pygoscelis papua paupua, and two Adelie Penguins (Pygoscelis adeliae) were included to determine if results varied between penguin species.

L-Thyroxine

Thirteen Chinstrap Penguins were given 0.03mg/kg po I-thyroxine dairy for 60 days. Two Adelie Penguins were given 0.5mg/kg l-thyroxine po bid for 30 days. Weight, appetite, physical condition, blood cellular indices, AST. cholesterol, triglycerides, uric acid, glucose and serum T-3 and T-4 levels were monitored.

Estradiol

Four Chinstrap Penguins were given 10-I5mg/kg im injections of estradiol valerate weekly for four weeks. Two Chinstrap and two Gentoo Penguins received 0.3-0.5 mg/kg po of 17B-estradiol for 30 days Weight, appetite, physical condition, blood cellular indices. AST, cholesterol, triglycerides, uric acid and glucose levels were monitored. Scrum estradiol levels were determined by a modified RIA procedure that will be presented elsewhere52. Representative body weights and hematocrits are given in Table 2.

Progesterone

Ten Chinstrap and two Rock Hopper Penguins were given 15-30 mg/kg medroxyprogesterone acetate injections weekly for four weeks. Weight, appetite, physical condition, blond cellular indices .AST. cholesterol, triglycerides, uric acid and glucose were monitored at weekly intervals. Progesterone levels were determined by modified RIA procedure. To determine if the molt-inducing effect of progesterone varied between species, two South Polar Skuas (Catharacta maccormicki) two kelp gulls, (Larus dominicanus) two Rosybill Docks, (Netta peposaca) and two Radjah Shell Ducks (Tadorna radja radjah) were given l5-30mg/kg medroxyprogesterone acetate injections weekly for four weeks.

GnRH Agonists


Two Chinstrap and two Macaroni Penguins were each given a single 1250 mcg/kg Intrapectoral injection of sustained