For those of you seeing avian patients, this time of year can provide some interesting challenges. With our patients eating healthy diets, and undergoing preventative health care, we are seeing hens becoming reproductively active at a young age.
Some of the older literature suggests that most larger psittacines won't breed until they are 6-7 years of age. However, with optimum health, you can expect that many conures, Amazons, Eclectus, macaws, cockatoos, pionus, Poicephalus and cockatiels will breed by their second or third year. South American and Central American birds (considered New World birds) usually breed with increasing daylight hours. Most African birds breed with decreasing daylight hours, and most breeders set up their birds on Labor Day and consider Memorial Day the official end of their breeding season, although some pairs will breed year round. Eclectus and cockatoos tend to breed year round as well. Cockatiels usually breed with increasing daylight, but some may cycle year round. Cockatiels are indeterminate layers and will often continue to lay eggs to complete their clutch if the eggs are taken away as they are laid. However, budgerigars (parakeets or budgies) are determinate layers and often lay just 4, 6 or rarely 8 eggs to complete the clutch.
Amazons, in particular, have an intense hormonal surge in the springtime, and often exhibit extreme behavioral changes at that time. Both males and females may become very possessive of their cages, and if allowed out of the cage, they often seek a dark closet, empty cardboard box, the dark areas of the home (cupboards, under the bed, empty paper bags). They may engage in "redecorating," chewing on wood moldings, chair legs, etc. They may attack any people that they consider to be threatening to their perceived human mate. Female Eclectus often seek out a dark area to "nest" in.
Since many birds are sexually dimorphic, this is important information to ascertain with your avian patients. Cockatiels are dimorphic, with hens having yellow dots on the wings and yellow bars on the tail feathers, and males (of the normal grey color) having a bright yellow face with bright orange cheek patches. Male budgies have a bright blue cere when sexually mature (4 months of age), unless they are a very pale color mutation and hens develop a tan or brown cere that may hypertrophy with sexual maturity. Spectacled Amazons are dimorphic, with cocks having five or more bright red covert wing feathers, and the hens lacking the red feathers. Male Eclectus are primarily green and hens are red, purple and orange. Most of the Poicephalus are dimorphic, and I refer you to a good atlas for the differences. Male African grey parrots have solid red secondary tail feathers, and those are tipped in silver in hens (after the first molt). Most adult cockatoos can be sexed by the eye color. Hens have red or brown irises, and cocks have such a dark brown iris that it appears black (shine a strong light into the eye for this).
Most Amazons, macaws, pionus, Timneh greys, conures and lories are monomorphic. A few species of lory are dimorphic; a good avian atlas can be invaluable when working with birds. While you might think that you can determine sex by behavior, this can fool you. I have seen male macaws sit on a toy bell or ball, trying to incubate it. Males may try to mount other males, and hens may try to mount hens. Masturbatory behavior may be exhibited in both male and female birds.
Both sexes may begin holding droppings for longer periods of time during breeding season, and this is because in the wild, they will not usually soil their nesting site (often in a tree hollow). So, when they do pass a dropping, it may be quite large, often more odorous than usual, and often the three components are admixed (urine, urates and feces), with a more diarrheic appearance to the feces.
Often, a bird may be presented with the clinical signs of behavior changes: more aggressive in the cage, territorial and biting family members. Often, it is reported that the bird is PU/PD, which also occurs as a result of hormonal activity in the hen. She will begin drinking much more water than usual, as the water is necessary for egg production. She may begin plucking chest feathers in an attempt to make a "brood patch," an area of chest skin that becomes thickened in some hens, and allows better contact with the eggs for incubation.
On physical examination, the hen may evidence a recent weight gain, as the developing follicles and enlargement of the oviduct are responsible for increased weight. The pelvic floor muscles often become loose, to allow the passage of an egg, and this is under hormonal control. The cloaca may also become looser, again from hormonal influence.
The plasma chemistries may show some changes reflecting hormonal activity. Early in the reproductive cycle, the hen will undergo vitelligenesis. During this process, yolk precursors, primarily proteins and lipid, are synthesized in the liver and transported to the ovarian cortex hematogenously. The regulation of yolk protein synthesis is controlled by gonadotrophin and steroid hormones. Vitellogenin, a phosphoglycolipoprotein, and a low density lipoprotein are both translocated across the oocytes plasma membrane via receptor mediation. Yolk precursors are assembled in the primary oocytes cytoplasm with proteolytic processing by cathepsin D into phosvitin, lipovetellin, triglycerides, cholesterol and phospholipids. Initially, for the first few months of follicle development, an equal amount of protein and lipids are deposited. However, during the final rapid growth phase, 7-14 days prior to ovulation in most species, an increasing amount of lipid is incorporated. It is thought that vitelligenesis ceases approximately 24 hours prior to ovulation.
During vitelligenesis, the plasma will usually appear lipemic due to the circulating lipoproteins used to plump the yolk. During calcification of the eggs, which occurs in the uterus portion of the oviduct, calcium ions are transported across the mucosa and carbonic anhydrase provides the carbonate ion to form the calcium carbonate shell. Approximately every 15 minutes, the uterus withdraws from the blood a weight of calcium equaling the total amount circulating at any one moment. During this time, the plasma calcium level will be greatly elevated, often with values well above 15 mg/dl, and often reaching levels of 20 or 30 mg/dl. With some individuals, the phosphorus level will often elevate proportionally, while in others, it may remain within normal limits. Elevated total plasma proteins and total serum solids are increased because of a need for protein for calcium transport, as well as the estrogen-controlled liver synthesis of lipid and proteins produced during yolk formation. Hypercholesterolemia may be seen during reproductive periods. Pre-albumin may be elevated in laying hens, as well. Alkaline phosphatase levels may also increase due to estrogen stimulation.
Radiographs often show the classic calcification of the medullary spaces of the long bones, particularly of the femur and tibia, which occurs approximately ten days before egg formation. In budgerigars, the primary sites of medullary calcification are the humerus and femur. This is called polyostotic hyperostosis.
Hematogenic changes may also occur that are associated with egg-laying. A slight increase in the white blood cell count (WBC) is typical. The packed cell volume may also increase to the high range of normal.
Not all hens that are reproductively active will go on to oviposit. Some may resorb the eggs, others may lay internally (where the egg enters the coelom instead of the infundibulum), which may or may not cause problems. Others may develop egg-binding or dystocia.
While not directly involved with reproductive activity, the uropygial gland is involved with calcium metabolism and should be evaluated during every physical examination. The gland, which is bilobed and heart-shaped, has a papilla with several wick feathers. The wicks allow the secretion to be picked up on the beak during preening. The secretion is then spread on the feathers. In addition to keeping feathers supple, it also has antibacterial and antifungal properties. The secretion has vitamin D precursors that are spread on the feathers. Once activated by exposure to UVB light, the secretion becomes active vitamin D3, which is necessary for proper calcium utilization. So, if hypovitaminosis A causes squamous metaplasia of the uropygial gland, or if the wick is not present or there are other problems with the gland, or the bird does not receive outdoor natural sunlight (not filtered through glass or plastic) or full-spectrum light indoors, the bird may not have normal blood calcium levels, even though calcium is being supplemented in the diet.
With many healthy young birds showing signs of reproductive activity, we must learn how to ascertain what is normal, reproductive activity, and what is a true medical problem. Many physical and biochemical changes are a normal part of avian reproductive physiology and now you will be able to interpret what these changes mean for your avian patients.
Copyright © 2006 Margaret A. Wissman, D.V.M., D.A.B.V.P.
All Rights Reserved
ExoticPetVet.net
www.exoticpetvet.net
