Immunolesion of melanopsin neurons causes gonadal regression in Pekin drakes (Anas platyrhynchos domesticus).

Several light sensitive receptors have been described in the avian brain that are thought to regulate the reproductive axis independently from the eyes and pineal gland. Recently, our lab has described the presence of three of these photoneuroendocrine systems in the Pekin duck: opsin, opsin 5, & melanopsin. We set out to test the hypothesis that melanopsin receptive neurons are necessary to maintain seasonal reproductive status along with growth and development in the Pekin drake. To accomplish these goals we first investigated 50-week-old Pekin drakes that were housed in the aviary at Hope College under long day length (18h lights on) conditions in floor pens. To specifically lesion melanopsin-receptive neurons, 3µl of an anti-melanopsin-saporin conjugate (MSAP, 100ng/ul) was injected into the lateral ventricle (n=10). Control drakes were injected with 3µl of equimolar unconjugated anti-melanopsin and saporin (SAP, n=10). Reproductive behaviors were analyzed weekly in a test pen with adult hens and MSAP drakes showed a significant (p<0.01) reduction in reproductive behaviors after week 2. After 5weeks, drakes were euthanized and body weights were measured, and brains, pituitaries, and testes collected and stored for analyses. Mature MSAP-treated drakes had significantly (p<0.001) reduced relative teste weights compared to SAP controls. qRT-PCR analyses of hypothalamus showed a significant reduction (p<0.001) in GnRH and melanopsin mRNA levels, but not opsin 5, vertebrate ancient opsin, or opsin 2 (rhodopsin). Immunocytochemical analyses showed a significant reduction (p<0.01) in tyrosine hydroxylase-immunoreactivity in the PMM. These data suggest that although blue light alone is not able to maintain testicular function, the blue-light sensitive melanopsin activity is critical to maintain gonadal function.

Increased water contamination and grow-out Pekin duck mortality when raised with water troughs compared to pin-metered water lines using a United States management system.

Controversy has developed as to whether or not pin-metered water lines or water troughs are more appropriate for Pekin ducks. We hypothesized that water troughs would show improved duck body conditions and environmental quality compared to pin-metered water lines. To test this hypothesis, we housed ducks in 2 barns, one with water lines and one with water troughs. Water troughs were constructed to meet RSPCA guidelines for number and density of ducks and with recently described verandas. Ducks were divided into 4 pens per barn (n=1,000 ducks/pen). The study was then repeated (n=8 pens per water source) in a cross-over design so the barns each contained the opposite water source to the first experiment. We scored the ducks' body condition using an established scoring rubric and analyzed using SAS Proc GLM-Mix as binomial data. Ducks housed with water troughs showed higher (thus worse condition; P<0.001) scores for eyes, nostrils, feather quality, feather cleanliness, and foot pads. We also compared water condition, water quality, and duck mortality using a Student t test for both water sources each week. We found that the water troughs showed higher iron (P<0.001), nitrites (P<0.001), pH (P<0.01), and bacterial growth (P<0.001). The bacterial growth was shown to have higher (P<0.001)E. coli, coliforms, and Staphylococcusin the water troughs. Water lines typically showed no bacterial growth in culture-based assays. Ducks housed with water troughs used greater (P=0.001) volumes of water compared to ducks housed with water lines. Ducks with water troughs also showed a greater percent (P=0.008) mortality at all ages compared to ducks with water lines. These data suggest that water troughs may not be beneficial for duck welfare and could adversely impact both environment and duck or human health.

Low light intensity in Pekin duck breeder barns has a greater impact on the fertility of drakes than hens.

The Pekin duck is an excellent model for the study of seasonal reproduction. To more completely understand the lighting requirements for maximal fertility in duck breeder houses, we housed adult (45 week old) drakes and hens in the Hope College aviary as 5 drakes and 25 hens. Light conditions in each floor pen were normalized based upon quantal energy and divided into the following categories: (1) to simulate summer, 14.5 h 65 lux with 9.5 h 1 lux; (2) to simulate winter, 8 h 65 lux with 16 h 1 lux; (3) winter augmented, 8 h 65 lux with 16 h at 15 lux. The experiment was repeated with rotation of light treatments among 3 pens until a final N = 6 was obtained. Daily, total number of eggs laid was tallied, and a daily average of eggs laid was calculated throughout the study. Weekly, eggs were weighed and the perivitilline membrane was assayed for the number of sperm holes as an indirect measure of drake fertility. As expected, winter conditions caused a reduction in the percent of eggs laid and a reduction in the number of fertilized eggs compared to the summer light conditions. The augmented winter light conditions prevented the loss in the percent eggs laid and fertilized eggs. Surprisingly, even after 4 wk of the study, the winter conditions did not cause a complete loss of fertility in the Pekin ducks. At the end of the study, no differences in the relative expression in brain deep brain photoreceptors or gonadotropin inhibitory hormone mRNAs were observed among any light treatment. Although a minimum (1 lux) of light can support some fertility, our findings suggest commercial Pekin duck barns may benefit from increasing the augmented light to 15 lux to maintain optimal fertility during winter months. Furthermore, our data suggest that drakes may be more sensitive to environmental light conditions than hens.

Expression of deep brain photoreceptors in the Pekin drake: a possible role in the maintenance of testicular function.

Several putative deep brain photoreceptors (DBPs) have been identified, such as melanopsin, opsin 5, and vertebrate ancient opsin. The aim of this study was to elucidate the role of DBPs in gonadal regulation in the Pekin drake. As previously reported, we observed opsin-like immunoreactivity (-ir) in the lateral septum (LS), melanopsin-ir in the premammillary nucleus (PMM), and opsin 5-ir in the periventricular organ. To determine the sensitivity of the DBPs to specific wavelengths of light, drakes were given an acute exposure to red, blue, or white light. Blue light stimulated an increase (P < 0.01) in the immediate early gene fra-2-ir co-expression in melanopsin-ir neurons in the PMM, and red light increased (P < 0.05) fra-2-ir co-expression in opsin-ir neurons, suggesting these neurons are blue- and red-receptive, respectively. To further investigate this photoperiodic response, we exposed drakes to chronic red, long-day white, short-day white, or blue light. Blue light elicited gonadal regression, as testes weight (P < 0.001) and plasma luteinizing hormone (LH) levels (P < 0.001) were lower compared to drakes housed under long-day white light. Photo-regressed drakes experienced complete gonadal recrudescence when housed under long-day red and blue light. qRT-PCR analyses showed that gonadally regressed drakes showed reduced levels (P < 0.01) of gonadotropin releasing hormone (GnRH) mRNA but not photoreceptor or GnIH mRNAs compared to gonadally functional drakes. Our data suggest DBP in the LS may be rhodosin and multiple DBPs are required to fully maintain gonadal function in Pekin drakes.