Molecular effects of nicarbazin on avian reproduction

Medical Management of Reproduction in Birds

Reproductive diseases are common medical problems of birds including dystocia, oviductal and ovarian disease, testicular tumors, as well as hormonally linked behavioral disorders such as feather destruction, self-trauma, aggression, or masturbation. The hypothalamic-pituitary-gonadal axis endogenously controls reproduction, although there are numerous exogenous factors (eg, presence of a mate, photoperiod, rainfall) that have a substantial influence on reproductive activity. Surgical intervention in female birds by means of salpingohysterectomy (oviduct removal) presents significant surgical and anesthetic risks due to the unique and highly vascular reproductive anatomy. This article presents current literature on the medical management of reproduction in birds.

In Vitro Assessment of Anticoccidials: Methods and Molecules

Simple Summary

Coccidiosis is a major problem in poultry production, leading to significant economic losses. Due to the outbreak of resistance to the available treatments, research is focusing on finding new molecules that work against the pathogen. Botanical compounds represent promising alternatives, but reliable in vitro tests are needed for their screening and to understand their mechanism of action. Research in vitro involves studies on the environmental phase of the parasite and studies on the endogenous development, which occurs inside the host cells and that requires cell cultures or in ovo models to be studied. This review aims to summarize the protocols that have been successfully applied so far, as well as to suggest potential cues to improve research on this field. Moreover, as the surge of botanicals as anticoccidial molecules is on the rise, the intent is to provide an overview of the methods to assess their effectiveness in vitro in comparison with conventional drugs.

Abstract

Avian coccidiosis is a disease causing considerable economic losses in the poultry industry. It is caused by Eimeria spp., protozoan parasites characterized by an exogenous–endogenous lifecycle. In vitro research on these pathogens is very complicated and lacks standardization. This review provides a description of the main in vitro protocols so far assessed focusing on the exogenous phase, with oocyst viability and sporulation assays, and on the endogenous phase, with invasion and developmental assays in cell cultures and in ovo. An overview of these in vitro applications to screen both old and new remedies and to understand the relative mode of action is also discussed.

Nicarbazin has no effect on reducing feral pigeon populations in Barcelona

BACKGROUND

Nicarbazin is an anti-coccidial product sometimes used as a contraceptive to reduce the size of feral pigeon populations. However, its effectiveness in reducing pigeon population size in cities has caused some controversy. Here, we evaluate its effectiveness in the city of Barcelona.

RESULTS

In 2017, the Barcelona City Council set 23 feeding stations with nicarbazin and ten with placebo (untreated corn). Censuses were undertaken before and after one year of treatment, within a 200-m radius around each feeder. We also censused 28 circles of 200 m radius distributed randomly 200 m from the feeders and 28 circles > 500 m from the feeders, which acted as controls. Population size across the whole city was also evaluated pre- and post treatment. We found that feral pigeon density did not change after one year of treatment, either in the circles around feeding stations with nicarbazin or in the areas around control stations at 200 and > 500 m from the feeders. Population size in placebo circles rose after a year by 10%. A pigeon census for the whole of Barcelona showed a 10% increase.

CONCLUSION

Overall, our results indicate that the nicarbazin treatment had no effect on feral pigeon population size, and we advise against its use as a pigeon control method, at least in large cities.

Anticoccidial drugs of the livestock industry

Coccidiosis is a parasitic disease of a wide variety of animals caused by coccidian protozoa. The coccidia are responsible for major economic losses of the livestock industry. For example, the annual cost due to coccidiosis to the global poultry industry has been estimated to exceed US$ 3 billion annually. Currently available drugs for the control of this disease are either polyether ionophorous antibiotics that are derived from fermentation products, or synthetic compounds, produced by chemical synthesis. Unfortunately, no new drugs in either category have been approved for use for decades. Resistance has been documented for all those of the drugs currently employed and therefore the discovery of novel drugs with unique modes of action is imperative if chemotherapy is to remain the principal means to control this disease. This chapter aims to give an overview of the efficacy and mode of action of the current compounds used to control coccidiosis in livestock and provides a brief outlook of research needs for the future.

Nicarbazin bait reduces reproduction by pigeons (Columba livia)

Development of effective methods for reducing populations of overabundant nuisance bird species continues to challenge wildlife biologists. Reproductive inhibition, although conceptually pleasing, has been difficult to implement because of the lack of a safe, approved avian contraceptive. Recently, however, nicarbazin received regulatory approval in the United States for use as a bait to decrease hatchability of resident Canada goose (Branta canadensis) and feral pigeon (Columba livia) eggs. In anticipation of the feral pigeon registration, we evaluated efficacy by exposing captive pairs of nesting pigeons to nicarbazin bait for 4 h daily. Egg production was unaffected, but only 9 of 22 eggs hatched, a 59% reduction from pre-treatment when each of the 11 test pairs produced 2 nestlings. In the recovery phase, when treated bait was removed, the 11 pairs produced 18 nestlings. All nestlings produced during the study appeared healthy and normal, and there was no mortality among the adult pairs. Nicarbazin is an effective and safe means of reducing hatchability of feral pigeon eggs that can be used within an integrated management plan to reduce feral pigeon populations.

On the use of pharmacological sterilisation to control feral pigeon populations

The use of chemosterilisation for controlling feral pigeon populations was investigated by: (1) quantifying the reproductive activity of pigeons in two Italian cities; (2) testing the efficacy of nicarbazin, an anticoccidial drug with rapid and reversible effects on the reproduction of laying hens, on groups of paired pigeons maintained in open aviaries; and (3) simulating the effects of the use of nicarbazin on a hypothetical population, allowing for the reproductive productivity recorded in (1) and the efficacy of this drug as obtained in (2). Breeding attempts were recorded all year round in both study sites with a minimum peak in September–October, a maximum in March–July, but with active nests in winter too. In terms of the sterility activity of the drug, the results showed only a partial inhibition of reproduction of pigeons fed ~38–82 mg nicarbazin day–1 (kg bodyweight)–1 (500 and 800 ppm in feed), which, according to the simulations, would produce only a fleeting reduction of their abundance in the field. Data do not seem to support the use of this drug as an effective control method for feral pigeons, and they cast doubts on the opportunity to make use of chemosterilants, which produce only partial and reversible effects. The use of this drug could perhaps be considered only as part of an integrated pest-management program, which necessarily has to include the reduction of carrying capacity of the urban environment.