applicants , have discovered a method for reversibly inhibiting the production and / or assembly of a competent sperm receptor in animals . according to the invention , applicants have identified that nicarbazin eliminated fertility and fecundity in birds as well as mammals via the inhibition of the synthesis and / or production of the primary protein making up the sperm receptor in vertebrates . the contraceptive method is also particularly useful in countries where it is desired to reduce an animal population without killing the animals , instead , the animals , when fed nicarbazin supplemented food , simply can no longer multiply . the term “ therapeutically effective amount ” as used herein means that amount of active compound or pharmaceutical agent that elicits the biological or medicinal response in a tissue , system , animal or human that is being sought by a researcher , veterinarian , medical doctor or other clinician . as used herein the term “ nicarbazin ” shall be interpreted to include nicarbazin including its derivatives , modifications , homologs and the like which retain activity . nicarbazin has been used in starter rations for several decades as an aid in the prevention of faecal and intestinal coccidiosis in broiler chickens . it may be used in combination with ionophore coccidiostatics . chemically , it is an equimolar complex of 1 , 3 - n , n ′- bis ( 4 - nitrophenyl ) urea and 4 , 6 - dimethyl - 2 ( 1h )- pyrimidone . these compounds are also known as 4 , 4 ′- dinitrocarbanilide and 2 - hydroxy - 4 , 6 - dimethylpyrimidine , respectively ( see fig1 ). nicarbazin is described as an electron donor - acceptor molecular complex ; the sites of the interaction are the electron - poor nh amide groups of the acceptor phenylurea and the electron - rich lone pairs of the nitrogen in the pyrimidone donor ring . applicants have identified that nicarbazin inhibits zona pellucida activity by transcription and / or translation . zona pellucida ( zp ) dna and amino acid sequences are well conserved in all mammalian species , such as mouse , chicken , pig , cow , dog , cat , marsupials , non - human primates and human and are generally available through public sources such as genbank . hence , the present invention contemplates the contraceptive / sterilant effectiveness of nicarbazine in heterologous ( eg : porcine zona pellucida , pzp 3 - a in mice ) as well as in homologous ( eg : canine zona pellucida , czp - 2 and czp - 3 in dogs ) systems . pharmaceutical compositions of the present invention comprise administering an effective amount of nicarbazin dissolved or dispersed in a pharmaceutically acceptable carrier to a subject . the phrases “ pharmaceutical or pharmacologically acceptable ” refers to molecular entities and compositions that do not produce an adverse , allergic or other untoward reaction when administered to an animal , such as , for example , an avian , as appropriate . the preparation of a pharmaceutical composition that contains at least one nicarbazin active ingredient will be known to those of skill in the art in light of the present disclosure , and as exemplified by remington &# 39 ; s pharmaceutical sciences , 18th ed . mack printing company , 1990 , incorporated herein by reference . moreover , for animal administration , it will be understood that preparations should meet sterility , pyrogenicity , general safety and purity standards . a pharmaceutical composition of the present invention may comprise different types of pharmaceutically acceptable carriers depending on whether it is to be administered in solid , liquid or aerosol form , and whether it needs to be sterile for such routes of administration as injection . a pharmaceutical composition of the present invention can be administered intravenously , intradermally , intraarterially , intraperitoneally , intralesionally , intracranially , intraarticularly , intraprostaticaly , intrapleurally , intratracheally , intranasally , intravitreally , intravaginally , intrarectally , topically , intratumorally , intramuscularly , intraperitoneally , subcutaneously , subconjunctival , intravesicularlly , mucosally , intrapericardially , intraumbilically , intraocularally , orally , topically , locally , inhalation ( e . g ., aerosol inhalation ), injection , infusion , continuous infusion , localized perfusion bathing target cells directly , via a catheter , via a lavage , in cremes , in lipid compositions ( e . g ., liposomes ), or by other method or any combination of the foregoing as would be known to one of ordinary skill in the art ( see , for example , remington &# 39 ; s pharmaceutical sciences , 18th ed . mack printing company , 1990 , incorporated herein by reference ). the actual dosage amount of a composition of the present invention administered to a subject can be determined by physical and physiological factors such as body weight , previous or concurrent therapeutic interventions , idiopathy of the animal and on the route of administration . the number of doses and the period of time over which the dose may be given may vary . the practitioner responsible for administration will , in any event , determine the concentration of active ingredient ( s ) in a composition and appropriate dose ( s ), as well as the length of time for administration for the individual subject . in certain embodiments , pharmaceutical compositions may comprise , for example , at least about 0 . 1 % of an active compound . in other embodiments , the active compound may comprise between about 2 % to about 75 % of the weight of the unit , or between about 25 % to about 60 %, for example , and any range derivable therein . in other non - limiting examples , a dose may also comprise from about 1 microgram / kg / body weight , about 5 microgram / kg / body weight , about 10 microgram / kg / body weight , about 50 microgram / kg / body weight , about 100 microgram / kg / body weight , about 200 microgram / kg / body weight , about 350 microgram / kg / body weight , about 500 microgram / kg / body weight , about 1 milligram / kg / body weight , about 5 milligram / kg / body weight , about 10 milligram / kg / body weight , about 50 milligram / kg / body weight , about 100 milligram / kg / body weight , about 200 milligram / kg / body weight , about 350 milligram / kg / body weight , about 500 milligram / kg / body weight , to about 1000 mg / kg / body weight or more per administration , and any range derivable therein . in any case , the composition may comprise various antioxidants to retard oxidation of one or more component . additionally , the prevention of the action of microorganisms can be brought about by preservatives such as various antibacterial and antifungal agents , including but not limited to parabens ( e . g ., methylparabens , propylparabens ), chlorobutanol , phenol , sorbic acid , thimerosal or combinations thereof . the nicarbazin pharmaceutical composition of the present invention may be formulated into a composition in a free base , neutral or salt form . pharmaceutically acceptable salts , include the acid addition salts , e . g ., those formed with the free amino groups of a proteinaceous composition , or which are formed with inorganic acids such as for example , hydrochloric or phosphoric acids , or such organic acids as acetic , oxalic , tartaric or mandelic acid . salts formed with the free carboxyl groups can also be derived from inorganic bases such as for example , sodium , potassium , ammonium , calcium or ferric hydroxides ; or such organic bases as isopropylamine , trimethylamine , histidine or procaine . in embodiments where the composition is in a liquid form , a carrier can be a solvent or dispersion medium comprising but not limited to , water , ethanol , polyol ( e . g ., glycerol , propylene glycol , liquid polyethylene glycol , etc ), lipids ( e . g ., triglycerides , vegetable oils , liposomes ) and combinations thereof . the proper fluidity can be maintained , for example , by the use of a coating , such as lecithin ; by the maintenance of the required particle size by dispersion in carriers such as , for example liquid polyol or lipids ; by the use of surfactants such as , for example hydroxypropylcellulose ; or combinations thereof such methods . in many cases , it will be preferable to include isotonic agents , such as , for example , sugars , sodium chloride or combinations thereof . in certain aspects of the invention , nicarbazin is prepared for administration by such routes as oral ingestion . in these embodiments , the solid composition may comprise , for example , solutions , suspensions , emulsions , tablets , pills , capsules ( e . g ., hard or soft shelled gelatin capsules ), sustained release formulations , buccal compositions , troches , elixirs , suspensions , syrups , wafers , or combinations thereof . oral compositions may be incorporated directly with the food of the diet . preferred carriers for oral administration comprise inert diluents , assimilable edible carriers or combinations thereof . in other aspects of the invention , the oral composition may be prepared as a syrup or elixir . a syrup or elixir , and may comprise , for example , at least one active agent , a sweetening agent , a preservative , a flavoring agent , a dye , a preservative , or combinations thereof . in certain preferred embodiments an oral composition may comprise one or more binders , excipients , disintegration agents , lubricants , flavoring agents , and combinations thereof . in certain embodiments , a composition may comprise one or more of the following : a binder , such as , for example , gum tragacanth , acacia , cornstarch , gelatin or combinations thereof ; an excipient , such as , for example , dicalcium phosphate , mannitol , lactose , starch , magnesium stearate , sodium saccharine , cellulose , magnesium carbonate or combinations thereof ; a disintegrating agent , such as , for example , corn starch , potato starch , alginic acid or combinations thereof ; a lubricant , such as , for example , magnesium stearate ; a sweetening agent , such as , for example , sucrose , lactose , saccharin or combinations thereof ; a flavoring agent , such as , for example peppermint , oil of wintergreen , cherry flavoring , orange flavoring , etc . ; or combinations thereof the foregoing . when the dosage unit form is a capsule , it may contain , in addition to materials of the above type , carriers such as a liquid carrier . various other materials may be present as coatings or to otherwise modify the physical form of the dosage unit . for instance , tablets , pills , or capsules may be coated with shellac , sugar or both . additional formulations which are suitable for other modes of administration include suppositories . suppositories are solid dosage forms of various weights and shapes , usually medicated , for insertion into the rectum , vagina or urethra . after insertion , suppositories soften , melt or dissolve in the cavity fluids . in general , for suppositories , traditional carriers may include , for example , polyalkylene glycols , triglycerides or combinations thereof . in certain embodiments , suppositories may be formed from mixtures containing , for example , the active ingredient in the range of about 0 . 5 % to about 10 %, and preferably about 1 % to about 2 %. sterile injectable solutions are prepared by incorporating the active compounds in the required amount in the appropriate solvent with various of the other ingredients enumerated above , as required , followed by filtered sterilization . generally , dispersions are prepared by incorporating the various sterilized active ingredients into a sterile vehicle which contains the basic dispersion medium and / or the other ingredients . in the case of sterile powders for the preparation of sterile injectable solutions , suspensions or emulsion , the preferred methods of preparation are vacuum - drying or freeze - drying techniques which yield a powder of the active ingredient plus any additional desired ingredient from a previously sterile - filtered liquid medium thereof . the liquid medium should be suitably buffered if necessary and the liquid diluent first rendered isotonic prior to injection with sufficient saline or glucose . the preparation of highly concentrated compositions for direct injection is also contemplated , where the use of dmso as solvent is envisioned to result in extremely rapid penetration , delivering high concentrations of the active agents to a small area . the composition must be stable under the conditions of manufacture and storage , and preserved against the contaminating action of microorganisms , such as bacteria and fungi . it will be appreciated that endotoxin contamination should be kept minimally at a safe level , for example , less that 0 . 5 ng / mg protein . in particular embodiments , prolonged absorption of an injectable composition can be brought about by the use in the compositions of agents delaying absorption , such as , for example , aluminum monostearate , gelatin or combinations thereof . nicarbazin has been used for over 50 years to control coccidiosis , an infection of protozoan parasites , in domestic poultry ( see review by chapman , 2001 ). while the exact mode of action of is unknown , several biochemical effects have been reported . one of the most acknowledged effects of nicarbazin on cells is to cause a leakage of potassium ions across the cell membrane along with an effect on mitochondrial energy production ( long , 1978 ). it is unclear how either of these effects influences the parasite itself , although nicarbazin has differential effects during the life cycle of the protozoan eimeria — directly inhibiting both the asexual and sexual aspects of reproduction ( danforth , 1997 ; xie , 1991 ). in the poultry industry , nicarbazin is commonly administered to growing , meat - type chickens ( e . g ., broilers ). however , when mistakenly added to the feed of egg - laying chickens , depigmentation of egg - shell color and egg production drop precipitously within a matter of days ( ott et al ., 1956 ; sherwood et al ., 1956 ). these older studies clearly demonstrated a drug dosage effect among broiler - breeder hens ; demonstrating that lower levels of nicarbazin (& lt ; 125 ppm ) produced a significant reduction in hatchability of fertile eggs . higher levels ( ca . 700 ppm ) eliminated egg production entirely . however , all studies demonstrated that normal hatchability and egg production returned within 7 - 10 days following the removal of nicarbazin from the feed . chapman ( 2001 ) and others ( e . g ., jones et al ., 1990 ) suggest that nicarbazin functions to reduce hatchability of chicken eggs via the creation of ‘ leaky membranes ’ within the egg . we hypothesized that the commonly accepted explanation of the decline in hatchability was incorrect , as it could not account for declines in either fertility or egg production at higher drug doses . offering an alternative explanation ; we further hypothesized that the main effect of nicarbazin was to alter the structure of the oocyte membrane by altering the structure and / or assembly of the primary protein composing the membrane ( i . e ., zona pellucida protein c ( zpc )). zpc is also the primary sperm receptor among birds , mice , rats , cows and humans . which thus would make the protocol useful in other animals besides just birds . in a preliminary effort to support this hypothesis , we isolated granulosa cells from primary follicles of a laying hen , and suspended them in a simple cell culture media ( 1 ml medium ( m ) 199 - hepes supplemented with hank salts ( gibco - brl ) plus 1 ml dulbecco modified eagle medium ( dmem ) containing 5 % fbs ). nicarbazin was added to the cells at a concentration of 10 mm . the cells were then disrupted with a sonicator and proteins precipitated and heat solubilized per barbato et al . ( 1998 ). proteins were concentrated , separated via gel electrophoresis and western blot performed with antibodies to chicken zpc . as can be seen in fig1 , nicarbazin treatment ( lanes 4 - 6 ) resulted in the absence of immunoreactive zpc ( control chzpc in lanes 1 and 3 ). several studies were designed and executed to determine the effects of oral doses of nicarbazin on the sperm receptor in the oocyte membrane . initially , both ducks and chickens were used to identify the main effect of nicarbazin treatment . our first study determined the dose - response relationship for the effect of nicarbazin in reducing egg production and / or hatchability in ducks . dnc concentrations in the blood and laid eggs established a linear dose - concentration relationship with fed nicarbazin dose . ( doses used in this study were — 0 mg / kg ( control ), 31 . 25 ppm , 62 . 5 ppm , 125 ppm , 250 ppm and 500 ppm ( these doses correspond to the range of doses known to affect hatchability in chickens , chapman , 2001 ). fig2 illustrates the decline in egg production both pre and post - nicarbazin treatment . since all hens in this experiment were artificially inseminated with sperm from untreated drakes , the effects on subsequent fertility were considered to be due entirely to the effect of nicarbazin on the female ducks . fig3 illustrates the profound effect of oral doses of nicarbazin on the fertility of eggs laid by treated hens . further , upon the withdrawal of nicarbazin - treated feed , even the hens receiving the highest dose of nicarbazin returned to normal egg production and fertility within 10 days . a subsample of eggs were collected during each week of the experiment , in order to dissect , extract and identify the zpc in the oocyte membrane using and anti - zpc antibody and western blotting technique . fig4 illustrates that at the 500 ppm dose of nicarbazin , zpc was undetectable after the 1st week of treatment , and remained absent thereafter . oocyte membranes from ducks receiving the 250 ppm dose had a clear decline in the intensity of zpc over time . since there appeared to be a decrease in the amount of zpc ( the primary sperm receptor ) present in the duck oocyte membranes , we reasoned that the lack of fertility in any laid eggs should be due to a decline in sperm attaching to the oocyte . fig5 illustrates a pair of sample membranes from both control and nicarbazin treated ducks . consistent with previous data from our lab ( e . g ., barbato et al ., 1998 ) 228 ± 15 sperm / mm2 of oocyte membrane were found in eggs from control ducks , whereas there were 0 ± 15 sperm / mm2 counted on the membranes from nicarbazin - treated ducks . as a follow - up experiment , we fed a group of 6 laying hens the 250 ppm nicarbazin treated feed , in an attempt to reduce , but not eliminate , zpc synthesis . egg membranes were collected from laid eggs and the most mature follicle dissected from both treated and control hens . the membranes were fixed with osmium tetroxide , sectioned via microtome and viewed with electron microscopy . fig6 clearly demonstrates the reduction in width of the inner perivitelline membrane , which is made up of 85 % zpc protein . this micrograph provides direct , visual confirmation of the previously presented data : that is , that oral nicarbazin dosages reduces the zp3 content of the oocyte membrane . further , the reduction is of sufficient magnitude to reduce sperm binding and , hence , fertility in treated animals . in an experiment performed by the world health organization in 1998 to evaluate the toxic effects of nicarbazin ( who food additives series 41 ; http / www . inchem . org ). groups of 12 male and 12 female fdrl rats were fed diets containing the phenylurea and the pyrimidone components at concentrations calculated to achieve doses of 0 , 50 , 150 , or 300 mg / kg bw per day of the phenylurea and 0 , 17 , 50 , or 100 mg / kg bw per day of the pyrimidone . treatment was administered continuously during the production of two litters per generation for three successive generations . in their results section the authors remarked , “ in subsequent generations , the f2a and f3a litters at the high dose had slightly fewer pups , but the effect was not reproduced in the f2b or fib litters .” in the conclusions , the authors suggested that reduced litter sizes were observed , but were inconsistent and thought to be of minor importance . however , the relative distribution of the active components of nicarbazin were significantly different that those observed in the avian species . if nicarbazin were to be re - formulated to result in similar concentrations in mammalian blood , we hypothesize that the nicarbazin - induced effect on fertility and fecundity will be observed in mammals . in an attempt to increase nicarbazin absorption in a mammalian species we paired nicarbazin with a typical pharmaceutical carrier , 5 % propylene glycol ( pgc ). a 500 ppm dose was fed to 8 adult , female rats for a 7 - day period , at which time the rats were killed and the ovaries removed and placed in rna later ( to preserve protein , rna and dna — 4 control rats were also sacrificed ). ovarian proteins and mrna were extracted via standard laboratory protocols . fig7 illustrates the results of a western blot for zpc , using a murine monoclonal antibody ( which cross - reacts with rat zpc ). upon finding a reduction in zpc - immunoreactive band intensity from ovarian samples obtained from treated animals , we designed pcr primers to identify mrna for rat zpc . by applying the quantitative rtpcr technique we were able to estimate the number of copies of the zpc mrna that were present in the ovarian tissue samples . table 1 shows the significant , 30 % reduction in copy number of the zpc gene . these data indicate that not only does nicarbazin reduce the protein expression of zpc in rats , but also significantly reduces the transcription of the zpc gene . the indirect biochemical evidence in the previous section led us to attempt a direct feeding experiment with mice . in this case , mice were fed a 0 . 5 % nicarbazin diet ( containing 5 % propylene glycol ). in addition , 7 . 5 % peanut butter was added to the diet to increase palatability . ten mating pairs of mice were given access to the diet for 4 - 5 hrs over a 2 week period . during this period non - treated mating pairs had a conception rate of 90 %, averaging 6 pups per litter . treated mice resulted in only a single pregnancy , having 2 pups ( 10 % conception rate having 0 . 2 pups / litter ). the pups were completely healthy , with no sign of teratogenic effects . after removal of the treated feed all previously treated mice were mated and conceived normal litters over the next month . barbato , g . f ., p . cramer and r . h . hammerstedt . ( 1998 ) evaluation of an in vitro sperm - egg binding assay assessing male infertility . biology of reproduction 58 : 686 - 699 . chapman , h . d . ( 2001 ). use of anticoccidial drugs in broiler chickens in the usa : analysis for the years 1995 to 1999 . poult sci 80 ( 5 ): 572 - 80 . danforth , h . d ., k . watkins , et al . ( 1997 ). evaluation of the efficacy of eimeria maxima oocyst immunization with different strains of day - old broiler and roaster chickens . avian dis 41 ( 4 ): 792801 . jones , j . e ., j . solis , b . l . hughes , d . j . castaldo and j . e . toler ( 1990 ) reproduction responses of broiler - breeders to anticoccidial agents . poultry sci . 69 : 27 - 36 . long , p . l ., k . n . boorman , et al . ( 1978 ). avian coccidiosis : proceedings of the thirteenth poultry science symposium , 14 - 16 sep ., 1977 . [ s . 1 . ], british poultry science , ltd . ott , w . h ., s . kuna , c . c . porter , a . c . cuckler and d . e . fogg ( 1956 ) biological studies on nicarbazin , a new anticoccidial agent . poultry sci . 35 : 1355 - 1367 . sherwood , d . h ., t . t . milby and w . a . higgins ( 1956 ) the effect of nicarbazin on reproduction in white rock breeder hens . poultry sci . 35 : 1014 - 1019 . xie , m . q ., t . fukata , et al . ( 1991 ). evaluation of anticoccidial drugs in chicken embryos . parasitol res 77 ( 7 ): 595 - 9 . according to the invention , nicarbazin specifically influences the expression of the zona pellucida 3 gene and protein in vertebrates . it is expected that other homologs of the zp3 gene will also be negatively affected by nicarbazine . for example , there is an insect homolog of zp3 that is a structural component of the wing vein . nicarbazin interferes with the expression of the insect homolog in the same manner as the vertebrate gene . in a quick experiment , 3 - 5 % nicarbazin preparation was added to the media ( food ) in fruit fly vials using ethanol as a carrier ( since fruit flies are attracted to ethanol ). at the high dose ( 5 %), the fruit fly eggs did not hatch . at 3 %, the flies hatched — but , had deformed wings and could not fly .
methods are disclosed for reversibly inhibiting sperm receptor activity in animals . nicarbazin , its derivatives and modifications which retain pharmacological activity are shown to inhibit activity of zona pellucida proteins and concomitant synthesis and / or assembly of the sperm receptor on the oocyte surface necessary for fertilization . nicarbazin is easily administered , for example by simple addition to feed of an animal and is and non - toxic to the animals , providing a safe and efficient means for controlling populations of mammals and avian species .