the following examples set forth presently preferred methods for the production of heartworm preventative drug - containing pet foods and related information . it is to be understood , however , that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention . in this example , an ivermectin - containing dog food product was produced using a co - extrusion process . the dry farinaceous ingredients used in this example were ( all percentages on a weight basis ): wheat flour — 14 %; rice flour — 15 %; corn flour — 32 %; corn gluten meal — 12 %; poultry meal — 8 %; brewer &# 39 ; s yeast — 2 %; sodium bicarbonate — 0 . 6 %; thoxyquin — 0 . 1 %; potassium sorbate — 0 . 3 %; and sugar — 5 %. the liquid co - extruded mixture contained ( all percentages on a weight basis : poultry fat — 81 . 13 %; gp ( glutamine peptide )— 11 . 32 %; cheese powder — 3 . 77 %; and poultry meal — 3 . 77 %. the extrusion equipment included a wenger x - 85 single screw extruder with a wenger model 7 ddc preconditioner . the extruder barrel was made up of a series of interconnected heads . the screw configuration , dies , adaptor parts , preconditioner shafts and beater elements were all wenger equipment . in order to effect the desired co - extrusion , a delivery pipe having approximately a ⅜ ″ delivery nipple was inserted into the center of the die so that the liquid portion was directed through the die with a surrounding annulus of the extruded farinaceous mixture . the liquid portion was pumped through the delivery pipe at a rate which was approximately 30 % of the extrusion rate of the farinaceous mixture . at the outlet of the extruder die , the product was cut using an knife and respective samples of the cut product were manually crimped using a hand - crimping tool . in this fashion , “ pillows ” of the pet food were obtained , with an outer farinaceous ingredient shell and an inner flowable filling containing ivermectin . following this treatment , the product was dried to a moisture level of less than 10 % by weight . three samples from the dryer were subsequently frozen and another sample was placed in a plastic bag and stored at room temperature , for a period in excess of six months . the following table sets forth the illustrative preconditioning and extrusion information . the products resulting from this test were analyzed to determine the content of ivermectin in the samples . in this analysis , each feed sample was ground in a retsch mill at low speed using a 2 mm grating screen , so that the ground material would pass through a # 10 mesh screen . a total of six samples , three frozen and three stored at room temperature , were processed . in each case , three 37 . 5 g of a sample was placed in a 250 ml bottle and 100 ml of methanol was added . the bottle was capped , the sample was sonicated for 20 minutes and shaken for 1 hour . 40 ml of the extract was added to a centrifuge tube and centrifuged for 5 minutes at 2000 rpm . 20 ml of the supernatant solution was then passed through a alumina column . the first five ml was rejected and the remainder of the liquid through the column was collected as a purified sample . 2 ml of the purified sample was mixed with a 5 ml mixture of acetonitrile : water ( 1 : 1 ), and a solid phase extraction ( spe ) was performed in accordance with the procedure described in doherty et al ., analytical chemists international , 81 : 869 ( 4 )( 1998 ). 2 ml of the working , 1 % ivermectin sample standard was also run through the spe procedure to determine if any loss of ivermectin was taking place . all samples from the spe treatment were evaporated under nitrogen using an analytical evaporator with a water bath temperature of 50 ° c . the dried samples were reconstituted in 2 ml of hplc mobile phase for analysis . two samples were also prepared using 2 ml of the working standard ivermectin solution ( containing 0 . 42 μg / ml ) and were run before and after the feed samples . gilson 305 pump , 231 sample injector , 401 dilutor and 115 uv detector hplc analytical column symmetry c 18 , 5μ 4 . 6 × 350 mm mobile phase acetonitrile / methanol / water 53 / 35 / 7 flow rate 1 ml / minute uv detection 245 nm the results of the hplc analyses ( two injections of each feed sample and two injections of the working standard solution ) confirmed that the pet food samples contained very close to the expected content ( 0 . 42 μg / kg ) of ivermectin . in particular , the average ivermectin content of the three frozen and the ambient - stored samples was 0 . 43 μg / kg . this demonstrated that storage conditions ( frozen versus ambient ) had little effect upon ivermectin potency , and an excellent ivermectin stability . in this example , an ivermectin - containing dog food was prepared using a wenger tx - 85 twin screw extruder equipped with a model 16 wenger ddc preconditioner . the dry ingredients fed to the extruder included ( all percentages by weight basis ): wheat middlings — 18 %; meat and bone meal — 18 %; soybean meal — 18 %; and corn — 46 %. in this run , two liquid dispersions were used which contained ( all percentages by weight basis ): first mixture , propylene glycol — 11 lbs and water — 11 lbs ; second mixture , propylene glycol — 48 . 82 %; water — 48 . 82 %; red no . 40 dye — 1 . 86 %; and ivermectin solution — 0 . 50 %. the amount of ivermectin used was calculated to provide a dose of approximately 1121 . 1 μg of ivermectin per kg of the dog food on a dry basis . the extruder barrel was made up of interconnected heads . the rotating elements within the barrel included extruder shafts and other elements . the extruder was equipped with dies and adaptors , inserts , and a cutting knife with knife blades was used . the foregoing components as well as the preconditioners shafts and beater elements were all wenger equipment . in the process , the dry ingredients were fed to the preconditioner where steam and water was added to moisturize and partially precook the mixture . this preconditioned material was then fed to the inlet of the extruder in the usual fashion . the first liquid mixture was added to the outlet end of the preconditioner for passage into the extruder barrel along with the preconditioned material , over a period of about 11 minutes . thereafter , the colored , ivermectin - containing liquid mixture was added over a period of about 22 minutes . finally , additional quantities of the first water / propylene glycol liquid mixture was again added , over about 11 minutes . after extrusion , the product was dried in a wenger dryer operating at 115 ° c ., followed by a cooler pass . the dryer discharge moisture was 6 . 25 %, wb . samples were collected of the colored ivermectin - containing dispersion , the raw material mixture , preconditioned material leaving the preconditioner and extruded samples . the dog food from this run was fed ad libitum to an intact female mixed breed dog weighing about 10 kg . on day 7 , blood was drawn from the dog four hours after eating and stored in an anti - coagulant tube with calcium edta in a refrigerator . seven days later , the same dog was again fed the ivermectin - containing feed ad libitum and blood was collected four hours post - feeding . this sample was also refrigerated in the same fashion as the first sample . the blood samples were then analyzed to determine the content of ivermectin therein , using hplc . the procedure used was described in dickinson , journal of chromatography , 58 : 250 - 257 ( 1990 ). in this procedure , 0 . 5 ml of each blood sample was purified using solid phase extraction ( spe ) cartridges and dissolved in a small volume of mobile phase for injection onto the hplc column . the method has a limit of detection of about 2 ng / ml and uses an internal standard . after preparation of the internal standard , a standard curve is constructed using ivermectin - spiked blood samples . a known 1 % ivermectin sample was used as the primary standard . the blood samples from the dog were then analyzed for ivermectin content with hplc peak heights corrected using the internal standard . the hplc setup consisted of the following : gilson 305 pump , 231 sample injector , 401 dilutor and 115 uv detector hplc analytical column : coulter - beckman ultrasphere xl c 18 , 3μ , 4 . 6 × 70 mm mobile phase : acetonitrile / methanol / water 49 / 33 / 18 flow rate : 1 ml / minute uv detection : 245 nm the results of this study demonstrated that the dog blood samples contained ivermectin in the range of about 5 - 8 ng / ml . in this example a series of extrusion runs were performed to determine the consistency of metering of ivermectin into a dog food mixture during extrusion . in each case , the farinaceous mixture included the following ingredients ( all percentages on a weight basis ): corn — 35 . 93 %; poultry meal — 28 . 94 %; rice — 22 . 95 %; corn gluten meal — 11 . 98 %; vitamin premix — 0 . 10 %; and mineral premix — 0 . 10 %. three ivermectin - containing liquids were prepared , containing : recipe # 1 , propylene glycol — 8 . 60 pounds ; water — 8 . 60 pounds ; red # 40 dye — 160 grams ; ivermectin solution — 0 . 212 ml ; recipe # 2 , propylene glycol — 8 . 60 pounds ; water -— 8 . 60 pounds ; red # 40 dye — 160 grams ; ivermectin solution — 0 . 433 ml ; recipe # 3 , propylene glycol — 8 . 60 pounds ; water — 8 . 60 pounds ; red # 40 dye — 160 grams ; ivermectin solution — 1 . 279 ml . in each run 8 . 0 kg of a respective ivermectin recipe was added to the farinaceous ingredients at the exit of the preconditioner , prior to entering the extruder barrel . the recipes were added at a rate equal to 2 % of the farinaceous mixture rate . the target for the runs using recipe # 1 was 6 μg ivermectin / kg of feed ; for runs using recipe # 2 , 12 μg / kg ; and for runs using recipe # 3 , 36 μg / kg . the extruder system employed was a wenger model tx 57 twin screw extruder with a model 2 ddc preconditioner . the extruder barrel was equipped with an extrusion die , a knife assembly was used to cut extrudate . the following table sets forth the preconditioning and extrusion information collected during this series of runs . in runs 101 - 103 , recipe # 1 was used ; in runs 104 - 106 , recipe # 2 was used ; and in runs 107 - 109 , recipe # 3 was used . as the extrudates emerged from the die , they were cut using the knife assembly and dried in a wenger multiple - pass drier . samples were collected at 15 minutes , 30 minutes and 45 minutes from the preconditioner , extruder and drier . the dried samples were analyzed to determine ivermectin content , using the technique described in example 1 . the results from the recipe # 1 , # 2 and # 3 runs were averaged , with the following results . for the recipe # 1 runs ( 101 - 103 ), the ivermectin content was 6 . 02 μ / kg ( dry basis ); for the recipe # 2 runs ( 104 - 106 ), the ivermectin content was 11 . 99 μg ( dry basis ); and for the recipe # 3 runs ( 107 - 109 ), the ivermectin content was 35 . 98 μ / g ( dry basis ). this confirms that the processing technique of this example gives extremely close ivermectin contents , as compared with the pre - extrusion goals .
improved daily ration mammal feeds are provided which include minor amounts of heartworm preventative drugs , ensure that a mammal consuming the feed receives quantities of drug sufficient to establish and maintain substantially constant concentrations of the drug in the pet &# 39 ; s bloodstream . the feeds may be produced by extrusion with addition of minor quantities of heartworm preventative drug so as to uniformly distribute the drug throughout the extruded product . ivermectin levels of from about 2 - 1500 μg / kg of extruded feed are preferred .