the practice of the invention will be better understood by reference to the following examples , which are to be considered as illustrative , and not as limiting . animal tolerance to reserpine was investigated using four cows in late lactation . a single daily injection of 5 mg / day of reserpine ( sandril ; eli lilly , indianapolis , in ) was administered intramuscularly in the hip region for 4 consecutive days , or 2 ml of 0 . 9 % nacl , without reference to stage of estrus cycle . the effect of reserpine on serum prolactin levels was also investigated with four nonlactating , nonpregnant cows . each cow was fitted with an indwelling jugular catheter of silastic tubing and the catheter kept open by flushing with a salin - heparin solution . the animal was allowed a 24 hour adjustment period to become accustomed to the investigators and the intermittent drawing of blood samples . a single 5 mg dose of reserpine was given via intramuscular injection in the hip region and blood samples were periodically withdrawn via the jugular catheter for 48 hours . seventy - two hours following the reserpine injection a 2 ml , 0 . 9 % saline injection was given intramuscularly and the schedule of blood sampling repeated . blood samples were allowed to equilibrate at room temperature for 4 hours , centrifuged and the serum removed and frozen . serum prolactin was analyzed using a double - antibody radioimmunoassay . prolactin in jugular blood at 0 , 0 . 5 , 2 , 3 , 6 , 8 and 12 hr . averaged 27 , 196 , 276 , 304 , 246 , 183 and 153 ng / ml , respectively , after reserpine ; after saline injection prolactin ranged from 18 to 40 ng / ml . for initial investigations in example 1 , 5 mg per day of reserpine was administered via a daily intramuscular injection for 4 consecutive days . side reactions noted were some labored breathing , nasal congestion and drowsiness on the afternoon following the 3rd and 4th injections . however , there was no trouble in getting animals to stand . in examples 2 and 3 , animals receiving reserpine injections developed identical side reactions . in addition , approximately one - third of the animals had some difficulty in standing on the afternoon of the last reserpine injection . by 48 hours after the last reserpine injection , the side reactions to reserpine were not apparent in any of the animals . seven nonpregnant heifers and cows were used in this study . cows had at least a 34 day dry period prior to the start of the treatment to induce lactation . all animals were given subcutaneous injections of 17β estradiol plus progesterone on days 1 to 7 of the treatment period and intramuscular injections of dexamethasone on days 18 to 20 as previously described . three of the animals received no additional injections ( control treatment group ). four of the animals were given intramuscular injections ( once a day injection in the hip region ) of 5 mg / day of reserpine on days 13 , 14 , 15 and 16 ( reserpine 1 treatment group ). blood samples were obtained periodically throughout the treatment period by tail venipuncture for both groups of animals . blood samples were handled and serum prolactin analyzed as in example 1 . in example 2 , reserpine was administered on days 13 , 14 , 15 and 16 of the treatment period . these days were chosen such that the prolactin levels in cows induced into lactation would possibly mimic the increase in serum prolactin which occurs in pregnant cows in the period immediately prior to parturition . eight nonpregnant parous cows were utilized in this study . cows had been dry for 35 days at the time of the first hormone injection . all cows received the 17β estradiol plus progesterone and the dexamethasone injections as indicated in example 2 . five of the animals also received 5 mg / day of reserpine on days 8 , 10 , 12 and 14 of the treatment period ( reserpine 11 treatment group ). reserpine was administered via an intramuscular injection in the hip region of the animals . blood samples were obtained via tail venipuncture on days 0 , 6 , 9 , 10 , 15 , 17 , 19 and 21 of the treatment period and analyzed for prolactin as described in example 1 . in example 3 the hormonal treatment to induce lactation in nonpregnant cows was modified with the administration of reserpine on days 8 , 10 , 12 and 14 . the days of reserpine administration for example 3 were chosen on the basis of information which indicated that mammary tissue from cows successfully induced into lactation was undergoing the cellular changes associated with lactogenesis during the interval between day 8 and day 16 of the treatment period . serum prolactin values remained low during the treatment period when 17β estradiol plus progesterone injections were administered . in the interval between day 16 and day 21 of the treatment period there was an apparent increase in serum prolactin levels although the variation between animals had increased markedly . this was particularly evident at days 15 to 16 . all five control animals averaged 97 ± 59 ng / ml on days 15 and 16 , but the omission of one cow with an extremely high serum prolactin concentration lowered the average to 40 ± 17 ng / ml . the milk production of animals in examples 2 and 3 is shown in table 1 : table 1 . ______________________________________milk production of cows hormonally induced into lactation experimental period highest daily milk yield milk yieldtreatment . sup . a days ( kg ) ( kg ) ______________________________________ 6control ( 3 ) 100 96 ± 163 ( range 4 - 10 ) 14reserpine i ( 4 ) 100 1121 ± 133 ( range 10 - 16 ) 11 5control ( 2 ) 100 865 ± 78 ( range 10 - 13 ) 17 5reserpine ii ( 5 ) 100 1314 ± 75 ( range 15 - 22 ) ______________________________________ . sup . a control = 17 . β - estradiol + progesterone . reserpine i = control treatment + 5 mg reserpine ( intramuscular injection ) on days 13 , 14 , 15 and 16 . reserpine ii = control treatment + 5 mg reserpine ( intramuscular injection ) on days 8 , 10 , 12 and 14 . the number of animals is indicated in parentheses . in example 2 the reserpine treated animals had a higher milk yield than the positive controls . relative to the control group , reserpine treated animals in example 3 also had a higher milk production for the experimental period . in both studies all of the animals receiving reserpine were successfully induced into lactation using the criterion of success as a peak milk yield greater than 9 kg / day . there were no apparent differences in milk production between the two reserpine groups although the reserpine ii treatment group tended to have a greater peak daily milk yield .
the administration of reserpine to nonlactating dairy cattle produces a marked increase in circulating serum prolactin levels . the parenteral administration of reserpine to nonlactating cows which have been hormonally induced into lactation , as by the parenteral administration of an estrogen and progesterone , and dexamethasone , results in a substantial rise in milk production .