Abstract
Daily subcutaneous injections of levels of less than 4.8 mg/d of 17-a-ethyl-19-nortest-osterone (Nilevar) were not successful in completely inhibiting estrus. Estrus in seven cows receiving 4.8 mg/d was successfully synchronized, and six of the seven cows settled at the post-treatment estrus. Oral doses of 24 mg/d, 48 mg/d, and 96 mg/d were not successful in inhibiting estrus. Round vaginal pessaries were expelled by mature dairy cows within 40 hr. from time of insertion. Twelve hydron plastic implants containing either 75 mg, 200 mg, or 300 mg of Nilevar were inserted approximately 10 cm lateral to the first lumbar vertebra. The 75 mg and 200 mg implants did not effectively inhibit estrus, but the 300 mg implants inserted on days 2, 12 and 16 of the estrual cycle inhibited estrus until removal 17 days later.
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