Conception rates of dairy cows following early not-pregnant diagnosis by ultrasonography and subsequent treatments with shortened Ovsynch protocol

Our objective was to determine the feasibility of prompt reinsemination of dairy cows when diagnosed not pregnant 27–29 days after first-service timed AI (TAI). We assumed that a first-wave dominant follicle was present at that time that would ovulate in response to GnRH once precocious luteal regression was induced after administration of PGF2α. Cows that had not been detected in estrus and reinseminated by Days 27–29 after a first-service TAI were diagnosed not pregnant by ultrasonography. Nonpregnant cows from three herds were assigned randomly to receive either no further treatment until reinsemination (controls; <F>n=189</F>); 25 mg i.m. of PGF2α and then reinsemination according to detected estrus (81 of 108) or at 72–80 h after PGF2α treatment (PGF) in the absence of estrus (27 of 108); or 25 mg i.m. of PGF2α followed by 100 μg i.m. of GnRH 48 h later (<F>PGF+GnRH</F>) and then reinsemination after detection of estrus (9 of 160) or at 16–20 h after GnRH (151 of 160). Blood samples were collected at the time of the not-pregnant diagnosis and again 48 h later. Concentrations of progesterone before treatment with PGF2α were elevated (<1 ng/ml) in 61% of the cows when PGF2α was administered and 81% of the cows given PGF2α had low (<1 ng/ml) concentrations of progesterone 48 h after PGF2α. Treated cows were re-inseminated earlier (<F>P<0.01</F>; <F>31±1</F> days) after first-service TAI than controls (<F>55±1</F> days). Conception rates after treatment were not different among treatments: PGF (22%), <F>PGF+GnRH</F> (23%), and control (23%). Average intervals from calving to conception were 22–23 days less (<F>P<0.001</F>) in treated cows than in controls. We concluded that treating nonpregnant cows with PGF2α on Days 27–29 after insemination produced acceptable conception rates when inseminations were made after detected estrus or when TAI was used after GnRH treatment. Further, both treatments reduced days between first-service TAI and second inseminations, and days from calving to conception. [Copyright &y& Elsevier]