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Comparison of effects of GnRH and prostaglandin in combination, and prostaglandin on conception rates and time to conception in dairy cows
Author(s) -
LEAN IJ,
PORTER JA,
RABIEE AR,
MORGAN WF,
TRANTER WP,
MOSS N,
RHEINBERGER RJ
Publication year - 2003
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/j.1751-0813.2003.tb13369.x
Subject(s) - artificial insemination , prostaglandin , medicine , herd , zoology , lactation , intramuscular injection , radioimmunoassay , insemination , ice calving , gonadotropin releasing hormone , endocrinology , hormone , pregnancy , biology , andrology , luteinizing hormone , genetics , sperm
Objective To assess the effectiveness of a gonadotrophin‐releasing hormone (GnRH) / prostaglandin program (GnRH‐PG‐GnRH, Ovsynch) on conception rates and time to conception of lactating dairy cows compared with a PG program (double prostaglandin injection). Design A randomised multi‐centre cohort study was conducted with 778 cows from nine dairy herds. Cows at different stages of lactation were randomly assigned, after matching for days open at the time of treatment, to either the PG or Ovsynch program. Procedure Cows on the PG program received two intramuscular injections of prostaglandin (2 mL, Prosolvin) 11 days apart. The Ovsynch program consisted of two intramuscular injections of GnRH (1 mL, Fertagyl) 9 days apart, separated by one injection of prostaglandin 40 h before the second GnRH injection. Milk samples were taken at the time of artificial insemination and assayed for progesterone by radioim‐munoassay. Results The Ovsynch program was not significantly different to PG in achieving conception, with overall conception rates of 37.6% and 41.4%, respectively, for each program. There was, however, a significant interaction between the effects of parity and treatment (P = 0.03), because conception rates were higher in older cows (parity 5 or more) on the PG program than for older cows on the Ovsynch program. There was no significant effect of treatment (P > 0.5) on time to conception after treatment, but older cows were slower to conceive (P < 0.0001). Conception rates differed (P <0.0001) among herds. Conclusion The median days to conception for both groups was 22 and mean days from treatment to conception were 36.3 ± 3.3 and 31.6 ± 2.7 for the Ovsynch and PG programs respectively, indicating that reproductive performance of cows was not significantly different with Ovsynch program or PG program. There appears to be a need to evaluate causes of reproductive failure in older cows.