ELSEVIER EFFECT OF BODY CONDITION ON REPRODUCTIVE EFFICIENCY OF LACTATING DAIRY COWS RECEIVING A TIMED INSEMINATION F. Moreira,t C. R~sco,~ M. F. A. Pires,3J. D. Ambrose,4 M. Drost,* M. DeLorenzo’ and W.W. Thatcherla ’ Department of Dairy and Poultry Sciences, University of Florida, Gainesville, FL, 32611 * Large Animal Clinical Sciences, University of Florida, Gainesville, FL, 32610 3 CNPGL-EMBRAPA, Coronel Pacheco, MG 36155-000, Brazil 4 Alberta Agriculture, 6909-l 16 Street, Edmonton, Alberta T6H 4P2, Canada Received for publication : August 11, 1999 Accepted: October 8, 1999 ABSTRACT Body condition may influence pregnancy rates to a timed insemination (Ovsynch/TAI) protocol and affect the economical performance of dairy farms. The objectives were to compare pregnancy rates using the Ovsynch/TAI protocol for the first service of lactating dairy cows with body condition scores < 2.5 (scale: 1 to 5, low BCS group) versus L 2.5 (control group) and to estimate the economic impact ofthe effect of body condition on reproductive performance. At 631t3 d post partum, cows were assigned to 2 experimental groups (low BCS = 81; control = 126), and were treated with GnRH at d 0 and with PGF2, 7 d later. At 48 h after PGF,,, cows received an injection of GnRH and were inseminated 16 h later. Pregnancy rates to the Ovsynch/TAI protocol were lower for the low BCS group than for the control group at 27 d (18.1 f 6.1 % < 33.8 *4.5 %; PcO.02) and at 45 d (11.1 *5.4 % < 25.6 *4.1 %; PcO.02) after insemination. Economic analysis indicated that reducing the percentage of the herd in low body condition increases net revenues per cow per year. Body condition influenced pregnancy rates to the Ovsynch/TAI protocol. Q 2000 by Else&r Science Inc. Key words: timed insemination, body condition, cattle Acknowledgments Authors would like to recognize Mr. Ron Saint John, Mr. Peter Gelber, and the staff at Alliance Dairies for managing the experimental cows. Thanks to Dr. Mario Binelli, Dr. Joan Burke, Dr. Thais Diaz, and Ms. Jessie Elliott for their help with collecting blood samples, and to Mr. Jesse J. Johnson for running the progesterone RIA. Partial funding for this project was provided from the Agricultural Sector, Animal Agricultural Group, Monsanto Co., and by the USDA- Cooperative States Research Service-Binational Agricultural Research and Development grant no. 94-34339-1212. Lutalyse@ was generously provided by the Pharmacia-Upjohn Co. and Cystorelin@ was donated by Sanofi Inc. a Reprint requests: P. 0. Box 110920, Department of Dairy and Poultry Sciences,University of Florida, Gainesville, FL, 32611. This is Florida Agriculture Experimental Station Journal SeriesNo. R-07339. Theriogenology 53:1306-1319. 2000 0095691WOO&see front matter 0 2000 Elsevier Science Inc. PII SOO93-691 X(00)00274-0