Photoperiod length and the estrus synchronization protocol used before AI affect the twin pregnancy rate in dairy cattle》.pdfVIP

Available online at Theriogenology 78 (2012) 1209–1216 Photoperiod length and the estrus synchronization protocol used before AI affect the twin pregnancy rate in dairy cattle a b b, C. Andreu-Vázquez , I. Garcia-Ispierto , F. López-Gatius * a Department of Animal Health and Anatomy, Autonomous University of Barcelona, Barcelona, Spain b Department of Animal Production and Center for Research into Animal Production (CIPA), University of Lleida, Lleida, Spain Received 9 February 2012; received in revised form 14 May 2012; accepted 22 May 2012 Abstract This study addresses potential management risk factors affecting the incidence of twin pregnancies in high-producing dairy cows. Special attention was paid to the estrus synchronization protocol used before the AI resulting in pregnancy. Possible factors affecting the twin pregnancy rate were analyzed through binary logistic regression procedures on 2015 pregnant cows from July 2010 to July 2011. Twin pregnancy was recorded in 361 of the 2015 pregnancy diagnoses made (17.9%). Twin pregnancy rates differed among herds (P 0.001) and ranged from 12.4% to 23.9%. Based on the odds ratios, the risk of twin pregnancy was reduced by factors of 0.65 or 0.71 when AI was performed during the warm season or an increasing photoperiod, respectively and increased by a factor of 1.11 for each unit increase in lactation number; by factors of 4.57 or 6.33 in cows that received a progesterone-releasing intravaginal device (PRID) plus