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Pre-breeding blood urea nitrogen concentration and reproductive performance of Bonsmara heifers within different management systems


This study investigated the association between pre-breeding blood urea nitrogen (BUN) concentration and reproductive performance of beef heifers within different management systems in South Africa. Bonsmara heifers (n = 369) from five herds with different estimated levels of nitrogen intake during the month prior to the commencement of the breeding season were sampled in November and December 2010 to determine BUN concentrations. Body mass, age, body condition score (BCS) and reproductive tract score (RTS) were recorded at study enrolment. Trans-rectal ultrasound and/or palpation was performed 4–8 weeks after a 3-month breeding season to estimate the stage of pregnancy. Days to pregnancy (DTP) was defined as the number of days from the start of the breeding season until the estimated conception date. Logistic regression and Cox proportional hazards survival analysis were performed to estimate the association of pre-breeding BUN concentration with subsequent pregnancy and DTP, respectively. After stratifying for herd and adjusting for age, heifers with relatively higher pre-breeding BUN concentration took longer to become pregnant when compared to those with relatively lower BUN concentration (P = 0.011). In the herd with the highest estimated nitrogen intake (n = 143), heifers with relatively higher BUN were less likely to become pregnant (P = 0.013) and if they did, it was only later during the breeding season (P = 0.017), after adjusting for body mass. These associations were not present in the herd (n = 106) with the lowest estimated nitrogen intake (P > 0.500). It is concluded that Bonsmara heifers with relatively higher pre-breeding BUN concentration, might be at a disadvantage because of this negative impact on reproductive performance, particularly when the production system includes high levels of nitrogen intake.

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The authors thank the participating farmers for providing the animals, facilities and farm records, and the Faculty of Veterinary Science, University of Pretoria for financial support. This research was performed under protocol number V072-810 as approved by the Animal Ethics Committee of the University of Pretoria.

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Any opinion, finding and conclusion or recommendation is that of the authors. There were no conflicts of interests

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Correspondence to Takula Tshuma.

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Tshuma, T., Holm, D.E., Fosgate, G.T. et al. Pre-breeding blood urea nitrogen concentration and reproductive performance of Bonsmara heifers within different management systems. Trop Anim Health Prod 46, 1023–1030 (2014).

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  • Beef cattle
  • Blood urea nitrogen
  • Reproductive performance
  • Nitrogen supplementation