Pre-breeding blood urea nitrogen concentration and reproductive performance of Bonsmara heifers within different management systems
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Date
Authors
Tshuma, Takula
Holm, Dietmar Erik
Fosgate, Geoffrey Theodore
Lourens, Dirk Cornelius
Journal Title
Journal ISSN
Volume Title
Publisher
Springer
Abstract
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 prebreeding
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.
Description
Keywords
Beef cattle, Blood urea nitrogen, Reproductive performance, Nitrogen supplementation, Days to pregnancy (DTP)
Sustainable Development Goals
Citation
Tshuma, T, Holm, DE, Fosgate, GT & Lourens, DC 2014, 'Pre-breeding blood urea nitrogen concentration and reproductive performance of Bonsmara heifers within different management systems', Tropical Animal Health and Production, vol. 46, no. 6, pp. 1023-1030.