title: A reference curve using blood selenium concentration to diagnose selenium deficiency and predict growth responses in lambs.
abstract: OBJECTIVE
  To quantify the relationship between blood selenium (Se) concentration and growth response to Se supplementation in lambs, in order to assess the reliability of current reference ranges and to predict the magnitude of likely responses to supplementation.
  
  
  METHODS
  Data from 24 Se-supplementation growth-response trials which used the following general protocol were collated and analysed: in each trial, weaned lambs (n=20-30) were allocated randomly to untreated or to Se-supplemented groups. Supplemented groups received 5 mg Se/month as Na2SeO3 in 20 trials, and 1 mg Se/kg liveweight as BaSeO4 in 4 trials. The duration of the trials was 150-196 days, during which time all lambs were weighed every 4-6 weeks and blood samples were taken at various intervals from 10 lambs/group.
  
  
  RESULTS
  Among the 24 trials, flock mean blood Se concentrations of the untreated lambs ranged from 32-569 nmol/l, and growth rate of supplemented lambs was -3 to 63 g/day higher than that of untreated lambs. The relationship between blood Se concentration (X) and growth response (Y) was described by the following hyperbolic-decay equation: Y = -2.6 (SE 3.6) + 1850 (SE 230) / X; (R2=0.74).
  
  
  CONCLUSIONS
  For Se-deficient lambs, the potential for a growth response to Se supplementation was strongly related to blood Se concentration. Economically significant liveweight gains of 10 g/day were observed when initial blood Se concentrations were 130 nmol/l.
  
  
  CONCLUSIONS
  Blood Se concentrations can be used to diagnose Se deficiency in lambs and to predict the magnitude of likely growth responses to Se supplementation.
authors: AgResearch Grasslands, Private Bag 11008, Palmerston North, New Zealand. neville.grace@agresearch.co.nz
authors: N D
authors: ND
authors: Grace
authors: S O
authors: SO
authors: Knowles