Evaluation of urinary bone turnover metabolites as indicators of phosphorus status in sows

Phosphorus (P) is an important component in several processes and the main component of the inorganic bone matrix together with calcium (Ca).The minerals can be released from the bones to the blood by the bone turnover processes associated also breaking down the organic matrix of the bone. For reproducing sows, the physiological demand for nutrients covers the supply to the growing fetuses and eventually for milk production. If the dietary supply of P and Ca does not support the physiological need, the P and Ca pool in the bones will be released. The release of minerals from the bone tissue is a normal procedure and a sign of a healthy bone function, however if the dietary supply does not meet the demand of the sow, the mineral release form the bone tissue (bone turnover) will be intensified above normal resulting in a high drainage of the bones making them more fragile. Breakdown metabolites of bone turnover can be measured in the urine and these constituents may be a useful tool to evaluate the physiological P status of the sow.

60 pigs were included in the experiment and randomly distributed to three groups. The animals were entering the experiment as gilts of 50 kg BW and the experiment continued throughout two reproductive cycles. The experimental diets differed in the dietary content of total P: Low (mean 3.5 g/kg), Medium (mean 4.1 g/kg) and High (mean 4.7 g/kg). All other nutrients and energy were according to Danish recommendations and were identical for all treatment. Urine samples were collected in early and late pregnancy, at farrowing and every week during lactation (4 week). The urine samples were analyzed for the metabolites pyridinoline (PYD), deoxypyridinoline (DPD) and carboxyterminal cross-linked telopeptide of type I collagen (CTX) by LC-MS/MS.

In general, the preliminary results show that the excretion of bone markers depends on the sows’ physiological stage as the urinary concentration decreased from late pregnancy until farrowing followed by and increase during lactation. Irrespective of dietary P supply, the excretion of metabolites seems to reach a peak in early pregnancy in the reproduction cycles. The results indicate that the urine concentration of the three markers were highest when the sows were fed reduced dietary P.

The concentration of bone metabolites quantified in urine seems to be a promising measure to evaluate the physiological P status of sows.

Disclosure of Interest: None Declared.