Potential for use of physiological and physical measurements to monitor sow muscle catabolism during lactation

Protein loss from skeletal muscle catabolism during lactation, whether a result of reduced feed intake during lactation or high demand from suckling piglets, appears to have the largest influence on subsequent reproductive performance (Clowes et al. 2003). The capacity to routinely identify significant muscle catabolism during lactation could therefore be a very useful management tool if productivity is to be optimised. Apart from physical measures of catabolism such as loin muscle depth (LM) and backfat (BF) loss, metabolic products of muscle catabolism such as creatinine, (Crea) and 3-methylhistidine (3MH) may hold potential. The aim of this experiment was to restrict feed intake in lactating sows to promote muscle catabolism, and then measure plasma (Crea, 3MH), whole blood (Crea) and physical (LM, BF) parameters that may reflect this catabolism. We hypothesised that plasma Crea and 3MH and whole blood Crea would increase with decreasing sow feed intake while LM and BF would decrease.

Four levels of feeding were offered to sows in lactation to induce muscle catabolism, with each treatment being composed of an equal mix of parity two and three sows (n = 10 per treatment). Sows were fed a commercial diet [14.5 MJ digestible energy (DE)/kg, 0.55 g standardised ileal digestible lysine/MJ DE] with feeding levels increased to achieve a plateau intake 10 days after farrowing. Control sows were fed to achieve 9 kg/d, R1 sows were restricted to 8 kg/d, R2 sows were restricted to 7 kg/d, and R3 sows were restricted to a peak intake of 6 kg/d. On d 0, 14 and 20 (weaning), BF and LM were measured by ultrasound 7 cm from the midline, at the head of the last rib. Sows were bled on these same days and plasma was analysed for levels of circulating 3MH (plasma amino acid quantitation) and Crea (general chemistry). Whole blood Crea was also measured using a hand-held Nova StatSensor Creatinine Meter (RHCG NSW, Australia). Data were analysed using the GLM procedure and a simple linear regression analysis (Genstat, 15th Edition; UK).

Measurement of whole blood Crea using a hand-held meter revealed a significant difference (P < 0.05) between sows fed 9 kg/d and sows fed 8 kg or less per day (Table 1). There were also significant differences in BF between treatments but this did not reflect the treatments and may have been influenced by the initial body condition of the sows. Correlations also existed between whole blood Crea and measures of BF (r = 0.22, P = 0.02; n = 39) and LM (r = 0.26, P = 0.006; n = 39). Plasma 3MH and Crea and LM were not responsive to feeding level. An increase in whole blood Crea is consistent with the hypothesis, and the significant correlation with LM depth suggests potential as a measure of muscle catabolism. It should be noted, however, that as a sow fails to meet her energy requirement through feed, reduced water intake might be concurrently reducing kidney function causing Crea levels to rise (Butani et al. 2002). As a consequence, further research is required to ascertain whether whole blood Crea reflects muscle loss or reduced water intake. Regardless, it appears whole blood Crea measured using a hand-held meter has potential as a useful management tool for lactating sows either as an indicator of muscle catabolism or as a measure of sub-optimal feed and water intake.

Table 1.  Mean levels of plasma 3-methylhistidine (3MH) and creatinine (Crea; µmol/L), whole blood Crea (µmol/L), backfat (BF) depth (mm) and loin muscle (LM) following graded levels of feed restriction in a 20 d lactation