Increasing dietary valine-to-lysine ratio for lactating sows had no effect on litter performance or sow tissue mobilisation

The correct ratio between lysine (Lys) and other essential amino acids is needed for optimal utilisation of dietary protein. The effects of the dietary valine to lysine ratio (Val:Lys) for lactating sows on litter growth and sow body mobilisation is equivocal (e.g. Richert et al. 1996; Gaines et al. 2006), however these studies were conducted in sows suckling around 10 piglets. Given the hyperprolificacy of modern sow genotypes with added demands for higher milk production, the hypothesis tested in the current study was that increasing the dietary Val:Lys ratio would improve litter growth and reduce sow tissue mobilisation.

A total of 565 sows (DanBred hybrids) were randomly allocated to one of six diets (n = 93) with analysed total Val:Lys ratios of 83.9, 86.4, 88.0, 90.5, 95.3, and 99.1% [calculated standardised ileal digestible (SID) Val:Lys ratios of 75.8, 79.0, 82.0, 85.0, 91.0, and 97.0%, with 7.1 g SID Lys/kg in all diets] in a complete block design from d 2 post-partum, at which point litters were standardised to 14 piglets per sow. The sows were fed semi-ad libitum twice per day until d 10, after which time feeding was increased to three times per day. Sow body weight (BW), backfat (BF) thickness and litter weight were recorded at d 2 and at weaning (d 26). On a random subsample of 12 second parity sows per dietary group, litter weights were recorded weekly. A milk sample was obtained and the BW and BF of sows registered at d 17. Prior to milk sampling the litter was removed from the sow for 45 min, after which an intramuscular injection with 2 mL oxytocin (Orion Pharma, Denmark) was given. Milk samples were analysed for dry matter (DM), lactose, fat, protein and urea. Statistical analysis was performed with the individual sow as the experimental unit (R: Free Software Foundation’s GNU General Public License). Milk composition, feed intake, average daily gain (ADG), BW loss and BF loss were analysed in a model testing the effects of Val:Lys, random effect of block and with BW, BF or litter weight at d 2 as a covariate.

Average daily feed intake (6.1 ± 0.7 kg, mean ± SD; P = 0.23) of the sows, litter size at weaning (13.0 ± 1.1, P = 0.23), ADG of the litter (2.93 ± 0.53 kg; P = 0.84; Table 1), and litter weight at standardisation (P = 0.30), d 10 (P = 0.29), d 17 (P = 0.06) and at weaning (P = 0.73), was similar among all dietary treatments. The loss of BW and BF from d 108 of gestation to d 2 post-partum (32.7 ± 10.9 kg and 0.9 ± 1.1 mm), from d 2 to weaning (22.1 ± 12.7 kg and 2.9 ± 1.7 mm; Table 1), from d 2 to d 17 (17.9 ± 11.7 kg and 2.6 ± 1.6 mm), and from d 17 to weaning (8.0 ± 7.9 kg and 0.7 ± 1.5 mm), were also all unaffected by the dietary Val:Lys ratio (P > 0.05). Milk yield (11.3 ± 1.4 kg/d; P = 0.49), and the DM (P = 0.33), lactose (P = 0.05), protein (P = 0.90), fat (P = 0.37) and urea (P = 0.35) concentrations of milk, were similarly not affected by dietary treatments. In conclusion and contrary to expectations, there was no effect of increasing the total dietary Val:Lys above 83.9% on litter performance and sow body mobilisation.

Table 1.  Effect of the calculated dietary valine-to-lysine ratio on the average daily gain (ADG) of the litter and sow body weight and backfat loss during lactation