Blending gestation and lactation diets during the transition period reduces energy mobilization by sows in late gestation, with no impact on subsequent lactation performance.

Fifty-three gilts and fifty-three multiparous () sows were used to evaluate a blended feeding program using gestation and lactation diets during the transition period on changes in sow back fat () depth and BW, blood metabolites, and litter growth performance in the subsequent lactation period. A 2 × 2 factorial experimental design was generated including the factors of parity and feeding program. The MP sows and gilts were assigned to one of two feeding programs on day 104 ± 1 of gestation: 1) 2 kg/d of a standard lactation diet until farrowing when sows received step-up access to the lactation diet until ad libitum access was given on day 4 of lactation () and 2) a dynamic blend of standard gestation and lactation diets that met estimated daily requirements for standardized ileal digestible Lys and net energy according to the NRC (2012) until day 4 of lactation where sows were provided ad libitum access to the lactation diet (). Litters were standardized to 13 ± 1 piglets within 24-h of birth. In gestation, ADFI was greatest for TRAN-MP sows (interaction;  < 0.05), with greater ADFI for TRAN versus CON sows (main effect; 2.95 vs. 2.13 ± 0.08 kg; < 0.05). Feeding program did not influence ADFI in lactation, but MP sows had greater ADFI versus gilts (main effect; 5.96 vs. 4.47 ± 0.28 kg; < 0.001). Immediately after farrowing, TRAN sows had greater BW and BF vs. CON sows, regardless of parity (main effect; 224.1 vs. 215.4 ± 4.1 kg and 17.3 vs. 16.2 ± 0.4 mm, respectively;  < 0.05). At weaning, no feeding program-related differences were observed for BW or BF, but MP sows had thicker BF compared to gilts (main effect; 14.4 vs. 13.4 ± 0.5 mm;  < 0.05). The TRAN-MP sows had heavier piglets at birth compared to all other groups (interaction; < 0.05) and MP sows had greater litter birth weight and average piglet BW at birth versus gilts (main effect;  < 0.05). No effect of feeding program was observed for piglet BW at weaning. On lactation day 1, serum beta-hydroxybutyric acid and non-esterified fatty acid concentrations were lower for TRAN compared to CON sows (main effect; 12.0 vs. 19.4 ± 7.8 mmol/L and 0.35 vs. 0.57 ± 0.10 mmol/L, respectively;  < 0.05) and serum glucose concentration was greater for TRAN compared to CON sows (main effect; 4.41 vs. 3.88 ± 0.22 mmol/L;  < 0.05), but these differences were no longer detectable at weaning. Therefore, a simple transition feeding program using a blend of a standard gestation and lactation diets reduced energy mobilization by sows in late gestation, with no impact on subsequent lactation performance.