PARTITIONING OF DIETARY-PROTEIN DURING LACTATION IN THE MEISHAN SYNTHETIC AND EUROPEAN WHITE BREEDS OF PIG

Litter size of commercial European sow lines can be increased by the i ntroduction of genes from the highly prolific, but obese Meishan. The introduction of these genes into sow lines may necessitate different n utritional strategies for lactation. A 2 x 2 x 2 factorial experiment was used to investigate the influence of breed type (Meishan synthetic 50% (M) or purebred European Landrace and Large White (W)) and parity (1 or 3) on response to dietary protein level (H=178g crude protein ( CP) per kg 8 g lysine per kg, L=136 g CP per kg 5 g lysine per kg over a 5-week lactation. M were lighter and fatter at farrowing than W (P< 0.001), consumed more food (M=7.33 v. W=6.98 (s.e.d. 0.17) kg/day, P<0 .05) but had higher maternal weight loss (M=16.2 v. W=11.9 (s.e.d. 1.8 8) kg, P<0.05) and higher fat loss (M=6.5 v. W=2.6 (s.e.d. 0.77) mm P- 2 P<0.001) during lactation. Litter growth rate was higher for M than for W (P<0.005) and for H than for L (P<0.005). Differences were found between breeds in the partitioning of food protein. Overall, higher c orrelations between lysine intake and litter growth rates were found i n M (r=0.55, P<0.001) than in W (r=0.13, P>0.05). Lysine intake and so w weight loss were more correlated in W (r=0.66, P<0.001) than in M (r =0.15), P>0.05). Fat loss was correlated with initial fat depth in M ( r=0.61, P<0.001) but not in W. Weaning to conception intervals showed a breed X diet interaction (log(e) days:ML=1.38, MH=1.55, WL=1.73, WH= 1.43, s.e.d. 0.14, P<0.05). It is concluded that M, with greater initi al fat reserves, catabolize more body fat to support greater milk outp ut. This is facilitated by provision of a high protein diet. The W sow s do not utilize the extra protein for mild production but instead use it to minimize weight loss (maintain protein status of their own body ) which may help prevent an extended weaning to conception interval.