EFFECT OF LEAN GROWTH GENOTYPE AND DIETARY AMINO-ACIDS REGIMEN ON THELACTATIONAL PERFORMANCE OF SOWS

The effect of dietary amino acid regimen and genetic capacity for lean tissue growth on the lactational performance of sows was determined i n primiparous sows with a high (350 to 390 g/d) or low (240 to 280 g/d ) genetic capacity for lean tissue growth from 18 to 110 kg of body we ight. During lactation, sows were offered daily 6.5 kg of one of four fortified corn-soybean meal diets containing .58, .77, .96, and 1.15% lysine (L). Litters were standardized to 14 pigs within 8 h after birt h. On d 2 of lactation, the high lean growth (LG) sows possessed more proteinaceous tissues and protein and less fat tissue and lipid. Durin g lactation (d 2 to 28 postpartum), high LG sows consumed more feed, m obilized more body protein, and lost less body lipid. Milk, milk energ y, and milk lysine yields (pooled across dietary regimens) were simila r between genotypes. As daily dietary lysine intakes increased from 27 to 62 g and total digestible lysine supplies (from diet and mobilized tissues) increased from 39 to 68 g, daily yields of milk, milk energy , and milk lysine increased, but the magnitude of the response differe d (P < .05) between genotypes, evidently because of differences in the ability of the high and low LG sows to mobilize energy from body tiss ue. Based on these data, the lactational capacities of high and low LG sows nursing 12 to 14 pigs are similar when similar supplies of lysin e and energy are available from dietary intake and mobilized body tiss ue stores. When supplies of ME do not limit milk synthesis, daily dige stible lysine intakes of at least 54 g (greater than or equal to 66 g from a corn-soy diet) are needed by these sows nursing litters of 12 t o 14 pigs to support milk synthesis and minimize maternal protein loss es. This is equivalent to a total digestible lysine need of 4.3 to 4.6 g/kg of milk produced. When ME provided by the diet is less than that needed to fuel maximum milk synthesis, however, the dietary amino aci d needs of genetically lean sows may be reduced because of their inabi lity to mobilize sufficient body fat stores.