Modern sows have been selected for increased mature body size and prolifacy while measured milk yields greatly exceed previously published levels. Optimum lysine to energy ratio in the lactation diet of such sows is likely to be influenced by lactation feed intake, lactation length as well as by body fatness at parturition. In a situation where high lactation feed intakes were achieved in a short lactation by high producing sows, a diet close to current commercial recommendations was compared to one with a lower lysine to energy ratio.

The study was conducted in a large commercial herd with Large White (LW) x Landrace (LR) first cross sows which had been mated to either LR or LW boars. Two lactation diets were formulated, one being close to current recommendations for modern, high producing lactating sows (Diet A) while the other had a 19 percent lower ratio of lysine to digestible energy (Diet B). The diets were based mainly on cereals (barley and wheat), both extracted and full-fat rape seed meal, soya bean meal and biscuit meal. The calculated nutrient content of the diets is presented in Table 1. A total of 85 sows were involved in the study and sows allocated to the two diets were balanced for parity and farrowing date. Feed allowances were increased gradually from a low level at day 1 after parturition which made it possible for sows to achieve an intake of 12 kg daily at Day 14 after parturition provided that a sow had previously consumed all food offered. Feeding management was good, with water being added to provide wet feed. Average temperature at sow level was 23.2°C (overall range 19 to 27°C).