Threonine requirement of finishing gilts and barrows

Two trials were carried out in order to study the threonine requirement of crossbred barrows and gilts (LWxLD)xP76 over the 60-100 kg body weight range. In trial 1, four wheat and soybean meal based diets were used: their digestible lysine (LYSd) level was limiting for growth and the ratio between digestible threonine and lysine (THRd/LYSd) was either 55, 60, 65 or 70%. In trial 2, four diets were formulated according to a factorial design 2x2: two LYSd levels and two THRd/LYSd levels (60 or 65%). The lowest LYSd level was similar to the one in trial 1 and the second level was closer to requirement. Feed supplies were adjusted on a body weight basis for each pen of five animals each. In trial 1, lower growth performance were obtained with THRd/LYSd below 60% (-21 g/d of average daily gain, +1.1 MJ NE/kg of feed conversion ratio) but no difference was observed among ratios above 60%. Trial 2 illustrates the impact of LYSd level on growth performance and indicates that LYSd requirement of pigs studied was 19 g/kg body weight gain. Like in trial 1, no significant difference was observed between THRd/LYSd ratios of 60 and 65% when LYSd level was low.When LYSd is less limiting, average daily gain decreased by 5% with THRd/LYSd ratio of 60% (vs. 65%) but this difference was not significant. This study indicates that THRd/LYSd ratio must not be lower than 60% during finishing period but fails to confirm the hypothesis according to which it would be higher than 65% over this period.