Lisina para frangos de corte de crescimento lento criados em sistema de semiconfinamento

Abstract

The experiment aimed to analyse the effects of the level of lysine in the ration on performance, carcass characteristics and economic indicators of broilers raised in a free-range system in the periods ranging 35 to 70 and from 35 to 84 days age. The experimental design was the completely randomised with five tretments and four repetitions of 15 broilers each. The treatments were constituted of the values of 0.680; 0.840; 1.000; 1.160 and 1.320% of total of lysine in the ration (0.586; 0.746; 0.906; 1.066 and 1.226% of digestible lysine). In the period form 35 to 70 days age the levels of lysine influenced the final live weight of the broilers and it was estimated the level in 1.130% which would afford the best final live weight (2630g). The level of 1.135% of lysine in the ration would result in a bigger gain of weight (1641g). The broilers presented a linear growth in the ration consumption and linear reduction in the efficiency of of lysine utilization with the increase of the lysine levels in the ration. It was estimated a value of 1.046% of total lysine (0,952% of diestible lysine) which would result in a best feed: gain ratio (2.98). In the period from 35 to 84 days age the following values were estimated: 1.189% of total lysine (1.095% of diestible lysine) to bigger live weight (3211g), 1.196% of total lysine (1.102% of diestible lysine) to bigger gain of weight (2220g) and 1.078% of total lysine (0.984% of diestible lysine) to best feed: gain ratio (3,28).The increasing levels of lysine in the ration resulted in a linear increase in the ingestion of lysine and linear reduction in the efficiency lysine utilization. In relation to the carcass characteristics of broilers slaughtered at 70 days age, quadractic effects on the live weight after fasting and on the absolute weight of the hot carcass, abdominal fat, breast, thigh+drumstick and wing were observed. The studied levels of lysine influenced quadracticly the yield of breast and back and the relative weight of abdominal fat and gizzard. The levels of lysine influenced quadracticly the breast and back yield and the relative weight of the abdominal fat and gizzard. Linear increases in the absolute weight of the back, heart, liver, cecos and feet and linear reduction in the absolute weight of the proventricle and in the relative weight of the small intestine were observed. In the period from 35 to 84 days age quadractic effects on the absolute weight of the hot carcass, carcass yield, breast thigh+drumstick and back, in the heart and in the small intestine were observed. Linear increases in the live weight after fasting, in the absolute weight of the wing and liver, in the breast and thigh+drumstick and a linear reduction in the relative weight of the proventricle were observed. The levels of lysine did not influenced the other studied parameters. It was estimated that the ration with the level of 1.160% of total lysine (1.066% of digestible lysine) determined the biggest rate of the gross margin average by liver weight and of the gross margin average by weight gain in both studied periods. After 35 days age it is recomended to the male broilers of slow growing raised in a free-range system ration with 1.135% of total lysine (1.041% of digestible lysine) and with 1.196% of total lysine (1.102% of digestible lysine) respectively, to the slaughter at 70 and at 84 days age.