Methioninecystine in broilers

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Data from the present studies, which were transformed to a relative scale, show a fairly consistent response in bird performance to increasing dietary levels of the respective amino acid. Exponential regression analysis describes the pooled dose-response relations well (Fig. 25.2). Given the very diverse nature of the experiments, the consistency of the responses especially in feed conversion and breast meat yield is striking. Over the dietary range of Met+Cys from about 6.5 to 9.5 g kg-1 the relative responses in all three parameters were in the range of 15-20%. The steepness of the response curve, however, was higher for weight gain, which means that the asymptotic maximum was approached at a lower dietary Met+Cys content.

Under the given set of performance and price conditions, feed cost kg-1 live weight gain reached a minimum at a dietary concentration of 9.0 g kg-1 Met+Cys (Fig. 25.3). The shape of the economic response curve is determined, first, by the decreasing feed to gain ratio which approached its asymptotic minimum (i.e. maximum in the relative curve of Fig. 25.2) with rising dietary amino acid concentration, and secondly, by the linearly increasing feed cost with higher dietary Met+Cys content due to the cost of the supplemental amino acid. The response in feed cost per kg breast meat to rising amino acid levels was not only affected by the feed to gain ratio, but also by the increasing yield of breast meat as percentage of live weight. This

Met + Cys in the diet (g kg-1) (b) Met + Cys in the diet (g kg~1)

  1. 0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0
  2. 0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0

Fig. 25.2. Relative responses to graded dietary Met+Cys levels (nine broiler experiments, approx. 15-40 days of age), (a) Weight gain; (b) feed to gain ratio; (c) breast meat yield (% of live weight).

Fig. 25.2. Relative responses to graded dietary Met+Cys levels (nine broiler experiments, approx. 15-40 days of age), (a) Weight gain; (b) feed to gain ratio; (c) breast meat yield (% of live weight).

extra benefit included in the economic calculation shifted the optimum dietary Met+Cys concentration to 9.8 g kg-1; i.e. 0.8 g kg-1 higher than with only feed cost per kg live weight gain responses considered.

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