Lysine in broilers

Lysine responses, although with less single data points, give a similar picture in that the responses in all three parameters are clearly

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

Fig. 25.3. Effect of dietary Met+Cys content on economics, (a) Feed cost kg-1 live weight gain; (b) feed cost kg-1 breast meat yield.

Fig. 25.3. Effect of dietary Met+Cys content on economics, (a) Feed cost kg-1 live weight gain; (b) feed cost kg-1 breast meat yield.

non-linear and the curves for feed conversion and breast meat are flatter than the growth response (Fig. 25.4).

Interestingly, the economic optima for the two situations are even more apart than in Met+Cys (Fig. 25.5). Feed cost per kg live weight gain is minimized at 10.3 g kg-1 lysine, whereas the minimum cost kg-1 breast meat occurs at 11.6 g kg-1, which is a difference of more than 10%, thus quite substantial from an industrial point of view. This demonstrates the relevance of a proper definition of the overall production goal.

The economic calculations above are only valid for the present input prices. For demonstration, Fig. 25.6 shows the corresponding economic responses for a set of three different cost levels per ton of feed. Compared to the level of US$140 per ton which was used so far, a lower or a higher level of US$120 or 160 per ton have a certain effect. With a higher feed cost, higher dietary lysine levels are more economical, because less of the expensive feed is consumed per unit of gain or breast meat yield. However, the differences are fairly moderate, being in the range of +0.1 g kg-1 dietary lysine per US$10 increase in feed cost per ton.

Likewise, the economic optimum levels are only slightly altered by price changes of supplemented amino acids. For example, a significantly varying price for L-lysine-HCl of US$2.0, 2.5, or 3.0 kg-1 results in economic optimum levels for the production goal breast meat of 11.9, 11.6 and 11.4 g kg-1 of Lys in

"S

y=81.20+18.91 x(1-e-°-965><<*-7-9!) R2 —0.87

7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5 _i_i_i_i_i_i_i_i_i_i_

y=79.60+20.86x (1 -e-°-717* <* -7-9>) R2 = 0.82

Fig. 25.4. Relative response to graded dietary lysine levels (six broiler experiments, approx. 20-40 days of age), (a) Weight gain; (b) feed to gain ratio; (c) breast meat yield (% of live weight).

the diet, respectively. This means that the resulting change in the dietary optimum is far less than the change of nutrient cost as an input variable. Similarly, a greatly varying price for DL-Met of US$2.5, 3.0 or 3.5 kg-1 results in economic optimum levels for cost of breast meat of 9.7, 9.5 and 9.3 g kg-1 of Met+Cys in the diet, respectively (data not shown).

  1. 26 -|-1-1-1-1-1-1-1-1-1-1
  2. 5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12.0 12.5

Fig. 25.5. Effect of dietary lysine content on economics, (a) Feed cost kg-1 live weight gain; (b) feed cost kg-1 breast meat yield.

Fig. 25.5. Effect of dietary lysine content on economics, (a) Feed cost kg-1 live weight gain; (b) feed cost kg-1 breast meat yield.

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