Responses in Turkeys

Weight gain and feed conversion potential of turkeys has also developed enormously during the last 20 years and as a result, questions about changes in the turkey's demand for dietary amino acids arose. With a focus on the response to dietary Lys level, a series of trials has been conducted at the University of Halle, Germany, with male BUT Big 6 turkeys over various age periods. The studies reported by Lemme et a I. (2002a) deal with the periods of 5-8 and 13-16 weeks of age, whereas

Lehmann et al. (1996) worked on the periods of 9-12 and 17-20 weeks of age. In each trial period, six levels of dietary Lys were tested. Weight gain and feed conversion rate improved in every treatment, and the responses to Lys could be fitted very well by exponential regression functions as previously shown for broilers. For space reasons, only the results for grower and finisher diets are reported. Unfortunately, there is a lack of acceptable data on amino acids other than Lys; therefore only this amino acid will be covered in this review.

m-to

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0.42

0.52

0.50

0.42

Feed cost kg-1 breast meat

Feed cost kg-1 gain

0.42

Feed cost kg-1 breast meat

Feed cost kg-1 breast meat

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co co

2.40

11.5

m to

Feed cost kg-1 breast meat

Feed cost kg-1 gain

Feed cost kg-1 breast meat

Feed cost kg-1 gain

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The impact of graded levels of dietary amino acids on feed cost per kg weight gain and feed breast meat in Peking ducks 21-49 days of age. (a) Met+Cys; (b) Lys; (c) Thr.

The grower results are summarized in Fig. 25.20, and finisher data for the 13-16 and 17-20 week periods are given in Figs 25.21 and 25.22. All three experimental data sets agree in the strong and very consistent response in growth rate, that always gave a better fit of the experimental functions (R2 0.98) than the more variable feed conversion data. Variability in the latter parameter indicates less sensitivity in this criterion, which may be due to two factors: first, feed losses may be harder to avoid in larger poults, or, secondly, responses were flat beyond an intermediate Lys level. This would mean in return that extra growth responses at higher Lys levels were a function of higher feed intake at largely unchanged feed conversion.

For the economic assessment, the different response pattern of growth versus feed conversion and the lack of good carcass composition data require some reconsideration of the economic parameters optimized for use with broilers. The calculation of feed cost per kg live weight gain would not be expected to give a meaningful result as such. In case there are further growth responses at higher dietary amino acid levels, these are also likely to trigger corresponding increases in breast meat proportion (see limited data reported by Lehmann et al., 1996, 1997).

Another parameter was introduced by Petri et al. (2001): the calculation of a 'gross margin', i.e. the margin over feed cost, calculated as the difference between income

(a)

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2.352.302.252.202.152.102.05-2.QQ-

13.0

14.0

y=2.31 -0.231 x(1-e-<°-959><<*-8-7))) R2=0.92

13.0

14.0

Fig. 25.20. Responses of growing turkeys to dietary Lys (male turkeys, 9-12 weeks of age, Lehmann et al., 1996). (a) Weight gain; (b) feed to gain ratio.

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cd cd

2.80

10.5

11.5

12.5

10.5

11.5

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Fig. 25.21. Responses of growing turkeys to dietary Lys (male turkeys, 13-16 weeks of age, Lemme et al., 2000a). (a) Weight gain; (b) feed to gain ratio.

from live body weight minus the cost of the feed consumed. Using feed cost figures of approximately US$215/190/198 ton-1, a reduced price of US$1.73 kg-1 of L-lysine-HC1, and a return of US$1.05 kg-1 of live turkey (Petri et ah, 2001, reflecting a contemporary Western European scenario), one can conduct this exercise with the results reported in Fig. 25.23.

It has to be noticed that the feed cost kg-1 gain remained rather unaffected by dietary Lys level over all periods calculated. The mathematical minimum shown in the figures is only slightly different from the values obtained with higher or lower lysine levels. This confirms that feed cost per kg gain alone may not be a meaningful tool to determine the optimum Lys content of a turkey feed. The calculations for gross margin indicate a stronger economic sensitivity and points to substantially higher values for the recommended lysine level in all periods evaluated. In fact, in two cases the predicted maximum gross margin is close to the highest dietary concentration tested, and in the finisher period (17-20 weeks of age) even beyond that level, i.e. 10.4 g kg-1 Lys being predicted versus 9.6 g kg-1 having been the highest level fed in the trial. This conclusion has to be handled with some care and requires more data.

Compared to NRC (1994) recommendations for growing turkeys, all figures derived from gross margin calculations are significantly higher, probably reflecting the continuous genetic progress in this species.

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  • co o) 5.00 -

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cd cd y=4.528+1.176x(1 -e-(o.406x(*-6.1 ))) R2=0.99

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FIg. 25.22. Responses of finishing turkeys to dietary Lys (male turkeys, 17-20 weeks of age, Lehmann et al., 1996). (a) Weight gain; (b) feed to gain ratio.

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Gaining Weight 101

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