## Valine assay

Quadratic (P < 0.01) responses in weight gain (Fig. 13.6) and feed efficiency occurred when graded doses (5.1-10.6 g kg-1) of digestible valine were fed (Baker et al., 2002). The broken-line digestible requirement estimates were 7.44 and 7.43 g kg-1 for weight gain and feed efficiency, respectively. The valine requirement (7.44 g kg-1) ratioed to the lysine requirement

Dietary digestible isoleucine (g kg-1)

Fig. 13.5. Fitted broken-line and quadratic plots of 13-day weight gain as a function of true digestible lie in the diet (Assay 5). Data points are means of four pens of four male chicks during the period 8-21 days posthatching. The minimal digestible lie requirement determined by broken-line analysis using least squares methodology was 5.89 g kg 1 (/= 292.0 + 72.25 (x< 5.89); r2 = 0.876). The pen means data also were fitted to a quadratic regression equation: y= -239.08 + 136.54x- 8.59x2; r2 = 0.810. The level of digestible lie that maximized weight gain (i.e. upper asymptote) was calculated to be 7.95 g kg 1, with 90% of this value being 7.15 g kg 1. The first intercept xvalue of the broken-line (on the plateau) and the quadratic fitted line occurred at 6.79 g kg-"1.

Dietary digestible isoleucine (g kg-1)

350 n

Dietary digestible valine (g kg-1)

Fig. 13.6. Fitted broken-line and quadratic plots of 13-day weight gain as a function of true digestible Val in the diet (Assay 6). Data points are means of four pens of four male chicks during the period 8-21 days posthatching. The minimal digestible Val requirement determined by broken-line analysis using least squares methodology was 7.44 g kg 1 (/ = 290.83 + 73.18 (x< 7.44); r2 = 0.963). The pen means data also were fitted to a quadratic regression equation: y= -618.42 + 200.39x- 1G.88x2; r2 = 0.950. The level of digestible Val that maximized weight gain (i.e. upper asymptote) was calculated to be 9.21 g kg 1 of the diet, with 90% of this value being 8.29 g kg-1. The first intercept x value of the broken-line (on the plateau) and the quadratic fitted line occurred at 8.11 g kg-1.

Dietary digestible valine (g kg-1)

Fig. 13.6. Fitted broken-line and quadratic plots of 13-day weight gain as a function of true digestible Val in the diet (Assay 6). Data points are means of four pens of four male chicks during the period 8-21 days posthatching. The minimal digestible Val requirement determined by broken-line analysis using least squares methodology was 7.44 g kg 1 (/ = 290.83 + 73.18 (x< 7.44); r2 = 0.963). The pen means data also were fitted to a quadratic regression equation: y= -618.42 + 200.39x- 1G.88x2; r2 = 0.950. The level of digestible Val that maximized weight gain (i.e. upper asymptote) was calculated to be 9.21 g kg 1 of the diet, with 90% of this value being 8.29 g kg-1. The first intercept x value of the broken-line (on the plateau) and the quadratic fitted line occurred at 8.11 g kg-1.

(9.60 g kg-1) was 77.5%, closely agreeing, therefore, with our original estimate of 77% (Baker, 1997) and with the recalculated ratio estimate (76%) of Mack et al. (1999), (see Table 13.1). Why the ideal valine:lysine ratio of broiler chicks is higher than that for pigs (68%) is not known (Baker, 1997).

Using 77.5% as an ideal ratio for valine, the predicted digestible valine requirement would be 8.29 g kg-1 (0.775 x 10.7), and this estimate agrees well with those calculated from the broken line/quadratic curve intercept method (8.11 g kg-1) as well as the value obtained by taking 90% of the upper asymptote from the quadratic fitted line (8.2 g kg-1). Dividing the 8.29 g kg-1 digestible valine requirement estimate by a maize-soybean meal valine digestibility value of 90% (NRC, 1994) yields a total valine requirement estimate of 9.21 g kg 1 for 0-21-day-old chicks fed a maize-soybean meal diet. The NRC (1994) total valine requirement estimate (maize-soybean meal basis) is 9.0 g kg-1. Thus, our 9.21 g kg 1 estimate herein is slightly higher. Previous work from our laboratory established that valine is among the four most limiting AA in soybean meal and in reduced protein maize-soybean meal diets (Han et al., 1992; Fernandez et al., 1994).

## Diet Tweak System

Trying To Lose Weight Can Be Tough. But... Not Losing Weight and Gaining What You Lost Back, Sucks. If you've ever felt that no matter what you do to lose weight nothing seems to work. If you've ever felt that there has got to be some kind of a system or way to lose weight...but just have not found it yet.

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