Optimum Digestible Valine to Lysine Ratio for Meat-Type Quails from 15 to 35 Days of Age

This study was conducted to estimate the dig. valine to lysine (Val:Lys) ideal ratio for meat-type quails from 15 to 35 d of age. A total of 385, 15-day-old not sexed quails, were randomly assigned to five treatments, each one seven times replicated with eleven quails per experimental unit. Experimental treatments consisted of five dig. Val:Lys ratios (0.65; 0.70; 0.75; 0.80 and 0.85). Ideal dig. Val:Lys ratio was estimated using polynomial regression and linear broken-line regression model. Significant effect was considered when p≤0.05. Feed conversion ratio was not affected by dig. Val:Lys ratios in any of the assessed phases. From 15 to 21 d of age Val:Lys ratios increased linearly feed intake, weight gain and body weight. From 15 to 28 d of age, weight gain and body weight were both optimized by the Val:Lys ratio of 0.77. A linear effect of dig. Val:Lys ratios was observed on weight gain and final body weight from 15 to 35 d of age. From 15 to 35 d of age, according to linear broken-line regression model, the dig. Val:Lys ideal ratios for optimum final body weight and weight gain were 0.77 and 0.76, respectively. Based on the results the estimated dig. Val:Lys ratio for optimum meat-type quail performance from 15 to 35 d of age is 0.77


INTRODUCTION
Increasing on commercial amino acid availability and rising on soybean meal and corn prices has become crystalline amino acid supplementation on low-protein diets an efficient strategy to reduce poultry production costs (Burley et al., 2013).Published reports have indicated that crystalline amino acid supplementation in lowprotein diets can support similar broiler performance to high-protein diets in different phases.Nevertheless, the decrease in dietary crude protein (CP) content has become possible due to the establishment of broiler digestible amino acid requirements (e.g.methionine, lysine, threonine, tryptophan), which deficiency resultant from reduction on dietary CP, is generally corrected by their dietary supplementation in crystalline form.
Digestible lysine requirements and its optimum relative ratio with dig.methionine + cysteine, threonine and tryptophan for meat-type quails from 15 to 35 d of age have been widely studied (Scherer et al., 2009;Ton et al., 2012;Ton et al., 2013;Ribeiro, 2015).Valine is considered the 4 th limiting amino acid in corn and soybean meal-based diets for broilers (Corzo et al., 2007;Rostagno et al., 2011).Based on this hypothesis, L-valine supplementation, as well as the amino acids afore mentioned, could potentially allow further reductions in dietary CP without compromising meat-type quail performance.Broiler responses to valine supplementation in different phases are available  (Corzo et al., 2007;Tavernari et al., 2013;Duarte et al., 2014), whereas data about meat-type quail valine needs, as well as its ideal relative ratio with dig.lysine are sparse.
The publication of Tables for Japanese and European Quails (Silva & Costa, 2009) represented an important advance in quail nutrition.However, as described by the authors, some amino acid nutritional recommendations for meat-type quails are based on broiler nutritional requirements described by NRC, (1994).Therefore, the determination of Val:Lys ideal ratio, on digestible basis, for meat-type quails could contribute for the update or creation of tables containing quail nutritional requirements.Thus, this study was conducted to determine the dig.Val:Lys ratio for optimum meat-type quail performance from 15 to 35 d of age.

Animal care and use
All the procedures involving animal care and use were previously approved by the institutional Animal Care and Use Committee of the Universidade Federal de Viçosa (protocol no.07/2016).

Bird husbandry and experimental design
One-day-old meat-type quails, vaccinated for Marek disease, were obtained from a local commercial hatchery.From 1 to 14 d post hatch, quails were housed in a controlled temperature room with a concrete floor covered with wood-shavings litter.Birds were fed diets (mash form) formulated according to Silva & Costa (2009) nutritional recommendations for meat-type quails at initial phase.On d 15 posthatch, 385 not sexed quails (initial body weight of 64 g ± 0.98 g), were housed in a ventilated double curtain-sided house; and randomly allotted to five treatment groups, each one seven times replicated.The experimental unit consisted of a 50 x 50 x 30 cm stainless steel cage, equipped with one nipple drinker and one stainless steel self-feeder, with eleven quails each.Quails had free access to feed (mash form) and water throughout the 20-day feeding trial.
Environmental temperature and humidity were daily measured by four thermo-hygrometers, in different places inside the experimental room.Lighting program consisted of the supply of 24 hours of light a day (natural + artificial).

Experimental diets
The experimental diets (Table 1) were formulated to contain 175.00 g crude protein/kg diet and 3,050 kcal AMEn/kg diet.The other nutrients were supplied according to Silva & Costa (2009) nutritional recommendations, except for digestible amino acids.Basal diet was formulated to meet the dig.methionine + cysteine, threonine and tryptophan relative ratios to dig.lysine described by Ribeiro (2015).A suboptimal level of digestible lysine (11.00 g/kg diet) was considered to formulate the diets.The values of chemical and nutritional composition of the ingredients used to formulate diets were those described by Rostagno et al. (2011).The experimental treatments consisted of five dig.Val:Lys ratios (0.65; 0.70; 0.75; 0.80 and 0.85), which were obtained through the graded supplementation of L-Valine in a basal diet, valine-deficient, in replacement to cornstarch.

Performance measurements
At 21, 28 and 35 d of age, all quails and feeders were weighed to determine bird performance.Feed intake was divided by weight gain to obtain feed conversion ratio.Mortality was daily recorded to adjust feed intake and feed conversion.

Statistical analysis
The effects of dietary dig.Val:Lys ratios were analyzed as one-way ANOVA and the optimum dig.Val:Lys ratio for each dependent variable assessed was estimated using both polynomial (linear or quadratic) and linear broken-line regression model.Significant effect was considered when p≤0.05.The software package used to analyze data was Sistema de Análises Estatísticas e Genéticas (SAEG, 2007).

RESULTS
Maximum and minimum temperature means recorded inside the experimental room during the current trial were respectively 21.34 and 26.59 °C, whereas the average humidity was 72.59%.Digestible Val:Lys ratios increased linearly (p<0.05)meat-type quail feed intake, weight gain and final body weight from 15 to 21 d of age (Table 2).From 15 to 28 d of age (Table 3), feed intake was not affected (p>0.05) by dig.Val:Lys ratios, whereas weight gain and final body weight showed a quadratic (p<0.05)response to dig.Val:Lys ratios, being both optimized at 0.77dig.Val:Lys ratio.From 15 to 35 d of age, a linear increase (p<0.05) on weight gain and final body weight was observed as dig.Val:Lys ratios increased, whereas feed intake was unaffected (p>0.05) by treatments (Table 4).From 15 to 35 d of age, according to linear brokenline regression model, the breakpoint (p<0.05) for weight gain and final body weight occurred at 0.76 and 0.77dig.Val:Lys ratio, respectively.Feed conversion ratio was not influenced (p>0.05) by treatments in any of the phases herein assessed.

DISCUSSION
Trials conducted to determine ideal amino acid profile for poultry involve expressing amino acid requirements as percentage of dig.lysine requirement, which is generally supplied in a suboptimal level.In the current study, dietary dig.lysine, as well as dig.valine, was limiting in basal diet.The suboptimal level of dig.lysine used to formulate the basal diet was 11.00 g/kg diet, which corresponds to 90% of dietary digestible lysine recommended by Silva & Costa (2009) for growingfinishing meat-type quails.Therefore, our discussion did not have focus on dig.valine requirement, but rather on its ideal ratio with dig.lysine.
Valine, leucine and isoleucine dietary supply is essential to maintain poultry growth.However it is crucial to provide the ideal dietary balance of these branched-chain amino acids (BCAA), once they share the same absorptive system in the intestine and may compete for the intestinal transporters (Broer, 2008).Moreover, antagonism among BCAA extrapolates

Table 1 -
Ingredients and calculated composition of experimental diets.

Table 2 -
Performance of meat-type quails fed experimental diets from 15 to 21 d of age.

Alves WJ, Viana GS, Barreto SLT, Muniz JCL, Hannas MI, Silva AD, Arnaut PR, Barros VRMS Optimum Digestible Valine to Lysine Ratio for Meat- Type Quails from 15 to 35 Days of Age
did not observe influence of dig.Val:Lys ratios on meat-type quail feed intake from 15 to 35 d of age.According to linear broken-line regression model, the estimated dig.Val:Lys ratio for optimum weight gain and final body weight from 15 to 35 d of age was 0.76 and 0.77, respectively.Similarly, Silva & Costa, (2009) recommended a 0.75 dig.Val:Lys ratio for meat-type quails at the same phase, while Corzo et al. (2007) and Rostagno et al. (2011) proposed a 0.78 dig.Val:Lys ratio for growingfinishing broilers.The estimate found in the current study was greater than that determined by

Table 3 -
Performance of meat-type quails fed experimental diets from 15 to 28 d of age.intake. 2 -weight gain.3 -feed conversion rate.4 -body weight.5 -Coefficient of variation

Table 4 -
Performance of meat-type quails fed experimental diets from 15 to 35 d of age.