Views on Ideal or Lower Protein Levels for Meat Chickens and Approaches to Second Tier Amino Acids

I. INTRODUCTION

Diet cost represents approximately 60 to 70% of total live production cost of broilers (Donohue and Cunningham, 2009). Price volatility of AA-contributing ingredients may largely impact diet cost and subsequently live production cost. Soybean meal has been considered the “golden standard” intact source of AA due to its excellent AA profile for poultry. Price volatility of soybean meal has created interest in utilizing alternative intact AA sources (canola meal, lupins, meat and bone meal) in conjunction with cereal grains having higher AA content than corn in diet formulation to reduce diet cost. In addition, the importance of accurate digestible AA values for feedstuffs should not be under estimated to ensure optimum performance in meat chickens. The addition of feed-grade AA can provide partial replacement of intact protein sources resulting in decreased CP content and lower dietary cost. When supplementing DLMet and L-Lys to decrease CP content in diet formulation, less limiting AA concentrations (Thr, Val, Ile, Arg, and Trp) may be lower than diets containing higher CP content resulting in poor growth performance and carcass characteristics of broilers (Corzo et al., 2007). Therefore, maintaining adequate concentrations of these less limiting AA in reduced CP diets may help alleviate poor growth performance of broilers.

II. REDUCED CRUDE PROTEIN DIETS

Despite the benefits from lowering dietary CP content, previous studies have reported suboptimal growth performance when broilers were provided reduced CP diets (Kerr and Kidd, 1999; Rezaei et al., 2004; Dean et al., 2006; Hernandez et al., 2012). Hernandez et al. (2012) examined the effects of feeding broilers reduced CP diets from 23.0 to 20.0% with increments of 1.5 percentage points from 8 to 21 d of age. These researchers noted that broilers fed the 21.5% CP diet had similar body weight (BW) gain and feed conversion ratio (FCR) to those consuming the 23.0% CP diet. However, broilers consuming the 20.0% CP diet had decreased BW gain and increased FCR by 9.4 and 9.6%, respectively. Similarly, Dean et al. (2006) observed a linear decrease in gain to feed ratio of broilers from 1 to 18 d of age when gradually decreasing dietary CP content by increments of 1.5 percentage points from 22 to 16.2%.

Poor growth performance of broilers fed reduced CP diets may also be observed in older broilers. From 28 to 45 d of age, decreasing CP content in broiler diets from 19.4 to 16.7% reduced average daily gain while also increasing FCR by 2.3 and 3.3%, respectively (Kerr and Kidd, 1999). The magnitude of lowering CP content can also be displayed in carcass characteristics of broilers. Rezaei et al. (2004) conducted a 6-wk trial to evaluate the effects of feeding reduced CP diets on growth performance and carcass characteristics of broilers. From 1 to 3 wk of age and 3 to 6 wk of age, the reduced CP diets were formulated to contain 17.8 and 16.1% CP, while the high CP diets were formulated to contain 20.8 and 18.1% CP, respectively. Results demonstrated that BW gain of broilers consuming the reduced CP diets was 5.5% lower compared with birds provided the high CP diets resulting in a 2.4% decrease in carcass weight. Additionally, breast meat yield was decreased and abdominal fat percentage increased by 6.7 and 35.4%, respectively, as dietary CP content was reduced by 3.0 and 2.0 percentage points in broiler diets from 0 to 3 and 3 to 6 wk of age, respectively.

The inclusion of DL-Met, L-Lys, and L-Thr has enabled nutritionists to formulate diets containing lower CP. However, when focusing solely on these AA, less limiting AA concentrations, such as Val, Ile, and Arg may be below optimum concentrations. Insufficient less limiting AA concentrations may produce confounding effects when research aimed at evaluating the effects of lowering dietary CP content on growth performance of broilers is conducted. Prior research demonstrated that the reduction of dietary CP content from 23 to 20% in diets fed to broilers from 7 to 21 d of age resulted in decreased concentrations of Val, Ile, Arg, and Trp by 15, 16, 10, and 18%, respectively, in the 20% CP diet (Pinchasov et al., 1990). Similarly, Waldroup et al. (2005) noted approximately 10% reductions in Val, Ile, Arg, and Trp concentrations when lowering dietary CP content from 22 to 18% leading to an 8.7% increase in FCR of broilers. Adding a mixture of essential AA (Gly, L-Val, L-Ile, L-Arg, LTrp, L-His, L-Phe, and L-Leu) to the 18% CP diet to obtain similar concentrations in the 22% CP diet resulted in broilers having similar FCR compared with birds fed the 22% CP diet. However, this strategy did not yield similar results when applied to a 20% or 16% CP diet indicating that other factors may influence poor growth performance of broilers (Waldroup et al., 2005). Kriseldi et al. (2018) evaluated reduced CP diets formulated to maintaining adequate AA concentrations on growth performance and nitrogen balance of broilers from 1 to 21 d of age in two experiments. Crystalline AA were added sequentially in the order of limitation (LVal, Gly, L-Ile, L-Arg, L-Trp, L-His, and L-Phe) in the experimental diets to decrease CP content by approximately 4 percentage points compared with a positive control diet containing DL-Met, L-Lys, and L-Thr. The sequential additions of AA with DL-Met through L-Trp allowed 4.0 and 2.2 percentage point reductions in CP from 1 to 14 and 1 to 21 d of age (Figure 1), respectively, without adversely impacting growth performance compared with a positive control diet containing DL-Met, L-Lys, and L-Thr.

III. DIGESTIBLE THREONINE

Threonine is the 3rd limiting amino acid for broilers fed corn-soybean meal based diets (Baker et al., 2002). The primary functions of threonine include lean meat accretion, feather development, mucin synthesis, and enzyme formation (Kidd and Kerr, 1996, Kidd, 2000, Horn et al., 2009). Ideal AA ratio concept is a popular method to express AA requirements relative to Lys. Utilising L-Thr in concert with ideal AA ratio concept in diet formulation allows nutritionists to meet an optimum digestible Thr to Lys ratio while maintaining cost effective diets. Formulating diets at a digestible Thr to Lys ratio below the broiler’s need for Thr limits their genetic potential in meeting performance objectives. Digestible Thr to Lys ratio has been reported to vary among various production periods with ratios ranging from 0.65 to 0.70 (Rostagno et al., 2011, Mehri et al., 2012). In commercial practice, digestible Thr to Lys ratios ranging from 0.63 to 0.68 have been utilised with lower digestible Thr to Lys ratios to reduce feed cost, whereas higher ratios were implemented to optimize growth performance and meat yield.

AUSTRALIA - VIEWS ON IDEAL OR LOWER PROTEIN LEVELS FOR MEAT CHICKENS AND APPROACHES TO SECOND TIER AMINO ACIDS - Image 1

Over the last several years, our laboratory has attempted to define the optimum digestible Thr to Lys ratio to optimize growth rate and meat yield in broilers from 1 to 49 d of age through a series of experiments due to the variation across published research and the inconsistent ratios used in commercial practice. Dozier et al. (2015) evaluated digestible Thr to Lys ratio in Hubbard × Cobb 500 male chicks from 1 to 14 d of age. Eight digestible Thr to Lys ratios ranging from 0.55 to 0.76 in increments of 0.03 were fed throughout the experimental period. Using broken-line methodology, digestible Thr to Lys ratios were determined at 0.70 and 0.68, respectively, for BW gain and FCR (Figure 2). Corzo et al. (2009a) determined digestible Lys and Thr requirements simultaneously in Ross × Ross female broilers from 14 to 28 d of age. Digestible Thr to Lys ratios were determined by dividing the Thr requirement by the Lys requirement for each response criterion. Six digestible Thr and Lys concentrations were fed with digestible Thr ranging from 0.46 to 0.86% and digestible Lys concentrations varied from 0.84 to 1.24% in increments of 0.08% for each AA. Digestible Thr requirements ranged from 0.73 to 0.79% and digestible Lys requirements varied from 1.06 to 1.11% depending upon the response criteria, which resulted in digestible Thr to Lys ratios of 0.69 and 0.70, respectively, for BW gain and FCR. Two experiments were conducted to examine growth and meat yield responses of male broilers fed diets varying in digestible Thr to Lys ratio from 21 to 35 (experiment 1) and 35 to 49 (experiment 2) d of age (Dozier et al., 2016). Calculated digestible Thr to Lys ratios ranged from 0.512 to 0.806 in increments of 0.040 (Hubbard × Cobb 500) and 0.552 to 0.793 in increments of 0.035 (Ross × Ross 708). In experiment 1 (from 21 to 35 d of age), optimum digestible Thr to Lys ratios for male Hubbard × Cobb broilers were estimated at 0.68 and 0.67 for BW gain and FCR from 21 to 35 d of age. In experiment 2 (from 35 to 49 d of age), optimum digestible Thr to Lys ratios of Ross × Ross 708 were determined at 0.63 and 0.68 for FCR with linear and quadratic broken-line models, respectively. Meat weights and yields were not affected by the dietary treatments in either experiment. These data indicated that a digestible Thr to Lys ratio of 0.67 to 0.68 optimizes growth performance of broilers throughout various phases of production. Dietary Thr affects FCR more consistently than meat yield responses. Supplementation of L-Thr can be used effectively to reduce diet cost with the reduction of soybean meal without compromising broiler performance.

AUSTRALIA - VIEWS ON IDEAL OR LOWER PROTEIN LEVELS FOR MEAT CHICKENS AND APPROACHES TO SECOND TIER AMINO ACIDS - Image 2

IV. DIGESTIBLE VAL

Valine is the 4th limiting AA for broilers fed diets utilising AA-contributing ingredients of vegetable origin (Baker et al., 2002; Thornton et al., 2006; Corzo et al., 2009b). Digestible Val to Lys ratio has been reported to vary among production periods with ratios ranging from 0.74 to 0.78 (Corzo 2007, 2008; Rostagno et al., 2011). Corzo et al. (2011) have reported acceptable performance with the inclusion of L-Val into broiler diets. Price spread among cereal grains, supplemental oil/fat, and protein meals determines the value of L-Val. Kidd and Hackenhaar (2005) reported that Val is the fourth limiting AA with broilers fed corn-soybean meal and wheat-soybean meal based diets utilising formulation scenarios with various ingredients. Growth rate and FCR are more sensitive response criteria than breast meat yield as digestible Val approaches the requirement (Corzo et al., 2007, 2008). Feed-grade production of L-Val has increased due to the demand in swine production and recently it has been entering into some broiler formulations due to the popularity of “all-vegetable” diets in antibiotic-free production. L-Valine has entered into formulation of broiler diets containing ingredients of vegetable origin. Utilizing L-Val in concert with the ideal AA ratio concept in diet formulation allows nutritionists to meet an optimum digestible Val to Lys ratio while decreasing nitrogen excretion and maintaining cost effective diets. Formulating diets at a digestible Val to Lys ratio below the broiler’s need for Val limits their genetic potential in meeting performance objectives. Corzo et al. (2011) have reported acceptable performance with the inclusion of LVal into broiler diets. Corzo et al. (2007) conducted a series of experiments to determine the fourth limiting AA of Ross × Ross 708 male broilers fed diets containing ingredients of vegetable origin and to delineate the digestible Val to Lys ratio from 21 to 42 d of age. In order to confirm that Val is the fourth limiting AA of diets consisting of ingredients of vegetable origin, corn-soybean meal diets were formulated to be marginal in dietary Ile, Val, Arg, and Gly plus Ser. Supplementing Val to the negative control diet (marginal in Val, Ile, Arg, and Gly) led to similar BW gain of broilers fed the positive control diet, but adding Ile, Arg, or Gly to the negative control diet had lower (P ≤ 0.05) BW gain compared with the birds fed the positive control diet. These results indicated that Val is the fourth limited AA for broilers fed diets containing corn and soybean meal. In a subsequent study, corn-peanut meal negative control diet was formulated to be adequate in all AA with the exception of Val (0.59% digestible Val).

AUSTRALIA - VIEWS ON IDEAL OR LOWER PROTEIN LEVELS FOR MEAT CHICKENS AND APPROACHES TO SECOND TIER AMINO ACIDS - Image 3

L-Valine was added to the negative control diet to achieve six digestible Val treatments ranging from 0.59 to 0.84% in 0.06% increments. Digestible Val to Lys ratio was determined to be 0.78, 0.77, and 0.74 for BW gain (Figure 3), total breast meat weight, and total breast meat yield. An optimum ratio was not determined for feed conversion ratio. Corzo et al. (2008) evaluated dietary Val requirements (total) of Ross × Ross male broilers with three experiments from 0 to 14, 14 to 28, and 28 to 42 d of age and determined the requirements to be 1.00, 0.95, and 0.85%, respectively. Tavernari et al. (2013) examined the digestible Val to Lys ratio in Cobb 500 male broilers from 8 to 21 and 30 to 43 d of age in two independent experiments. In each experiment, seven experimental diets were provided to broilers that consisted of six diets ranging in digestible Val to Lys ratio (0.69 to 0.84 – 8 to 21 d of age; 0.70 to 0.85 – 30 to 43 d of age) and a positive control diet. Optimum Val to Lys ratio for BW gain and FCR were determined to be 0.77 and 0.75 and 0.75 and 0.77 from 8 to 21 and 30 to 43 d of age, respectively. Moreover, Berres et al. (2011) ascertained the digestible Val requirement of Cobb × Cobb 500 male broilers from 21 to 42 d of age. Seven digestible Val concentrations were fed ranging from 0.71 to 0.97% in increments of 0.04-0.05%. Based on broken-line methodology, digestible Val requirements were estimated at 0.82 and 0.81%, respectively, for BW gain and FCR. No dietary treatment differences were observed for carcass and breast meat yields. Data from these experiments indicate that the digestible Val to Lys ratio of 0.77 to 0.78 optimizes growth performance and meat yield of broilers. Feed-grade Val can be added to diets approximating 0.52 kg/ton without any adverse response in growth performance and breast meat yield of broilers (Corzo et al., 2011). Increasing L-Val supplementation at or beyond 0.78 kg/ton resulted in poor growth performance and meat yield. Optimum ratios of Ile, Arg, and Trp were not maintained purposely to determine the maximum inclusion of L-Val without supplementing these AA. Breast meat yield was adversely affected at L-Val supplementation of 1.04 and 1.30 kg/ton compared with the control-fed birds and this reduction in breast meat yield may be related to a decrease in the Ile ratio with the highest inclusion rates of L-Val.

V. DIGESTIBLE ISOLEUCINE

Dietary Ile is considered the fifth limiting AA in diets containing ingredients from vegetable origin. The addition of poultry meal or a meat blend product to the diet can result in Ile becoming fourth limiting. Dozier et al. (2011) determined that Val and Ile become co-limiting for broilers fed diets containing animal protein meals from 2.5% inclusion. With animal protein meal inclusion exceeding 5% of the diet, Ile may become the fourth limiting AA. With L-Val being available for diet formulation, digestible Ile becomes the pressure point in least-cost formulation to optimize performance objectives. Kidd et al. (2000) determined that feeding broilers diets containing a 10% reduction of the Ile requirement (NRC, 1994) resulted in a 0.46% reduction in breast meat yield compared with birds fed diets formulated to contain Ile at 100% of NRC 1994 recommendations. Dozier et al. (2012) examined interactive effects of digestible Val and Ile ratios to Lys on growth performance and meat yields of broilers from 28 to 42 d of age. Increasing digestible Ile to Lys ratio from 0.63 to 0.73 led to a 0.4% higher total breast meat yield (21.6 vs. 22.0%). Hence, it is important to employ an adequate dietary Ile concentration in least-cost formulation to optimize meat yields. de Castro Tavernari et al. (2012) evaluated digestible Ile to Lys ratio of Cobb male broilers from 7 to 21 and 30 to 43 d of age in two experiments. Optimum digestible ratios were estimated using linear response plateau and quadratic responses with a regression analysis. Digestible Ile ratio estimates varied due to response criterion and statistical analysis. Overall, digestible Ile ratios were estimated at 0.66 and 0.68, respectively, for broilers from 7 to 21 and 30 to 43 d of age. Digestible Ile ratios determined from the quadratic responses ranged from 0.68 to 0.70 and 0.72 to 0.75, respectively, from 7 to 21 and 30 to 43 d of age. Rostagno et al. (2011) has reported the digestible Ile to Lys ratio as 0.67 and 0.68, respectively, for broilers from 1 to 21 and 22 to 42 d of age for optimum growth performance. In addition, Kidd et al. (2004) determined the total Ile requirements to vary between 0.67 to 0.71%, 0.64 to 0.66%, and 0.55 to 0.66%, respectively, from 18 to 30, 30 to 42, and 42 to 56 d of age. The variation in the Ile requirement was due to response criteria of interest (BW gain, FCR, and carcass characteristics). Maintaining an adequate Ile minimum in diet formulation is needed to optimize growth performance and meat yield of broilers.

VI. CONCLUSIONS

Feeding reduced CP diets can achieve acceptable performance when formulating to optimum ratios of digestible Thr (0.67-0.68), Val (0.76-0.78), and Ile (0.67-0.69). Ingredient composition and price spread among cereal grains and oilseed meals along with oil/fat prices will dictate the cost savings with using feed-grade L-Thr and Val in diet formulations. Further reductions in CP can be achieved beyond using L-Val if essential AA concentrations are maintained. Digestible Lys specifications and the associated AA ratios will determine the amount of reduction in CP that can be achieved without compromising growth performance. However, Gly may be semi-essential with low CP diets fed during the starter period and may be considered when feeding diets consisting of ingredients from vegetable origin.

Abstract presented at the 30th Annual Australian Poultry Science Symposium 2019. For information on the latest edition and future events, check out https://www.apss2021.com.au/.

Views on Ideal or Lower Protein Levels for Meat Chickens and Approaches to Second Tier Amino Acids

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Prichemin (Chelated Minerals of Amino Acids)