The effect of dietary inclusions of guanidinoacetic acid on D1-42 broiler performance and processing yields

DESCRIPTION OF PROBLEM

Creatine is a necessary component in energy metabolism, supplying phosphate groups to adenosine diphosphate and recycling them to adenosine triphosphate (ATP) that can be used for maintenance and growth. This creatine-ATP recycling system does not occur in all cells, only in those where there is great variability in energy demand, including muscle cells [1]. Creatine is especially important in growing animals such as broiler chickens, as it is not only used in energy metabolism but may also be directly used for formation of muscle and other tissues [2]. Approximately 1.7% of the creatine cycle 1 pool in an adult mammal is irreversibly converted to creatinine and excreted each day, thus it must be replaced through endogenous synthesis or intake [3]. Growing animals, such as young broiler chickens, may have a greater need for creatine synthesis and intake as it is not only functioning in the ATP recycling pool but is also being used to stock muscles as they are formed [4]. Between two-thirds and threefourths of the daily creatine requirement of broilers can be synthesized de-novo, in the liver [5]. The additional daily required creatine must be supplied through dietary sources.

The effect of dietary inclusions of guanidinoacetic acid on D1-42 broiler performance and processing yields - Image 1

The prevalence of “all vegetable” diets is increasing, potentially as part of a marketing strategy to meet a perception of value set by customers and retailers [6]. Animal by-products, such as meat and bone meal, are sources of creatine; however, creatine concentration variability may be apparent as a result of product processing [3, 5]. When exposed to low pH, moisture, or elevated temperatures, such as those used in animal by-product processing, creatine can degrade to creatinine and is no longer of use to the animal [7, 8]. All vegetable diets containing only plant-based ingredient may supply less dietary creatine, thus putting a greater burden on de novo synthesis in growing broilers, potentially contributing to marginal available nutrients required for creatine synthesis [9, 10].

As diet formulation trends migrate toward less animal protein inclusion, the supplementation of creatine, or its precursors, may be beneficial for the performance of broiler chickens. In the body, creatine is synthesized de novo from arginine and glycine in a catalyzed, two-step reaction, the first step taking place in the pancreas and kidneys and the second in the liver. The product of the first reaction is a compound known as guanidinoacetic acid (GAA), which is methylated to form creatine, the form active in ATP recycling [3]. Creatine itself may not be effective as a feed additive because of its instability and cost, but GAA is more stable, less expensive, and easily converted to creatine by the body [11]. Córdova-Noboa et al. demonstrated a four-point improvement in feed conversion ratio (FCR) and a 100-g increase in final body weight in broilers fed with a vegetable protein–based diet supplemented with 600 mg/kg of CreAmino [12] from day of hatch until 50 D of age [13]. Ringel et al. reported similar improvements to performance [14], while Michiels et al. reported increased breast meat yield from 29.4 to 30.4% [1].

The objectives of this experiment were to determine the effects of GAA inclusion on the performance and processing yields of broilers fed with diets with basal ingredients containing either conventional (CON) or nonanimal protein (NAP) sources from D1-42.

MATERIALS AND METHODS

Experimental Design

A total of 1,728 Hubbard x Cobb 500 straight-run broiler chicks were obtained from a commercial source [15] on the day of hatch. Upon arrival at the Penn State University’s Poultry Education and Research Center, chicks were weighed and randomly assigned to one of four dietary treatments. Treatments were applied in a randomized complete block design to 12 replicate pens of 36 broilers from day of hatch through d42. One pen of broilers represented the experimental unit. Lighting schedule and environmental temperature were determined based on local industry recommendations and Penn State University standard operating procedures. All animals were reared in accordance to an approved institutional animal care and use committee protocol (IACUC 47990).

Feed Manufacture

Experimental diets were commercially formulated and manufactured. Diets were arranged in a 2 x 2 factorial varying in basal ingredients (CON or NAP) and GAA inclusion (0 or 0.06% CreAmino). Corn and soybean meal-based diets were formulated to be isocaloric (Table 1). An ingredient matrix for CreAmino (96% GAA), which contributed metabolizable energy (2,540 kcal/kg) and digestible arginine (77%), was used in the formulation. Feed and water were provided ad libitum throughout the experiment. Diets were fed as crumbles during the starter period (d1-21) and pellets during grower (d22-35) and finisher (d36-42) periods. The analyzed nutrient contents of the diets are presented in Table 1.

Live Performance and Carcass Yield Measurements

Body weight and feed refusal were measured by pen on days 1, 21, 35, and 42, and mortality was recorded daily. Live weight gain (LWG), feed intake (FI), and mortality-corrected FCR were calculated for each feed phase period. On d42, 20 birds per treatment were sampled for carcass yield determination. A total of 10 males and 10 females per treatment were selected from the pen closest to the treatment average pen weight. Birds were electrically stunned and euthanized by exsanguination before being processed for carcass yield determination. Furthermore, breast yield (BY) was determined as the percentage of breast muscle tissue weight, including both pectoralis major and pectoralis minor, relative to the eviscerated carcass weight. Wing yield, thigh yield, drum yield, and fat pad yield were also determined in a similar manner.

The effect of dietary inclusions of guanidinoacetic acid on D1-42 broiler performance and processing yields - Image 2

Statistical Analysis

Treatments were arranged in a 2 x 2 factorial in a randomized complete block design. Main effects consisted of basal ingredients and GAA inclusion. Data were analyzed using the GLM procedure of SAS [16], and significance was designated to be P ≤ 0.05. Significant main effects and interactions were further explored using F-protected Fisher’s low stocking density tests.

RESULTS AND DISCUSSION

Live Performance

When considering overall (d1-42) period live bird performance, main effects did not interact (P > 0.05). Basal ingredient source did not affect d1-42 FCR (P > 0.05); however, d1-42 FCR improved with inclusion of GAA, seen as a 0.019 FCR reduction (P = 0.0024; Table 2). Mousavi et al. reported an interaction between GAA inclusion, either none or 600 g/ton, and ME level, either 90, 95, or 100% of breed recommendation for ME, where FCR improved when GAA was added to the 95 and 100% ME diets [17]. These findings align with the present study where FCR was improved when included in diets adequate in metabolizable energy. Other work further supports these findings with similar improvements in broiler performance with the addition of GAA to diets that contained a variety of basal ingredients. Córdova-Noboa et al. reported a 0.042 FCR improvement from d0 to d50 when broilers were fed a diet supplemented with 600 g/ton GAA compared with broilers fed the same diet without GAA supplementation [13]. In addition, these authors reported 0.019 FCR improvement from d0 to d55 using a similar strategy [18]. Neither FI nor LWG differed when considering basal ingredients or GAA inclusion over the 42-d experimental period (Table 2; P > 0.05). In the starter (d1-21) period of the present study, GAA inclusion improved FCR by 0.040 (P = 0.0171) and increased LWG by 28 g/bird (P = 0.0010). FI did not differ with GAA inclusion (P > 0.05; Table 3). Starter (d1-21) period performance metrics were not affected by basal ingredient source (P > 0.05; Table 3). Neither main effect affected FCR or LWG during the grower (d22- 35) period (P > 0.05). Grower period FI decreased by 35 g/bird when broilers were provided diets containing basal ingredients including NAP compared with those fed with CON (P = 0.0377). However, basal ingredients did not affect FI in other growth periods or the overall study period (P > 0.05). Grower period FI did not differ with GAA inclusion (Table 3; P = 0.6321). During the finisher period, again the FCR was reduced by 0.037 with GAA inclusion (P = 0.0474). No other parameters differed with either main effect (Table 3; P > 0.05). Tossenberger et al. [19] demonstrated a decrease in broiler liver GAA and an increase in breast muscle creatine concentrations when GAA was supplemented at 0.6 g/kg in the diet from hatch through d35 when compared with a non–GAA-supplemented diet. Other experiments have seen a similar increase in muscle creatine level with dietary GAA inclusion [1, 14, 20]. This indicates a reduction of de-novo creatine synthesis from arginine and glycine, which could spare the amino acids for use in other biochemical functions, improving performance. Dilger et al. [21] reported that 1.2 g/kg of GAA can be supplemented in an arginine deficient diet from d8 to d17 without negatively affecting performance in chicks that were fed a nutrient-adequate diet until d7. DeGroot et al. [22] continued this line of research by feeding an arginine-deficient diet from d1 to d28, demonstrating that 1.2 g/kg supplemental GAA was sufficient to return body weight gain and gain-to-feed ratio to those of a positive control adequate in arginine. In the current experiment, the inclusion of GAA did not further improve performance of birds fed with the NAP diet, as hypothesized. As the conversion of GAA to creatine requires a methyl group, the NAP diet may also have been marginal in methyl donors such as methionine, betaine, or choline [23]. While GAA inclusion could have still spared arginine and glycine, a lack of methyl donors in the NAP diet could have resulted in inefficient conversion of the GAA into creatine [19, 24].

The effect of dietary inclusions of guanidinoacetic acid on D1-42 broiler performance and processing yields - Image 3

Processing Yields

Processing yield data are presented in Table 4. When considering BY, the main effects of GAA inclusion and basal ingredient interacted (P = 0.0443) (Figure 1). The addition of GAA to the diet containing CON increased the BY by 1.78% points when compared with CON with no GAA. The addition of GAA to NAP diets did not affect BY. In humans, an increase in intramuscular phosphocreatine can increase cell volume [25]. This increase in volume is thought to be caused by the osmotic draw of water into the cell, which can increase both protein and glycogen synthesis and decrease accumulation of lactic acid [26, 27]. Breast muscle of broiler chickens primarily consists of fast twitch muscles that have a high glycolytic metabolism [28, 29]. The inclusion of GAA in broiler diets could have affected the concentration of phosphocreatine in muscle cells, especially those in the breast resulting in increased breast weight seen in the main effect of GAA inclusion. Córdova-Noboa et al. [18] reported an interaction where birds fed a diet containing poultry by-product meal and GAA at 600 g/ton increased BY by 0.59% points. However, these authors reported a numerical decrease in BY when GAA was included in a diet without poultry by-product meal. There is limited literature on the effects of the interaction between basal ingredient and GAA inclusion on BY, and at this time, the mechanism of action requires additional research. In the current experiment, GAA inclusion did not decrease BY in either treatment; instead, it was unaffected by the NAP diet. Breast weight increased by 45 g with the inclusion of GAA (P = 0.0354). Perhaps, this increase in tissue weight can be explained by the aforementioned osmotic draw of water into cells. Finally, drum yield was 0.4% points higher in birds fed NAP than CON (P = 0.0264), and no other carcass yield parameters differed (P > 0.05).

CONCLUSIONS AND APPLICATIONS

1. The addition of 0.06% GAA improved performance over the starter, finisher, and overall d1-42 periods and increased d42 breast weight.

2. When GAA was included in diets with basal ingredients containing CON sources, BY increased; however, BY did not differ when GAA was included in diets with basal ingredients containing NAP sources.

3. GAA may have the potential to improve broiler performance and BY when included in broiler diets containing either conventional or nonanimal basal ingredients.

This article was originally published in 2020 Journal of Applied Poultry Research 29:220–228. https://doi.org/10.1016/j.japr.2019.10.008. This is an Open Access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).