Effects of protein source and nutrient density in the diets of male broilers from 8 to 21 days of age on their subsequent growth, blood constituents, and carcass compositions

Birds, Diets, and Housing

Feed ingredients, including corn, soybean meal, DDGS, and MBM, were analyzed for their total AA and CP compositions (AOAC International, 2006) and the nutrient matrix was used to formulate least-cost diets using linear programming (Table 1). Digestible AA values were calculated from digestibility coefficients (Ajinomoto Heartland, 2004) and the analyzed total AA content of the ingredients.

A randomized complete block design was used, with all 8 treatments being equally represented in each block. Ten blocks were identified by their locations in the broiler facility. The 8 treatment diets were arranged in a 2 (protein sources) × 2 (AA densities) × 2 (AME levels) factorial design. Each diet contained either high DDGS (hDDGS) or high MBM (hMBM), moderate or high AA densities, and moderate or high AME levels (Table 1). The hDDGS diets contained 6% DDGS and 2% MBM and the hMBM diets contained 2% DDGS and 6% MBM. Other diets included the hDDGS diet with high AA and AME densities (DHH); the hDDGS diet with high AA and moderate AME densities (DHM); the hDDGS diet with moderate AA and high AME densities (DMH); the hDDGS diet with moderate AA and AME densities (DMM); the hMBM diet with high AA and AME densities (MHH); the hMBM diet with high AA and moderate AME densities (MHM); the hMBM diet with moderate AA and high AME densities (MMH); and the hMBM diet with moderate AA and AME densities (MMM).

The moderate AA level was based on digestible AA requirements of male broilers with a standard performance from 8 to 21 d of age (Rostagno et al., 2011), and the high AA level was based on a 10% performance level above that for the moderate AA level. The calcium, sodium, total mineral, vitamin, and medication premix levels were the same among all 8 diets.

All birds had ad libitum access to fresh water and feed throughout the whole experiment. The photoperiod from 0 to 7 d of age was 23L:1D and from 8 to 54 d of age was 20L:4D. All methods and management procedures used in the current study were approved by the Institutional Animal Care and Use Committee of Mississippi State University.

Blood Characteristics

On d 20, 2 birds from each pen were randomly selected and blood samples were collected from the brachial vein in nonheparinized tubes. After allowing the blood to clot (2-h period), samples were centrifuged at 1,900 × g for 10 min at 4°C to in order extract serum. For determination of high-density lipoprotein cholesterol (HDLC) concentration, serum samples were pipetted into Vitros HDL tubes (DT HDL Cholesterol Kit, Ortho Clinical Diagnostics, Rochester, NY) and centrifuged at 1,500 × g for 10 min at 4°C. All serum and supernate (HDLC) samples were stored at −20°C and warmed to room temperature before testing. Serum cholesterol (CHOL), triglycerides (TRIG), total protein (TP), uric acid (UA), and HDLC concentrations were analyzed on a Kodak Ektachem DT-60 analyzer (Eastman Kodak Co., Rochester, NY). Serum or supernate samples (10 μL) were applied to the appropriate Vitros DT slide and the slides were then scanned by the analyzer.

Growth Performance and Carcass Traits

At 8, 21, 42, and 54 d of age, BW and FI were determined on a per pen basis. Body weight gain, FI, and FCR were determined within grow-out phases from 8 to 21, 22 to 41, and 42 to 54 d of age. Daily mortality was recorded and FCR was adjusted by accounting for the BW of the birds that died.

Four chicks from each pen were processed at 42 and 55 d. Birds were weighed individually and were cooped for 16 h before processing. Carcass weights and abdominal fat pad weights were obtained by automated processing. Carcasses were chilled by storage in an ice-water slurry for approximately 4 h. Wings, leg quarters (drumstick and thigh), and boneless and skinless breast and tenders weights were obtained by manually deboning individual carcasses.

Feed cost per carcass weight gain or BW gain was calculated. Ingredient prices were obtained from current ingredient market information (Feedstuff, Bloomington, MN). The price of each diet was calculated by Creative Formulation Concepts software (CFC, Pierz, MN). The cost of feed in each feeding phase was determined by multiplying FI by feed price. Carcass weight at 8 d was estimated as 60% of live BW.

Statistical Analysis

A randomized complete block design was used, with all 8 treatments being equally represented in each block. A 2 × 2 × 2 factorial arrangement of treatments was used, and all parameters were analyzed using SAS version 9.2 (SAS Institute, 2010). A 3-way ANOVA (PROC MIXED) was used to determine the significance of responses to dietary protein source, AA and AME levels, and their interactions. The dietary protein source and AA and AME levels were designated as fixed effects; block was a random effect. Linear correlations were conducted among the parameters 20-d CHOL, TP, UA, TRIG, and HDLC, 8- to 20-d BW gain, FI, and FCR, and 42- and 55-d carcass weight. Pearson product-moment correlation analysis of the PROC CORR procedure was used. Global effects, differences among least squares means, and correlations were considered to be significant at P ≤ 0.05.

Blood Constituents

Growth Performance

Carcass Composition

Dietary treatments from 8 to 21 d of age did not affect carcass, tender, or wing weights (Table 5). However, broilers fed hDDGS diets with a high AA density deposited more fat by 55 d of age than did those fed hDDGS diets with a moderate AA density or hMBM diets with a high AA density (P = 0.048). Three-way interactive effects (protein source × AA level × AME level) were found for breast and leg quarter weights at 55 d of age (P = 0.032 and P = 0.033, respectively). Chicks fed an MMM diet grew more breast muscle than those fed DMM or DHH diets (P = 0.032). Chicks fed a DHM diet also grew more breast muscle than those fed a DHH diet, and birds fed an MMM diet gained more leg quarter muscle than birds fed DMH, MHM, DMM, or MMH diets. Birds fed DHH or DHM diets gained more leg quarter muscle than those fed DMM or MMH diets.

Blood Constituents

Higher serum concentrations of CHOL and TRIG at 20 d were induced in broilers by increasing the AME of the hMBM diets. A previous study has shown that TRIG and CHOL are associated with the fatty acid metabolic pathway, and that TRIG concentration is positively associated with energy intake (Bacon et al., 1981). However, CHOL or TRIG levels were not affected by the AME level in the hDDGS diet. The lack of response of TRIG to the high energy level may be due to the high fiber content of the hDDGS diet. Previous studies have shown that high fiber content may decrease lipid digestibility by reducing bile acid in chyme (Smits and Annison, 1996; Smits et al., 1998). Accordingly, the absorption of poultry fat in the gut of the broilers fed the DDGS diet may have been altered due to its high fiber content.

Consistent with previous works by Collin et al. (2003) and Zhao et al. (2009), higher dietary AA levels increased serum UA concentrations in the current study. Serum UA concentration was correlated to TP. This was expected, as UA is the major end product of protein metabolism in avian species (Sturkie, 1986), and the excess nitrogen from the high-AA-density diets is excreted through its assimilation in UA.

Higher serum HDLC concentrations were observed in broilers fed hDDGS diets when compared with those fed hMBM diets. This may also be a result of the high fiber content of DDGS. Research on humans has shown that high dietary fiber may increase propionate levels in the colon, which may result in higher serum HDLC levels (Venter et al., 1990). Cecal microbes in chickens may use nonstarch fibers in DDGS to produce propionate, thereby increasing HDLC levels. Higher serum HDLC concentrations were also observed in broilers fed diets with a lower AA density. This was likewise demonstrated in a study using rats (Madani and Belleville, 2000). High-density lipoproteins transport cholesterol and fat to the liver from cells in peripheral tissues, including those in artery walls. High serum HDLC concentrations may prevent coronary heart diseases in human (Gordon et al., 1977; Després et al., 2000). Distillers dried grains with solubles or a lower protein density in the diet may have the potential to improve the cardiovascular function of birds by increasing HDLC level.

Growth Performance

In the current study, high nutrient density diets lowered the FI of the birds. This is consistent with earlier findings by other researchers (Dale and Fuller, 1979; Hernández et al., 2004; Zhao et al., 2009). However, the actual AA (12.8 vs. 12.0 g of digestible Lys, 4.9 vs. 4.7 g of digestible Met, 7.9 vs. 7.5 g of digestible TSAA, and 8.3 vs. 7.8 g of digestible Thr of broilers fed high- or moderate-AA diets, respectively) intakes were similar between the groups fed either the high- or moderate-AA diets. And the actual AME (3,103 vs. 3,043 kcal for birds fed high or moderate AME diets, respectively) intakes were similar between groups fed either the high- or moderate-AME diets. By consuming smaller amounts of high nutrient density diets, the birds consumed similar amounts or even more of the key nutrients than those birds fed lower nutrient density diets. The current results showed that dietary protein source did not affect FI, which is consistent with previous research showing that chickens exhibit no preference between MBM and DDGS diets (Cantor and Johnson, 1983; Rochell et al., 2012). If DDGS comprise 25% of diets, chicks will consume more feed due to the low energy content of DDGS (Wang et al., 2007b). In the current trial, hDDGS diets, which contained 6% DDGS, did not affect FI.

Chicks fed diets with a higher AME gained more BW, which was in agreement with early experiments showing that high-energy diets improved broiler BW gain (Grover et al., 1972; Reece and Mcnaughton, 1982; Zhao et al., 2009), and the BW gain of chicks fed an hDDGS diet was the same as those fed an hMBM diet. Consistent with previous research by Zhai et al. (2013), BW gain was not affected by dietary AA density alone. However, chicks fed hMBM diets with high AA and AME densities gained the most BW, whereas chicks fed hDDGS diets with moderate AA and AME densities grew more slowly from 8 to 21 d of age. This suggests that protein source or AA density do not exert independent effects on BW, but that they rather interact with AME level in affecting growth. A 3-way interaction for 8- to 21-d FCR was observed. In this interaction, the high dietary nutrient density groups (hDDGS and hMBM diets) resulted in a lower FCR. These results are in agreement with studies in which increases in dietary nutrient density decreased FCR (Saleh et al., 2004; Zhao et al., 2009; Delezie et al., 2010). Interestingly, among the observed effects of the 8 treatment groups, the groups of birds that exhibited the highest and lowest FCR were these that were fed hDDGS diets. This result indicates that broiler chickens fed DDGS exhibit a more sensitive FCR response to nutrient density than those fed an MBM diet.

The current results showed that a high nutrient density in grower diets from 8 to 21 d of age improves FCR only during the grower feeding phase and does not persist in to the latter phases. Previous studies have shown that young birds with a poor performance due to early nutrient restriction exhibit compensatory growth during the latter grow-out period. Indeed, BW eventually reaches normal levels within the latter growing phases (Summers et al., 1990; Zubair and Leeson, 1996; Cristofori et al., 1997; Pinheiro et al., 2004; Zhan et al., 2007; Zhai et al., 2013).

Carcass Traits

Except for abdominal fat pad weight, the weights of the carcass parts examined at 42 d of age were not affected by the dietary treatments that were imposed from 8 to 21 d of age. Nevertheless, the long-term effect that dietary treatment had on abdominal fat pad weight extended through 55 d of age. This suggests that an early dietary regimen may have a long-term effect on fat deposition. It is well accepted that body fat content varies depending on energy intake (Keren-Zvi et al., 1990; Cabel and Waldroup, 1991; Summers et al., 1992); those results are consistent with the current trial. When chickens fed high-AA-diets are fed a higher dietary AME level (3,100 vs. 2,998 kcal/kg) from 8 to 21 d of age, fat deposition at 42 d of age is increased. In addition, dietary protein level may also affect chicken fat deposition. Broiler chickens fed a 26% CP diet deposited less fat than those fed a 22% CP diet (Marks and Pesti, 1984), and chicken fed a 22.5% CP diet deposited less fat than those fed a 19% CP diet (Aletor et al., 2000). Those results are also consistent with the current trial, in which a higher AA density level in the diets (22.88%) reduced fat pat weight at 42 d of age when compared with a lower AA density in the diets (20.80%) of birds fed moderate AME levels. However, when chickens were fed hMBM diets, fat pad weight at 55 d of age was increased in the birds fed a high-AA-level diet. Those results suggest that fat deposition may have been affected by the interaction of ingredient type and nutrient density in the diets.

Interestingly, although early nutrition manipulation did not affect total carcass yield at 55 d of age, it did affect breast and leg quarter yield. When broiler chickens were fed MMM diets from 8 to 21 d of age, the highest breast and leg quarter weights were produced from 43 to 55 d of age. The broiler chickens fed lower nutrient densities at an early age appeared to exhibit compensatory growth with a subsequently expected increase in breast and leg quarter meat yield from 43 to 55 d of age. It is suggested that the morphology, mucin production, and enzyme excretion of the digestive systems of the broilers may have adjusted to the different nutrient densities of the diets, as indicated in earlier research (Bedford, 1996; Horn et al., 2009). The birds fed a lower density diet at an early stage may have been allowed more opportunity to develop digestive systems that become capable of absorbing more nutrients more efficiently during the latter phases of their growth. With the accumulated effects of compensatory growth, the MMM group of broilers produced the most breast and leg quarter meat by 55 d of age.

Dietary treatment did not affect feed cost based on BW gain; however, feed cost based on carcass weight at 55 d of age was decreased by an increase in the energy level of the diet fed from 8 to 20 d of age. Higher energy diets are more expensive on a feed-weight basis (Table 1); however, because they lead to a significant decrease in FI, the total cost of feed to achieve a given carcass weight by 55 d of age is less. This suggests that high-energy diets not only improve FCR, but that they also lower broiler meat production costs.

The current results showed that serum CHOL and HDLC level at 20 d of age were positively correlated to abdominal fat weight at 42 d of age. This is consistent with a previous study showing that abdominal fat pad weight was positively correlated with serum CHOL (Musa et al., 2007). In addition, serum CHOL concentrations in the present study were positively correlated with HDLC. These effects lasted through 42 d of age, which suggests that higher serum CHOL and HDLC levels in young broilers may serve as predictors of an increase in subsequent fat deposition. Nevertheless, serum TRIG at 20 d of age was not correlated with abdominal fat pad weight at 42 or 55 d of age, indicating a lack of association between serum TRIG and abdominal fat deposition. Although serum TRIG concentration at 20 d of age was not correlated with carcass weight or the weight of its cut-up parts at 42 d of age, a higher serum TRIG was associated with lower carcass, wings, and leg quarter weights at 55 d of age. A lower level of muscle production is indicative of lower protein anabolism or higher protein catabolism. Sanz et al. (2000) reported that a higher serum TRIG is indicative of lower lipid utilization in the tissues of birds. Because muscle tissue consists mainly of protein and lipid, a lower utilization of lipid may lead to a higher utilization of protein, which results in a decrease in the deposition of muscle protein.

In conclusion, high AA or AME densities in grower diets from 8 to 21 d of age may improve the growth performance of broilers during the grower feeding phase without affecting growth performance during the latter feeding phases, from 22 to 55 d of age. However, early diet manipulation (from 8 to 21 d) may affect meat yield during the latter grow-out phases (from 22 to 55 d). Grower diets from 8 to 21 d of age with a high AME density may increase carcass production profit margins. In addition, dietary regimens involving protein source and AA or AME densities during the grower phase from 8 to 21 d of age may alter serum CHOL and HDLC concentrations, as well as fat accumulation by 42 and 55 d of age. Furthermore, blood constituents at 20 d of age are associated with subsequent fat deposition and meat production at 42 and 55 d of age.