Ó 2022 The Authors. Published by Elsevier Inc. on behalf of Poultry Science Association Inc. This is an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Improving broiler performance at market age regardless of stocking density by using a pre-starter diet o ,* A. Navarro-Villa,* J. Polo ,y D. Sola-Oriol,z and R. Franco-Rossell A. I. Garcıa-Ruiz *,1 * Trouw Nutrition R&D, Ctra. CM-4004 km 10.5, El Viso de San Juan, Toledo, 45950, Spain; yAPC Europe, S.L., Granollers 08403, Spain; and zAnimal Nutrition and Welfare Service, Department of Animal and Food Science, Universitat Aut onoma de Barcelona (UAB), 08193, Spain Primary Audience: Researchers, Nutritionists, Veterinarians and Poultry Producers SUMMARY Broiler early nutrition has caught the attention of nutritionists due to the positive correlation between early growth rate and market weight. Early nutrition strategies such as low Ca levels or the use of highly digestible ingredients (e.g., spray-dried porcine plasma [SDPP]) have been reported to improve gut and muscle development, immunity, and overall growth of the bird. On the other hand, recent works suggested that stocking density represents the main constrain for modern chickens to express their full genetic potential. The current study aimed to elucidate the potential effects of pre-starter feeding strategies on contrasting livestock stocking densities. The study followed a factorial design of 2 contrasting starter programs (standard [0−11d] vs. pre-starter [0−4 d] + standard [4−11 d]) by 3 stocking densities (low, medium, and high, 27, 33, and 39 kg/BW/m2, respectively). Birds placed at low stocking density showed higher BW and better FCR than those at high stocking density (P < 0.05) being this evident only after d 28. On the other hand, birds fed on pre-starter diet led to higher BW at 4 d (P < 0.001) and the effects on BW were maintained until market age (+2.54%; P < 0.05). The pre-starter diet also led to heavier carcasses (+2.2%; P < 0.05), improved uniformity (P < 0.10) and showed a lower incidence of lameness at high stocking densities (P < 0.05) compared to birds fed the standard starter diet. Results of the current study confirm that, regardless of the stocking density used, pre-starter diets (0−4 d) could lead to a better early growth and market weight. Key words: broiler, pre-starter diet, stocking density, performance 2022 J. Appl. Poult. Res. 31:100232 https://doi.org/10.1016/j.japr.2021.100232 DESCRIPTION OF PROBLEM period between hatching and farm allocation could range from 24 to 72 h. This period is con- There is a growing interest in the use of sidered too long for the first water and feed more specific diets in young chicks to reduce intake allowance (de Jong et al., 2017). Another stress-related factors derived from water and identified stressful factor is caused by the shift feed deprivation in the first hours of life. The of energy source in the first few hours post- hatching, going from endogenous lipids and 1 Corresponding author: ai.garcia@trouwnutrition.com proteins in the yolk toward a more complex 2 JAPR: Research Report exogenous source of carbohydrates in conven- production cycle. Despite the fact the genetic tional starter diets (Leeson and Summers, 2005). companies (e.g., Ross 308 [Aviagen 2019] or And finally, the limited digestibility in young Cobb 500 [Cobb-Vantress 2018]) have their own chicks due to an immature enzyme system and recommendations, conventional starter diets are limited absorption capacity (Lamot et al., 2019) commercially supplied during the first 10 d of calls for specific pre-starter diets. life, even up to 21 d, and may not meet the opti- In general, pre-starter diets provide highly mal nutritional requirements (Gutierrez et al., digestible ingredients or higher levels of 2008). Thus, following a 3-phase feeding pro- nutrients (Leeson, 2008). The use of these pre- gram (starter, grower, and finisher) could be starter diets may improve early growth and more practical than 4-phase feeding programs health. Likewise, it could have some effects on that use a pre-starter diet in the first days of life. subsequent growth phases (e.g., carryover Formulating starter diets represents a huge chal- effects). Willemsen et al. (2008) established a lenge for nutritionists since nutritional require- positive correlation between body weight at 7 d ments change rapidly during the first week of and body weight at market age. However, posi- life due to the continuous and rapid development tive effects on bird performance are not of organs (e.g., those of the gastrointestinal tract uniquely related to improvements in nutritional or immune system) (Christensen, 2009; aspects, other factors such as husbandry and Lilburn and Loeffler, 2015). To overcome these handling of the animals play a key role growth issues, the use of pre-starter diets adding highly of the bird as well. For instance, according to digestible ingredients may facilitate the limited Leeson (2018) the main restriction for modern digestibility of the young chicks (Barekatain and chickens to express their full growth potential Swick, 2016). at market age is the use of high stocking density Spray dried porcine plasma (SDPP) is a com- due to its restrictive effect on feed intake. plex mixture of functional components including Stocking density, calculated as the number immunoglobulins, albumin, transferrin, fibrino- of birds or body mass (in kg or lb) per unit of gen, lipids, growth factors, bioactive peptides, housing surface in m2 or ft2, represents one of enzymes, hormones, and amino acids commonly the key husbandry factors that develops an used in feed for young animals (Torrallar- important role on traits such as bird perfor- dona, 2010; Perez-Bosque et al., 2016). Porcine mance, animal welfare (e.g., behavior) and or bovine spray-dried plasma (SDP) has shown health status of the flock (e.g., immunity to be effective improving the intestinal barrier response) (Thaxton et al., 2006). Broiler pro- function, balancing the inflammatory process, ducers, in general, tend to quantify their reve- reducing the incidence of diarrhea, and improving nues by increasing the number of birds feed intake in weaned pigs (Torrallardona et al., produced per barn, and thus, the more kilo- 2003; Peace et al., 2011; Pujols et al., 2016). In grams of chicken per area the higher the reve- young chicks, the use of SDPP has resulted in nues (Cengiz et al., 2015). However, higher growth performance improvement (Jamroz et al., stocking densities, greater than 33 kg/m2, have 2011; Henn et al., 2013; Campbell et al., 2019a) been associated with lower bird performance and has shown beneficial effects in gut health due to a higher competition for the fixed num- (Beski et al., 2015a). Furthermore, as observed in ber of feeders (Leeson and Summers, 2005; young pigs, the benefits of adding SDP in chick Cengiz et al., 2015), greater chances for com- diets are improved when birds are growing under promised immunity (Heckert et al., 2002; challenging conditions (Campbell et al., 2006; Thaxton et al., 2006) and, other welfare con- Beski et al., 2016; Gonzalez-Esquerra, 2019b). cerns, such as foot-pad dermatitis, scratches, Moreover, according to Walters et al. (2019) and bruising among others (Estevez, 2007). SDP can be considered as an alternative to reduce For logistics reasons, producers tend to mini- the use of non-therapeutic antibiotics, replacing mize the number of diets offered to birds to the use of bacitracin methylene disalicylate in reach market weight. This strategy, contrarily, the diet. makes it more difficult to match the exact nutri- During the incubation period, the embryo tional requirements of the bird throughout the has limited access to minerals, except Ca,  ET AL: PRE-STARTER DIETS AND STOCKING DENSITIES 3 FRANCO-ROSSELLO which is absorbed from the eggshell and incor- wood shaving was used as bedding material. porated in the yolk and embryonic tissues Water and feed were offered ad libitum (Johnston and Comar, 1955). The yolk is the throughout the entire production cycle. The main source of phosphorus (P) necessary for barn temperature was gradually decreased from the development of the skeleton and at hatching 32˚C at placement to 21˚C at 42 d and the light time its storage is minimal (Yair and Uni, 2011; schedule decreased from 24 h light for the first Li et al., 2014). This physiological limitation 3 d to 16:8 (light:dark) thereafter. could delay bone mineralization after hatching, especially when chickens are fed a conventional Experimental Design starter diet with Ca levels ranging from 9 to 10.5 g/kg, due to the well-known interference A total of 6 experimental treatments were of Ca in P availability (Driver et al., 2005). In tested in 2 starter programs (standard [0−11 d] this sense, Mansilla et al. (2020) showed that vs. pre-starter [0−4 d] + standard [4−11 reducing the Ca content in pre-starter diets (0 d]) £ 3 stocking densities factorial arrange- −4 d) can increase early growth without ment. The target stocking densities, were estab- compromising bone mineralization. lished, based on the expected BW at the end of The current study aimed to investigate the cycle (42 d), as follows: low stocking den- whether providing low Ca, SDPP and highly sity at 27 kg BW/m2, the medium stocking den- digestible ingredients such as micronized soy sity at 33 kg BW/m2 (or standard stocking or maize flakes in the pre-starter period (0−4 d) density according to the Boletın Oficial del could result in better growth at market age and, Estado, 2010) and the high stocking density at more particularly, if such strategies could alle- 39 kg BW/m2, which was estimated to be viate somehow the problems associated with achieved with 26, 31, and 37 birds/pen, respec- high stocking densities. tively. The experimental period lasted for 42 d and animals underwent a 3- or 4-phase feeding program. The effect of dietary treatments, stocking density and their interaction was eval- MATERIALS AND METHODS uated for broiler performance, flock uniformity, Animals and Housing and carcass traits. The present study was approved by the Experimental Diets Trouw Nutrition Animal Care Committee and followed recommendations of the Castilla-La Birds received 2 contrasting starter pro- Mancha Animal Welfare department grams (standard starter or pre-starter) from (Boletın Oficial del Estado, 2013). placement up to the fourth day, both feeds A total of 1,504 one-day-old Ross 308 male were formulated to be iso-energetic, but for- broiler chicks (SADA Inc., Alcala del Rio, Sev- mulation did not result in similar digestible ille, Spain), vaccinated against Marek, Coccidi- amino acid contents between the two diets. osis, Infectious Bronchitis and Gumboro Outside of the reduced Ca in the pre-starter diseases, were randomly placed in 48 identical diets, formulation was done to meet or exceed pens with a total area of 3.06 m2 (2.91 the CVB recommendations (Centraal, 2018) m £ 1.05 m). In an attempt to achieve contrast- for broilers. Subsequently, all birds received a ing stocking densities 26, 31, or 37 birds were common 3-phase feeding program: Starter placed per pen to achieve an expected density (from 4 to 11 d), Grower (from 11 to 28 d) of 27, 33, and 39 kg BW/m2 respectively at 42 and Finisher (from 28 to 42 d) based on the d. The floor area occupied by feeders was not CVB recommendations. Feed-form presenta- considered on measuring the expected density. tion was 2 mm pellet for pre-starter and starter During the first 5 d, the diets were distributed phases, and 3.5 mm pellet for grower and fin- on feed trays. From 3 d onward, additionally 1 isher phases. Pre-starter and standard starter tube feeder was used. All pens were equipped diets were formulated based on a maize-soy- with 4 functional nipple drinkers, and fresh bean meal-wheat diet and supplemented with 4 JAPR: Research Report NSPs enzymes (Axtra XB TPT containing NSPs enzymes as pre-starter and starter diets, 1,220 U xylanase and 152 U b-glucanase, and 500 FTU/kg of phytase enzyme. The pre- DuPont, Marlborough, UK) and 1,000 FTU/kg starter diet was formulated with a lower Ca of phytase enzyme (Phyzyme XP TPT, level relative to the standard starter diet DuPont, Marlborough, UK) to achieve a (4 g/kg vs. 10 g/kg Ca, respectively). Addition- digestible P level of 4.6 g/kg. Grower and fin- ally, the pre-starter diet was formulated using a isher diets were supplemented with equal concentrate that contained highly digestible Table 1. Ingredient composition and calculated nutrient content of pre-starter (0−4 d), starter (0−11 d), grower (11−28 d), and finisher diets (28−42 d). Ingredient, %1 Pre-starter Starter Grower Finisher Maize 29.82 51.45 45.00 7.00 Wheat 12.00 12.00 21.95 62.62 Soybean meal (47% CP) 16.52 22.70 20.19 18.86 Soya oil 2.068 2.710 3.323 4.810 Soy protein concentrate (63% CP) 7.00 7.00 6.90 4.55 concentrate2 30 - - - Salt 0.091 0.091 0.180 0.181 Mono-Ca-phosphate 0.213 0.369 0.399 0.035 Mono-Na-phosphate 0.767 0.765 - - Calcium carbonate 0.124 1.615 0.654 0.555 Sodium bicarbonate - - 0.221 0.205 L-Lysine HCl (98%) 0.189 0.215 0.201 0.208 DL-Methionine (99%) 0.336 0.245 0.233 0.222 L-Threonine (98%) 0.072 0.040 0.049 0.054 Vitamin and mineral premix3 0.500 0.500 0.500 0.500 Commercial phytase4 0.200 0.200 0.100 0.100 Commercial NSPase5 0.100 0.100 0.100 0.100 TOTAL 100.00 100.00 100.00 100.00 6 Calculated nutrient and energy content of the diet, % AME, kcal/kg 2,850 2,850 2,925 3,000 Moisture 10.9 (9.4) 11.4 (7.5) 10.6 (9.3) 8.9 (8.8) Ash 4.7 (4.5) 6.1 (5.9) 4.5 (4.2) 3.8 (3.9) CP 24.0 (24.5) 21.0 (21.7) 19.5 (19.4) 18.3 (19.7) EE 4.7 (3.7) 5.4 (4.7) 5.9 (4.9) 6.4 (5.9) CF 2.4 (2.2) 2.5 (2.3) 2.9 (2.7) 2.8 (2.8) Lys, g/kg 15.03 12.78 11.87 11.09 Met, g/kg 6.76 5.60 5.30 5.02 Met + Cys, g/kg 11.03 9.06 8.60 8.30 Thr, g/kg 10.17 8.28 7.86 7.36 Ca 0.400 (0.420) 1.000 (0.975) 0.550 (0.530) 0.450 (0.435) P 0.602 (0.593) 0.603 (0.640) 0.598 (0.415) 0.530 (0.330) Dig P 0.460 0.460 0.350 0.290 Inositol P 0.238 0.227 0.226 0.235 1 Units per all items unless specified. 2 A protein-energy concentrate that contains SDPP, sugar, maize flakes, and micronized soy. Analyzed nutrient values of concen- trate: AME (calculated) 2,938 kcal/kg, 9.6% Moisture, 3.2% Ash, 24.9% CP, 2.3% EE, 2.2% CF, 0.290% Ca and 0.345% P. 3 Provided per kg of complete diet: 10,000 IU vitamin A (trans-retinyl acetate), 2,500 IU vitamin D3 (cholecalciferol), 50 IU vitamin E (all-rac-tocopherol-acetate), 2.0 mg vitamin B1 (thiamine-mononitrate), 6 mg vitamin B2 (riboflavin), 40 mg vita- min B3 (niacin), 4.0 mg vitamin B6 (pyridoxine HCl), 25 mcg vitamin B12 (cyanoco-balamin), 2.0 mg vitamin K3 (bisulfate menadione complex), 10 mg pantothenic acid (d-Ca pantothenate), 1.0 mg folic acid, 150 mcg d-biotin, 0.25 mg Se (Na2SeO3),1.0 mg I, 15 mg Cu (CuSO45H2O), 67.7 mg Fe (FeSO47H2O), 90 mg Mn (MnSO4H2O), and 80 mg Zn (ZnO). 4 FTU/kg, PhyzymeÒ XP TPT, DuPont. 5 U/kg, Axtra XB TPT, DuPont. 6 Analyzed values are presented within brackets below the corresponding calculated value.  ET AL: PRE-STARTER DIETS AND STOCKING DENSITIES 5 FRANCO-ROSSELLO ingredients such as SDPP (Appetein GS, APC spectrophotometry based on a colorimetric test Europe S.L., Granollers, Spain), sugar, maize (AXFLOW Method G-103-93 Rev. 10). flakes, and micronized soy. Ingredient and nutrient composition of the diets are shown in Statistical Analysis Table 1. Main effects (diets and stocking densities) Performance, Flock Uniformity, and Carcass and the interaction were analyzed using the Traits Measurements MIXED procedures of SAS (v. Studio, SAS Institute Inc., Cary, NC). The blocking factor On arrival (d 1) and at the end of each feeding (location in the barn) was included in the model phase (4, 11, 28, and 42), birds and remaining as random effect. Differences among means feed were weighed to determine average bird were identified using Tukey multiple compari- BW, average daily gain (ADG), ADFI, and FCR. sons (P < 0.05). Mortality statistical analysis Weight of dead birds per pen was recorded daily was performed as a binomial distribution using and used to correct FCR for each feeding phase. the GLIMMIX procedure of SAS studio. Birds were also weighed individually on d 4, 11, and 42 and flock uniformity was calculated as pro- portion of broilers within 5% of the average BW. RESULTS AND DISCUSSION Mortality and lameness were recorded daily. Mortality was calculated as the ratio of dead The current study reveals that there was no chickens to total chickens at the beginning of interaction (P > 0.100) between the diets up to the study and lameness was calculated as the 4 d and the stocking density in broiler perfor- ratio of lame chickens to total chickens at the mance along the whole cycle. In contrast, main beginning of the study. The designation of factors separately did affect broiler perfor- lameness was made according to an internal mance (Table 2). procedure considering all chicks with difficulty The negative impact of stocking density on to walk, difficulty to stand or showing partial or animal performance at market weight because total immobility as lame. of the lower feed intake at higher stocking den- At 42 d of age, after weighing all the animals sities, due to the difficult access to feeders or individually, 5 animals per pen were selected competition among birds, was not observed. within §5% of pen average BW, identified and Only during the first 4-d phase (Table 2), fasted for approximately 12 to 14 h before slaugh- broilers reared at higher stocking densities tering. Birds were electrically stunned and reduced (P < 0.05) ADG and (P < 0.001) ADFI completely exsanguinated to death. Carcass (with- and showed poor (P < 0.001) FCR. Bird perfor- out neck) and breast (pectoralis mance in the period from 4 to 28 d did not major + pectoralis minor) yields were determined appear to be negatively influenced by increas- after a chilling process of 2.5 h. ing the stocking density, but birds did reach a lower (P < 0.05) final BW at 42 d and worse (P Laboratory Analysis < 0.001) FCR compared to those at lower den- sities. These findings are similar to those Analytical determinations of feeds were per- reported in previous studies (Feddes et al., formed in duplicate and according to the meth- 2002; Dozier et al. 2006; Zuowei et al., 2011; ods of AOAC (2012): dry matter (method Simitzis et al., 2012). 934.01), crude protein with the Dumas method In the present study, stocking density did not using a LECO analyzer (method 968.06), crude affect (P > 0.05; Table 2) ADFI but had nega- fiber (method 962.09), crude fat (method tive effects on FCR and ADG during the fin- 2,003.05), and ash content (method 942.05). The isher phase and for the overall rearing period (P determination of Ca was carried out by spectro- < 0.05). Additionally, no significant variation photometry based on a colorimetric method in any performance measurements was (AXFLOW Method G-209-98 Rev. 2) and P observed between medium stocking density and determination was determined by low stocking density, or between medium 6 Table 2. Influence of the diets (0−4 d) and stocking density on growth performance of broiler chickens from placement in the barn to 42 d of age. Diet (0−4 d) Stocking density (kg BW/m2) P-value High (39 kg Medium Low (27 kg Diet £ Standard Pre-starter SEM1 BW/m2) (33 kg BW/m2) BW/m2) SEM2 Diet Density Density 0 to 4 d BW 0 d, g 42.7 42.6 0.10 42.7 42.7 42.6 0.14 0.596 0.784 0.887 BW 4 d, g 99.7 104.7 0.91 101.7 103.1 101.8 0.95 <0.001 0.080 0.599 ADG, g 14.2 15.5 0.22 14.7b 15.1a 14.8ab 0.23 <0.001 0.035 0.446 ADFI, g 14.2 14.3 0.19 13.7c 14.3b 14.7a 0.20 0.897 <0.001 0.591 FCR, g/g 1.000 0.917 0.0039 0.932b 0.945b 0.997a 0.005 <0.001 <0.001 0.590 4 to 11 d BW 11 d, g 327.2 340.2 3.61 333.0 335.5 332.6 3.83 <0.001 0.610 0.224 ADG, g 32.5 33.6 0.41 33.0 33.2 33.0 0.44 0.001 0.842 0.231 ADFI, g 36.0 37.4 0.37 36.4 37.0 36.7 0.40 <0.001 0.327 0.210 FCR, g/g 1.107 1.114 0.0044 1.102b 1.115b 1.114b 0.0049 0.166 0.046 0.725 11 to 28 d BW 28 d, g 1,489 1,524 20.3 1,498 1,516 1,506 21.2 0.006 0.475 0.523 ADG, g 68.3 69.6 1.01 68.5 69.4 69.0 1.05 0.042 0.490 0.687 ADFI, g 97.7 99.6 1.22 98.2 99.3 98.5 1.27 0.019 0.438 0.636 FCR, g/g 1.431 1.431 0.0046 1.433 1.432 1.428 0.0054 0.925 0.738 0.817 28 to 42 d BW 42 d, g 2,790 2,857 24.4 2,772b 2,838ab 2,860a 27.5 0.011 0.021 0.257 ADG, g 92.9 95.2 1.04 91.0b 94.4ab 96.7a 1.28 0.126 0.012 0.387 ADFI, g 160.8 163.9 1.66 160.6 163.8 162.7 1.94 0.127 0.418 0.100 FCR, g/g 1.733 1.724 0.0148 1.766a 1.736a 1.683b 0.0164 0.511 <0.001 0.344 0 to 42 d ADG, g 65.5 67.1 0.63 65.1b 66.7ab 67.2a 0.71 0.016 0.030 0.263 ADFI, g 99.9 102.0 1.01 100.0 101.7 101.1 1.10 0.023 0.259 0.290 JAPR: Research Report adj FCR3, g/g 1.430 1.400 0.0098 1.446a 1.412ab 1.386b 0.0118 0.032 0.003 0.354 Abbreviations: ADG, average daily gain; ADFI, average daily feed intake; BW, body weight; FCR, feed conversion ratio. a,b,c Values in the same row without a common superscript letter significantly differ, P ≤ 0.05. Values are least square means and pooled SEM 1 Standard error of the mean: (n = 24 replicates). 2 Standard error of the mean: (n = 16 replicates). 3 Calculate FCR adjusted to 2.5 kg on global period (FCR0-42 d = FCR0 to 42d-(avBW42d/1,000 − 2.5) £ 0.331).  ET AL: PRE-STARTER DIETS AND STOCKING DENSITIES 7 FRANCO-ROSSELLO stocking density and high stocking density for agreement with our results and the overall period (P > 0.05). Similar findings Mehmood et al. (2014). were also observed by McKeith et al. (2020), According to Feddes et al. (2002) and Bes- who reported no significant differences between sei (2006) the decreased final BW in birds at standard densities (0.23 m2 per bird) and low high stocking density may be explained by the stocking densities (0.27 m2 per bird) on FCR close proximity of the birds during growth, and and BW. Consequently, increasing the available therefore not being able to dissipate the meta- surface per broiler did not significantly influ- bolic heat. Furthermore, the aggravated lame- ence the FCR or BW (0−42 d). ness percentage observed mainly around Despite the higher (P < 0.05; Table 2) BW market age may not be the main factor contrib- observed at lower stocking density at 42 d of uting to the decreased final BW of birds at high age, no differences (P > 0.05) in feed intake stocking density. were observed throughout the whole cycle, In the present study, stocking density and with the exception of the first week of life, diets up to 4 d did interact on lameness percent- when chicks at low stocking density consumed age. Birds at high stocking density and fed on more feed than chicks at high stocking densities pre-starter diet reduced lameness percentage (P (P < 0.001; Table 2). Thus, the initial hypothe- < 0.05) compared to those fed on standard sis of having limited access to feeders due to starter diet (Figure 1). The benefits of SDPP in increased stocking density as well as the com- performance were evident and the ability to petition between birds to reach the feeders was modulate the immune response, reducing rejected and might not well be the explanation. expression of pro-inflammatory cytokines Lana et al. (2001) observed a similar response under challenging conditions or physiological regarding increased feed intake during the early stress, has been demonstrated in weaned piglets period (1−7 d of age) in those birds at low (Bosi et al., 2004; Perez-Bosque et al., 2016) stocking densities (10 birds/m2) compared to and in broiler chickens (Campbell et al., 2006; those at high stocking densities (16 birds/m2) Beski et al., 2016). Campbell et al. (2012) and attributed the latter fact to environmental found that increasing stocking density and sup- comfort, litter, and air quality. Conversely, plementing the diets with SDPP under coccidia Guardia et al. (2011) found an increase in feed vaccination challenge reduced mortality and intake during the starter phase on those birds at improved broiler performance (BW and FCR). higher stocking density and hypothesized that Thus, pre-starter diets containing SDPP might untrained chicks could more easily find feed or alleviate the percentage of lameness under water in denser flocks than in flocks at low stressful circumstances such as high stocking stocking density. However, no effect on ADFI densities. Nevertheless, Zuowei et al. (2011) as birds grew older was observed, which is in associated the aggravated leg weakness with Figure 1. Influence of the diets (0 to 4 d) and stocking density on Lameness percentage in the overall period (0 to 42 d). Values are least square means. 8 JAPR: Research Report increased feed intake in broilers at high stock- Feed intake was not affected at the 4-d ing density from 36 to 42 d of age. phase, but the efficiency of feed conversion Previous studies demonstrated the positive improved (P < 0.001) with the pre-starter diet effect of feeding broilers with a pre-starter diet (Table 2). This was in line with the findings of during the first hours or days of life on their Beski et al. (2015b), who observed no differen- performance parameters up to market age ces in feed intake up to 35 d between broilers (Saki, 2005; Hooshmand, 2006; Willemsen et al., fed on diets that contained 2% SDPP and con- 2008). trol birds, but the supplementation of SDPP Many nutritional strategies have been stud- shows better growth at the end of the cycle. ied with the aim of improving broiler perfor- Similarly, King et al. (2005) also found that mance during the first 7 d of age showing SDPP improved FCR during the first 14 d of higher live weight, greater feed intake and bet- age. However, in contrast to these results, ter feed efficiency, but without any influence in Ullah et al. (2012) concluded that the reason for the subsequent phases (Noy and Sklan, 2002; the improvement in final BW may be due to a Longo et al., 2007). Otherwise, our work con- higher feed intake during the first week of birds firms the better performance of broilers fed pre- fed on a pre-starter diet with higher energy and starter diets for a period of only 4 d. Body optimum lysine level. weight and FCR significantly improved (P < The present study reduced dietary Ca con- 0.001) after completing the 4-d phase and the tent from 10 g/kg of the standard starter diet to differences observed in BW were maintained 4 g/kg in the pre-starter diet, in line with during the subsequent phases (Table 2). These Torres et al. (2018). Sebastian et al. (1996) results are supported by the findings of found that increasing dietary Ca from 6 to Beski et al. (2015b), and Gonzalez- 12.5 g/kg impaired BW at 21 d, Paiva Esquerra et al. (2019a), who reported that sup- et al. (2013) showed that increasing dietary Ca plementing broiler starter diets with SDPP from 6 to 9 g/kg reduced weight gain at 21 d, improved BW in the first 10 d and throughout and Mansilla et al. (2020) found that increasing the study, even when all birds were fed the dietary Ca content from 4 to 10 g/kg the first 4 same common grower and finisher diets. Some d reduced ADG. Mansilla et al. (2020) also studies established that a functional protein found that tibia ash content decreased at 4 d by such as SDPP, which can mediate immune lowering Ca levels but did not affect bone function and response by alleviating stressful health during grow-out period. Thus, higher conditions, results in improved overall perfor- levels of Ca needed for optimal bone minerali- mance (Campbell et al., 2019b; Walters et al., zation could interfere P availability for other 2019). The present study confirmed the benefi- tissues, nutrient digestibility and therefore cial effects of SDPP supplementation to the broiler performance (Driver et al., 2005; pre-starter diets of broiler chickens. Paiva et al., 2013; Li et al., 2017). On the other Table 3. Influence of the diets (0−4 d) and stocking density on carcass traits of broiler chickens at 42 d. Diet (0−4 d) Stocking density (kg BW/m2) P-value Pre- High (39 kg Medium (33 kg Low (27 kg Diet £ Standard starter SEM1 BW/m2) BW/m2) BW/m2) SEM2 Diet Density Density BW 42 d3, g 2,790 2,861 28.9 2,772b 2,838ab 2,866a 31.9 0.014 0.024 0.325 Carcass weight, g 1,869 1,910 21.4 1,852b 1,894ab 1,922a 23.5 0.042 0.020 0.208 Carcass yield, % 67.03 66.70 0.16 66.88 66.67 67.05 0.196 0.178 0.434 0.098 Breast weight, g 520.5 527.7 7.49 509.4b 525.0ab 537.9a 8.39 0.344 0.015 0.362 Breast yield, % 18.67 18.42 0.127 18.40 18.47 18.77 0.164 0.248 0.312 0.765 Values in the same row without a common superscript letter significantly differ, P ≤ 0.05. Values are least square means a,b,c and pooled SEM. 1 Standard error of the mean: (n = 24 replicates). 2 Standard error of the mean: (n = 16 replicates). 3 Five animals per pen were selected within §5% of pen average BW.  ET AL: PRE-STARTER DIETS AND STOCKING DENSITIES 9 FRANCO-ROSSELLO Figure 2. Influence of the diets (0 to 4 d) and age on Flock Uniformity percentage. Values are least square means § SE. hand, according to Mansilla et al. (2020) birds Menocal et al. (2021) found improved carcass fed low Ca diets showed higher feed intake dur- weight and yield feeding 2% SDPP up to 7 d of ing the pre-starter phase which was responsible age. Likewise, birds at lower stocking density for the improvement of BW during the first had higher (P < 0.05) carcass and breast weight week. (Table 3). Similarly, Dozier et al. (2006) In our study birds fed the pre-starter diet had reported lower carcass and breast fillet weight higher carcass weight (+2.2%, P < 0.05), which due to an increase of stocking density. It was might be related to the final BW (+2.54%, P < expected that crowded birds would not grow to 0.05) results (Table 3). Abdulla et al. (2017), their full potential, which might be also related reported that birds fed 15 g/kg Ca had lower to final BW. The breast and carcass yields were carcass weight compared to those fed 10 or not significantly (P > 0.05) affected by the diets 12.5 g/kg Ca and also concluded that there was up to 4 d, neither by stocking density. This was a possible relation with BW, lower in those in agreement with previous works including birds fed 15 g/kg Ca. Furthermore, Arce- SDPP (Longo et al., 2007; Henn et al., 2013; Figure 3. Influence of stocking density and age on Flock Uniformity percentage. Values are least square means § SE. 10 JAPR: Research Report Beski et al., 2015b) or different stocking densi- ACKNOWLEDGMENTS ties (Feddes et al., 2002; Zuowei et al., 2011; Simitzis et al., 2012). In contrast, The authors would like to acknowledge the Cengiz et al. (2015) observed a decrease in rela- Poultry Research Centre staff, the European tive carcass yield in birds at higher stocking Regional Development Fund (ERDF) and the density which was linked with a reduction in Centro para el Desarrollo Tecnologico Indus- feed intake and thus, a lower weight gain. trial (CDTI project IDI-20180885) for making In the current study flock uniformity was not this research work possible. influenced (P > 0.05) by stocking densities (Figures 2 and 3). This result is not consistent with Feddes et al. (2002) who found higher var- DISCLOSURES iability in animals at low stocking density The work was funded by Trouw Nutrition. which could have resulted in greater floor space R. Franco-Rossello, A. Navarro-Villa and A. I. allowing fast-growing birds to grow to their full Garcıa-Ruiz work at Trouw Nutrition. D. Sola- potential. In contrast, Mehmood et al. (2014) Oriol works at the University Autonomous of reported that birds reared at lower stocking den- Barcelona. J. Polo works at APC; APC supplied sities exhibited better uniformity concluding the spray dried porcine plasma necessary for that having ample space could satisfy the natu- the present study. The authors have no conflicts ral behavior of the birds resulting into better of interest to report. uniformity. However, in the current study, uni- formity decreased across ages (P < 0.001; Fig- ures 2 and 3), and stocking density and age did REFERENCES interact (P < 0.05) on uniformity (Figure 3). Hence, our results are more in line with Abdulla, N. R., T. C. Loh, H. Akit, A. Q. Sazili, Mehmood et al. (2014), as the decrease in uni- H. L. Foo, K. Y. Kareem, R. Mohamad, and R. A. Rahim. 2017. Effects of dietary oil sources, calcium formity at 42 d was not as severe for birds at and phosphorus levels on growth performance, carcass low stocking density. 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