Lysine is the first limiting amino acid in corn-soybean meal-based diets for pigs during the postweaning period (ROSTAGNO et al., 2011; NRC, 2012), and is commonly used as a reference when estimating the nutritional requirement for other essential amino acids (NEMECHEK et al., 2012). The standardized ileal digestible lysine (SID Lys) requirement of pigs is affected by several factors, such as genotype (TAYLOR et al., 2012), the environmental and sanitary conditions of the production system (KORNEGAY et al., 1993; MANNO et al., 2005), the dietary protein level (KERR and EASTER, 1995; RENAUDEAU; NOBLET, 2001), and the piglets’ age at weaning (TRINDADE NETO et al., 2002). Therefore, as piglets’ dietary SID Lys requirements vary, their levels should be monitored continuously, sequentially and independently of the feedstuff lysine added to the diet.
The SID Lys levels estimated by Rostagno et al. (2017) for piglets are 1.35, 1.25, and 1.13% from 28 to 35, 35 to 49, and 49 to 63 d of age, respectively. Taylor et al. (2012) stated that few studies have estimated high-performance-piglets’ SID Lys requirements immediately after weaning, and the SID Lys levels recommended by Rostagno et al. (2011, 2017) for modern lines may be inadequate for maximizing post-weaned piglets’ productive performance.
Many studies have reported increased lysine metabolism efficiency for growth when pigs are subjected to a period of moderate lysine restriction during the grower phase (CHIBA et al., 2002; FABIAN et al., 2002); however, few studies have evaluated moderate SID Lys restriction during the early post-weaning phase (NEMECHEK et al., 2012).
Several studies have investigated lysine requirements during specific phases (FONTES et al., 2005; HILL et al., 2007; SCHNEIDER et al., 2010; NEMECHEK et al., 2012; KAHINDI et al., 2017), however, little information exists regarding SID Lys requirements in multi-phase feeding (PF) programs, or possible adaptation to lysine-deficient diets.
Therefore, in order to better understand postweaned piglet nutrition, this study was designed to evaluate the effects of different SID Lys levels on the performance and carcass composition of weaned piglets fed a three-phase feeding program from 28 to 63 d of age.
Material and Methods
The protocol used in this study was reviewed and approved by the Animal Care and Use Committee of the Universidade Federal Viçosa (36/2012), and complied with the ethical principles of animal experimentation defined by the Colégio Brasileiro de Experimentação Animal (COBEA, 1991). The trial was conducted in the swine experimental facility at the Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.
Ninety-six commercial hybrid piglets (Topigs Norsvin, 46 castrated males and 50 females) that had been weaned at 28 d of age with an initial body weight of 8.82 ± 0.28 kg were allotted in suspended cages (1.6 x 1.02 x 1.1 m) based on their initial body weights. The experimental unit was each suspended cage, and in the block-formation the piglets’ initial body weight was considered as criterion. Three weaned piglets were housed in each suspended cage, which was equipped with water nipples and semi-automatic feeders. All of the animals’ were considered for growth-performance.
The animals were distributed in a randomized block design composed of four treatments, with eight replicates of three animals each. Each treatment consisted of a standard three-phase feeding (PF) program, including pre-starter I (28 to 35 d), pre-starter II (35 to 49 d), and starter (49 to 63 d) phases. The treatments were as follows: PF 1, SID Lys levels of 1.05, 0.95, and 0.85%; PF 2, SID Lys levels of 1.15, 1.05, and 0.95%; PF 3, SID Lys levels of 1.25, 1.15, and 1.05%; and PF 4, SID Lys levels of 1.35, 1.25, and 1.15% from 28 to 35, 35 to 49, and 49 to 63 d of age, respectively (Table 1, 2, and 3).
The experimental diets were corn-soybean meal-based, and were supplemented with minerals, vitamins, and synthetic amino acids in order to meet or exceed the nutritional requirement of high genetic potential for lean-meat-deposition piglets (7 to 30 kg) according to Rostagno et al. (2011) recommendations, except for SID Lys. For each phase, a basal diet was mixed, and lysine hydrochloride was added, replacing the inert, in order to achieve the desired SID Lys concentrations in the final diets.
The ratio of each essential amino acid to lysine was verified in all the experimental diets, and amino acids were added to the diets in place of inert, whenever necessary to ensure that no essential amino acids were limiting. When choosing the amino acid ratios, we followed the recommendations of Rostagno et al. (2011). Food and water were provided ad libitum throughout the experimental period.
The environmental conditions (temperature and relative air humidity) inside the heated nursery were monitored three times daily (7 am, 12 am, and 5 pm) using dry bulb, wet bulb, and black globe thermometers (Incoterm Ind. de Thermometers Ltda., Porto Alegre, Rio Grande do Sul, Brazil) that had been placed in an empty suspended cage located in the center of the piglet shed, at half the height of the animals’ bodies. The data obtained were converted into the black globe temperature and humidity (BGTH) index, as proposed by Buffington et al. (1981), in order to characterize the thermal environment to which the animals were exposed. Thermal variations were also measured daily (7:00 am) using maximum-minimum thermometers (Incoterm Ind. de Thermometers Ltda., Porto Alegre, Rio Grande do Sul, Brazil).
All piglets were weighed at the beginning of the experimental period (day 28), day 35, day 49, and at the end of the experimental period (day 63) to determine average daily gain (ADG). Average daily feed intake (ADFI) during the different periods was calculated as the difference between the total feed supplied, orts and wastes collected from the floor. The feed conversion ratio (FCR) was calculated based on the ADFI and ADG.
At the end of the experimental period, the animals were fasted for 12 h and then weighed. One animal from each experimental unit weighting closest to the pen average was slaughtered according to Brazilian legislation (BRASIL, 2000). Whole carcasses, including feet and heads, were weighed and sectioned in half. The right half of each carcass was weighed and stored in a freezer (Metalfrio DA420) at -12 ºC.
Six animals at 28 d of age with similar initial body weight of the experimental units were also slaughtered to evaluate body composition at the beginning of the experimental period, before being frozen for subsequent processing and analyses.
The right-half-carcasses were individually ground in a commercial meat grinder after defrosting. The ground material was then homogenized, and samples were pre-dried at 60 °C in a drying oven for 72 hours, pre-degreased in a Soxhlet apparatus for 4 h, dried again at 60 °C for 1 hour, and finally ground in a ball mill. Protein analyses were conducted using the 955.04 method (AOAC, 2000) and lipid levels were determined using the 960.39 method (AOAC, 2000) at the Laboratory of Animal Nutrition, Department of Animal Science, Universidade Federal de Viçosa. Protein and fat deposition were calculated as the difference between the carcass composition values obtained at 28 and 63 d of age.
Performance and carcass composition data from 28 to 63 d of age were analyzed in a randomized block design using the Proc GLM procedure in SAS (SAS Institute Inc., Cary, NC, USA). Treatment means were compared by Tukey’s test. For 28 to 35 d of age, the data were analyzed using the Proc REG procedure in SAS (SAS Institute Inc., Cary, NC, USA). Significance was declared at P < 0.05.
Results and Discussion
During the experimental period, the temperature and relative air humidity were 25.9 ± 1.96 °C and 69 ± 9.1%, respectively, and the maximum and minimum temperatures and BGTH index were 27.0 ± 1.65 °C, 25.3 ± 1.55 °C, and 75.1 ± 2.3, respectively. Close and Stanier (1984) stated that an air temperature ranging from 23 to 28 °C is ideal for piglets from 28 to 63 d of age, and Alebrante et al. (2011) stated that a BGTH index value of 74.3 ± 1.79 characterize thermoneutrality for pigs from 15 to 30 kg, so we can infer that, in the present study, the animals were kept in a thermoneutral environment conditions.
The ADFI of weaned piglets fed a three-PF program was not significantly affected (P > 0.05) by the SID Lys levels tested, regardless of the phase analyzed (Table 4). Similar ADFI results were obtained by Kendall et al. (2008), Yang et al. (2009), Schneider et al. (2010), and Kim et al. (2001) while working with post-weaned piglets. However, Taylor et al. (2012) reported a significant voluntary FI reduction when piglets were fed the highest dietary lysine level tested (1.60%). This may be explained by the higher lysine level used by those authors, which was above the highest level used in the present study. According to Edmonds et al. (1987), excess protein, and, consequently, amino acids, in the diet may negatively affect FI in pigs.
The dietary energy level is the main factor that affects voluntary FI in pigs (YANG et al., 2009), so the absence of any ADFI variation in the present study may have been because the experimental diets were isoenergetic.
Consistent results obtained by a number of studies indicate that, from 28 to 63 d of age, piglet FI is little-affected by dietary nutritional composition. Stress during weaning causes functional and structural alterations in small intestine mucosa (SPREEUWENBERG et al., 2001; BOUDRY et al., 2004), induces mucosal inflammatory reactions (MCCRACKEN et al., 1999), and promotes an imbalance in the intestinal microflora (CASTILLO et al., 2007; BAUER et al., 2011), so we can also infer that it plays a major role in defining the piglet FI pattern in the first weeks post-weaning by making pigs less sensitive to nutritional variations, except for those associated with excess protein and amino acids. In addition, the thermal environment also affects the voluntary FI of pigs (COLLIN et al., 2001); however, in the present study, the thermal environment was characterized as thermoneutral, so it should not have affected the piglet FI pattern.
The average daily lysine intake (ADLI) significantly increased (P < 0.05) linearly from 28 to 35 d, and weaned piglets fed diets containing the highest lysine levels, consequently, ingested larger quantities of this amino acid (Table 4). These results are in accordance with those obtained by Kim et al. (2001), Taylor et al. (2012), and Nemechek et al. (2012).
The SID Lys levels tested had no significant effect on the piglets’ ADG (P > 0.05), regardless of the phase analyzed (Table 4). Despite not varying significantly, a gradual numeric increase was detected in absolute ADG between PF1 and PF3, being PF3 31.60, 13.40, and 9.50% higher from 28 to 35, 28 to 49, and 28 to 63 d of age, respectively. For the pre-starter I phase (28 to 35 d), the absence of a significant effect, despite the higher ADG variation, can be explained by the high coefficient of variation obtained (25.14%).
An improved growth rate in post-weaned piglets caused by an increased lysine concentration in the diet has also been reported by Yi et al. (2006), Kendall et al. (2008), Yang et al. (2009), and Kim et al. (2001). Although their results are qualitatively similar, the lysine levels estimated for obtaining a high ADG varied among studies due to several reasons, such as genotype (SCHNEIDER et al., 2010), facility sanitary status (GANDRA et al., 2012), thermal environment (CLOSE; STANIER, 1984), and the animals’ social interactions (PLUSKE et al., 2003), which may compromise the expression of piglets genetic potential for growth.
Although the ADG did not vary significantly among the PF programs tested (P > 0.05), the PF1 animals had a significantly lower fBW than those in the other treatments at 63 d of age (P < 0.05). Considering the results obtained by Mahan and Lepine (1991) and Mahan et al. (1998), who reported a direct connection between body weight at weaning and at the end of the nursery phase with the body weight at 150 d of age, we can infer that the subsequent performance of animals fed PF1 could be compromised.
From 28 to 35 d of age, the dietary SID Lys level significantly affected piglets FCR (P < 0.05), which increased linearly, but no significant difference was found between the two highest SID Lys levels tested (1.25 and 1.35%), demonstrating that 1.25% SID Lys meets weaned piglets’ requirements for body weight gain (Table 4). A positive effect of dietary SID Lys levels on the FCR of post-weaned piglets was also reported by Nemechek et al. (2012) and Taylor et al. (2012).
From 28 to 49 d of age, despite no significant FCR variation (P > 0.05), PF3 FCR was 6.34% improved when compared to PF1. No significant differences in the FCR were found between animals fed PF3 and PF4.
During the entire experimental period (28 to 63 d of age), PF4 piglets had a significantly higher FCR than PF1 and PF2 piglets (P < 0.05), but not PF3 piglets (P > 0.05). A positive effect of SID Lys levels on piglet FCR during the nursery phase was also reported by Yi et al. (2006), Kendall et al. (2008), Yang et al. (2009), and Kim et al. (2001).
The improvement in the FCR observed in this study indicates that although piglet ADG did not significantly differ among the PF programs investigated, the gain composition may have changed, with an increase in the carcass protein deposited. Protein deposition carries a high amount of water, because it is closely associated with the protein present in lean tissue and visceral organs, so in general, protein deposition positively affects feed efficiency for body weight gain (DE LANGE et al., 2003).
The protein deposition rate (PDR) significantly differed among the PF programs tested (P < 0.05), with the highest values obtained in pigs fed PF3 and PF4, which were similar (P > 0.05) (Table 4). Similarly, Fontes et al. (2005) and Oliveira et al. (2006), when evaluating females and castrated males from 15 to 30 kg, observed a linear PDR increase due to increase in the SID Lys level concentration (0.90 to 1.36%).
However, the fat deposition rate (FDR) did not significantly differ among the PF programs tested (P>0.05), which contradicts the results obtained by Taylor et al. (2012). According to those authors, post-weaned piglets fed lysine-deficient diets would have a suboptimal PDR and, consequently, more energy available for FDR (TAYLOR et al., 2012).
From 28 to 35 d of age, a 1.25% SID Lys level, which corresponds to an estimated ADLI of 4.13 g/d, meets the requirements for better performance in post-weaned piglets. The PF3 treatment, corresponding to SID Lys levels of 1.25, 1.15, and 1.05% from 28 to 35, 35 to 49, and 49 to 63 d of age, respectively, provided the best performance and PDR results of post-weaned piglets from 28 to 63 d of age.
This article was originally published in Semina: Ciências Agrárias, Londrina, v. 39, n. 2, p. 719-730, mar./abr. 2018. DOI: 10.5433/1679-0359.2018v39n2p719. This is an Open Access article distributed under a Creative Commons Attribution License.