Interrelationships between sex and dietary lysine on growth performance and carcass composition of finishing boars and gilts1 Pau Aymerich,†,‡,2, Carme Soldevila,† Jordi Bonet,† Mercè Farré,$ Josep Gasa,‡ Jaume Coma,† and David Solà-Oriol‡, Vall Companys Group, Lleida 25191, Spain; ‡Animal Nutrition and Welfare Service, Department of Animal and † Food Sciences, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain; and $Department of Mathematics, Area of Statistics and Operations Research, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain ABSTRACT: The main goals of this study were had a greater ADG and feed efficiency (G:F; to determine whether boars and gilts respond P < 0.001) than gilts, but there was no evidence differently to the standardized ileal digestible ly- of differences in ADFI (P = 0.470). Increasing sine to net energy ratio (SID Lys:NE) and model SID Lys:NE had a greater linear impact on boars the response to optimize growth performance. ADG (P = 0.087), G:F (P = 0.003), and carcass A total of 780 finishing pigs, 390 boars and 390 leanness (P = 0.032). In contrast, gilts showed gilts [Pietrain NN × (Landrace × Large White)], a greater linear increase in SID Lys intake per with an initial individual body weight of 70.4 ± kg gain (P < 0.001) and feed cost per kg gain 9.2 for boars and 68.7 ± 8.0 kg for gilts, were used (P = 0.005). The best fitting BLL models showed in a 41-d dose–response experiment. Pens (13 pigs that boars maximized ADG at 3.63 g SID Lys/ per pen) were randomly allocated to a dietary Mcal NE [95% confidence interval (CI): (3.32 to treatment (2.64, 3.05, 3.46, 3.86, 4.27 g SID Lys/ 3.94)], although another model with a similar Mcal NE) by block and sex, with six replicates fit, compared with the Bayesian information cri- per treatment and sex. Two isoenergetic diets terion, reported the optimum at 4.01 g SID Lys/ (2,460 kcal NE/kg), representing the extreme SID Mcal NE [95% CI: (3.60, 4.42)]. The optimum to Lys:NE, were formulated and then mixed. Pigs maximize ADG for gilts was estimated at 3.10 g were individually weighed at days 0, 22, and 41, SID Lys/Mcal NE [95% CI: (2.74, 3.47)]. Thus, when the experiment finished. The differential ef- the present study confirmed that boars and gilts fect of SID Lys:NE on growth performance and have a different linear response to SID Lys:NE, carcass composition between sexes was analyzed explained by the greater protein deposition po- with orthogonal polynomial contrasts to com- tential of boars. Likewise, BLL models indicated pare the linear and quadratic trends in each sex. that boars require a higher SID Lys:NE to maxi- In addition, broken-line linear (BLL) models to mize ADG from 70 to 89 kg. These results sug- optimize average daily gain (ADG), including gest that split feeding of finishing boars and gilts average daily feed intake (ADFI) as a covariate, could be beneficial in terms of both performance were fitted when possible. As expected, boars and cost return. Key words: boars, finishing pig, gilts, lysine, requirements This research was supported by the Catalan Industrial 1 Doctorates Plan of the Department for Universities and Re- search, Ministry of Business and Knowledge of Generalitat de Catalunya. 2 Corresponding author: paymerich@vallcompanys.es Received April 30, 2020. Accepted July 13, 2020. 1 2 Aymerich et al. © The Author(s) 2020. Published by Oxford University Press on behalf of the American Society of Animal Science. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. Transl. Anim. Sci. 2020.4:1-13 doi: 10.1093/tas/txaa129 INTRODUCTION The available literature lacks research that com- pares the lysine requirements of boars and gilts in Historically, entire male pig production was commercial conditions using low feed intake sire- common in some European countries such as lines, such as Pietrain. If, as hypothesized, boars Spain, the British Isles, and Portugal (Bee et al., have greater SID Lys:NE requirements than gilts, 2015). However, with the increasing pressure to ban it might be productively and economically worth- castration in the EU and as a result of the Council while to split-feed pigs by sex (Coffey et al., 1995) or Directive 2008/120/EC, in 2017 boars already ac- use precision feeding systems (Pomar et al., 2010). counted for 34% of the EU male pig population Thus, the present work studied the effect of SID (Kress et al., 2019), representing around 45 million Lys:NE on the growth performance (70 to 106 kg) pigs (Agri-Food Data Portal—Pigmeat Productions; and carcass composition of finishing boars and agridata.ec.europa.eu). As this has been a recent gilts. The objectives of this work were 1) to deter- change, most of the studies conducted to determine mine whether boars and gilts respond differently to lysine requirements for growth performance used the standardized ileal digestible lysine to net energy barrows instead of boars (Szabó et al., 2001; Ettle ratio (SID Lys:NE) and 2) to model the response to et al., 2003; Main et al., 2008; Elsbernd et al., 2017). SID Lys:NE in order to determine the SID Lys:NE During recent decades, some works have already requirement to maximize performance. studied the differential response of boars compared with gilts (Campbell et al., 1988; Van Lunen and MATERIALS AND METHODS Cole, 1996; King et al., 2000; O’Connell et al., 2006; Moore et al., 2013), whereas others focused on the All the procedures described in this work fol- differences as a result of castration (Williams et al., lowed the EU Directive 2010/63/EU for animal 1984; Otten et al., 2013; Moore et al., 2016). In add- experiments. ition, there have been some modeling studies that compared lysine requirements based on growth and Experimental Design and Animals feed intake data (Quiniou et al., 2010; NRC, 2012; van der Peet-Schwering and Bikker, 2018). In this study, the differential response between Boars are known to have a greater potential finishing boars and gilts to increasing SID Lys:NE for growth than gilts from 40 to 70 kg body weight was analyzed in a 41-d dose–response experiment (BW) until market weight (Campbell et al., 1988; with five increasing levels. The trial was conducted Van Lunen and Cole, 1996; Moore et al., 2013; in a commercial-experimental farm integrated into Cámara et al., 2014), resulting in a leaner body Vall Companys Group (Alcarràs, Spain). The study and carcass composition (Andersson et al., 2005; sample consisted of a total of 780 finishing pigs, Giles et al., 2009; Gispert et al., 2010; Aymerich 390 boars and 390 gilts [Pietrain NN × (Landrace et al., 2019). As no evidence of differences in feed × Large White)], with an initial individual BW of intake has been reported in the literature (Van 70.4 ± 9.2 for boars and 68.7 ± 8.0 kg (mean ± SD) Lunen and Cole, 1996; O’Connell et al., 2006; for gilts. When the pigs entered the growing-finish- Moore et al., 2013; Cámara et al., 2014), theoret- ing facilities, they were separated into pens (13 pigs ically the greater protein deposition potential of per pen) of similar weight based on visual observa- boars would represent a greater lysine requirement tion. They were then weighed, and large pigs that to maximize average daily gain (ADG). Most stud- were in pens classified as small were exchanged with ies have found differences in requirements between small pigs in pens classified as large, and vice versa, boars and gilts in the finishing phase (Campbell until we had three BW blocks (19.1 ± 2.6, 21.9 ± et al., 1988; O’Connell et al., 2006); however, some 2.6, and 24.7 ± 2.6 kg, for small, medium, and large studies have not (Van Lunen and Cole, 1996; King categories, respectively). At the start of the experi- et al., 2000). ment, the pens were randomly allocated by block to Translate basic science to industry innovation Finishing boars and gilts lysine requirements 3 each treatment, and the resulting distribution was 41 of the experiment, pigs in the heaviest BW block checked to avoid confounding effects related to barn were moved to the slaughterhouse (Patel S.A.U; location. Pen was used as an experimental unit, with L’Esquirol, Spain), and individual carcass compos- six replicates per treatment and sex. Each pen had a ition was measured with AutoFom III (Frontmatec half slatted concrete floor (3 × 3 m), one-hole wet– Food Technology, Kolding, Denmark). Measured dry Maxi Grow Feeder (Rotecna, Agramunt, Spain), parameters included hot carcass weight (HCW; head and an additional nipple waterer at the opposite and feet on), carcass leanness (CL), backfat thick- side. The farm was both naturally and semi-forced ness (BFT), and ham fat thickness (HFT), whereas ventilated. Natural light was provided through the carcass yield (CY) was calculated afterwards. The windows used for ventilation, and artificial light was same procedure was performed on medium and only used when required by the farm care personnel. small BW block pigs at days 48 and 55, respectively. Although the trial was conducted during winter, the underfloor heating system was only used on the Feeding first days of the growing period, before starting the trial. Ad libitum access to feed and water was en- Two isoenergetic diets (2,460 kcal NE/kg) were sured during the entire trial. Pigs were individually formulated based on maize, wheat, and soybean weighed and monitored using electronic ear tags at meal (Table 1). Diets were formulated to meet or the beginning, at day 22 and before marketing the exceed the requirements for each nutrient, except heaviest pigs (day 41 of the trial). The pigs came lysine. The essential amino acid (AA) was formu- from a healthy sow farm, and no relevant health lated based on the ideal protein ratios (NRC, 2012; issues were observed during the experiment. At day FEDNA, 2013). The high ratio diet was 4.27 g SID Table 1. Ingredient composition and calculated nutritional composition of the two diets used for blending the five dietary treatments (as-fed basis) Ingredient composition, % Feed A Feed B Calculated composition1 Feed A Feed B Maize 45.00 45.00 Dry matter, % 87.56 87.42 Wheat 34.13 39.51 Crude fiber, % 2.76 2.74 Soybean meal 47% 15.20 11.20 Sugars, % 2.68 2.54 Animal fat 1.60 1.50 Starch, % 47.90 51.03 Calcium carbonate 1.20 1.20 Ether extract, % 3.75 3.66 Dicalcium phosphate 0.20 0.20 Crude protein, % 15.69 13.55 Sodium chloride 0.40 0.40 Total Lys, % 1.14 0.73 Lysine sulphate 0.91 0.33 SID Lys, % 1.05 0.65 l-Threonine 0.27 0.04 SID Met+ Cys/Lys ratio 0.61 0.62 dl-Methionine 0.22 — SID Thr/Lys ratio 0.66 0.65 l-Valine 0.12 — SID Trp/Lys ratio 0.21 0.21 l-Tryptophan 0.07 — SID Val/Lys ratio 0.65 0.79 l-Isoleucine 0.06 — SID Ile/Lys ratio 0.55 0.69 Phytase2 0.02 0.02 ME, kcal/kg 3,268 3,257 Acids mix3 0.30 0.30 NE, kcal/kg 2,460 2,460 Vit–min premix4 0.30 0.30 SID Lys:NE ratio, g/Mcal 4.27 2.64 Ashes, % 3.74 3.57 Total Ca, % 0.58 0.57 STTD Ca, % 0.45 0.44 Total P, % 0.36 0.35 STTD P, % 0.30 0.30 Cl, % 0.28 0.28 K, % 0.58 0.52 Na, % 0.16 0.16 1 SID = standardized ileal digestible; ME = metabolizable energy; NE = net energy; STTD = standardized total tract digestible. 2 6-Phytase (750 FTU/kg). 3 Blend of formic and lactic acid. 4 Provided per each kg of complete feed: 4,500 IU vitamin A, 2,000 IU vitamin D3, 15 mg vitamin E, 0.7 mg vitamin K, 1.0 mg vitamin B1, 4.0 vitamin B2, 1.2 vitamin B6, 0.02 vitamin B12, 15 mg niacin, 12 mg pantothenic acid, 107 mg coline, 90 mg Fe from iron sulphate, 100 mg Zn from zinc sulphate, 50 mg Mn from manganese oxide, 20 mg Cu from copper sulphate, 1.8 mg I from potassium iodide and 0.25 mg Se from sodium selenite. Translate basic science to industry innovation 4 Aymerich et al. Lys/Mcal NE (Feed A), and the low ratio diet was intake, g SID Lys intake per kg gain, and feed 2.64 g SID Lys/Mcal NE (Feed B). To reduce SID cost per kg gain were measured and calculated Lys:NE, the amount of soybean meal included was for Period 1 (days 0 to 22), Period 2 (days 22–41), decreased and the amount of wheat increased. In and Overall (days 0 to 41). In addition, HCW, addition, the amount of crystalline AA included CY, CL, BFT, and HFT were calculated per pen was also reduced ensuring that the ideal protein using the individual data from pigs that could be ratios were met in both diets. The two extreme feeds traced at the slaughterhouse. The effect of SID were mixed in five different proportions (Table 2) in Lys:NE on the studied productive parameters the farm using a robotic feeding system (DryExact was initially analyzed in a linear model includ- Pro; Big Dutchman, Vechta, Germany). Feed in- ing SID Lys:NE, sex, initial BW block, and all take was measured weekly by determining the the interactions between factors as fixed effects. amount of feed remaining in each trough. Interactions that were not significant (P > 0.050) and/or biologically meaningless for the Overall Diet Sampling and Analysis period were not included in the final model be- cause simplification was prioritized. As not all After pelleting, feed samples were collected for pigs could be completely traced at the slaughter- each successive blending batch (5,000 kg), and crude house, the number of pigs per pen was included protein (CP) was analyzed (ISO 16634-2:2016) to en- as a weighting factor in the carcass trait models. sure that CP was within the range of the calculated In addition, CY, CL, BFT, and HFT were linearly composition. In addition, AA composition (Method adjusted using HCW as a covariate. The differen- 994.12, AOAC International, 2007) was analyzed in a tial effect of SID Lys:NE on growth performance blend of all the different batches (Table 3). between sexes was analyzed implementing orthog- onal polynomial contrasts to compare the linear Calculations and Statistical Analyses and quadratic trends in each sex. Afterwards, the model was conditioned to determine the linear or Pen BW, ADG, average daily feed intake quadratic effect of SID Lys:NE on each sex. The (ADFI), feed efficiency (G:F), g SID Lys daily models were performed using the stats package Table 2. Blend ratios, calculated composition, and price for the five dietary treatments (as-fed basis) Item1 T1 T2 T3 T4 T5 Feed A, % 0 25 50 75 100 Feed B, % 100 75 50 25 0 SID Lys, % 0.65 0.75 0.85 0.95 1.05 NE, kcal/kg 2,460 2,460 2,460 2,460 2,460 SID Lys:NE, g/Mcal 2.64 3.05 3.46 3.86 4.27 Formula cost, €/t2 223.4 231.0 238.5 246.1 253.6 1 SID = standardized ileal digestible; NE = net energy. 2 Calculated as a weighted average of the formula cost and inclusion of Feeds A and B. Table 3. Analyzed and calculated amino acid content of the experimental feeds (A and B) used for blending and obtain the five dietary treatments (%, as-fed basis) Feed A Feed B Item Calculated Analyzed Calculated Analyzed Crude protein 15.7 15.9 13.6 13.7 Lysine 1.14 1.14 0.73 0.77 Methionine 0.44 0.40 0.21 0.21 Methionine + cysteine 0.71 0.65 0.47 0.45 Threonine 0.78 0.76 0.50 0.53 Valine 0.78 0.78 0.60 0.61 Leucine 1.21 1.21 1.11 1.10 Isoleucine 0.63 0.64 0.51 0.52 Histidine 0.38 0.37 0.35 0.34 Arginine 0.87 0.90 0.76 0.80 Translate basic science to industry innovation Finishing boars and gilts lysine requirements 5 (R Core Team, 2019), ANOVA with the car variable. The models reported in the results section package (Fox and Weisberg, 2019), and the effect are the best fitting models achieved by iteratively of SID Lys:NE was contrasted using the emmeans modifying the initial parameter values and select- package (Lenth, 2020). ing the model with a lower Bayesian information Broken-line linear (BLL) regression models criteria (BIC). Finally, the 95% confidence interval were fitted when possible to determine the break (CI) for the BLL parameters (Venables and Ripley, point at which ADG was maximized for each sex 2002) was estimated with the nlstools package (Baty using the stats package (R Core Team, 2019). The et al., 2015) to compare the requirements of boars models used were adapted from Robbins et al. and gilts. For all tests, results were considered sig- (2006) by including ADFI as a covariate to improve nificant when P ≤ 0.05, and a tendency when 0.05 < the predictability of the model: P ≤ 0.10. Yij = L + U∗ (R − Xi ) + π∗Zij + eij RESULTS if Xi ≤ R, and when Xi > R then The analyzed protein and AA content of the Yij = L + π∗Zij + eij experimental feeds (Table 3) were consistent with where Yij is the response in ADG as a result of the the calculated composition of the diets. Overall, difference between the break point (R) and SID there was no evidence of significant interactions Lys:NE (Xi) times a factor (U) before reaching (P > 0.050) between block and treatment or sex. the plateau (L). In both equations, we assumed a Only a tendency for an interaction between block linear effect (π) of ADFI (Zij) on the dependent and SID Lys:NE (P = 0.051) was observed for SID Figure 1. Effect of sex on body weight (A), average daily gain (B), average daily feed intake (C), and gain to feed (D) of finishing boars and gilts. For A, data represent the three weighing days. For B, C and D results are provided for Period 1 (70 to 89 kg), Period 2 (89 to 106 kg) ,and the overall experiment (70 to 106 kg). Solid line and black bars represent boars, whereas dashed line and gray bars represent gilts. Error bars represent the SEM. Translate basic science to industry innovation 6 Aymerich et al. Lys per kg gain; however, as it represented a dif- between sexes is provided and used to determine ferent effect only in medium category pigs, it was whether there was a differential response between not considered biologically meaningful. Therefore, sexes. In addition, the effect of SID Lys:NE on each a model including only the interaction between sex is also provided. Growth performance results of SID Lys:NE and sex was preferred for the sake of Period 1 (70 to 89 kg) are summarized in Table 4. simplification. An overview of the main effects of Strong evidence of a different linear response to sex is presented in Fig. 1 for the main growth per- SID Lys:NE was found for some performance vari- formance variables. Initially boars weighed 1.7 kg ables. Nevertheless, there was no evidence of a dif- more than gilts (70.4 vs. 68.7 kg, P = 0.001), but ferent quadratic response to SID Lys:NE between this difference was even greater at day 22 (90.7 boars and gilts for any of the variables analyzed. vs. 87.7 kg, P < 0.001) and at the end of the trial Regarding ADG, linear trends between sexes when (108.0 vs. 102.9 kg, P < 0.001). The increase in the SID Lys:NE was increased were not significantly difference in BW throughout the experiment was different (P = 0.115). Nevertheless, boars showed the result of a greater ADG of boars during Period a linear increase (P < 0.001), but gilts just a ten- 1 (P = 0.001) and Period 2 (P < 0.001). No evi- dency (P = 0.100). The ADFI of both boars and dence of differences in ADFI between boars and gilts was not linearly or quadratically affected by gilts was observed (P > 0.100), and therefore the SID Lys:NE. Although G:F increased linearly greater growth was considered the result of an in- when SID Lys:NE was increased in both boars creased G:F of boars (P < 0.001). The Overall re- (P < 0.001) and gilts (P = 0.005), boars showed sults reported a greater ADG (0.914 vs. 0.837 kg, a greater linear increase than gilts (P = 0.003). P < 0.001) and G:F (0.421 vs. 0.388, P < 0.001) Furthermore, there was a greater linear increase in of boars, but no evidence of a difference in ADFI SID Lys/kg gain (P = 0.001) and in feed cost per kg (2.17 vs. 2.16 kg, P = 0.470). As expected, the im- gain (P = 0.004) when SID Lys:NE was increased proved performance of boars was also reflected in a for gilts compared with boars. leaner carcass composition. Hot carcasses of boars In the second period (Table 5), from 89 to were heavier (89.7 vs. 86.6 kg, P < 0.001), and CY 106 kg BW, there were no significant interactions was greater for gilts (77.2 vs. 78.7%, P < 0.001). between sex and the linear or quadratic response to Boars had greater CL (64.4 vs. 63.5%, P < 0.001) SID Lys:NE. Only a tendency for a different linear and lower BFT (14.1 vs. 14.7 mm, P = 0.009) and response to increased SID Lys was reported for HFT (8.82 vs. 10.29 mm, P < 0.001). SID Lys per kg gain. Neither boars (P = 0.328) nor gilts (P = 0.764) showed a linear increase in ADG Differential Response to SID Lys:NE when SID Lys:NE was increased. Moreover, boars’ G:F linearly increased (P = 0.003) whereas gilts In this section, the comparison of the linear just showed a tendency (P = 0.098). The difference and quadratic trends depending on SID Lys:NE between the response in ADG and G:F could be Table 4. Interactive effects between standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and sex on growth performance and economics of finishing boars and gilts in Period 1 (70 to 89 kg)1 SID Lys:NE, g/Mcal2 P-value Item 2.64 3.05 3.46 3.86 4.27 SEM L×S 3 Q×S 4 Linear Quadratic ADG, kg Boars 0.830 0.918 0.934 0.934 0.968 0.0235 0.115 0.626 <0.001 0.168 Gilts 0.823 0.882 0.857 0.882 0.885 0.100 0.483 ADFI, kg Boars 2.11 2.21 2.15 2.08 2.10 0.048 0.579 0.832 0.288 0.356 Gilts 2.10 2.14 2.11 2.11 2.09 0.776 0.532 G:F Boars 0.394 0.416 0.436 0.452 0.461 0.0072 0.003 0.612 <0.001 0.303 Gilts 0.392 0.412 0.406 0.417 0.424 0.005 0.751 SID Lys/gain, g/kg Boars 16.5 18.1 19.5 21.1 22.8 0.36 0.001 0.757 <0.001 0.779 Gilts 16.6 18.2 21.0 22.9 24.8 <0.001 0.875 Feed cost/gain, €/kg Boars 0.568 0.557 0.547 0.547 0.550 0.0100 0.004 0.594 0.146 0.323 Gilts 0.570 0.561 0.588 0.592 0.599 0.007 0.811 1 A total of 780 pigs (Pietrain NN × (Landrace × Large white) in pens of 13, with six replicates per treatment and sex. 2 Calculated SID Lys:NE. 3 Interaction between sex and the linear response to SID Lys:NE. 4 Interaction between sex and the quadratic response to SID Lys:NE. Translate basic science to industry innovation Finishing boars and gilts lysine requirements 7 partly related to a tendency for ADFI to decrease Table 6 provides the experimental results on in both boars (P = 0.052) and gilts (P = 0.089). As BW and growth performance for the Overall period. in the previous period, increasing levels of SID The top half of the table shows that there was no Lys:NE increased SID Lys per kg gain linearly in evidence that increasing SID Lys:NE resulted in a both boars and gilts (P < 0.001). However, gilts greater linear increase in BW of boars at day 22 tended to show a greater linear increase than boars (P = 0.712) or day 41 (P = 0.591). However, when (P = 0.100). SID Lys:NE was increased boars showed a linear Table 5. Interactive effects between standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and sex on growth performance and economics of finishing boars and gilts in the Period 2 (89 to 106 kg)1 SID Lys:NE, g/Mcal2 P-value Item 2.64 3.05 3.46 3.86 4.27 SEM L×S 3 Q×S 4 Linear Quadratic ADG, kg Boars 0.875 0.918 0.933 0.906 0.920 0.0254 0.630 0.505 0.328 0.296 Gilts 0.783 0.836 0.781 0.802 0.812 0.764 0.915 ADFI, kg Boars 2.27 2.25 2.29 2.16 2.17 0.044 0.853 0.971 0.052 0.525 Gilts 2.21 2.34 2.18 2.17 2.17 0.089 0.559 G:F Boars 0.386 0.408 0.408 0.420 0.425 0.0092 0.314 0.494 0.003 0.535 Gilts 0.356 0.357 0.360 0.372 0.374 0.098 0.727 SID Lys/gain, g/kg Boars 16.9 18.5 20.9 22.6 24.8 0.55 0.100 0.537 0.000 0.773 Gilts 18.4 21.1 23.7 25.8 28.2 0.000 0.559 Feed cost/gain, €/kg Boars 0.580 0.568 0.585 0.586 0.600 0.0154 0.409 0.476 0.236 0.556 Gilts 0.631 0.649 0.665 0.667 0.680 0.021 0.674 1 A total of 780 pigs (Pietrain NN × (Landrace × Large white) in pens of 13, with six replicates per treatment and sex. 2 Calculated SID Lys:NE. 3 Interaction between sex and the linear response to SID Lys:NE. 4 Interaction between sex and the quadratic response to SID Lys:NE. Table 6. Interactive effects between standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and sex on body weight, growth performance, and economics of finishing boars and gilts in the overall experi- ment (70 to 106 kg)1 SID Lys:NE, g/Mcal2 P-value 2.64 3.05 3.46 3.86 4.27 SEM L × S3 Q × S4 Linear Quadratic Body weight, kg Day 0 Boars 70.4 70.7 70.4 70.4 70.4 0.79 0.563 0.844 0.879 0.912 Gilts 68.4 68.6 68.5 68.8 69.1 0.506 0.867 Day 22 Boars 88.7 90.9 91.0 90.9 91.8 1.00 0.712 0.693 0.055 0.461 Gilts 86.5 87.9 87.4 88.2 88.6 0.156 0.857 Day 41 Boars 105.3 108.6 108.5 108.2 109.2 1.11 0.591 0.492 0.037 0.259 Gilts 101.3 103.8 102.2 103.2 104.0 0.173 0.871 Growth performance ADG, kg Boars 0.851 0.918 0.933 0.921 0.946 0.0149 0.087 0.348 <0.001 0.049 Gilts 0.804 0.861 0.822 0.845 0.851 0.103 0.497 ADFI, kg Boars 2.18 2.23 2.21 2.11 2.14 0.038 0.651 0.878 0.084 0.353 Gilts 2.15 2.23 2.14 2.14 2.13 0.268 0.476 G:F Boars 0.390 0.412 0.423 0.437 0.444 0.0051 0.003 0.326 <0.001 0.196 Gilts 0.375 0.386 0.384 0.396 0.400 <0.001 0.925 SID Lys/gain, g/kg Boars 16.7 18.2 20.1 21.8 23.7 0.27 <0.001 0.465 <0.001 0.663 Gilts 17.3 19.5 22.2 24.0 26.3 <0.001 0.549 Feed cost/gain, €/kg Boars 0.573 0.561 0.565 0.564 0.572 0.0074 0.005 0.314 0.965 0.210 Gilts 0.596 0.600 0.622 0.622 0.634 <0.001 0.867 1 A total of 780 pigs [Pietrain NN × (Landrace × Large white)] in pens of 13, with six replicates per treatment and sex. 2 Calculated SID Lys:NE. 3 Interaction between sex and the linear response to SID Lys:NE. 4 Interaction between sex and the quadratic response to SID Lys:NE. Translate basic science to industry innovation 8 Aymerich et al. increase in BW at day 41 (P = 0.037), but the increase Lys:NE was increased. The interaction between was not significant for gilts (P = 0.173). Regarding sex and the linear effect of SID Lys:NE was signifi- overall growth performance, there was evidence of cant for both CL (P = 0.016) and BFT (P = 0.026) a different response to SID Lys:NE between boars but not for HFT (P = 0.230). Regarding boars, and gilts for most variables studied. Average daily increasing SID Lys:NE led to a linear increase gain tended to show a greater linear increase for in CL (P < 0.001), and a linear decrease in BFT boars than gilts (P = 0.087). Consistently, boars’ (P < 0.001) and HFT (P = 0.002). However, there ADG increased linearly (P < 0.001), whereas there was only a quadratic (P = 0.044) effect of SID was no significant effect for gilts (P = 0.103). As in Lys:NE on BFT, but no evidence of an effect on Period 1, boars showed a greater linear increase in CL or BFT for gilts (P ≥ 0.129). G:F (P = 0.003), whereas gilts showed an increase in SID Lys per kg gain (P < 0.001) and feed cost Estimation of SID Lys:NE Requirements of Boars per kg gain (P = 0.005) when SID Lys:NE was and Gilts increased. The interactive effects between sex and SID Dose–response BLL models were fitted to Lys:NE on carcass characteristics are reported predict ADG for each sex and period. For the ini- in Table 7. There was no significant interaction tial period, models could be fitted for each sex, between sex and the linear (P = 0.151) or quad- and different responses were found. For boars, ratic (P = 0.135) effect of SID Lys:NE on HCW. two models reported similar fits (BIC = 316.1 and Nevertheless, boars’ HCW increased linearly 316.5). The best fitting model for boars was as (P = 0.027), whereas there was no evidence of an follows: increase for gilts (P = 0.821). Similarly, the CY of gilts was linearly (P = 0.042) reduced when SID ADG (g) =367 + 286 × ADFI (kg) Lys:NE was increased, whereas the CY of boars − 92.6 × (4.05 − SID Lys : NE) was not (P = 0.904); however, there was no signifi- cant interaction in the linear response (P = 0.180). if SID Lys:NE ≤ 4.05, and when SID Lys:NE > In accordance with the results on growth perform- 4.05 then ance, boars had a greater linear increase in lean tissue and a reduction in fat content when SID ADG (g) = 367 + 286 × ADFI (kg) Table 7. Interactive effects between standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and sex on carcass weight and composition of finishing boars and gilts (70 to 106 kg)1 SID Lys:NE, g/Mcal2 P-value 2.64 3.05 3.46 3.86 4.27 SEM L×S 3 Q×S 4 Linear Quadratic HCW, kg Boars 87.2 90.06 90.66 89.6 90.96 0.95 0.151 0.135 0.027 0.197 Gilts 86.7 87.16 85.7 86.5 87.36 0.821 0.405 CY, %5 Boars 77.27 77.0 77.46 77.27 77.16 0.28 0.180 0.836 0.904 0.649 Gilts 79.2 78.5 79.06 78.6 78.37 0.042 0.869 CL, %5 Boars 63.7 63.57 64.86 64.8 65.56 0.31 0.016 0.320 <0.001 0.688 Gilts 63.1 63.5 63.57 63.8 63.6 0.181 0.305 BFT, mm5 Boars 14.77 14.7 13.86 13.87 13.36 0.30 0.026 0.142 <0.001 0.933 Gilts 15.17 14.6 14.46 14.3 14.97 0.396 0.044 HFT, mm5 Boars 9.25 9.306 8.606 8.69 8.287 0.23 0.174 0.484 0.002 0.903 Gilts 10.61 10.37 10.176 10.12 10.18 0.129 0.377 1 A total of 780 finishing pigs [Pietrain NN × (Landrace × Large white)] in pens of 13 were used in a 41 days growth trial, with two periods, including six pens per treatment and sex. All pigs reaching marketing were transported to a commercial slaughter and packing plant (Patel, Spain) to collect individual data on carcass composition, but only 650 pigs could be completely traced. Observations per pen were weighted using the number of pigs per pen for which carcass data was available. 2 Calculated SID Lys:NE. 3 Interaction between sex and the linear response to SID Lys:NE. 4 Interaction between sex and the quadratic response to SID Lys:NE. 5 Adjusted for HCW. 6 SEM was 0.97 for HCW, 0.29 for CY, 0.33 for CL, 0.31 for BFT, and 0.24 for HFT in the indicated means. 7 SEM was 0.27 for CY, 0.32 for CL, 0.029 for BFT, and 0.25 for HFT in the indicated means. Translate basic science to industry innovation Finishing boars and gilts lysine requirements 9 in which ADG was transformed to gram to facili- if SID Lys:NE ≤ 3.63, and when SID Lys:NE > tate the fitting process, and maximum growth was 3.63, then reached at 4.05 g SID Lys/Mcal NE [95% CI: (3.56, ADG (g) = 405 + 249 × ADFI (kg) 4.54)]. Whereas the other model gave an optimum for maximum growth of 3.71 g SID Lys/Mcal NE in which maximum growth was reached at 3.63 g SID [95% CI: (3.30, 4.12)]. Lys/Mcal NE [95% CI: (3.32, 3.94)]. Contrastingly, The best fitting model for gilts (BIC = 307.4) in the maximum growth in the model with just slightly the first period was modified because the intercept the worst fit was reached at 4.01 g SID Lys/Mcal of the model was insignificant as it was close to 0; NE [95% CI: (3.60, 4.42)]. therefore, the model was fitted without an intercept For gilts, the model that best described growth as follows: (BIC = 296.2) depending on the SID Lys:NE and feed intake was as follows: ADG (g) =415 × ADFI (kg) 98.9 × (3.13 − SID Lys : NE) ADG (g) =270 + 267 × ADFI (kg) − 82.3 × (3.10 − SID Lys : NE) if SID Lys:NE ≤ 3.13, and when SID Lys:NE > 3.13, then if SID Lys:NE ≤ 3.10, and when SID Lys:NE > 3.10, then ADG (g) = 415 × ADFI (kg) ADG (g) = 270 + 267 × ADFI (kg) with maximum growth reached at 3.13 g SID Lys/ in which maximum growth was achieved at 3.10 g Mcal NE [95% CI: (2.74, 3.51)]. SID Lys/Mcal NE [95% CI: (2.74, 3.47)]. The two It was not possible to adjust a model in the best fitting models in the overall period are shown second period for gilts. Fit was possible for boars, in Fig. 2. but the slope (U) was not significant, and therefore, the models were not considered. DISCUSSION Finally, models for the overall period could be fitted for both boars and gilts. Like in the first phase, In the context of an increasing production of for boars there were two models with similar fitting entire males, this study focused on determining (BIC = 289.2 and 290.3). The best fitting model was whether boars and gilts respond differently to SID the following: Lys:NE, and modeling their response to optimize growth performance. Consistent with the literature, ADG (g) =405 + 249 × ADFI (kg) − 92.4 this study observed that boars have a greater ADG × (3.63 − SID Lys : NE) and G:F than gilts and a similar ADFI. The greater Figure 2. Fitted broken-line linear models to predict ADG as a function of increasing the standardized ileal digestible lysine to net energy ratio (SID Lys:NE) and ADFI. Maximum ADG was estimated for boars (A) at 3.63 g SID Lys/Mcal NE [95% CI: (3.32, 3.94) g SID Lys/Mcal NE] and for gilts (B) at 3.10 g SID Lys/Mcal NE [95% CI: (2.74, 3.47) g SID Lys/Mcal NE]. Translate basic science to industry innovation 10 Aymerich et al. ADG of boars has been related to a higher potential The current study reports evidence that boars for lean tissue deposition (Hendriks and Moughan, and gilts respond differently to increasing SID 1993; Rikard-Bell et al., 2013b), starting around 50 Lys:NE, although due to the great variability only to 70 kg BW (Whittemore et al., 1988; Giles et al., a tendency was found for ADG. The response of 2009; Carabús et al., 2017). Studies analyzing growth boars up to a higher SID Lys:NE is explained be- data have observed that gilts’ ADG compared with cause more lysine is needed to reach their greater boars’ ADG starts to decline around 40 to 70 kg BW protein deposition potential. Thus, as the experi- (Campbell et al., 1988; Quiniou et al., 2010; Cámara ment was in accordance with previous literature et al., 2014). In addition, boars greater G:F might be that shows no significant differences in ADFI explained by their greater growth potential and con- between boars and gilts (O’Connell et al., 2006; sidering that there was no evidence of differences in Cámara et al., 2014), boars responded to diets that ADFI (O’Connell et al., 2006; Cámara et al., 2014). are more concentrated in dietary lysine to maxi- Moreover, in agreement with the literature, boars mize performance. The response for ADG was dif- were generally leaner than gilts (Cámara et al., 2014; ferent to Moore et al. (2013), who found linear and Carabús et al., 2017) and had a reduced carcass yield, quadratic effects of dietary lysine in both finishing which might be partly attributed to the removal of boars and gilts in a SID Lys:NE range from 2.3 to the testicles (Gispert et al., 2010). The differences 4.6 g/Mcal. However, Rikard-Bell et al. (2013a) re- in BFT were in agreement with Rikard-Bell et al. ported that boars have a response in ADG up to a (2013b). However, the small difference compared higher SID Lys:NE than gilts in a range from 2.4 with HFT might explain why other authors did not to 4.2 g SID Lys/Mcal NE. It is possible that the obtain this result (Gispert et al., 2010; Trefan et al., SID Lys:NE range in our study was not sufficient 2013). Finally, as genetic improvements during the to significantly limit growth in gilts. Using a lower last decades could be responsible for part of the dif- bottom SID Lys:NE boundary might have pro- ferences between studies, reference values should be vided a better understanding of the form of the dif- carefully considered. ferent responses between sexes. A reduction in ADG and G:F at the highest ly- Differential Response to SID Lys:NE sine levels has been reported in other studies (Van Lunen and Cole, 1996; O’Connell et al., 2006; These results confirmed the different pro- Moore et al., 2013). This outcome differs from the ductive performance response of boars and gilts findings presented here, in which ADG did not de- to SID Lys:NE. As mentioned in the introduction, crease at lysine levels above the requirement. A hy- some works have already studied this response in pothesis is that the reduction in growth at high recent decades (Campbell et al., 1988; Van Lunen lysine levels is explained by an increase in heat and Cole, 1996; King et al., 2000; O’Connell et al., production when CP levels are above the require- 2006; Moore et al., 2013; Rikard-Bell et al., 2013a). ment for growth. Le Bellego et al. (2001) showed However, so far there is no single experiment in that reducing CP while using synthetic AA to fulfill the literature that compares the linear or quad- ideal protein requirements increased the efficiency ratic trends between sexes in one statistical model. of ME and NE use. Otherwise, excess AA has to Most authors just report the effect of dietary lysine be deaminated, which has an energy cost (Bender, on each sex. As recently shown by Aymerich et al. 2012). Hence, it could conceivably be hypothesized (2020), comparing the linear or quadratic response that the high CP diets used in the high lysine treat- in a single model gives an indication of how certain ments of some of the works reviewed, most of them we can be that the effect of SID Lys:NE differs be- above 17% (Campbell et al., 1988; Van Lunen and tween categories of a factor. However, being linear Cole, 1996; King et al., 2000; O’Connell et al., 2006; or quadratic should be considered carefully as this Moore et al., 2013), might explain why there was a could be strongly influenced by the range of SID reduction in feed efficiency and ADG. Lys:NE in which the experiment evaluated the ef- The carcass composition results corroborated fects on pig performance. Throughout the discus- the findings of Moore et al. (2013), reporting a sion, as most experiments used a ratio between SID linear effect of SID Lys:NE only on the backfat Lys and metabolizable energy (ME) or digestible thickness of boars, while there was no linear effect energy (DE), a ratio of 0.71 between NE and DE on gilts. Similarly, Lambe et al. (2013) showed that and 0.74 between ME and NE is assumed to make fatness of entire male Pietrain sire-line pig carcasses comparisons with the results from other studies increased only when the lysine content of the diet possible (Noblet and van Milgen, 2004). was reduced, and not for a lower CP. In addition, Translate basic science to industry innovation Finishing boars and gilts lysine requirements 11 Rikard-Bell et al. (2013b) showed that when SID a similar BIC, is considered, then the CI would not Lys:NE was increased from 3.3 to 3.8 g/Mcal, there be overlapped because it reported a higher break was only a significant increase in boars’ lean tissue point. Therefore, in agreement with the different deposition. The different linear effect between sexes linear effects of SID Lys:NE on growth perform- reported in this experiment supports the different ance, boars required greater dietary SID Lys:NE, linear responses observed in growth performance mainly for the period 70 to 89 kg, to maximize results. It confirmed that the greater response of growth performance. boars to increasing SID Lys:NE entailed an in- The greater requirements for boars compared crease in carcass leanness. Therefore, at the lower with gilts corroborate the findings of some pre- ratios, SID Lys intake was limiting boars’ protein vious studies (O’Connell et al., 2006; Rikard-Bell deposition, and consequently, energy was used for et al., 2013a), contradict other studies (Van Lunen fat deposition, increasing BFT. However, the results and Cole, 1996; King et al., 2000), and some studies also suggest that gilts cannot increase lean depos- did not show relevant differences (O’Connell et al., ition when offered more SID Lys. Nevertheless, the 2006; Moore et al., 2013). However, most of these inconsistency with some of the available literature studies did not report a CI for the requirement es- might be a result of different statistical analyses, timates, and thus, doubts arise about comparisons experimental diet formulation strategies, or genetic of requirements of the two sexes. For instance, the lines. requirement for boars to optimize ADG from 70 to 106 kg (3.63 to 4.01 g SID Lys/Mcal NE) was Modeling SID Lys:NE Requirements slightly lower to that reported by Rikard-Bell et al. (2013a; >4.24 g SID Lys/Mcal NE), whereas it was Several studies have aimed to model the re- slightly higher than that reported by Moore et al. sults from a dose–response trial to determine an (2016; 3.4 g SID Lys/Mcal NE) using BLL models. optimum for different parameters such as ADG or The requirement for gilts, although low compared G:F. It is widely acknowledged that the model used with some studies (O’Connell et al., 2006; Shelton (broken-line linear, quadratic polynomial, bro- et al., 2011; Moore et al., 2013), was similar to ken-line quadratic) is a major factor in determining Rikard-Bell et al. (2013a; 3.2 g SID Lys/Mcal NE) the optimum level (Pesti et al., 2009). In the pre- and greater than Main et al. (2008; 2.6 g SID Lys/ sent study, BLL was preferred because quadratic Mcal NE). trends were not reported for almost any variable. These results suggest that the requirements for The objective of the fitted models was to describe boars were 117% higher than gilts or even more, the differential response to SID Lys:NE on ADG whereas the review in Dunshea et al. (2013) sug- of boars and gilts reported in the results section. gested that they were only 108%. However, Williams Although models could be fitted, having a lower et al. (1984) suggested that the requirements for bottom SID Lys:NE level would have made the boars might be 125% the requirements of barrows, fitting process easier. For instance, Robbins et al. considering that barrows and gilts have similar re- (2006) suggested that a minimum of four points quirements (Main et al., 2008). The differences in below the requirement are needed to fit the shape requirements might be partly due to the poten- of a quadratic response. tial ADG, which in this study was 11% greater for Including ADFI as a covariate in the model, boars (940 vs. 844 kg), assuming a 2.15 kg ADFI. which explained 0.40 to 0.60 of the ADG variability, However, data from studies in which the SID enabled fitting a BLL model to predict the ADG Lys:NE of the diets fed to pigs could have been of gilts depending on SID Lys:NE, although there limiting boars’ growth should be used carefully to was only one level that theoretically limited growth. model requirements. Furthermore, as suggested As a result, both dose–response broken-line linear by Lerman and Bie (1975), dose–response growth models for gilts and boars could be fitted for Period models need to be linked to lysine cost models to 1 and Overall, and the requirements between sexes determine exactly which is the best level from an were compared using the CI of the break point, economic standpoint. The present models are a first the SID Lys:NE at which ADG was maximized. step for determining which are the economically op- Seventy to 89 kg BW boars showed a response in timal diets for each sex. Nevertheless, the results al- ADG up to a higher SID Lys:NE compared with ready suggest that feeding gilts with an optimal diet gilts. Nevertheless, in the Overall period, the CIs for boars may increase the production cost of gilts. were overlapped, considering the best fitting model; In conclusion, the different responses in however, if the boars’ second best fitting model, with growth performance and carcass composition of Translate basic science to industry innovation 12 Aymerich et al. boars and gilts to increasing SID Lys:NE along Coffey, R. D., G. R. Parker, and K. M. Laurent. 1995. Feeding with the modeling outcomes indicate that finishing growing-finishing pigs to maximize lean growth rate. University of Kentucky. ASC-147. http://i.animalgenome. boars (70 to 110 kg) have a greater SID Lys:NE org/edu/PIH/prod_grow_finish.pdf requirement than gilts to maximize growth per- Dunshea, F. R., J. R. Allison, M. Bertram, D. D. Boler, formance and carcass leanness. This is explained L. Brossard, R. Campbell, J. P. Crane, D. P. Hennessy, by the greater protein deposition and therefore L. Huber, C. de Lange, et al. 2013. The effect of im- growth potential of boars starting from 50 to munization against GnRF on nutrient requirements of male pigs: A review. Animal 7:1769–1778. doi:10.1017/ 70 kg to market weight, when there are no evident S1751731113001407 differences in ADFI. Therefore, the present work Elsbernd, A. J., C. F. de Lange, K. J. Stalder, L. A. Karriker, suggests that feeding boars and gilts diets with and J. F. Patience. 2017. SID lysine requirement of im- different SID Lys:NE during the finishing period munologically and physically castrated male pigs during might be beneficial from both the performance and the grower, early and late finisher periods. J. Anim. Sci. cost-return perspectives. 95:1253–1263. doi:10.2527/jas.2016.0544 Ettle, T., D. A. Roth-Maier, and F. X. Roth. 2003. Effect of Conflict of interest statement. 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