This study aimed to update the first-liming amino acid (lysine) requirements of fattening pigs maintained and raised in Japan using 146 fattening pigs with an average weight of 62 kg. Five diets were prepared with total lysine concentrations of 0.45%, 0.65%, 0.85%, 0.95%, and 1.05%. Six replicates were used for each lysine concentration. The feeding trial lasted for 4 weeks until the average weight of the pigs reached 92 kg. The total lysine concentration of the diets affected feed efficiency throughout the 4 weeks and was lowest in pigs fed diets with a total lysine concentration of 0.45% and highest in pigs fed 0.85%. The total lysine requirement was estimated using feed efficiency as the response index. The linear and quadratic models estimated 0.68% and 0.75% of the requirement for the first 2 weeks and 0.66% and 0.72% for the 4-week period, respectively. These estimates were equivalent to the total lysine requirement of 0.72% for the 50–70 kg body weight (expected gain of 850 g/d) in the Japanese Feeding Standard for Swine 2013 and higher than the 0.59% for the 70–115 kg body weight (expected gain of 1000 g/d).

1 INTRODUCTION

Currently, the pig feeding standards available are the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013) and the NRC Swine Feeding Standard (National Research Council, 2012). When comparing the amino acid requirements listed in the standards, the Japanese standard is ∼20% lower for the first-limiting amino acid (lysine) in pigs. The reason for this may be that the NRC feeding standard incorporates requirements estimated from hybrid pigs such as high-performance pigs (PICs) (Kendall et al. 2012; Yi et al., 2006) and requirements estimated from fattening pigs treated with growth hormones (Yen et al., 2005) into the modeling process. Meanwhile, the introduction of hybrid pigs is also progressing in Japan, and according to the Japan Pork Producers Association (2023), ∼27% of producers have already introduced high-performance pigs from overseas breeding companies. In addition, according to the Ministry of Agriculture, Forestry and Fisheries (2019), the daily gain of pure breeds raised in Japan at 30–105 kg has increased from 850 g/d in 2008 to 970 g/d in 2018. Based on the above, it is reasonable to assume that the amino acid requirements of pigs maintained and raised in Japan are higher than those listed in the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013).

Global warming countermeasures of the Ministry of Agriculture, Forestry and Fisheries call for livestock feed, including that for pigs, with an improved amino acid balance to avoid excessive nitrogen excretion in manure (Ministry of Agriculture, Forestry and Fisheries, 2022). Diets with lower protein content—an amino acid balanced diet—can reduce dinitrogen monoxide, one source of greenhouse gases excreted by pigs (Deng et al., 2007). To improve the amino acid balance of diets fed to pigs, it is necessary to accurately determine their amino acid requirements not only to maximize the genetic potential of pigs but also to deal with global warming.

This study aimed to update the first-limiting amino acid (lysine) requirements of fattening pigs maintained and raised in Japan.

2 MATERIALS AND METHODS

2.1 Ethical considerations

This feeding trial was conducted on three separate occasions from June 2017 to July 2018. Although retrospective, the experimental protocol was reviewed and approved by the Animal Experimentation Committee of the R&D Center of the Nosan Corporation (Date of approval: January 11, 2024; Approval numbers: 2023D-23, 2023D-24, and 2023D-25).

2.2 Animals and facilities

Fattening pigs of the (Large White × Landrace) ×Duroc crossbreed, with an average body weight of 62 kg were produced at the R&D Center of the Nosan Corporation and used in this study. The study was conducted in the R&D Center of the Nosan Corporation started with 150 pigs, but four pigs were removed owing to accidents, such as injuries; therefore, the data shown are from a total of 146 pigs (81 barrows and 65 gilts).

The feeding test was conducted via group feeding with three barrows and two gilts (22 pig pens: four pens each for 0.45%, 0.95%, and 1.05%, five pens each for 0.65% and 0.85%), two barrows and three gilts (four pig pens: one pen each for 0.45%, 0.65%, 0.85%, and 0.95%), two barrows and two gilts (three pig pens: one pen each for 0.45%, 0.95%, and 1.05%), and one barrow and three gilts (one pig pen for 1.05%) housed in 4.00 × 2.04 m pig pens.

2.3 Experimental feeds

The lysine requirements were estimated using five experimental diets with total lysine concentrations of 0.45%, 0.65%, 0.85%, 0.95%, and 1.05% (0.36%, 0.54%, 0.73%, 0.82%, and 0.91% as standardized digestible [SID] lysine). These diets consisted corn, milo, wheat, soybean meal, and rapeseed meal, with L-lysine sulfate and L-threonine (Shintoa Corporation, Tokyo, Japan), and DL-methionine (Sumitomo Chemical, Tokyo, Japan) added to adjust the amino acid concentrations. The chemical composition of the experimental feeds is shown in Table 1, and the ratio of each amino acid to lysine is shown in Table 2. To confirm that the limiting amino acid in each experimental feed was lysine, the requirement of each amino acid on total basis listed in the NRC Swine Feeding Standard (National Research Council, 2012) and the ratio of each amino acid requirement to the lysine requirement are shown in Table 3. Further, comparisons of the “ratio of each amino acid to lysine” and “ratio of each amino acid requirement to lysine requirement” of each experimental feed are shown in Table 4. The values for each amino acid shown in Table 4 were >100, confirming that lysine was the limiting amino acid in each diet.

TABLE 1. Calculated chemical composition of the test diets (%).

	0.45%	0.65%	0.85%	0.95%	1.05%
CP^a	11.2	14.0	16.8	18.3	19.4
TDN^b	77.5	77.5	77.5	77.5	77.5
Ca	0.61	0.60	0.60	0.60	0.60
P	0.42	0.44	0.48	0.49	0.51
Lys^c	0.45	0.65	0.85	0.95	1.05
Met + Cys	0.43	0.50	0.57	0.64	0.71
Arg	0.58	0.80	1.03	1.14	1.23
His	0.29	0.36	0.44	0.47	0.50
Ile	0.41	0.54	0.68	0.75	0.80
Thr	0.41	0.52	0.63	0.69	0.75
Val	0.54	0.67	0.81	0.88	0.93
Trp	0.13	0.17	0.21	0.23	0.25
Leu	0.99	1.18	1.37	1.47	1.54
Phe + Tyr	0.80	1.04	1.29	1.41	1.50

^a Crude protein.
^b Total digestive nutrients.
^c Total basis.

TABLE 2. Concentration ratios of each amino acid of test diets to that of lysine (lysine = 100, ①).

	0.45%	0.65%	0.85%	0.95%	1.05%
Lys	100	100	100	100	100
Met + Cys	94	76	67	67	67
Arg	128	123	122	120	117
His	64	55	51	50	48
Ile	90	83	80	79	76
Thr	90	80	75	73	72
Val	119	104	95	92	88
Trp	28	26	25	24	23
Leu	220	182	161	155	147
Phe + Tyr	177	160	152	149	143

TABLE 3. Requirement of each amino acid listed in the NRC (%, total basis) and ratio of requirement of each amino acid to lysine requirement (%).

	NRC	Ratio of each amino acid to lysine (②)
Lys	0.97	100
Met + Cys	0.57	59
Arg	0.44	45
His	0.34	35
Ile	0.52	54
Thr	0.64	66
Val	0.65	67
Trp	0.17	18
Leu	0.98	101
Phe + Tyr	0.94	97

TABLE 4. Comparison of “Ratio of each amino acid to lysine” and “Ratio of each amino acid's requirement to lysine requirement” of test feeds ([① ÷ ②] × 100).

	0.45%	0.65%	0.85%	0.95%	1.05%
Lys	100	100	100	100	100
Met + Cys	160	130	115	114	114
Arg	283	272	268	265	258
His	182	158	147	142	136
Ile	167	155	149	147	142
Thr	137	121	113	110	108
Val	178	155	142	138	132
Trp	161	147	141	138	134
Leu	215	179	160	153	145
Phe + Tyr	183	165	157	153	148

2.4 Feeding trial outline

The feeding trial lasted for 4 weeks until the average weight of the pigs reached 92 kg. The pigs were fed ad libitum, and drinking water was always available. The temperature and humidity were not controlled. The ventilation volume was controlled by an inverter system. In addition, body weight gain, feed intake, and feed efficiency were recorded for the first and second 2 weeks. Because these values were recorded for each pig pen, the number of replicates for each lysine concentration was six.

2.5 Statistical analysis

The effect of total dietary lysine concentration on growth performance—body weight gain, feed intake, and feed efficiency—was tested by one-way analysis of variance (ANOVA) with total dietary lysine concentration as a factor, using the GLM procedure in SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Differences between means were tested using the Tukey Statement of the GLM procedure in SAS. The dose–response relationship of the total lysine concentration of the experimental feeds was tested for feed efficiency. Because the intervals of total lysine concentration in the diets in this study were not equally spaced, the optimal coefficients were calculated using the OPROL function of the IML procedure in SAS. The CONTRAST statement of the GLM procedure was used to test whether feed efficiency responded linearly and/or quadratically to total lysine concentrations in the experimental feeds.

Here, lysine requirements were estimated by fitting a broken-line model using feed efficiency as a response index. The NLIN procedure in SAS version 9.2 (SAS Institute Inc., Cary, NC, USA) was used to fit both the linear and quadratic models (Robbins et al., 2006). To estimate the lysine requirement per kilogram of body weight gain, body weight gain was used as a response index to the total lysine intake per day and fitted to a broken-line model.

3 RESULTS

Figure 1a shows the body weight gain during the first and second halves, and the entire 4 weeks of the feeding trial period. Regardless of the period, the average body weight gain was the lowest in pigs fed diets with a total lysine concentration of 0.45%. However, owing to high variability, the effect of total lysine concentration in the experimental feeds on daily body weight gain was not statistically significant (p-values for the first half, second half, and full 4-week periods were 0.2926, 0.2996, and 0.1733, respectively).

Details are in the caption following the image — **FIGURE 1**
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The effects of total lysine concentrations on growth performances of pigs. (a) Daily body weight gain, (b) daily feed intake, (c) feed efficiency a, b and x, y; p < 0.05.

Figure 1b shows the feed intake results. The total lysine concentration in the experimental feeds had no clear effect on feed intake (p-values = 0.8489, 0.8454, and 0.8307 for the first half, second half, and throughout the 4-week period, respectively).

Figure 1c shows the results of feed efficiency for the first two half, the second half, and throughout the 4-week period. The total lysine concentration of the diets affected feed efficiency during the first 2 weeks (p-values of 0.0944 and 0.0744 for the first and second weeks, respectively), with pigs fed diets containing 0.45% and 0.85% total lysine having the lowest and highest efficiencies, respectively. Dietary total lysine concentration affected feed efficiency throughout the 4 weeks (p = 0.0078) with pigs fed the 0.45% and 0.85% diets having the lowest and highest efficiencies, respectively. The feed efficiency of pigs fed the 0.45% diet was lower (p < 0.05) than that of pigs fed the 0.85% or 0.95% diets.

We tested whether feed efficiency was dependent on the total lysine concentration in the experimental feeds. Although we could not detect a linear effect, we detected a quadratic effect with—p = 0.0409, 0.0321, and 0.0035—for the first half, second half, and full 4 weeks, respectively.

Since there was no effect of the total lysine concentration in the experimental feeds on body weight gain and feed intake, the lysine requirement was estimated using feed efficiency as a response indicator. The feeding trial period was divided into the first 2 weeks, the second 2 weeks, and the full 4 weeks, and an attempt was made to estimate the lysine requirements for each. Because the parameters used for the calculation for the second period did not meet the conditions of the model, no estimates could be obtained for this period. The estimated lysine requirements for the first 2 weeks and the full 4 weeks are shown in Table 5. The estimates of total and SID lysine levels are also shown.

TABLE 5. Lysine requirements (%) of fattening pigs estimated by the broken-line model.

	Estimate	Approximate SE	Approximate 95% confidence limits
Total lysine
First half
Linear model	0.68	0.08	0.35	1.01
Quadratic model	0.75	0.21	−0.13	1.64
Entire period
Linear model	0.66	0.07	0.34	0.98
Quadratic model	0.72	0.23	−0.28	1.71
SID lysine
First half
Linear model	0.56	0.07	0.26	0.87
Quadratic model	0.63	0.18	−0.16	1.43
Entire period
Linear model	0.55	0.07	0.26	0.84
Quadratic model	0.60	0.21	−0.30	1.50

The estimates on a total lysine basis are as follows: the linear model estimated a requirement of 0.68% for the first 2 weeks and 0.66% for the full 4 weeks; the quadratic model estimated a requirement of 0.75% for the first 2 weeks and 0.72% for the full 4 weeks. The approximate 95% confidence limits are listed in Table 5.

The estimates on a SID lysine basis: the linear model estimated a 0.56% requirement for the first 2 weeks and 0.55% requirement for the full 4 weeks; the quadratic model estimated a 0.63% requirement for the first 2 weeks and 0.60% for the full 4 weeks. The approximate 95% confidence limits are listed in Table 5.

To estimate the total lysine requirement per kilogram of body weight gain, we attempted to fit a broken-line model employing daily body weight gain as a response index to total lysine intake per day; however, no estimate could be obtained because the parameters used did not meet the conditions of the model.

4 DISCUSSION

Here, the lysine requirement as a concentration in the feed was estimated using feed efficiency as a response indicator with both linear and quadratic models. When testing whether feed efficiency responded dose dependently to lysine concentrations in the experimental feeds, a linear effect was not detected, but a quadratic effect was. This may be because pigs fed diets with a total lysine concentration of 0.85% had the highest feed efficiency, whereas pigs fed 0.95% and 1.05% diets had lower efficiencies. Because we detected a quadratic effect, it was reasonable to adopt the lysine requirements estimated by the quadratic model. Based on the above results, when feed efficiency was used as the response index, the total and SID lysine requirements of fattening pigs weighing 60–90 kg were 0.72% and 0.60% for SID lysine, respectively. These estimates are equivalent to the total lysine requirement of 0.72% for 50–70 kg body weight (expected daily body weight gain of 850 g/d) in the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013) and higher than 0.59% for 70–115 kg body weight (expected gain of 1,000 g/d). This was lower than the total lysine requirements of 0.97% for 50–75 kg body weight and 0.84% for 75–115 kg body weight listed in the NRC Swine Feeding Standard (National Research Council, 2012).

The highest lysine requirement among the studies cited by the NRC Swine Feeding Standard (National Research Council, 2012) is of 24.6 g SID lysine/kg body weight gain reported by O'Connell et al. (2006). In their study, the total lysine requirement of pigs reared in groups from 80 to 100 kg body weight, similar to the conditions of this study, was 0.93% as indexed by body weight gain and 0.96% as indexed by the feed conversion ratio. These values are 0.25% higher than those obtained in this study. O'Connell et al. (2006) tested male and female pigs. The sex of the tested pigs may partially explain their higher requirements because barrows were also tested in this study. In an experiment by Main et al. (2008), who tested PIC pigs, the total lysine requirement of barrows weighing 60–85 kg was 0.96%. Similarly, in a study by Suárez-Belloch et al. (2015), who also tested PIC pigs, feed conversion ratios of fattening pigs weighing 90–130 kg decreased consistently as SID lysine concentrations in the feed increased from 0.32% to 0.63%. Therefore, it is reasonable to assume that the SID lysine requirement of pigs tested by Suárez-Belloch et al. (2015) was >0.63%. In a study by Lu et al. (2020) on PIC pigs (PIC380 × Camborough, 2058 heads, barrow), the body weight gain was 1069 g/d, feed intake was 2639 g/d, and feed efficiency was 0.405 during the 30–135 kg body weight period. The highest daily gain of 60–90 kg body weight in the pigs in this study was 1065 g/d in the 0.65% total lysine group, the highest feed intake was 2808 g/d in the 0.65% total lysine group, whereas the lowest feed intake was 2602 g/d in the 0.85% total lysine group. The feed efficiency was 0.40 in the 0.85% total lysine group, which was the highest. The comparison between the study by Lu et al. (2020) and the present study showed no large differences in growth performances between PIC pigs and the pigs in this study. According to information published by the PIC (https://www.pic.com/resources/pic-nutrition-and-feeding-guidelines-metric/), the SID lysine requirement for fattening pigs weighing 75–100 kg is 0.77%, which is 28% higher than the SID lysine requirement estimated in this study. The difference in SID lysine requirements, despite the lack of large differences in growth performances, may be due to the higher protein accumulation in the PIC pigs.

Feeding pigs a lysine-deficient diet resulted in a higher intramuscular fat content (Katsumata et al., 2005, 2012, 2018). We prepared a lysine-deficient diet based on the lysine requirements estimated in this study and tested whether it would increase intramuscular fat content. Pigs fed this lysine-deficient diet had lower daily gain and higher intramuscular fat content in the longissimus dorsi muscle (Katsumata et al., unpublished data). These results indicate that the total lysine concentrations in the lysine-deficient diet did not meet the requirements. Actually, this lysine-deficient diet met the total lysine requirement listed in the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013). This means that the total lysine requirement listed in the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013) does not meet the requirement of pigs currently being raised in Japan. These results indicate that pigs cannot reach their full potential in terms of growth performance unless the feed is prepared according to the requirements estimated in this study.

This study aimed to update the amino acid (lysine) requirements of fattening pigs maintained and raised in Japan. Using feed efficiency as a response index, the total and SID lysine requirements of fattening pigs weighing 60–90 kg were found to be 0.72% as total lysine and 0.60% as SID lysine. This study and our unpublished results on intramuscular fat content indicate that the amino acid requirements listed in the Japanese Feeding Standard for Swine (National Agriculture and Food Research Organization, 2013) do not meet the amino acid requirements for pigs currently being raised in Japan. The nutrient requirements of pigs, including their amino acids requirements, should be regularly updated.

ACKNOWLEDGMENTS

This research was supported by grants from the NARO Bio-oriented Technology Research Advancement Institution (Research Program on the Development of Innovative Technology).

CONFLICT OF INTEREST STATEMENT

The authors declare no conflict of interests in this article.

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Volume95, Issue1

January/December 2024

e70011

An estimation of lysine requirements of fattening pigs maintained and raised in Japan

Abstract

1 INTRODUCTION