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Lysine is an essential amino acid and the most commonly limiting amino acid in swine.
As an essential amino acid for swine, lysine must be incorporated into the diet. The lysine content in the raw materials commonly used in feed manufacture is relatively low compared to the total protein content in the diet. Lysine is the first limiting amino acid in swine, which means that it is essential for growth and performance, but it may be present in limited amounts in certain ingredients. For example, cereals such as corn (0.2-0.3%) and wheat (0.3-0.4%), which are common in swine diets as energy sources, have a low lysine content. In contrast, ingredients such as soybean meal (2.5-3.0%) or fish meal (4-5%) are rich in lysine so that meeting the energy needs, without exceeding the maximum recommended levels of protein, with the combination of cereal and protein sources in the formula, lysine would be deficient. Thus, the use of synthetic lysine supplements is common in feed manufacture.
Lysine supplementation
L-lysine is a very hygroscopic amino acid, a characteristic that makes it difficult to handle during the feed manufacturing process if it is marketed in its pure form, limiting its use. Although pure solid L-lysine can be found on the market, its use in animal feed is very scarce. One of the most commonly used forms is lysine monohydrate (lysine-HCl), which is obtained by oxidative fermentation of microorganisms on a hydrocarbon substrate (sugar, starch, molasses, etc.) in the presence of a nitrogen source (ammonium salts, ammonia, protein hydrolysates, etc.). The commercial product has a minimum purity of 98%, with 78% lysine and 19-20% chlorine.
Lysine sulfate is also produced through a fermentation process using bacteria such as Escherichia coli. The fermentation process involves the use of a nutrient medium containing a carbon source, a nitrogen source, and other necessary nutrients. After fermentation, the lysine sulfate solution is concentrated to 65%. The lysine sulfate salt together with fermentation by-products is 46.8% by weight of L-lysine (as free amino acid). It is spray dried, which involves atomizing the lysine sulfate solution in a stream of hot air, to dry the droplets to a dry powder. In some cases, additional purification steps are carried out to produce highly purified lysine sulfate by chromatography or crystallization, complex processes that make the final product more expensive, resulting in higher quality products. Lysine sulfate is also available in liquid form, obtained by fermentation from Corynebacterium glutamicum, which apart from being a producer of glutamic acid, under ideal temperature and pH conditions (28ºC and pH=7) if it has carbon sources (molasses, soybean meal, etc.), it is a good producer of lysine. The liquid forms contain 25% lysine and the solid forms about 50%.
Other forms available are liquid concentrates, such as lysine-50, which is obtained by a process similar to that of hydrochloride. This product is easy to handle and does not yield chlorine.
When obtained by fermentation, all these forms of synthetic lysine contain other nutrients of interest in addition to lysine, including significant amounts of essential amino acids.
In general, no major differences have been observed between studies comparing the bioavailability of commercial lysines, whether in hydrochloride, sulfate, or liquid form.
Table 1. Nutritional values of different available forms of lysine. Source: FEDNA.
| L-Lysine HCl | L-Lysine sulfate | L-Lysine 50 | |
|---|---|---|---|
| Dry matter, % | 98.5 | 95.0 | 54.0 |
| Crude protein, % | 94.5 | 75.0 | 50.0 |
| Lysine, % | 78.0 | 50.0 | 50.0 |
| Other AA% | - | 0.2 | - |
| Ash, % | 0.5 | 4.0 | 0.3 |
| S, % | - | 7.8 | - |
| Cl, % | 19.3 | - | 0.1 |
| K, % | - | - | 0.07 |
| Ca, % | - | 0.13 | - |
| ME, kcal/kg | 3950 | 3700 | 2545 |
| NE, kcal/kg | 2180 | 2145 | 1485 |
Recent findings
1. Excess dietary Lys reduces feed intake, stimulates jejunal CCK secretion and alters essential and non-essential blood AA profile in pigs.
The present work stated that commercial diets are frequently formulated to meet or exceed nutrient levels including those of limiting essential amino acids (AA) covering potential individual variations within the herd. However, the provision of dietary excess of AA, such as Lys, may lead to reduced appetite and growth in pigs. This study evaluated the effect of Lys dietary excesses on performance and satiety biomarkers in post weaning pigs. A total of twenty-four pigs aged 21 d and weighing 6.81 ± 0.12 kg (mean ± SEM) were individually housed and offered 1 of 4 dietary treatments for 3 weeks: a diet containing a standardized ileal digestible Lys reaching 100% (T0), 120% (T1), 150% (T2) or 200% (T3) of the NRC (2012) requirements. The study concluded that excess dietary Lys inhibits hunger in pigs. Moreover, the results provide evidence of pre- and post-absorptive mechanisms modulating these responses. Lys dietary excesses should be narrowed, when possible, to avoid negative effects of the AA on appetite in pigs.
2. Dietary supplementation with lysine (protein) in late pregnancy does not enhance mammary development in multiparous sows.
The present study was conducted to determine if providing standardized ileal digestible (SID) Lys at 40% above estimated requirements (NRC, 2012), with the concomitant increased protein intake, from days 90 to 110 of gestation stimulates mammary development in multiparous sows. From day 90 of gestation, Yorkshire × Landrace multiparous sows (parities 2 and 3) were fed 2.6 kg/d of either a conventional diet (CTL, control, n = 17) providing 14.8 g/d of SID Lys or a diet providing 20.8 g/d of SID Lys via additional soybean meal (HILYS, n = 16). The diets were isoenergetic. The study concluded that feeding Lys (via protein) above current NRC recommendations during late gestation does not improve mammary development of multiparous sows. Hence, the use of a two-phase feeding strategy to provide more Lys (protein) to multiparous sows during this period is not necessary.
3. Standardized ileal digestible lysine requirement of pregnant sows under commercial conditions.
The present work was conducted to determine standardized ileal digestible (SID) lysine (Lys) requirements for pregnant sows individually housed under commercial farm conditions. A total of two hundred multiparous sows (parity = 5.1±2.0) on day 42 of gestation were randomly allocated to five dietary treatments with a balanced parity. Experimental diets were formulated to contain 0.22%, 0.32%, 0.42%, 0.52%, and 0.62% of SID Lys for the mid-gestation period (days 42 to 76) and 0.36%, 0.46%, 0.56%, 0.66%, and 0.76% of SID Lys for the late gestation period (days 77 to 103). All indispensable amino acids except Lys were provided at 110% of their requirement estimates. It was concluded that the mean values of the SID Lys requirement for the mid-gestation period and the late gestation period are 11.1 and 16.1 g/d (1.36 and 1.79 g/Mcal metabolizable energy; 0.44% and 0.58%), respectively, for maximal total born piglets alive per litter.
4. Nitrogen and lysine utilization efficiencies, protein turnover, and blood urea concentrations in crossbred grower pigs at marginal dietary lysine concentration.
Nitrogen utilization efficiency (NUE) and lysine utilization efficiency (LUE) are key indicators of sustainable pork production and vary depending on nutritional and non-nutritional factors. The objective was to study NUE and LUE together with concentrations of blood urea nitrogen (BUN) and other metabolites in growing pigs fed diets with marginal Lys concentrations at 11-13 wk (40.5 kg mean BW) and 14 to 16 wk (60.2 kg mean BW). The cereal grain-soybean meal-based diets contained 10.6 and 7.9 g Lys/kg DM in periods 1 and 2, respectively. Feed intake and BW were measured for 508 individually penned pigs, and blood samples were collected 5 h after morning feeding at weeks 13 and 16. A subgroup of 48 barrows was used in a nitrogen (N) metabolism trial at weeks 13 and 16. It was concluded that the maximum LUE was in the range of 70-72% under the conditions of this study, and only small differences between the periods and sexes existed. Protein synthesis, rather than degradation, appears to affect NUE. BUN concentration may be useful for estimating NUE in a large group of animals fed a diet with a marginal Lys concentration.
5. Compensatory gain based on lysine level in finishing pigs after being fed lysine deficient 97% corn diets for 3 or 6 wk.
The objective of the present work was to evaluate increasing the concentration of lysine on the compensatory gain of finishing pigs during their recovery period after being fed a 97% corn holding diet for 3 or 6 wk. One thousand six hundred and eighty pigs with a starting body weight of 73.5 ± 2.2 kg were blocked by starting body weight and assigned to a nested arrangement. Twenty replicates of seven treatments were comprised of two restriction lengths [3 weeks (3 wk) vs. 6 weeks (6 wk)], and three lysine concentrations during recovery (Lys:ME same as control:100; control + 10%: 110; control + 20%: 120) plus one control (CONT) that remained nutrient unrestricted. It was concluded that the use of restrictive diets reduced ADG and increased days to market. The use of recovery diets in which the Lys:ME ratio was greater than control pigs, resulted in increased compensatory growth.
