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Of the total energy consumed by growing pigs, on average 40% will be used to maintain basal activities, thermoregulation, and tissue replacement, while 60% will be used for muscle and lipid tissue growth. Ingested and recycled proteins will be used for tissue growth and repair, enzymatic and hormonal functions, transport of substances, immune responses, water and electrolyte balance, muscle contraction, cell signaling, and pH maintenance, presenting specific demands in relation to the amino acid profile and amounts of these that must be provided in the diet for the different processes, not being stored when supplied above the capacity of use.
With this in mind, we present the basis of the amino acid and protein requirements for growing pigs and their updates in TBAS 2024. The protein requirements for animals are based on the main concepts outlined below:
- Meeting the digestible amino acid requirements is done to cover the daily essential amino acid needs, which are the amino acids that pigs cannot synthesize in their metabolism.
- Essential amino acids are required in proportional amounts, establishing an amino acid standard called ideal protein.
- The standard amino acid reference in the ideal protein is the amino acid lysine because it is found in smaller quantities in feed in relation to the animal's demand, because it does not present endogenous synthesis and because it is used in great proportion, or almost exclusively, for the synthesis of muscle protein.
- Meeting the total protein requirements is done to cover the non-essential amino acid requirements of the animal, thus preventing essential amino acids from being diverted and used in the synthesis of non-essential amino acids.
- Amino acid requirements are established considering standardized ileal digestibility, which is related to absorbed amino acids and without interference from basal endogenous losses.
Lysine, optimal protein, and digestible protein requirements for growing pigs
The requirements presented in TBAS (2024) are based on determining the digestible lysine requirements for growing animals, updating the ratio of amino acids in the ideal protein, and determining the ratio of essential nitrogen to total nitrogen that will allow the needs of digestible protein, and consequently of non-essential amino acids, to be met.
Standardized ileal digestible lysine requirements
Determining standardized ileal digestible lysine (SID Lys) requirements is based on factorial models, determining digestible lysine requirements for maintenance and production.
Thus, in terms of energy, the lysine requirement for maintenance is determined by the lysine balance equal to zero, which is established in different types of experimental trials. In TBAS 2024, the digestible lysine requirement for growing animals was updated, the value defined by Faria (2019) at (0.039 x Average Weight0.75).
Digestible lysine requirements for production were established based on data from dose-response experiments with different levels of lysine conducted at UFV and published in indexed journals.
Considering the database used in the update, a total of 165 experimental results were considered to establish the lysine requirement equations. These requirements are based on the average body weight of the animals in the stage and the rate of weight gain in the production stage. In this scenario, digestible lysine requirements were updated for castrated male, female, entire male, and immunocastrated male pigs (Table 1). Note the use of different equations for entire and immunocastrated males.
Table 1. Standardized ileal digestible lysine requirement in g/day for growing pigs.
| Equations for estimating SID Lys requirements | |
|---|---|
| Castrated male pigs | Dig. Lys = (0.039 W0.75) + (16.844 + 0.0829 W - 0.0004 W2) G |
| Female pigs | Dig. Lys = (0.039 W0.75) + (16.235 + 0.136 W - 0.0009W2) G |
| Entire male pigs (up to 105 kg wieght) | SID Lys = (0.039 W0.75) + (16.074+ 0.1531 W - 0.0012 W2) G |
| Immunocastrated male pigs (105 to 155 kg)1 | SID Lys = (0.039 W0.75) + (18.71) G |
As with energy equations, digestible lysine demands are related to the average weight of the animal in the phase and the expected rate of weight gain for the phase. Since the calculation is based on recommendations in grams per day, depending on the ME requirements, the ME level of the diet, and the expected intake, the percentage of digestible lysine in the diet will be established.
Tables 2, 3, and 4 summarize SID Lys requirements and the concentration of digestible lysine in the diets.
Table 2. SID Lys requirements and % SID Lys in diets for females with high genetic potential and superior performance.
| Age (days) | 63 | 91 | 119 | 147 | 175 |
|---|---|---|---|---|---|
| Weight (kg) | 26.65 | 49.11 | 76.93 | 106.96 | 136.24 |
| Gain (kg/day) | 0.643 | 0.889 | 1.041 | 1.077 | 1.017 |
| SID Lys requirement (g/day) | 12.79 | 19.17 | 23.27 | 23.37 | 19.93 |
| Feed consumption (kg)1 | 1.054 | 1.804 | 2.730 | 3.117 | 3.362 |
| SID Lys (%) | 1.21 | 1.06 | 0.91 | 0.75 | 0.59 |
1Diets containing 3350 kcal/kg ME from 49 to 182 days of age. Adapted (Hannas et al. 2024)
Table 3. ME SID Lys and % SID Lys requirements in diets for castrated male pigs with high genetic potential and superior performance.
| Age (days) | 63 | 91 | 119 | 147 | 175 |
|---|---|---|---|---|---|
| Weight (kg) | 27.07 | 51.51 | 81.89 | 113.68 | 144.04 |
| Gain (kg/day) | 0.692 | 0.970 | 1.124 | 1.137 | 1.043 |
| SID Lys requirement (g/day) | 13.48 | 20.20 | 24.61 | 25.34 | 22.98 |
| Feed consumption (kg)1 | 1.160 | 2.081 | 2.978 | 3.538 | 3.678 |
| SID Lys (%) | 1.16 | 0.97 | 0.83 | 0.72 | 0.62 |
1Diets containing 3350 kcal/kg ME from 49 to 182 days of age. Adapted (Hannas et al.2024)
Table 4. ME SID Lys and % SID Lys requirements in diets for entire and immunocastrated male pigs with high genetic potential and superior performance.
| Age (days) | 63 | 91 | 119 | 147 | 175 |
|---|---|---|---|---|---|
| Weight (kg) | 25.83 | 48.62 | 79.40 | 116.17 | 156.06 |
| Gain (kg/day) | 0.623 | 0.928 | 1.194 | 1.372 | 1.444 |
| SID Lys requirement (g/day) | 12.42 | 19.90 | 25.71 | 25.61 | 28.73 |
| Feed consumption (kg)1 | 0.995 | 2.081 | 2.513 | 2.816 | 4.050 |
| SID Lys (%) | 1.25 | 1.13 | 1.02 | 0.91 | 0.71 |
1Diets containing 3250 kcal/kg ME from 49 to 182 days of age. Adapted (Hannas et al.2024
Essential amino acid standard in ideal protein for pigs
The concept of ideal protein was considered to determine the requirements of other amino acids. The proportions of the other essential amino acids were reviewed based on experiments conducted at UFV, in other institutions, and in a database reviewed in the scientific literature. Under specific conditions, especially related to animal health, this ratio may be modified and other proportions should be considered.
Table 5 shows the amino acid ratio in the ideal protein suggested for growing pigs. From 63 to 175 days of age.
Table 5. Ratio of amino acids in the ideal protein for growing pigs.
| Amino acid | Digestibility |
|---|---|
| Lysine | 100 % |
| Methionine | 33 |
| Methionine + Cysteine | 60 |
| Threonine | 68 |
| Tryptophan | 20 |
| Arginine | 42 % |
| Valine | 69 % |
| Isoleucine | 55 % |
| Leucine | 100 % |
| Histidine | 33 % |
| Phenylalanine | 54 % |
| Phenylalanine + Tyrosine | 100 % |
Total and digestible protein levels for pigs
Supplying crystalline amino acids along with applying the ideal protein concept in swine diet formulations allows diets to be formulated with lower protein levels. In this sense, nutritionists should ensure that the total protein supplied to the animals also covers the demands of non-essential amino acids as well. To this end, based on studies of the relationship between essential nitrogen and total nitrogen, the minimum levels of digestible protein and total protein that swine diets must have were established.
The procedures and calculations used to determine essential nitrogen and total nitrogen concentrations and their ratios can be found in TBAS 2024. Simply stated, it is possible to estimate the minimum levels of crude protein and digestible protein based on the proportion of digestible lysine present in crude protein and digestible protein, which are 6.2% and 7%, respectively.
As an example, 119-day-old female pigs with an average weight of 76.9 kg and a digestible lysine requirement of 0.91% had a crude protein requirement of: (0.91 x 100) / 6.2 = 14.68% and a digestible protein requirement of: (0.91 x 100) / 7 = 13.0%.
Final considerations
Understanding the growth potential of pigs, aligned with the application of equations to determine nutritional requirements and updated nutritional concepts, allows the formulation of more efficient diets with better economic returns, as well as the customization of feeding programs according to the characteristics of the swine production system.
