Figure 1.
In this model, amino acid intake (AAI) should be presented as the percentage or ratio to control treatment for better distinguishing differences of NR among three AA deleting treatments. To keep the linear relationship between the NR and the first limiting amino acid, the NR should also be converted to the percentage or ratio of the control treatment. The model assumes that deleting the first limiting amino acid (as A) reduces NR to the greatest extent (largest slope); deleting C does not reduce the NR at all (slope = 0), as it remains in excess (over 20%) relative to the first limiting amino acid. Deleting B results in a reduction in the NR intermediate between A and C (0 < Slope B (dashed) < Slope A), and part of B is in excess relative to the first limiting amino acid. In other words, A is the first limiting amino acid while B is second limiting amino acid. According to the principle of the “wooden barrel”, all essential AAs can be controlled by the same limitation by adjusting the amount of AAs in the diet. In this model, B is 10% more than A, which means that we should reduce 10% of B from the control treatment to achieve the minimum addition and ensure it is co-limiting with A [
9]. Then, we can calculate the ratio of A and B.
Figure 1.
In this model, amino acid intake (AAI) should be presented as the percentage or ratio to control treatment for better distinguishing differences of NR among three AA deleting treatments. To keep the linear relationship between the NR and the first limiting amino acid, the NR should also be converted to the percentage or ratio of the control treatment. The model assumes that deleting the first limiting amino acid (as A) reduces NR to the greatest extent (largest slope); deleting C does not reduce the NR at all (slope = 0), as it remains in excess (over 20%) relative to the first limiting amino acid. Deleting B results in a reduction in the NR intermediate between A and C (0 < Slope B (dashed) < Slope A), and part of B is in excess relative to the first limiting amino acid. In other words, A is the first limiting amino acid while B is second limiting amino acid. According to the principle of the “wooden barrel”, all essential AAs can be controlled by the same limitation by adjusting the amount of AAs in the diet. In this model, B is 10% more than A, which means that we should reduce 10% of B from the control treatment to achieve the minimum addition and ensure it is co-limiting with A [
9]. Then, we can calculate the ratio of A and B.
Figure 2.
Comparison of serum urea nitrogen levels of seven- to nine-month-old heifers fed corn–soybean based TMRs among the four treatments (n = 24); PD–Lys = 30% Lys deleted TMR diet (diagonal stripes bar), PD–Met = 30% Met deleted TMR diet (vertical stripes bar), PD–Thr = 30% Thr deleted TMR diet (horizonal stripes bar), PC = theoretically balanced amino acid TMR diet (gray bar); The y-axis represents the serum urea nitrogen levels of four treatments; the x-axis was the age of heifers. Error bars indicate SEM. The a,b above the bars indicate the significant differences among treatments (p < 0.05).
Figure 2.
Comparison of serum urea nitrogen levels of seven- to nine-month-old heifers fed corn–soybean based TMRs among the four treatments (n = 24); PD–Lys = 30% Lys deleted TMR diet (diagonal stripes bar), PD–Met = 30% Met deleted TMR diet (vertical stripes bar), PD–Thr = 30% Thr deleted TMR diet (horizonal stripes bar), PC = theoretically balanced amino acid TMR diet (gray bar); The y-axis represents the serum urea nitrogen levels of four treatments; the x-axis was the age of heifers. Error bars indicate SEM. The a,b above the bars indicate the significant differences among treatments (p < 0.05).
Figure 3.
The pattern diagram (b) when Met and Thr are converted to an equivalent slope (a) with Lys. The y-axis represents the ratio of NR after deleting Lys, Met, Thr to that of the PC treatment; the x-axis is the ratio of the amino acid intake (AAI) in the amino acid deleting treatments to that in the PC treatment. (Lys, ■) = Lys intake and NR level in PD–Lys treatment, (Met, ▲) = Met intake and NR level in PD–Met treatment, (Thr, ◆) = Met intake and NR level in PD–Thr treatment, and (PC, ●) = Lys, Met, Thr intake and NR level in PC treatment; all values =1.
Figure 3.
The pattern diagram (b) when Met and Thr are converted to an equivalent slope (a) with Lys. The y-axis represents the ratio of NR after deleting Lys, Met, Thr to that of the PC treatment; the x-axis is the ratio of the amino acid intake (AAI) in the amino acid deleting treatments to that in the PC treatment. (Lys, ■) = Lys intake and NR level in PD–Lys treatment, (Met, ▲) = Met intake and NR level in PD–Met treatment, (Thr, ◆) = Met intake and NR level in PD–Thr treatment, and (PC, ●) = Lys, Met, Thr intake and NR level in PC treatment; all values =1.
Table 1.
Composition and nutrient levels of basal total mixed ration (TMR) (dry matter basis).
Ingredients | Contents, % | Nutrient Levels 2 | Levels |
---|
Corn | 45.67 | Metabolizable energy, (MJ/kg) | 10.13 |
Soybean meal | 11.97 | Crude protein, % | 14.95 |
Wheat bran | 15 | Ether extract, % | 3.04 |
Alfalfa hay | 25 | Ash, % | 7.58 |
Limestone | 1.06 | Neutral detergent fiber, % | 29.22 |
Salt | 0.3 | Acid detergent fiber, % | 13.99 |
Premix 1 | 1 | Calcium, % | 1.12 |
Total | 100 | Phosphorus, % | 0.60 |
| | Lysine, % | 0.51 |
| | Methionine, % | 0.07 |
| | Threonine, % | 0.49 |
Table 2.
Amino acid (AA) levels of TMRs (dry matter basis).
Items | Treatments 1 (%) |
---|
PC | PD–Lys | PD–Met | PD–Thr |
---|
Total AA content | | | | |
Lysine | 1.00 | 0.66 | 1.00 | 1.00 |
Methionine | 0.33 | 0.33 | 0.22 | 0.33 |
Threonine | 0.72 | 0.72 | 0.72 | 0.45 |
AA content in basal diet | | | | |
Lysine | 0.51 | 0.51 | 0.51 | 0.51 |
Methionine | 0.07 | 0.07 | 0.07 | 0.07 |
Threonine | 0.45 | 0.45 | 0.45 | 0.45 |
Exogenously added AA | | | | |
Lysine | 0.49 | 0.15 | 0.49 | 0.49 |
Methionine | 0.25 | 0.25 | 0.15 | 0.25 |
Threonine | 0.23 | 0.23 | 0.23 | 0.00 |
Table 3.
Effects of deleting Lysine (Lys), Methionine (Met), and Threonine (Thr) levels in corn–soybean based TMR on the growth performance of heifers aged seven to nine months old (n = 72).
Table 3.
Effects of deleting Lysine (Lys), Methionine (Met), and Threonine (Thr) levels in corn–soybean based TMR on the growth performance of heifers aged seven to nine months old (n = 72).
Items 1 | Treatments 2 | SEM | p Value 3 |
---|
PD–Lys | PD–Met | PD–Thr | PC | T | M | T × M |
---|
BW, kg | | | | | | | | |
Average | 273.7 | 273.9 | 276.3 | 274.8 | 2.98 | 0.4798 | <0.0001 | <0.0001 |
6 mon | 227.5 | 227.0 | 229.9 | 228.5 | 4.08 | 0.4647 | | |
7 mon | 258.0 | 257.8 | 259.3 | 257.6 | 4.00 | 0.7016 | | |
8 mon | 282.7 | 284.3 | 282.5 | 280.3 | 4.52 | 0.3667 | | |
9 mon | 326.4 | 326.8 | 333.4 | 333.0 | 4.02 | 0.0997 | | |
ADG, kg | | | | | | | | |
Average | 1.04 | 1.09 | 1.09 | 1.11 | 0.029 | 0.1566 | <0.0001 | <0.0001 |
6–7 mon | 0.98 | 1.02 | 0.94 | 0.95 | 0.075 | 0.2848 | | |
7–8 mon | 0.95 | 0.95 | 0.90 | 0.89 | 0.079 | 0.4946 | | |
8–9 mon | 1.21 c | 1.30 bc | 1.44 ab | 1.48 a | 0.080 | 0.0013 | | |
DMI, kg | | | | | | | | |
Average | 7.15 | 7.16 | 7.16 | 7.05 | 0.050 | 0.1073 | <0.0001 | <0.0001 |
6–7 mon | 6.25 | 6.20 | 6.26 | 6.28 | 0.091 | 0.2942 | | |
7–8 mon | 6.99 | 6.98 | 6.94 | 6.84 | 0.089 | 0.0916 | | |
8–9 mon | 8.21 | 8.28 | 8.16 | 8.25 | 0.088 | 0.2297 | | |
Feed conversion rate, G/F | | | | | | | | |
Average | 0.146 | 0.152 | 0.152 | 0.156 | 0.008 | 0.1452 | 0.0001 | 0.0002 |
6–7 mon | 0.156 | 0.164 | 0.151 | 0.155 | 0.011 | 0.2138 | | |
7–8 mon | 0.135 | 0.134 | 0.127 | 0.130 | 0.010 | 0.5009 | | |
8–9 mon | 0.147 c | 0.158 bc | 0.176 ab | 0.181 a | 0.012 | 0.0057 | | |
Table 4.
Effects of deleting Lysine, Methionine, and Threonine levels in corn–soybean based TMRs on nitrogen metabolism of heifers aged seven to nine months old (n = 16).
Table 4.
Effects of deleting Lysine, Methionine, and Threonine levels in corn–soybean based TMRs on nitrogen metabolism of heifers aged seven to nine months old (n = 16).
Items 1 | Treatments 2 | SEM | p Value |
---|
PD–Lys | PD–Met | PD–Thr | PC |
---|
Intake N, g·(kg−1 BW0.75) d−1 | 2.92 | 2.97 | 2.90 | 2.87 | 0.020 | 0.2961 |
Fecal N, g·(kg−1 BW0.75)·d−1 | 0.90 | 0.82 | 0.80 | 0.79 | 0.015 | 0.1223 |
Urine N, g·(kg−1 BW0.75)·d−1 | 1.06 b | 1.16 a | 1.02 b | 0.88 c | 0.033 | 0.0011 |
Total excrete N, g·(kg−1 BW0.75)·d−1 | 1.96 b | 1.98 a | 1.82 ab | 1.67 ab | 0.032 | 0.0208 |
N retention, g·(kg−1 BW0.75)·d−1 | 0.96 b | 0.99 b | 1.08 ab | 1.20 a | 0.034 | 0.0324 |
Digestible N, g·(kg−1 BW0.75)·d−1 | 2.02 | 2.15 | 2.06 | 2.08 | 0.020 | 0.2908 |
N utilization, % | 33.08 b | 33.26 b | 34.96 b | 41.77 a | 1.210 | 0.0048 |
N digestibility, % | 69.50 | 72.38 | 70.79 | 72.6 | 0.512 | 0.0798 |
Table 5.
The proportions of amino acid intake and nitrogen retention in PD–Lys, PD–Met, and PD–Thr to those in the PC treatment.
Table 5.
The proportions of amino acid intake and nitrogen retention in PD–Lys, PD–Met, and PD–Thr to those in the PC treatment.
Items 1 | Based on Metabolic Body Weight, g·(kg−1 BW0.75)·d−1 | The Ratio to PC |
---|
NR 2 | AAI 2 | NR | AAI |
---|
Lys | Met | Thr | Lys | Met | Thr |
---|
PD–Lys | 0.96 | 0.60 | 0.29 | 0.65 | 0.80 | 0.67 | 1.00 | 1.00 |
PD–Met | 0.99 | 0.90 | 0.20 | 0.65 | 0.83 | 1.00 | 0.69 | 1.00 |
PD–Thr | 1.02 | 0.90 | 0.29 | 0.40 | 0.85 | 1.00 | 1.00 | 0.62 |
PC | 1.20 | 0.90 | 0.29 | 0.65 | 1.00 | 1.00 | 1.00 | 1.00 |
Table 6.
The appropiate amino acid ratio of Lysine (Lys), Methionine (Met), and Threonine (Thr) based on the nitrogen retention (NR) of heifers aged seven to nine months old, fed corn–soybean meal-based TMRs.
Table 6.
The appropiate amino acid ratio of Lysine (Lys), Methionine (Met), and Threonine (Thr) based on the nitrogen retention (NR) of heifers aged seven to nine months old, fed corn–soybean meal-based TMRs.
Items 1 | S | P | C | R |
---|
Lys | 0.61 | 1.00 | 69.99 | 100.00 |
Met | 0.57 | 0.98 | 22.36 | 31.95 |
Thr | 0.26 | 0.79 | 39.78 | 56.84 |
Table 7.
The amino acid ratio of calves and cows in previous studies.
Stage | Index 1 | Lys: Met: Thr Ratio | Reference |
---|
Calves | NR | 100:26:66 | Gerrits et al., 1997 [37] |
Calves | maximum ADG | 100:31:77 | Hill et al., 2008 [7] |
Calves | maximum ADG | 100:35:63 | Wang et al., 2011 [8] |
Beef cattle | body amino acids | 100:31:61 | NRC (2016) [38] |