Miscellaneous Species
Research Report 6

Threonine in Kitten

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Dietary Crude Protein Slightly Increases the Requirement for Threonine in Kittens

ObjectivesInvestigate the interaction between graded levels of threonine and dietary crude protein.
Experimental DesignPrevious studies have indicated that the essential amino acid requirements for kittens are not positively correlated with the concentration of dietary nitrogen, as they are in other species. This difference is primarily an increased requirement for maintenance rather than for growth. This high protein requirement is the result of highly active nitrogen catabolic enzymes in the liver.

Studies have shown that when either threonine or isoleucine were fed below the NRC requirement (80 and 90% respectively) increasing dietary nitrogen from 200 to 300 g/kg in the diet resulted in increased weight gain. Past experiments suggest that cats are not susceptible to amino acid imbalances as are other species. However, an amino acid response has been observed in kittens fed a diet limiting in threonine (Titchenal et al., 1980).

Experiment 1
Forty-eight male kittens were used, food intake, weight gain and nitrogen retention were measured at six concentrations of dietary L-Threonine (4.0, 5.0, 6.0, 7.0, 9.0 and 12.0 g/kg diet) and four concentrations of dietary crude protein (150, 200, 300 and 500 g/kg diet).

Experiment 2
To verify and study the growth effect seen at 6.0 g threonine/ kg diet seen in experiment 1. Twenty-four kittens (12 males and 12 females) were fed 6.0 g threonine/kg diet with either 200, 300 or 500 g CP/kg diet.

Table 1. Diet Composition
Level of dietary crude protein
Ingredients150200300500
------------------------- g/kg ------------------
Soy protein grade II
Essential amino acid mixtue1
L-Threonine
L-Alanine
Amino acid mixture2
Sodium acetate
Starch
Cerelose
Animal tallow
Hydrogenated beef tallow
Mineral mixture
Vitamin mixture
Choline chloride
Taurine		100
60
0-8
0-6
0
15.6
100
402-404
200
50
50
10
30
1.5		100
60
0-8
0-6
50
22.2
100
345-348
200
50
50
10
30
1.5		100
60
0-8
0-6
150
35.3
100
232-235
200
50
50
10
30
1.5		100
60
0-8
0-6
350
61.5
100
6-8
200
50
50
10
30
1.5
1Essential amino acid composition (g/kg mixture): L-Arginine HCl, 180.5; L-Histidine HCl, 144.0; L-Cystine, 109.0; L-Methionine, 81.1; L-Tyrosine, 62.9; L-Phenylalanine, 38.1; L-Threonine, 87.5; L-Tryptophan, 19.9; L-Valine, 82.8
2Amino acid composition (g/kg mixture); L-Arginine HCl, 88.2; L-Histidine HCl H20, 30.1; L-Isoleucine, 36.8; L-Leucine, 87.2; L-Lysine, 72.7; L-Cystine, 25.2; L-Methionine, 29.1; L-Tyrosine, 33.0; L-Phenylalanine, 29.1; L-Tryptophan, 10.7; L-Valine, 43.6; L-Asparagine H20, 72.7; L-Glutamine, 193.8; Glycine, 71.7; L-Proline, 79.5; L-Alanine, 96.9

The diets were formulated so that all diets contained a basal level of threonine 4 g/kg diet. A mixture of threonine, alanine and starch were added to achieve the desired threonine level. As threonine was increased, L-Alanine was decreased isonitrogenously. A third amino acid mixture containing essential amino acids (other than threonine) and dispensable amino acids was used to increase the CP level.

Essential amino acids made up 44% of this mixture, the balance consisting of dispensable amino acids, asparagine, glutamine, glycine, proline and alanine. Sodium acetate was added on an equimolar basis to balance the hydrochloride associated with the crystalline amino acids.

 

Results

Experiment 1
The effect of dietary CP on food intake varied according to the level of dietary threonine. At the two lowest threonine levels, there was no significant difference, the responses observed at threonine levels >6.0 g/kg showed definite differences (Figure 1). The responses were significant between the low (150 and 200) and high (300 and 500) at threonine levels at and above 6.0 g/kg of diet.

The pattern of weight gain and nitrogen retention followed the food intake trends. Weight gain and nitrogen retention differences were significant between low and high CP treatments at 6.0 g/kg of diet and above (Figure 2 and 3).

Concentrations of threonine and serine exhibited much different patterns than those of the other amino acids. Plasma threonine increased linearly, with increasing dietary threonine, but was not affected by dietary crude protein.

Evidence of threonine deficiency was demonstrated in kittens fed the lowest level of dietary threonine. The kittens developed evidence of vestibular dysfunction, manifested by disequilibrium, abnormal righting reflex, head tremor, impaired physiological nystagmus and placing reflexes.

Experiment 2
In this study, there were no significant differences among any of the diet conditions in food intake or weight gain (Table 2). Nitrogen retention was significantly greater in the 500 g CP/kg diet group compared with the 200 g CP/kg group, but there was no difference between the 300 and 500 or 300 and 200 g/CP/kg diet groups. By day 11 all of the essential amino acids were significantly elevated in the plasma of kittens fed CP at 500 g/kg when compared with the 200 g CP group, and many of them were elevated in the 300 g CP group. Plasma threonine concentrations were not significantly different among groups.

Table 2. Food intake, weight gain, nitrogen retention and plasma threonine in kittens fed 6.0 g thr/kg diet
Dietary Crude Food Intake 1Weight gain1Nitrogen Plasma Thr2
------------------ g/day ---------------umol/L
200 g/kg diet
300 g/kg
500 g/kg diet
Pooled SEM		53
55
63
3		17
24
25
2		0.68b
0.84ab
1.07a
0.05		60
52
57
4
1Represent daily means of the last 8 d of the 12-d experimental period
2Samples collected on d 11 of the experimental period; n=8/group. different letters represent differences between diet groups, P < 0.05
DiscussionThe pattern of increased growth, seen when CP was increased from 200 to 300 g/kg at all levels of dietary threonine, provides evidence that the nitrogen requirement in kittens is above previously reported 180-200 g/kg diet. From experiment 1 there was some indication, that under some circumstances, increasing dietary CP above 300 g/kg may improve growth. When threonine was held at 6.0 g/kg kittens ate the most and retained the most nitrogen on the 500 g CP/kg diet. Broken line analysis of nitrogen retention data indicated that there was a slight positive relationship between the requirement for threonine and the level of CP in the diet.

The plasma threonine results are consistent with other studies that showed that plasma threonine becomes elevated when high CP diets are fed and overall threonine catabolism in the cat does not increase more than two to threefold in response to high dietary CP. Plasma serine appeared to be affected by both the level of dietary threonine and dietary CP. None of the other plasma amino acids showed this unusual pattern. It is unlikely that the synthesis of serine from threonine was greater when kittens were fed low levels of dietary threonine.

The differential effect of CP on the requirements for threonine and methionine in kittens may be accounted for by metabolism and transport differences between the two amino acids. These factors may determine whether the concentration of the limiting amino acid becomes low enough in the brain to cause feeding depression associated with an amino acid imbalance.
ConclusionThe results from these studies indicated that the requirement for nitrogen in the kitten was between 200 and 300 g/kg diet. The requirement for threonine showed a slight positive relationship with the level of dietary CP, so that the requirement was 4.9 g/kg at both 150 and 200 g CP/kg diet and 6.0 g/kg diet at 300 and 500 g CP/kg diet.

Cats appeared to be less susceptible to a typical nutritional amino acid imbalance response than are other species. This may explain the lack of a stronger relationship between dietary CP and the requirement for dietary threonine. In general, when the amino acid disproportion was not extreme, an increase in dietary CP led to an increase in food intake, which provided more of the limiting amino acid for growth. But when the amino acid disproportion was extreme, with threonine as the limiting amino acid, the extra CP caused an amino acid imbalance response .

The dietary threonine requirement for kittens should be considered between 2 and 2.5% of the dietary crude protein of the diet.
BibliographyHammer, V. A., Rogers, Q.R. & Morris, J.G. 1996. Dietary crude protein increases slightly the requirement for threonine in kittens. J. Nutr. 126:1496-1504.

Titchenal, C.A. , Rogers, Q.R., Indrieri, R.J. & Morris, J.G. 1980. Threonine imbalance, deficiency and neurologic dysfunction in the kitten. J. Nutr. 110: 2444-2459.