Amino Acid Composition of Hair and Quantitative Hair Loss in Adult Cats and Dogs

Amino acids are constantly lost from the body in the form of hair. As cat and dog hair is mainly composed of amino acids (Table 22.3), the contribution of hair loss to the overall amino acid requirements may be significant. Hair proteins contain high levels of cysteine and the amount of cysteine required for hair growth may constitute a significant proportion of the total sulphur amino acid requirements of adult cats and dogs, especially for those

Table 22.3. Amino acid composition of cat, dog, horse, sheep and human hair protein. (From Hendriks et al., 1998b.)

Content (mol 100 moh1 of residue)

Table 22.3. Amino acid composition of cat, dog, horse, sheep and human hair protein. (From Hendriks et al., 1998b.)

Content (mol 100 moh1 of residue)

Amino acid

Cat

Dog

Horse

Sheep

Human

Cysteine

15.8

16.7

14.4

13.1

17.8

Methionine

0.9

0.9

0.2

0.5

0.6

Aspartate

5,6

5.3

6.0

5.9

4.9

Threonine

6.4

6.2

5.5

6,5

6,8

Serine

10.6

10.5

9.6

10.8

11.7

Glutamate

11.4

11.1

11.3

11.1

11.4

Glycine

9.5

7.8

6.4

8,6

6.4

Alanine

5.1

5.1

5.5

5.2

4.6

Valine

4.9

4.9

5.9

5.7

5,8

Isoleucine

2.5

2.5

3,6

3.0

2.6

Leucine

6.7

6.1

7.5

7.2

5,8

Tyrosine

3.0

2.7

1.9

3.8

2.0

Phenylalanine

2.3

1.7

2.5

2.5

1.6

Histidine

1.2

0.9

1.1

0.8

0.9

Lysine

2.9

3.9

2.9

2.7

2.7

Arginine

6.1

6,3

7.9

6.2

5,8

Proline

4.9

7.3

7.8

6.6

8.4

breeds with a relatively dense and long hair coat (e.g. Persian, Longhaired Scottish Fold, Pekinese and Collie). The effect of hair colour will most likely not effect requirements as the amino acid composition of different coloured (black, white, grey and ginger) hair from cats has been found to be not significantly different (Hendriks et al., 1998b). However, coat colour and in particular the colour black was recently shown to be dependent on the level of aromatic amino acid intake in kittens (Yu et al., 2001).

The replacement of hair in cats and dogs is a cyclic phenomenon resulting from the cyclic events which occur in individual hair follicles. Three stages are identified including an active growth phase (anagen), transition phase (catagen) and a resting phase (telogen). Variation in the length of the anagen phase or rate of hair production will affect the amount of hair produced whereas the length of the telogen phase will determine the timing of the next moult. Hair density is affected by the timing of the shedding of the old hair when the new hair has grown (Johnson, 1972). Baker (1974) and Ryder (1976) determined the inactivity of hair follicles of cats throughout the year and showed that hair growth follows a sinusoidal pattern throughout the year with one moult occurring around spring. This hair replacement pattern differs from that of dogs where two moulting seasons are observed (Rougeot, 1981; Mundt and Stafforst, 1987). Quantitative estimates of amino acid losses from hair are difficult to determine as it involves estimation of the amount of hair produced at various phases of the hair growth cycle. As there are over 150 breeds of dogs, representing a large range of body weights (1 kg for a Chihuahua to over 70 kg for a Newfoundland) and over 100 breeds of cats, it may be difficult to provide one overall estimate to describe hair growth for all cats and dogs. Stafforst (1982) provided information on the monthly hair growth of five dogs of varying breeds throughout the year. Average monthly hair growth rates varied from 14.3 to 94.5 mg cm 2 body surface area depending on the month of the year. Interestingly the total amount of hair grown per year was remarkably similar for the dogs and showed similar seasonal growth rates despite the fact that two of the dogs were short-haired and three dogs were long-haired breeds. This may indicate that the anagen phase is similar between breeds but the telogen phase differs. Estimates of yearly hair growth in the dogs ranged from 5.5 to 6.7 g cm 2 body surface area (Stafforst, 1982). Hendriks et al. (1997b, 1998a) provided mathematical functions describing hair growth and hair loss, respectively, in adult domestic short-haired cats throughout the year. Total yearly hair growth and hair loss were found to be similar (32.7 vs. 28.1 g kg-1 body weight) but out of phase by approximately 75 days. The quantitative hair replacement pattern described by Hendriks et al. (1998a) in cats showed that the density of the coat closely follows the temperature pattern throughout the year (Fig. 22.1). The densest and sparest coats were obtained at day 168 and 351 of the study which coincided with the average minimum and maximum daily temperatures, recorded at day 167 and 350, respectively.

Estimates of the amount of amino acids required for hair growth at any point in time throughout the year can be calculated by multiplying the concentration of each amino acid in hair by the total body hair growth rate at a specific point in time or during a specified period. Table 22.4 presents the monthly levels of hair protein required for the synthesis of hair in adult cats and dogs per unit surface area. The estimates for dogs are approximately 10-15 times higher compared to the estimates in cats. In comparing these estimates it has to be taken into account that the estimates for cats are based on growth rates over the entire body whereas those for dogs relate to the growth rate of hair on the side of the thorax. The latter site may not be representative of the hair growth rate over the entire body. Equations to calculate the surface area from body weight measurements of adult cats are provided by Greaves (1957) and Bartorelli and Gerola (1963). Price and Frazier (1998) present many of the published results for adult dogs. Further research is required to determine whether there is a difference in the anagen phase between long-haired and short-haired canine and feline breeds or, as the data suggest in dogs, the difference lies in the length of the telogen phase of the follicle cycle.

Fig. 22.1. Sine-functions3 describing daily hair growthb (...) and hair iossb (----) rate and the daily change in body hair0 (——) throughout the year in adult domestic short-haired cats (longitude 174"38'E, latitude 40"22'S). ®f(x) = a + b x sin(0.0172 x (x - d)) where a = horizontal shift, b = half amplitude and d = phase shift of the sine. b Ave rage value of 83.2 and 50.0 for parameter a and b, respectively taken from Hendriks etal. (1997b, 1998a). Values for parameter d for hair growth and loss from Hendriks etal. (1997b) and Hendriks etal. (1998a), respectively. °y = 58.6 x sin(0.0172 x x) + 14.9 x cos(G.G172 x x).

Day of study

Fig. 22.1. Sine-functions3 describing daily hair growthb (...) and hair iossb (----) rate and the daily change in body hair0 (——) throughout the year in adult domestic short-haired cats (longitude 174"38'E, latitude 40"22'S). ®f(x) = a + b x sin(0.0172 x (x - d)) where a = horizontal shift, b = half amplitude and d = phase shift of the sine. b Ave rage value of 83.2 and 50.0 for parameter a and b, respectively taken from Hendriks etal. (1997b, 1998a). Values for parameter d for hair growth and loss from Hendriks etal. (1997b) and Hendriks etal. (1998a), respectively. °y = 58.6 x sin(0.0172 x x) + 14.9 x cos(G.G172 x x).

Table 22.4. Monthly hair protein required for hair growth in adult cats and dogs.

Hemisphere

Hair protein (mg cm

"2 surface area)

Southern

Northern

Cats3

Dogsb

January

July

4.08

57.8

February

August

4.33

86.9

March

September

4.98

64.9

April

October

4.54

45.4

May

November

3.97

31.7

June

December

2.90

30.4

July

January

2.02

38.0

August

February

1.33

67.4

September

March

1.07

27.0

October

April

1.41

13.2

November

May

2.07

24.4

December

June

3.12

34.0

3From Hendriks et al. (1997b) measured over the entire body.

bFrom Stafforst (1982) measured at a 10 cm2 area at the side of the thorax.

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