Effects of coat length and faecal hair removal on measured nutrient digestibility in cats

Abstract

Objectives

This experiment was conducted to evaluate the effect of coat length and faecal hair removal on measured nutrient digestibility in longhair and shorthair cats.

Methods

A total of 14 adult domestic cats, with a mean ± SD body weight of 4.5 ± 1.21 kg and a mean ± SD age of 3.3 ± 1.38 years, were used for a nutrient digestibility trial. The nutrient digestibility of cats was measured by hair-included faeces and hair-removed faeces. Food was provided twice daily (09:00 h and 16:00 h) and water was provided ad libitum. Cats were adapted to a steel cage and diet for 16 days before a 10 day collection period. During the collection period, food offered, food refused and faecal output were measured daily and used for digestibility analysis.

Results

The digestibility of dry matter, crude protein and neutral detergent fibre (NDF) of longhair cats was underestimated by 8% (P = 0.02), 9% (P = 0.04) and 14% (P = 0.04), respectively. In shorthair cats, the digestibility of dry matter, crude protein and crude ash increased by 4% (P = 0.01), 5% (P = 0.02) and 15% (P <0.01), respectively, with hair-removed faeces. The nutrient digestibility between longhair and shorthair cats showed no difference when hair-included faeces were used. However, when using hair-removed faeces, the digestibility of NDF and amino acids in longhair cats were about 4–8% higher than in shorthair cats (P <0.05).

Conclusions and relevance

This study showed that the nutrient digestibility values were affected by whether the hair in faeces was removed or not. Removing hair from faeces is a more precise method with which to evaluate the apparent nutrient digestibility of domestic cats.

Introduction

The daily hygiene routine of grooming in cats results in the formation of hairballs (trichobezoars), when the animals lick and ingest their own hair. ¹ The ingested hair moves through the stomach and intestines by peristalsis, and the hair becomes entangled into a solid mass. ² Specifically, it has been reported that feline hairball formation may be associated with longhair cats or cats that display frequent grooming and swallowing of hair. ³ Usually, ingested hair is eliminated in faeces, but large quantities can accumulate in the digestive tract, forming trichobezoars that can cause digestive problems. ⁴

According to Harkey, ⁵ human hair (depending on its moisture content) consists of approximately 65–95% protein, 15–35% water and 1–9% lipids. Through conventional 24 h acid hydrolysis, it was determined that the total weight of cat (Felis catus) hair consists of approximately 67% crude protein (CP). ⁶ The amount of hair found in faeces per day was 25–75 mg/kg of body weight. ⁶ The trichobezoars in faeces were approximately 87–143 mg per cat per day and 4.7–11 mg/g faeces dry matter (DM). ¹ Therefore, the large amount of hair normally present in faeces may influence the determination of nutrient digestibility in domestic cats. As hair has been shown to consist mainly of amino acids, ⁷ the digestibility of amino acids may also be underestimated. This may be particularly significant for the amino acid cysteine, because cysteine has been found in high concentrations in cat hair. ⁷

Therefore, this study was conducted to compare the apparent digestibility of nutrients in domestic cats using hair-included faeces and hair-removed faeces by hair length of different breeds.

Materials and methods

Ethics

All animal procedures were approved by the Institutional Animal Care and Use Committee (IACUC) of Seoul National University (SNUIACUC-160712-22) before beginning the experiment. The present study was conducted according to guidelines provided by SNUIACUC.

Animals

Fourteen adult domestic cats (six longhair cats [Persians] and eight shorthair cats [domestic shorthairs]), with a mean ± SD age of 3.3 ± 1.38 years and a mean ± SD body weight of 4.5 ± 1.21 kg, were used to conduct the study. In total, seven females and seven males, all of which were spayed or castrated, respectively, were used. Each cat’s good health status was confirmed prior to beginning the study by veterinarians working at Irion Animal Hospital (Seoul, Republic of Korea).

Experimental design

The evaluation method of nutrient digestibility was divided into two types: (1) hair-included (HI) digestibility; and (2) hair-removed (HR) digestibility. The experimental period was 26 days, including an adaptation phase (days 0–16), followed immediately by a faecal collection phase (days 17–26). The faecal collection phase (days 17–26) was composed of two periods, one (days 17–21) for analysing HI samples and the other (days 22–26) for analysing HR samples.

Housing and management

Cats were housed individually in stainless steel cages (0.77 × 0.51 × 0.63 m) at the Irion Animal Hospital (445 Dosan-daero, Gangnam-gu, Seoul, Republic of Korea) in a light-controlled (14 h light, 10 h dark) room. The room was maintained at a constant temperature of 22–23°C. Within each cage, there was a shelf (0.51 × 0. 29 m) elevated (0.3 m) off the floor, a litter box (0.33 × 0.44 × 0.16 m) and water dishes secured to the cage door. All cats remained healthy throughout the study, based on a physical examination. Litter boxes were cleaned between 08:00 h and 09:00 h, and between 15:00 h and 16:00 h. Each day, food was weighed and divided into two equal proportions, placed in stainless steel bowls and left out at 09:00 h and 16:00 h. Bowls were removed before the next meal, and any remaining food was weighed and recorded. Water was provided ad libitum.

Diets

The cats were offered individually calculated amounts of dry extruded diet (chicken-based grain-free commercial feed with 2% refined cellulose and 3% sugar beet pulp for hairball prevention, provided by Daehan Feed). Initially, the amount was defined according to the energy requirements for adult cat maintenance, estimated as ME = 100 × BW^0.67, where ME is metabolisable energy and BW is body weight. ⁸ Food was provided twice daily (09:00 h and 16:00 h). Water was provided ad libitum. Cats were adapted to the steel cage and diet for 16 days before a 10 day collection period. During the collection period, food offered, food refused and faecal output were measured daily and used for analysis of digestibility. All food consumption was measured with electronic scales (WZ-3A; CAS), and were accurate to within 0.1 g. The analysed chemical composition of the experimental diet is presented in Table 1.

Table 1

Analysed nutrition values of experimental diet

Criteria	Experimental diet (%)
Moisture	6.47
Crude protein	33.01
Crude ash	7.56
Crude fat	15.40
Calcium	1.33
Total phosphorus	0.89
Crude fibre	3.59
Acid detergent fibre	11.52
Neutral detergent fibre	33.98
Total amino acid	21.39
Aspartic acid	1.99
Threonine	0.99
Serine	0.96
Glutamic acid	2.94
Glycine	1.97
Alanine	1.56
Valine	0.85
Isoleucine	0.71
Leucine	1.62
Tyrosine	0.69
Phenylalanine	0.83
Lysine	1.68
Histidine	0.58
Arginine	1.54
Proline	1.37
Methionine	0.82
Cysteine	0.29

Feed ingredients: fresh salmon, fresh chicken, chicken meat powder, tapioca, potato powder, cellulose powder, linseed, chicken fat, dried yeast, salt, chicken hydrolysate powder, taurine, vitamin C, vitamin E, methionine, lysine, choline chloride, organic mineral, vitamin premix, mineral premix, yucca extract, grape seed extract (natural antioxidant), probiotics, enzymes, FOS (probiotics), herbs

Sample collection

On the first day of faecal collection, all faeces were removed from the cages and discarded before 09:00 h. Faecal output was collected at this time for the next 10 days (5 days for HR samples and 5 days for HI samples). During the collection phase, total faecal outputs were collected. To ensure complete collection, cats were acclimated to a multi-tier litter box with no litter, which allowed urine to flow to the bottom and faeces to remain on the top. Fresh faecal samples (within 15 mins of defaecation) were obtained during the collection phase. Fresh faecal samples were weighed and stored at −20°C until further analysis. Total faeces were collected, composited, dried at 55°C in a drying oven (AMP Daw Model 18; Daihan Scientific) and ground through a 1 mm screen (Wiley Mill Intermediate; Thomas Scientific) for HI samples.

In our attempt to compare the apparent digestibility of nutrients in domestic cats using HI and HR samples, we were unable to find published studies that removed hair from cat faeces. Thus, we developed the following protocol based on our observations of cat faecal traits. For collected HI samples, we collected fresh total faecal output and dried it at 55°C in a drying oven (AMP Daw Model 18; Daihan Scientific). For HR samples, we removed all the hair using pincettes and then ground the faeces through a 1 mm screen (Wiley Mill Intermediate; Thomas Scientific).

Hairball (trichobezoar) quantification in cat faeces

Faecal hair excretion was quantified according to the method of Loureiro et al. ¹ Stored, frozen faecal samples were gently washed with tap water over a sieve with a 0.8 mm screen size until all faecal material was removed and only hair remained. The remaining hair was collected and dried in a forced air oven at 55°C for 24 h (AMP Daw Model 18; Daihan Scientific) and washed in a 1:1 (v/v) solution of diethyl ether and petroleum diethyl ether until all foreign materials were removed from the sample. The isolated hair samples were weighed and classified according to the length of the cats’ hair: from either shorthair cats or longhair cats. The samples are presented in Figure 1, and pooled hairball samples for chemical analysis are presented in Figure 2. The analysed values of the chemical composition of cats’ hairballs isolated from faeces were as follows: moisture 5.67%, CP 58.93%, crude ash 4.66%, crude fat 4.77%, calcium 1.2% and total phosphorus 0.69%. The average weight ratio of dried faeces samples and the hair isolated from faeces are presented in Table 2.

Figure 1

Hairballs isolated from faeces

Figure 2

Pooled hairball samples

Table 2

Average weight ratio of dried faecal samples and the hair isolated from faeces (total from 5 days)

Criteria*	Dried faeces (g)	Hair isolated from faeces (g)	Ratio (%)
Longhair cats	59.18	5.62	9.49
Shorthair cats	65.82	4.84	7.35

*

A total of 14 domestic cats with a mean ± SD age of 3.3 ± 1.38 years

Chemical analysis

Experimental diet, hairball samples and excreta samples (HI and HR) were analysed for DM (procedure 930.15), ⁹ crude ash (procedure 942.05) ⁹ and ether extract (procedure 920.39), ⁹ and nitrogen, using the Kjeldahl procedure with Kjeltec (Kjeltec 2200; Foss Tecator). Experimental diet and excreta samples were analysed for CP content (nitrogen × 6.25; procedure 988.05), ⁹ and hairball samples also were analysed for CP content (nitrogen × 5.78). ⁷ The experimental diet and faecal samples were analysed for amino acid composition by using a 2-ninhydrin procedure with Hitach L-8900 (Beckman Instruments). Calcium and total phosphorus of samples were analysed by ICP-OES (Icap-7400 Duo; Thermo Scientific). The neutral detergent fibre (NDF) and acid detergent fibre (ADF) of samples were analysed by a Fiber Analyzer A2000 (ANKOM A2000; ANKOM Technology).

Statistical analysis

The experimental data was analysed using the Student’s t-test procedure of SAS, ¹⁰ and a main effect in the statistical model was the length of the cat’s hair. Individual cats were used as a unit to analyse nutrient digestibility. Differences were determined using Fisher’s protected least significant difference. A probability of P <0.05 was accepted as statistically significant and P <0.01 was considered highly significant. The pooled SEM was determined according to the Student’s t-test procedure of SAS.

Results and discussion

HI vs HR samples in longhair cats

The apparent nutrient digestibility and apparent amino acid digestibility in longhair cats using HI and HR samples are presented in Tables 3 and 4, respectively. There were no significant differences in nutrient digestibility of crude fat, crude ash, ADF, calcium and total phosphorus between the two treatments in longhair cats. However, the digestibility of DM, crude protein and NDF in longhair cats was underestimated when calculated using HI samples by about 8% (P = 0.02), 9% (P = 0.04) and 14% (P = 0.04), respectively.

Table 3

Apparent nutrient digestibility using hair-included faeces and hair-removed faeces in longhair cats*

Criteria	Longhair cats*		SEM	P value
	Hair included	Hair removed
Nutrient digestibility (%)
Dry matter	72.04	80.10	1.830	0.02
Crude protein	73.37	82.35	2.080	0.04
Crude ash	27.67	40.84	4.167	0.12
Crude fat	93.44	95.28	0.676	0.18
ADF	55.63	71.50	4.126	0.07
NDF	65.93	80.77	3.547	0.04
Calcium	3.05	14.60	4.967	0.23
Total phosphorus	14.29	28.20	4.712	0.15

*

A total of six longhair domestic cats

ADF = acid detergent fibre; NDF = neutral detergent fibre

Table 4

Apparent amino acid digestibility using hair-included faeces and hair-removed faeces in longhair cats*

Criteria	Longhair cats*		SEM	P value
	Hair included	Hair removed
Nutrient digestibility (%)
Total amino acid	76.53	85.65	2.283	0.04
Aspartate	70.65	82.11	2.781	0.03
Threonine	72.53	83.49	2.749	0.04
Serine	72.90	84.85	2.748	0.03
Glutamic acid	76.87	85.49	2.183	0.04
Glycine	82.87	90.04	1.615	0.02
Alanine	78.64	86.75	2.003	0.04
Leucine	76.11	85.14	2.464	0.06
Arginine	85.25	91.44	1.730	0.07
Cysteine	42.24	75.40	7.122	0.02

*

A total of six domestic longhair cats

The average weight ratio of dried faecal samples and the hair isolated from faeces (total over 5 days) of longhair cats was 9.49% (Table 3), which is higher than that of shorthair cats (7.35%). As mentioned above, because of the moisture value (5.67%) of the hairballs, which was included in the faeces, the digestibility of DM of HI faeces was underestimated. The analysed CP value of hairballs isolated from faeces was 58.93%. According to Hendriks et al, ⁷ the CP content of cat hair was 62.15%. The digestibility of CP in HR faeces was higher than in HI faeces. According to Beynen et al, ¹¹ feeding of a diet with added cellulose resulted in a statistically significant decrease in the frequency of hairball vomiting. Fibres may cause greater peristaltic stimulation, increasing the propulsion of hair through the gut, but further research is needed to validate this mechanism. ¹ In the present study, we used an experimental diet with 2% refined cellulose and 3% sugar beet pulp for hairball prevention. Cellulose is a NDF and sugar beet pulp is composed of 36.25% NDF and 21.58% ADF (analysed value). Therefore, NDF digestibility would have been affected by the presence of hair in faecal samples, but further research is needed to validate this result.

The apparent amino acid digestibility in HR faeces was higher than in HI faeces for total amino acids, aspartate, threonine, serine, glutamic acid, glycine, alanine and cysteine: about 9% (P = 0.04), 12% (P = 0.03), 11% (P = 0.04), 12% (P = 0.03), 8% (P = 0.04), 7% (P = 0.02), 8% (P = 0.04) and 33% (P = 0.02), respectively. According to Hendriks et al, ⁷ cat hair was shown to consist mainly of protein and amino acids. In the present study, the digestibility of amino acids was revealed to be underestimated by about 7–33% in longhair cats, if we use the conventional apparent digestibility method, which uses HI faecal samples to calculate the cats’ nutrient digestibility.

HI faeces vs HR faeces in shorthair cats

The apparent nutrient digestibility and apparent amino acid digestibility of shorthair cats using HI faeces and HR faeces are shown in Tables 5 and 6, respectively. The digestibility of DM, CP and crude ash when using HR samples for calculation were higher than using HI samples in shorthair cats: about 4% (P = 0.01), 5% (P = 0.02) and 15% (P <0.01), respectively. It can be assumed that the digestibility of DM, CP and crude ash of shorthair cats were underestimated by about 4%, 5% and 15%, respectively, when calculated using HI faeces.

Table 5

Apparent nutrient digestibility using hair-included faeces and hair-removed faeces in shorthair cats*

Criteria	Shorthair cats*		SEM	P value
	Hair included	Hair removed
Nutrient digestibility (%)
Dry matter	75.86	80.25	0.954	0.01
Crude protein	77.00	82.33	1.206	0.02
Crude ash	19.56	35.33	3.192	<0.01
Crude fat	95.32	95.98	0.393	0.42
ADF	59.98	68.02	2.455	0.10
NDF	71.49	76.50	1.419	0.08
Calcium	0.12	6.44	3.588	0.40
Total phosphorus	14.89	21.84	3.320	0.31

*

A total of eight domestic shorthair cats

ADF = acid detergent fibre; NDF = neutral detergent fibre

Table 6

Apparent amino acid digestibility using hair-included faeces and hair-removed faeces in shorthair cats*

Criteria	Shorthair cats*		SEM	P value
	Hair included	Hair removed
Nutrient digestibility (%)
Total amino acid	78.72	79.32	1.099	0.80
Aspartic acid	73.19	74.19	1.311	0.72
Threonine	74.96	75.71	1.321	0.79
Serine	76.07	78.07	1.235	0.44
Glutamic acid	78.88	79.20	1.085	0.89
Glycine	84.61	85.49	0.710	0.55
Alanine	80.22	80.93	0.964	0.73
Leucine	77.77	77.90	1.254	0.96
Arginine	86.04	86.27	0.855	0.90
Cysteine	57.82	67.92	2.730	0.06

*

A total of eight domestic shorthair cats

There were no significant differences between the two treatments in amino acid digestibility in shorthair cats. According to the results shown in Table 2, the average weight ratio of dried faecal samples and the hair isolated from faeces (total over 5 days) of shorthair cats was 7.35%, which is lower than that of longhair cats (9.69%). Because there was less hair in the faecal samples from shorthair cats than in those from longhair cats, the presence of hairballs in the faeces did not show a significant effect on amino acid digestibility.

Shorthair cats vs longhair cats using HI faeces

Comparison of apparent nutrient digestibility and apparent amino acid digestibility of longhair and shorthair cats using HI faeces are shown in Tables 7 and Table 8, respectively. There were no significant differences between the two treatments with regard to nutrient digestibility and amino acid digestibility when using HI faeces. Even though the length of hair was different, both types of experimental cats were domestic cats, and the nutrient digestibility did not show a significant difference when using the conventional digestibility trial.

Table 7

Comparison of apparent nutrient digestibility of longhair cats and shorthair cats using hair-included faeces*

Criteria	Hair-included faeces		SEM	P value
	Longhair cats	Shorthair cats
Nutrient digestibility (%)
Dry matter	72.03	75.86	1.263	0.14
Crude protein	73.37	77.00	1.539	0.26
Crude ash	24.86	20.55	3.207	0.53
Crude fat	93.44	95.32	0.623	0.14
ADF	55.63	59.98	3.727	0.58
NDF	65.93	71.49	3.857	0.35
Calcium	0.43	2.54	3.846	0.72
Total phosphorus	14.29	14.89	4.018	0.95

*

A total of 14 domestic cats with a mean ± SD age of 3.3 ± 1.38 years

ADF = acid detergent fibre; NDF = neutral detergent fibre

Table 8

Comparison of amino acid digestibility of longhair cats and shorthair cats using hair-included faeces*

Criteria	Hair-included faeces		SEM	P value
	Longhair cats	Shorthair cats
Nutrient digestibility (%)
Total amino acid	76.53	78.72	1.616	0.58
Aspartic acid	70.65	73.19	1.914	0.58
Threonine	72.53	74.96	1.950	0.56
Serine	72.90	76.07	1.939	0.44
Glutamic acid	76.87	78.88	1.539	0.59
Glycine	82.87	84.61	1.066	0.44
Alanine	78.64	80.22	1.390	0.64
Leucine	76.11	77.77	1.815	0.67
Arginine	85.25	86.04	1.304	0.78
Cysteine	42.24	57.82	5.113	0.20

*

A total of 14 domestic cats with a mean ± SD age of 3.3 ± 1.38 years

Shorthair cats vs longhair cats using HR faeces

Comparison of apparent nutrient digestibility and apparent amino acid digestibility of longhair cats and shorthair cats using HR faeces are shown in Tables 9 and 10, respectively. There were no significant differences between the two treatments with regard to nutrient digestibility of DM, CP, crude fat, crude ash, crude fat, ADF, calcium and total phosphorus. However, NDF digestibility in longhair cats was 4% higher than that of shorthair cats (P = 0.03).

As mentioned above, more hair was found in the faeces of longhair cats than of shorthair cats; this suggests that the removal method of hair in the faeces samples had a more significant influence on the apparent digestibility value in longhair cats than in shorthair cats. As Lourciro et al reported, ¹ fibres helped the hair to be excreted with the faeces. Also, in the present study, using an experimental diet with 2% refined cellulose and 3% sugar beet pulp for hairball prevention, NDF digestibility was affected by the presence of hair in faecal samples. The NDF digestibility in longhair cats increased more than that of shorthair cats when hair in the faeces was eliminated before calculating the apparent digestibility. The reason for this is that the hair in the faeces from the longhair cats was easy to separate cleanly because of its thread-like appearance in faeces. However, hair in the faeces of the shorthair cats existed as small knots, making it difficult to separate hair and faeces completely.

Table 9

Comparison of apparent nutrient digestibility of longhair and shorthair cats using hair-removed faeces*

Criteria	Hair-removed faeces		SEM	P value
	Longhair cats	Shorthair cats
Nutrient digestibility (%)
Dry matter	80.10	80.25	0.773	0.93
Crude protein	82.35	82.33	0.798	0.99
Crude ash	39.05	35.90	2.563	0.57
Crude fat	95.28	95.98	0.397	0.41
ADF	71.50	68.02	1.377	0.22
NDF	80.77	76.50	1.028	0.03
Calcium	13.08	7.02	4.132	0.49
Total phosphorus	28.20	21.84	3.186	0.35

*

A total of 14 domestic cats with a mean ± SD age of 3.3 ± 1.38 years

ADF = acid detergent fibre; NDF = neutral detergent fibre

Table 10

Comparison of amino acid digestibility of longhair and shorthair cats using hair-removed faeces*

Criteria	Hair-removed faeces		SEM	P value
	Longhair cats	Shorthair cats
Nutrient digestibility (%)
Total amino acid	85.65	79.32	1.492	0.03
Aspartate	82.11	74.19	1.824	0.02
Threonine	83.49	75.71	1.799	0.03
Serine	84.85	78.07	1.529	0.02
Glutamic acid	85.49	79.20	1.495	0.03
Glycine	90.04	85.49	1.000	0.02
Alanine	86.75	80.93	1.340	0.02
Leucine	85.14	77.90	1.697	0.03
Arginine	91.44	86.27	1.147	0.02
Cysteine	75.40	67.92	2.397	0.13

*

A total of 14 domestic cats with a mean ± SD age of 3.3 ± 1.38 years

The amino acid digestibility when using HR faeces for total amino acid, aspartate, threonine, serine, glutamic acid, glycine, alanine, leucine and arginine in longhair cats was higher than that of shorthair cats: 6% (P = 0.03), 8% (P = 0.02), 8% (P = 0.03), 7% (P = 0.02), 6% (P = 0.03), 5% (P = 0.02), 6% (P = 0.02), 7% (P = 0.03) and 5% (P = 0.02), respectively. As mentioned above, the average weight ratio of dried faecal samples and the hair isolated from faeces of longhair cats were higher than those of shorthair cats (Table 2). According to Hendriks et al, ⁷ the total amino acid composition of cat hair protein was 58.72%, whereas the average value of total amino acid composition of cat faeces was 19.82% in this study. Because of the difference of the distribution ratio of amino acid in faeces and hair, and the hair content in faecal samples, along with whether hair was removed or not, longhair cats showed higher amino acid digestibility than shorthair cats when using HR faeces.

Conclusions

The nutrient digestibility between longhair and shorthair cats showed no difference when using HI faeces. However, when using HR faeces, the NDF and amino acid digestibility in longhair cats were higher than in shorthair cats by about 4–8%. Therefore, calculating the apparent nutrient digestibility with the removal of hair in faecal samples was considered a more precise method in domestic cats than analysis of nutrient digestibility with the total collection method.