Previous Page Table of Contents Next Page


Growth and partition of fat depots in male British Saanen goats

L.A. Mtenga,1 E. Owen,2 V.R.M. Muhikambele,1 G.C. Kifaro,1 D.S.C. Sendalo,1
N.F. Massawe,1 S.M. Kiango1 and D.R. Nkungu1

1 Department of Animal Science and Production, Sokoine University of Agriculture
P. O. Box 3004, Morogoro, Tanzania
2 University of Reading, Department of Agriculture, Earley Gate
P.O. Box 236, Reading RG6 2AT Berkshire, UK

Abstract
Introduction
Materials and methods
Results
Discussion
Conclusion
References

Abstract

Thirty-four male British Saanen goats were reared on milk substitutes and then given a barley-based concentrate diet ad libitum. They were slaughtered serially at birth (3.5 kg), weaning (9.5 kg), 24.5, 36.5, 48.5 and 72.5 kg live weight. Weights of fat depots were recorded. With the exception of channel fat, all fat depots increased significantly (P<0.001) with increasing slaughter weight. Growth coefficients were greater than 1 (P<0.001), highest for subcutaneous fat (1.887), followed by gut fat (1.802), dissected fat (1.687), intermuscular fats (1.619) and lowest for channel fat (1.127). Relative to total fat, greatest change in proportion of fat occurred between birth and 24.5 kg of live weight. There was little consistent change in proportion of subcutaneous fat relative to change in total body fat.

Introduction

Fat growth and development in farm animals is of importance from several points of view. Firstly, as a reserve of energy, fat can determine the survival of the animal in periods of food scarcity. Secondly, as a major carcass tissue, it may affect the complex industry of meat production, including feeding, deciding on the optimum slaughter weight, and grading of the carcass and meat quality. In the latter context, some fat depots are more valuable than others, e.g. subcutaneous and intermuscular fat are more desirable than kidney and gut fats. Within fat depots in the carcass, fat in the expensive joints, provided it is not in excess, is more valuable than fat in less expensive joints. Thirdly, Adler and Wertherimer (1968) discounted statements that fat is a passive organ and pointed out that lipogenesis occurs mainly in the adipose tissues. Fourthly, the rigid relationship between body weight, and muscle and bone demonstrated by Butterfield (1974) and Berg and Butterfield (1976), implies that the use of genetic and environmental factors in manipulating body composition is likely to have greater effects on the proportion of fat than on other carcass tissues.

Defining the pattern of fat growth in breeds of goats is therefore essential to an understanding of body and carcass composition problems associated with production and marketing. Goat carcass value is influenced markedly by both amount and distribution of fatty tissue depots. In cattle, several studies have shown that the partitioning of fat among the depots is influenced by slaughter weights (Berg and Butterfield 1976). Growth and partition of fat depots in goat carcasses has not been studied thoroughly and results from controlled experiments are particularly scarce. This study attempts to define growth and distribution of fat depots in male British Saanen goats slaughtered at different weights.

Materials and methods

A total of 34 male Saanen goats were purchased at birth and serially slaughtered at birth (3.5 kg), weaning (9.5 kg), 24.5, 36.5, 49.5 and 72.5 kg live weights at Reading University farm. The animals were artificially reared on Denkavit Lamb ewe milk replacer until weaning at 35 days of age. The milk replacer contained (g/kg DM) 245 crude protein, 200 oil, 2.5 fibre, 30,000 IU vitamin A, 14,000 IU vitamin D3 and 30 IU vitamin E. After weaning, they were fed ad libitum fattening barley-based concentrate diet consisting of (g/kg DM) barley (750), flaked maize (50), soyabean meal (100), fish meal (50), molasses (30), limestone (15), salt (4) and mineral supplements (1). The diet contained 228 g/kg DM crude protein and 17.4 MJ/kg DM of gross energy.

The animals were slaughtered and kidney fat, gut fat and channel fat (fat found around pelvis bones) from the whole animal were separated and weighed. Subcutaneous and intermuscular fat were obtained by dissecting both the right and left sides of the carcass. Dissected fat weight was obtained by summing up weights of subcutaneous and intermuscular fat.

Mean weights of the various fat depots were expressed as a percentage of empty body weight (EBW = live weight - gutfill weight) and analysed. Fat depots were also expressed as a percentage of total fat weight. Data for each fat depot were transformed to logarithms to establish part and whole allometric relationships of the type Y = axb where Y is the fat depot weight, x is EBW, and b is the growth coefficient describing proportionate growth of fat in a depot to EBW.

Results

Mean weights and mean weights expressed as percentages of empty body weight of various fat depots at six grouped slaughter weights are shown in Table 1. With the exception of channel fat, weight at slaughter had a significant (P<0.001) effect on the proportion of all fat depots. Both the absolute weight and the proportions of these fat depots increased with increase in slaughter weight. However, the increase in proportions was small in the liveweight range of 24.5 to 49.5 kg.

In the allometric equations for growth of fat depots relative to empty body weight (Table 2), the growth coefficients were significantly greater than 1.00, indicating that, as empty body weight increased, the proportion of these fat depots increased, confirming the results by direct comparison of percentages in Table 1.

More of the variation in fat depot weights could be accounted for by variation in empty body weight using allometric equations. The largest growth coefficient was for subcutaneous fat, showing it to be the latest developing depot, while kidney and channel fat were the earlier developing depots.

The relationship between the various fat depots was also studied by expressing weights of fat as a percentage of total body fat (Table 3). Total body fat proportion progressively increased with increasing empty body weight (Table 3). The proportion of intermuscular fat relative to body fat showed little consistent change with increase in total fat weight. At birth, most of the fat was accumulated in three major depots: gut, kidney and intermuscular (Table 1). With increase in total body fat, the most notable change was the increase in proportion of subcutaneous fat (Table 3). The increase was accompanied by a decrease in the proportion of kidney fat. Table 3 also indicates that the major changes in proportions of fat depots occurred early in life, i.e. before total body fat exceeded 2.4 kg (corresponding to 24.5 kg live weight).

Table 1. Mean weights (g) and mean weights expressed as percentages (%) of empty body weight (in brackets) of various fat depots.1,2


Component

Slaughter stage

Birth

Weaning

24.5 kg

36.5 kg

49.5 kg

72.5 kg

SED

No. of animals

4

4

8

8

8

2


Gut fat

27 (0.82)

157 (1-75)

901 (4.36)

1680 (5.24)

2695 (6.28)

6268 (9.47)

0.40***

Total channel fat

8(0.26)

22(0.25)

69(0-33)

116(0.36)

138(0.32)

256(0.39)

0.04

Total kidney fat

27(0.82)

99(1.11)

289(1.40)

705(2.19)

1039(2.43)

2651(3.99)

0.06***

Subcutaneous fat

6(0.21)

133(1-49)

433(2.11)

796(2.49)

953 (2.22)

3157(4.78)

0.37***

Intermuscular fat

27 (0.82)

163 (1.81)

657 (3.20)

1138 (3.55)

1758 (4.11)

3623 (5.47)

0.27***

Dissected fat

33 (1.03)

296 (3.30)

1090 (5.31)

1934 (6.03)

2706 (6.33)

6780 (10.25)

0.50***

1 For ease of tabulation, standard deviations and coefficients of variation are excluded.
2 SED = Average standard error Of difference (percentage data only).
*** = significant at P<0.001.

Table 2. Allometric regression equations showing growth of fat depots relative to empty body weight.1

Component

b log x + a

SED

R2

Gut fat

1.802x*** - 11.262

0.036

98.77

Total channel fat

1.127x* - 7.044

0.057

92.32

Total kidney fat

1.455x*** - 8.813

0.055

95.61

Subcutaneous fat

1.887x*** - 12.956

0.103

91.26

Intermuscular fat

1.619x*** - 9.734

0.039

98.14

Dissected fat

1.687x*** - 9.930

0.053

96.93

1 *, **, *** indicate that the b value is significantly different from 1.00 at P<0.05, P<0.01, or P<0.001, respectively.

Discussion

The present findings agree with the literature on goats (Wilson 1958; Ladipo 1973), sheep (Hammond 1932; Gaili 1976), cattle (Jones 1976; Berg et al 1978) and pigs (Richmond and Berg 1972) in that most of the fat depots increased in weight at a faster rate than body weight. The results in the present study indicate that subcutaneous fat grows faster in post-natal life than all other fat depots, a finding similar to those of Palsson and Verges (1952) and Gaili (1976) using lambs. Kirton et al (1972) also noted that, apart from omental fat, subcutaneous fat was the last fat depot to mature. Whilst the order of fat depot development was similar to those of cattle (Williams 1978), it was slightly different from that given by Palsson and Verges (1952), who described gut fat as slower growing than intermuscular fat. Kirton et al (1972) also found channel and intermuscular fat in male lambs to be early maturing.

The present results also contrast sharply with those reported by Ladipo (1973), using a mixture of male dairy goat breeds slaughtered between 22 and 54 kg live weight. He reported fat depots to increase in the following order of increasing rate: subcutaneous, gut (caul and mesenteric) fat, intermuscular fat, and finally visceral fat (kidney, channel and heart fat). Per unit of empty body weight, the growth rates of intermuscular and visceral fat depots in Ladipo's study were twice that of subcutaneous fat. The fact that Ladipo (1973) used a mixture of breeds merits interpretation of the results with caution, because breed differences have been observed in fat growth rates and distribution in farm animals (Berg and Butterfield 1976).

Relative to total body fat, gut fat was the largest contributor to the total fat reaching a peak at about 2.4 kg total body fat, corresponding to 24.5 kg live weight (Table 3). This fat depot, together with that of the kidney and channel fat, is usually trimmed off the carcass in lambs and cattle and sold as cooking fat. The ratio of dissected carcass fat (subcutaneous plus intermuscular fat) to other fat depots of the body may, therefore, be a more important criterion in determining meat quality in goats, and was 1.87, 1.06, 0.87, 0.77 and 0.74 at birth (3.5 kg), weaning (9.5 kg), 24.5, 36.5, 49.5 and 72.5 kg live weight, respectively. Table 3 demonstrates that the greatest change in proportions of the various fat depots occurred between birth and 24.5 kg live weight in male Saanen goats. This period may, therefore, be critical in the study of genetic and environmental factors affecting growth and distribution of fat depots.

Table 3. Partition of body fat depots in male goats slaughtered at different live weights.

Slaughter weight group

Number of animals

Total body fat (g)

Total body fat as % of EBW

Fat depots as % of total

Intermuscular

Subcutaneous

Kidney

Channel

Gut

Birth (3.5 kg)

4

95

2.93

27.65

7.00

28.33

8.87

27.99

Weaning (9.5 kg)

4

575

6.41

28.24

23.24

17.32

2.90

28.30

24.5 kg

8

2350

11.40

27.98

18.51

12.28

2.98

38.25

36.5 kg

8

4435

13.82

25.67

17.95

15.85

2.61

37.92

49.5 kg

8

6583

15.35

26.71

14.46

15.83

2.08

40.91

72.5 kg

2

1599

24.10

22.70

19.83

16.56

1.62

39.29

Subcutaneous fat made the least contribution at birth, but rose sharply to its mature proportion at weaning. The conclusion by Ladipo (1973) that proportions of intermuscular fat decreased with increase in carcass fat, can be interpreted to correspond to the 24.5 to 72.5 kg liveweight interval in the present study.

Conclusion

The present study shows that the various fat depots in goats grow faster relative to empty body weight. They also grow at different rates relative to each other. There is, however, need for further studies taking into account breed and nutrition influences in fat growth and distribution.

References

Adler J.H. and Wertheimer H.E. 1974. Aspects of fat deposition and mobilization in adipose tissues. In: Lodge G.A. and Lamming G.E. (eds), Growth and Development of Mammals. Butterworths, London, UK. pp. 51-65.

Berg R.T. and Butterfield R.M. 1976. New Concepts of Cattle Growth. University of Sydney Press, Sydney, Australia. 240 pp.

Berg R.T., Anderson B.B. and Liboriussen T. 1978. Growth of bovine tissues. 3. Genetic influences on patterns of fat growth and distribution in young bulls. Animal Production 27:71-77.

Butterfield R.M. 1974. Beef Carcass Composition. Australian Meat Research Council Review 18. Sydney, Australia. pp. 1-30.

Gaili E.S.E. 1976. Body composition of male Sudan desert goats. World Review of Animal Production 12:83-87.

Hammond J. 1932. Growth and Development of Mutton Qualities in Sheep. Oliver and Boyd, London, UK.

Jones S.D.M. 1976. Aspects of Beef Production from British Friesian Bulls (a) Genetic Variation and (b) Target Growth Rates during the Finishing Period of grass/cereal Systems. PhD thesis, University of Reading, Reading, UK. 475 pp.

Kirton A.H., Fourie P.D. and Jury K.E. 1972. Growth and development of sheep. New Zealand Journal of Agricultural Research 15:214-227.

Ladipo J.K. 1973. Body Composition of Male Goats and Characterization of their Depot Fats. PhD thesis, Cornell University, Ithaca, New York, USA. 343 pp.

Palsson H. and Verges J.B. 1952. Effects of plane of nutrition on growth and development of the carcass quality in lambs. Journal of Agricultural Science (Cambrige) 42:1-149.

Richmond R.J. and Berg R.T. 1972. Bovine growth and distribution in swine as influenced by live weight, breed, sex and ration. Canadian Journal of Animal Science 52:47-56.

Williams D.R. 1978. Partition and distribution of fatty tissues. In: Boer H.D. and Martin J. (eds), Patterns of Growth and Development in Cattle. Martinus Nijhoff, The Hague, The Netherlands. pp. 219-232.

Wilson P.N. 1958. The effect of plane of nutrition on the growth and development of the East African Dwarf goats. Journal of Agricultural Science (Cambridge) 54:105-130.


Previous Page Top of Page Next Page