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THE ENERGY REQUIREMENTS OF ANGORA GOATS

M.J. HERSELMAN and W.A. SMITH1

Grootfontein College of Agriculture, Middelburg, CP.

1Department of Animal Science, University of Stellenbosch, Stellenbosch.

 

INTRODUCTION

The Angora goat is one of the most efficient farm animals in respect of the production of fibre per unit of body mass and is therefore maintained primarily for this production function. Meat characteristics and growth per-formance are generally not considered to be priorities in Angora goat farming. Favourable mohair prices in the past have also lead to a situation where high reproduction rates and low mortality rates were neglected, because most of the income under these circumstances was generated from hair production by the ewe and wether component of the flock. However, during the past four years this situation has changed drastically and at present the price of kids' hair is about four times that of adult (strong) hair. This situation has far reaching effects in the mohair industry because a relatively large proportion of the income is now generated by the kid and young goat components of the flocks (Laubscher, Terblanche & Herselman, 1989). Characteristic problems in the An-gora goat, such as losses during cold spells, high abortion rates, low reproduction rates and retarded growth in kids, have suddenly become major financial stumbling blocks in the mohair industry. All factors influencing the kid and young goat component of a flock are therefore of great financial consequence.

Investigations of several problems of Angora goat farming revealed an energy deficiency as the common cause of most of the above-mentioned problems. These findings lead to energy supplementation practices which are used extensively on the farm (Wentzel, Morgenthal, Van Niekerk & Roelofse, 1974; Wentzel, Le Roux & Botha, 1976; Wentzel, Viljoen & Botha, 1979; Wentzel, 1982; Wentzel, 1987). It has become apparent that the Angora goat is no longer well adapted to produce and survive in its historical habitat in the R.S.A. without suffi-cient supplementary feeding. The limited scale of these problems in other countries may suggest that a more robust animal with less mohair (Van Rensburg, 1971) could conceivably be better adapted to harsh environments (Van Rensburg, 1971).

This experiment was undertaken to determine the energy requirements for main-tenance, growth and hair production and to establish whether the high hair production function of these animals is not somehow linked to increased energy requirements. The NRC (1981) uses a value of 101.38 kcal ME/W0.75/day, derived from pooled experimental data with several types of goats (Angora excluded), as the energy requirement for the maintenance of goats. Although the NRC (1981) uses a 33% efficiency of ME utilization for mohair fibre production (±46 kJ/g fibre), these values have yet to be established.

 

EXPERIMENTAL PROCEDURES

Twenty-six South African Angora kids (5 months) were allocated randomly into two groups and fed different diets on an ad libitum basis for 28 weeks. The two diets are tabulated in Table 1.

 

TABLE 1 The composition of the two diets used in the growth trials

 

Diet 1

Diet 2

Maize meal

50.2%

27.8%

Fish meal

5.3%

2.7%

Voermol Super

18 8.6%

7.9%

Lucerne

34.4%

39.7%

Slaked lime

1.4%

1.2%

Bone meal

 

0.6%

Wheat straw

 

19.9%

NaCl

0.2%

0.2%

ME (kJ/kg)

11.61

8.96

Crude protein (CP)

18.07%

13.66%

ME/CP

1.556

1.525

Ca

0.91%

0.89%

P

0.35%

0.34%

 

Feed intake and body mass were recorded weekly, while hair production was measured every 8 weeks as described by Herselman (1990). Body protein and body fat were estimated from body mass (W) by means of allometric relationships es-tablished by Herselman (1990). Energy retention was subsequently estimated from body protein and body fat. Allometric relationships between cumulative metabolizable energy intake (ME intake) and body mass (W), body protein, body fat, hair production and energy retention were fitted on the data of each of the 26 Angora kids. Thereafter, these relationships were used to calculate the following data for each animal at 2 kg intervals of body mass:

Daily ME intake (kJ/day)

Daily gain with hair growth excluded (ADGhf) (g/day)

Daily gain with hair growth included (ADGt) (g/day)

Daily hair production (HP) (g/day)

Daily energy retention (ERhf) (kJ/day)

 

These values were also calculated per unit of metabolic mass (W0.75). In this way 249 records, each containing all the above-mentioned variables, were ob-tained as a database for the estimation of energy requirements by means of simple and multiple regression methods. A second database (94 records), con-taining average ME intake and production data (ADGhf and hair growth) for each individual animal in this experiment, as well as similar data obtained from an unpublished experiment carried out in 1969 at the Grootfontein College of Agriculture (Anon. 1969), was also used. Because all goats in the present ex-periment were kept on a relatively high plane of nutrition and the mean values between animals differed negligably, inaccurate extrapolation of the regres-sion to the maintenance level of intake can be expected. However, very low intakes were recorded for goats in the 1969 experiment. Far more accurate ex-trapolations were obtained where these data were used in conjunction with data of the present experiment.

 

RESULTS AND DISCUSSION

It was assumed that energy required for hair growth at the maintenance level of ME intake is part of the maintenance energy requirements. For this purpose several linear and multiple regressions were fitted on the data to obtain the maintenance energy requirement of 434.9 kJ/W0.75/day. Although much lower and higher maintenance requirements for several types of goats are reported, this value compares well with mean values of 424.3 kJME/W0.75/day (NRC, 1981) and 432.83 kJME/W0.75/day (Kearl, 1982) reported for all goats.

To estimate the energy cost of production (gain in body mass and hair production), an approach similar to that used by Garrett, Mayer & Lofgreen (1959) was used. In this case however single and multiple regression methods were used. The average energy required for gain (hair free) and hair production were 31.9 kJME/g and 136.8 kJME/g respectively. The energy cost of gain compares well with values of 28.0 kJME/g (Kearl, 1982) and 30.3 kJME/g (NRC, 1981) reported as means for all goats. The energy cost of hair production is however much higher than the value of 45.8 kJME/g proposed by the NRC (1981), which has been calculated empirically with the assumption that energy for hair production is utilized with an efficiency of 33%.

The findings of this study support the view that hair production tends to decrease the total efficiency of energy metabolism. This decrease in efficiency, as well as most of the specific problems related to the Angora goat, can possibly be the result of changes taking place in the hormonal regulation of the intermediary metabolism to provide more protein for keratin synthesis. Because energy utilization for protein synthesis is low (Webster, 1980), the increased keratin production may cause the energy metabolism to be less effi-cient.

The practical importance of energy requirements applies mostly to non-grazing systems such as feeding schemes in kraals to overcome serious droughts. Under such conditions a maintenance ration is usually fed just to keep animals alive. Because energy required for maintenance is dependent on body mass, it is advisable to allow animals to lose a considerable amount of weight, depend-ing on the initial condition of these animals. The maintenance requirements of Angora goats at different live weights are given in Table 2.

 

TABLE 2 Maintenance energy requirements of Angora goats

Mass

kg

ME

MJ/day

TDN

kg/day

Lucerne

kg/day

 Pellets

kg/day

Chocolate grain

kg/day

25

4.86

0.324

0.648

0.499

0.416

30

5.57

0.372

0.743

0.572

0.476

35

6.26

0.417

0.834

0.642

0.535

40

6.92

0.461

0.922

0.710

0.591

45

7.56

0.504

1.007

0.775

0.646

 

Lucerne ME = 7.5 MJ/kg

Pellets TDN = 65%

Chocolate grain ME = 11.7 MJ/kg

 

 

CONCLUSION

The energy requirements for maintenance (434.9 kJ/W0.75/day) and growth (31.9 kJ/g, hair excluded) of Angora goats do not differ significantly from those of other goats. Energy required for hair production (134.9 kJ/g) is however ap-proximately three times higher than the value reported by the NRC (1981). Fur-ther investigation in this regard may be necessary.

 

REFERENCES

GARRETT, W.N., MAYER, J.H. & LOFGREEN, G.P., 1959. The comparative energy re-quirements of sheep and cattle for maintenance and gain. J. Anim. Sci. 18, 528.

HERSELMAN, 1990. Die energiebehoeftes van Angorabokke. M.Sc. Thesis. Univer-sity of Stellenbosch, RSA.

KEARL, L.C., 1982. Nutrient Requirements of Ruminants in Developing Countries. Int. Feedstuffs Institute, Utah Agric. Exp. Sta., Utah State University, Logan, Utah 84322, USA.

LAUBSCHER,J., TERBLANCHE E. LE F. & HERSELMAN, M.J., 1989. Die invloed van kuddesamestelling op die winsgewendheid van Angorabokboerdery onder eksten-siewe weidingstoestande. S. Afr. J. Ext., 18, 28.

NATIONAL RESEARCH COUNCIL, 1981. Nutrient Requirements of Goats: Angora, Dairy and Meat Goats in Temperate and Tropical Countries. National Academy Press. Washington, D.C.

VAN RENSBURG, S.J., 1971. Reproductive physiology and endocrinology of normal and habitually aborting Angora goats. Onderstepoort J. Vet. Res. 38, 1.

WEBSTER, A.J.F., 1980. The energetic efficiency of growth. Livest. Prod. Sci. 7, 243.

WENTZEL, D., 1982. Non-infectious abortion in Angora goats. Proc. 3rd Int. Conf. Goats Tuscon, Arizona, USA.

WENTZEL, D., 1987. Effects of nutrition on reproduction in the Angora goat. Proc. IV Int. Conf. Goats Brazilia, Brazil, 1987 p 571.

WENTZEL, D., LE ROUX, MARITA, M. & BOTHA, L.J.J., 1976. Effect of the level of nutrition on blood glucose concentration and reproductive performance of preg-nant Angora goats. Agroanimalia 8, 59.

WENTZEL, D., MORGENTHAL, J.C., VAN NIEKERK, C.H. & ROELOFSE, C.S., 1974. The habitually aborting Angora doe: II. The effect of energy deficiency on the in-cidence of abortion. Agroanimalia 6, 129.

WENTZEL, D., VILJOEN, K.S. & BOTHA, L.J.J., 1979. Physiological and en-docrinological reactions to cold stress in the Angora goat. Agroanimalia 11, 19.

 

Published

Karoo Agric 4 (3), 18-20