The effect of methods of castration on live weight, dressed percentage and linear body measurements of indigenous Tswana goats raised under semi-intensive management in Southeast Botswana

Nsoso S J, Mannathoko G G, Tadubana T T and Malela L

Botswana College of Agriculture, Private Bag 0027, Gaborone, Botswana
Tel +267 3650158; Fax +267 3928753
SNSOSO@TEMO.BCA.BW

Abstract

The aims of this study were to investigate the effect of different methods of castration on body weight, linear body measurements and dressed percentage of indigenous Tswana goats raised under semi-intensive management over time. Thirty-two (32) male indigenous Tswana goats aged 4 months were randomly divided into four groups of eight, balancing for weight in summer. One group was randomly chosen to be a control i.e. not castrated and the other three randomly allocated to groups which were immediately castrated using burdizzo, rubber ring and short scrotum respectively. The initial average live weights were 12.50±1.69kg, 13.75±1.69kg, 12.25±1.69kg and 12.00±1.69kg for control, burdizzo, rubber ring and short scrotum castrates respectively. The goats were managed as a single mob together with a large group of females under semi-intensive system with regular supplementary feeding, adequate medical care and water was provided ad libitum. All the goats were weighed monthly.

At 12 months of age the short scrotum and control had the typical tainted smell, which would render the meat unsuitable for human consumption. At 14 months of age three goats were randomly selected from each group and slaughtered by exsanguinations, while the remaining goats were slaughtered at 22 months of age. Data with unequal subclasses were analysed using General Linear Model procedure, while data with equal sub-classes were analysed using ANOVA procedure in Statistical System Analysis. Live weight was not significantly affected by method of castration (P>0.05) at the same age and stage of development. Live weight increased steadily in all groups from around 12 kg to a maximum of approximately 29kg at 22 months of age. The dressed percentages were significantly higher in burdizzo (47.86±1.37 and 42.07±0.88%) and rubber ring (43.44±1.37 and 42.05±0.76%) than control (42.50±1.37 and 36.80±0.88%) and short scrotum (41.73±1.37 and 37.02±0.88%) at 14 and 22 months of age respectively. None of the linear measurements differed significantly at 14 months of age. However, at 22 months of age, height at withers was significantly higher in the burdizzo (61.00±1.26cm), short scrotum (59.23±1.26cm) and rubber ring (58.75±1.09cm) groups than the control group (53.16±1.26cm). Diagonal length also differed significantly between the burdizzo (54.50±1.59cm) and control (47.33±1.59cm) groups only.

Together the higher dressing percentage, and longer and deeper body linear measurements of the goats castrated using burdizzo suggests that farmers should use this method of castration.

Key words: Botswana, castration, dressing percentage, linear body measurements, live weight, Tswana goats

Introduction

The indigenous Tswana goats are an integral part of the smallholder farming system in Botswana. In particular a large number of the farming families in Botswana keep indigenous Tswana goats (Botswana Agricultural Census Report 1999). Goats play a vital role by providing milk and meat as a source of protein and are a major source of income especially for rural people. Goats also fulfil social functions e.g. they are slaughtered during marriages and funerals, and as a form of food security.

To realise the full potential of goat production, management of goats is very important. Management aspects include; nutrition, health, hoof trimming and castration. Castration involves cutting blood supply to the testis either by crushing the blood vessels, cutting, vaccinating and/or elevating temperature of the testes (Frandson and Spurgeon 1992). Several methods are used to castrate male goats, for example; burdizzo, elastrator or rubber ring, surgical and short scrotum. According to Devendra and McLeroy (1988) some advantages of castration are that:

• The meat, is not tainted especially if kids are slaughtered after more than four months of age
• Castrates have better quality meat than entire males
• Castrates grow relatively faster than entire males
• Males goats are sexually precocious with fertile mating being recorded at three months of age
• Castrates are easier to manage than entire males

The objectives of this study were to compare the performance of indigenous male Tswana goats castrated using three methods; burdizzo, rubber ring and short scrotum with a control i.e. uncastrated group in terms of live weight, body linear measurements and dressed percentage over time raised under semi-intensive management in southeast Botswana.

Materials and methods

Animals

Thirty-two (32) indigenous male Tswana goats aged four months were randomly, divided into four groups of eight balancing for weight. The initial average weights were 12.50±1.69kg, 13.75±1.69, 12.25±1.69 and 12.00±1.69 for the four groups. Group one was chosen as control i.e. entire males. The other three groups were immediately castrated using burdizzo, rubber ring and short scrotum methods respectively.

Management

The goats were subjected to semi-intensive management with regular supplementation and adequate medical care. All the experimental animals were managed as a single mob together with a large group of females. During the day the goats were let out to graze natural pasture from 08:00 - 17:00. They were kraaled overnight. The natural pasture is categorised as hard-veld. Water was provided twice daily, in the morning before the goats went out to graze and at kraaling time.

Measurements

Live weight was recorded after over night kraaling monthly. At 14 month of age three goats were randomly selected from each group, weighed just before slaughter, linear measurements i.e. diagonal length, neck length and height at withers were taken using venire calipers following standard definitions of these traits by Fisher and de Boer (1994). The goats were then slaughtered by exsanguinations and the carcass weighed. The dressing percentage was also calculated using standard definition of carcass weight of Fisher and de Boer (1994). The remaining animals were slaughtered at 22 months of age and the same linear measurements and dressing percent were recorded as at 14 months of age.

Statistical analysis

Data on live weight and all measurements at 22 months of age were analysed using General Linear Model procedure in Statistical Analysis System (SAS 1999-2000) and results separated using t-test. This is because the numbers of observations in each group were not equal, 1-2 animals died in each group. The results reported are least squares means. The body linear measurements and dressed percentage at 14 months of age were based on equal numbers of observations in each sub-class. These were analysed using Analysis of Variance in SAS (SAS 1999-2000) and results separated using Duncan multiple range t-test.

Results and discussion

Body weight

There was no significant difference (P>0.05) in live weight between the groups of the goats at the same age and stage of development. The live weights increased from approximately 12 kg at 4 months of age to nearly 29kg at 22 months of age (Figure 1).

These findings are similar to those of Chopra (1988), Phad et al (1995) and Singh et al (1996), where methods of castration did not have significant effect on the live weight of goats. The increase in live weight with time represents growth and development of farm animals as suggested by Butterfield (1988), where weight and other measurements increase with age.

There was a drop in live weight between 14 and 16 months of age (Figure 1). This period coincided with the onset of the 2002 drought, which negatively affected the performance of grazing animals in Botswana. Towards the end of the 15 month, the goats were supplementary fed and this was continued until the end of the experiment.

Towards the end of the experiment the burdizzo and short scrotum had slightly higher growth rates than rubber ring and control groups (Figure 1). The study of Owen et al (1977) on indigenous Tswana goats revealed a live weight of 19.23±1.14kg and 23.93±4.37kg for entire males and castrated males respectively at similar ages to goats of the present study. More recently Nsoso et al (2002) also reported significantly higher average weight in castrates (22.37±0.67 and 34.38±0.55kg) than entire males (14.37±0.76 and 31.22±1.27) at 0-12 and 13-24 months respectively. Together these studies show that castrated males had significantly higher weight gains than entire males. As suggested by Owen et al (1977), castration is a useful technique for increasing the rate of maturity of late maturing indigenous breeds and therefore farmers should take advantage of this.

Body linear measurements

At 14 months of age linear body measurements of indigenous Tswana goats were not significantly affected by method of castration, while at 22 months, burdizzo and short scrotum had significantly higher diagonal length and height at withers than control and rubber ring groups (Tables 1 and 2). These results are supported by the findings of Nsoso et al (2002), which showed that there were significant higher height at withers in castrates (56.54±0.88 and 65.32±0.72 cm) than entire males (49.15±1.00 and 62.27±1.66 cm) at 0-12 and 13-24 months respectively. In the latter study diagonal body length was also significantly higher in castrates (51.83±0.61 and 60.20±0.49 cm) than entire males (43.03±0.69 and 54.84±1.15 cm) at 0-12 and 13-24 months respectively. Together these results show that castrates develop longer and deeper bodies. The impact of these changes on the yield of meat should be investigated.

Dressed percentage

The dressing percentage was not significantly affected by method of castration at 14 months of age (Table 1). However, at 22 months of age, burdizzo and rubber ring castrates had significantly higher dressing percentages than control and short scrotum (Table 2). These results are in agreement with the findings by Singh et al (1996) on Beetal-Assam local goats, which indicated that castrates produced significantly more dressed percentages than entire males. Dawa et al (1996) in Cameroon found similar results that castrated males produced significantly heavier carcass (+0.21kg) and more meat per 100kg live weight (+3.9kg) than females. Dawa et al (1996) also reported similar results in two sheep breeds, where castrates produced significantly heavier carcasses and significantly more meat than entire males and females. These findings are also supported by those of Owen et al (1978) on indigenous Tswana goats, were they found that indigenous castrated goats were significantly larger and heavier carcasses than entire males. Farmers should castrates animals destined for slaughter at later ages.

Conclusions

Generally castration method had no effect on growth at the same age and stage of development. The dressing percentage was significantly higher in burdizzo and rubber ring groups than entire males and short scrotum. Castration using burdizzo also promoted development of carcasses with longer diagonal length and deeper height at withers. The short scrotum and entire males had undesirable effect on all parameters and the meat also had a tainted smell at 12 months of age. The burdizzo castration method is recommended.

Acknowledgements

The authors thank Botswana College of Agriculture for providing funds and indigenous Tswana goats for this study and all those who helped during data collection.

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