Last update: November 18, 2010 02:23:33 PM E-mail Print

     

Reproduction and trace minerals

 

JH Hoon


Grootfontein Agricultural Development Institute, P/Bag X529, Middelburg (EC), 5900

e-mail: Jan Hoon

 


INTRODUCTION

Twenty-one inorganic minerals are essential in animal nutrition. Of these 21 minerals, seven are required in reasonably large quantities and are known as the macro minerals. The other 14 minerals are required in very small quantities and are known as the micro or trace minerals. All 14 minerals are required by the animal and, therefore, of nutritional significance. However, animal nutritionists tend to concentrate on six of these trace minerals, as it has been found that deficiencies of these minerals can occur in practice. This group include zinc (Zn), manganese (Mn), copper (Cu), cobalt (Co), selenium (Se) and iodine (I). These trace minerals play an important role in optimal growth, production and reproduction and general health.

In this study, the supplementation of Angora goats with Zn, Mn and Se was investigated. The deficiency symptoms of Zn in small stock are mainly low intake and growth rate, hardening of the skin (parakeratosis) with the accompanying loss of hair, increase in the incidence of foot rot, lower fertility in rams, decreased immunity and subsequent increase in susceptibility for diseases, high occurrence of udder problems, bone abnormalities, etc. Deficiency symptoms of Mn are mainly characterised by delayed, very short and irregular oestrus, poor conception especially in young ewes, normally developed but still born lambs, skeletal abnormalities, etc. The deficiency symptoms of Se are basically lower reproduction rates due to resorption of fertilised eggs and suppression of sperm activity, early born, weak lambs and white muscle disease in lambs. The major problem with these micro minerals is that deficiencies occur in different grades and that it is very difficult to diagnose a moderate deficiency.

Despite the fact that trace element supplements are used on a large scale in the small stock industry, many questions are still asked by farmers regarding the cost efficiency of these supplements. The aim of the study was to determine the effect of supplementation of Angora ewes with a commercial trace mineral supplement on reproduction rate of ewes and growth rate of kids in order to establish guidelines and make recommendations that will benefit producers financially.


MATERIAL AND METHODS

This project was executed at seven localities in the Angora goat producing areas over a period of three years (Middelburg, Willowmore, Steytlerville, Jansenville, Murraysburg, Beaufort West, Cradock). At each locality, a flock of the farmer’s own ewes was mated as one group. The flock was randomly divided into two groups (control and treatment) and the groups were individually tagged and numbered with two different colour ear tags. The ewes of the treatment group received a 1 ml subcutaneous injection of a commercial trace mineral supplement 4-6 weeks before mating and again 4-6 weeks before kidding. The commercial product Multimin® (Virbac) consists of a combination of chelated Zn and Mn, as well as Se in the form of sodium selenite. A minimum of 70 ewes per group was used and all the ewes were managed as one group for the duration of the study.

The following data were collected at all the localities: weaning percentage, body weight of kids at 42-day age and weaning. Where possible, ewes were also scanned for pregnancy to determine conception and/or scanning percentages.

 

RESULTS AND DISCUSSION

The average conception, scanning and weaning percentages of the ewes and the body weight of kids at 42-day age and at weaning of the two groups at the different localities over the experimental period, are presented in Table 1 and 2 respectively.

Table 1. Reproduction data of the ewes of the different groups

 

CONTROL

SUPPLEMENTATION

Conception & scanning percentages (%)

Middelburg

87.0 &100.0

90.0 & 100.0

Willowmore

98.0 & 100.0

97.0 &110.0

Steytlerville

94.8 &102.0

94.9 &101.0

Jansenville

91.0 & 94.0

85.0 & 90.0

Murraysburg

96.0 & 100.0

97.0 &103.0

Weaning percentages (%)

Middelburg

88.7

90.7

Willowmore

65.0

70.0

Steytlerville

78.0

87.0

Jansenville

71.0

62.0

Murraysburg

75.7

79.1

Beaufort West

60.0

69.0

Cradock

65.0

65.5

Conception percentage = Number of ewes pregnant/Number of ewes mated

Scanning percentage = Number of kids scanned/Number of ewes mated

Weaning percentage = Number of kids weaned/Number of ewes mated

The results indicated relatively small differences in the reproduction data (conception rate and scanning percentages) between the control and supplementation groups, although it favoured the supplementation groups at most of the localities. With the exception of Jansenville, the weaning percentage was equal or higher for the supplementation groups at all the localities. It is, however, important to keep in mind that many other on-farm factors could have influenced the weaning percentages at the different localities, e.g. losses due to predators, etc.

 

Table 2. Growth data of the kids of the different groups (±SE)

 

CONTROL

SUPPLEMENTATION

42-day body weight - Kids (kg)

Middelburg

14.7 ± 0.2

15.1 ± 0.3

Willowmore

12.8 ± 0.2

13.3 ± 0.3

Steytlerville

8.1 ± 0.2

8.1 ± 0.2

Jansenville

8.2 ± 0.2

8.0 ± 0.2

Murraysburg

10.6 ± 0.2

11.0 ± 0.2

Beaufort West

11.2 ± 0.2

10.9 ± 0.2

Cradock

13.9 ± 0.3

14.3 ± 0.3

Weaning weight – Kids (kg)

Middelburg

18.2 ± 0.3

18.5 ± 0.4

Willowmore

12.8 ± 0.2

13.3 ± 0.3

Steytlerville

15.7 ± 0.3

15.4 ± 0.3

Jansenville

16.2 ± 0.4

15.6 ± 0.3

Murraysburg

15.1 ± 0.3

15.2 ± 0.3

Beaufort West

16.3 ± 0.3

15.7 ± 0.3

Cradock

18.4 ± 0.4

19.0 ± 0.4

ab Values with different superscripts differ significantly (P<0.05)

With regard to the body weight of kids at 42-day age and weaning, the trend was generally in favour of the supplementation groups, although no significant differences (P>0.05) were observed. The large differences in body weight of kids that were observed among the different localities, can be attributed to differences in environmental and grazing conditions, as well as the fact that the kids were not weighed at exactly the same age.

 

Blood samples of 10 animals per group at all the localities were collected approximately four weeks after the first supplementation, i.e. with the onset of the mating period. The full blood samples were analysed for selenium (Se) to determine the effect of supplementation on the levels of Se in the blood. The mean values for blood Se in the full blood samples of the control and treatment groups at the different localities are presented in Table 3.

 

Table 3. Mean blood Se values (ng Se/g blood) for the control and treatment groups (±SE)


CONTROL (ng/g)

SUPPLEMENTATION (ng/g)

Jansenville

222.6 ± 9.2

202.5 ± 8.3

Willowmore

209.2 ± 15.9a

277.0 ± 8.7b

Beaufort West

290.7 ± 8.7

311.8 ± 8.7

Middelburg

213.0 ± 8.7

223.8 ± 8.7

Steytlerville

184.5 ± 8.7

191.6 ± 9.2

Murraysburg

219.2 ± 8.7

226.5 ± 8.7

Cradock

151.2 ± 6.0

169.2 ± 7.1

ab Values with different superscripts differ significantly (P<0.05)

With the exception of Jansenville, blood Se values for the ewes of the supplementation groups were higher than the control groups, although not significant (P>0.05) at most of the localities. A marginal shortage in the Se status of sheep and goats can be classified as values less than 40 ng/g and a shortage less than 20 ng/g, while an excess will be values of more than 800 ng/g. The blood Se levels for Angora goats at the different localities in this study indicated that these animals received a sufficient supply of Se, even without supplementation. It would, therefore, appear that supplementation of Angora goats and sheep at these localities, specifically for possible Se-deficiencies, will not be of economic value to the producer.

An economic analysis, using the SM2004 computer simulation model, was done on the combined data of all the localities over the three year period to determine the economic viability of trace mineral supplementation of Angora ewes. The average weaning weight of kids and weaning percentages over the three year period were used in the analysis. Body weight of ewes, fleece weight, etc., were kept the same for the two groups. Average meat and mohair prices over the trial period, as well as a cost of R2.00/ewe for the trace mineral supplement in the treatment group, were used in the calculation. The average production and reproduction data and gross margin/ewe of the control and supplementation groups are presented in Table 4.

 

Table 4. Average production and reproduction data and gross margin/ewe

 

CONTROL

SUPPLEMENTATION

42-day weight – kids (kg)

12.5

12.8

Weaning weight – kids (kg)

17.0

17.2

Weaning percentage (%)

75.0

78.7

Gross margin (R/ewe)

454.04

471.68

An average gross margin of R454.04 and R471.68 per ewe for the control and supplementation groups respectively, was determined.  In general, the economic analysis indicated that the supplementation of Angora ewes with a commercial trace mineral supplement during the experimental period was economically viable.

The economic analysis also indicated that an increase of 0.6% in the weaning percentages of ewes (6 kids per 1000 ewes) during the trial period was sufficient to cover the cost of the supplementation. Any increase in the weaning percentages of ewes of more than 0.6%, which can specifically be attributed to the effect of the trace element supplement, will therefore make the practice of trace mineral supplementation a financially viable option.

 

CONCLUSION

From the results it would appear that supplementation of Zn, Mn and Se by means of commercial product (Multimin® - Virbac) in general had a positive effect on the reproduction of Angora ewes, although differences were relatively small at most localities. At some localities, however, no differences in production and reproduction traits could be observed and some of the results were even in favour of the control groups. Good grazing conditions was probably one of the reasons for the small differences observed between the control and treatment groups. From the mean blood Se values, it would appear that supplementation of goats specifically with Se, will not be of economic value to the producer. The average gross margin per ewe, as determined with the SM2004 model, indicated an economic advantage in the use of an injectable trace mineral supplement for Angora goats. As the cost of this trace mineral supplement is relatively low, an increase of less than 1% in the weaning percentages of the ewes as a result of the supplement was sufficient to make this practice economically viable. It is, however, important to keep in mind that in this study many other on-farm factors could have influenced certain traits such as weaning percentage, e.g losses due to problem animals, etc.

 

ACKNOWLEDGEMENTS

The following organizations and people supported and participated in the execution of this project:

Department of Agriculture – Grootfontein ADI

Participating farmers

Mohair SA

Eastern Cape Department of Agriculture

University of Pretoria – Department of Animal and Wildlife Sciences

Virbac

CMW