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INFLUENCE OF EWE AGE AND MANAGEMENT SYSTEM ON BODY WEIGHT AND REPRODUCTION

OF SOUTH AFRICAN ANGORA GOAT EWES

 

M.A. Snyman

 

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

E-mail: Gretha Snyman

 


INTRODUCTION

Reproductive performance is the most important trait that determines income from all livestock enterprises. The relatively low reproductive rate and high kid mortality rate of Angora goats are well documented (Terblanché, 1988; Geyer, 1998). There are numerous internal and external factors that contribute to the actual number of kids born per ewe that was mated. There are even more factors that determine whether a kid born alive will survive to weaning age. Age of dam is one of the internal factors that have a marked influence on overall efficiency of the flock (Van der Westhuizen et al., 2004). There is a tendency among Angora goat stud breeders to retain stud ewes in the breeding flock until the age of up to 12 years. Body weight of the ewe, and therefore all factors influencing body weight per se, is another important factor contributing to reproductive efficiency. A positive relationship between reproduction and body weight has been reported for sheep (Safari & Fogarty, 2003) and goats (Constantinou, 1989).

The effect of ewe age and different management systems, as practiced on-farm in 12 Angora goat studs, on body weight and reproductive performance of ewes was investigated. Body weights of maiden ewes at their first mating at 18 months of age and at the subsequent scanning for pregnancy, and their first kidding performance have also been related to management system.

 

MATERIALS AND METHODS

The data used for this study were collected from 2000 to 2004 on the 12 Angora goat studs, ran under different management systems. The management practices followed in the various studs from mating until weaning were grouped into five major management systems and are summarised in Table 1.

 

The data set analysed for this study contained data of 6271 ewes. Of these ewes, 392 had 5 kidding opportunities, 1033 ewes had 4, 1146 ewes had 3, 1414 ewes had 2 and 2286 ewes only had 1 kidding opportunity during the five years of data recording. This amounted to 14644 ewe records, where each record included body weight before mating, body weight at scanning (ultrasound scanning for pregnancy diagnosis), number of kids scanned, born and weaned for each year the ewe was present in the flock. Data collected during the kidding seasons included the following information for each ewe: Ewe ID, Sire ID (if known), Kid ID, kidding date, birth weight, sex, birth and rearing status, rearing group and weaning weight of her kid/s. Ewes that failed to kid, aborted or delivered stillborn kids or ewes that died before kidding, were also recorded.

 

Table 1. Management systems (MS) followed in the various studs

MS

(Studs)

Management practices before mating

Management practices during pregnancy

Management practices during kidding

Management practices during lactation

Young ewes up to 18 months of age

1

(1,7,8)

Ewes on veld, no supplementation

Ewes on veld, no supplementation

Ewes kid in veld, no supplementation

Ewes on veld, some years supplemented with chocolate grain

Kids in veld, no supplementation

2

(2,3,4,6,10)

Ewes on veld, no supplementation

Ewes on veld, no supplementation

Ewes kid on pastures

Ewes on veld, some years supplemented with chocolate grain

Kids in veld, no supplementation

3

(5)

Ewes on veld, no supplementation

Ewes supplemented with energy blocks third trimester of pregnancy

Ewes kid on pastures

Ewes on veld, some years supplemented with pellets / blocks

Kids in veld, no supplementation

4

(9,11)

Flushing of ewes

Ewes supplemented with energy blocks third trimester of pregnancy

Ewes kid on pastures

Ewes on veld, some years supplemented with licks

Kids in veld, no supplementation

5

(12)

Ewes on pastures

Ewes on pastures

Ewes kid on pastures

Ewes on pastures

All kids on pastures

 

From the reproduction data, the following reproduction parameters were calculated for each stud for each kidding season: number of ewes scanned pregnant per 100 ewes scanned, number of kids scanned per 100 ewes scanned, number of ewes aborted per 100 ewes mated, number of ewes kidded per 100 ewes mated, number of kids born per 100 ewes mated, number of kids born per 100 ewes that kidded, percentage of stillborn kids, kid survival rate and number of kids weaned per 100 ewes mated. The average reproductive performance of ewes in each stud, in terms of these parameters, was calculated. Least squares means for number of kids scanned, born and weaned were obtained by fitting the fixed effects year, stud, age of the ewe and management system in a GLM-model (SAS, 2004), using all 14644 data records.

 

As data recording started with the September 2000 kidding season, no body weights of the ewes before mating and at scanning were available for 2000. Therefore, only 10803 records of ewes with both body weight records were included in the analyses involving body weight. The GLM-model fitted to obtain least squares means for body weight included fixed effects for year, stud, age of the ewe and management system (SAS, 2004).

 

The data set also included data on body weights of kids. The effect of age of ewe and ewe management system on birth, weaning and 8-month body weight of kids was determined using 7432 records. The fixed effects included in the GLM-model were stud-year of birth, sex, birth/rearing status of the kid, age of dam, ewe management system and a covariate for age of the kid at weighing.

 

The 10803 records of ewes with both body weight before mating and at scanning, were used to determine the effect of body weight on reproductive performance. The effect of body weight at first mating of maiden ewes on their first kidding performance was evaluated by dividing the body weight of these maiden ewes into eight subclasses. The fixed effects for year, stud and body weight subclass were included in the model fitted to 2099 maiden ewe records to obtain least squares means for number of kids scanned, born and weaned at first kidding performance per body weight subclass. The effect of management system on body weight and reproductive performance at first mating of maiden ewes was evaluated using a GLM-model, which included fixed effects for stud and management system, fitted to 2099 maiden ewe records.

 

RESULTS AND DISCUSSION


The age structure of the ewes mated in the various studs from 2000 to 2004 is presented in Table 2. It is evident that 10.7 % of the ewes in the project was eight years and older.

 

The average reproductive performance of the ewes in the various studs from 2000 to 2004 is summarised in Table 3. There was a wide range with regard to reproductive performance among the various studs. Percentage of ewes scanned pregnant varied from 75.8 % to 92.3 % among the different studs (average = 86.1 %), while scanning percentage ranged from 77.9 % to 121.2 % kids per ewe scanned (average = 101.1%). Kidding percentage (ewes kidded per 100 ewes mated) varied from 62.2 % to 88.1 % for the different studs (average = 79.8 %).  Percentage multiple births varied between 0.6 % and 37.9 % (average = 19.3 %), while kid survival rate ranged from 80.6 % to 92.2 % (average = 85.6 %). Weaning percentage (kids weaned per 100 ewes mated) ranged from 54.4 % to 105.3 % (average = 80.6 %). Apart from a high kid mortality rate, which is regarded by breeders as the most important factor contributing to low weaning percentages, nearly 20 % of the ewes did not conceive or lost their foetuses before birth. An average of 10.1 % of the ewes that was scanned pregnant did not kid, which implies that they lost their kids between scanning and kidding.

 

Table 2. Age structure of the ewes in the data set

Ewe age

Ewes in full data set

 

Ewes with mating and scanning weights

Number

(n=14644)

%

 

Number

(n=10803)

%

2

2921

19.9

 

1914

17.7

3

2855

19.5

 

2124

19.7

4

2337

16.0

 

1773

16.4

5

2054

14.0

 

1559

14.4

6

1633

11.2

 

1203

11.1

7

1273

8.7

 

985

9.1

8

929

6.3

 

743

6.9

9

447

3.1

 

373

3.5

10

136

0.9

 

97

0.9

11

46

0.3

 

26

0.2

12

13

0.1

 

6

0.1

 

Table 3. Average reproductive performance of ewes in the different studs from 2000 to 2004

 

Stud

Ewes scanned pregnant

Ewes scanned pregnant but did not kid

Kids scanned / 100 ewes scanned

Ewes kidded / 100 ewes mated

Ewes aborted / 100 ewes mated

Kids born / 100 ewes kidded

Kids born / 100 ewes mated

Still-born kids (%)

Kid survival rate (%)

Kids weaned / 100 ewes mated

1

91.2

6.7

104.3

85.4

5.6

118.2

101.1

2.1

92.2

91.4

2

86.9

5.3

103.4

84.5

2.6

133.1

112.4

2.2

83.0

91.4

3

84.7

18.8

86.6

72.4

2.8

106.2

76.9

1.4

86.4

65.6

4

88.6

16.3

103.8

76.7

1.9

117.4

90.1

0.7

90.6

81.0

5

83.0

6.49

104.3

82.7

4.2

119.2

98.5

2.2

80.6

77.5

6

92.3

4.3

106.5

86.7

0.9

118.6

102.7

0.1

87.7

89.9

7

76.3

19.5

79.7

68.1

10.0

105.7

72.0

2.1

82.0

57.8

8

89.4

13.9

102.8

78.5

6.6

117.7

92.5

2.6

84.0

75.7

9

 

 

 

73.5

0.1

120.5

87.5

0.3

91.0

79.5

10

75.8

11.4

77.9

62.2

4.6

100.6

62.5

1.1

88.0

54.4

11

90.4

4.6

99.8

84.4

0.3

124.5

105.5

1.0

88.7

92.2

12

88.5

3.5

121.2

88.1

0.1

137.9

121.5

1.1

87.6

105.3

Avg

86.1

10.1

101.1

79.8

4.1

119.3

95.6

1.5

85.6

80.6

 

Body weights of ewes before mating and at scanning (42 days after mating) are given in Table 4 for the different studs. Body weight of ewes before mating ranged from 33.7 kg to 44.5 kg (average = 34.6 kg) among studs, while body weight at scanning ranged from 37.0 kg to 46.4 kg (average = 38.6 kg). Body weight of ewes differed significantly among the studs.

 

Table 4. Body weight (± s.e.) of ewes in the different studs

Stud

Body weight before mating (kg)

Body weight at scanning (kg)

1

35.3±0.2 2,3,4,5,6,7,8,10,11,12

42.4±0.3 2,3,4,5,6,7,9,10,11,12

2

36.3±0.2 1,3,4,5,6,7,8,10,11,12

40.2±0.2 1,3,5,6,7,8,9,10,11,12

3

34.3±0.2 1,2,4,5,6,7,8,10,11,12

37.3±0.2 1,2,4,6,7,8,10,11,12

4

37.9±0.3 1,2,3,5,6,7,10,11,12

40.3±0.3 1,3,5,6,7,8,9,10,11,12

5

37.0±0.2 1,2,3,4,6,7,8,10,12

37.3±0.2 1,2,4,6,7,8,10,11,12

6

39.8±0.3 1,2,3,4,5,7,8,10,11,12

45.3±0.3 1,2,3,4,5,7,8,9,10,11,12

7

33.7±0.2 1,2,3,4,5,6,8,10,11,12

39.1±0.3 1,2,3,4,5,6,8,9,10,11,12

8

37.6±0.2 1,2,3,5,6,7,10,11,12

42.6±0.3 2,3,4,5,6,7,9,10,11,12

9

 

37.0±0.2 1,2,4,6,7,8,10,11,12

10

41.1±0.4 1,2,3,4,5,6,7,8,11,12

38.6±0.4 1,2,3,4,5,6,7,8,9,11,12

11

37.1±0.2 1,2,3,4,6,7,8,10,12

43.7±0.2 1,2,3,4,5,6,7,8,9,10,12

12

44.5±0.2 1,2,3,4,5,6,7,8,10,11

46.4±0.3 1,2,3,4,5,6,7,8,9,10,11

Average

34.6±0.2

38.6±0.2

 

1,2,3,4,5,6,7,8,9,10,11,12 Specific trait differed significantly (P<0.01) from those studs indicated in the superscripts

 

The effect of ewe age on reproductive performance and body weight of ewes is summarised in Table 5. All reproductive parameters recorded had a typical U-shaped relationship with age of dam, where the 2- and 3-year old ewes and ewes older than 9 years of age reproduced poorer than the 4- to 9-year old ewes. Although 11- and 12-year old ewes had high scanning percentages, their kidding percentages were considerably lower, indicating that they lost their kids between scanning and kidding. The same trends were prevalent in all studs, regardless of the reproductive rates of or management systems followed in the different studs. Body weight of ewes before mating increased from 26.8 kg in young ewes to 37.7 kg in 5-year old ewes, after which it increased steadily to 41.4 kg in 11-year old ewes. Body weight of ewes at scanning followed the same trend.

Table 5. Effect of ewe age on reproductive performance and body weight (± s.e.) of ewes

 

Ewe age

Number of kids scanned per ewe scanned

Number of kids born per ewe mated

Number of kids weaned per ewe mated

Number of kids weaned per kids born alive

Body weight before mating (kg)

Body weight at scanning (kg)

2

0.78±0.01 3,4,5,6,7,8,9,10,11

0.70±0.01 3,4,5,6,7,8,9

0.56±0.01 3,4,5,6,7,8,9

0.81±0.01 3,4,5,6,7,8,9

26.8±0.1 3,4,5,6,7,8,9,10,11,12

30.7±0.1 3,4,5,6,7,8,9,10,11,12

3

0.94±0.01 2,4,5,6,7,8,9

0.89±0.01 2,4,5,6,7,8,9

0.76±0.01 2,4,5,6,7,8

0.86±0.01 2,5,6,7,8

32.3±0.1 2,4,5,6,7,8,9,10,11,12

36.6±0.1 2,4,5,6,7,8,9,10,11,12

4

1.07±0.01 2,3,5,6,7,8

1.05±0.01 2,3,6,7,10

0.90±0.01 2,3,7,10

0.88±0.01 2

35.7±0.1 2,3,5,6,7,8,9,10,11

40.3±0.1 2.3,5,6,7,8,9,10,11

5

1.12±0.01 2,3,4,7,10

1.09±0.01 2,3,7,10

0.95±0.01 2,3,10

0.90±0.01 2,3

37.7±0.1 2,3,4,6,7,8,9,10,11

42.4±0.1 2,3,4,6,7,8,9,10,11

6

1.16±0.01 2,3,4,10

1.12±0.02 2,3,4,10,11

0.95±0.02 2,3,10

0.90±0.01 2,3

38.7±0.1 2,3,4,5,7,8,9,10,11

43.5±0.1 2,3,4,5

7

1.19±0.02 2,3,4,510

1.17±0.02 2,3,4,5,8,9,10,11

0.99±0.02 2,3,4,9,10

0.91±0.01 2,3,9

39.3±0.1 2,3,4,5,6

44.0±0.2 2,3,4,5

8

1.13±0.02 2,3,4,10

1.07±0.02 2,3,7,10

0.91±0.02 2,3,10

0.89±0.01 2,3

39.4±0.2 2,3,5,6

43.7±0.2 2,3,4,5

9

1.11±0.03 2,3

1.04±0.03 2,3,7,10

0.84±0.03 2,7

0.86±0.02 2,7

39.6±0.2 2,3,5,6

43.4±0.2 2,3,4,5

10

0.99±0.05 2,5,6,7,8

0.84±0.06 4,5,6,7,8,9

0.69±0.06 4,5,6,7,8

0.87±0.04

40.5±0.4 2,3,4,5,6

44.2±0.5 2,3,4,5

11

1.09±0.09 2

0.84±0.10 6,7

0.68±0.11

0.95±0.08

41.4±0.8 2,3,4,6

44.8±0.9 2,3,4,5

12

1.10±0.19

0.81±0.21

0.80±0.22

0.96±0.15

39.6±1.7 2,3

42.5±1.9 2,3

 

2,3,4,5,6,7,8,9,10,11,12   Specific trait differed significantly (P<0.01) from those age groups indicated in the superscripts

 

Similar relationships to those of the reproduction traits were observed between age of dam and body weights of their kids (Figures 1 to 3). Kids born to young ewes (2-year old ewes) had lower body weights up to 16 months of age than kids born to 4- to 8-year old ewes. Birth, weaning and 8-month body weights of kids born to ewes older than 9 years of age, were also lower.

 

Figure 1. Relationship between ewe age and birth weight of kids

 

Figure 2. Relationship between ewe age and weaning weight of kids

Figure 3. Relationship between ewe age and 8-month body weight of kids

 

The effect of management system on reproductive performance and body weight of ewes is presented in Table 6 for the five major systems followed in the various studs. Management system had a significant influence on reproductive performance of ewes in the different studs. Higher reproductive rates, in terms of kids scanned, born and weaned, were observed under those management systems involving additional or supplementary feeding at the various stages of the reproductive cycle. Management system also had a significant influence on body weight of kids (Table 7).

 

Table 6. Effect of ewe management system on reproduction and body weight (± s.e.) of ewes

Management system

Number of kids scanned per ewe scanned

Number of kids born per ewe mated

Number of kids weaned per ewe mated

Body weight before mating (kg)

Body weight at scanning (kg)

1

0.98±0.03 2,3,4,5

0.81±0.03 2,3,4,5

0.71±0.03 2,4,5

35.3±0.2 2,3,4,5

40.9±0.2 2,3,4,5

2

1.02±0.03 1,3,4,5

0.93±0.03 1,4,5

0.79±0.03 1,3,4,5

36.1±0.2 1,3,4,5

39.5±0.2 1,3,4,5

3

1.06±0.03 1,2,4,5

0.93±0.03 1,4,5

0.73±0.03 2,4,5

36.7±0.2 1,2,5

36.9±0.2 1,2,4,5

4

1.12±0.03 1,2,3,5

1.06±0.03 1,2,3,5

0.91±0.03 1,2,3,5

36.8±0.2 1,2,5

43.3±0.2 1,2,3,5

5

1.25±0.03 1,2,3,4

1.20±0.03 1,2,3,4

1.06±0.03 1,2,3,4

44.2±0.2 1,2,3,4

45.9±0.3 1,2,3,4

 

1.2,3,4,5   Specific trait differed significantly (P<0.05) from those management systems indicated in the superscripts

 

 

Table 7. Effect of ewe management system on body weight (± s.e.) of kids

Management system

Birth weight of kids (kg)

Weaning weight of kids (kg)

8-month body weight of kids (kg)

1

2.88±0.04 2,3,4,5

15.42±0.37 2,3,5

19.74±0.53 2,3,4,5

2

3.21±0.04 1,3,4,5

16.87±0.37 1,3,4,5

21.52±0.52 1,3,4,5

3

3.06±0.04 1,2,4,5

14.71±0.37 1,2,4,5

20.65±0.52 1,2,4,5

4

2.72±0.04 1,2,3,5

15.74±0.40 2,3,5

22.44±0.55 1,2,3,5

5

2.55±0.04 1,2,3,4

20.54±0.40 1,2,3,4

26.52±0.56 1,2,3,4

 

1.2,3,4,5   Specific trait differed significantly (P<0.05) from those management systems indicated in the superscripts

 

The effect of body weight before mating and at scanning on reproductive performance is summarised in Table 8. Body weights before mating and at scanning had a significant positive relationship with number of kids born per ewe mated, number of multiple births and number of kids weaned per ewe mated. Ewes carrying twin kids had higher body weights at scanning than dry ewes or ewes carrying single kids. For every kilogram increase in body weight before mating, 0.0237 and 0.0218 more kids will be born and weaned respectively.

 

The effect of management system on body weight and reproduction of maiden ewes is presented in Table 9. Body weight before mating of young ewes ran on pastures until 18 months of age, was higher than that of maiden ewes in the other management systems, with resultant higher reproductive rates. The effect of body weight at first mating on the reproductive performance of these maiden ewes is summarised in Table 10. Number of kids scanned, born and weaned per maiden ewe at first kidding increased with an increase in body weight at first mating. Kid survival rate followed the same trend.

 

Table 8. Effect of body weight (± s.e.) on reproductive performance of ewes

Trait

Body weight before mating (kg)

Body weight at scanning (kg)

Reproductive status

1. Gave birth to normal kid/s

37.6±0.2 5

41.9±0.2 2,3,4,5

2. Aborted

37.4±0.3 5

40.9±0.3 1,5

3. Stillborn kid/s

37.4±0.4 5

41.1±0.5 5

4. Kid/s died after birth

38.0±0.4 5

40.9±0.4 1,5

5. Ewe did not kid

36.2±0.2 1,2,3,4

39.3±0.2 1,2,3,

Number of kids scanned per ewe scanned

0

35.9±0.2 1,2

38.7±0.2 1,2

1

37.1±0.2 0,2

41.2±0.2 0,2

2

39.4±0.2 0,1

44.4±0.2 0,1

3

38.5±1.6

42.6±1.7

Regression

y = 0.1947 + 0.0237 x

y = -0.2272 + 0.0316 x

Number of kids born per ewe mated

0

36.4±0.2 1,2,3

39.5±0.2 1,2,3

1

37.2±0.2 0,2,3

41.4±0.2 0,2,3

2

39.2±0.2 0,1

44.1±0.2 0,1,3

3

40.3±0.7 0,1

46.4±0.7 0,1,2

Regression

y = 0.0397 + 0.0237 x

y = -0.4684 + 0.0334 x

Number of kids weaned per ewe mated

0

36.6±0.2 1,2,3

40.1±0.2 1,2,3

1

37.3±0.2 0,2,3

41.6±0.2 0,2,3

2

39.3±0.2 0,1

44.2±0.2 0,1

3

41.2±1.1 0,1

45.6±1.2 0,1

Regression

y = 0.0781 + 0.0218 x

y = -0.3484 + 0.0299 x

 

0,1,2,3,4,5   Specific trait differed significantly (P<0.01) from those categories indicated in the superscripts

 

Table 9. Effect of management system on reproductive performance and body weight (± s.e.) of maiden ewes

Management system

Number of kids scanned per ewe scanned

Number of kids born per ewe mated

Number of kids weaned per ewe mated

Body weight before mating (kg)

Body weight at scanning (kg)

1

0.71±0.02 4,5

0.60±0.03 2,3,4,5

0.45±0.03 2,4,5

25.2±0.2 4,5

29.5±0.2 2,4,5

2

0.75±0.02 4,5

0.66±0.02 1,4,5

0.54±0.02 1,4,5

25.7±0.1 4,5

28.8±0.2 1,4,5

3

0.68±0.03 4,5

0.72±0.04 1,4,5

0.51±0.04 4,5

25.8±0.3 4,5

29.0±0.3 4,5

4

0.90±0.03 1,2,3

0.89±0.04 1,2,3

0.72±0.04 1,2,3,5

26.9±0.3 1,2,3,5

33.2±0.3 1,2,3,5

5

0.99±0.03 1,2,3

0.99±0.03 1,2,3

0.84±0.03 1,2,3,4

35.0±0.3 1,2,3,4

37.1±0.3 1,2,3,4

 

1.2,3,4,5   Specific trait differed significantly (P<0.05) from those management systems indicated in the superscripts

 

Table 10. Effect of body weight (± s.e.) at first mating on reproductive performance of maiden ewes

Weight class (kg)

n

Number of kids scanned per ewe scanned

Number of kids born per ewe mated

Number of kids weaned per ewe mated

Number of kids weaned per kids born alive

1. <15.0

4

0.34±0.24 5,6,7,8

0.20±0.25 4,5,6,7,8

 

 

2. 15.0 – 19.9

116

0.32±0.05 3,4,5,6,7,8

0.29±0.05 3,4,5,6,7,8

0.24±0.05 3,4,5,6,7,8

0.79±0.09

3. 20.0 – 24.9

717

0.64±0.02 2,4,5,6,7,8

0.54±0.02 2,4,5,6,7,8

0.41±0.02 2,4,5,6,7,8

0.75±0.02 4,5,6

4. 25.0 – 29.9

813

0.81±0.02 2,3,6,7,8

0.77±0.02 1,2,3,5,7

0.62±0.02 2,3,5,6,7,8

0.82±0.02 3,5

5. 30.0 – 34.9

311

0.84±0.03 1,2,3,7,8

0.87±0.03 1,2,3,4,7

0.75±0.03 1,2,3,4

0.89±0.02 3,4

6. 35.0 – 39.9

104

0.94±0.06 1,2,3,4,8

0.88±0.06 1,2,3

0.77±0.06 1,2,3,4

0.87±0.04 3

7. 40.0 – 44.9

31

1.04±0.09 1,2,3,4,5,8

1.07±0.10 1,2,3,4,5

0.89±0.10 1,2,3,4

0.88±0.07

8. 45.0 – 49.9

3

1.60±0.27 1,2,3,4,5,6,7

1.23±0.29 1,2,3

1.18±0.29 1,2,3,4

0.99±0.22

 

1.2,3,4,5,6,7,8   Specific trait differed significantly (P<0.05) from those weight classes indicated in the superscripts

DISCUSSION

From the results it is evident that body weight, age of the ewe and management system all have a significant effect on reproduction of Angora goats. The effect of body weight and flushing on ovulation rate and reproductive performance has been well documented (Cockrem, 1979; Gunn et al., 1984). More ewes in this study that received either flushing treatment or were run on pastures before mating were pregnant at scanning than ewes that were run on veld without any supplementation before mating.

 

In this survey, 14 % of the ewes did not carry a kid/s at scanning. It is well established that 20 - 30 % of sheep embryos die in the first weeks of pregnancy (Edey, 1969; Kelly, 1984). The factors responsible for these losses have still to be fully explained. It is also known that progesterone plays a crucial role in maintaining pregnancy in the ewe (Denamur, 1974). Nutrition in early pregnancy and peripheral progesterone concentration are inversely related (Parr et al., 1982; Williams & Cumming, 1982; Parr et al., 1987; McKelvey & Robinson, 1988; Ashworth, 1995). Sheep fed high-energy rations after mating during the first part of gestation had reduced progesterone levels and showed an increase in embryo mortality. Low-plane feeding at this time had little effect on embryo survival or plasma progesterone concentration (Mani et al., 1995). However, embryos of young ewes and older ewes that are in poor condition at mating are at risk (Robinson, 1983). Most of the ewes in this survey were run on veld from mating through the first part of pregnancy. Overfeeding just after mating is therefore not a problem that would adversely affect embryo survival.

 

When undernutrition is severe, however, there can be a significant decrease is pregnancy rate in sheep, although this does not appear to be attributable to any inadequacy in corpus luteum function (Abecia et al., 1994). Nutritional restriction during mid-pregnancy may have a significant effect on foetal mortality (Kelly et al., 1989). Osuagwuh (1992) also concluded that for economic animal production it is not necessary to feed pregnant West African Dwarf goats on high concentrate rations throughout pregnancy, but they should not be underfed between days 61 and 120 of pregnancy. In this survey, 84 % of the ewes that were run on veld without supplementation during pregnancy and was scanned pregnant, did eventually kid, compared to 92 and 93 % of the ewes that either received supplementation during the last part of pregnancy or were run on pastures.

 

Louw (1981) reported that low energy nutrition of Angora goats during the third trimester of pregnancy, could cause poor udder development and delay the onset of milk and colostrum production. Low protein and/or energy intake during this period could also lead to poor mothering instinct. Most veld types in the Angora goat areas are unable to fulfil the protein and energy requirements of late pregnant and lactating Angora goat ewes (Louw, 1981; Wentzel, 1982). Although information on the feed requirements of these animals and the degree in which natural grazing supplies this, is relatively limited, there is at least sufficient proof that the most important deficiency experienced by ewes and growing animals is that of energy. It is also not surprising that the major problems in the Angora goat industry can be traced to an energy deficiency (Wentzel, 1982). Occasional examples of this deficiency are low conception rates, high rates of abortion, high peri-natal losses, poor milk production in lactating ewes, poor growth in small kids and young goats and high losses during unfavourable weather conditions. The actual elimination of these problems on farms through the supply of the necessary energy supplementation is sufficient proof that optimal production and reproduction in the Angora goat is possible in practice through the correction of a single deficiency (Wentzel, 1982). The general lower reproductive performance of ewes under Management system 1 (ewes run continuously under veld conditions), is further evidence that veld alone cannot adequately supply the nutritional requirements of pregnant and lactating Angora goat ewes.

 

Ewe selection has a dual purpose. The first is the immediate improvement of the productive performance of the flock and, therefore, the income from the flock. The second aim is long-term genetic improvement. To optimise the rate of genetic improvement, a balance between selection intensity (number of replacement animals needed per year) and generation interval (the average age of the parents when the progeny is born) must be established. The most important factor that will determine the replacement rate, and hence the number of ewe age groups that can be kept, is kidding percentage and kid survival rate. The more young goats available at selection age, the more animals can be replaced. With a weaning percentage of 80 %, replacement rates of 20 to 25 % could be easily achieved. Analysis of data on South African stud Angora goats revealed a generation interval of 5.11 years, which could be reduced considerably. Theoretically, genetic progress in selection for a single trait could be increased by approximately 12 % if the number of ewe age groups is decreased to five and that of ram groups to two. This issue should be addressed in the Angora goat industry.

 

It could be argued that a high proportion of young ewes in the flock (with fewer ewe age groups) will negatively affect the current performance of the flock due to the generally lower efficiency of the young ewes. This should be weighed against achieving optimum genetic gain as well as the lower efficiency of older ewes. The lower reproductive efficiency of young ewes could most probably largely be ascribed to their lower body weight. A body weight of 25 to 27 kg at 18 months of age is generally regarded as a minimum to ensure that young ewes conceive and are able to carry their foetuses to parturition. However, 40 % of young ewes in this study had mating body weights of less than 25 kg; the range being from 15 to 45.8 kg, depending on the respective rearing environments. Young ewes with mating weights less than 25 kg also had lower survival rates of their kids.

 

From the results on post-weaning growth rates of kids in the same survey (Snyman, 2007), it was evident that the growth rate of ewe kids is severely stunted after weaning, for at least an 8-month period. This contributes directly to the young ewes not being able to reach an acceptable weight before mating at 18 months of age. It would be advantageous to ensure that ewe kids have every opportunity to grow out sufficiently to reach the required body weight before mating at 18 months of age. The high reproductive rates achieved by maiden ewes under Management system 5, is evidence that young ewes that had the opportunity to grow out sufficiently, are able to reproduce well. This is evident from the higher conception rate (P<0.01) of these young ewes. The better nutritional conditions that these ewes were under during pregnancy, also contributed to lower losses between scanning and kidding.

 

CONCLUSIONS

From the results presented, it is evident that age of the ewe, body weight and management system all have a significant effect on reproduction of Angora goats. The practice of keeping ewes older than seven to eight years of age in the breeding flock is detrimental for optimising overall productivity. Not only will it slow down genetic progress, but income of the current herd is also adversely affected by retaining unproductive older ewes. To optimise productive and reproductive efficiency and rate of genetic progress, breeders should keep a maximum of 5 to 6 dam age groups.

 

Furthermore, it is imperative that breeders ensure that young replacement ewes have every opportunity to grow out sufficiently to reach the required body weight before mating at 18 months of age. Older ewes should also be in a good body condition before the onset of the reproductive cycle. The nutrition of the ewes throughout the reproductive cycle should be adequate to ensure optimum reproduction, with emphasis on certain critical periods. These are before, during and directly after mating, to ensure successful ovulation, fertilization, morula formation, blastocyst implantation and embryonic development. The second important period is the third trimester of pregnancy. Adequate nutrition during this period will ensure good udder development and early onset of milk and colostrum production, as well as viable and healthy kids. Management during kidding and nutrition during the first six to eight weeks of lactation is also imperative to ensure a high weaning percentage.

 

ACKNOWLEDGEMENTS

The author wishes to convey her sincere appreciation to all people who participated in the project and to Mohair South Africa for funding the project.

 

REFERENCES

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Ashworth, C.J., 1995. Maternal and conceptus factors affecting histotrophic nutrition and survival of embryos. Livest. Prod. Sci. 44, 99-105.

Cockrem, F.R.M., 1979. A review of the influence of live weight and flushing on fertility made in the context of efficient sheep production. Proc. N. Z. Soc. Anim. Prod. 39, 23-42.

Constantinou, A., 1989. Genetic and environmental relationships of body weight, milk yield and litter size in Damascus goats. Small Rum. Res. 2 : 163-174.

Denamur, R., 1974.  Luteotrophic factors in the sheep.  Journal of Reproduction and Fertility 38, 251.

Edey, T.N., 1969. Prenatal mortality in sheep : A review. Anim. Breed. Abstr. 37(2), 173-190.

Geyer, A.C., 1998. Strategiese beplanning en risikobestuur vir ekstensiewe Angorabokboerdery in die Karoo. Ph.D thesis, University of the Orange Free State, Bloemfontein.

Gunn, R.G., Doney, J.M. & Smith, W.F., 1984. The effect of level of pre-mating nutrition on ovulation rate in Scottich Blackface ewes in different body conditions at mating. Anim. Prod. 39, 235-239.

Kelly, R.W., 1984.  Fertilization failure and embryonic wastage.  Lindsay, D.R. & Pearce, D.T. (eds) Reproduction in Sheep.  Cambridge University Press, Cambridge, pp. 127-133.

Kelly, R.W., Wilkens, J.F. & Newnham, J.P., 1989.  Fetal mortality from day 30 of pregnancy in Merino ewes offered different levels of nutrition.  Aust. J. Exp. Agric. 29, 339-342.

Louw, D.J., 1981. Invloed van energie- en proteïenvoeding op melkproduksie van Angorabokooie. Karoo Agric. 2(2), 29-34.

Mani, A.U., Watson, E.D. & Mckelvey, W.A.C., 1995.  Effect of undernutrition on progesterone concentration during the early luteal phase and mid-gestation in goats.  Vet. Rec. 136, 518-519.

Mckelvey, W.A. & Robinson, J.J., 1988.  The use of reciprocal embryo transfer to separate the effects of pre- and post-mating nutrition on embryo survival and growth of the ovine conceptus.  Proc. 11th Int. Cong. of Anim. Reprod. and Artif. Ins. (Dublin) 2, Paper No.176.

Osuagwuh, A.I.A., 1992. Effects of strategic feed supplementation during pregnancy on birth weight and perinatal survival of West African Dwarf kids. J. Agric. Sci. (Camb)  119, 123-126.

Parr, R.A., Cumming, I.A. & Clarke, I.J., 1982.  Effects of maternal nutrition and plasma progesterone concentrations on survival and growth of the sheep embryo in early gestation.  J. Agric. Sci. (Camb)  98, 39-46.

 

Published

Grootfontein Agric 9 (1)