PRODUCTION AND REPRODUCTION PERFORMANCE OF THREE SOUTH AFRICAN ANGORA GOAT CYP17 GENOTYPES

 

M.A. Snyman1#, K-H. Storbeck2 & P. Swart2

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

2 Department of Biochemistry, University of Stellenbosch, Private Bag X1, Matieland, 7602

#Email: Gretha Snyman

 

INTRODUCTION

South African Angora goats are known for their inability to cope with stress, especially during severe cold, wet and windy weather (Wentzel et al., 1979; Fourie, 1984). Previous research has shown that the Angora goat is unable to produce sufficient cortisol (the adrenal steroid hormone released in response to physiological stress) in response to cold stress (Van Rensburg, 1971; Herselman & Pieterse, 1992; Herselman & Van Loggerenberg, 1995; Engelbrecht et al., 2000; Engelbrecht & Swart, 2000). A single enzyme, cytochrome P450 17α-hydroxylase/17,20 lyase (CYP17), was implicated as the probable cause of the problem (Storbeck et al., 2008). Two CYP17 genes have been identified within the South African Angora population, namely ACS- (GenBank accession no. EF524063) and CYP17 ACS+ (GenBank accession no. EF524064) (Storbeck et al., 2007). The two CYP17 genes express enzymes with significantly different activities (Slabbert, 2003; Storbeck et al., 2007; Storbeck et al., 2008; Storbeck et al., 2009). CYP17 isoforms have also been associated with different physiological cortisol responses in Merino sheep (Hough et al., 2010; Hough, 2012; Qui, 2015).

 

Three unique genotypes (named He, Hu and Ho) were subsequently identified. The Ho genotype has only one CYP17 gene, namely ACS-. The He genotype has both CYP17 genes (ACS+ and ACS-) at two different loci. Crossing Ho and He goats has been shown to yield an intermediate genotype, Hu, which receives both ACS- and ACS+ from the He parent, but only ACS- from the Ho parent (Storbeck et al., 2008).Thus all animals will have an ACS- gene, but the Ho genotype lacks an ACS+ gene. A schematic presentation of the two genes of CYP17 in the Angora goat, yielding three genotypes, is presented in Figure 1.

 

 

Figure 1. Schematic presentation of the two genes of CYP17 in the Angora goat, giving rise to three genotypes

 

An insulin-induced stress experiment confirmed that there was a significant difference in the ability of the three different genotypes to produce cortisol in response to physiological stress (Storbeck et al., 2008; Hough et al., 2010). The He genotype was the best cortisol producer during the insulin-induced stress test, with the Ho genotype producing the least cortisol. Subsequent to the insulin-induced stress test, a simulated cold stress test was performed at the Grootfontein Agricultural Development Institute (GADI) (Swart, 2012). While the Ho genotype again produced the least cortisol during the cold stress test, it was the rectal temperature of the Hu genotype that dropped significantly more than that of the other two genotypes. The He genotype was the best performer in both the insulin-induced and cold stress tests and therefore represents the hardiest genotype.

 

In addition to being important in cortisol production, the CYP17 enzyme is vital for the production of estrogens (female sex hormones) and androgens (male sex hormones) (Payne & Hales, 2004). The effect of the CYP17 genotypes on the reproductive fitness of Angora ewes was thus investigated (Swart, 2012, 2013). The results indicated that the Ho genotype is a poor reproducer; 62.5% of the Ho group was poor reproducers, while the Hu and He groups contained 35% and 42% poor reproducers respectively. Poor reproducers were defined as ewes weaning less kids than they had kidding opportunities in the flock. However, a larger sample group needs to be investigated before final recommendations can be made to the industry.

 

This study formed part of a bigger project which investigated the possibility of breeding more hardy Angora goats without negatively affecting the reproductive fitness of the goats or decreasing the quality of mohair that South Africa is known for. Data gathered to date suggest that the He genotype is the hardiest and should be selected for. However, information of the relative production and reproduction performance of the three genotypes is lacking. The aim of this study was therefore to evaluate growth, mohair production and reproduction of the three Angora goat CYP17 genotypes to ultimately be able to make recommendations to the industry as to the way forward regarding implementation of selection practices incorporating the CYP17 genotype.

 

MATERIAL AND METHODS

Experimental resources

Resources from the GADI-Biobank, including blood samples and phenotypic data were used for this study. An assessment of the available Angora ewes and their reproduction and production data in the GADI-Biobank was performed. Samples from 480 ewes with reproduction, body weight and hair data from three flocks participating in the Angora Biobank were included in the study. For each flock, ewes with good, average and poor reproductive performance, and having recorded body weight and fleece data, were selected for genotyping of the CYP17 locus. The average number of kids born per ewe mated in the three flocks were 99%, 72% and 122% for Flocks 1, 2 and 3 respectively (Snyman, 2011). The corresponding number of kids weaned per ewe mated were 78%, 58% and 105%. Adult body weights of the ewes in the respective flocks were 37.0 kg, 33.4 kg and 44.5 kg. Blood samples from the identified ewes were obtained from the GADI-Biobank.

 

Experimental procedures

Genomic DNA was isolated from the blood samples and genotyping was carried out using an ARMS-qPCR (amplification refractory mutation system qPCR) assay at the University of Stellenbosch. Genotypes of 466 ewes were available for inclusion in the study.

 

The following production and reproduction data were obtained from the Angora Biobank database and analysed with suitable models:

 

Body weight, fleece and reproduction data recorded for Flock 1 from 2000 to 2015, Flock 2 from 2000 to 2014 and Flock 3 from 2000 to 2010 were available for analyses. Body weight data included birth weight, weaning weight, 8-month, 12-month and 16-month body weight, as well as body weight recorded annually on the ewe flock before mating. Fleece data included fleece weight and fibre diameter recorded at the second and third shearings at 12 and 18 months of age respectively. Fleece weight, fibre diameter, style and character were also recorded annually on the ewe flocks during the winter shearing. The PROC GLM procedure of SAS (2009) was used to determine the effect of genotype on body weights and fleece traits at the different ages.

 

Individual reproduction records included information on whether the ewe kidded or not, whether the ewe aborted or not, number of kids born, stillborn kids, kids that died soon after birth, kids reared by a foster mother, kids reared as orphans, number of kids weaned and total weight of kid/s weaned. Total lifetime reproductive performance in the flock for the ewes genotyped was calculated for number of kids born, number of kids weaned and total weight of kid/s weaned. The PROC GLM procedure of SAS (2009) was used to analyse the effect of genotype on individual reproductive performance, as well as flock lifetime reproductive performance. The CHISQ procedure of SAS (2009) was used to determine if there were any differences among the three genotypes in whether the ewe kidded or not, whether the ewe aborted or not, number of kids born, kids reared by a foster mother, kids reared as orphans and number of kids weaned.

 

RESULTS

The distribution of the animals across the CYP17 genotypes for the pooled data and for the three flocks are summarised in Table 1. The highest percentage animals had the Hu genotype in all flocks, as well as in the pooled data. Ho was the least represented, except in Flock 2, where Ho and He were evenly represented.

 

Table 1. Number (%) of animals per genotype in the dataset and in the different flocks

 Genotype

Pooled

Flock 1

Flock 2

Flock 3

 He

171 (36.7%)

132 (41.5%)

6 (16.7%)

33 (29.5%)

 Hu

240 (51.5%)

153 (48.1%)

24 (66.6%)

63 (56.2%)

 Ho

55 (11.8%)

33 (10.4%)

6 (16.7%)

16 (14.3%)

 Total

466

318

36

112

 

The effect of genotype on body weight from birth until adult age is presented in Table 2. Animals of the Hu genotype were heavier from weaning age onwards, although this difference in body weight was only significant at 8 months of age and in the adult ewes. No differences were observed between the He and Ho animals.

 

Table 2. Effect of genotype on body weight of animals from birth until adult age

 Trait

He

Hu

Ho 

 Birth weight (kg)

2.92 ± 0.11

2.90 ± 0.11

2.87 ± 0.11

 Weaning weight (kg)

15.7 ± 0.6

16.0 ± 0.6

15.9 ± 0.7

 8-month body weight (kg)

19.8 ± 0.7

20.4b ± 0.7

19.3a ± 0.8

 12-month body weight (kg)

22.3 ± 0.9

22.5 ± 0.8

22.4 ± 0.9

 16-month body weight (kg)

26.5 ± 0.9

27.2 ± 0.9

26.3 ± 1.0

 Adult ewe body weight (kg)

40.1a ± 0.4

40.9b ± 0.3

39.8a ± 0.4

a,b Values with different superscripts differ significantly (P  <0.05)

 

The effect of genotype on the fleece traits from second shearing until adult age is presented in Table 3. No differences were evident at the second or third shearings. Adult ewes of the He genotype (1.35 kg) produced heavier (P <0.05) fleeces than both the Hu (1.27 kg) and Ho (1.24 kg) genotypes. Fibre diameter of the fleeces of the Ho ewes (33.0 µm) was higher (P <0.05) than that of the fleeces of the He ewes (32.2 µm). The fleeces of the Ho ewes had the best style. 

 

Table 3. Effect of genotype on fleece traits of animals from second shearing until adult age

 Trait

He

Hu

Ho 

 Fleece weight – 2nd shearing (kg)

1.29 ± 0.14

1.23 ± 0.13

1.22 ± 0.14

 Fibre diameter – 2nd shearing (µm)

26.3 ± 0.7

26.5 ± 0.7

26.3 ± 0.7

 Fleece weight – 3rd shearing (kg)

1.35 ± 0.06

1.33 ± 0.05

1.34 ± 0.06

 Fibre diameter – 3rd shearing (µm)

28.2 ± 0.5

28.4 ± 0.5

28.6 ± 0.6

 Adult fleece weight – winter shearing (kg)

1.35a ± 0.03

1.27b ± 0.02

1.24b ± 0.03

 Adult fibre diameter – winter shearing (µm)

32.2a ± 0.3

32.7 ± 0.2

33.0b ± 0.3

 Style of fleece – winter shearing

2.97 ± 0.04

2.92b ± 0.04

3.04a ± 0.07

 Character of fleece – winter shearing

3.01 ± 0.04

2.98 ± 0.04

2.93 ± 0.06

a,b Values with different superscripts differ significantly (P <0.05)

 

The effect of genotype on the reproductive performance of ewes is presented in Table 4. No significant differences were recorded in reproductive performance among the genotypes. The Ho had the lowest and the He the highest number of kids born and weaned per year. Hu ewes had the best lifetime flock reproductive performance. 

 

Table 4. Effect of genotype on reproduction of ewes

 Trait

He

Hu

Ho 

 From individual reproduction records

 Total weight of kids weaned / year (kg)

18.3 ± 1.0

18.2 ± 0.8

18.1 ± 1.1

 Number of kids born / year

1.07 ± 0.05

1.06 ± 0.04

1.03 ± 0.06

 Number of kids weaned / year

0.93 ± 0.06

0.90 ± 0.04

0.89 ± 0.06

 From lifetime flock reproduction 

 Number of kidding opportunities

4.64

4.23

4.44

 Total weight of kid weaned / lifetime (kg)

68.3 ± 4.4

72.1 ± 2.8

67.42 ± 4.9

 Number of kids born / lifetime

4.71 ± 0.22

4.72 ± 0.14

4.39 ± 0.25

 Number of kids weaned / lifetime

3.77 ± 0.24

3.83 ± 0.15

3.58 ± 0.26

 

The effect of genotype on the number of kids born in the different flocks in terms of percentage of ewes of each genotype which gave birth to either 0, 1, 2 or 3 kids is summarised in Table 5. No significant trend was observed in Flock 1. In Flock 2 approximately 20% more Ho ewes did not give birth to any kids, compared to the He and Hu genotypes, while approximately 20% less Ho ewes gave birth to 1 kid. In Flock 3 there was no Ho ewes that did not produce a kid. Looking at the pooled data, there was no difference among the genotypes in terms of percentage of ewes of each genotype which gave birth to either 0, 1, 2 or 3 kids. 

 

Table 5. Effect of genotype on number of kids born in the different flocks

Flock / Number of lambs born

He

Hu

Ho 

Percentage of ewes of a specific genotype that had x number of lambs

 Flock 1 (P =0.1956)

 

 

 

 0

15.94

13.38

11.49

 1

63.91

69.41

65.54

 2

18.80

16.62

22.30

 3

1.35

0.59

0.68

 Flock 2 (P =0.1629)

 

 

 

 0

31.25

31.71

52.94

 1

66.63

66.85

47.06

 2

3.13

2.44

0.0

 Flock 3 (P =0.0254)

 

 

 

 0

8.25

3.85

0.0

 1

49.48

61.54

59.68

 2

42.27

34.62

40.32

 Pooled (P =0.1088)

 0

15.62

13.65

14.34

 1

62.22

67.35

61.48

 2

21.03

18.60

23.77

 3

1.13

0.40

0.41

 

The effect of genotype on the number of kids weaned in the different flocks in terms of percentage of ewes of each genotype which weaned either 0, 1, 2 or 3 kids is summarised in Table 6. There was no significant trend observed in Flock 1, and ewes were spread evenly among genotypes in terms of number of kids weaned category. In Flock 2 more Ho ewes did not wean a kid compared to the He and Hu genotypes. Furthermore, less Ho ewes weaned 1 kid and none weaned 2 kids. In Flock 3 less Ho ewes weaned 0 kids, while no definite trend was observed among genotype for ewes weaning either 1 or 2 kids. As was the case with number of kids born, again there was no difference in the pooled data among the genotypes in terms of percentage of ewes of each genotype which weaned 0, 1, 2 or 3 kids.

 

Table 6. Effect of genotype on number of kids weaned in the different flocks

Flock / Number of lambs weaned

He

Hu

Ho 

Percentage of ewes of a specific genotype that weaned x number of lambs

 Flock 1 (P =0.5498)

 

 

 

 0

27.22

24.56

24.32

 1

61.20

64.26

64.86

 2

11.58

10.88

10.81

 3

0.0

0.29

0.0

 Flock 2 (P =0.3152)

 

 

 

 0

53.13

49.59

67.65

 1

43.75

47.97

32.35

 2

3.13

2.44

0.0

 Flock 3 (P =0.1007)

 

 

 

 0

13.40

17.79

6.45

 1

51.55

56.25

59.68

 2

35.05

25.96

33.87

 Pooled (P =0.7896)

 0

26.57

26.21

25.82

 1

59.32

60.63

59.02

 2

14.11

12.96

15.16

 3

0.0

0.20

0.0

 

The effect of genotype on the occurrence of ewes that did not kid and ewes that aborted in the different flocks is summarised in Table 7. No definite trend could be observed across the flocks. In Flock 1, no differences were recorded among genotypes, while in Flock 2, significantly more Ho ewes did not kid than ewes of the other genotypes. In Flock 3, there were significantly more He ewes that did not kid, while all the Ho ewes kidded. In the pooled data, no significant differences among genotypes were recorded. As far as abortions are concerned, no significant differences were observed among the genotypes, although the Hu ewes had the most abortions in Flocks 2 and 3 and in the pooled data.

 

Table 7. Effect of genotype on the occurrence of ewes that did not kid or aborted in the different flocks

 Flock

He

Hu

Ho 

 

Percentage of ewes of a specific genotype that did not kid

 Flock 1 (P =0.1354)

10.38

9.12

5.41

 Flock 2 (P =0.0154)

15.63

17.89

41.18

 Flock 3 (P =0.0110)

7.22

36.36

0.0

 Pooled (P =0.5461)

10.20

8.70

9.02

 

Percentage of ewes of a specific genotype that aborted

 Flock 1 (P =0.8199)

2.11

1.91

1.35

 Flock 2 (P =0.9459)

1.59

6.88

1.59

 Flock 3 (P =0.3297)

1.03

1.92

0.0

 Pooled (P =0.5534)

2.27

2.97

2.05

 

The effect of genotype on the occurrence of kids being fostered or reared as orphans in the different flocks is summarised in Table 8. The highest percentage of kids that had to be fostered was born to Ho ewes in Flock 1. Most kids that had to be reared as orphans were also born to Ho ewes in Flock 1. All orphans in Flock 3 were born to He ewes.

 

Table 8. Effect of genotype on the occurrence of kids being fostered or reared as orphans

 Flock

He

Hu

Ho 

 

Percentage of ewes of a specific genotype that had kids being fostered

 Flock 1 (P =0.0369)

2.26

0.74

2.70

 

Percentage of ewes of a specific genotype that had kids being reared as orphans

 Flock 1 (P =0.7007)

3.31

2.79

4.05

 Flock 3 (P =0.2633)

1.03

0.0

0.0

 Pooled (P =0.0183)

1.89

0.49

1.64

 

DISCUSSION

The distribution of animals across the three CYP17 genotypes of 36.7% for He, 51.5% for Hu and 11.8% for Ho is in accordance with that of Angora veld rams genotyped with the same genotyping method in 2013 (Swart, 2013). In the latter study, 38.0% rams had a He, 46.4% a Hu and 15.6% a Ho genotype. The current distribution differs somewhat from earlier genotyping using a different genotyping method, where 42.9% He, 40.6% Hu and 16.5% Ho animals were observed (Storbeck et al., 2011). However, this previous method could not always accurately distinguish between He and Hu genotypes. An 80% correlation between the two genotyping methods was found (Swart, 2011).

 

In this study, animals of the Hu genotype were heavier from weaning age onwards, although this difference in body weight was only significant at 8 months of age and in the adult ewes. No differences were observed between the He and Ho animals. These results are in accordance with preliminary results found for the fine hair goats kept at the Jansenville Experimental Station born between 2000 and 2008 which included 117 He, 119 Hu and 62 Ho animals. No significant difference in body weight was observed among the genotypes for these ewes genotyped with the earlier method (Swart, 2010; Storbeck et al., 2011).

 

Adult ewes of the He genotype (1.35 kg) produced heavier (P <0.05) fleeces than both the Hu (1.27 kg) and Ho (1.24 kg) genotypes in the current study. Fibre diameter of the fleeces of the Ho ewes (33.0 µm) was higher than that of the fleeces of the He ewes (32.2 µm; P <0.05) and the Hu ewes (32.7 µm; P >0.05). The He ewes thus produced the heaviest fleeces with the lowest fibre diameter. In the earlier study on the fine hair ewes, no significant differences in any of the fleece traits were observed among the genotypes (Swart, 2010; Storbeck et al., 2011).

 

No significant differences were recorded in reproductive performance among the genotypes, although the Ho ewes had the lowest (1.03 and 0.89) and the He ewes the highest (1.07 and 0.93) number of kids born and weaned per year respectively. In a preliminary study 98 ewes of Flock 1 were genotyped with the same genotyping method used in the current study. In this earlier study 62.5% of the Ho ewes were poor reproducers, while the Hu and He groups had 35% and 42% poor producers respectively. Ewes were classified as poor reproducers when they weaned fewer kids than they had kidding opportunities. However, only eight ewes with Ho genotypes were identified in the sample group and there was no significant difference between the Ho and other genotypes (Swart, 2012). Hough (2012) also reported that reproduction of Merino sheep seemed to be unaffected by the CYP17 genotype.

 

CONCLUSIONS

The CYP17 genotype plays a role in the stress coping ability of the animal via cortisol production in the adrenal cortex. The He CYP17 genotype was previously identified as the hardiest genotype pertaining to stress coping ability in the Angora goat. From the results of this study no evidence could be found that selection for any of the three genotypes would adversely affect any growth, mohair production or reproduction function of Angora ewes. CYP17 genotype also had no observable effect on the reproductive fitness of rams, as measured by testosterone production. As far as mohair production is concerned, the adult He ewes produced the heaviest fleeces with the finest fibre diameter. Furthermore, although not significant, the He ewes produced the highest number of kids born and weaned per year among the three genotypes. It could therefore be suggested that the He genotype is the best adapted genotype for farming purposes and selection for this genotype should not negatively impact on reproductive performance.

 

For breeders interested in incorporating the CYP17 genotype into their selection strategy, it is recommended that to start with, all Ho genotype rams could be culled. Preferably only He sires should be used. As the Hu genotype is in abundance in the population, it would be unfeasible to cull possible Hu sires with desirable production characteristics. These sires should, however, only be mated to He genotype ewes. Mating of Hu sires to Ho ewes would yield 50% Ho and 50% Hu progeny, while a mating between a Hu sire and Hu ewes will yield 25% Ho, 50% Hu and 25% He progeny. It is not possible to get rid of the ACS- gene, as all the animals possess this gene. An effort can, however, be made to get rid of the animals that does not have the ACS+ gene (the Ho genotype), thereby increasing the frequency of the ACS+ gene in the population.

 

ACKNOWLEDGEMENTS

Mohair South Africa is acknowledged for funding of the project. Angora breeders who participated in the Angora Biobank project are acknowledged for their contribution.

 

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Published

Grootfontein Agric 16 (1) (11)