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Experiment on oestrous synchronisation for artificial insemination with frozen semen in yak

Zh. Yun

Dangxun Yak Research Centre, Lhasa 850000, Tibetan Autonomous Region, P.R. China

Summary

Irregular oestrus, silent oestrus, pseudo-oestrous and anoestrous in yak on the high and cold Tibetan Plateau pasture are very common and cause lower conception and calving rates, longer service period, dispersed service and calving, poorer production, and economic loss due to higher costs of labour and logistics. To solve the problems above, triplet hormones (containing testosterone propionate, luteosterone and estradiol benzoate), prostaglandin (PG) and follicle-stimulating hormone (FSH) No. 2 were used to induce oestrus synchronisation in 80 yak cows divided into 5 groups. The results showed that the 77.5% of the animals showed oestrus in 7 days after the treatments and resulting conception rate was 71.1%. Due to the low cost of the triplet hormones, it was used to treat another 780 yak in 1992. The conception rate in this second trial was 68.1%, twice that in the control group. These results suggest that oestrus synchronisation of yak should be an effective and practical approach in improving yak reproduction.

Keywords: Artificial insemination, frozen semen, hormone, oestrus synchronisation, yak

Introduction

There are 3.8 million yak in Tibet, one of the top five largest animal husbandry areas in China. Reproduction of yak, an animal exhibiting seasonal oestrus, is severely affected by altitude, temperature, humidity and nutrition under the extensive feeding and management systems. Normally, yak come to oestrus from July to October with a long service period but the conception rate is very low, especially in the drier years. This is because over 40% of the cows tend to have irregular oestrus, silent oestrus, pseudo-oestrus and anoestrus. Therefore oestrus synchronisation by external hormone treatments to prepare animals for artificial insemination (AI) in the extensive pastoral areas represents a possibility worth exploring. This study aimed to test and adapt a practical protocol of using a hormonal treatment regimen as a means of improving yak reproduction in smallholder herds.

Materials and methods

Trial phase in 1991

The study site was the Longren Village of Dangxun County. The area is located at an altitude of 4700 metres above sea level (masl), with an average temperature of 11.5°C, and with an annual rainfall of 280 mm and relative humidity of 6575% in August and September. The summer pasture is good quality in terms of biomass and nutritive value.

A total of 240 cows ranging in age from 4 to 8 years were divided into three herds:

1. Herd A: 80 experimental cows were further subdivided into 5 groups for treatments with different hormones and doses by muscle injection:

a. Group 1: 4 mL triplet hormones (containing testosterone propionate, 25 mg; luteosterone, 12.5 mg; estradiol benzoate, 1.5 mg per mL), 2 mL PG and 100 mg FSH;

b. Group 2: 3 mL triplet hormones and 2 mL PG;

c. Group 3: 3 to 5 mL triplet hormones;

d. Group 4: 4 mL PG;

e. Group 5: 200 mg FSH (Table 1).

Animals failing to come into oestrus 7 days after the treatment were given a repeat injection.

2. Herd B: 80 cows, which came to oestrus naturally, were serviced by AI (Table 2);

3. Herd C: 80 cows, which came to oestrus naturally, were serviced by natural mating (Table 2).

Extension phase in 1992

Based on the preliminary trial and economic evaluation, 780 cows from four villages in the county were included in the treatment of the triplet hormones only and serviced by AI in the extension phase in 1992. A total of 5887 cows expressing natural oestrus and mating in the same areas were surveyed as controls.

Results and discussion

Trial phase

Among the 80 treated cows, 62 showed oestrus within 7 days following the injection of hormones. From the 76 cows involved in the AI, the conception and calving rates were 71 and 55%, respectively. Among the different groups, those treated with the triplet hormones, PG and FSH showed the best results: a total of 13 cows came to oestrus and were serviced by AI. The conception and calving rates were 100 and 73%, respectively. A comparison of cows treated with single injections in the group, which got the triplet hormones, indicated that the latter had better conception and calving rates of 68 and 55%, respectively (Table 1).

Table 1. Oestrus synchronisation and AI in yak treated with different hormones.

Group

No.

Oestrus in 7 days after injection (No.)

AI

Conception

Calving (No.)

Reproductive rate (%)

     

No.

%

No.

%

   

1

15

15

15

100

15

100

11

73

2

15

15

15

100

10

67

10

67

3

20

16

19

95

13

68

11

55

4

15

9

15

100

9

60

6

40

5

15

7

12

80

6

50

6

40

Total

80

62

76

95

54

71

44

55

In herds B and C, 65 and 42 cows came to oestrus naturally. The conception and calving rates after AI and natural mating were 72% and 56%, and 67% and 40%, respectively for herds B and C (Table 2). Compared to the average calving rate (55%) for the oestrus-synchronised group, the average calving rate was even a little bit lower (48%).

Table 2. Data from cows showing natural oestrus and serviced by natural mating and artificial insemination (AI).

Service

No.

Oestrus

Conception

Calving (No.)

Reproductive rate (%)

   

No.

%

No.

%

   

AI

80

65

81

47

72

45

56

Natural

80

42

53

28

67

32

40

Total

160

107

67

75

70

77

48

Extension phase in 1992

After the trial phase, only the treatment with triplet hormones was selected for further extension in a large-scale trial due to its desirable results and lower cost compared to that of the treatment with the triplet hormones together with PG and FSH. The dosage for each cow was 2 to 3 mL of the triplet hormones (1 mL/100 kg body weight). From the experiences of the trial phase, AI was done only when cows come to oestrus the second time after the treatment. Among the 780 treated cows in four villages, 684 (88%) came to oestrus within 10 days after the injection, and only 531 (68%) cows that had a second oestrus were serviced by AI. The average service time was 54 days (39 to 61 days). The conception and calving rates were 80% (427/531) and 96% (411/427), respectively. In contrast, among the 5887 cows used as controls, only 1982 (34%) showed oestrus and natural mating was used. The service period was prolonged to 89 days.

The results of the large-scale trial (the extension phase) show that oestrus synchronisation could be successfully induced by treatment with the triplet hormones within a short time at a low cost in the field in smallholder herds. This can facilitate the use of AI with frozen semen from top breeding bulls. These practices could be used to improve the yak reproduction and to provide better economic returns to farmers.

Acknowledgements

The author would like to thank Li Yuchao, Zhao Xuekun, Yang Binwen, Liu Decai, Dawa Lob Sang and Yang Xilin for technical support during the field study.

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