A study on the improvement of yak reproductive performance by introducing wild yak blood

Y. Shoudong

Qinghai General Station of Animal Husbandry and Veterinary, Xining, 810001, Qinghai, P.R. China

Summary

Wild yak semen was used in an experiment to study the possibility of increasing the reproductive performance of domestic yak by both artificial insemination (AI) and controlled natural mating. AI and natural mating raised reproductive and survival rates to 68.1% and 64.4%, respectively. Superior benefits were achieved in the study.

Keywords: Domestic yak, reproduction, wild yak

Introduction

In highland pasture ecological environment, yak reproductive ability is rather poor. There is a need to improve the yak reproductive performance. Through the years from 1992 to 1997, frozen semen from wild yak and semi-wild yak bulls were used by AI and controlled natural mating, respectively, to improve the reproduction in yak herds at Saishitang Farm. This paper summarises the results of the project.

Materials and methods

Study area

Saishitang farm is located at the southern Qinghai Plateau, at an altitude of 3500–4930 metres above sea level (masl). The AI station was set up on natural grassland for autumn transhumance (which is roughly at the altitude of 4000 masl). The pasture of the area is of the alpine meadow type and plant species are mainly sedge and gramineous. There are no distinctive four seasons but only cold and warm seasons can be identified. The climate is typically continental with frequent gusts of wind during the cold period. The annual average temperature is 0.6°C and precipitation about 300 mm. There is no frost-free period in the year. The annual growing period of vegetation is about 120 days. The crop species are mainly barley and rape.

Animals

The yak cows used in study were from individual herders, and were aged between 4.5 to 10 years. Most of them were not pregnant in the previous year and were non-lactating at the time of the study. These yak cows were assigned to different groups and given ear tags. Each animal's code, coat colour, physical description and reproductive performance were recorded. Animals were in above-average nutritional status at this time of the year (July to early September), with improving body condition throughout the breeding period.

Semen and semi-wild yak bulls

Frozen semen pellets of wild yak and semi-wild yak were obtained from the Datong Yak Farm. After being thawed, the sperm vigour in the semen was 0.3–0.4 and each pellet had about 10 million viable sperms. The semi-wild yak bulls were evaluated by bull standards and transported to the study area. They were kept in 10 herder households where they were trained to be used for the controlled natural mating.

Synchronised oestrus technique

All cows in the study were treated with hormones to improve oestrus and conception rate by synchronised oestrus technique. A lot of attention was given to cows, which had missed the first oestrus and needed the second insemination or controlled natural mating. The two hormone reagents were tested and optimised to determine the best doses and injection time and satisfactory results were obtained. The hormone treated cows showed a 55% synchronisation rate which was significantly (P<0.01) higher than that of cows in the control group, and conception rate was as high as 72.73%.

The heat period of the yak cow is comparatively short, with less vaginal mucus and weaker symptoms than that of the bovine. The proper AI time should be at the time when the cow accepts detector bull to mount and the follicle development is at advanced stage as ascertained by rectal palpation. This usually happens before 08:00 hour in the morning or after 19:00 hour in the evening.

All the tested cows in the study (including the control cows) were kept from contact with any bulls from outside. At the end of the mating period, all the tested cows were kept in herder households and had good care, and they kept a state of above-average body condition to help their pregnancies and calving and calf survival.

Results and discussion

Artificial Insemination using frozen semen

From 1992 to 1996, 304 cows were inseminated, 266 were re-examined and 194 were found to be pregnant by AI (72.93%). A total of 181 resulting calves survived, thus the reproductive and survival rate was 68.1% (Table 1).

Table 1. Reproductive and survival rate of artificial insemination (AI) group.

Year	No. of cows	Cows serviced		Pregnant cows	Calving		Survived calves
		No.	%		No.	%	No.	%
1993	91	33	36.3	25	19	76.0	19	76.0
1994	182	108	59.3	78	61	78.2	61	78.2
1995	175	54	30.9	54	35	64.8	30	55.6
1996	149	20	13.4	20	15	75.0	11	55.0
1997	89	89	100.0	89	64	71.9	60	67.5
Total	686	304	44.3	266	194	72.9	181	68.1

Results in Table 1 show that through a set of combined techniques such as introducing wild yak genetics, synchronised oestrus treatment, AI, improved management and sufficient nutrition supplement, a high reproductive and survival rate can be achieved in yak.

Controlled natural mating

From 1992, 10 semi-wild yak bulls were used to service yak cows in 10 herder households. In the subsequent 5 years, a total of 755 yak cows were involved in the study. Out of these, 616 cows (81.59%) got mated, 500 cows (81.17%) conceived and 486 calves survived to weaning. The overall reproductive and survival rate was 64.4% (Table 2).

From Table 2, it is concluded that when the bulls are chosen properly and the male/female proportion are reasonable, with correct controlled natural mating method, a high reproductive and survival rate could be achieved in highland yak production.

Table 2. Reproductive and survival rate of controlled natural mating group.

Year	No. of cows	Cows mated	No. of newborn	Weaned calves (%)	Reproductive and survival rate
					No          %
1993	125	99	80	80.8
					80	64.0
1994	135	109	88	80.7	85	63.0
1995	140	121	96	79.3	92	65.7
1996	135	120	98	81.7	95	70.3
1997	220	167	135	82.6	134	62.7
Total	755	616	500	81.2	486	64.4

From this study, we can draw the following conclusions:

1. Through introduction of wild yak genetics, offspring vitality can be greatly improved, as can the reproductive rate.
2. AI requires some basic techniques, in the difficult areas, it is suggested to use the semi-wild yak bulls in the controlled natural mating to improve reproduction in yak cows.
3. Introduction of wild yak is not only good for yak reproductive performance, but is also helpful for the protection of the environment in highland pasture. Through these technologies it should be possible to improve the welfare of the people through improved yak production.
4. The methods of introducing wild yak genetics in domestic yak production should be combined with other techniques and pre- and post-production services such as advanced management (proper female/male ratios, controlled milking and timely weaning), disease control, pasture management, shelter construction, speeding up of finishing and recycling of herds and marketing to increase profit margins.