F. Changxiu,1 W. Jianwen1 and P. Jiabi2
1. Sichuan Provincial General Station for Breeding and Improvement of Animal and Poultry, Chengdu 610041, Sichuan,
2. Heifer Project International, China Office, Chengdu 611731, Sichuan, P.R. China
Live weights of 2.5-year-old male and female crossbreds between Holstein and yak were 310 and 305 kg, respectively. These were 192.2% and 168.6% higher than weights of pure yak. The milk yield of the crossbreds was 1019 kg, which was 4.5 times as much as that of the pure yak. The F1 of (Holstein × Yellow cattle) × yak produced 607.9 kg of milk in the first lactation, which was 2.43 times as much as the pure yak. However, due to the sterility of male hybrids, this heterosis could not be fixed. Furthermore, the continuous upgrading of the hybrids by Holstein was considered undesirable as they are not adapted to the plateau environment. In addition, the conception rate and the survival rate of hybrid calves produced by AI were very low and the cost for producing one hybrid calf was more than 200 RMB Yuan (US$ 1 = 8.2 Yuan during this study). Based on these results, the following suggestions are made with regard to yak improvement in Sichuan:
Keywords: Hybridisation, improvement, suggestion, yak
In the north-west Plateau of Sichuan Province, there are 4.07 million head of yak, representing 30% of the total yak population in China. This is the home of the famous Chinese yak, Maiwa and Jiulong. The lactation length is 5 to 6 months with a milk yield of 200 to 205 kg. Yak are slaughtered at about 5 years of age with a carcass weight of only 50 to 80 kg. To improve milk and meat production, farmers cross their yak with the native Yellow cattle. But the milk and meat production of the hybrids are not much better because the Yellow cattle are not much better. In the 1950's, some Holstein bulls were introduced to the Plateau for use in crossbreeding with yak. The milk and meat production of the hybrids were double that of the pure yak, making the crosses to become very popular with the farmers. However, the Holstein bulls did not adapt to the environment of the Plateau and died in large numbers. In the middle of 1970's, the agricultural department in Sichuan started to use artificial insemination (AI) on yak with frozen Holstein semen as an alternative to natural mating. From 1976 to 1991, more than 40 thousand head of yak were bred with AI and about 10 thousand hybrid calves were born. However, the AI stopped from 1992 to 1998 because of budgetary constraints. In 1999, some counties, including Hongyuan, Aba and Ruo'egai started to use AI again. In addition, the Livestock Improvement Station in Aba Prefecture and other county bureaus of animal husbandry introduced about 45 head of male Simmental × Yellow cattle and Holstein × Yellow cattle hybrids for crossing with yak. To date there are about 15 thousand head of female hybrids, including 3800 head of Holstein crossbreds.
Since the mid 1970's, a lot of studies have been conducted on crossing involving Holstein, Simmental, Shorthorn, Hereford, Charolais and Holstein × Yellow F1 with female yak. All of the hybrids expressed high heterosis on growth and milk traits. The milk yield of the Holstein × yak F1 was more than two times that of pure yak. The Simmental or Hereford × yak F1 expressed significant hybrid vigour in meat production and the live weight gain increased by 42% to 98% compared with the pure yak.
The bodyweight at birth of male and female Holstein × yak F1 were higher than that for pure yak by 73.7 and 76.3%, respectively. Corresponding figures for 6-month weights were 59.2 and 66.9% and for 12-month weights 82.7and 73.2%, respectively. The weight of 2.5 year old male and female (Holstein × Yellow cattle) × yak hybrids were 310 kg and 305 kg which were 196.2% and 168.6%, respectively, higher than that for the pure yak.
A study conducted in Waqie Farm in the Hongyuan County in 1981 showed that Holstein × yak F1 produced 5.27 kg of milk/day, on average, from May to August. This was 3.3 times the daily milk production of pure yak. The milk fat produced by the Holstein × yak F1 was 127.7% more than that of yak. The lactation length of the hybrids was 285 days with a total lactation milk yield of 1019 kg when the animals were fed with some concentrates in the cold season.
The Holstein × yak F1 is popular amongst farmers because of its adaptability, higher milk and meat production and good overall economic benefits. However, backcrossing to Holsteins compromised adaptability. Most farmers backcrossed F1 females to yak bulls but the offspring grew more slowly with less meat and milk production compared to the F1 crosses.
The conception and the survival rates of hybrid calves by AI were very low. From 1976 to 1990, 37,091 head of yak were serviced by AI, but only 7610 calves were born and survived. The reproductive rate was 20.5%. This compares to 53.2% by natural breeding on yak. In addition, the cost for producing one hybrid calf was more than 200 RMB Yuan. The farmers could not afford this. So, the production of hybrids could not be sustained.
The high enthusiasms of farmers in some areas have been attracted due to the great economic benefits associated with crossbreds; there is much enthusiasm by farmers in some areas, for example, Hongyuan, Ruo'egai and Aba. As a result, the price of a crossbred (F1) cow (3000 to 4000 RMB Yuan) is 3 to 4 times that of purebred yak cows. Farmers in Maiwa Township of Hongyuan County are even willing to pay for AI service for the crossbreeding.
There is a milk processing plant with capacity for 20 tonnes of fresh milk everyday in Hongyuan County. This is the main outlet for farmers in this and surrounding counties.
The government is paying particular attention to yak production. The projects of Jiulong yak and Maiwa yak selection and breeding are currently being carried out in Jiulong County and Hongyuan County.
The selection in Jiulong yak should focus on growth and meat production while that for the Maiwa yak should be milk production. In Hongyuan and the other surrounding counties, selection should focus on both meat and milk. Jiulong yak and Maiwa yak can be used to improve local yak. The hybridisation between Holstein or Simmental and yak can be done in Hongyuan, Ruo'egai and Aba etc.
The Simmental semen and Simmental × Yellow cattle F1 bulls can be used to hybridise with yak. Simmental × Yellow cattle hybrids are adaptable to the Plateau conditions. Even though their body size is rather large, their high milk and meat production is very good and farmers find them acceptable.
There are specific considerations for the breeding female yak to be used for hybridisation. Breeding female should be 5 to 8 years old, should have a large body frame and, given the value of the male genotypes used and the offspring expected, should be strong and healthy to ensure the production of a strong calf. The animals should be kept on good grazing with salt supplement as necessary.