Behavioural responses by yaks in different physiological states (lactating, dry or replacement heifers), when grazing natural pasture in the spring (dry and germinating) season on the Qinghai-Tibetan plateau
Introduction
The yak (Bos grunniens) plays an important role on the Qinghai-Tibetan plateau, where it has been acclimated to the harsh environmental conditions (e.g. cold, low oxygen and high ultraviolet radiation) in Alpine grassland. Yak husbandry depends throughout the year on the natural forage produced by alpine rangeland. Appropriate grazing management of such alpine areas must ensure, not only availability of forage, but also an environment for sustainable development. However, achieving good grazing management of alpine rangelands presupposes knowledge of how yaks interact with the vegetation.
The spring season is a key period for yak production in the grazing ecosystem of the alpine area because the most calving are occurred at this time. The interval of calving in yaks is proximate 20–24 months. Therefore, the calving rate of yaks is between 50 and 60%. The yaks live through an approximately 5-month winter period with scarce forage. At beginning of the spring season, the pastures provide very little forage available for the yaks to graze. If the herdsmen are unable to manage adequately the scarce resources, the yaks would become very emaciated, and may even die from starvation. The spring season is also a transitional period when the sparse dry forage is superseded by fresh germinating forage. As above, we believe that it is important to indicate why it is important to investigate their behaviour.
Previous work conducted with dairy cows on temperate, intensively managed grass swards (Gibb et al., 1999) has shown that lactating cows eat more at pasture than dry cows by increasing the time spent grazing at the expense of reducing ruminating time, rather than by an ability to overcome significantly the constrains on bite mass, bite rate and intake rate imposed by sward state. Penning et al. (1995) have also shown that sheep are able to alter their grazing time in relation to their physiological state. In the current experiment, we investigated the effects of different physiological states (lactating, dry and replacement heifer) on the behaviour of yaks grazing under different pasture conditions (dry and germinating).
Section snippets
Study site
The experiment was conducted from April to May 2006 in Wushaoling (N37°12.479′ and E102°51.695′, altitude 3154 m) of Tianzhu, Tibetan Autonomous County, Gansu Province, Northwest China. The climate of the research area is dominated by the southeast monsoon and high atmospheric pressure from Siberia, with severe, long winters and short, cool summers. The mean annual temperature is −0.1 °C, and mean annual precipitation is 416 mm. The pasture is alpine meadow with the sedges as the main species.
Climate and sward measurements
The data on sward characteristics are shown in Table 1. The soil water content at soil depth of 10 and 20 cm is shown in Fig. 1. The soil water content at soil depth of 20 cm was higher than that at 10 cm, but no significant difference in statistical analysis (P > 0.05).
The ground surface and air temperature showed a significant linear increase during the experimental period (Fig. 2). The surface and air temperature in May was significantly higher than in April (P < 0.05). Humidity measured at and
Effects of physiological state on grazing behaviour
The experimental design and analysis were constrained by the numbers of suitable yaks available and a degree of independence between replicates, and was also constrained by the effect of social facilitation on the behaviour of yaks during measurements.
The ash content of the herbage in the germinating period was lower than in the dry period (P < 0.05), but the ash content of the faeces in the germinating period was higher than that in the herbage (P < 0.05), and did not differ from the ash content
Conclusion
The results show that the quality of forage and sward condition can affect yaks grazing and ruminating behaviour greatly. The eating time of the yaks in different physiological states over 24 h did not differ significantly in the dry or germinating period. Under the condition of less forage supplied, the physiological states are not the main factor affecting the behaviour of yaks. In the dry period with inadequate forage and poor quality of forage, the yaks were estimated to eat less than in the
Acknowledgements
We thank P.Y. Zhao for assistance with the fieldwork and X.L. Liu for supplying animals and caring for my daily life in field. We would like to thank Prof. Malcolm Gibb at North Wyke for his assistance in revising this manuscript. This work was financially supported by the Hundreds-Talent Program, Chinese Academy of Sciences.
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