Grazing behavior of lactating and non-lactating yaks in the summer season of the Qinghai-Tibetan plateau

The effect of the physiological states of lactating vs. non-lactating (dry) on grazing behavior and herbage intake by yaks was examined in the summer season in the Qinghai alpine area under continuous stocking management. Intake rates were estimated over periods of 1 h by weighing the animals before and after grazing, retaining the feces and urine excreted, and applying a correction for insensible weight loss (the 1-h weight changes of yaks when non-eating before or after the intake rate measurement). It is hypothesized that the lactating yaks should eat more and spend more time eating than nonlactating yaks, because they expend more energy. In our experiment, there were no differences in the effect of physiological state (lactating vs. dry) of yaks observed on the rate of insensible weight loss, intake rate, grazing jaw movement rate, bites per grazing jaw movement, or bite mass. The dry yaks tended to eat more and spend more time eating than lactating yaks, but not significantly so. Compared with the dry yaks, the lactating yaks had a significantly lower bite rate and bites per bolus.

利用夏季自然发情的云南黄牛进行奶牛胚胎移植效果研究

利用夏季自然发情的云南黄牛为受体,开展了奶牛体内冷冻胚胎移植.留用的114头受体牛中,本地黄牛59头,年龄在3～10岁,均为经产牛,最终移植27头,西杂牛56头(其中2岁以下的青年牛26头),移植29头(青年牛11头),两个品种受体利用率分别为45.8%和51.8%;移植后妊娠率分别为59.3%和55.2%;解冻的63枚胚胎移植给了56头受体牛,A级胚胎单独移植和B、C级胚胎搭配移植最终妊娠结果分别是58.5%(24/41)和53.3%(8/15);发情后第6 d和第7 d移植妊娠率分别为56%和58.1%.结果表明,1～10岁的西杂牛和3～10岁体型较大的本地黄牛均可作为受体移植奶牛胚胎;利用自然发情的云南黄牛做受体移植效果较为理想,是一种经济、方便、适合云南广大农村推广的技术途径;A级胚胎单独移植和B、C级搭配移植可获得较为理想的妊娠结果;处于发情后第6 d和第7 d的云南黄牛都可以作为桑囊期奶牛胚胎的移植受体.

黄土沟壑区砂石覆盖果园土壤剖面水分分布

以黄土高原沟壑区砂石覆盖苹果园为研究对象,对600 cm范围内土壤剖面水分含量的时间分异和空间分布状况进行了研究。结果表明:600 cm土层范围内,一周年内可划分为冬季增墒期和夏季失墒期两个阶段;土壤剖面水分空间分布随土壤深度的增加呈现波动性变化且稳定性不同,土壤含水量变化幅度随土层深度增加而变小,据此可将600 cm范围内的土壤剖面划分为速变层、相对稳定层、缓变层和稳定层;土壤水分在不同层次上的分布差异,8月土壤剖面不同层次含水量差异最大,11月次之,5月再次之,1月土壤不同层次含水量差异最小。综合看来,除土壤表层因砂石覆盖水分增加外,土壤剖面含水量随土壤深度的增加而减少且趋于稳定,水分下渗能力减弱;冬季土壤含水量多且分布均匀,夏季土壤水分减少且主要集中在上层,此时土壤不同层次水分含量差异大。

Dynamics of the buoyant plume off the Pearl River Estuary in summer

Field measurements of salinity, wind and river discharge and numerical simulations of hydrodynamics from 1978 to 1984 are used to investigate the dynamics of the buoyant plume off the Pearl River Estuary (PRE), China during summer. The studies have shown that there are four major horizontal buoyant plume types in summer: Offshore Bulge Spreading (Type I), West Alongshore Spreading (Type II), East Offshore Spreading (Type III), and Symmetrical Alongshore Spreading (Type IV). River mouth conditions, winds and ambient coastal currents have inter-influences to the transport processes of the buoyant plume. It is found that all of the four types are surface-advected plumes by analysing the vertical characteristic of the plumes, and the monthly variations of the river discharge affect the plume size dominantly. The correlation coefficient between the PRE plume size and the river discharge reaches 0.85 during the high river discharge season. A wind strength index has been introduced to examine the wind effect. It is confirmed that winds play a significant role in forming the plume morphology. The alongshore wind stress and the coastal currents determine the alongshore plume spreading. The impact of the ambient currents such as Dongsha Current and South China Sea (SCS) Warm Current on the plume off the shelf has also assessed. The present study has demonstrated that both the river discharge and wind conditions affect the plume evolution.

Studies on mass summer mortality of cultured zhikong scallops (Chlamys farreri Jones et Preston) in China

Mass mortalities of cultured zhikong scallops (Chlamys farreri) have occurred each summer in most culture areas of northern China since 1996. Among the hypothesized causes are high culture density, infectious disease and genetic inbreeding. To investigate these potential agents, C. farreri were deployed at three densities (low, medium and high) at three sites (Jiaonan, Penglai and Yantai) in the summer of 2000. Scallops were sampled for survival, growth and histopathology before, during and after a mortality episode. Most of the mortality occurred in July and August, during and toward the later part of the spawning season, when water temperature reached 23-26 degrees C. Final cumulative mortalities reached 85% to 90% at all three sites. Scallops in the medium and high densities had higher initial death rates than did those at the low density. High densities also inhibited growth. Ciliates from the genus Trichodina, larvae of various organisms and anomalous secretions were observed in sections of the gill cavity, with highest prevalence during and at the end of the mortality period. Prokaryotic inclusion bodies were found in the soft tissues, but their prevalence was low and apparently without correlation with mortalities. Genetic analysis with random amplified polymorphic DNA markers showed slightly lower heterozygosity in the cultured stocks (0.301) than in the wild stocks (0.331). It is possible that the mortalities are caused by a combination of several factors such as stress associated with reproduction, high temperature, overcrowding and poor circulation in the growout cages, opportunistic invaders or pathogens, and possibly inbreeding. (c) 2005 Elsevier B.V. All rights reserved.

Survival, growth and immune activity of scallop Chlamys farreri cultured at different depths in Haizhou Bay (Yellow Sea, China) during hot season

Survival, growth and immune response of the scallop, Chlamys farreri, cultured in lantern nets at five different depths (2, 5, 10, 15, and 20 m below the sea surface) were studied in Haizhou Bay during the hot season (summer and autumn) of 2007. Survival and growth rates were quantified bimonthly. Immune activities in hemolymph (superoxide dismutase (SOD) and acid phosphatase (ACP)) were measured to evaluate the health of scallops at the end of the study. Environmental parameters at the five depths were also monitored during the experiment. Mortalities mainly occurred during summer. Survival of scallops suspended at 15 m (78.0%) and 20 m (86.7%) was significantly higher than at 2 m (62.9%), 5 m (60.8%) or 10 m (66.8%) at the end of the study. Mean shell height grew significantly faster at 10 m (205.0 mu m/d) and 20 m (236.9 mu m/d) than at 2, 5 or 15 m in summer (July 9 to September 1); however, shell growth rate at 20 m was significantly lower than at the other four depths in autumn (September 2 to November 6). In contrast to summer, scallops at 5 m grew faster (262.9 mu m/d) during autumn. The growth of soft tissue at different depths showed a similar trend to the shell. Growth rates of shell height and soft tissue were faster in autumn than in summer, with the exception of shell height at 20 m. SOD activity of scallops increased with depth, and ACP activity was significantly higher at 15 and 20 m than at other depths, which suggests that scallops were healthier near the bottom. Factors explaining the depth-related mortality and growth of scallops are also discussed. We conclude that the mass mortality of scallop, C. farreri, during summer can be prevented by moving the culture area to deeper water and yield can be maximized by suspending the scallops in deep water during summer and then transferring them to shallow water in autumn.

Feeding behaviour of yaks on spring, transitional, summer and winter pasture in the alpine region of the Qinghai-Tibetan plateau

Of the present estimated world population of 14.2 million yaks, approximately 13.3 million occur within Chinese territories (Food and Agriculture Organization of the United Nations, 2003). Although there is an extensive bibliography covering the species, few studies have been conducted in the area of foraging behaviour. The present study was conducted at pasture during the spring, transitional, summer and winter seasons to determine the daily temporal patterns of grazing and ruminating behaviour by yaks. During each study period, two 24 h recordings were undertaken with each of six mature dairy yaks. One study period was conducted on each of the transitional, summer and winter pastures, whereas, due to the considerable changes occurring in the morphology of the spring pasture, three separate studies were completed during March, April and May. During the second of these studies (April), the effect of level of concentrate supplementation on grazing and ruminating behaviour was also examined. Behaviour recordings were made using solid-state behaviour recorders. Short-term intake rates (IR, g min(-1)) were calculated by weighing yaks before and after approximately 1 h of grazing, retaining the faeces and urine excreted and applying a correction for insensible weight loss. Yaks spent less time grazing during the dry season (the early period on the spring pasture) compared with the later green swards (the later period on the spring pasture, the transitional pasture and the summer pasture) (P < 0.05). When the forage quality improved, but there was still insufficient mass (the later period on the spring pasture), the yaks extended their grazing time at the expense of other activities. During the early periods on the spring pasture, the short-term IR by yaks was up to 53 g DM min(-1), significantly higher than at other times (P < 0.05). The level of concentrate offered had little or no effect on grazing or ruminating time. The total eating time of the yaks offered 0.5 or 1.0 kg concentrate was 2.9 and 4.5 h day(-1) respectively, significantly lower than unsupplemented yaks (6.8 h) (P < 0.05). In general, yaks can regulate their foraging behaviour according to the changes of sward conditions in order to achieve optimal grazing strategies. (C) 2007 Published by Elsevier B.V.