Estimates of genetic and phenotypic covariance functions for postweaning growth and mature weight of beef cows

Annual weights of cows from 19 to 119 months of age in two herds were analysed fitting a random regression model, regressing on orthogonal polynomials of age in months. Estimates of covariances between random regression coefficients were obtained by restricted maximum likelihood, and the resulting estimates of covariance functions were used to construct covariance matrices for all ages in the data. Analyses were carried out fitting regression coefficients corresponding to overall animal effects only and fitting regressions for animals' additive genetic and permanent, environmental effects. Different definitions of fixed effects subclasses were examined. Models were compared using likelihood ratio tests and estimated standard deviations for the ages in the data. Cubic regressions were sufficient to model both population trajectories and individual growth curves. Random regression coefficients were highly correlated, so that estimation forcing their covariance matrices to have reduced rank (2 or 3) did not reduce likelihoods significantly, allowing parsimonious modelling. Results showed that records were clearly not repeated measurements of a single trait with constant variances. As cows grew up to about 5 years of age, variances. As cows grew up to about 5 years of age, variances increased. Estimates of genetic correlations between 3-year-old and older cows were close to unity in one herd but more erratic in the other. For both herds, genetic correlations between weights on 2-year-old cows and older animals were clearly less than unity.     

Comparative study on the regulation of body fluids and mammary circulation at different stages of lactation in crossbred Holstein cattle feeding on different types of roughage

The present study was carried out to evaluate the effect of prolonged feeding of urea‐treated rice straw, compared with feeding of hay, on the regulation of body fluids, milk yield and mammary circulation at early lactation (30 days postpartum), mid‐lactation (120 days postpartum) and late lactation (210 days postpartum) in crossbred Holstein Friesians. Sixteen first lactating crossbred Holstein Friesians (HF), consisting of eight animals of two breed types, 87.5%HF and 50%HF, were selected and each breed was randomly allocated into two groups. Each group, consisting of four animals from the same breed, was fed either 5% urea‐treated rice straw or pangola hay (Digitaria decumbens) as the source of roughage in combination with a similar concentrate throughout the experiments. During the course of lactation there were no significant differences in body weight, heart rate, mean arterial blood pressure, plasma osmolality, plasma volume and blood volume among groups of 87.5%HF animals and 50%HF animals fed either hay or urea‐treated rice straw. Water turnover rate, total body water space and total body water as a percentage of body weight of 50%HF animals were significantly higher than those of 87.5%HF animals fed either hay or urea‐treated rice straw. The packed cell volume was significantly higher in all lactating periods of both groups of 50%HF animals in comparison with 87.5%HF animals. The ratio of DM intake to milk production for 87.5%HF animals fed either hay or urea‐treated rice straw was significantly lower than that of 50%HF animals in early lactation. The udder blood flow and milk secretion of 87.5%HF were significantly higher in early lactation and markedly declined when lactation advanced in comparison with those of 50%HF animals fed either hay or urea‐treated rice straw. The ratio of mammary blood flow to milk yield for all groups was in a similar range during early lactation although it significantly increased in mid‐ and late lactation for both groups of 87.5%HF animals. From these results it can be concluded that both 50%HF and 87.5%HF animals feeding on urea‐treated rice straw as a roughage source do not show any undernutritional effects in comparison with those fed with hay during the course of lactation. The physiological response differences between breeds are that 87.5%HF animals, which have a genetic makeup closer to the exotic bos taurus breed and a high milk yield, show a poor adjustment to the tropical environment and poorer lactation persistency in comparison with 50%HF animals.     

Selection response in Tribolium to an index modified by introducing between-family or within-family or both restrictions in two steps

A fundamental strategy in selection programs is to combine maximum rate of response and minimum rate of inbreeding, these goals being in conflict with each other. Maximum selection response can be achieved at a cost of erosion in the effective number of breeding animals (a measure of the inbreeding level); reciprocally, the maximum effective number under selection can be preserved with a low response. The simultaneous consideration of both factors makes it difficult to decide on the use of individual (more effective in conserving effective number) or combined selection (maximizes response but yields low effective size). Q uinton et al. (1992) showed that comparing selection methods at the same level of inbreeding, rather than at the same selection intensity, changes the perspectives of current selection theory. If low to moderate inbreeding levels are considered, then phenotypic selection can yield higher response than selection on more accurate methods. Different methods have been proposed for maximizing selection response at the same level of inbreeding, i.e. to restrict the number of close relatives selected (N icholas and S mith 1983), to use false high heritability estimates in the genetic evaluation (G rundy and H ill 1993), to use assortative (S mith and H ammond 1986) or compensatory (G rundy et al. 1994) matings, to adjust estimated breeding values for the relationship with the already selected ones (G oddard and S mith 1990), to avoid matings of related individuals (T oro and P erez -E nciso 1990), or to use factorial rather than hierarchical matings (W oolliams 1989; L eitch et al. 1994). Q uinton and S mith (1995) compared the merits of these methods using stochastic simulation; they concluded that none of the methods was best over all conditions, and that the use of false high heritabilities, or adjusted estimated breeding values with the relationships, does not seem to be recommended; besides, mating together those individuals with the lowest relationship has little effect on the accumulated inbreeding. W ray and G oddard (1994), and B risbane and G ibson (1995) indicated that if G_n is the genetic mean after n generations of selection and F_n is the mean inbreeding coefficient, a reasonable selection objective is G_n ? DF_n, where D is the value of a unit of inbreeding relative to a unit of genetic gain. M euwissen (1997) showed that these methods do not guarantee maximum genetic gains at some level of inbreeding and presented a rule for maximizing the genetic response with a predefined rate of inbreeding. His algorithm can be used to put a constraint on the variance of the selection response by replacing the additive relationship matrix by the prediction error variance (W oolliams and M euwissen 1993). W ei (1995a) developed a restricted phenotypic selection by considering limits on the number of individuals that will be selected from a family or on the family number selected. This less sophisticated method balances response and inbreeding. A restriction on the family number may lead to an increased response (but a decreased effective size), whereas restricting the proportion of selected individuals from a family is an efficient way to control the inbreeding (decreased response). W ei (1995b) generalized the method by introducing both restrictions. In this study, rates of response were compared under between-family, within-family, or both restrictions for a two-trait selection index in a short-term experiment with Tribolium.     

內蒙及察北蒙古羊杂交改良研究报告第三号——五一牧場杂交兩代結果

五一牧場位于察哈尔盟(現已併入錫林郭勒盟)的东南部,东經116°,北續48°,海拔1,500公尺以上,面积約有60,000公頃。場境内有閃电河、黑风河和羊腸子河。全場有放牧地44,944公頃,打草地3,000公頃,耕地面积約3,000公頃。根据多倫气象站1955年測定的气象材料、年平均温度1.76℃,最高温度35.4℃,最低温度-33.4℃,冬季时間漫長,全年有五个月的平均温度在零下。年降水量429.5毫米,蒸发量1,507.8毫米,风向多为西北风,全年无霜期105天。适于当地种植的作物有燕麦、莜麦、豌豆、粟、蕎麦和馬鈴薯等。該場屬于干旱草原,按自然情况划分牧場。冬季春季牧場为沙窩地区,屬砂質土壤。夏季牧場为平原地区,屬粘質壤土,带硷性,牧草以禾本科为最多。平原地区多为硷草,沙窩地区为沙丘草,一般草高40厘米,每公頃产下草約750公斤。     

中国杉木研究动态

(单位:千公顷)森林和有林地国家合计疏林郁闭林1.苏联2.巴西3.加拿大4.美国5.4t伊尔6.印度尼西亚7.中国8.澳大利亚9.波利维亚10.印度1 37 0C07 91 600928 600000357 4805 L4 480300820264 100436 4001 95 256298 076,‘O白乃山忆口﹄.︹︺‘.1 .1.走7 LS砖0105了501 77 5903 0001 138951 IG 8951 7 20097 8471 15 04765 085硅1 658106 74322 75044 01066 7605 3935 1 84157 234森林最丰富的10个国家~~…     

美国濒危物种进出口管理工作

美国依据《濒危野生动植物国际贸易公约》和国内一系列有关法律对濒危物种进出口实行严格管理。作者介绍了美国的管理经验。建议我国进一步完善管理法规、严格管理程序、健全管理机构、加强口岸管理和重视重要经济、药用动物及制品的进出口管理。     

苏联2005年林业发展纲要明确了改革方向

1989年5月,苏联发表《2005年林业发展纲要》,明确了林业改革方向和重点:林业财政基本上仍保持国家预算制;突出了监督和森林经理的作用;基层干部林务员的地位,职工的培训受到特别重视;遵循计算采伐量,消除过伐和采伐不足,可以提高采伐量0.5-1倍;向天然更新倾斜,同时又要求工业人工林在21世纪中期成为用材的一个主要来源。     

森林遗传资源保存的现状和策略

综述了世界森林遗传资源保存的历史和现状,作者认为中国森林遗传资源的保存策略应为系统管理、有效保存、合理利用、丰富发展。     

关于保护和发展我国森林的思考

作者认为保护和发展我国森林的根本指导思想和理论基础是森林生态经济系统思想和森林生态经济学理论。本文还就林业发展方向、林业生态工程项目、工业用材林和薪炭林营造、资源综合高效利用,以及加强山区现有天然林的保护提出了具体看法。