Evaluation of a contract breeding management program in selected Ohio dairy herds with event-time analysis I. Cox proportional hazards models

An observational study was conducted in order to assess the impact of a contract breeding program on the reproductive performance in a selected group of Ohio dairies using event-time analysis. The contract breeding program was offered by a breeding co-operative and featured tail chalking and daily evaluation of cows for insemination by co-operative technicians. Dairy employees no longer handled estrus detection activities. Between early 2002 and mid-2004, test-day records related to production and reproduction were obtained for 16,453 lactations representing 11,398 cows in a non-random sample of 31 dairies identified as well-managed client herds of the breeding co-operative. Of the 31 herds, 15 were using the contract breeding at the start of the data acquisition period, having started in the previous 2 years. The remaining 16 herds managed their own breeding program and used the co-operative for semen purchase.

Cox proportional hazards modeling techniques were used to estimate the association of the contract breeding, as well as the effect of other significant predictors, with the hazard of pregnancy. Two separate Cox models were developed and compared: one that only considered fixed covariates and a second that included both fixed and time-varying covariates. Estimates of effects were expressed as the hazard ratio (HR) for pregnancy.

Results of the fixed covariates model indicated that, controlling for breed, herd size, use of ovulation synchronization protocols in the herd, whether somatic cell score exceeded 4.5 prior to pregnancy or censoring, parity, calving season, and maximum test-day milk prior to pregnancy or censoring, the contract breeding program was associated with an increased hazard of pregnancy (HR = 1.315; 95% CI 1.261–1.371). The results of the time-varying covariates model, which controlled for breed, herd size, use of ovulation synchronization protocols, somatic cell score above 4.5, parity, calving season, and testing season also found that the program was associated with an increased hazard of pregnancy (HR = 1.387; 95% CI 1.327–1.451).

The fixed and time-varying covariates models both found similar sets of predictors when analyzing the association of the contract breeding program with hazard of pregnancy. Both models identified a 30% or greater increase in hazard of pregnancy associated with use of the contract breeding program, suggesting that herds subscribing to the program achieved pregnancies in a more timely fashion.     

食品中亚硝胺类化合物的危害及控制研究进展

亚硝胺是对人类健康危害性极高的化合物之一。本文阐述N-亚硝基化合物的危害及在食品中的分布状况,综述应用辐照和天然植物提取物等阻断剂消除和控制食品中N-亚硝基化合物技术措施的研究进展。     

廊坊地区地下水开采引起的环境地质问题及防治对策

从廊坊地区供水水源地的水文地质特征和地下水动态分析入手,指出由于长期的超量开采导致地下水水位急剧下降,从而引发的一系列环境地质问题。如何有效地利用地下水资源,以满足人类生活、经济发展和城市建设的可持续发展已成为需急解决的问题,需采取一系列相关措施有效解决并防治环境地质问题。     

商业银行经营缺乏创新的危害及原因分析

商业银行的同质化倾向是其经营缺乏创新的反映,这对信贷资金供给、商业银行发展、宏观经济调控都产生了危害。创新不足的外部原因是缺少引导与激励商业银行创新的环境,内部原因是商业银行自身缺乏创新动力与创新能力,这需要从监管设计、行业促进、银行变革三方面突破,提升商业银行系统的活力,提高资源配置效率。     

Influence Analysis of Main Geological Factors on Gas Content in No. 3 Coal Seam of Mayixi No. 1 Shaft

运用瓦斯地质理论，从煤体（埋深、厚度、变质程度）、煤体围岩、地质构造3个方面定性定量地对马依西一井3^#煤层瓦斯含量进行分析，得出煤层厚度，变质程度，围岩封闭性和地质构造是该矿3^#煤层瓦斯含量主要地质影响因素。     

黑沙蒿生态生物学特性及群落地理分布规律相关性研究

黑沙蒿 ( Artemisia ordosica Krasch.)是我国北方温带荒漠和草原地带沙漠化的主要标志型半灌木植被黑沙蒿群落的建群种。其分布范围跨越了典型草原、荒漠化草原和草原化荒漠三个自然带。除具有中等饲用价值外 ,耐沙埋、抗风蚀、扎根深、分枝多、结实率高等生态生物学特性使其在农牧过渡带成为固定流沙的先锋植物。本文着重研究黑沙蒿的繁殖生态生物学特性及群落功能特征 ,最终揭示其地理分布规律。对合理开发、科学利用和管理黑沙蒿这一宝贵的沙地植物资源具有重要指导作用。     

中国土壤科学复兴之道──献给我国土壤地理工作者

本文对整个土壤形成过程中“风化过程和成壤过程同时同地进行”的理论,作了新的补充;并在明确其局限性的基础上,针对这二个过程的实质,结合我国主要土壤的发生演变及其地理分布规律进行了总结研究以后,发现当前土壤工作中出现一些不容忽视的缺陷。其中较为重大的有:（1）在对待具体土壤性征尤其诊断层（diagnostic horiron）时,强调“统一形成”有余,而对“生物小循环”仅仅是在“地质大循环”轨道中某一比较稳定环节上,在有限深度内进行的实质考虑不够;（2）对于生物小循环中植物对营养元素的选择性吸收和以有机质、植物残体与腐殖质状态的积累和腐殖质作为“一个自然体的土壤”的基本特征等比较重视,而对矿质元素的生物反馈、淋溶迁移、生物成矿尤其粘土矿物的生物起源等有所忽视;（3）在进行土壤理化试验研究,尤其模拟实验时常将土（earth）代壤（soil）。促使研究工作背离实际,难于反映本质和满足生产需要。当前我国土壤地理工作面临的抉择是:要么“穿新鞋走老路”;要么改弦易辙,在充分发扬我国古代紧密联系生产实际的优良传统的基础上,善于吸取国外先进经验,尤其现代先进技术,在充分发挥我国土壤资源丰富和对土壤耕作培肥经验等优势,以及在土壤形成过程中对生物小循环新认识的优势,尤其黄土高原特有土壤形成过程研究成果的优势,并以建立一个既有我国特色、紧密联系生产,又能定量化、标准化并便于国际交流和有助于正确探索全球环境变迁的土壤系统分类制为突破口,把我国土壤科学的水平不断推向前进。     

泥石流沉积与环境及其在防灾减灾上的意义

列出了5种泥石流沉积类型或亚相。A相:泥石流混杂层;B相;表泥层;C相:冲刷层;D相:底泥层;E相:泥层。一个沉积旋回的标准泥石流相序是始于D相,往上是A相、C相或B相,而C相是沉积间断的标志。泥石流沉积体随时间和空间有不同的分布和变化。在泥石流扇形地的不同部位,泥石流沉积相的系列与标准沉积相系列相比会有一定的差异,但保留主要因子。     

1998年大邑山区山地灾害及其成因

１９９８年９月是名,四川省大邑县部分山区了特大暴雨袭击,引发了严重的泥石流、滑坡等山地灾害,导致２人死亡,１人失踪,直接经济损失达５×１０＾７多元。从地形、地质、暴雨及人类活动等方面分析了山地灾害的成晨和发展趋势,提出了灾害防治建议。