Heifer development systems: dry-lot feeding compared with grazing dormant winter forage

Two hundred ninety-nine Angus-based, nulliparous heifers (253 ± 2 kg initial BW) from 3 production years were utilized to compare traditional postweaning dry lot (DL) development with a more extensive winter grazing system utilizing a combination of corn residue and winter range (EXT). Heifers developed in the DL were offered a common diet after the weaning period for 208 d in yr 1, 194 d in yr 2, and 150 d in yr 3 until breeding. Heifers developed in EXT grazed corn residue for 135 d in yr 1, 106 d in yr 2, and 91 d in yr 3, and then fed in the DL until breeding (yr 1) or grazed dormant winter grass for approximately 60 d before being fed in the DL (yr 2 and 3). All 3 years, heifers were estrus synchronized, with timed AI performed in yr 1. In yr 2 and 3, estrus was detected and those detected in estrus were artificially inseminated approximately 12 h later. Heifers were exposed to bulls 10 d after the last AI for 60 d while grazing summer pasture. During the winter grazing period, EXT heifers gained less (P = 0.01) BW than DL heifers and EXT heifers had lighter (P = 0.02) BW at breeding. Fewer (P < 0.01) EXT heifers reached puberty before breeding. Conception to AI was not different (P = 0.23); however, AI pregnancy rate tended (P = 0.08) to be less in EXT heifers. Final pregnancy rates were not different (P = 0.38) between treatment groups. Although EXT heifers had lighter (P = 0.02) BW at pregnancy diagnosis; however, they did compensate with greater (P = 0.05) ADG after breeding, resulting in similar (P = 0.22) precalving BW. Winter development system did not influence (P > 0.10) percentage of calving in the first 21 d, calf birth date, and calf birth BW, or dystocia score. Pregnancy rate after the second breeding season was not different (P = 0.56) between treatments. Heifer development using extended winter grazing reduced (P < 0.01) the cost of producing a pregnant heifer by $45 compared with DL.     

Heifer development systems: a comparison of grazing winter range or corn residue

Two experiments at 2 Nebraska locations evaluated effects of heifer development system on growth and pregnancy rate. In Exp. 1, heifers (n=270, BW=225 ± 2 kg) grazed winter Sandhills range (WR) or west central Nebraska corn residue (CR) with a supplement (0.45 kg/animal; 31% CP; 80 mg·animal(-1)·d(-1) of monensin). In Exp. 2, heifers (n=180, BW = 262 ± 3 kg) grazed eastern Nebraska WR or CR with a supplement (0.45 to 0.90 kg/d; 31% CP; 80 to 160 mg·animal(-1)·d(-1) of monensin). The CR heifers tended to have less (P=0.10) ADG compared with WR heifers before breeding in Exp. 1; however, prebreeding ADG was similar (P=0.77) in Exp. 2. Prebreeding BW, percentage of mature BW at breeding, and pregnancy determination BW were similar (P ≥ 0.14) for CR and WR in both experiments. Percentage of heifers pubertal at breeding, AI conception, and AI pregnancy rate (Exp. 2) and final pregnancy rate in both experiments were also similar (P ≥ 0.27) for CR and WR heifers. Precalving BW, percentage of calves born in the first 21 d, calf birth date, calf birth BW, and dystocia score were all similar (P ≥ 0.21) for CR and WR heifers in both experiments. Cow BW at weaning, calf weaning BW, adjusted 205-d calf BW, and second season pregnancy rates were not affected (P ≥ 0.16) by treatment. Heifer development system did not affect (P ≥ 0.56) the cost of producing 1 pregnant heifer in Exp. 1 or 2. Development on CR may reduce ADG before breeding, but did not affect pregnancy rate. Heifer development using CR or WR postweaning resulted in similar reproductive performance and development cost.     

Relationship between nutrition and reproduction in beef cattle

The primary nutrient consideration for optimum reproductive performance in beef cattle is energy. Low energy intake delays the onset of puberty in heifers and bulls. Heifers should reach approximately 66 per cent of mature body weight by 14 to 15 months of age and be bred 30 days prior to breeding the main cow herd. Body conditioning scores (BCS) (1 = emaciated, 9 = obese) should be used to evaluate pregnant cows entering their third trimester. Cows should calve with body conditioning score 5 to 7. Forage quality and environmental factors influence maximum dry matter intake and nutrient requirements and must be considered in the clinical setting. Crude protein dietary content should be 11 to 12 per cent for lactating beef cattle. Mineral (calcium, phosphorus, magnesium, potassium, sulfur, sodium, chloride) nutrition is not a major cause of decreased reproductive performance in beef cattle. Trace mineral deficiencies (particularly selenium, copper, and zinc) can cause decreased reproductive performance. Diagnosis of these trace mineral deficiencies can be confirmed by elemental analysis of blood or tissues.     

Effects of nutrition on reproduction in dairy cows

It is clear that nutrition is closely related to reproduction in the dairy cow. In addition to classic nutrient deficiency and excess, dry cow body condition and postpartum energy balance have a major impact on fertility. Dry cow rations must be designed to prevent milk fever, dystocia, retained placenta, other calving problems, and metritis. Most importantly, milk yield and reproductive performance should be regularly monitored to detect nutritionally associated health and performance changes that precede impairment of reproductive function.     

优质后备奶牛的营养与培育

犊牛、后备牛是高产奶牛的基础,后备牛阶段的生长发育对奶牛的整个一生都至关重要.对奶牛后备牛阶段的生理特点、营养物质需要、合理的配种和分娩年龄进行了论述.     

Heifer mastitis and dry-cow mastitis: A bacteriological survey in Sweden

A bacteriological investigation was performed on 145 heifers and 55 dry-cows with clinical mastitis during July 1976–June 1977. Areas in Sweden from which heifer and dry-cow mastitis has been reported as a problem were included. Mastitis occurred more frequently in the Swedish Fresian breed (SLB) than in the Swedish Red and White breed (SRB) of dairy cattle. C. pyogenes was isolated in pure culture from 15% and 4%, respectively, of the cases of heifer and dry-cow mastitis from which this bacterium could be isolated. Corresponding figures for pure culture of P. indolicus, micro-aerophilic cocci and S. dysgalactiae were 2% and 0%, 0% and 0% and 44% and 35%, respectively. The bacteria most frequently isolated together with C. pyogenes in the heifer material were P. indolicus (69%), the microaerophilic cocci (59%) and S. dysgalactiae (31%). Corresponding data for the dry-cow material were 92%, 35% and 50%, respectively. Thus, C. pyogenes was the causative agent of heifer and dry-cow mastitis in only about 40% of the mastitis cases investigated, and the most characteristic feature of these forms of mastitis involving C. pyogenes was mixed infection.     

日本鳗鲡和欧洲鳗鲡的营养研究进展

鳗鲡（鳗鱼）是我国经济鱼类之一,更是近年来名特优水产养殖种类之一。鳗鲡属鳗鲡目,鳗鲡亚目,鳗鲡科,为肉食性鱼类。对日本鳗鲡的营养需要量的研究,早在２０世纪６０年代就已经开始,日本和我国台湾省等学者在这方面作了大量研究。目前对蛋白质、必需氨基酸、必需脂肪酸、钙、磷等需要量已大体研究清楚,对维生素和微量元素的缺乏症也作了一些试验,但对其确切需要量还缺乏深入研究。本文对日本鳗鲡和欧洲鳗鲡在营养需要和饲料组成及其特点存在种间差异等作以浅述。１营养元素１１维生素维生素在生物生长过程中有着不可替代的作用,对…     

微量元素硒在公猪营养和繁殖中的生理作用

硒通过参与硒蛋白的合成在猪营养中发挥重要作用.硒蛋白是调节体内抗氧化系统的中心,其中谷胱甘肽过氧化物酶是猪抗氧化功能研究最多的硒蛋白.但其他硒蛋白在公猪精液生产和维持精液质量中也有重要作用.公猪精液的特点是含有大量易氧化的长链多不饱和脂肪酸,需要有效的抗氧化防御.猪对硒的需求因环境和其他条件的不同而不同,同时处于繁殖期...     

牛繁殖技术的新进展

动物繁殖技术是生物技术的重要分支。繁殖技术从20世纪50年代人工授精技术到20世纪70年代胚胎移植技术的应用,似乎才真正开始动物繁殖技术的新纪元。牛的繁殖技术在过去的50年里取得了显著进展,这是一个以人工授精起始的连续过程。随着体外受精、精子分离和核移植（克隆）等技术的发展,这些连续性的繁殖技术将是目前和未来提高生产力的强有力手段。     

Haemophilus somnus-induced Otitis and Meningitis in a Heifer

The purpose of this report is to describe the lesions of otitis and meningitis associated with Haemophilus somnus infection in a heifer.

The animal was found dead in its pen. At necropsy, there was a severe fibrinopurulent meningitis and suppurative otitis media and interna. The external ear canal contained inspissated debris. Haemophilus somnus was recovered in pure culture from the meningeal exudate. The identity of the organism was confirmed by fluorescent antibody and agar gel immunodiffusion tests. Possible pathogenetic mechanisms are discussed.

     

母猪营养研究进展

受试验动物、研究方法等诸多客观条件的限制，母猪营养研究资料明显少于商品猪，其中，以国外资料为主，国内资料较少且多为综述性文章或译文，科学试验报告很少。由此，母猪营养仍是研究热点。本文拟对母猪营养研究予以综述，其中以能量、蛋白质（氨基酸）营养为主，并侧重于营养需要量研究。１能量１．１能量概念描述猪的能量需要和饲料的能量浓度主要有消化能（DE）及代谢能（ME）两体系。DE是动物采食饲料的总能减去未被消化以粪形式排出的饲料能量的差值；ME是DE减去尿能及消化道气体能的差值（杨凤，１９９３）。通常能量利用研究…     

配种前营养水平对母猪繁殖性能的影响

提高母猪繁殖性能可带来巨大的经济效益。母猪的繁殖性能与卵泡发育相关。配种前营养水平对母猪繁殖性能有重要的影响。文章综述配种前营养水平对后备母猪和哺乳母猪与卵泡发育相关的繁殖性能的影响。     

Computer modeling of sheep reproduction: II. Accelerated reproduction in sheep

A computer simulation program was written in SLAM (Simulation Language for Alternative Modeling) to simulate certain biological aspects involved in alternative systems of reproduction in sheep. Four fundamental lambing schemes, once a year, three times in 2 yr, twice a year and continuous schemes, along with modifications of these schemes, are simulated. Parameters of greatest effect in this simulation were the average spread of the estrous season (SA), the measure of asymmetry (SD) and the maximum proportion of ewes exhibiting estrus (MX). It was demonstrated that the greater the SA values (longer estrous seasons and shorter anestrous seasons), the more advantageous it was to breed frequently. The SD and MX parameters influenced to a lesser degree the lambing results obtained from these simulations. The relative merits of certain breeds and locations for out-of-season breeding were studied and evaluated for annual and seasonal fertility.