过渡期奶牛的营养之谜

奶牛在产犊前后间隔总共6周的过渡期非常关键,应该给予高度重视.过渡期间不良的饲养管理会引起牛奶产量下降、繁殖效率降低和代谢疾病的增加等一系列问题,从而降低牧场的整体营业收入.本文对奶牛过渡期间的代谢变化以及临产阶段的营养管理和注意事项进行了阐述,并分析了为什么临产阶段日粮没有理论上设想的那么行之有效的原因.     

Calf nutrition from birth to breeding.

The general principles of growth and nutrients required are no different for young calves than for any other species. Additional complexity is introduced, however, by the need to transition the young preruminant to functioning ruminant. The nutritional and digestive physiology of dairy calves as future ruminants needs to be the governing factor in designing practical feeding systems to meet nutrient requirements. Key aspects common to all systems include the composition and amount of liquid feed, water availability, and the first starter feeds offered. This article focuses on nutrition of calves before weaning and to breeding age, with primary emphasis on the preweaning and transition phases.     

Concentrations of conjugated linoleic acid (cis-9, trans-11-octadecadienoic acid) are not increased in tissue lipids of cattle fed a high-concentrate diet supplemented with soybean oil

Conjugated linoleic acid (CLA), a mixture of isomers of linoleic acid, has many beneficial effects, including decreased tumor growth in animal cancer models. The cis-9, trans-11 isomer of CLA (CLA9,11) can be formed in the rumen as an intermediate in biohydrogenation of linoleic acid. Recent data, however, indicate that tissue desaturation of trans-fatty acids is an important source of CLA9,11 in milk. Our objective was to determine whether supplementing a high-corn diet with soybean oil (SBO; a source of linoleic acid) would increase concentrations of CLA in ruminal contents and tissue lipids. Four ruminally cannulated steers were utilized in a Latin square design with 28-d periods. A control diet (80% cracked corn, 2.0% corn steep liquor, 8.0% ground corn cobs, and 10% supplement [soybean meal, ground shelled corn, minerals, and vitamins]) was supplemented with 2.5, 5.0, or 7.5% (DM basis) SBO. Supplemental SBO did not affect ruminal pH or concentrations of the major VFA. The proportion and amount (mg FA/g DM ruminal contents) of CLA9,11 were not increased by increasing dietary SBO. However, the proportion and amount of the trans-10, cis-12 CLA isomer (CLA10,12) in ruminal contents increased linearly (P < 0.006) as dietary SBO increased. Trans-18:1 isomers in ruminal contents increased linearly (P < 0.02) as dietary SBO increased. The proportion of CLA10,12 was correlated positively (P < 0.001) with proportions of trans-C 18:1 isomers in ruminal contents. Conversely, CLA9,11 was correlated negatively (P < 0.05) with the proportions of trans-18:1 in ruminal contents. The same high-corn diet, supplemented with 0 or 5% SBO, was fed to 20 Angus-Wagyu heifers for 102 d in a randomized complete block design to determine the effect of added SBO on tissue deposition of CLA. Supplemental SBO did not affect feed intake, gain:feed, or carcass quality. Tissue samples were obtained from the hindquarter, loin, forequarter, liver, large and small intestine, and subcutaneous, mesenteric, and perirenal adipose depots. The concentration of CLA9,11 was greatest in subcutaneous adipose tissue but was not affected in any tissue by SBO. Supplementing high-corn diets with SBO does not increase CLA9,11 concentrations in tissues of fattening heifers. Research is needed to identify regulatory factors for pathways of biohydrogenation that lead to increased concentrations of CLA10,12 in ruminal contents when high-oil, high-concentrate diets are fed.     

Grassland vegetation changes and nocturnal global warming

Global minimum temperatures (TMIN) are increasing faster than maximum temperatures, but the ecological consequences of this are largely unexplored. Long-term data sets from the shortgrass steppe were used to identify correlations between TMIN and several vegetation variables. This ecosystem is potentially sensitive to increases in TMIN. Most notably, increased spring TMIN was correlated with decreased net primary production by the dominant C4 grass (Bouteloua gracilis) and with increased abundance and production by exotic and native C3 forbs. Reductions in B. gracilis may make this system more vulnerable to invasion by exotic species and less tolerant of drought and grazing.     

Radar detection of the nucleus and coma of comet hyakutake

Radar observations of comet Hyakutake (C/1996 B2) made at the Goldstone Deep Space Communications Complex in California have detected echoes from the nucleus and from large grains in the inner coma. The nucleus of this bright comet was estimated to be only 2 to 3 kilometers in diameter. Models of the coma echo indicate backscatter from porous, centimeter-size grains ejected anisotropically at velocities of tens of meters per second. The radar observations suggest that a comet's activity may be a poor indicator of its size and provide evidence that large grains constitute an important component of the mass loss from a typical active comet.     

Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.     

The confidential enquiry into perioperative equine fatalities (CEPEF): mortality results of Phases 1 and 2

Objectives To document the equine perioperative mortality rate and to highlight any factor associated with an increased risk of death up to 7 days after anaesthesia. Study design A prospective observational epidemiological multicentre study. Methods Data were recorded from all equidae undergoing general anaesthesia in 62 clinics. Power calculations indicated that 45 000 cases were required to detect the significance of important variables. Details of each horse, operation, anaesthetic agents and clinic personnel were recorded. Outcome at 7 days was recorded as: alive, put to sleep (PTS) or dead. Data were analysed by a standard multilevel logistic regression approach, considering the effects of clustering at the level of clinic. Results Data were collected from 41 824 cases over 6 years. A total of 39 025 (93.3%) were alive on day 7 and 785 were dead giving an overall death rate of 1.9% (95% CI: 1.8–2.0) and 2014 (4.8%) were PTS. About 5846 horses undergoing emergency abdominal surgeries (‘colics’) were excluded from subsequent analyses. A total of 35 107 ‘noncolic’ horses were alive at 7 days and 328 dead giving a death rate for noncolics of 0.9% (95% CI: 0.8–1.0). Five hundred and forty‐three (1.5%) noncolic horses classified PTS were excluded from further analyses. There were 109 (33%) deaths from cardiac arrest or post‐operative cardiovascular collapse, with 107 (32%) from fractures and myopathies. Fracture repair, out of hours surgery, and age below 1 month was associated with increased risk of dying whereas the use of acepromazine and intravenous anaesthetic agent maintenance of anaesthesia was associated with reduced risk. Conclusions A number of potential contributors to the high risk of anaesthetic‐related mortality have been identified. Further investigation of the underlying mechanism for their apparent harmful effects and development of alternative techniques is merited.