气相色谱-串联质谱法快速检测当归中102种农药残留

建立了当归中102种农药残留的快速检测方法。样品采用优化的QuEChERS前处理方法,利用气相色谱-串联质谱 (GC-MS/MS) 检测,动态多反应监测 (dMRM) 模式,基质匹配外标法定量。结果表明:在样品前处理过程中,经对提取溶剂、提取体系、净化体系的组成和用量进行筛选优化后,样品采用乙腈、1.0 g氯化钠、4.0 g无水硫酸镁、1.0 g柠檬酸钠和0.5 g柠檬酸二钠盐提取,无水硫酸镁800 mg、PSA 150 mg、C₁₈ 150 mg净化,通过基质匹配外标法校正,当归中基质效应对目标化合物的定性、定量影响明显减弱。在0.02~0.64 mg/kg范围内,102种农药的质量浓度与对应的峰面积间呈良好的线性关系,R2均大于0.99,检出限为0.002 5~0.025 mg/kg,定量限为0.005~0.05 mg/kg;在0.04、0.08和0.32 mg/kg 3个添加水平下,102种农药的平均回收率为52 %~128%,RSD为1.0%~10 %。该方法快速简便、耗时短,具有良好的灵敏度、正确度和精密度,为提高当归中农药安全水平,降低健康风险提供了一种快速、高效、可靠的分析手段。     

贵州足球场草坪建植及优化管理模型研究

在一定的生境和管理条件下,以修剪高度、修剪次数和施Ｎ、Ｐ、Ｋ量为因素,利用二次正交回归设计,用模糊综合评分法评定草坪质量,最佳３因子水平为：修剪高度５－７．４ｃｍ,修剪次数４－６次／月,施Ｎ量为２．５－３．７ｇ（ｍ＾２．年）,施Ｐ、Ｋ量各为１．２５－１．８５ｇ／（ｍ＾２．年）,建立了草坪质量与养护３因子间的显相关回归模型。     

Myoglobin oxidation in a model system as affected by nonheme iron and iron chelating agents

A model system was used to study the effect of nonheme iron on myoglobin oxidation at pH 5.6 and pH 7.2 at 23 degrees C. The addition of ferrous iron significantly (p < 0.05) increased the rate of myoglobin oxidation in the absence of lipid, demonstrating that iron promoted myoglobin oxidation independent of the effect of lipid oxidation. The addition of the type II, iron chelating antioxidants sodium tripolyphosphate (at pH 7.2) or milk mineral (at pH 5.6) negated the effect of added iron, slowing oxidation of myoglobin. A clear concentration dependence was seen for iron-stimulated myoglobin oxidation, based on both spectral and visual evidence. Further investigation is needed to determine the possible role for nonheme ferrous iron on myoglobin oxidation in vivo or in meat.     

Nitrite inhibition of Clostridium botulinum: electron spin resonance detection of iron-nitric oxide complexes

Vegetative cells of Clostridium botulinum were shown to contain iron-sulfur proteins that react with added nitrite to form iron-nitric oxide complexes, with resultant destruction of the iron-sulfur cluster. Inactivation of iron-sulfur enzymes (especially ferredoxin) by binding of nitric oxide would almost certainly inhibit growth, and thus is probably the mechanism of botulinal inhibition by nitrite in foods.     

Effects of a topically applied anaesthetic on the behaviour,pain sensitivity and weight gain of dairy calves following thermocautery disbudding with a local anaesthetic

ABSTRACT

Aims: To compare the effect of a topically applied anaesthetic to no pain relief or meloxicam on the behavioural responses, pain sensitivity and weight gain of calves following disbudding with or without sedation.

Methods: A total of 364, 2–6 week-old calves from three commercial farms were systematically allocated to one of six treatment groups. All calves received a cornual nerve block prior to disbudding, with half restrained in a crate and half sedated with xylazine. Within these groups one third received no further treatment (control), one third were treated with meloxicam >10?minutes prior to disbudding and one third received a topical anaesthetic applied to the horn bud wounds following disbudding. The frequency of ear flicks, head shakes, head scratches and pain sensitivity of the wound were recorded on up to eight occasions over 24 hours after disbudding. Calves were weighed before, and 7 and 28 days after, disbudding to determine average daily weight gain (ADG).

Results: Compared to calves in the crate-control group, all other groups had reduced ear flicks at all times following disbudding (p?<?0.01). Treatment with meloxicam and topical anaesthesia in addition to sedation reduced head scratches compared to calves in the crate-control group (p?≤?0.013). At 22 hours after disbudding head shakes were reduced in sedated calves treated with topical anaesthetic compared to calves in the crate-control group (p?<?0.001). Pain sensitivity was lower in all sedated calves than unsedated calves (p?<?0.001). The ADG between Days 0–7 was 0.14 (95% CI?=?0.015–0.274) kg/day greater in sedated calves treated with meloxicam than calves in the crate-control group (p?=?0.03), and the ADG between Days 0–28 tended to be 0.06 (95% CI=?0.01–0.13) kg/day greater in sedated calves treated with topical anaesthetic than calves in the crate-control group (p?=?0.09).

Conclusion and clinical relevance: Sedation of calves for disbudding reduced the pain experienced in the following 24 hours. There was a benefit to providing calves with topical anaesthetic following disbudding on behavioural responses and pain sensitivity, which was similar to that of treating calves with meloxicam.     

An outbreak of toe ulcers,sole ulcers and white line disease in a group of dairy heifers immediately after calving

Abstract

CASE HISTORY: An outbreak of severe lameness was reported on a 780-cow spring-calving dairy herd in the Manawatu region within 1–3 weeks of calving, which affected over 90% of a group of 150 dairy heifers. Approximately 3 weeks before the planned start of calving heifers had been fed maize and grass silage on a concrete feed pad for 3–4 h per day, and mixed with a group of adult cows.

CLINICAL FINDINGS: During treatment for lameness, the feet of 28 lame heifers were closely examined. Seventy lesions were recorded in the claws of these heifers. The predominant lesion was severe solar and white line haemorrhage, with much of the haemorrhage focussed at the site at which sole ulcers are normally seen. White line disease was seen in nine claws and sole ulcers in four. Additionally, a lesion which is not commonly recorded in New Zealand, a toe abscess arising from separation of the white line from the sole in the abaxial region of tip of the toe was recorded in 11 claws. The clinical impression was that the soles of the affected heifers were very thin. This was supported by examination of the feet of eight heifers using ultrasonography that indicated heifers with hoof horn haemorrhages had very thin soles (estimated mean 4.1 mm) and that these soles were thinner than those in non-lame heifers without haemorrhages.

DIAGNOSIS: The pattern of disease seen in these heifers closely matched that seen in an outbreak of lameness in heifers in Florida, which was linked to thin soles resulting from excess hoof horn wear. The clinical signs and findings of the examination using ultrasonography strongly implicated thin soles as the underlying cause of lameness on this farm. An on-farm investigation revealed a combination of heifer behaviour and prolonged exposure to wet concrete on the feed pad were the primary causes of excess wear that resulted in thin soles.

CLINICAL RELEVANCE: This was an unusual outbreak of lameness in a group of newly calved heifers. The problem highlights the value of good management during the transition of heifers at pasture to the lactating herd standing on concrete for long periods, in the control of lameness.