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The present field study investigated the efficacy of early Mycoplasma hyopneumoniae vaccination in a farrow-to-finish pig herd with respiratory disease late in the fattening period due to combined infections with M hyopneumoniae and viral pathogens. Five hundred and forty piglets were randomly divided into three groups of 180 piglets each: two groups were vaccinated (Stellamune Once) at either 7 (V1) or 21 days of age (V2), and a third group was left non-vaccinated (NV). The three treatment groups were housed in different pens within the same compartment during the nursery period, and were housed in different but identical compartments during the fattening period. The efficacy was evaluated using performance and pneumonia lesions. The average daily weight gain during the fattening period was 19 (V1) and 18 g/day (V2) higher in both vaccinated groups when compared with the NV group. However, the difference was not statistically significant (P>0.05). The prevalence of pneumonia was significantly lower in both vaccinated groups (V1: 71.5 and V2: 67.1 per cent) when compared with the NV group (80.2 per cent) (P<0.05). There were no significant differences between the two vaccination groups. In conclusion, in the present herd with respiratory disease during the second half of the fattening period caused by M hyopneumoniae and viral infections, prevalence of pneumonia lesions were significantly reduced and growth losses numerically (not statistically significant) decreased by both vaccination schedules.

The efficacy of chlortetracycline (CTC) in-feed medication to treat pigs with clinical respiratory disease was investigated in a farrow-to-finish pig herd infected with Mycoplasma hyopneumoniae, and with clinical respiratory disease in growing pigs. In total, 533 pigs were included. The animals were vaccinated against M hyopneumoniae and porcine circovirus type 2 at weaning. At onset of clinical respiratory disease, they were randomly allocated to one of the following treatment groups: chlortetracycline 1 (CTC1) (two consecutive weeks, 500 ppm), chlortetracycline 2 (CTC2) (two non-consecutive weeks, with a non-medicated week interval in between, 500 ppm) or tylosin (T) (three consecutive weeks, 100 ppm). Performance (daily weight gain, feed conversion ratio), pneumonia lesions at slaughter and clinical parameters (respiratory disease score) were assessed. Only numeric differences in favour of the CTC2 group were obtained for the performance and the clinical parameters. The prevalence of pneumonia lesions was 20.5, 13.1 and 23.0 per cent (P<0.05) for the CTC1, CTC2 and T groups, respectively. The study demonstrated that CTC, when administered at onset of clinical respiratory disease via the feed at a dose of 500 ppm during two alternative weeks, was able to decrease the prevalence of pneumonia lesions, and numerically reduce performance losses and clinical signs.

Abstract:The friction stir welding (FSW) process is mainly used in industrial applications for joining low melting temperature materials such as aluminium and magnesium. FSW has many advantages in comparison with conventional fusion arc welding. Therefore the interest to use this technique for joining steel plates has grown. However such usage is still limited because of the lack of adequate tool materials. This review gives an overview of possible tool materials for FSW of steels focussing on tungsten, tungsten carbide, pcBN and a few ultra-high temperature ceramics.Keywords: FSW, tool material, steel plates INTRODUCTIONFriction stir welding has in comparison with conventional fusion arc welding many metallurgical, environmental and energetic advantages [1]. There are also less process parameters to control which facilitates its use. This solid state joining process is implemented in industrial applications for materials with low melting temperatures such as aluminium and magnesium alloys [2,3]. However, the development of friction stir welding of steel has progressed more slowly due to the higher temperatures reached and therefore the limited durability of the welding tools.Previous research has already shown that it is possible to weld mild steel and other low to medium carbon ferrous alloys. Even high carbon steels and stainless steels can be welded successfully with a tungstenbased tool material. The emphasis of this review is to evaluate the feasibility of materials for the production of FSW tools for high strength steels [4][5][6][7][8]. TOOL REQUIREMENTSThe tools have to withstand severe conditions during the friction stir welding process. The heat generated during this process, causes high temperatures in the contact zone and also high temperature gradients. According to [9] the work material temperature is possibly increased to about 80% of its melting temperature. For HSLA steels, the temperature can thus reach 1100°C.To build up resistance against fatigue and fracture, a high fracture toughness of the tool is required. It is also important that the ductile to brittle transition temperature of the tool material is sufficiently low. Indeed, materials that are brittle at room temperature might fail during the initial plunge stage.It is necessary that the tool's hardness and strength don't decrease much in these high temperature circumstances to ensure that tool deformation and wear are limited.The thermal conductivity of the tool material is a measure for the rate of heat removal. It affects the temperature field, flow stress and the weld microstructure. A high thermal conductivity avoids the formation of hot spots on the tool and allows the use of a cooling mechanism to lower the temperature of the tool. However, high thermal conductivity causes an excessive removal of heat from the weld region which implies the need of higher welding forces [10].To obtain a smooth weld surface, a low coefficient of friction between tool material and workpiece is required. From experience it is known that FSW of steel ...