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Veterinary Record (1996) 139, 93-94 THE tendency among pigs towards impaired reproductive efficiency during the summer has been reported by many authors with perhaps the first report being MacLean (1969). The main symptom of this summer infertility syndrome is a marked fall in fertility (Love 1978, 1981, Stein and others 1984, Hennessy 1987, Hancock 1988. Since no data exist concerning this syndrome in Spain, a retrospective study was performed in order to establish whether seasonal variations existed in the reproductive performance of sows kept under intensive housing conditions. The study was based on the individual registers of 932 large white cross landrace sows, all between their first and eighth parturitions, from an intensive piggery in north west Spain. On this farm artificial insemination is practised systematically using the seminal rich fraction diluted in a commercial solvent (MR-A;Kubus, SA) ensuring at least 3 x 109 sperm cells per 100 ml dose.After oestrus diagnosis by standing reflex, most of the sows were inseminated once every 12 hours for 36 hours. The first insemination was made at the time of the first positive oestrus diagnosis. Sows were checked by heat diagnosis twice daily. In this herd pregnancy tests are made hormonally, by injecting 400 iu of pregnant mare serum gonadotrophin and 200 iu of human chorionic gonadotrophin (PG-600; Intervet) on day 21 after mating, negative responders returning to oestrus between three and seven days after the injection. The sows were penned individually adjacent to the boars' stalls and tethered by the neck. The minimum and maximum average temperatures for each year in the area, given as the mean temperature for 24 hours averaged over the entire month, and the highest and lowest temperature for that month were as follows: for 1990, minimum (December) 24°C (range 13-2°C to -6.2°C) with 78 per cent relative humidity and maximum (July) 21-30C (35-80C to 5-0°C) with 51 per cent relative humidity; for 1991, minimum (January) 2-3°C (11-8°C to -6-2°C) with 78 per cent relative humidity, maximum (August) 21-8°C (34-80C to 6-2°C) with 49 per cent relative humidity; and for 1992, minimum (January) 1.7°C (14-20C to -2-40C) with 73 per cent relative humidity and maximum (July) 20-70C (34-4°C to 6.8°C) with 51 per cent relative humidity.The following parameters were studied: (1) return to oestrus rate; (2) abortion rate; (3) fertility; (4) litter size, live births and TABLE 1: Variations in litter size, live births and stillbirths (mean ± sem) of sows mated in different seasons over a three-year period Season Litter size Live births Stillbirths Winter 9.65 ± 0-16a 9.33 + 0.14a 0-53 + 0Q05C Spring 9-65 ±0-16a 9.11 +0.14a 0*63 ±0.07c Summer 8.42 ± 0.20b 8-17 + 0.17b 0.87 ±0.07d Autumn 9-48 ± 0-14a 9.15 + 0-12a 0.65 + 0Q05C a-b within a column, means with different superscripts are different (P<0.0001) c-d within a column, means with different superscripts are different (P<0.001)TABLE 2: Variations in fertility, return to oestrus rate and abortions of sows mated in the...

In the present work, the thermal stability, changes in chemical structure during thermal degradation, and the kinetics of thermal degradation of a phenolic foam were studied. An 8.5 wt% of Pinus radiata wood flour reinforcement was added to the phenolic foam. A commercial phenolic resol was used as the matrix for the foam. The wood flour-reinforced foam showed a structure similar to the phenolic foam according to the Fourier transform infrared spectroscopy results. The wood flour increased the thermal stability of the phenolic foam in the first stage of thermal degradation (T 5% ), decreased it in the second step (T 25% ), and negligibly influenced the final stage. The activation energies of the degradation processes of the studied materials were obtained by the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa model-free kinetic methods and a 2-Gaussian distributed activation energy model. The values of the activation energies obtained by the model-free kinetic methods for the first degradation stage of the phenolic foams were in a range between 110 and 170 kJ mol À1 , whereas for the wood flour it was 162 kJ mol À1 for almost all of the conversion range of its main degradation stage. The applied models showed good fits for all the materials, and the activation energies calculated were in agreement with the values found in the literature.

The aim of this study was to assess the relationship of the evolution of the corpus luteum (CL) volume that was determined ultrasonographically with the pregnancy status in lactating dairy cows during early pregnancy. Ultrasound examinations were carried out on 76 cows following artificial insemination (AI). Plasma concentrations of progesterone were determined from blood samples collected at each ultrasound examination. Conception was confirmed by ultrasonography on day 30 after AI. Around day 14 post-insemination (p.i.), the CL volume tended to decrease in pregnant and non-pregnant cows, and, after day 19 p.i., both groups differed significantly, indicating the luteal regression in non-pregnant cows. Reaching signification on day 20. The diminution in CL volume was also reflected in the plasma progesterone concentration. However, the patterns of CL volume, estimated by ultrasonography, differed more evidently and earlier between both groups (around 1 week p.i., at day 9 p.i. P < 0.05, whereas progesterone started to differ around 2 weeks p.i., at day 14 p.i, P < 0.05). These results indicate that the estimation of the CL volume by ultrasonography could be useful for assessing the presence of a functional CL.