Evaluation of Substance P concentrations in the blood plasma of jugular and tail vein of healthy German Simmental cows.

Background: Cattle strongly mask their pain, making the recognition and assessment of pain difficult. Different subjective and objective parameters to assess pain have been described. Substance P (SP), which is a neurotransmitter, is used to objectively evaluate nociception in cattle. However, SP concentrations have mainly been described in diseased animals, or animals subjected to painful procedures. To this day, no evaluation of SP in healthy adult cattle has been published. The objectives of this pilot study were to 1) assess the SP concentrations in healthy adult German Simmental cattle in the blood plasma, 2) compare the concentrations between the blood of the jugular and the tail vein, and 3) assess the concentrations in the blood of the tail vein every 6 h over a period of 24 h. A total of 52 healthy cattle of the German Simmental breed were included in this study. Animals were 5.0 ± 1.3 (mean ± SD) years old and between 117 and 239 (175.0 ± 34.1) days in milk. Blood samples were taken from the jugular vein (BJV, 07:45 a.m.) and the tail vein (TV1, 08:00 a.m.) each. Additional blood samples were taken every 6 h over the course of 24 h from the tail vein (TV2 - TV5). SP concentrations were analyzed using a commercial ELISA kit.

Results: Mean (± SD) and median SP concentrations were 1.087 ± 436 pg/ml and 984 pg/ml for BJV (range 502 - 2,337 pg/ml), and 920 ± 402 pg/ml and 818 pg/ml for TV1 (range 192 - 2,531 pg/ml), respectively. There was a significantly positive correlation between SP concentrations of BJV and TV1. SP concentrations between BJV and TV1 were significantly different, as were SP concentrations in the tail vein between sampling times over the course of 24 h.

Conclusions: The results of this study show that blood samples to assess SP concentrations in cattle can be taken from the jugular as well as from the tail vein. There are high variations in concentrations between animals, and it is hard to define reference ranges for SP in healthy animals. Repeated blood samples should not be taken by repeated punctation of a vein but by use of a jugular vein catheter, which is a major limitation of the present study.