Castrated Male Pigs with IMPROVEST

Improvest® (Pfizer Animal Health) is approved in a number of countries for immunological castration of male pigs. There is an increasing amount of research evaluating the growth performance and carcass characteristics of immunologically- compared to physically-castrated male pigs. However, there has been little if any research comparing the responses of these two genders during pre-harvest handling and transport, particularly under conditions similar to those that apply in commercial practice. These would include the feeding of Ractopamine, which is routinely used in many industries, and the range of handling intensities that animals are likely to experience. Therefore, the objective of this study was to determine the effects of gender, Ractopamine feeding, and handling intensity on physical and physiological responses to standardized handling and transportation procedures.

The study was carried out using a split-plot design with a 3 × 3 × 3 factorial arrangement of treatments: 1) Gender [Physically-castrated males (PC), Gilts (G), and Immunologically-castrated males (IC)], 2) Ractopamine Inclusion Level [0, 5, and 7.5 ppm], and 3) Handling Intensity [Gentle, Moderate, and Aggressive]. The Gender × Ractopamine Level treatment subclass was the whole plot and the Handling Intensity treatment was the sub-plot. The study involved 180 pigs housed in pens of 4 (15 pens/gender, and Ractopamine inclusion level). First and second Improvest® doses (2 ml product) were administered at 16 and 20 weeks of age, respectively. Ractopamine was fed from week 21 to 24 of age after which the Handling Intensity treatment was applied, which consisted of moving the animals individually through a handling course using Gentle, Moderate, or Aggressive handling. Following the handling procedure, pigs were loaded onto a livestock trailer in groups of 36 and transported for 30 minutes followed by a 15 minute waiting period before they were unloaded. Physical indicators of stress (skin discoloration, open mouth breathing, vocalization, and muscle tremors) were monitored throughout the handling and transportation process. Venous blood samples (to measure blood acid-base parameters) and rectal temperatures were taken 2 hours before the handling procedure (baseline) and after the pigs were unloaded from the trailer.

There were few differences between the genders for responses to handling and transport. PC had greater (P < 0.01) rectal temperature and blood lactate after transport than IC, suggesting that IC responded less to the handling and transport procedures than did PC; however, the gender differences were small.

Ractopamine inclusion level had no effect (P > 0.05) on any of the parameters measured during the handling and transport procedures.

Aggressively handled pigs had greater (P < 0.05) post-handling rectal temperature (38.89, 38.89, and 39.06°C for Gentle, Moderate, and Aggressive, respectively; SEM 0.24) and exhibited a greater incidence of physical indicators of stress after handling than those on the Gentle and Moderate handling treatments.

The results of this study suggests that the response to handling and transportation was relatively similar in all of the genders.

Keywords: Handling, Transport, Immunological castration, Pigs.