Abstract

Nutritional requirements of heavy immunocastrated (IM) pigs and therefore appropriate feeding strategies have not yet been determined. Thus, the effects of changes in dietary net energy (NE) content were studied in 41 IM pigs, fed ad libitum diets with low, medium, and high NE content (LNE, MNE, and HNE diets, with 8.5, 9.3, and 10.0 MJ NE/kg, respectively), from 84 days of age until slaughter at an average age of 172 days and an average body weight of 122.5 kg. In the period from 143 to 170 days of age, there was a tendency for a greater NE intake (p = 0.08) in pigs fed the HNE diet along with greater (p < 0.01) backfat gain. Dietary treatment affected carcass composition, as lower backfat thickness (p = 0.01) and lower area of fat over the longissimus muscle (p = 0.05) were observed in the LNE and MNE pigs. In addition, greater lean meat content (p = 0.04) was observed in the LNE pigs. Reducing the NE of the diet by replacement of cereals and soybean meal with high-fiber ingredients resulted in lower indole production in the ascending colon (p < 0.01) and greater skatole production (p < 0.01) in the cecum. Greater villus area, width, height and perimeter, crypt depth, and thickness of the intestinal mucosa in the jejunum, ileum, ascending colon, and descending colon were found in the LNE group (p < 0.01) than in the HNE group, while those in the MNE group was intermediate. Cell proliferation was not affected by dietary treatment (p > 0.05). The present results show that a reduction in dietary NE concentration lowers lipid deposition, without affecting performance or energy efficiency in IM pigs. This technique provides an advantage in terms of improved leanness, without affecting growth rate in IM pigs after immunization, which is particularly important when the backfat thickness is a determinant of carcass value and IM pigs are fattened to higher weights (e.g., in heavy pig production) or when a longer delay between immunization and slaughter is practiced.

Highlights

  • In many countries, male piglets are still surgically castrated shortly after birth as a preventive measure against the development of boar taint

  • In Exp. 2, one pig died during the experiment, two were excluded due to umbilical hernia (1 in the low net energy (NE) (LNE) group and 1 in the medium NE (MNE) group), and one was excluded due to broken forelimb, providing 41 pigs weighing on average 122.5 kg at the end of Exp. 2 (Table 2)

  • In IM pigs, rapid changes in hormonal status 10 to 15 days after immunization [2] result in increased voluntary feed intake, greater average daily gain (ADG) [3, 24], and altered energy metabolism associated with increased lipid deposition [25, 26]

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Summary

Introduction

Male piglets are still surgically castrated shortly after birth as a preventive measure against the development of boar taint. The vaccination against gonadotropin-releasing hormone (i.e., immunocastration) has been proposed as an alternative to surgical castration that improves animal welfare and allows to benefit from lean tissue growth and feed efficiency of entire males (EM) for most of the growing period [1]. After effective immunization, a substantial increase in daily feed intake (DFI) is observed in immunocastrated (IM) pigs, resulting in reduced feed efficiency and increased body fatness as compared with EM [3, 4]. These negative consequences can be limited either by restricting feed allowance after immunization [5] or by shortening the time interval between immunization and slaughter, which gives pigs less time to deposit fat [6]. By influencing the rate of apoptosis, diet can alter the availability of L-tryptophan, the precursor of skatole, in the colon and can affect skatole production, while skatole absorption can be reduced by accelerating the intestinal transit time [13, 14]

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