In swine production, one of the stages, where there is a higher percentage of mortality, is between the birth and the weaning of piglets. The mortality of piglets is associated in part with the stress of the sows, due to the restriction of high motivation behaviours such as to root and due to the establishment of social hierarchy in piglets.
One strategy that has been used in various species to reduce stress is the use of classical music. However, in a previous study carried out by the authors, it was found that the sow’s response stimulated stress-type behaviours with classical music instead of relaxation. In this study, the use of frequency-modified music by composer and sound behaviourist, Janet Marlow, was proposed and adjusted to the auditory comfort range of the swine hearing range, as environmental enrichment. Frequency-modified music has been clinically tested in horses with results that positively influenced their performance in races (Stachurska et al., 2015). It is hypothesized that music that is frequency-modified based on hearing range, produces a relaxing effect in piglets that stimulates affirmative social behaviour, improves weight gain and reduces mortality.
Purpose of Modifying Stress Behaviours in Piglets
- Piglets show aggression to other piglets within the first week of life while forming a teat order.
- Introducing new pigs into a group may lead to aggression as the pigs establish social ranks. Pigs may spend 1–2 minutes nosing each other, vocalising, and then biting until one of the pigs retreats.
- During oestrous cycles, sows may show severe aggression toward newly added sows.
- During breeding, boars may fight and become very vocal.
- Using tranquillizers such as azaperone (2.2 mg/kg) or amperozide (1 mg/kg) can help reduce aggression but may not be economical.
- Tail biting is seen mostly in confined pigs.
- Overcrowding and boredom seem to be the main causes of aggression. Slatted floors without bedding, low-salt diets, and low-iron soil seem to predispose pigs to tail biting.
- When the sow is stressed, usually, the sow will bark to warn piglets walking by her head and then later attack them, biting them to death.
- Regrouping or overcrowding increases stress levels as well. These two factors (confinement and crowding) lead to chronic stress, delayed puberty, and failure to reproduce. On the other hand, acute and mild stress such as transport and gentle handling accelerate oestrous cycles.
Environmental enrichment in the early stages is usually successful. Feeding smaller quantities more frequently and providing toys, bedding to root, corn on the cob, and clean tires can be enriching and mentally stimulating for pigs. The inclusion of species-specific swine music is an enhancement to their enrichment to diminish stress.
Swine Hearing Range Data
The hearing of pigs ranges from 42 Hz to 40.5 kHz with a region of best sensitivity from 250kHz to 16kHz. Because these animals are unable to localise high-frequency tones, it seems unlikely that selective pressure to use the interaural spectral difference cue for sound localisation is behind their high-frequency hearing. Instead, researchers suggest that these and other hoofed mammals evolved high-frequency hearing in order to use monaural locus cues which prevent front/back locus reversals.
Process for Composing Swine-Specific Music
Using the Logic Pro program, original music based on the swine hearing range sensitivity was originally composed and modified by frequency and decibel levels accordingly. The music was designed to be broadcast at a comfortable volume in an agricultural setting considering the modest amount of noise and squealing coming from multiple pigs. Speakers were provided which were pre-loaded with repeating, modified swine music placed near three large areas of the pigs interacting during less daily activity. The music permeated the environment with specific tones, volume and frequency content to elicit calm behaviour. Proposing that the music will trigger an ear/behaviour response to the piglet’s listening comfort as opposed to the transmission of other pig sounds causing reactive stress behaviour.
Included in the compositions are sounds of nature such as water streams and songbirds vocalising to add to the environment. The goal here is to help the pigs feel their natural life to ease stress in an unnatural setting.