Neonatal Piglet Interest in Rope Enrichment: History
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Subjects: Agriculture, Dairy & Animal Science | Veterinary Sciences
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Emiline Sundman

In the United States swine industry, preweaning mortality represents the highest mortality rate of any production phase, nearly half attributed to crushing. The overarching aim of this entry was to determine if enrichment ropes would entice neonatal piglets away from the sow and reduce preweaning mortality.

  • environmental enrichment
  • piglet
  • livability
  • attractants
  • neonate

1. Introduction

In the United States (USA) swine industry, preweaning deaths represent the highest mortality rate of any production phase at approximately 17.5% [1]. This reduces production efficiency and incurs substantial economic losses for producers as well as being an animal welfare concern. A 2012 nationwide survey of the USA swine industry reported that nearly half of all preweaning mortality was attributed to piglet crushing [2]. Newborn piglets are more susceptible to crushing due to their small physical size, limited energy reserves, and poor internal temperature regulation [3]. Piglets display cyclic behavior that includes suckling and resting in warm locations [4]. Suckling and heat seeking can be accomplished by resting close to the sow, which in turn can increase crushing risk. Thus, in the first 72 h of a piglet’s life, they are especially vulnerable, and this is when most crushing deaths occur [3].
Previous research to reduce preweaning mortality, specifically crushing, has often focused on altering sow behavior and the farrowing environment. For instance, management practices such as modified pen designs, farrowing assistance, and cross-fostering, as well as additions to the farrowing environment such as neoprene mats and nest building material have been investigated. Sow maternal behavior and genetics as they relate to crushing have also been explored [5]. While some of these methods have shown positive effects on decreasing crushing, implementation of these practices is challenging and piglet crushing remains an issue.
It has been suggested that if piglets could be enticed away from the sow, their survival rate would increase [6]. Environmental enrichment (EE) is one approach reported in the scientific literature. Environmental enrichment can be defined as “an improvement in the biological functioning of captive animals resulting from modifications to their environment”[7]. Previous work to reduce crushing by enriching the piglet’s environment is more limited than the sow-related literature. The addition of an artificial udder [8], additional heating resources [9] and sensory enrichment such as blue lighting and thyme scent [10] have been successful in attracting piglets but did not reduce preweaning mortality. Thus, a model that can both successfully attract piglets and alter crushing incidence still needs to be identified and validated.
Weaner and grower pigs are attracted to enrichment materials that are odorous, deformable, destructible, and chewable [11], and hanging objects at eye level have also been shown to maintain pig interest [12]. Pigs display oral-nasal-facial behaviors [13], which means that they will use their mouths and snouts to interact with their environment. Compared to other areas of the body, the pig’s snout has the highest density of tactile mechano-receptors, and they have a very highly developed sense of smell [14]. These traits could be manipulated to draw pigs towards objects through the application of odorous products. For example, weaned pigs preferred feeders sprayed with sow fecal semiochemicals, and their application significantly reduced aggression and tended to increase feeding behavior [15]. A milky cheese attractant was preferred by piglets during lactation after prenatal flavor exposure [16]. Adding flavors, including milky cheese, to creep feed increased preweaning feed intake, post-weaning average daily gain (ADG) and gain-to-feed (G/F) ratio [17]. Neither attractant has been presented through a neonatal piglet enrichment model.
Based on the critical need to improve preweaning livability rates, this proof-of-concept study aimed to determine if enrichment ropes would entice neonatal piglets away from the sow and reduce preweaning mortality. There were three specific objectives to achieve this aim: (1) to describe piglet enrichment use; (2) to evaluate the impact of three attractants on piglet enrichment use; (3) to compare piglet growth rate and livability among the three attractants.

2. Enrichment and Treatments

The enrichment device consisted of a polyvinyl chloride (PVC) pipe placed on the divider between two farrowing stalls, from which up to seven cotton ropes were suspended (Figure 1). Authors hypothesized that an absorbent hanging cotton rope dipped in piglet-relevant attractants would be an effective enrichment. Therefore, sows and their litters were assigned to one of three treatments: (1) sunflower oil (OIL, n = 7 sows, 41 piglets), (2) semiochemical (SC, n = 8 sows, 51 piglets), or (3) milky cheese (MC, n = 11 sows, 69 piglets). Treatment ropes were first applied to the stall at the start of Day 2, replaced with a new rope and fresh treatment at the start of Days 3, 4 and 5, and removed at the beginning of Day 6. Treatments were applied by soaking the bottom 20 cm of each rope in the treatment solution for 15 s, and then hanging the rope to air dry for 10 min. Ropes were applied to the stall in one of the seven numbered locations on the enrichment device.

Figure 1. Photograph of the PVC (polyvinyl chloride) device used to hang enrichment ropes. The device, which measured 1.7 m in length, had a 2.7 cm cutout taken out of the bottom of the PVC. This cutout was placed over the top of the 2.5 cm thick plastic siding between two farrowing stalls. In this figure, the rope/eyebolt locations visible (from bottom to top of the photo) are 5, 3, 1, 2, 4, 6.

3. Behavior

Color video was recorded continuously from Days 2 to 5. The sampling protocol was continuous sampling of all piglets in the litter on Day 2 during the daylight hours (07:00–22:00 h). Frequency and duration of rope investigations, defined as purposeful snout contact with the rope with the mouth open or closed, were recorded. Average frequency and duration of investigations across all treatments were analyzed descriptively and will be presented as the means ± SD. Ropes were exposed to 161 piglets, of which 121 piglets (75%) interacted with ropes at least once. Of the piglets that interacted with the rope, there was a high level of individual variation in investigational total frequency (1 to 21) and duration (1 to 52 s) (Figure 2). Regardless of rope treatment, piglets displayed on average 4.5 ± 3.81 total frequency of investigations, and the average total time spent interacting with the ropes was 9 ± 9.4 s, respectively. On average, a single bout lasted 1 s (range < 1–14). Environmental enrichment rope treatment was not a source of variation for frequency (Figure 3A; p = 0.20) or duration (Figure 3B; p = 0.21) of investigations.
Animals 12 00211 g004 550
Figure 2. Descriptive measures of piglet individual variation in total frequency (A) and duration (B) of piglet purposeful investigations with environmental enrichment ropes on Day 2, the first day of placement. OIL = sunflower oil, MC = milky cheese, and SC = semiochemical.
Animals 12 00211 g005 550
Figure 3. Average (±SE) frequency (A) and duration in seconds (B) of piglet purposeful investigations with environmental enrichment ropes on the first day of placement (Day 2 relative to farrowing). Ropes were dipped in one of three treatments: OIL = sunflower oil, MC = milky cheese, and SC = semiochemical. Frequency (Figure 3A; p = 0.20) and duration (Figure 3B; p = 0.21) of interactions was not different between treatments.

Overall, the high level of interaction by piglets in the Day 2 environment after farrowing is an important and novel finding, as it suggests that even at this young age, piglets are attentive to and interacting with their environments. Piglet interest in the ropes on Day 2 suggests that environmental enrichments are practical for piglets even at this young age.

Rope length and end fray length were assessed daily and used as indirect enrichment use measurements. Rope characteristics data are presented descriptively as the means ± SD. All placed ropes measured 33.0 cm in length with 2.5 cm of fraying at the rope end. At removal, mean rope length regardless of treatment was 33.4 ± 0.8 cm and mean rope fray length was 8.4 ± 6.6 cm. By month, the average rope length at removal was 34 ± 0.1 cm in July and 33 ± 0.1 cm in August, and rope fray length was 13.8 ± 5.2 cm in July and 2.8 ± 0.6 cm in August. Average rope length and rope fray length by treatment can be found in Figure 4.
Animals 12 00211 g006 550
Figure 4. Descriptive measures of environmental enrichment rope length after removal from the farrowing stall 24 h after placement. The total rope length consisted of frayed and unfrayed sections. Ropes were dipped in one of three treatments: OIL = sunflower oil, MC = milky cheese, and SC = semiochemical.
No damage or visible missing parts of the rope were noted at removal, which is consistent with observations when ropes have been used to collect oral fluids [18]. Many ropes were visibly dirty upon removal, indicating piglets contacted the ropes. Ropes and fray length were longer at removal than at placement. This may be explained by the rope unwinding over time due to piglet contact. The increase in rope length and fray was similar across treatments. Casual observation suggests that average rope length and fray was longer in July than in August and may be partially explained by a change in rope spool between these months.

4. Mortality and Weight Gain

Environmental enrichment rope treatment was not a source of variation for litter average weight gain (OIL 9.5 ± 1.01 kg, SC 9.2 ± 0.98 kg, MC 8.4 ± 0.84 kg; p = 0.71). A total of 79 piglets died in the preweaning period, for a total preweaning mortality of 38% across all treatments. Of this number, 41 piglets died before the enrichment ropes were added (Days 0 to 1), 16 piglets died while the enrichment ropes were in the stalls (Days 2 to 5), and 22 piglets died after the enrichment ropes were removed (Days 6 to weaning). The 16 piglets that died from Days 2 to 5 were necropsied. Half (8 of 16) of these piglets were identified as dead by crushing, and 3 piglets were identified with no milk in their stomach (Table 1). Of the 16 piglets that died during the experimental period (Days 2 to 5), 68.8% (11/16) did not touch an enrichment rope on Day 2. Four of those piglets died on Day 2, and none of those piglets touched an enrichment rope on Day 2. 12 of the piglets died from Days 3 to 5, and only 5 (41.7%) of those piglets had touched an enrichment rope on Day 2.
Table 1. Descriptive results of number (#) of piglets that died on Day 2 to 5, when the enrichment ropes were present in the farrowing stall. All piglets were necropsied to identify those that were crushed 1 and to check for milk presence in the stomach 2.
  Treatments 3 Total
  OIL SC MC
# of sows 7 8 11 26
# of piglets on Day 2 41 51 69 161
Crushed + milk 1 1 6 8
Crushed + no milk 0 0 0 0
Not crushed + milk 3 1 1 5
Not crushed + no milk 0 2 1 3
Total # piglets dead 4 4 8 16
1 Piglets were classified as crushed through external signs of trauma, including bruising (injury that included discoloration and inflammation of the skin without exposure of underlying tissues) and compression of parts of the body, or if they were found underneath the sow; 2 piglets stomach contents were checked and classified as milk present (milk) or milk not present (no milk); 3 ropes dipped in OIL = sunflower oil; SC = semiochemical; MC = milky cheese.

Piglets in the MC had the lowest percent mortality while the enrichment was in the stall (p = 0.01), piglets in SC had the lowest percent mortality after the enrichment was removed (p < 0.0001), and piglets in SC had the lowest percent mortality over the entire preweaning period affected by the rope enrichment (Days 2 to weaning; p = 0.03; Table 2)

Table 2. Preweaning performance measures of litters provided with environmental enrichment ropes over Days 2 to 5 after farrowing. Results are presented as the LSMeans ± SE where statistical analysis was performed, or as the mean ± SD where results are presented descriptively.
  Treatments 1 p-Value
  OIL SC MC
Number of sows 7 8 11  
Average sow parity 4 3.8 4  
Average litter size (#) 6.3 ± 3.09 8.0 ± 4.00 8.6 ± 3.21  
Average weaning age (d) 20.3 ± 1.89 20.1 ± 1.96 19.6 ± 2.66  
  Litter Body Weight (kg)  
Average birth weight 3.0 ± 0.48 3.0 ± 0.70 3.3 ± 0.38  
Average weaning weight 12.4 ± 2.89 12.3 ± 2.20 11.9 ± 2.94  
Average weight gain 9.5 ± 1.01 9.2 ± 0.98 8.4 ± 0.84 0.71
  Litter Mortality (%) 2  
Days 2 to 5 3 10.7 ± 1.29 a 9.2 ± 1.07 a 6.1 ± 0.74 b 0.01
Days 6 to weaning 4 7.4 ± 1.03 a 4.0 ± 0.65 b 10.8 ± 0.98 c <0.0001
Days 2 to weaning 5 19.2 ± 1.71 a 13.7 ± 1.29 b 18.2 ± 1.27 a 0.03

1 Ropes dipped in OIL = sunflower oil; SC = semiochemical; MC = milky cheese; 2 average percent mortality (%), calculated as the average number of piglets dead at the end of the time period / the average number of piglets alive at the beginning of the time period × 100; 3 Days 2 to 5, when enrichment ropes were in the stall; 4 Days 6 to weaning, after enrichment ropes were removed from the stall. Weaning age ranged from 15 to 22 days of age; 5 Days 2 to weaning mortality, defined as all piglets that were alive at rope placement and dead before weaning; a, b, c Different superscripts within a row indicate significance at p ≤ 0.05.

There are concerns that placement of EE could interfere with piglet nursing behavior; however, of the 75% of piglets interacting with the ropes on Day 2, none died. This is an interesting finding that may warrant further investigation. Of the 16 piglets that died during the study period, half were attributed to crushing, and only three did not have milk present in their stomachs. Although half of the piglets that died were assigned to the MC treatment, this treatment group had more sows and larger litters.

While piglets were observed interacting with the EE, an important unanswered question is how often and how long does a piglet need to interact with the enrichment to receive benefits in terms of livability, growth, and/or welfare? The high individual variation both within and between litters could provide a starting point, and future studies investigating the relationship between individual piglet enrichment use and performance measures are warranted. In this study, although there was not a significant difference across treatments in piglet rope interactions, there was an effect of rope treatment on piglet mortality. It would be recommended that future work measure piglet distance from and time spent near the enrichment ropes, because some piglets may not directly interact with the ropes but still may be drawn away from the sow, thus reducing the risk of crushing.

5. Conclusions

When provided with environmental enrichment designed with neonatal piglet anatomy and behavior considerations, piglets showed high individual variation in their investigations of enrichment. A total of 75% of piglets touched the ropes at least once on Day 2, indicating that neonate piglets are attentive to their environment early in life. There was a high variation in frequency and duration of individual piglet investigations across all treatments. The milky cheese enrichment was investigated the most by piglets and had the lowest mortality during the enrichment period (Days 2 to 5). This proof-of-concept study provides pivotal information for implementing environmental enrichment into larger commercial scale studies.

This entry is adapted from the peer-reviewed paper 10.3390/ani12020211

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