Development of improved disease monitoring tools and management strategies to promote health in finishing pigs

Aims and objectives:

• To assess the biological response of pigs to management interventions designed to reduce the level of infectious challenge.
• To determine the factors affecting this response, and model the cost-benefit balance of such interventions in different circumstances 

Summary of findings 

Poor health in finishing pig herds can lead to reduced animal welfare and substantial financial losses arising from increased feed costs, a lower throughput from reduced growth rates and higher veterinary medicine costs. There is additional concern surrounding the morale of staff dealing with poorly performing pigs. Where chronic disease persists, the sustainability of pig production is questionable, and threats from new diseases are always emerging.

This research has investigated a number of preventative disease management strategies for pigs with the potential to improve detection, limit the spread of disease, and thus improve the overall health and productivity of finishing pigs. The focus was to evaluate strategies that would offer improved monitoring and control of endemic disease within finishing herds, yet could be employed by producers immediately, at little or no extra cost. A number of these tools should be regarded as providing disease indicators to prompt further veterinary investigation.

The use of a disinfection routine in different finisher pig housing systems, all-in/all-out (AIAO) and continuous flow (CF), was examined for effects on air quality, pig heath and productivity. The three treatments were an AIAO system cleaned and disinfected between batches of pigs, a CF system with cleaning and disinfection between incoming pens of pigs and a CF system with no disinfection between incoming pens of pigs. The use of disinfection significantly reduced the number of bacteria present on pen surfaces (P < 0.001), but the washing/disinfection activity caused increased concentrations of ammonia (P < 0.05). There were no effects on other air quality parameters, nor on pig health or productivity. The AIAO room had lower concentrations of airborne bacteria (P < 0.005) and ammonia (P < 0.01) than the CF systems. Pig health and productivity did not differ between systems, although weekly health scores reflecting the severity of disease were correlated with productivity (P < 0.01). The extent of reduced performance in pigs displaying specific clinical disease signs was quantified from health data of individual pigs, and showed that pigs that suffered respiratory or enteric problems at some point in the finisher period had an average daily gain (ADG) of 0.42±0.10 and 0.62±0.03 kg/day respectively.

Pigs that displayed no clinical symptoms had a growth rate of 0.79±0.01 kg/day. Serum acute phase proteins (APPs) measured in a sub-population of pigs were significantly and negatively related to the growth rate of the pigs in the final two weeks before slaughter (P < 0.05), but were not different between the three systems.

The health and growth patterns of over 700 pigs, housed indoors and managed in accordance with commercial farm practice, were monitored from birth to slaughter. This study explored whether pigs which became clinically ill, or had stunted growth, displayed any characteristics that could make them identifiable from birth, and whether there were longer term consequences of an early growth check on lifetime health and performance. Analysed on an individual level, the probability of pigs developing illness later in life was significantly associated with total litter size, birth to wean ADG and weaning weight. In multivariate analysis, weaning age rather than weaning weight was most influential on lifetime growth of pigs. Of pigs marketed for slaughter, significant differences existed between the growth rate of birth weight groups (light: <1kg, medium: 1-1.69kg, and heavy: >1.7kg) in each production stage (P < 0.001) until entering the finisher building, where there was no difference. The data suggest the development and physical competency of pigs at birth and in early stages influences long term health and growth performance.

Oral fluid (OF) was tested, as an alternative to serum, for measurement of Acute phase proteins (APPs) and the virus Porcine Reproductive and Respiratory Syndrome (PRRS) in individuals and groups of pigs. APPs were evaluated for their ability to determine the presence of sub-clinical disease in growing pigs and its relationship to reduced performance. OF was obtained during the finisher stage from a sub-group of 80 pigs from the longitudinal study population monitored for lifetime growth as described in the previous paragraph. The concentration of APPs in serum and OF was significantly correlated (P < 0.05). Concentrations of Haptoglobin (Hp) and C-reactive protein (CRP) in OF of individual pigs were negatively related to their ADG over the finishing period and over their lifetime (P < 0.001). The concentration of CRP within a pooled OF sample was negatively related to the pen gain per day during the finishing period (P < 0.01). Measurement of APPs in OF could provide a convenient, low stress method to objectively assess the level of immune activation associated with sub-clinical disease that could be contributing to sub-optimal growth in pigs, but presently requires further development and validation.

In order to develop more effective disease surveillance approaches, the effectiveness of a rope chewing methodology to collect pooled OF samples from groups of pigs, as a lower cost diagnostic fluid, was determined. Providing a single length of rope to a pen of ≤ 25 pigs generated chewing by over 80% of the pen group within a 60 minute period. An increased number of pigs in a fully slatted (FS) system chewed the rope and for a longer period (P < 0.001) than those in a straw kennel (SK) system. Increasing the number of ropes from 1- 4 increased the mean total chewing time of pigs only in the FS system. The quantity of OF collected from rope was plentiful (12.5 ± 1.7 ml extracted by hand squeezing), and this correlated to both the percentage of pigs to chew the rope and the mean total chew time (P < 0.001). Subject to further research on analytical sensitivity for infectious agents within OF, this method could enable groups of ≤ 25 pigs to be screened for diagnostic purposes with the use of only one sample.

To evaluate an alternative method for early detection of disease, the daily water use of pen groups of pigs housed in a continuous flow building was automatically monitored throughout the finisher phase alongside pig performance and health parameters. Mean live weight, daily live weight gain, number of pigs per pen, environmental temperature and drinker type were significant factors associated with mean water consumption per pig per day (P <0.001). Data from pens in which feed intake was measured demonstrated significant associations between water intake and Food Conversion Ratio (P <0.001). During the first four weeks of pigs moving into the building, there was a strong tendency for reduced water consumption within a given week to be associated with  the severity of scour observed in the following week (T = 0.067). This demonstrates potential for automated recording of water consumption to be used as a tool for the early identification of disease, indicating reduced performance of growing pigs.

The findings of this thesis demonstrate a number of approaches that can increase the accuracy and consistency of monitoring disease and production in growing pigs. The results from the technologies piloted in these studies suggest that practical and cost-effective methods can be developed to identify disease earlier, in the sub-clinical stage. Arresting disease before it reaches a clinical stage could offer far greater possibilities for the farmer to reduce performance loss and for the UK pig industry to improve the health and welfare of pigs and the sustainability of pork production.