During the production period from birth to slaughter there are some pigs that grow markedly slower, despite conditions that seem to support the rapid growth of their contemporaries. This reduction in growth inevitably leads to weight variation within a group and results in system inefficiencies. The aim of this thesis was to identify risk factors involved in poor growth and to develop management and nutritional treatments to enable light pigs to maximise their growth at different stages of production. Risk factor analysis for a large dataset showed that, in particular, low birth and weaning weight result in poor growth to finishing. Some light pigs do, however, have the capacity to compensate for low weight at earlier stages of production. Preweaning intervention demonstrated that low birth weight pigs cross fostered into litters with similar weight littermates had a significantly higher weaning weight than those in mixed litters with heavier pigs; however the provision of supplementary milk to such litters had no further beneficial effect. A post weaning feeding regime formulated for low birth weight pigs, with a higher nutrient specification diet based on more digestible ingredients, not only showed improved performance to 10 weeks of age, but also enabled low birth weight pigs to meet the BW of heavier birth weight pigs. In contrast, a high specification diet (higher in amino acid: energy content) had no effect on the growth of low birth weight pigs when offered from 9 weeks of age, suggesting a critical window for intervention. Overall, the crucial stages of postnatal growth for light pigs have been identified, and preweaning and early post weaning treatments have been developed. These not only improve the performance of low birth weight pigs but also allow them to catch up with heavier birth weight pigs.

Lameness is a major cause of lost productivity for the pig industry. The objective of this PhD was to develop an objective motion capture method for growing pigs and assess (1) the repeatability and sensitivity of the method (2) the gait characteristics of pigs housed on different floor types and (3) gait differences in pigs with conformational deficiencies, joint disease and/or clinical lameness. Infrared camera-based motion capture was applied to three different cohorts of pigs in three experiments, including an observational study following 84 gilts from grower- to second-parity stage. 3D coordinate data of reflective skin markers attached to head, neck, trunk and leg anatomical landmarks were collected. Temporal (time), linear (displacement) and angular (joint angles) kinematic gait parameters were calculated. Repeatability of the method varied with amount of overlying tissue and/or prominence of anatomical landmarks used for marker placement, but not necessarily with walking speed. Gait development of pigs reared on fully-slatted, partly-slatted or deep straw-bedded floors was not different. Lameness detection and evaluation was possible using relative linear and temporal kinematics. The within-stride trajectory of head and pelvic regions during walking differentiated pigs with front and multi-leg lameness from normal pigs, respectively. The ipsilateral swing-to-stance time ratio detected lameness in hind legs, but was not affected during multi-leg lameness. The frequency and magnitude of irregular steps was increased in lame pigs and in pigs with subclinical joint lesions of osteochondrosis diagnosed post slaughter. Step irregularity (as reflected in the step-to-stride length ratio) was also predictive of impending lameness. The step-to-stride length ratio is a dimensionless and ideal parameter to monitor pigs of different age and size, moving at a self-chosen walking speed. Flexion asymmetry and joint flexion patterns were indicative of locomotor problems in some cases. Gait analysis therefore offers potential for automated prediction and early detection of lameness.

Classical swine fever virus (CSFV) is a highly infectious disease of pigs, which has devastating economic and social consequences. To minimise the potential for future outbreaks, it is important to assess the risk of CSFV introduction to the UK via porcine products. In doing so, the first aim was to determine the oral infectious dose 50% (oral PID50) of a highly virulent strain of CSFV. Previous work carried out at AHVLA has identified the oral PID50 of a moderately virulent CSFY strain, and so the aim of this study was to evaluate whether virulent strains have a lower or similar infectious dose, in order to represent a worst-case .scenario of susceptible pigs consuming pork containing CSFV. Through oral inoculation of pigs, the oral PIDso of Brescia was found to be 105.47 TCID50 with a 95% confidence interval of 105.1 to 105.8 TCID50.

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African swine fever virus (ASFV) replicates primarily in blood monocytes and macrophages in the lymphoid tissues and organs. Type I interferon (IFN) participates in the host innate immune response to viral infection. IFN regulates the expression of many different genes, known as IFN-stimulated genes that restrict viral replication, including the Mx genes. Using the MDBKt2/MxCAT bioassay, an assay used to detect Type I IFN (lFNu/P), the induction of biologically active IFN occurring during in vivo infection with virulent ASFV strains OURT8811 and Georgia 200711 was observed. There was no detection of biologically active IFN during infection with the avirulent strain OURT88/3. The effect of recombinant porcine IFNul (rpoIFNul) on ASFV replication in porcine macrophages was assessed. Only the replication of avirulent OURT88/3 was affected by the pre-treatment of rpoIFNu 1. Virulent strains Georgia 200711, OURT8811 and Pr4 were unaffected by the rpoIFNul -induced antiviral state. Multigene families (MGF), MGF 360 and MGF 5051530 have been implicated in evasion of the antiviral effects of IFN. The replication of recombinant Pr4~35 strain, which lacks six genes ofMGF 360, and two genes from MGF 5051530, was reduced in rpoIFNul treated cells, compared to untreated cells. The MGF genes missing in the Pr4~35 strain is similar to the avirulent OURT88/3 strain. Porcine Mx 1 has been shown to associate with ASFV replication sites, and human MxA has been shown to inhibit viral replication of tissue-adapted strain BA 71 V. SiRNA knockdown of Mxl was carried out in pre-treated rpoIFNul alveolar macrophages, and preliminary data suggests that Mx 1 is not essential for inhibiting the avirulent OURT88/3 strain. A human embryonic kidney cell line expressing the human IFN-stimulated gene viperin reduced ASFV DNA replication while not affecting infectivity of the virus. ASFV capsid protein pE120R was reduced in viperin expressing cells. This suggests that IFN-stimulated gene viperin can target ASFV replication, although the mechanism has not been determined.

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Piglet mortality is an animal welfare problem with great economic importance. This study investigated housing and nutritional strategies to improve sow welfare whilst safeguarding the survival of new-born piglets and their welfare and performance from birth to the post weaning period. The first experiment compared the effect of different space allowances in a loose farrowing pen on sow behaviour and piglet survival. The behaviours of sows which lead to crushing of piglets, the main reason for mortality, differed between the two pen sizes. A second experiment examined the effect of maternal diet supplementation in late gestation and lactation with docosaheaxanoic acid (DHA) on piglet survival and growth in crated or loose farrowing systems. Performance did not differ between systems. DHA supplementation resulted in fewer stillborn piglets, despite prolonged farrowing duration. Sows given DHA had more vital piglets, with reduced latency to stand, to get to the teat and suckle, but also had reduced weaning weight. A detailed study to investigate the mechanisms underlying this finding measured the behavioural and physiological characteristics of new born piglets. The same effects of DHA on the farrowing process and piglet vitality were apparent, but could not be explained by differences in blood lactate, glucose or thermoregulation of piglets in the perinatal period. A final experiment investigated a new approach to try and improve weaning weight, by stimulating foraging behaviour through sequential presentation of creep feeds differing in flavour. This treatment increased creep feed consumption in both crate and loose housing systems, with a beneficial effect on post weaning growth. The thesis demonstrates ways in which piglet survival and growth can be enhanced by appropriate pen design and nutritional strategies in both conventional and alternative farrowing systems.

This thesis investigated strategies to improve detection and control of disease in finishing pigs. It was found that a disinfection routine in finisher pig housing reduced bacteria on pen surfaces. All-in/all-out systems had lower concentrations of airborne bacteria and ammonia than continuous flow systems, however pig health and productivity did not differ between systems. Serum acute phase proteins (APPs) were significantly related to a reduced average daily gain (ADG) of pigs in the two weeks before slaughter. The lifetime growth of >700 pigs was monitored to explore consequences of early growth on lifetime health and performance. The probability of pigs showing illness later in life was associated with litter size and early growth rate. Early stage differences existed between the growth rate of light and heavy birth weight groups. Oral fluid (OF) was utilised for measurement of APPs, to determine the presence of subclinical disease in pigs. C-reactive protein (CRP) and Haptoglobin (Hp) in the OF of individual pigs was negatively related to their ADG over the finishing period and lifetime respectively. CRP within a pooled OF was negatively related to pen finishing ADG. To collect pooled OF samples from groups of pigs, a single length of rope in a pen of ≤ 25 pigs generated >80% chewing, in 60 minutes. A higher proportion of pigs chewed the rope when housed in a fully slatted system than in a straw system. An interaction occurred between the housing system and the number of ropes provided. Daily water use patterns of finisher pigs were evaluated for early disease detection. The mean daily quantity of water consumed per pig within a given week differed in relation to the severity of scour observed in the following week at a level approaching significance. These findings demonstrate possible techniques to identify disease in the sub-clinical stage.