Porcine haptoglobin levels measured at 7–14 days after weaning were independent of age, weight or gender

Acute phase proteins (APP) are cytokine-induced plasma proteins produced mainly in the liver in response to infection, inflammation and stress. The levels of some APP have been used as diagnostic indicators for a number of diseases (Petersen et al. 2004) and for health monitoring. Haptoglobin (Hp) is an APP responsible for collecting and recycling free haemoglobin. The high level of variation in Hp levels of apparently healthy pigs has been attributed to factors such as age, gender, source herd and pig husbandry (Piñeiro et al. 2009). This study investigated the range in Hp levels from a single breed of pigs, 7–14 days after weaning and from a single piggery under the same housing and management conditions. The hypothesis tested was that age, collection date (season), gender and (or) weight would affect Hp levels.

A single serum sample was taken 10 days (10.5 ± 2.7: mean ± SD) after weaning from 810 pure bred Large White pigs of mixed sex (49% female and 51% male), housed at The University of Queensland Gatton piggery. Haptoglobin levels were determined by ELISA using a standard validated on a commercial kit. The ELISA antibody set included rabbit anti-human Hp (capture), mouse anti-human Hp (detection) and rabbit anti-mouse IgG-AP (Sigma-Aldrich. Missouri, USA.). Each serum was tested at dilutions of 1 : 30,000, 1 : 1000 and 1 : 50 and Hp levels were calculated from plate specific standard curves using four-parameter logistic fit (4PL) analysis (SoftMax^® Pro 5 software). Sera were collected over different seasons in the first (summer), second (autumn) and final (spring) quarters of the calendar year (2013). Data were grouped according to collection quarter (1, 2 and 4) and by pig age at the time of collection (32–37, 38–42 and 43–47 days of age). The descriptive statistics of the observed Hp concentrations were determined using Microsoft Excel^® (Table 1). Distribution and ANOVA analysis (R: Free Software Foundation’s GNU General Public License) were used to determine the effect and significance of collection date, age, weight and gender of the pigs on the log-transformed Hp levels.

Table 1.  Descriptive statistics of serum haptoglobin (Hp) levels in pigs, during the second week after weaning, grouped by collection dates into quarters of the year (2013) and into three age groups

The distribution of log transformed Hp level was bimodal after allowing for differences in the main effects of age and collection date (season). Within the sample population, 2% of pigs had Hp concentrations within the acute range of 3,000–8,000 µg/mL (PHASE™ Tridelta Development Ltd. Ireland), while the majority of pigs (54%) had Hp levels <1.0 µg/mL (0.4 ± 0.2: mean ± SD µg/mL). No significant difference was observed between the Hp levels in females (336 ± 38.9: mean ± SD µg/mL) and males (361 ± 39.5: mean ± SD µg/mL). Haptoglobin levels decreased with increasing pig age in quarters 1 and 4 but increased with increasing pig age in quarter 2 (Table 1). Significantly higher Hp levels were observed in pigs sampled in the 4th quarter (P < 0.001). However, ANOVA analysis also determined that pig age, weight and gender did not have a significant effect on Hp level. Despite controlling for breed, time after weaning, source herd, housing and management, sizeable variation in Hp levels were observed. The relative elevation of Hp levels observed in quarter 4 and the bimodal distribution of response indicated other factors, such as season, pathogen loads and other stressors, should be considered in future studies.