In total, 41 Landrace x Yorkshire crossbred sows (parity 1–5) and 406 piglets were randomly allocated to one of the following three groups: i.) CONTROL (20 sows and 161 piglets, 81 and 80 piglets from primiparous and multiparous sows, respectively), the piglets were administered iron dextran 200 mg intramuscularly and toltrazuril orally at 3 days of age (20 mg/kg, Coxzuril 5%® containing toltrazuril 50 mg/ml, BIC Chemical co. ltd., Nakhonpathom, Thailand); ii.) NEGATIVE (n = 84 piglets, 44 and 40 piglets from primiparous and multiparous sows, respectively), two piglets from each litter served as negative control. The negative control piglets were not treated with iron until 7 days of age, and toltrazuril was given at 5 days of age and iii.) TREATMENT (21 sows and 161 piglets, 81 and 80 piglets from primiparous and multiparous sows, respectively), the piglets were fed with an oral suspension of iron and toltrazuril combination at 3 days of age (Baycox® iron oral 1 ml containing toltrazuril 50 mg and iron 228 mg as iron dextran, Bayer Animal Health GmbH, Germany). In all litters, 10 piglets with individual body weight at birth above 1.0 kg were included in the experiment.
This experiment followed the guidelines of The Ethical Principles and Guidelines for the Use of Animals for Scientific Purposes by the National Research Council of Thailand and was approved by the Institutional Animal Care and Use Committee (IACUC) in accordance with the university regulations and policies governing the care and use of experimental animals (protocol ID. 1831089). The experiment was carried out in a commercial swine herd in Thailand and included 41 sows and 406 piglets. The numbers of primiparous (parity number 1) and multiparous sows (parity numbers 2–5) were 21 and 20, respectively. Sows were kept in a closed housing system equipped with an evaporative cooling system to reduce the impact of high ambient temperature. During gestation, the sows were kept in individual stalls (1.2 m2) and fed a commercial gestation diet twice a day, following a standardised feeding pattern. On average, the sows received 2.5 kg of feed per sow per day to meet or exceed their nutritional requirements (NRC, 2012).
Gestating sows were moved to the farrowing house approximately 1 week before the expected date of parturition. The sows were placed in individual crates (1.5 m2) at the centre of the farrowing pens (4.2 m2), which were fully slatted with a concrete base at the centre for sows and with steel slats at both sides of the farrowing crate for piglets. Each pen was provided with a warm creep area for piglets, which was placed on one side of the pen (0.60 m2). A heating lamp was provided to piglets in the creep area during the first week after farrowing and was turned on during the night or when the environmental temperature fell below 30 ºC. Sows were fed a commercial lactation diet twice a day. Feed offered to sows was reduced to 2.0 kg for 2–3 days before farrowing. After farrowing, the amount of feed offered to sows was increased daily according to the litter size and body condition of the sow until ad libitum feed was reached after 1 week of lactation. Sows and piglets had ad libitum access to water by one nipple drinker for the sow and one nipple drinker for the piglets. The parturition process was carefully monitored. The sows were interfered as little as possible during parturition. Birth intervention was performed only when dystocia was clearly identified. Dystocia was considered when an interval of > 30 min had elapsed from the birth of the previous piglet. The routine procedures performed on piglets included weighing, tail docking and teeth clipping on the first day of life. At 3 days of age, 200 mg (1 ml) of iron dextran was administered intramuscularly (Gleptosil®; Alstoe Ltd. Animal Health, Leicestershire, England) to all the piglets in the CONTROL group. For the TREATMENT group, the administration of iron dextran was omitted, and 1.0 ml of a combined product of toltrazuril and iron (Baycox® Iron, Bayer Animal Health GmbH, Germany) was provided orally to all piglets at 3 days of age.
The sow parameters recorded during the experiment were body condition score, backfat thickness (measured the day before parturition at the last rib and 6–8 cm from the midline using A-mode ultrasonography; Renco-Lean meter®; Minneapolis, MN, USA), gestation length (calculated from the date of first insemination to the date of farrowing), farrowing duration (defined as the time interval between the expulsion of the first and last piglets), total number of piglets born per litter (TB), number of piglets born alive per litter (BA), number of stillborn piglets per litter and mummified foetuses per litter. The occurrence of dystocia was also recorded.
Piglet parameters recorded during the experiment consisted of birth order and rectal temperature 24 h after birth, measured using a digital thermometer (Verridian Dual Scale 9-Second Digital Thermometer Model 08-357; Verridian Healthcare Co. Ltd., IL, USA; display resolution of 0.01 ± 0.1 ºC accuracy). All piglets were dried immediately after birth with drying powder, weighed and then weighted again at 7 and 21 days of age. Average daily weight gain (ADG) from birth to 7 days (ADG7) and from birth to 21 days (ADG21) of age was calculated. Mortality of piglets was recorded at 7 and 21 days of age to calculate piglet pre-weaning mortality at 7 and 21 days, respectively. The occurrence of diarrhoea was also observed and recorded, and diarrhoea severity was defined as normal, mild, moderate and severe: “normal” referred to piglets without signs of diarrhoea, “mild” referred to piglets with a mild degree of diarrhoea, having pasty to semi-liquid faeces, “moderate” referred to piglets with some moderate degree of diarrhoea, having semi-liquid to liquid faeces without any signs of dehydration, and “severe” referred to piglets with severe degree of diarrhoea, having liquid faeces and apparent dehydration.
Blood samples were obtained from randomly sampling piglets (77, 67 and 74 samples in CONTROL, NEGATIVE and TREATMENT groups, respectively). The blood samples were collected from the jugular vein of the piglets at 2 (n = 56), 7 (n = 80) and 21 days (n = 82) of age. The piglets in each group were randomly chosen for blood collection, and the blood samples were kept in EDTA tubes. In total, 218 blood samples were collected. Haemoglobin, haematocrit and red blood cells (RBC) were evaluated by an Auto Hematology Analyzer (Mindray BC-5150, Shenzhen Mindray Bio-Medical Electronics Co., Ltd., ShenZhen, P.R. China). Anaemia was defined as a haemoglobin level below 8.0 g/dl (Svoboda et al. 2017).
The statistical analyses were carried out using SAS version 9.4 (SAS Institute Inc., Cary, NC, USA). Descriptive statistics of sow performance and piglet characteristics, including non-missing values, mean values and range, were generated using the MEANS procedure of SAS. The distribution of the data was determined using the UNIVARIATE procedure of SAS. Piglet was defined as an experimental unit. Continuous traits (i.e., ADG, body weight, haemoglobin, haematocrit, RBC and other blood parameters) were analysed by using multiple ANOVA, applying the GLM procedure of SAS. The statistical models included treatment group (CONTROL, NEGATIVE and TREATMENT) as the main effect and parity number of sows (primiparous and multiparous) as a fixed effect, as well as the interaction between parity and treatment group. Differences of least square means were compared using the least significant difference (LSD) test. Categorical data (i.e., piglet mortality at 7 and 21 days postpartum and piglets with anaemia) were analysed by using logistic regression, applying the GENMOD procedure of SAS. The statistical models included the effect of treatment group (CONTROL, NEGATIVE and TREATMENT), parity number of sows (primiparous and multiparous) and the interaction between parity and treatment groups. Least square means were obtained from the statistical models and compared by using the LSD test. In addition, ADG from birth to 21 days of age was compared among groups of diarrhoea scores (i.e., normal, mild, moderate and severe) by using one-way ANOVA. A P value < 0.05 was considered statistically significant.