A comparison of 4 iron supplementation protocols to protect suckling piglets from anemia

Abstract

Pigs are routinely supplemented with iron during the suckling period to prevent anemia, but recent studies have shown that despite iron treatment many fast-growing pigs are iron deficient at weaning. The objective of this study was to determine if oral iron supplementation provided free-choice from a week of age until weaning could prevent iron deficiency. Results showed that the industry standard treatment of a single iron injection at 4 days of age did not always prevent iron deficiency at weaning, indicating the need to provide additional iron to fast-growing suckling pigs either orally or by a second injection. It appears that providing piglets daily access to iron-enriched peat moss or injecting a second 200-mg dose of iron intramuscularly are both effective in meeting the piglets iron requirements during the suckling period.

There is strong evidence that the standard practice of injecting piglets intramuscularly with 100 or 200 mg of iron at 3 or 4 d of age doesn’t meet the needs of large, fast-growing piglets under modern farming conditions (1–3). Various studies have found the prevalence of pigs with iron deficiency (Hb < 110 g/L) at weaning to be about 25%, with the biggest piglets being most likely to be affected (1–3). Iron deficiency may result in anemia and lead to poor growth performance during the early nursery stage (4,5). This can be resolved by using a second iron injection near the end of the suckling period (6) but this requires additional handling of pigs and there is reluctance at the farm level to adopt this solution.

Another reason to examine the current approach to controlling iron deficiency in suckling pigs is the growing interest among consumers for pork that is produced from pigs raised in a more natural way. There is renewed interest, therefore, in oral supplementation of iron as opposed to the standard intramuscular injection. In addition, recent advances in our understanding of iron absorption and the impact of large parenteral doses of iron on induction of hepcidin expression and the regulation of iron in the body provides a further reason to investigate alternative strategies for iron supplementation (7).

Several commercial oral iron products are available, including powders and pastes, which require restraining the piglet and manually placing the product in the pig’s mouth, as well as products that can be scattered in the creep feeder area for free-choice consumption (8,9). One example of this latter approach involves mixing powdered iron with peat moss and providing this iron-rich product in the creep area. Pigs root in the peat moss in a manner similar to what they would do if raised outdoors where they have access to soil.

The primary objective of this study was to compare different iron supplementation strategies to determine if, at weaning, there is a difference in hematological parameters indicative of iron status among the different approaches. Specifically, a goal of the study was to determine whether oral iron supplementation could replace injectable iron protocols without risking an increased prevalence of anemia.

The study was approved by the Animal Care Committee at the University of Guelph and was conducted at the Arkell Swine Research Station, University of Guelph.

A total of 12 litters were included in the trial with all pigs individually identified with an ear tag. Treatment was allocated at the litter level and litters were chosen randomly before treatment was assigned. Pigs in 3 litters were assigned to Group 1 or 2 and pigs in the remaining 9 litters were assigned to Group 3 or 4 and pigs were assigned treatment using systematic random sampling. Group 1 pigs were injected with 200 mg (1 mL) of gleptoferron (Gleptosil; Ceva Animal Health, Cambridge, Ontario) at 4 d of age. Group 2 pigs were injected with 200 mg of gleptoferron at 4 d of age and again with 200 mg of gleptoferron at 14 d of age. Group 3 pigs were injected with 200 mg of gleptoferron at 4 d of age and from wk 1 of age until weaning they were provided with free-choice access to peat moss (Sweet Peat; Grand Valley Fortifiers, Cambridge, Ontario) containing chelated iron [8500 mg/kg body weight (BW) of added iron]. Group 4 pigs were given 1 dose (2 mL/pig) of an oral paste containing 40 mg of ferrous fumarate (MS Ferro Paste; MS Schippers Canada, Lacombe, Alberta) at 4 d of age and from 1 wk of age until weaning were provided with iron-fortified free-choice peat moss.

The trial was conducted in 1 farrowing room containing 12 farrowing crates. Cross fostering was carried out before pigs were assigned to treatments. Two pigs in Group 1 and 1 pig in Group 4 were fostered pigs. The average number of pigs per litter for Groups 1 and 2 was 11.3. The average number of pigs per litter for Groups 3 and 4 was 12.6. Creep feed was not provided for any of the litters. The amount of peat moss given daily per litter was recorded based on the number of 250-g cups that were used.

Pigs were weighed at Day 4 and at weaning to determine average daily gain (ADG). At weaning, blood samples (3 mL) were collected via the infra-orbital sinus into tubes containing ethylenediamine tetra-acetic acid (EDTA) and submitted to the Animal Health Laboratory (AHL), University of Guelph, for complete blood (cell) count (CBC) using the ADVIA 2120/2120i hematology system (Siemens Healthcare Diagnostics, Deerfield, Illinois, USA). The blood analysis included determination of red blood cell (RBC) count, hemoglobin (Hb), hematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular hemoglobin (MCH), mean cell hemoglobin concentration (MCHC), and red blood cell distribution width proportion (RDW).

Data were entered into Microsoft Excel for PC 2007 (Microsoft, Redmond, Washington, USA), imported into Stata (Stata/SE 14.2 for Mac; StataCorp, College Station, Texas, USA), and validated. Descriptive statistics such as means, medians, standard deviations (SD), and proportions were calculated for each treatment group. Continuous variables were assessed for normality using the Shapiro-Wilk test and normality diagnostic plots. Univariable analysis was conducted on each outcome of interest (hematological parameters and growth performance) for each treatment group. One-way analysis of variance (ANOVA) was used when outcome was normally distributed and the Kruskall-Wallis test when outcome was not normally distributed. Multiple comparison tests were used to determine the significant differences among treatment groups or weight of pigs. Medians (± SD) were reported when outcome was not normally distributed. A mixed-effects multi-level linear regression method with litter (clustering) as random effects was used to determine the association of Hb with treatment.

A Chi-square test was used to determine the association of Hb status based on the 3 categories: anemic (Hb < 90 g/L), iron deficient (Hb 90 to 110 g/L), and normal (Hb > 110 g/L) with treatment and with the weaning weight categories of the pigs. Pigs were categorized as small (< 5.5 kg) (26 pigs), medium (5.5 to 7.5 kg) (67 pigs), and large (> 7.5 kg) (53 pigs) based on weaning weights. The piglet iron status was categorized based on cut-off values described by Bhattarai and Nielsen (1). The weight of peat moss consumed per litter during the nursing period was calculated.

A total of 148 pigs were included in this trial with 18, 16, 58, and 56 pigs in Groups 1, 2, 3, and 4, respectively. The average weight at Day 4 was 2.2 kg ± 0.4 kg. The average weaning weight was 6.9 kg ± 1.6 kg. One pig from Group 3 died. Age of pigs at weaning ranged from 16 to 21 d. Day 4 and weaning weights were normally distributed. There were no significant differences in any of the growth parameters among treatment groups. Hematological parameters and ADG were not normally distributed. For the mixed model, 2 extremely low Hb values (< 75 g/L) were dropped from analysis, in order to approach normality. The RDW mean proportions for large pigs at weaning was greater (18.9 ± 3.4) than for small pigs (17.5 ± 3.2) or for medium weight pigs (17.9 ± 3.1) (P = 0.04), but there were no other significant differences in the hematological parameters among pigs in these weight categories. Specifically, there were no significant differences in Hb levels among small (125.9 g/L ± 17.4 g/L), medium (128.0 g/L ± 13.6 g/L), and large (127.1 g/L ± 13.7 g/L) pigs at weaning (P = 0.8). One sample in Group 4 was clotted and so hematological results were not reported for this sample.

A total of 3 pigs were anemic, 12 pigs were iron-deficient, and 131 pigs had normal hemoglobin levels at weaning. Group 1 (the industry standard of an IM injection of 200 mg of iron at 4 d of age) had 1 (5.5%) anemic pig and 5 (27.8%) iron-deficient pigs at weaning. Group 2 pigs receiving a second iron injection all had normal Hb levels. Group 3 pigs receiving an iron injection at 4 d of age and peat moss from 7 d of age until weaning had normal Hb levels except for 1 (1.8%) iron-deficient pig. Two (3.6%) pigs in Group 4 (oral paste and then peat moss) were anemic and 6 (10.7%) pigs were iron-deficient at weaning. The weaning weights of anemic pigs (7.1 kg ± 1.9 kg), iron-deficient pigs (6.9 kg ± 1.9 kg) and normal pigs (6.9 kg ± 1.5 kg) were similar (P = 0.9).

The descriptive statistics of hematological parameters among treatment groups are included in Table 1. The concentrations of Hb and the Hct, MCV, MCH, MCHC were significantly higher for pigs in Groups 2 and 3 compared to Groups 1 and 4 (P < 0.05). For pigs in Groups 2 and 3, RDW was significantly lower compared to Groups 1 and 4 (P < 0.05).

Table 1.

The mean (± standard deviation) values of hematological parameters of pigs at weaning among 4 iron supplementation treatment groups.

Treatments*	Group 1 (n = 18)	Group 2 (n = 16)	Group 3 (n = 56)	Group 4 (n = 58)	P-value
Hemoglobin (g/L)	121.5 (± 20.2)a	131.5 (± 5.2)b	134.5 (± 10.5)b	124.5 (± 13.4)a	< 0.001
Red blood cell count (1012 cells/L)	6.35 (± 0.7)	6.4 (± 0.5)	6.4 (± 0.6)	6.4 (± 0.6)	0.7
Hematocrit ratio	0.40 (± 0.06)a	0.44 (± 0.02)b	0.44 (± 0.03)b	0.42 (± 0.04)a	< 0.001
Mean corpuscular volume (fL)	64 (± 6.3)a	68 (± 4.7)b	68 (± 3.9)b	65 (± 4.5)a	< 0.001
Mean corpuscular hemoglobin (pg)	19 (± 2.3)a	21 (± 1.8)b	21 (± 1.2)b	19 (± 1.5)a	< 0.001
Mean cell hemoglobin concentration (g/L)	298.5 (± 10.3)a	305.5 (± 6.7)b	304.5 (± 7.2)b	296.0 (± 9.2)a	< 0.001
Red blood cell distribution width proportion	19.8 (± 4.9)a	16.2 (± 0.76)b	16.0 (± 0.93)b	19.5 (± 2.9)a	< 0.001

^*Treatments

Group 1 — Injected with 200 mg of gleptoferron at 4 d of age.

Group 2 — Injected with 200 mg of gleptoferron at 4 and 14 d of age.

Group 3 — Injected with 200 mg of gleptoferron at 4 d of age and provided with iron-enriched peat moss, free-choice from 1 wk of age until weaning.

Group 4 — Given 2 mL of an oral paste containing 40 mg of ferrous fumarate at 4 d of age and provided with iron-enriched peat moss, free-choice from 1 wk of age until weaning.

^a,bValues with different superscripted letters in the same row are significantly different.

The weaning Hb levels in Groups 2 and Group 3 were significantly higher (127 and 133 g/L) than in Group 1 and Group 4 (P < 0.01) when controlling for litter. No significant differences were found between Group 1 and Group 4 (P = 0.6). A total of 45.6% of the model variation was explained at the litter level.

On average, litters provided with peat moss (n = 9) each consumed 7.2 kg of the iron-enriched product over an average of 14.5 d. On an individual basis, each pig consumed on average 568 g of peat moss during the trial.

The industry standard iron supplementation of 200 mg of iron injected intramuscularly during the first week of life was not sufficient to meet the nutritional iron needs of at least some of the suckling pigs in this study and this was in agreement with previous studies (1–3). In this study there were 18 pigs in Group 1 receiving this standard treatment, and at weaning 1 pig was classified based on Hb levels as anemic and 5 others were considered iron-deficient. This proportion of iron-deficient or anemic pigs is almost identical to that in a study involving 20 Ontario farms that reported over 30% of pigs were either iron-deficient or anemic at the time of weaning (3). As with other studies (7,8) that have used a second injection of 200 mg of iron at 14 d of age to ensure sufficient iron stores during the suckling period, the pigs in Group 2 had normal hemoglobin levels at weaning, indicating that this approach appears to be an effective method of preventing iron deficiency in pigs entering the nursery. Furthermore, the mean Hb levels and other hematological parameters associated with iron status were statistically higher for Group 2 pigs compared to Group 1. However, the second injection of iron at 14 d of age requires a significant labor commitment (8) and compliance among producers may be low.

In contrast to restraining and injecting each individual pig, iron supplementation via peat moss that is offered free-choice in weeks 2 and 3 of the suckling period appears to also be an effective means to meet the piglet’s iron requirement and may be more appealing from a labor standpoint. The mean values for hemoglobin and other hematological values indicative of iron status were similar between Groups 2 and 3. In Group 4, pigs were not injected but instead provided with an oral iron in the form of a paste. It has been reported in some studies that absorption of iron from a single oral dose during the early suckling period is not sufficient to meet the piglets’ requirements (9,10) and even with free access to peat moss fortified with iron for the second and the third week of suckling, there was evidence that some of the pigs treated with the oral paste were iron-deficient at weaning. The amount of iron in a single dose (40 mg) is relatively low compared to the injectable treatment (200 mg) but iron fumarate is readily absorbed from the gut and not dependent on administration before gut closure Although the timing of the oral iron administration is somewhat controversial, the authors of a recent review of iron administration recommended 3 d of age rather than the first 12 h of life (10). Despite the administration of the lower dosage in the oral paste, pigs in Group 4 at weaning were comparable to those in Group 1 with respect to hematological parameters. There has been concern that the very large dose of parenteral iron typically given to pigs in the first few days of life may stimulate a negative feedback through the induction of hepcidin (11). In this trial, it appeared that pigs injected with 200 mg of gleptoferron at 4 d of age were able to utilize oral iron from the peat moss product adequately, but further studies are warranted to examine if the second injection of iron (Group 2) is associated with a decrease in iron absorption after weaning.

It is expected that larger pigs require more iron because of a greater blood volume and increased hemoglobin requirements (2). However, similar to Bhattari and Nielsen (1), this study found no difference in mean Hb concentrations among small, medium, and large pigs at weaning, although large pigs had a significantly higher RDW. It must be considered that this size comparison involves pigs within different iron treatment groups. Hemoglobin concentrations are the most widely used parameter to assess iron status in piglets, but Hb alone may not be sensitive enough to detect an early change in iron status. Evaluating Hb concentrations alone may under-estimate the iron requirements of piglets (1). Additional hematological indices might serve as better early indicators of iron deficiency rather than traditionally used Hb values. For example, RDW measures variation in size of red blood cells and is considered one of the most reliable parameters indicating iron deficiency. The RDW increases during iron deficiency and it is therefore noteworthy that the large piglets herein had a higher RDW than the small and medium sized piglets, suggesting the large pigs may be beginning to develop iron deficiency.

This study suggests that a single iron treatment at 4 d of age is not sufficient to meet the needs of all piglets and additional iron is required. It appears that providing piglets daily access to iron-enriched peat moss or injecting a second 200 mg dose of iron intramuscularly are both effective in meeting the piglets’ iron requirements during the suckling period. The decision for most producers is likely related to individual preference.