pig diets with zinc oxide or BioplexTM Zinc

Supplementation of weaner pig diets with zinc oxide or BioplexTM Zinc

Post-weaning diarrhoea is a major problem of the pig industry. In some instances, infected piglets will die but in most cases there is a reduction in the efficiency of digestion and the absorption of nutrients. This causes a decrease in growth rate from which the pig may never fully recover. As a result, the time taken to reach market weight can be significantly increased. The increase in mortality rates and decrease in growth has a major influence on profitability.

Zinc oxide (ZnO) has traditionally been added to pig weaner diets to supply 100g of added Zn per tonne of feed (approximately 0.125 kg ZnO/t) for the prevention of Zn deficiency. More recently, the beneficial effects of adding high levels of ZnO to weaner diets has been reported. For example, Holm (1990) reported that in commercial trials mortality rate was reduced from 2.2 to 0.7% and growth rate increased from 281 to 327 g/day when pigs received a diet containing 3.2 kg of ZnO/t for the two weeks after weaning.

Other reports indicate a satisfactory response to the addition of 2.4 kg ZnO/t (Holm, 1988; Gadd, 1993). The use of ZnO is considered an inexpensive alternative to the use of antibiotics for the control of post-weaning scours, and one that does not require veterinary approval. As a consequence the supplementation of diets with ZnO for two to three weeks after weaning is now widely practised, although there is only limited information to support its correct use.

Although Zn toxicity is rare, it has been shown to occur when diets containing 2 kg ZnO/t were fed for six weeks (Pritchard et al., 1985). As a precaution, it is recommended that calcium (Ca) levels in the diet be increased to 1.1% to reduce the risk of Zn toxicity, as the Ca ion competes with the Zn ion for absorption sites in the small intestine (Kristianson and Wegger (1974) as referenced by Kavanagh (1992)). It is also suggested that high Zn diets should only be fed for between one and three weeks post-weaning, but there is little evidence to indicate the consequences if weaners are fed high levels of ZnO for prolonged periods of time.

The increased use of piggery waste for composting and subsequent use in the horticultural industry has identified high concentrations of Zn in faecal matter from weaner production units as a problem. This is assumed to be a direct consequence of using high concentrations of ZnO in weaner diets. Organically bound or bioplexed Zn has a higher bioavailability than inorganic Zn, resulting in maximum retention and, as a consequence, reduced levels of Zn being excreted. Therefore, the use of Bioplex Zn as a replacement for ZnO could overcome the problems currently being experienced with the use of piggery effluent provided we get a similar positive response in piglet performance.


EXPERIMENT 1. ZINC OXIDE SUPPLEMENTATION FOR WEANER PIGS

The hypothesis of this experiment was that the supplementation of weaner diets with ZnO would have a beneficial effect on the growth of piglets post-weaning, and that this may be due to a reduction in the incidence and severity of post-weaning diarrhoea. The aim was to record the performance of weaner pigs fed diets supplemented with different levels of ZnO for different periods of time in a commercial environment.


MATERIALS AND METHODS

In a 3 x 3 factorial design, ZnO-supplemented diets (1.5, 3.0 and 4.5 kg/t of standard weaner diet) were fed to pigs for either 7, 14 or 21 days post-weaning, after which time they received a control diet (0.1 kg ZnO/t). There was also an additional treatment in which pigs received the control diet for the duration of the experiment (21 days). The base diet was formulated to contain 14.5 MJ DE/kg, 0.85 g available lysine/MJ DE and 1.1% Ca.

A total of 283 pigs were weaned at 21 days of age and housed in groups of 12 to 15 in a controlled environment commercial weaner facility. Piglets had no access to creep feed prior to weaning and were fed ad libitum throughout the experiment. Jugular blood samples were drawn from six randomly selected pigs per treatment at weekly intervals, commencing on the day of weaning (i.e. 21, 28, 35 and 42 days of age). Blood samples were analysed for Zn and copper (Cu).


RESULTS

Post-weaning diarrhoea was not observed at all during this experiment, therefore the effect of ZnO supplementation on this condition could not be determined. There was a significant linear response between average daily gain (ADG) and duration of supplementation for piglets fed diets containing either 1.5 or 3.0 kg ZnO/t (Table 1). Compared to the pigs on the control treatment there was a significant increase in ADG when diets containing either 1.5 or 3.0 kg ZnO/t were fed for 21 days.

This equated to an increase in live weight after 21 days of 2.1 kg. There was no response in ADG at the higher level of supplementation; but there appeared to be a trend for growth rate to decline when the higher level of ZnO was fed for the maximum period.

Plasma Zn concentrations increased as the concentration of ZnO in the diet increased. Plasma Zn in pigs after three weeks on a diet containing 3 kg ZnO/t was three times greater than that for the control treatment (Table 2). Concentrations returned to base levels once ZnO was removed from the diet. There was a negative correlation between plasma Zn and Cu concentrations. For example, for pigs fed diets containing 3 kg ZnO/t for three weeks post-weaning, there was a 3-fold increase in plasma Zn and a 4-fold decline in plasma Cu concentrations.

Some individual pigs had Cu concentrations of 0.17 mg/L, which is approaching the level considered deficient.
Supplementing weaner diets with ZnO does have a positive effect on ADG, and this is independent of any potential effects due to a reduction in postweaning diarrhoea. However, the results from this experiment would suggest that if diets containing 4.5 kg ZnO/t are fed for more than 14 days, then there may be a decline in growth rate.


Table 1. The effect of level and duration of ZnO supplementation on the live weight and average daily gain (ADG) of pigs postweaning (21 days).





Table 2. The effect of level and duration of ZnO supplementation on plasma concentrations of zinc and copper in pigs post-weaning (21 days).





EXPERIMENT 2. BIOPLEX™ ZN vs ZN OXIDE SUPPLEMENTATION FOR WEANER PIGS

The aim of the second study was to evaluate the use of Bioplex™ Zn as an alternative to ZnO in weaner pigs on a commercial piggery in Western Australia. As well as studying the effect on performance, the other main interest was the comparative impact on concentration of Zn in faecal material.


MATERIALS AND METHODS

This experiment was conducted at Wandalup Farms, a commercial high-health status intensive piggery in Western Australia. Pigs were weaned at 21 days of age in groups of approximately 800 and housed in climate controlled weaner rooms containing 26 pens of approximately 30 piglets for five weeks. During this time, they received a first stage weaner diet for the first two weeks, followed by a second stage weaner diet for the next three weeks. All pigs were water medicated with Apralan™ for the first five days, and during the second week post-weaning received Acid-Pak™ via drinking water for five days. Pigs were accommodated on fully mesh floors, but pen divisions were open mesh and the spread of disease from one pen to another was possible.

The experiment involved four treatments, each with four pens containing 26 (Group 1) or 27 (Group 2) pigs. Therefore, there was a total of 424 pigs on the experiment (4 treatments x 4 replicates x 26 or 27 pigs/pen). The start of the experiment was staggered over two weeks with two replicates for each treatment commencing in the first week (Group 1), and the remaining two the following week (Group 2). In this way, two weaner rooms were used in order to increase the chance of the experiment occurring at a time when the likelihood of an outbreak of E. coli scours was greatest. The experiment was conducted in July to September 2001.

The treatments were:

Control: no added Zn besides that included in the mineral premix
ZnO: 3 kg ZnO/t in 1st stage, and 2 kg ZnO/t in 2nd stage
Bioplex™ 100: 100 ppm Zinc as Bioplex™ Zn
Bioplex™ 250: 250 ppm Zinc as Bioplex™ Zn

All diets contained 125 ppm Zn from ZnO and 125 ppm Cu from Cu sulfate as part of a mineral – vitamin premix. The concentration of Zn in each of the diets is presented in Table 3.

Pigs were allocated to pens, and hence treatments, on the day of weaning by visual assessment. The following day pigs were individually identified and their weights recorded. All pigs were individually weighed on day 17, which corresponded to the time when pigs changed from stage 1 to stage 2 diets, and again at the end of the experiment (Day 39).

Three faecal samples were collected from each pen on day four and again on day 38 of the experiment, dried and analysed for concentration of Zn using inductive coupled plasma atomic absorption spectrophotometer. There was insufficient faecal matter produced prior to day four to collect a sufficiently large sample.

Feed usage was recorded on a pen basis and hourly temperatures were recorded at two points in each room for the duration of the experiment.


Table 3. Concentration of Zn (ppm) in feed and faecal samples on a dry matter basis.





RESULTS

A total of 424 pigs began the experiment over a two week period with equal numbers allocated to each treatment. The starting weight of pigs on the Bioplex™ 100 treatment was significantly heavier than those on the other three treatments due to the way that they were initially allocated to treatment by visual assessment (Table 4). This was taken into account by using starting weight as a co-variate in all subsequent statistical analyses. Pigs on the Bioplex™ 100 treatment had a significantly lower ADG than those on the other three treatments for the first phase of the experiment, but during the second phase growth rate of pigs on the control treatment was the lowest. Over the whole period of the experiment, pigs fed the control diet had the lowest ADG and weighed approximately 1 kg less at the end than those fed the diet containing ZnO.

A superior ADG throughout the experiment meant that pigs fed the Bioplex™ 250 diet weighed approximately 2.3 kg more than the control pigs at the end of the 39-day period. There was also a significant difference between the final weights of pigs on the two Bioplex™ treatments, suggesting that perhaps Bioplex™ Zn at 100 ppm did not meet the requirements of pigs of this stage of development.

Males were significantly heavier than females at weaning (6.81 vs 6.34 kg, respectively). However, there was no significant difference between the growth rate of males or females during any phase of the experiment, with growth rates of 400 and 394 g/day for males and females, respectively, over the 39-day period. There were no interactions between sex and treatment, with males and females fed the diet containing Bioplex™ 250 both being the heaviest at the end of the experiment.

Feed consumption was measured on a pen basis. Data according to sex and shed were pooled to give a total of eight measurements of voluntary feed intake (VFI) and feed conversion ratio (FCR) per treatment (Table 5). Due to the relatively low number of measurements per treatment, some caution should be taken in interpretation of these results. There was no significant difference in VFI among treatments. However, pigs fed the diet containing Bioplex™ 100 tended to consume less feed during the first phase of the experiment, but during the second phase pigs fed the diets containing ZnO that had the lowest VFI. Over the whole experiment, pigs fed the control diet had the poorest FCR, although this was not statistically significant.

Average temperatures for Group 1 and 2 were 23.3 and 21.5°C, respectively, which was lower than recommended for this class of pig. While temperatures immediately post-weaning were generally above 24°C, the mean temperature over the two points in each room was frequently lower.

A sudden decrease in temperature in the shed housing Group 2 about two weeks from the start of the experiment due to an equipment malfunction coincided with an outbreak of E. coli scours in that shed over the following two days. However, this was controlled by water medication and was not confined to any particular treatment. This was the only outbreak of post-weaning diarrhoea for the whole experiment.

Mortality rates for pigs over the whole experiment on the Control, ZnO, Bioplex™ 100 and Bioplex™ 250 treatments were 1.9, 0.9, 1.9 and 2.9%, respectively. Losses were not confined to any particular pen or shed.

The Zn concentration in diets containing ZnO was, as expected, higher than for either the control or diets containing Bioplex™ Zn (Table 3). All diets contained some Zn in the mineral vitamin premix. Zinc concentration in faecal material at the beginning of the experiment tended to be higher for the Bioplex™ Zn treatments than for either the Control or ZnO treatments.

However, it is not known if the Zn levels in faecal material at this early stage are a true reflection of intake, since feed intake during the period immediately following weaning would be relatively low and variable. The level of Zn measured in faecal material at this time could be a carry-over from what was consumed during lactation (creep feed and sow’s milk), rather than a reflection of consumption. The digestive system of the piglet immediately post-weaning would also be undergoing major changes, and this may be reflected in relatively high concentrations of Zn in faecal material. A sample of faecal material taken ten days postweaning may have given a better indication of normal faecal Zn concentrations post-weaning than the one that was taken in this experiment.

The concentration of Zn in faecal material at the end of the experiment was significantly greater in the pigs fed the ZnO diets compared to any of the other treatments. Compared to those pigs fed the Bioplex™ 250 diet, those consuming the ZnO diet had faecal Zn concentrations nearly 5-fold greater. There was no significant difference in Zn concentrations between pigs fed the control diet and those fed either of the Bioplex™ Zn diets.


Table 4. Live weight and average daily gain (ADG) of weaner pigs fed diets containing different sources of supplemental zinc.





Table 5. Voluntary feed intake (VFI) and feed conversion ratio (FCR) of weaner pigs fed diets containing different sources of supplemental zinc.





GENERAL DISCUSSION

The beneficial effects of feeding weaner pigs Zn has been demonstrated in two experiments, both conducted with pigs reared under commercial conditions. In the first experiment, the efficacy of feeding various levels of ZnO for between one and three weeks showed that while there was a positive response in growth, feeding high levels of ZnO for an extended period of time could have detrimental effects on piglet performance.

The feeding of ZnO has been reported by producers to result in high concentrations of Zn in effluent, and for environmental reasons this is not sustainable. Therefore, the option of using Bioplex™ Zn as an alternative to ZnO was examined. Pigs receiving the diet containing 250 ppm Bioplex™ Zn had a superior growth rate over both phases of the experiment, and consequently were approximately 11% heavier than those fed the diet containing no supplemental Zn.

It is difficult to explain why pigs fed diets containing Bioplex™ 100 had the lowest ADG during the first phase of the experiment, but then recovered to have a similar ADG to that of the Bioplex™ 250 treatment in the second half of the experiment. If the concentration of Zn in the Bioplex™ 100 was insufficient to give any growth promotion benefits in the period immediately postweaning, then no difference between ADG for the control and Bioplex™ 100 would be expected, but this was not the case.

On the basis of this performance data, the addition of 250 ppm of Zn from Bioplex™ Zn to the diet of weaner pigs has advantages over the current recommendation of adding high levels of ZnO. This advantage in live weight at eight weeks of age would be expected to have longer-term benefits. Using the AUSPIG simulation model (Black et al, 1986), it was predicted that increasing the live weight of pigs at eight weeks of age from 20 to 22 kg reduced the age at sale, assuming that pigs are sold at the same target live weight of 110 kg, by four days and increased profitability by Aus$1.40 per pig.

Assuming the price of ZnO was Aus$3.200/T, and that for Bioplex™ Zn was Aus$12.200/T, then the extra cost per pig of adding the Bioplex™ 250 compared to ZnO, based on the amount of diet consumed in this experiment in the five weeks postweaning, was Aus$0.26 per pig. Given the predicted reduction in cost of production during the period through to slaughter, addition of Bioplex™ Zn to the diet of pigs post-weaning at 250 ppm is a very cost effective strategy. This does not take into account the cost benefit of an almost 5-fold reduction in Zn levels in faecal material.


REFERENCES

Black, J.L., R.G.Campbell, I.H. Williams, K.J. James and G.T. Davies. 1986. Simulation of energy and amino acid utilisation in the pig. Research and Development in Agriculture. 3:121- 145.

Gadd, J. 1993. Zinc oxide comes of age. Pork Journal, April 1993, 18-19.

Holm, A. 1988. Danish Vet. Journal 71:1-11.

Holm, A. 1990. E. coli associated diarrhoea in weaner pigs: zinc oxide added to the feed as a preventative measure? Proceedings IPVS Congress. p. 154.

Kavanagh, N.T. 1992. The effect of feed supplemented with zinc oxide on the performance of recently weaned pigs. Proceedings IPVS Congress. p. 616.

Kristianson, P.H. and I. Wegger. 1974. Annual Report. Inst. for Ster. Res. Pp. 33-47.

Pritchard, G.C., G. Lewis, G.A.H. Wells and A. Stopforth. 1985. Zinc toxicity, copper deficiency and anaemia in swill-fed pigs. Vet Rec. 117(21):545-548.


ACKNOWLEDGEMENTS

The support provided by staff from Wandalup Farms, the Medina Research Centre and the WA Department of Agriculture is acknowledged. The authors would in particular like to show their appreciation for the technical assistance provided by Darryl D’Souza, Jan Hooper, Stacey McCullough, Roland Nicholls, Vic Raynor and Megan Trezona.

Authors: B.P. MULLAN¹, R.H. WILSON², D. HARRIS³, J.G. ALLEN¹ and A. NAYLOR^4
1 Department of Agriculture, South Perth, Western Australia, Australia,
² Wandalup Farms, Mandurah, Western Australia,
³ Chemistry Centre, East Perth, Western Australia,
⁴ Alltech Australia, Dandenong South, Victoria, Australia