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New doubts over iron supplies

New doubts over iron supplies

by Peter Best
 
Bigger litters and increased growth performance are challenging decades-old standards for the amount of iron received and required by both sows and piglets
Anyone who assumes that the story of iron for baby pigs is totally understood may need to think again. Some top specialists in the field have told a meeting held in the USA that the changing scene for such factors as sow productivity and weaning age is conspiring to make our iron-supply ideas much less clear-cut than they were 10 years ago.
"Iron is such an important component of growth and health in the pig, I think it does need a review," Dr Don Mahan of Ohio State University told Pig International when we interviewed him at the 2008 Alltech international symposium on animal health and nutrition. "Today's sows stay longer in the herd and they are depleting their body stores of iron with time. Secondly, litters are bigger; sows developing 12 pigs will transfer more iron than for 10 pigs. The third factor is that milk production today is much greater and this also has consequences for the amount of iron transferred."
Remember that the sow's iron status regulates the piglet's at birth and up to weaning, he urged. The quantity of the mineral present in the sow determines how much the baby pig will have in its own body when it is born and how much it will receive in milk. These provide the reservoir to support functions including oxygen transport that allow the animal to achieve good growth.
 
Anaemic sows
The levels and timing of iron supplementation for fast-growing pigs have become a research topic once again in the USA, not least due to the evolution in management practices that has seen weaning trend to a later age and sows being retained in herds for more parities. These changes affect the iron status of the sow and pig, so they may create opportunities for herd managers to go for faster growth by adjusting the delivery of extra iron — most often, given through intramuscular injection.
But it seems we should also be keeping an eye on the sows. Don Mahan noted how the better facilities and management and nutrition of US herds in 2008 are setting a target of retaining sows for up to 6 parities, whereas replacement after a second parity was common only a few years ago. Add to this the productivity increase from farrowing bigger litters and producing more milk to rear them, to see why concerns have surfaced over the possibility that more sows will suffer from anaemia.
Dr Mahan talks of potential borderline anaemic conditions in adult sows and reports a rising number of observations by veterinarians advising herds. The telltale sign is a pale discolouration of the ears, he reports. The sow can seem lethargic and not interested in eating. Her milk output may drop and she diverts energy to keeping healthy. The herd may end up losing sows quicker as a result.
Higher-milking sows producing faster-growing pigs is a formula anyway for increased iron requirements for the production of tissue and of haemoglobin to transport oxygen around the body. Today's data say we need more iron in our pigs than we are providing to them, Dr Mahan continued. An Ohio study of pigs which had been injected with a 200mg dose showed that their haemoglobin values generally went down to borderline anaemic as the weaning weight increased, indicating that many of them did not have enough iron in them when weaned despite receiving a typical dosage by injection soon after birth.
The situation may become worse as more herds decide to wean later, with weaning between 24-28 days already common on US units. Revised strategies may be necessary on the iron given to the sow as well as the supplementation of her progeny.
 
Testing the transfer
We should begin by referring to the sow and her ability to transfer iron to the litter. More than 10 years ago, said Dr Mahan, data in Denmark showed a reduction in the iron stores of sows with increasing age. In other words, their transfer capabilities diminished with each successive parity. It was confirmed by a finding of lower haemoglobin concentrations in later-parity newborn pigs.
Unpublished Ohio work has added evidence on the accumulation of iron and other trace minerals in sows during gestation. A steady rise in the sow's iron status was detected from Day 45 to parturition, building to a peak value at Day 100 or about 2 weeks before farrowing. Comparing this peak and readings taken 14 days later revealed that 50% of the total iron to be found in a newborn pig had been transferred from the sow in those last 2 weeks of pregnancy.
More revelations have come from an Ohio test of feeding 120 parts per million of added iron (with other trace minerals) to sows in their second parity. Separate iron sources were tested to compare organic with inorganic supplements. Piglets had been left uninjected so all the mineral supply to them came from their mothers. Haemoglobin counts suggested that the transfer to the newborns had been inadequate in the case of the inorganic-group sows. Injecting the pigs afterwards (again a 200mg dose) brought an immediate response in the progeny of both groups.
Clearly, Dr Mahan commented, we do need to be iron-injecting piglets even when the sow has received a supplement of organic iron in her feed. But the groups had differed for litter size. In one the average was 12.5 pigs/sow while the other averaged only 10. So sows on organic iron were carrying 2.5 more pigs to term and therefore had to transfer more iron — implying that there may have been no increase in the quantity transferred per pig even if their iron status was better as farrowing approached.
 
Needs after weaning
Strong support for re-visiting the iron story was offered to the Alltech symposium by Dr Gretchen Myers Hill, who is professor of animal science and director of the swine nutrition laboratory at Michigan State University, USA. Most work on the trace mineral requirements of pigs dates back to the 1950's and 1960's, she warned. We know without doubt that the muscle accretion patterns were different then. Over the half-century since mineral needs were measured, the daily weight gain and feed conversion measurements of growth performance of pigs on commercial units have moved significantly to greater efficiency. Meanwhile we have also seen a rise in the weaning age on US units from 14-18 days to 21 days or even a European-style 28 days.
Doubts over the consequences for current iron requirements relate to the post-weaning phase of the young pig's life as well as to the neonatal period. According to Dr Myers Hill's presentation, the iron present in nursery diets may be inadequate. Haemoglobin concentration is a poor indicator of iron status because the body can maintain it by drawing on reserves stored in the spleen and liver stores until an extreme deficiency of the mineral has occurred, she commented. Even if we did use haemoglobin values to indicate status, however, there are good reasons for believing that they are not maintained in today's pigs during the nursery phase by a supplementation level of 80-100ppm of iron as suggested by NRC (once more based on 1960's research).
Michigan studies of hepatic stores of iron in piglets at weaning and on leaving the nursery demonstrate a decrease in the amount stored from the start to the end of this period, even when the pigs had been supplemented with up to 150ppm of ferrous sulphate in their diet. On current indications the requirement for supplementation seems to be over 100ppm, Dr Myers Hill remarked.
Dr Mahan had observed to us that pigs weaned with marginal iron stores may well be set up for poor performance in the critical post-weaning stage, even though there is enough iron in the nursery diet. Therefore it is important they go into the nursery with a good iron status and then are fed an adequate diet in the weaning phase.
A problem in practice can be with measurements. Some of a commercial feed's iron content could include a contribution from the dicalcium phosphate, corn and soybean meal present, but this is of unknown bioavailability. Probably justifiably, Dr Mahan commented, it tends to be ignored in practice. When you analyse a diet with no iron it will automatically show 300 parts per million and that theoretically should meet the animal's requirement but in practice it does not. Add 200mg on top of that and you are probably getting close to the level that the pig actually needs.  PIGI
 
Click here to hear Dr Don Mahan interviewed by Peter Best, Editor of Pig International 

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本站最後更新:2017-12-11 週一 ,16:47



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