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| Bio-Mos: Healthier mares breed healthier foals © HYGAIN Feeds 2008 - Download complete file in pdf here |
The immune status in breeding mares is important to the successful production of healthy foals which have strong resistance to infection and disease. Horses are unable to transfer immune protection via the placenta to their foetus, unlike some other species. As a result, foals are born with no specific immune defences. They are entirely reliant on obtaining antibodies (immunoglobulin (Ig) types A, G and M) present in the colostrum or 'first milk' that is produced by the mare within the 24 hours following parturition. These Igs convey a degree of undifferentiated 'innate' immunity. The ability of the foal to absorb and utilise colostrum Igs is limited to the first 18 hours following birth, when intracellular gaps in the gut wall allow the uptake of these proteins intact, so they can be assimilated into their immune system as the primary, undifferentiated recognition system for dealing with invading pathogens. Prior to giving birth, it is standard practice that the mare is kept at the place where she will be foaled down for more than 2 weeks. This allows time for her to build up suitable antibodies to any pathogens in her immediate environment, ensuring the Igs expressed in colostrum are optimised to give the foal maximum innate protection. Supply of adequate levels of good quality colostrum is essential if offspring are to survive their first few weeks of life before their own acquired immune system develops to a sufficient level to provide them with protection against those pathogens present in their immediate environment. Foals that do not receive adequate amounts for whatever reason normally succumb to various ailments, and their chances of serious illness or mortality are far higher. Colostrum and milk quality Composition and consistency of colostrum can be a major problem, as it varies widely between individual animals, both in Ig content and volume. A lactation study using 29 mares (Csapo-Kiss et al., 1995) showed that the volume of milk a mare produces on a daily basis can vary between 300-800 cm3. There are also considerable differences in the protein fraction related to Ig levels between individual animals. It is known that nutrition, exposure to disease, age, season, breed and body condition are all factors that contribute to colostrum quality and volume (Quigley et al., 2005; Midgal, 1991). However, average production tends to be similar for all horses, although milk produced per 100 kg live-weight of the mare is proportionally higher in smaller mares (Doreau & Matruzzi, 2006). Table
1. Composition of mare's milk relative to humans and cows (Davies et al., 1093) Colostrum is more nutrient dense than the milk subsequently produced in mares. Table 2 shows the content of colostrum versus later milk (taken from Frape, 1998). Table
2. Changes in milk characteristics from foaling Igs, present within the protein fraction, facilitate the initializing and mobilization of immune responses necessary for inactivating the pathogen and dealing with any consequential disease symptoms. This is why efficient Ig absorption across the gut plays a key role in securing adequate immune protection in new-born mammals. For insurance purposes and to confirm adequate colostrum intake, the IgG status of foals can be assessed before they are 4 days old. Blood levels should exceed 800 mg/dl for adequate protection to be conferred. If sufficient colostrum and adequate amounts of maternal Ig is consumed within the receptive time, then innate protection will normally last for the two weeks, declining with time. Once innate immunity has reduced to a sub-optimal level, the animals own acquired system should be sufficiently developed to fight disease. Interaction between gut active oligosaccharides and immunity It
is now known that specialist oligosaccharides (mannan-oligosaccharides or MOS)
can influence the expression of certain immune parameters, including Ig. Trials
in calves, piglets and avian species have shown that feeding MOS can increase
the amount of Ig secreted in colostrum, as well as improve the uptake and expression
within recipients. In-depth research conducted at the Rowett Institute, in Scotland
(Kelly, 2004) has determined that such compounds are important in the signalling
between the gut and the immune system, ensuring more rapid response to invasive
threats, including vaccinations. Feeding trials run in the USA with mares (Ott, 2005) have shown that dams receiving 10 g per head per day of MOS in the form of commercial Bio-Mos™ (Alltech Inc, USA) from 56 days pre-foaling had higher levels of all three Ig isotypes (A, G and M) in their blood serum (Table 3). Table
3. Effect of feeding MOS on mare serum Ig levels (Ott, 2005) Mares fed MOS has significantly higher levels (P<0.05) of IgA in blood serum throughout the trial period, with those fed MOS having 55% more IgA than the control group. Although variability in colostrum parameters for the other Ig isotypes meant that no significant differences between the control and the MOS could be discerned, consistently large numeric improvements in Ig levels were observed in serum from mares fed MOS. Comparing the levels of the three types of Ig measured in mare serum during the whole trial period, IgG was increased by 19% and IgM by 23% in animals supplemented with MOS. Further analysis of the milk produced by these mares, at the same time points after parturition, showed consistently higher levels if all three Ig isotypes, A, G and M, for mares fed MOS relative to those in the control group (Table 4) The significantly higher colostrum Ig levels were carried forward, resulting in numeric increases in milk Ig content. Samples of foal blood serum, taken 8 hours after birth, showed large numeric increases in all three Ig levels, resulting in a 66% increase in circulating Ig. Table
4. Effect of feeding MOS on mare colostrum Ig levels and foal serum levels at
1 day old (Ott, 2005) The concurrent increase in foal serum Ig levels suggests that improvements in colostrum immuno-protein quality were directly passed onto the progeny via suckling. In practical terms, what do these changes mean for the foal's health? Further work on the same foals, which were monitored to 56 days of age for diarrhoea, showed major differences between the dietary treatments (P=0.021). Although all the foals were treated and recovered from the scours they showed, any diarrhoea in young animals causes retardation in growth and gastric damage. Conclusions Appropriate levels of immunity, manifested as Igs, in the dam is essential in the formation of colostrum containing suitable levels to protect her foal. From the research conducted in the USA, benefits in supplementing dams in terms of their own and their progeny's immune status were evident. These benefits may be observed as reduced diarrhoea and disease or improved growth and development. Trials horses have demonstrated that MOS, fed as the commercial product Bio-Mos™, can affect Ig levels in dams, their colostrum and progeny. References:
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