10 Aug 2015
Maedée Burge Rogers
Job Title
Figure 1. Oral fluid therapies are quick and easy to administer on farm. Farmers can be trained to stomach tube and drench cows.
Oral fluid therapy in cattle has been a vital tool in the management of dehydration for many years. However, there has been an expanding repertoire of commercially available oral fluid therapy options aimed not just at the dehydrated animal, but at cases that may require more tailored treatment.
These products have the potential to broaden the use of oral fluid therapy to be used not only as a treatment, but also as an adjunct to other therapies and as pre-emptive measures to reduce the risk of diseases such as ketosis, hypocalcaemia and hypomagnesaemia. The common ingredients found in these oral drenches, the science behind them and their rationale for their use are discussed.
The approach to fluid therapy in cattle is based around two main techniques – oral fluid therapy, usually administered via stomach pumps into the rumen, and intravenous fluid therapy.
While oral fluid therapy is relatively quick and easy to perform, sometimes the severity of dehydration or other complicating factors warrant more aggressive treatment with intravenous fluids and electrolytes. The use of both techniques is well founded and routinely used in the treatment of clinical dehydration, but there is more scope for fluid therapy to be used beyond purely dehydrated animals to aid treatment or reduce the risk of sequelae developing in disease.
A number of commercial oral fluid therapy options have become available that are targeted not just at animals in need of rehydration, but at groups that may require more specialised support. These products contain extra ingredients, in addition to isotonic electrolytes, to complement their rehydration abilities and may provide animals with additional support, tailored to their needs.
These products include “rumen tonics”, formulations aimed at anorectic cattle, and those aimed at freshly calved cows. They are generally presented as powders, which are mixed into a defined volume of warm water (usually around 20L) and administered via stomach pump into the rumen.
These products provide water and electrolytes for rehydration in mild cases of dehydration, but the addition of other ingredients, such as rumen buffers, yeast and propionate, can stabilise, treat or help prevent other problems. Understanding the action of these extra ingredients can aid more informed decision making, but also broaden the use of such adjunctive fluid therapy options. Incorporation of these products into the general care and pre-emptive disease management on farm can reduce the number of clinical problems.
These therapies are relatively cheap and farmers can easily be taught how to administer them (Figure 1). The therapies can even be included as part of set protocols – for example, on a farm where hypocalcaemia is a problem, every freshly calved cow could receive a dose of a fresh cow product to reduce the risk of succumbing to milk fever while other factors on the farm are being tweaked to reduce the incidence.
Fluid therapies can contain a plethora of ingredients, and the reason for inclusion of some ingredients or the differences between two products is not always very clear. Table 1 lists the contents of some of the common commercially available formulations. In-depth analysis of all these ingredients is beyond the scope of this article, but a selection of the common ingredients (highlighted in the table) and their action, rationale and uses are described.
Most of the commercially available formulations contain calcium. Those aimed at freshly calved cows or anorectic animals generally contain higher concentrations of calcium to address possible hypocalcaemia. Freshly calved animals, especially dairy cows, are at risk of developing hypocalcaemia due to the massive increase in calcium demand from milk production.
A US survey suggested around half of dairy cows in their third to sixth lactations develop subclinical hypocalcaemia (plasma calcium levels between 1.38 and 2mmol/L; Reinhardt et al, 2011). Clinical hypocalcaemia has its obvious problems, with cows succumbing to milk fever, but hypocalcaemia has also been linked to increased risk of retained metal membranes and metritis, ketosis, reduced feed intake, displaced abomasums and possibly mastitis (Goff, 2014). Anorectic cattle on the other hand will have reduced intakes of calcium and, therefore, have less calcium available for absorption, which may lead to the development of a secondary hypocalcaemia.
Fresh cow and off-feed products contain relatively large quantities of calcium to address this increased predisposition (Selekt Fresh Cow 500 and Selekt Off Feed sachets contain 500g calcium propionate, equivalent to 108g calcium). The recommended oral dose of calcium is 50g to 90g, given at calving and then repeated 24 hours later (Goff et al, 2002; Goff, 2014).
One sachet will provide cows with the required dose, but, as they are on the high end of this dose, it is not recommended to give more than one sachet within 12 hours to avoid toxic doses of calcium orally. It has been reported a single oral dose of 250g may be enough to kill some cows (Goff et al, 2002). Oral fluid therapy with such formulations can act as a useful tool in the management of hypocalcaemia on farm. Routine drenching of freshly calved cows with a fresh cow formulation will help rehydration, while also providing a substantial source of calcium to reduce the risk of clinical milk fever.
The calcium salt used in the majority of formulations is calcium propionate. This is absorbed more slowly within the gastrointestinal tract than other calcium salts (such as calcium chloride), but is less caustic and also has less of an effect on blood pH than other salts. Calcium has been shown to be absorbed within the rumen (Schroder, 2006), in addition to the intestine (Goff, 2014). The propionate salt of calcium also has the theoretical benefit of providing a glucogenic precursor for the ruminal flora.
Freshly calved cows are at high risk of ketosis and, while the provision of such precursors in theory should reduce the rate of ketosis, studies have actually found one-off administrations of calcium propionate do not reduce the incidence of ketosis, and had no significant effect on non-esterified fatty acids or beta-hydroxybutyrate concentrations in the blood (Benzaquen et al, 2015; Goff et al, 1996; Melendez et al, 2003).
Magnesium also plays an important part in the milk fever complex. Low magnesium can cause clinical signs in itself, such as recumbency, neurological signs and tetany, but hypomagnesaemia is also a major risk factor for the development of hypocalcaemia (Goff, 2014). Magnesium is mainly absorbed in the rumen in adult cattle.
This absorption can be reduced under high pH conditions (above pH6.5) or in the presence of low sodium or high potassium (Ram, 1998; Goff, 2014). Freshly calved cows show a reduction in plasma magnesium within the first few days after parturition. It has also been shown animals treated with oral calcium supplements may show a greater decline in serum magnesium (Kronqvist et al, 2011). Therefore, the addition of magnesium to fluids given to freshly calved cows is a valid choice.
Reduced feed intakes will reduce the amount of magnesium available to the animal (Goff, 2014) and so anorectic animals are at risk of developing hypomagnesaemia in a similar manner to their development of hypocalcaemia, as previously described.
The majority of adult cow rehydration powders contain the magnesium salt, magnesium sulphate heptahydrate. This salt is highly soluble (necessary for use in fluid therapy) and therefore available for absorption within the rumen. It is, however, a rather large molecule and will only contain approximately 9% magnesium (Goff, 2014) and so relatively large amounts of this molecule need to be added to provide a significant source of magnesium.
Cows that have a reduced dry matter intake will show a reduction in serum potassium levels. Renal excretion of potassium is very efficient, but may not slow down rapidly enough in response to a sudden drop in intakes, so excessive excretion may exacerbate the problem of reduced intakes (Sattler et al, 2014). In dehydrated adult cattle, an alkalosis often develops (Pederson, 2013), causing a shift of potassium from the extracellular fluid to intracellular fluid, and thus inducing a circulating hypokalaemia. Potassium concentration in the rumen is directly linked to serum potassium concentrations (Idink et al, 2015).
Oral potassium is the preferred treatment option for hypokalaemia. The addition of potassium to rumen drenches therefore provide a source to replenish this deficiency. The use of potassium chloride will also provide chloride ions, a strong anion, which may help to reduce hypochloraemic alkalosis.
The fact anorectic animals and dehydrated animals are at higher risk of developing hypokalaemia provides the rationale for the addition of extra potassium in off-feed and rehydration products. Treatment of clinical hypokalaemia may require up to 60g to 100g/100kg bodyweight per day of potassium chloride, the fluid therapy formulations generally contain a high enough concentration to provide this (Selekt Off Feed provides 80g, Agger’s Restore contains 100g).
Sodium bicarbonate and disodium phosphate are added to some formulations as rumen buffers (Pro-Rumen contains both compounds). These compounds act to stabilise the pH and raise it in the case of ruminal acidosis. Animals at risk of acidosis include high-yielding cattle receiving a large proportion of their diet as concentrates, and transitioning cows increasing their concentrate intake.
Cows at risk of overt or subacute ruminal acidosis may benefit from the addition of such buffers that will stabilise rumen pH. Studies have shown the addition of rumen buffers may increase milk production and improve feed conversion efficiency (Cruywagen et al, 2015; Marden et al, 2008; dePeters et al, 1984), however the reported effectiveness of sodium bicarbonate varies within the literature dependent on the type of diet the animals are fed (dePeters et al, 1984). Sodium phosphate salts have also been shown to be an effective treatment for hypophosphataemia (often seen concurrently with hypocalcaemia; Braun, 2007; Grunberg, 2013; Idink et al, 2015). Calcium and phosphate disorders are closely interlinked, but increasing phosphate concentration above 80g per day may inhibit calcium homeostasis, predisposing to hypocalcaemia.
Yeast is added to a number of products, especially those aimed at anorectic or freshly calved cows. It is thought to act as both a prebiotic and a probiotic within the rumen (Uyeno, 2015). The most commonly used yeast is Saccharomyces cerevisiae. Dried live yeast has been shown to be the most effective form (Uyeno, 2015). The idea behind the use of yeast is to buffer the pH of the rumen and promote the rumen’s fibre-digesting capabilities by supporting the ruminal microbiota. Although its full mechanism of action is still not fully understood, it is thought to do this in a number of ways:
Yeast-containing products could therefore be useful in the management of cases where the rumen may have undergone a level of upset, such as pH disturbance, following antibiotic therapy that may have altered the rumen flora or following gastrointestinal diseases such as displaced abomasum or ruminal stasis.
The improvement in fibre digestion and feed conversion may also be of use in preventing or helping to treat animals with ketosis (for example, anorectic animals or those in early lactation). As discussed previously, dried live yeast is the most effective form, but it is worth noting some formulations list yeast extract as an ingredient, not live yeast, so these may not provide all the benefits of one that contains a live dried yeast.
Both Selekt and Agger’s Off Feed formulations list gentian root as one of the ingredients. This comes from the plant Gentiana lutea, used as a herbal remedy in humans for digestive disorders and a derivative is used in the medical treatment of sinusitis. This is added to Off Feed formulations as an appetite stimulant, to increase the dry matter intake of anorectic cattle; however, the author could not find reference to its use in ruminants in the scientific literature.
Understanding the rationale behind the ingredients in some of these oral rehydration therapies, and the science that backs them up (or not, as the case may also be), may help to improve our decision making and broaden our use of these therapies. Fluid therapy has moved on from just treatment of severely dehydrated animals and these new oral therapies provide us with a broader range of options, allowing fluid therapy to be used as an adjunct to other therapies and as pre-emptive measures to help reduce the risks of secondary problems developing.
