Ration evaluation and formulation

23 Ration evaluation and formulation

Feeding horses is often described as being a combination of art and science and the area of ration evaluation is probably the best illustration of this. Ration evaluation can provide a useful indicator of the appropriateness of a horse or ponies’ diet, in terms of energy, macro- and micronutrient intake, as well as energy source. However, there are limitations to the accuracy of the information obtained from a ration evaluation and interpretation of the data should reflect this.

Practical ration evaluation invariably involves assessment of the suitability of a horse’s current diet relative to its individual circumstances, with suggested changes being made where warranted. In most cases, a nutritionist will be presented with a dietary history of some kind, although there are notable exceptions to this where no dietary history is available, for example in acute welfare cases. Dietary history may also be scant where a radical change in circumstances, such as removal of a horse from pasture, or a recent purchase has occurred. Where available, a horse’s current ration, as well as previous dietary history, is of immense value to a presiding nutritionist and will usually be the starting point for most evaluations.

Information needed for ration evaluation

There is a range of information that must be gathered in order to practically evaluate a current ration or indeed formulate a new ration, all of which will be discussed in this chapter including the factors mentioned in Box 23.1.

Integrity of the information

The integrity of the information regarding the current diet may be greater when it is gathered by the nutritionist themselves, or by another appropriate person. Being physically present during at least one feeding period is desirable and is likely to increase the accuracy of the dietary information obtained. The client or feeding manager can be questioned regarding the feeds used and their feeding habits and management. A nutritionist should also weigh all of the allocated quantities of feeds, supplements and forages. This presents a good opportunity to sample the components of the diet for any required laboratory analysis.

Information regarding a horse’s current ration, as well as any other dietary history, can be unreliable and lack accuracy when provided by the owner, trainer or other third party. This can be due to:

Predicted versus actual analysis

The reliance on predicted or published nutrient content of feeds and forages as opposed to actual laboratory analysis may also affect the accuracy of the ration evaluation. With respect to end users, the use of predicted analysis is usually driven by economical constraints. The number of establishments that are prepared to undertake full nutritional laboratory analysis of feedstuffs, forages and grazing is relatively low.

Nutrient analysis of forage, for example alfalfa, can vary considerably depending on factors such as stage of growth at harvest, type of grass, fertility of the soil as well as the soil type and underlying geology of the land (Van Soest et al 1978). All of these factors will also affect the nutrient content of pasture. Whilst historical pasture analysis is sometimes available during ration evaluation, it is usually restricted to large professional establishments. It is therefore more common for a nutritionist to draw on published nutrient values for pasture and forage (NRC 2007), which introduces inherent inaccuracies. Localized regions of pasture inadequacy in trace minerals such as copper, for example in parts of Ireland, or extreme reductions in pasture quality (e.g., in UK moorland) may not be captured.

Proprietary feed and forage companies can usually provide analytical information regarding their feed or forage products, which is likely to be based at least in part on actual laboratory analysis, especially where the legally required declared analysis (e.g., protein, oil, ash and crude fiber) is concerned. Feed companies are also able to provide an accurate prediction of micronutrient content of proprietary feeds, where a vitamin and mineral premix has been used. It is, however, still relatively common for feed manufacturers to use published values for the prediction of other nutrients of importance such as starch, sugars, amino acids, etc.

Laboratory analysis of concentrate feed or forage can be carried out simply to confirm adherence to the declared analysis, or can offer more comprehensive information beyond this. Samples must be as representative of the feed or forage as possible, in order to avoid large discrepancies occurring between predicted and actual analysis due to sampling error.

Assessment of current ration

Energy content of feeds and forages

The energy content of feeds and forages must be obtained for accurate ration analysis, either through the use of predicted values or calculation from proximate analysis using published equations. The energy value of feeds can also be derived in vivo from feeding trials, although this would usually be beyond the scope of practical ration evaluation. Energy, which is usually described in terms of either joules (e.g. in Europe) or calories (e.g. in USA [1 kcal = 4.184 kJ], is most often expressed as digestible energy (DE), although in Europe net energy (NE) or derivatives thereof as discussed in Chapter 4 are routinely used).

Feeds can also be described using the horse feed unit (HFU) or in French, l’unite fouragire cheval (UFC). The UFC corresponds to the NE value of 1 kg of standard barley (87% DM) in a horse at maintenance (2250 kcal). The UFC value of other feeds can be calculated by dividing their relative NE content in kcal by that of barley or from prediction from chemical analysis.

There are a number of published equations that can be used to calculate the DE or UFC content of feedstuffs from their chemical composition which have been previously reviewed (Harris 1999) and are summarized below. The energy value assigned to a feed, whether estimated or calculated, must always be in the same format as the target energy requirements, for example DE for NRC requirements (NRC 2007), UFC for INRA requirements. See Box 23.2.

Forage and feed sampling

Forage sampling

Forage samples should ideally be taken using a hay bore, which consists of a long metal cylinder that can be inserted to a given depth into a bale of hay, haylage or straw usually driven by an electric drill (Fig. 23.1). In this manner, several samples can be taken from many bales to build up a representative mixed sample of a particular batch of forage. Where possible the sub-samples of hay should be mixed but there is also a reliance on the laboratory to resample for analysis in an appropriate way. Bales of haylage should be carefully re-sealed following sampling to avoid aerobic spoilage. Where a hay bore is not available, simple grab samples can be used to give an estimate of forage analysis, but again multiple samples should be taken from multiple bales from varying regions and depths within the bale where possible as this will require bales to be opened. In instances where forage is suspected of contributing to health issues such as colic or sporadic respiratory disease it may be necessary to establish the variability in nutritional value or quality of the forage. In this instance many single bales may need to be analyzed, with composite samples being taken from each individual bale.

For haylage, samples should be placed into sealed bags, expelling the air as far as possible prior to sealing. This is particularly important where fermentation characteristics or microbiological analysis of haylage is required. Due to the variable instability of haylage, once removed from their anaerobic environment (Cecilia 2009), samples of haylage should always be shipped to the laboratory immediately. Ideally, these should be sent on a next day delivery service, avoiding the possibility of haylage samples remaining in the post or being unprocessed over a weekend.

Complementary feed assessment and sampling

Complementary feed refers to any feed that is fed alongside forage or grazing to provide a balanced diet for the horse and in this context is synonymous with the term concentrate feed. Whilst legally within Europe the term complementary feed also incorporates feed supplements, these have not been included in this part of the discussion and will be addressed separately.

Proprietary complementary feed offers a certain amount of nutritional information as part of the legally required statutory statement. This usually consists of a guaranteed or typical nutritional analysis, plus a list of ingredients which may be expressed in percentage terms or simply in descending order of inclusion. The nutritional analysis may include reference to the content of moisture, crude protein, oil, crude fiber and ash. Additional information pertaining to the level of added fat soluble vitamins A, D, and E, as well as trace minerals such as copper may be provided. Whilst there may be some uniformity between countries (for example in Europe) we can expect a degree of variation in the information legally required across the world.

For complementary feeds, a similar approach to forage is required and multiple grab samples should be taken from several bags of feed. Ideally feed bags should be opened out on the floor, well mixed and then sampled accordingly. A simple protocol for concentrate feed sampling is described below.

Laboratory analysis of feed and forage samples

Appropriate sample preparation, extraction and analysis of the analytes requested is then required, ideally using an established, experienced laboratory with appropriate external accreditation. Where laboratory results show any unexpected deviation from declared analysis or established levels, repeat analysis should always be requested.

The analysis requested from the laboratory will depend on what information is required and the specific ration evaluation questions being asked. For example, analysis may be undertaken in order to assess the suitability and/or quality of a particular batch of forage, or a feed mix may be analyzed to enable calculation of a DE value. Alternatively laboratory analysis of a proprietary feed may be required to check for adherence to the declared analysis or typical analysis provided by the manufacturer. Individual raw materials may be analyzed so that they can be added to a database enabling the formulation of proprietary feeds or a ration of straights. “Straights” are a colloquial term that refers to a mixture of straight feeding stuffs such as oats, barley, alfalfa, sugar beet, etc. that can be mixed to provide a complementary or concentrate feed for horses. Table 23-1 gives examples of some of the analytical profiles that could be requested for different situations.

Assessment of grazing consumption

For horses or ponies that spend time at pasture, an assessment of grass intake must be made. This is often problematic and represents a significant area for inaccuracy within the overall ration evaluation, both in terms of energy and macro- and micronutrient intake. However, if the animal is maintaining bodyweight when out at pasture (or being fed conserved forages) this reflects adequate energy intake. In contrast, animals increasing or losing bodyweight in such circumstances may have access to too much or too little pasture or forage, respectively. This may be due to factors such as herbage yield, stocking density, etc. or may reflect a clinical issue. This is of course more significant in animals where grass represents a significant portion of their diet including brood mares, leisure horses or ponies and endurance horses. Voluntary dry matter intake (VDMI) will be influenced by grazing behavior, which can be affected by a number of factors such as quality and quantity of grazing, gender, age, breed, breeding status and also whether the animals are at grass in isolation or with a group. This has been reviewed extensively in Chapters 3 and 18, and also previously (NRC 2007). The effect of forage quality on voluntary intake is not simple in horses and appears to vary between individuals with some increasing and others decreasing their voluntary intake in response to a reduction in forage quality and dry matter digestibility (Edouard et al 2008). The effect of sward height was more straightforward, with horses choosing grass with a higher sward when patches are of an equal quality (Edouard et al 2009), presumably to maximize intake.

Whilst it is recognized that the rate of intake of pasture is commonly affected by body size and mouth morphology in other mammals, the effect in horses and ponies has only recently been reported to conform to this model. Ponies appear to be able to increase their rate of consumption by increasing bite size; however, their overall intake seems to be limited by the maximum achievable processing speed (the time taken to bite and masticate), which is greater in larger horses as it increases with body size (Fleurance et al 2009).

Ultimately, dry matter intake of horses and ponies at grass, which is discussed in greater depth in Chapter 18, can vary widely between individuals and most estimates suggest a range of between 1.6–3.6% of bodyweight (NRC 2007) with lactating mares typically at the higher end of this range for VDMI (2.6–3.1%). Ponies are estimated to have a high VDMI in comparison to horses, which may approach 5% of body weight when stabled and provided with ad-libitum fiber based complete feed. Ponies also appear to have the capability to consume a high proportion of their predicted VDMI in a relatively short period of time when grazing time is restricted (Dugdale et al 2011). It has been reported that ponies are capable of ingesting nearly 50% of their total daily dry matter intake during only 3 hours of grazing (Ince et al 2011).

In young horses (yearlings and 2-year-old Salle Francais breed), intake relative to metabolic bodyweight was 82 g OM/kg LW0.75/day and did not vary with age. However, the 2-year-old horses exhibited a reduced foraging time and a higher rate of intake (Pascal et al 2000).

When using ration evaluation software programs, the contribution of grass to total daily dry matter intake can either be indicated manually by the user, or in some instances will be predicted by the software. This is often achieved simply by subtraction of the dry matter contribution of other feeds from a predicted total dry matter intake. Time spent at grass is also sometimes used to predict grass intake by ration evaluation programs, although the derivation of the calculations used for this practice is questionable given the paucity of data in this area.

An estimate or assumption of VDMI of grass must be made and used to assess the contribution of grass to energy, protein and macro- and micronutrient intake. Information regarding the nutrient analysis of grazing is also therefore required. For horses or ponies at grass that exhibit optimal body condition, maintenance requirements for energy and protein can be assumed to be satisfied. However, comparable assumptions cannot be made for broodmares or youngstock.

Grass intake will obviously be affected by factors such as availability, palatability and digestibility of the grazing. This in turn will be affected by the stocking density and also the pasture maintenance program including use of fertilizer, overseeding and the removal of droppings. A common sense approach needs to be taken to adjust the likely VDMI upwards or downwards based on at least the availability of grass and stocking density. For example, overgrazed or drought stricken pasture and/or a high stocking density will severely reduce the VDMI compared to well managed grazing with a low stocking density.

Matching intake to requirements

Bodyweight and condition

There is a lack of awareness of body condition and also some resistance amongst horse owners to accept that horses or ponies are overweight, leading to inaccuracy of owner assessment (Wyse et al 2008). Body weight can be assessed easily where there is access to a weighbridge, or alternatively an estimation of bodyweight can be made using measurements of heart girth, length, and wither height (Carroll & Huntington 1988). A number of commercially available weigh tapes are also available, which simplifies this process. A good correlation exists between bodyweight calculated using a weight tape in comparison to that measured on a weighbridge (Ellis & and Hollands 1998). However, weigh tapes may be more useful for determining differences in bodyweigh over time for individual animals as their accuracy can be variable. In addition, this method is less useful in pregnant mares, growing horses, very fit as well as extremely thin or fat animals, as discussed in Chapter 22.

Body condition score should also be assessed and there are a number of scoring systems available. A condition score system can involve an overall assessment of the whole body according to an arbitrary scale of, for example, 1–5. Alternatively, condition score of different regions of the body, such as neck, withers, loin, tail head and ribs can be assessed in isolation and a mean condition score calculated accordingly. The latter method may be more robust where horses are not of a standard shape such as broodmares and horses in race training. However, in obese animals that require caloric restriction, changes in body condition may not always be apparent with initial weight loss as shown previously in ponies (Dugdale et al 2010, Henneke et al 1983). Body condition score should not be relied upon in isolation to trigger further caloric restriction and is therefore ideally used in conjunction with actual bodyweight. (Further recommendations can be found in Chapter 28.)

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Jun 8, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Ration evaluation and formulation

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