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.

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

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.

Figure 23.1 Hay bale corer. Caution is required when sampling some very high DM bales that the friction does not present a fire risk.

Photo courtesy Andrew Theodorou.

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.

• Open a bag of feed by cutting open down both sides and open up the bag completely.

• Using a clean scoop or shovel mix the contents of the bag thoroughly.

• Wearing latex gloves or using an inverted plastic bag take 10–12 samples of the feed bag covering all areas of the spread feed into a single clean sample bucket or bag to form a composite sample.

• Repeat this process with up to 10% of the total feed batch.

• Thoroughly mix the composite sample and then take two representative samples.

• Retain one sample and send the second to the laboratory.

Assessment of pasture

Pasture sampling should be carried out using an established format, which may include walking a large “W” or “M” within each paddock and cutting representative samples of grass at numerous points. Areas of heavy contamination with urine or dung should be avoided and in order to minimize soil contamination samples should not be cut too close to the ground or pulled rather than cut (Fig. 23.2). Additionally samples should ideally be taken on dry days to avoid soil contamination from splash back. Further details on pasture sampling procedures and precautions have been previously provided (MacNaeidhe 1995).

Figure 23.2 Example of collecting grass for analysis – avoiding soil contaminated herbage. Sample along the length of meter rule, cut at grazing height, and place samples into ice-box immediately.

Photo courtesy of Andrew Theodorou.

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.

Table 23-1 Examples of Analysis Requested for Different Feed Types for Specific Purposes

DM = dry matter; CP = crude protein; O = oil.

Assessment of forage consumption

Assessment of forage intake requires a record of both the weight of forage offered, which can be easily achieved when horses are fed individually, but is more problematic in group fed animals. Wastage of forage should also be recorded in order to increase accuracy. Wastage of forage can be particularly high in performance horses (Geor 2005), that may self-limit forage intake when a high level of energy rich concentrate feed is fed. Where hay is soaked or steamed, the weight offered should be recorded prior to such treatment.

An indication of the dry matter of forage is advantageous and is a necessity where haylage is considered. The dry matter content of haylage can vary considerably both between suppliers and to a lesser extent from batch to batch from the same supplier. A moisture probe can be used to provide an estimate of the dry matter content of haylage by sampling at multiple sites. This enables increased accuracy of a ration assessment that is carried out on a yard. In addition it will provide important information for the horse owner or trainer to help ensure a more consistent intake of forage dry matter. This is essential information during ration evaluation as large differences in the dry matter content of haylage between batches will affect the delivery of energy and nutrients to the horse. Dry matter analysis is also relevant when soaked feeds such as sugar beet are used.

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 LW^0.75/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