Feeding of ruminants
Rationing is one of the key steps to achieve optimal performance in your ruminant breeding. It is necessary to balance the intake of forages and concentrates to meet the animal's needs and ensure optimal rumen function without creating health or environmental risks.
Description
The coverage of needs is achieved through forages which can be supplemented by concentrates.
Forage consists of plants or mixtures of plants used for feeding livestock. It is the main ingredient of the herbivore's ration. It can be fresh, conserved dry or by wet method, i.e. ensiled. There are several types of cultures for forage:
- Annual forage crops (6 months): roots, tubers and cabbages.
- Annual forages (6 months): e.g. maize silage.
- Artificial pastures (2 to 10 years): legumes.
- Temporary pastures (2-5 years): grasses, grass-legume associations.
- Permanent pastures (6 years or more): natural pastures, sown pastures older than 6 years.
- Grazing lands, moors, alpine pastures (spontaneous, low productivity).
Concentrates are provided as a supplement to forage. They increase the energy and protein value of the ration. There is also a wide variety of concentrates:
- Cereals and seeds: barleys, wheats, maize… in grains, rolled or flours.
- Tubers: beets, potatoes, cassava...
- Oilseed cakes: residues from pressing oilseeds and protein crops.
- Commercial feeds: pellets of alfalfa (rich in fiber), or containing soy (rich in nitrogen).
- By-products of the agro-food industry: pulps, bran, brewers grains, hulls...
Animal needs
Needs are divided into two categories. Maintenance needs, to keep the animal alive without any production, and production needs, for growth, gestation, fattening and milk production in the case of dairy animals.
First, the animal's characteristics must be specified:
- Species and breed.
- Type of production.
- Sex, age.
- Weight, body condition.
- Lactation indicators for dairy animals: stage, milk potential, quantity and composition of milk (butterfat and protein content).
From these data, it is possible to calculate protein needs (PDI unit), energy needs (UFL unit for milk production or UFV unit for meat production), as well as vitamins and minerals.
Then, the intake capacity (IC) of the animal must also be specified.
Feeding and health
Rations can be described by the forage/concentrate ratio. A ration with a high forage/concentrate ratio will have a lower energy density than a ration with a low forage/concentrate ratio. However, too much concentrate causes health problems mainly due to lack of fiber in the ration (rumen acidosis) and the amount of forage in the ration must be maximized as they are very economical sources of nutrients. It is therefore essential to take all these factors into account to balance this ratio.
Moreover, for effective nitrogen digestion, both nitrogen and energy sources are needed. If there is too much fermentable nitrogen in the ration compared to the amount of fermentable energy, the risks of mastitis, metritis and reduced fertility increase. This also causes an economic loss and increased urine excretion which can have harmful environmental consequences. If there is too much energy, needs will not be met, because some proteins will be only "virtual". Indeed, there will not be enough fermentable nitrogen compared to available energy to create proteins. This situation must therefore be avoided.
Ration formulation
The ration is the amount of feed to be given to an animal to cover its maintenance and production needs in energy, nitrogen, minerals, trace elements and vitamins. Rationing is necessary to avoid underfeeding or overfeeding the animal. This calculation of quantities is very important as it determines the amount of forage and concentrates to provide and thus the quantity needed to produce for feeding the herd.
Once needs are identified, the characteristics of the forage(s) must be determined. This corresponds notably to the bulk value in UEM (sheep), UEL (dairy cow) or UEB (cattle) depending on the species raised. To do this, simply consult the INRAE tables available.
Then proceed to rationing. Calculate whether the planned intake covers the needs and ensures a good ruminal protein balance and thus good rumen function. If not, adjust quantities until optimal performance is achieved.
Glossary to know for the French PDI system:
- IC: Intake Capacity. It is the ability of an animal to consume more or less a feed offered ad libitum.
- PDI: Digestible Intestinal Protein. There are different types of PDI:
- PDIA: PDI from dietary proteins not degraded in the rumen.
- PDIM: PDI from true proteins synthesized by the rumen microbial population.
- PDIME: PDIM corresponding to the potential synthesis of the feed in fermentable energy in the rumen.
- PDIMN: PDIM corresponding to the potential synthesis of the feed in degraded nitrogen in the rumen.
- PDIE: PDIA + PDIME.
- PDIN: PDIA + PDIMN.
- UFL: Forage unit for milk. Net energy amount for milk production contained in 1 kg of reference barley.
1 UFL = 1700 kcal for milk production.
- UFV: Forage unit for meat. Net energy amount contained in 1 kg of reference barley for maintenance and growth of the animal, at a production level of 1.5. 1 UFV = 1820 kcal net energy for meat production.
There is another system for these calculations, the Dutch DVE system.
Indicators for evaluating ration imbalance
Indicators to observe[1]
Body condition score
The body condition score is an indicator ranging from 1 to 5. This score decreases when the animal ingests too little energy and increases when energy intake is too high. This evaluation is done by observing the animal from behind and comparing it to a scale. On the right is an example scale for dairy cows.
Body condition varies according to lactation stage. It is common for it to decrease during the first two to three months of lactation. However, this decrease should be limited to 1 point.
Rumen fill score
Similarly, the rumen fill score is a rating between 1 and 5 by observing the animal's left rear side. A score of 1 corresponds to a very hollow flank while a score of 5 corresponds to a full rumen. Below is an example for dairy cows of these scores and their interpretation.
Rumination
Rumination time is a good indicator of the fiber content of the ration. It should be at least 8 hours. To evaluate rumination, two points must be observed:
- At least 50% of lying cows must be ruminating.
- This rate should reach 90% two hours after feeding.
If lower values are observed, the ration must be corrected to increase fiber content.
Fecal matter
Fecal matter being a reflection of digestion, it is a very good indicator of ration quality. A score can also be established from 1 to 5, on the scale described in the table. If the score is not acceptable, the ration must be reviewed and more digestible feeds added.
| Score 1 | Score 2 | Score 3 | Score 4 | Score 5 |
|---|---|---|---|---|
| Shiny feces, with homogeneous consistency. No undigested elements visible or palpable.
Ideal score for dry and lactating cows. |
Shiny feces, with homogeneous consistency. Some undigested elements are visible and palpable.
Acceptable score for dry and lactating cows. |
Slightly dull feces, with heterogeneous consistency. Undigested fibers stick to fingers.
Acceptable score for pregnant heifers or dry cows, but unacceptable for lactating cows. |
Dull feces, with clearly visible undigested elements.
Inadequate score, requiring ration revision. |
Dull feces, with easily recognizable coarse particles.
Inadequate score, requiring ration revision. |
Milk production
Milk production is also a very good indicator of ration quality. This evaluation can be individual or by groups (primiparous/multiparous; first, second, third lactation…).
Number of metabolic diseases
If many cases of diseases such as milk fever, acidosis or ketosis occur, the farmer must review the rations.
Indicators from milk production data
Milk composition allows evaluation of protein and energy supply of the ration by quantifying milk urea, fat content (TB) and protein content (TP). Interpretations of irregularities compared to threshold values for dairy cows are described below.
| Indicator | Low value | Average | High value |
|---|---|---|---|
| Urea | Protein deficiency | 150-300 mg/L | Protein excess |
| TB | Excess concentrates;
Chopped forage presentation |
3.5-4.2 % | Energy deficiency |
| TP | Energy deficiency;
Protein deficiency; Limiting AA deficiency (lysine, methionine) |
3.1-3.4 % | Genetic ceiling |
Decision support tools (OADs)
Several software tools can help formulate rationing. For example, Obione allows rationing for dairy cows, suckler cows and fattening, sheep and goats.
There is also Wisium which offers several OADs including applications aimed at improving nutritional performance. Although this represents an investment, it can be profitable in the long term to calculate rations as precisely as possible for maximum performance without exceeding necessary quantities.
