The needs of the mare in foal

The duration of gestation in the mare is about 11 months. In general, foaling extends over a period between January and May for racing mares and between March and July for sport, leisure and draft mares. Foaling in the spring allows the rich and abundant grass resources to be exploited, which are sufficient to cover the needs of the lactating mare. The cost of the daily ration (grass production) is lower than a ration supplemented with concentrates which are needed if the grass has not started to grow (February-March).

The beginning of gestation (embryonic phase) is characterised by significant cell multiplication and the establishment of the foal’s tissues and organs. This phase ends around 40 days gestation. It is then referred to as the foetus.
From conception to the 6th month of gestation, the growth and development of the embryo and then of

The mare’s weight gain is significant over the final 3 months and represents 6.4 to 8% of her weight, i.e. between 40 and 50 kg for a 550 kg mare.

Energy and protein requirements

The table below represents the energy and protein requirements of the mare in foal (based on: Nutrition et alimentation des chevaux, W. Martin-Rosset et al. 2012).

While the needs of a gestating mare are the same as a maintenance horse for the first 5 months, there is then a gradual increase of about 35% in energy requirements and 80-85% in protein during the second half of gestation.

Due to the space taken up by the foetus in the mare’s belly during gestation, the ingestion capacity, illustrated by the average consumption of Dry Matter (DM), only increases by approximately 30%. The nutritional density of the ration (nutritional value/kg), especially in terms of protein, therefore, has to increase slightly.
The quality of proteins, characterised by their essential amino acid content, especially lysine, have to be taken into account. Lysine requirements increase by 80% during the second half of gestation.

Mineral and vitamin requirements

The table below represents the Calcium (Ca) and Phosphore (P) requirements of the mare in foal (based on: Nutrition et alimentation des chevaux, W. Martin-Rosset et al. 2012).

Requirements double (Ca) or even a little more (P) in the second half of gestation.

For other minerals, requirements for magnesium, sodium, chloride, potassium remain stable, while those for copper, zinc, manganese, iron and selenium increase by 20%.

Selenium requirements are approximately 0.1 to 0.2 mg per kg of DM ingested, or 1 to 2 mg for a saddle mare. Combined with vitamin E, this trace element appears to have a beneficial effect on placental retention during foaling and on the quality of the mare’s colostrum.
Vitamin A and E requirements increase by 60% and vitamin D requirements by 80%.

Practical rationing

When the mare is covered in spring, the grass generally meets her early gestation and even lactation needs. This is the case if the sufficient high quality grass is available (grass in the deciduous stage >4-5 cm high). A salt stone or even a suitable mineral and vitamin supplement (CMV) will complete her daily ration.

During the summer and then in the autumn, when the plant cover is more advanced and/or in smaller quantities, good quality forage (meadow hay harvested under good conditions) must be provided to supplement grazing. Ideally it should be freely available. Up to 8 months of gestation, all needs can be covered exclusively by forage (+CMV).

Generally speaking, the nature of the ration and the quantities to be distributed will depend on the date of foaling in relation to when they are turned out on grass.

Remember

• One kilogram of hay consumed will provide 0.44 to 0.61 HFU and 20 to 102 g of MADC. This data will vary depending on the composition of the grass and the flowering stage at harvest, hence the importance of a forage analysis in order to find the best combination possible. The mineral content of the hay is also very dependent on the type of paddock.
• Un kilo de céréales apporte entre 0.87 (avoine) et 1.12 (maïs) UFC et entre 65 (maïs) et 117 (blé) g de MADC.
• Quality protein sources: 
  • One kilogram of hay consumed will provide 0.52 to 0.63 HFU and 79 to 131 g of MADC as well as more than 20g of calcium. 
  • One kilogram of hay consumed will provide 0.44 to 0.8 HFU and 360 to 400 g of MADC. Pay attention to the conditions of use!
• Commercial feeds for farm animals contain more protein than feeds suitable for working horses. Be sure to choose a feed that is suitable for your animals.
• The phosphocalcium ratio of the ration (Phosphorus/Calcium) should be between 1 and 2.

Mares are capable of processing many plants. The ration must therefore also be considered in terms of practicality and economic approach, depending on:

• The objectives: racing, sport, leisure
• The age at which they are bred
• The full term date
• Access to pasture
• Raw materials available nearby
• Storage and handling capacities
• Time spent on feeding
• The technical ability of the person providing care
  ... In order to optimise the cost of foals produced.

NB: With forage of average nutritional value, the requirements, especially for protein, will not be covered. Because forage is generally the main feed for livestock, it is essential to know its nutritional values in order to correctly supplement the ration. Evaluate, or better yet, have an analysis carried out on your forages.

It is important to monitor the body condition of each mare during gestation so that she is neither too fat when she foals (as being overweight is detrimental to good foaling and milk production), or too thin (difficult to replenish her reserves during lactation). It is also important to prepare her lactation and fertility as well as possible for a possible future gestation.

A study (Chavatte-Peugnet 2014) measured the weight of broodmares and the development of their future foals by comparing:

• A batch of broodmares fed during gestation at 80% of their nutritional requirements exclusively with forage.
• A batch of broodmares fed barley and forage at 100% of their requirements over the same period.

The batch of mares fed exclusively on forage lost weight during the winter (body condition score of 2.5/5) and returned to their initial body condition score at the 3rd month of lactation. The development and growth of foals up was measured up to the age of 2. An increased predisposition to osteochondrosis in foals at 6 months of age from the “barley+forage” batch was observed after radiographic examinations.

In other words, the broodmare mobilises her reserves as a priority to contribute to the good development of the foetus whatever its body condition.

=>A slight weight loss in winter in the mare in foal is not detrimental to the good development of the future foal.

Regularly monitor your breeding mares:

• In terms of their teeth to optimise the value of rations in periods of high need
• In terms of their feet via regular trimming and treating cracks.