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Introduction
The feeding of sows is divided into two clearly differentiated phases: gestation and lactation. The first is more closely associated with maintenance, the second with production. During lactation the sow usually has a negative balance of nutrients, and mobilizes part of her body reserves for the production of milk. Therefore, it is important to promote the highest possible intake of nutrients during lactation with the aim of minimizing the sow’s weight loss. This will be beneficial both for the growth of the litter and for the productivity of the following reproduction cycle.
The sow’s intake is affected by the interaction of different factors, not just nutritional but also those connected with the animal, handling or system of production.
Non-nutritional factors
•Genetic base: the progress in genetics in recent years has given rise to sows that are more prolific, bigger, leaner and with a greater lactation capacity Therefore, as the nutritive requirements are greater due to the increase in productivity, the voluntary intake during lactation will be even more critical. Besides an individual variability, there are differences between breeds and genetic lines.
• Throughout lactation, voluntary intake increases in a typically exponential manner, reaching the maximum plateau level at around week 2-3, coinciding with the peak of milk production.
• Intake increases with the number of parturitions (principally until the 3rd-4th parturition) and is clearly inferior for primiparous sows.
• Milk production and feed intake tend to affect each other mutuallyTherefore a higher production of milk due to the genetic base, litter size and weight at weaning can increase the voluntary feed intake.
• Environmental conditions of temperature, humidity, ventilation, air quality and photoperiod.
• Sanitary conditions, welfare and social interaction of the animal.
Factors related to nutrition
• Feeding during gestation: it is well known that an excessive body condition at the end of gestation will reduce intake during lactation. However, supplying a greater volume of fibrous diets stretches the digestive tract which improves intake during lactation.
• Nutritive composition of the diet:
- A high nutritive concentration can facilitate greater intake of nutrients.
- A sufficient protein-energy relation should be assured: protein deficiency can provoke greater corporal mobilizations and lower milk production.
- Energy source (fat vs starch. Adding fat allows the energy concentration to increase easily, it also increases palatability and could be important in summer as fat generates less metabolic heat when digested. Starch increases the plasmatic levels of insulin and IGF-1, and this favours follicular maturing and the following ovulation rate.
- Use digestible raw material, with an absence of antinutritive factors and palatable.
- Certain vitamins, minerals or additives can improve the digestion process, the physiology and the health status of the animal.
• Form of feed administration, manual or ad libitum, number of meals per day, mix of feed with water, etc. The farmer’s ability is determinant for:
- Capacity to stimulate and adjust the feed intake to the animal’s appetite.
- Making a progressive increase in the feed supply throughout lactation, being able to restrict the supply during the first days of lactation.
Feeding in hot periods
The decrease in ingestion during summer due to high temperatures is well known, and it is recommendable to use refrigeration and/or ventilation systems that can improve the thermic comfort of the sow, especially in hot regions.
For sows fed ad libitum, above the thermoneutrality zone (22ºC approx), there is a reduction in the size of the meals, while with very high temperatures (27-30ºC) there is also a reduction in the number of meals.
In hot periods there is generally a big fluctuation of temperature during the day, which could be up to 10ºC. In such circumstances the greater part of voluntary intake is in the early morning when the environment is cooler.
Conclusions
It is extemely important to maximize ingestion during lactation since it is affected by many factors, not only nutritional factors but also those related to the animal, production system or environment. While finally, of special relevance, are the sound management practices.
In hot periods action can be taken by improving the environmental conditions (ventilation/refigeration), or nutrition (palatability and nutritive density), or by modifying management (time and number of meals).
