This first general chapter of the book serves as an introduction to the remaining where we deal with the main evolutionary aspects of breeding sows with high prolificity. This chapter introduces the milestones that mark the needs of the current breeding sows, also the relevance of the daily milk production, the reproductive control and the pillars that define its efficiency, the bases of the management of the nutrition, as well as the objective to maintain their optimal body condition and the importance of water to reach their genetic potential.

Introduction

Litter size is one of the main parameters that define the productivity in a farm and is closely related to the sensitivity analysis of the productive parameters that determine profitability (Ocepek M, 2017).

In the last decade, genetic companies have carried out important work in selection for prolificity with an increase of 0.2 piglets/year over the past 20 years (Figure 1), which we already observe in practice with large litters at birth (Quiniou, 2012). The prolificity of sows has been increased while the individual weight of the piglet at birth has been decreasing causing an increase in the variation of piglet size (Figure 2). In addition, the maturation of the piglets at birth is lower (lower liver weight). In the same line, the current sows are leaner and less fat, and it is estimated that the lipid content of piglets at birth is 2% lower than we knew (Manner MJ, 1963). This means that, piglets at birth have less body fat and therefore a lower amount of liver glycogen, which aggravates their viability after birth (Canario, 2014).

Table 1. Characteristics of the modern sow

The problem arises when we have a positive relationship between total births and stillbirths, and especially with a greater dispersion over the average weight with a significant percentage of piglets with low weight, less vitality and viability, which will significantly affect the number of weaned piglets. At the same time the potential for milk production is increased, but not the appetite (voluntary feed intake) of the sows, which leads to a greater mobilization of body reserves during lactation. This is summarized in Table 1.

The influence of nutrition on prolificity begins at birth of the future breeding pigs, continues through the growth and development phase, concluding with gestation, farrowing, weaning to insemination and lactation phases. In order to optimize pigs per sow lifetime, we must work globally in all these productive phases. There are innumerable works that show the strict relationship between proper sow nutrition and sow productivity. In other words, working towards adequate sow body condition for reproduction will more likely ensure good results, starting from the basis that nutrition is based on equilibrium, and not on maximums or minimums. Both thin and fat body condition in sows has a negative impact on their productive parameters, and therefore on prolificacy. The consequences of the low feed intake in lactation are shown in Figure 3.

Figure 3. Consequences of the low feed intake in lactation (Palomo, A)

Profitability of sows is dependent on specific things, such as:

a) Proper farrowing management: colostrum intake, specific plan of cross fostering and action with nurse sows.
b) Some environmental conditions within its thermoneutrality.
c) Diet adapted to your needs in each production phase.
d) Biosecurity and health prevention programs that will give us the best health status.

The physiological processes that chronologically take place during the reproductive cycle of a sow, as well as the main symptoms that we observe in practice, are:

a) Fertilization phase: takes place in the first hours after insemination and conditioned to the half-life of the oocytes (6-8 hours) and the sperm (20-24 hours in the female genital tract).

b) Implantation phase: occurs 12-14 days after insemination, at which time the sow recognizes its gestation. Resorptions prior to this period give rise to cyclic repetitions, usually of a noninfectious component.

c) Fetal ossification phase: occurs between 30-35 days of gestation. Fetal death from this moment forward is not resolved with a reabsorption, but with a mummification.

d) Immunotolerance phase: occurs between 60-70 days of gestation, from which time the fetus can be infected and be born viremic.

e) Immunocompetence phase: after 70 days of gestation the immune system of the fetus can fight any disease, which does not necessarily mean that it is capable of overcoming it.

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