Pedro González Añover, D.V.M., Ph.D, Veterinary-technologist of swine section R&D department (Miavit GmbH)

The benefits of swine production in the reproductive area are determined by the number of piglets obtained per sow and year. The number of offspring per sow is determined, in turns, by the age at first farrowing, the interval among farrowings and the number of piglets in each farrowing (prolificacy). Prolificacy in swine, as in other multiparous species, depends on the number of ovulations and/or the embryo losses during pregnancy.

To right understand the mechanisms determining the first issue of the introduction (number of ovulations), first of all we should understand the most determining factor among this point. This aspect is the follicular dynamic. Follicular dynamic is an amazing area of the sow reproduction, which we usually overlook (it´s always been seen as a complicated issue), but contributes in an important way to the global reproductive output of the farm.

 Follicular development and ovulation

Primordial follicles form the stock from which all follicles emerge. Approximately 500,000 primordial follicles are present in both ovaries by 10 d after birth in swine. Primordial ovarian follicles in this population are not stimulated to grow at the same time, and only a small number begin their development with any new estrous cycle while the rest remain quiescent. In mammals, this characteristic increases the possibilities of having progeny throughout a rather long reproductive life.

Mineral balance

High-producing sow genotypes are generally considered to have heavier mature weights and larger skeletal frame sizes than non high-producing sows. Heavier initial breeding weights of similarly aged, high-producing gilts would not only provide more body fat for subsequent reproductive needs; they also offer a higher body mineral content as a result of their larger skeletal frame. But it must be kept in mind, that both hard and soft tissue mineral reservoirs may be depleted over several reproductive cycles if the dietary minerals do not meet the animal's requirements.

Embryo losses during pregnancy

Another factor affecting the productivity of the sow is due to the embryo losses. These losses are partly due to intrinsic deficiencies of the embryo affecting its viability and partly due to competition among embryos of highly-prolific dams for the uterine space necessary for implantation and adequate placental development; inadequacy of placental growth causes inadequate supply of nutrients and oxygen to the conceptus. The consequence for some embryos is death, which diminishes the number of piglets at farrowing and, hence, prejudices farm efficiency. Other foetuses with deficient placental development may survive, but their life-conditions and growth are compromised by a reduced size at birth, which at the end will reduce the global output of the farm, due to a less amount of weaned piglets per sow and year, with lower ADG and worse FCR.

1. What determines the development of embryos during gestation?
2. Why does the amount of minerals decrease after several litters? How to avoid it?
3. How to avoid all the negative consequences during the gestation period? 

You can find answers for these and other questions in the full version of the article in the magazine «Profitable Pig Production», № 2 (20) 2014.