Biological potential of fecundity of sows

Abstract

The profitability of pig production considerably depends on the number of born alive and fostered piglets. The development regarding the number of piglets born for German Landrace (DL), Large White (DE) and Pietrain (PI) in Germany during 1980 - 2006 is limited (DL: 10.4 - 11.0; DE: 11.0 - 11.0; PI: 10.2 - 10.0). Comparing international data, variations between 10.2 to 13.6 piglets born alive are observed. Reproductive performance in sows is mainly determined by (1) the number of ovulated follicles and fertilized oocytes, (2) the divvy of surviving embryos and foetuses, and (3) the morphological and functional performance of the uterus to support foetal development up to birth. The question whether the ovary and/or uterus are limiting factors can be answered as followed. The pool of ovarian follicles is not the limiting one, although only about 0.5 % of oocytes present in the ovary are ovulated during the sows' lifetime. Selection for ovulation rate increases the number of ovulating follicles, but not of piglets born alive. Limiting is the uterine capacity. This physical, biochemical and morphological limitation of the uterus include space, nutrients, gas exchange and surface of the placenta. Although a relationship exists between uterine dimension and the number of foetuses/piglets, uterine length alone is not a prerequisite of higher uterine capacity. Placental efficiency (indicating how much gram foetus is supported by one gram placenta) and the degree of placental blood supply appear to be essentially for litter size. At present, the (really) assumed potential of fecundity is 15.0 piglets born alive, 2.4 litters/year, <10 % losses and 32.5 piglets per sow/year (compared to current data of 11.1, 2.26, 13.8 and 21.5, respectively).