EFFECTS OF A ROTATIONAL CROSSBREEDING WIT H 2 COMPLEMENTARY PIG BREEDS ON FERTILITY TRAITS .1. GLS-MEANS OF FERTILITY TRAITS IN DIFFERENT BREEDING GROUPS

Title of the paper: Effects of a rotational crossbreeding with two com plementary pig breeds on fertility traits. I. GLS-means of fertility t raits in different breeding groups. In the present study, some reprodu ction traits of pigs were investigated in a long term rotational cross breeding experiment between German Landrace (GL) and German Pietrain ( GP) breeds. The results may be summarised as follows: 1. The improveme nt of fertility through rotational crossbreeding was evident, especial ly the breeding group ROT(GL) had a better performance than purebreds, F1 as well as ROT(GP). 2. The higher prolificity of German Landrace c ompared to Pietrain as well as crossbreds compared to purebreds was no t due to a higher ovulation rate but to a decrease of early embryonic mortality. 3. The number of embryoes at 28th day p.c. was mainly deter mined through uterus weight and ovulation rate. 4. The uterus weight i s a breed-specific trait. A positive relationship between the ''uterus capacity'' and the embryonic survival rate (r = 0.25) is observed onl y after eliminating breed effects. It is supposed that not only the ca pacity but also the activity of the uterus play an important role in f ertility.