Use of boar spermatozoa for artificial insemination. II. Fertilizing capacity of fresh and frozen spermatozoa in gilts inseminated either at a fixed time or according to Walsmeta readings.

A fertility trial was conducted comparing two methods of defining the optimum time to inseminate frozen boar semen. One hundred sixty-four gilts were inseminated, one-half at a fixed insemination time of 32 to 34 h after calculated onset of estrus and the remainder were inseminated on the basis of changes in the vaginal mucosal electrical resistance. Inseminations were made when the instrument (an inversely scaled ohmmeter) reading fell between 54 to 64 on a scale of 1 to 100. Both fresh and frozen boar semen were used. Pregnancy rates and live embryos/gilts from inseminations made at the fixed time and inseminations made on the basis of ohmmeter readings did not differ significantly for either fresh of frozen-thawed spermatozoa. Pregnancy rates and number of live embryos/gilt were significantly higher for gilts inseminated with fresh spermatozoa than for those inseminated with frozen-thawed spermatozoa (82%, 11.6 vs 61%, 8.2, respectively). Inseminations were conducted from January to September. Pregnancy rates were significantly higher for inseminations made for the first quarter or the year (January, February and March) than for inseminations made for the third quarter (July, August and September). No benefit was derived from using an ohmmeter to time insemination with frozen-thawed boar spermatozoa.