Gilts reproductive efficiency is one of the primary factors of successful piglets' production. This performance, among other things, is expresses by the number of pregnant gilts, with desirable genetic traits, body weight and age, sexual maturity status, and general good health, provided for the replacement of sows in primary herd. This goal is very difficult to achieve in practical conditions. The main reason is occurrence of prolonged preinsemination anoestrus (oestrus was not detected even after 8 months of age). This paper review the occurrence of prolonged preinsemination anoestrus, based on the results of our and study of other authors. All studies consistently show that, in most of these gilts, pubertal cyclic ovarian activity were established, that silent oestrus occurred in only 4% of the cyclic gilts, and that this problem can be solved by applying appropriate technologies for oestrus detection, and by treatment with adequate hormonal preparations.

Mycoplasma hyopneumoniae is a primary agent associated with mycoplasma pneumonia and the porcine respiratory disease complex (PRDC). Various reports have indicated that different strains of M. hyopneumoniae are circulating in the swine population. Lysates from lung swabs from naturally infected pigs of different ages were tested according to a new variable number of tandem repeats (VNTR) genetic typing method based on the polyserine repeat motif of the P146 lipoproteoadhesin, which can be applied directly on clinical material without isolation of M. hyopneumoniae. The aim was to determine the diversity of M. hyopneumoniae isolates from conventional farrow-to-finish pig farms located in different geographical areas of Serbia. PCR amplification was carried out using M. hyopneumoniae -specific designed, conserved primers (p146MH-L and p146MH-R) flanking the region encoding the repeat motif, followed by sequencing and cluster analysis. Five groups of M. hyopneumoniae with thirteen to twenty-four serine repeats were observed. Analysis of three samples from each farm indicated that the specific isolate is ubiquitous in pigs of different ages. Furthermore, seven clusters were observed within 27 tested samples. The results indicated a considerable diversity among M. hyopneumoniae field isolates in the swine population from conventional farrow-to-finish farms in Serbia and suggest close genetic relatedness of the corresponding isolates.

Due to the prolonged preinsemination anoestrus (the sings of oestrus were not found even after eight months of age) 25 to 40% of gilts are culled on the farms in Vojvodina. The question is if those gilts did not reach puberty at all or if it was the result of an inadequate technology in oestrus detection. Concerning this issue, a morphological examination of the genital organs of 175 gilts, in which oestrus was not detected during the first 8 to 9 months of age, was carried out. The average age of these gilts was, at sacrifice, 267 days (242 to 278 days). In further research, the treatment of delayed puberty gilts and control gilts was carried out with hormone preparations from the progestin group (Regumate, Altrenogest) or placental gonadotropin (PMSG - 'Folligon'). Based on examination of the gilts' genital organs, in which oestrus was not detected even after 8 months of age, it was established that 38.9% of those gilts did not reach sexual maturity at all, i.e. did not have cyclic ovarian activity. With the other 61.1% of the examined gilts, the puberty ovarian cyclicity was established, as their ovaries had the functional structures (preovulatary follicles, corpora hemorrhagica, corpora lutea and corpora albicantia). Thus, one oestrus cycle was reached by 57.9% while two oestrous cycles were reached by 42.1% out of the total number of sexually mature gilts. A high degree of oestrous reaction (80%), a high farrowing rate (87.5%) and a satisfactory average number of live-born piglets per litter were established in the delayed puberty gilts treated with the Regumate preparation. The obtained results distinctly show that a great number of gilts reached the puberty cyclic ovarian activity while the absence of oestrus detection was the result of inadequate technology in oestrus detection on farms

The reproductive performance of gilts significantly affects the number of annually produced piglets per sow. The paper presents the results of an analysis of the reproductive performance of gilts on a big pig farm in Vojvodina (Republic of Serbia), with a capacity of around 5,500 sows. Out of the total of 19,000 female piglets selected for reproduction, insemination, aged 210 days, a total of 5,420 (28.5%) gilts are prepared, and 70% of these are inseminated. A total of 29.3% gilts are culled for reproduction because of longterm pre insemination anestria (estrus was not established until the age of 9 months). It is believed that the basic reason for the occurrence of long-term anestrias is the inadequate technology for detecting estrus on the farm (once every 24 hours, without direct contact between the test boar and the gilts). As a consequence, there are significant economic losses in piglet production on the examined farm

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