Few studies evaluating protocols for fixed-time artificial insemination in gilts have been performed.
The use of a single hormone for fixed-time artificial insemination protocols in pubertal gilts can be difficult because they are in different phases of the oestrous cycle. This is in contrast to scenario of fixed-time artificial insemination in weaned sows, for which several hormonal protocols to induce follicle growth and ovulation are available . Protocols proposed for fixed-time artificial insemination in gilts involve the use of progesterone (P4) analogue, followed or not by the use of eCG, to stimulate follicle growth, and an ovulation inductor such as GnRH, hCG or porcine luteinizing hormone – pLH , the use of pLH is more efficient than hCG to induce ovulation after using P4 analogue and eCG in pubertal gilts. Embryo survival has not been impaired in gilts submitted to a double for fixed-time artificial insemination, after the use of P4 analogue
and GnRH, compared to gilts inseminated according to the onset of oestrus . The reproductive performance of gilts with double for fixed-time artificial insemination after synchronization with P4 analogue followed by eCG and pLH application was similar to that of a control group in which multiple inseminations were performed. In weaned sows, the use of pLH
at oestrous onset followed by a single for fixed-time artificial insemination 24 h later resulted in similar reproductive performance to that obtained with multiple inseminations without pLH application .Usually, 5 mg of pLH by the intramuscular route is the recommended dose for swine, although there are studies showing the possibility of using 2.5 mg by the intramuscular route . On a commercial scale, the intramuscular application could require more labour, considering the difficulty of accessing the animal’s neck. The vulvar submucosal route could be a practical alternative as it has been shown to be effective for farrowing induction using a single administration of prostaglandin, allowing reduction of the dose to a quarter of the usual recommendation . The use of a single hormone application and reduction in the number of hormones used in protocols for a single or double fixed-time artificial insemination have been considered in some studies,
showing effectiveness to synchronize ovulation and reduce the number of inseminations .This tendency in recent studies will likely facilitate the use of fixed-time artificial insemination in the routine of commercial farms due to reduction of costs and labour with hormonal protocols. Information about the possibility of using a single fixed-time artificial insemination combined with induced ovulation in spontaneous oestrus is lacking for gilts. This study aimed to evaluate the effect of different doses and routes of pLH administration at the onset of oestrus, combined with a single fixed-time artificial insemination, on the interval between onset of oestrus and ovulation and reproductive performance of gilts.