Selection of impubertal gilts by ultrasonography optimizes their oestrus, ovulatory and fertility responses following puberty induction by PG600.

In a group of gilts, occurrence of puberty is spread over several weeks. The optimal time to apply puberty induction is therefore difficult to define, as treatment of puberal gilts is meaningless. Changes in uterine aspect around puberty can be detected by ultrasonography. Two experiments were carried out to assess the effect of PG600(®) (400 UI of eCG and 200 UI hCG) administration to 6 months old gilts shown to be impubertal by ultrasonography on cyclicity and reproductive performance. Impubertal Large White gilts (n=94) were treated with either PG600 or solvent (controls). Administration of PG600 to impubertal gilts increased significantly the proportion of females displaying pubertal uterine ultrasound images 3 days after treatment (100% versus 65% in controls). The number of days to puberty was significantly reduced in gilts injected with PG600 (3.3 days) versus controls (4.7 days). In gilts of the PG600 group, ovulation rate was higher at the 1st oestrus compared to the 2nd, while this did not happen in controls. Progesterone concentrations were higher at mid-luteal phase in the PG600 treated gilts compared to controls (significant treatment by time interaction). Similar proportions of gilts returned to oestrus (89% versus 74% for controls). Following insemination at the 2nd oestrus, pregnancy rate and number of live embryos were unaffected by treatment. The combination of ultrasonography and PG600 optimizes the use of exogenous hormones by targeting treatment to gilts that need it, therefore facilitating the introduction of gilts into all in/all out system.

Discrepancy between in vitro and in vivo assays for the susceptibility of Bacillus C.I.P. 5832 to antimicrobial agents.

In vitro, avoparcin, flavomycin, virginiamycin bacitracin, trimethoprim + sulfadimethoxine, colistin, spiramycin, oxolinic acid, lincomycin + spectinomycin and a mixture of organic acids were able to inhibit Bacillus C.I.P. 5832. In vivo, none of these antibacterial agents, at the levels incorporated in feeds, could affect the viable bacillus count in the caecal content of chickens. In another in vitro assay, olaquindox, carbadox and tylosin were also effective in inhibiting Bacillus C.I.P. 5832. But, concomitantly administered with carbadox or tylosin, Bacillus C.I.P. 5832 still promoted growth and feed conversion of fattening pigs. These results, as well as data of the quoted literature, suggest that the current in vitro techniques should not be used to screen the susceptibility of Bacillus C.I.P. 5832 to antimicrobial agents. Only in vivo assays seem to be of value.