118 A SINGLE INTRAUTERINE INFUSION OF SUSTAINED RELEASE RECOMBINANT BOVINE INTERFERON τ ON DAY 13 EXTENDS CORPUS LUTEUM LIFESPAN IN CYCLIC COWS

Bovine interferon (bIFN) τ has been implicated as a mediator of maternal recognition of pregnancy in cattle. (Geshi et al. 2001 Theriogenology 55, 325) reported that daily intrauterine infusion of recombinant (r) bIFNτ from Day 13 to 24 extended interestrous intervals in heifers. The objective of this study was to determine whether a single infusion of sustained release bIFNτ into the uterine horn would extend corpus luteum lifespan in cyclic cows. RbIFNτ was prepared from the Silkwarm-Baculovirus gene expression system (1 mg mL–1, 1 × 108 IU mg–1, Nagaya et al. 2004 J. Vet. Med. Sci. 66, 1395–1401). Two sustained release carriers, liposome and aluminum hydroxide (Al) gel were tested. Liposome encapsulated (lipo) BSA (control) and rbIFNτ were prepared from a lipid mixture solution contained 2 mg of each protein by the Bangham method including lyophilization and rehydration. The same amount of BSA or rbIFNτ was adsorbed to Al-gel containing 2.5 mg Al. Adsorption was allowed to proceed for 5 min at room temperature and unbound proteins were removed by centrifugation. Subsequently, lipo- or Al-gel adsorbed BSA and rbIFNτ were adjusted to 0.5 mL with saline and loaded into 0.5-mL AI straws. BIFNτ free from liposome or unbound to Al-gel was measured by RIA. Eight Japanese Black cows were used in this study. Their signs of oestrus were monitored twice a day. Cows were randomly assigned to four groups, receiving a single infusion of 1) lipo-BSA (n = 3); 2) lipo-rbIFN τ (n = 3); 3) BSA with Al-gel (n = 4); or 4) rbIFNτ with Al-gel (n = 4) on Day 13 (oestrus = Day 0). The BSA or rbIFNτ solution was introduced into the uterine horn ipsilateral to the corpus luteum by the cervical route. Blood samples were collected and rectal temperatures were recorded immediately preceding the infusion (0 h), thereafter every 3 h until 12 h, and 24 h after the infusion. Total white blood cells (WBC) were counted. Data were analysed by ANOVA using the STATVIEW program. Unbound bIFNτ in liposomal encapsulation and adsorption to Al-gel were estimated to be ∼90% and 2%, respectively. Corpus luteum lifespan was normal in controls (lipo-BSA; 21.6 ± 0.33 and BSA in Al-gel; 21.2 ± 0.25 days) but was extended in cows receiving rbIFNτ with Al-gel (27.0 ± 0.40 days; P < 0.01), whereas lipo-rbIFNτ was less effective. Rectal temperatures increased following rbIFNτ treatment with a peak at 6 h after infusion (P < 0.05). Correspondingly, total WBC was decreased following rbIFNτ treatment with a minimum at 9 h. Those changes were larger in liposomal encapsulation than in adsorbed to Al-gel. In conclusion, a single infusion of bIFNτ adsorbed to Al-gel can extend corpus luteum lifespan in cyclic cows.