Investigations into the mechanisms controlling parturition in cattle.

A pronounced increase in fetal cortisol concentrations stimulating an increase in estrogen production at the expense of progesterone precursors in the placenta, luteolysis, and progesterone withdrawal is considered as a key event during the complex signal cascade leading to the initiation of parturition in cattle. However, there are many questions concerning the exact functional and/or temporal relationships between these individual processes which finally result in the expulsion of the calf and the timely release of the placenta. Thus, parturition was induced in 270-day pregnant cows using the progesterone receptor blocker aglepristone (group AG, n=3), the prostaglandin F(2α) analog cloprostenol (group PG, n=4), and the glucocorticoid dexamethasone (group GC, n=4) to characterize the effect on maternal steroid and prostaglandin levels and to identify immediate subsequent changes in placental morphology and gene expression as compared with untreated controls sampled on day 272 (group D272, n=3) and cows during normal parturition (group NT, n=4). All calves of the treatment groups were born on days 271-272, whereas gestational length in NT cows was 280.5±1.3 days. However, none of the treatments significantly induced the prepartal remodeling of placentomes characterized by a decline in trophoblast giant cells and reduction of the caruncular epithelium. Data on placental CYP17 and COX2 expression confirm that these key enzymes are upregulated by GC, whereas placental aromatase expression was not affected by any treatment. Maternal progesterone and prostaglandin profiles suggest differential effects of the treatments on luteal function and placental or uterine prostaglandin production. The results provide new information on the initiation of parturition in cattle but raise many new questions.

Use of the progesterone (P4) receptor antagonist aglepristone to characterize the role of P4 withdrawal for parturition and placental release in cows.

In late pregnant cows, progesterone (P(4)) is mainly of luteal origin. However, the trophoblast may provide high local P(4) concentrations in the uterus. To test for the importance of a complete P(4) withdrawal for parturition-related processes and placental release, the P(4) receptor (PGR) blocker aglepristone (Ap) was administered to three cows on days 270 and 271 of pregnancy. A complete opening of the cervix was observed 46.5±7.3 h after the start of treatment. However, expulsion of the calves was impaired obviously because of insufficient myometrial activity, and placental membranes were retained for at least 10 days. Measurement of P(4) concentrations indicated that PGR blockage induced luteolysis. To investigate the role of P(4) withdrawal for the prepartal tissue remodeling of the placentomes, the caruncular epithelium was evaluated by morphometry, and the percentage of trophoblast giant cells (TGCs) relative to the total number of trophoblast cells were assessed. Caruncular epithelium in Ap-treated cows (D272+Ap) was immature (30.5±3.3%) and not different from untreated controls (elected cesarean section (CS) on day 272; D272-CS; 31.5±1.4%), whereas it was significantly reduced at normal term (D280.5±1.3; 21.0±6.1%; P=0.011). Correspondingly, the percentage of TGCs were 20.1±1.4 in D272+Ap, 22.1±4.8 in D272-CS, and 9.8±3.9 at term (P=0.001). No effect was detected on placental estrogen synthesis. The results showed that in late pregnant cows, P(4) withdrawal only induces a limited spectrum of the processes related to normal parturition and is not a crucial factor for the prepartal tissue remodeling in placentomes and the timely release of the placenta.

The assessment of carcass composition of Awassi male lambs by real-time ultrasound at two different live weights.

The accuracy of ultrasonography to measure fat thickness (FT) and longissimus dorsi muscle (LM) traits (area, depth and width) in live Awassi male lambs and predict carcass FT and LM traits was studied. Twenty six Awassi male lambs were randomly divided into light (L) (n=13) and heavy (H) (n=13) finishing lambs. Slaughter weight of lambs in L and H groups were 40 and 45kg, respectively. FT and LM traits, cross-sectional area between the 12th and 13th rib were measured using real-time ultrasound in vivo and on the carcass after slaughter. All ultrasound and carcass measurements were the same except live weight (LW) (P<0.001), cold carcass weight (CCW) (P<0.001) and carcass LM width (P<0.05). Overall, correlation coefficients between ultrasound and carcass FT, LM depth, width and area were 0.79, 0.82 (P<0.001); 0.60, 0.58 (P<0.05); 0.48, -0.17 (P>0.05) and 0.89, 0.87 (P<0.001), respectively, for lambs in L and H groups. The introduction of ultrasound FT and ultrasound LM area as independent variables in addition to LW in the multiple regression equations further improved the variations for carcass FT (84%, 71%), carcass LM area (79%, 79%), CCW (72%, 65%) for lambs in light and heavy groups whereas no improvement was observed for carcass yield. These results indicate that in vivo ultrasound FT and measurement of the LM area in association with LW could be used to estimate carcass FT, carcass LM area and CCW in different LW Awassi lambs.