Luteinizing hormone (LH) profiles after either porcine LH or GnRH treatment in Holstein cows with or without FSH-stimulation
Using porcine LH (pLH) in lieu of GnRH for synchronizing ovulation in non-stimulated dairy cows resulted in a prolonged and elevated LH profile which favourably altered the expression of intrafollicular proteins associated with improved oocyte competence, and increased pregnancy rates. The wide variability in superovulatory responses and embryo yield in FSH-stimulated cows could potentially be reduced using pLH if the altered (i.e., prolonged and elevated) LH profile attained in non-stimulated cows could be established in superovulated cows. As a first step, our objective was to characterize LH profiles after giving pLH or GnRH in non-lactating Holstein cows subjected to different levels of ovarian stimulation. Cows (n=13) assigned to no ovarian stimulation (NS; 0 mg FSH) received 100 μg GnRH followed by 500 μg cloprostenol (PGF) 7 d later. In ovarian-stimulated groups, cows received decreasing doses of FSH, twice daily over 4-d, with PGF treatments given with the sixth and seventh FSH, to attain either partial stimulation (PS; n=8, 200 mg FSH) or full stimulation (FS; n=12, 400 mg FSH). Cows received either 100 μg GnRH or 25 mg pLH 2-d after PGF in NS and 1-d after last FSH in PS and FS groups. Blood samples were collected to determine LH concentrations from 30 min before GnRH- or pLH- treatment, up to 20 h post-treatment and plasma LH concentrations were measured by radioimmunoassay using an anti-bovine LH monoclonal antibody. In GnRH-treated cows, mean (± SE) plasma LH (ng/mL) increased from 0.3±0.1 to a peak of 14.3±1.3 (NS), 6.3±0.8 (PS) and 17.0±2.6 (FS) by 1.5 h, remained elevated for up to 4 h after GnRH treatment (P≤0.01) returning to baseline by 8 h after treatment in all three groups. In pLH-treated NS and FS cows, plasma LH increased from 0.2±0.2 to a mean peak of 2.1±0.2 and 1.1±0.1 by 1.5 h, and maintained above-basal concentrations (P<0.0001) up to 20 h after treatment, respectively. In pLH-treated PS cows, however, LH concentrations increased from 0.1±0.2 to a mean peak of 1.3±0.2 ng/ml by 3 h, and remained above basal concentrations for up to 10 h post-treatment (0.5±0.2; P<0.01). In summary, LH concentrations in non- and FSH-stimulated cows given pLH remained elevated for a longer period than in cows given GnRH. Whether giving pLH to superovulated cows will reduce variability in ovarian response and improve embryo quality remains to be seen.
LH, Porcine LH, GnRH, Dairy Cow