Somatomedin-like activity in cattle: the effect of breed, lactation and time of day.
Somatomedin-like activity (SLA) was measured in plasma samples from cattle using the porcine costal cartilage disk bioassay. In 40-day-old pre-ruminant bull calves, SLA was highest in the plasma of eight Friesians (mean potency 0.97 +/- 0.06 (S.E.M.) units/ml), lowest in five Aberdeen Angus x Friesians (0.78 +/- P < 0.05) and intermediate in six Hereford x Friesians (9.89 +/- 0.09). Plasma levels of SLA were significantly (P < 0.01) lower in eight lactating Friesian (high-yielding) cows (0.53 +/- 0.04) than in five dry cows (0.76 +/- 0.06). Levels of SLA in the plasma of a further eight lactating Hereford x Friesian (low-yielding) cows (0.76 +/- 0.07) were similar to the levels in the plasma of the five dry dairy cows. Large diurnal changes in plasma SLA occurred in lactating Hereford x Friesian and Friesian heifers. In three Hereford x Friesian heifers plasma levels of SLA were lowest at 19.00 h (0.39 +/- 0.07) and highest at 03.00 h (0.77 +/- 0.08). A similar pattern was present in plasma samples from three Friesian heifers; the lowest levels of SLA being at 21.00 h (0.37 +/- 0.07) and the highest at 05.00 h (0.61 +/- 0.13). Throughout the period of 24 h the overall mean levels of SLA were significantly (P < 0.01) higher in the plasma samples from the three Hereford x Friesian heifers (0.6 +/- 0.01) than in the samples from the three Friesian heifers (0.49 +/- 0.02 units/ml).
D000818:Animals; D001947:Breeding; D002417:Cattle / Q000097:blood* / Q000235:genetics; D002940:Circadian Rhythm; D005260:Female; D007774:Lactation; D008297:Male; D011247:Pregnancy; D013002:Somatomedins / Q000097:blood*
D013002:Somatomedins