Effect of prepartum administration of growth hormone-releasing factor on somatotropin, insulin-like growth factor I, milk production, and postpartum return to ovarian activity in primiparous beef heifers.
Simpson. R B RB; Armstrong. J D JD; Harvey. R W RW
Key Findings
- Pre‑partum GRF‑1‑29 increased circulating somatotropin (GH) dramatically compared with untreated cows.
- Treated cows lost more body weight in the first 80 days after birth (about 20 % more) than controls.
- Return to ovarian activity was delayed by roughly 3‑4 weeks in GRF‑treated cows.
- Milk production was not significantly different between treated and control groups.
- Post‑partum GH pulse frequency dropped in treated cows, and higher early IGF‑I levels were linked to earlier ovarian return.
Practical Outcomes
- For biohackers, this animal data hints that GRF‑1‑29 can shift GH/IGF‑I dynamics and may influence weight loss and reproductive timing, but the findings are limited to cattle and may not translate to humans. The dosing used (2.5–12.5 µg/kg subcutaneously for 7 days before birth) is not a proven or safe protocol for people, so it should not be adopted without further human research.
Summary
Giving a growth‑hormone‑releasing peptide (GRF‑1‑29) to pregnant cows a week before they gave birth raised their growth‑hormone levels, made them lose more weight after birth, and delayed the return of their ovarian cycles, while milk output stayed the same. The study was done in beef heifers, not people.
Abstract
Forty-one primiparous beef heifers were used over 2 yr to evaluate the effect of prepartum administration of a growth hormone-releasing factor analog (GRF-A) or growth hormone-releasing factor (GRF(1-29)-NH2) on somatotropin (ST), insulin-like growth factor I (IGF-I), milk production, heifer BW, and postpartum (PP) return to ovarian activity. Beginning on d -11 +/- 1 from parturition, heifers were administered (s.c.) GRF-A ([desNH2-Tyr1,D-Ala2,Ala15]GRF(1-29)-NH2, 2.5 micrograms/kg; Yr 1) or GRF(1-29)-NH2 (12.5 micrograms/kg; Yr 2) (GRF; n = 17) or vehicle (CON; n = 24) for seven consecutive days. Blood samples were collected at 20-min intervals from -60 to 300 min from the first and fourth injections. Samples were also collected at 20-min intervals for 6 h on d 25 and 69 +/- 1 PP. Area under the curve of ST (nanograms.minute-1.milliliter-1) was greater (P less than .01) in GRF than in CON heifers (9,671 +/- 677 vs 2,611 +/- 237). Increases in ST after GRF-A or GRF(1-29)-NH2 were similar. On d 25 +/- 1 PP, frequency of ST release (pulses per 6 h) was greater (P less than .01) in CON (3.3 +/- .2) than in GRF (2.1 +/- .2) heifers. Milk production was similar (P greater than .1) for the two treatments. Heifer BW loss from d -16 to 81 after parturition was greater (P less than .01) in GRF (88 +/- 5) than in CON (68 +/- 5) heifers. Postpartum return to ovarian activity (progesterone greater than 1 ng/mL for two consecutive weeks) was delayed (P less than .05) in GRF (97 +/- 14) vs CON (71 +/- 8) heifers. After accounting for variation due to treatment and year, a negative (P less than .02) correlation (r = -.39) was detected between concentrations of IGF-I during the first 30 d PP and PP interval to ovarian activity. These results indicate that prepartum administration of GRF altered the release pattern of ST after parturition and was associated with greater PP BW loss and delayed PP return to ovarian activity in heifers.
Study Information
pubmed
1992
10.2527/1992.7051478x