Effect of active immunization against growth hormone-releasing factor on growth and onset of puberty in beef heifers.
Simpson. R B RB; Armstrong. J D JD; Harvey. R W RW; Miller. D C DC; Heimer. E P EP; Campbell. R M RM
Key Findings
- Active immunization against GRF‑1‑29 dramatically lowered circulating growth hormone, IGF‑1, and insulin in heifers.
- Treated heifers ate less, grew slower, had poorer feed efficiency, and accumulated more fat compared to controls.
Practical Outcomes
- The results reinforce that GRF‑1‑29 is a key driver of growth hormone and IGF‑1 signaling, which in turn influences growth, metabolism, and puberty. For biohackers, this suggests that boosting GRF (rather than blocking it) could support anabolic and metabolic benefits, while antagonizing it might blunt growth and could theoretically aid weight‑loss or delay reproductive maturation, though no human protocols are provided.
Summary
In this study, young cows were vaccinated against a hormone called growth hormone‑releasing factor (GRF‑1‑29). The vaccine made the animals produce fewer antibodies that block GRF, which led to lower levels of growth hormone, IGF‑1, and insulin, reduced feed intake and weight gain, more fat, and a later start of puberty.
Abstract
Angus and Charolais heifers (195 +/- 7 kg) were actively immunized against growth hormone-releasing factor (GRF) to evaluate the effect on concentrations of somatotropin (ST), insulin-like growth factor I (IGF-I), insulin (INS), growth, and onset of puberty. Primary immunizations were given at 184 +/- 7 d of age (d 0 of experiment) by injecting (s.c.) 1.5 mg of GRF-(1-29)-Gly-Gly-Cys-NH2 conjugated to 1.5 mg of human serum albumin (GRFi, n = 22) or 1.5 mg of human serum albumin (HSAi, n = 21). Booster immunizations of .5 mg of antigen were given on d 62, 92, 153, and 251. Antibody binding (percentage at 1:2,000 dilution) to [125I]GRF on d 69 was greater (P less than .01) in GRFi (53.7 +/- 4.5) than in HSAi (10.1 +/- .6) heifers. Serum concentration (ng/ml) and frequency (peaks/5 h) of ST release, respectively, on d 78 were lower (P less than .01) in GRFi than in HSAi heifers (3.3 +/- .1 vs 5.6 +/- .2 and .9 +/- .3 vs 2.3 +/- .2). Serum IGF-I (ng/ml) was lower (P less than .01) in GRFi than in HSAi heifers on d 69 (41 +/- 5 vs 112 +/- 4). Serum INS (microU/ml) on d 78 was lower (P less than .05) in GRFi (2.2 +/- .1) than in HSAi (3.8 +/- .2) heifers. Feed intake, ADG, and feed efficiency were lower (P less than .05) in GRFi than in HSAi heifers. Hip height was lower (P less than .01) and fat thickness was greater (P less than .05) in GRFi than in HSAi heifers by d 132 and 167, respectively. Percentage of heifers attaining puberty (progesterone greater than 1 ng/ml for two consecutive weeks) by d 209 and 379 (12.9 and 18.5 mo of age), respectively, was lower (P less than .05) in GRFi (40.9 and 45.5) than in HSAi (81.0 and 100). In conclusion, growing heifers were successively immunized against GRF. Active immunization against GRF resulted in decreased serum concentration of ST, IGF-I, and INS. In addition, GRF immunization led to lowered feed intake, ADG, and feed efficiency, increased fat depth, and delayed onset of puberty in heifers. We propose that ST and IGF-I are important metabolic mediators involved in the initiation of puberty in heifers.
Study Information
pubmed
1991
10.2527/1991.69124914x