Injection of Synthetic Human Growth Hormone-Releasing Factors in Dairy Cows. 1. Effect on Feed Intake and Milk Yield and Composition

In a first experiment, 21 cows (98 d in lactation, 609 kg BW) were randomly used to determine the dose-response release of growth hormone (GH) to [desamino-Tyr1, D-Ala2, Ala15] growth hormone-releasing factor (1–29)NH2 analog (GRF-A; 0, 0.12, 0.37, 1.11 and 3.33 μg kg−1 BW) or to human growth hormone-releasing factor (1–29)NH2 (GRF; 3.33 and 10.00 μg kg−1 BW) after s.c. administration. The interaction (P < 0.01) between the two releasing factors and the doses on GH concentrations indicated that the analog was more potent than the original molecule; at the 3.33 μg kg−1 BW dose, the analog elicited a 3.5 times higher GH response than GRF. In a second experiment, the effects of daily s.c. injections for 10 d of either saline, GRF (10 μg kg−1 BW) or GRF-A (0.6 or 1.8 μg kg−1 BW) on GH concentrations and lactational performance were determined using 32 cows (n = 8 per treatment) averaging 91 d in lactation and subjected to a random block design. The three releasing factor treatments similarly increased GH concentrations measured during the 8 h following the injection on d 1 and 10. GRF at the dose of 10 μg kg−1 BW and the analog at the doses of 0.6 and 1.8 μg kg−1 BW increased milk yield by 9.6, 11.7 and 17.6%, respectively, when compared to the control; both releasing factors had no effect on milk composition. Insulin-like growth factor I concentrations were increased 8 h after the last injection, from 73.4 ng mL−1 in control cows to an average of 107.6 ng mL−1 in treated cows. Results show that the [desamino-Tyr1, D-Ala2, Ala15] human growth hormone-releasing factor (1–29)NH2 analog is more potent than human growth hormone-releasing factor (1–29)NH2 in stimulating GH release and milk production in dairy cows. Key words: Growth hormone-releasing factor, analog, growth hormone, milk production, insulin-like growth factor 1, cows (dairy)

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EFFECT OF TWO-MONTH TREATMENT WITH GROWTH HORMONE-RELEASING FACTOR ON MILK PRODUCTION AND PLASMA CONSTITUENTS IN DAIRY COWS

Canadian Journal of Animal Science ◽

10.4141/cjas88-083 ◽

1988 ◽

Vol 68 (3) ◽

pp. 741-749 ◽

Cited By ~ 4

Author(s):

H. LAPIERRE ◽

G. PELLETIER ◽

D. PETITCLERC ◽

P. DUBREUIL ◽

J. MORISSET ◽

...

Keyword(s):

Growth Hormone ◽

Dairy Cows ◽

Milk Production ◽

Milk Yield ◽

Feed Intake ◽

Human Growth ◽

Milk Composition ◽

Daily Injection ◽

Growth Hormone Releasing Factor ◽

Long Term Treatment

Seventeen dairy cows averaging 252 d of lactation were used to study the effect of long-term treatment with a human growth hormone-releasing factor (hGRF(1–29)NH2) on lactational performance and concentration of plasma constituents. For 57 d, the cows received a daily subcutaneous injection of either saline (S, n = 8) or 10 μg kg−1 BW of hGRF(1–29)NH2 (GRF, n = 9). Milk production and feed intake were recorded daily, while milk composition was determined weekly. Treatment with GRF increased 4% fat-corrected milk yield (13.9 vs. 15.8 kg d−1), and fat yield, (0.58 vs. 0.66 kg d−1). It did not affect protein yield (0.46 vs. 0.52 kg d−1), or feed intake (17.2 vs. 17.8 kg d−1) (means of the 57 d of treatment, S vs. GRF). The GRF-treated cows gained more weight than the control cows, 5.5 vs. 4.2%, respectively. Blood samples were collected hourly, from 2 h before to 8 h after the daily injection on d 1, 15, 29, 43 and 57, to determine plasma constituent concentrations. GRF treatment decreased calcium and cholesterol concentrations, but increased free fatty acids concentration. All constituents measured remained within the normal range. The weights of the cows and their calves and milk yield (14 first wk postpartum) at the subsequent lactation were not affected by previous GRF treatment. In conclusion, treatment with GRF during the last 2 mo of lactation increased milk production and altered levels of some plasma constituents without any detrimental effect on the subsequent lactation. Key words: Growth hormone-releasing factor, milk production, plasma constituents, cows (dairy)

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THE MAINTENANCE OF LACTATION IN THE RABBIT AFTER HYPOPHYSECTOMY

Journal of Endocrinology ◽

10.1677/joe.0.0430651 ◽

1969 ◽

Vol 43 (4) ◽

pp. 651-662 ◽

Cited By ~ 42

Author(s):

A. T. COWIE ◽

P. E. HARTMANN ◽

A. TURVEY

Keyword(s):

Growth Hormone ◽

Immune Responses ◽

Milk Yield ◽

Human Growth Hormone ◽

Synergistic Effects ◽

Human Growth ◽

Milk Composition ◽

Bovine Growth Hormone ◽

Partial Recovery ◽

Milk Secretion

SUMMARY Twenty-one rabbits were hypophysectomized during the second week of lactation. Hypophysectomy inhibited milk secretion within 3–7 days. Restoration of the milk yield to pre-operative levels was obtained when daily injections of either sheep prolactin (50 or 100 i.u.) or human growth hormone (HGH) (2·5 or 5 mg.) were administered; partial recovery of the milk yield was obtained with 25 i.u. sheep prolactin/day or 1·25 mg. HGH/day. Neither bovine growth hormone (BGH), adrenocorticotrophin (ACTH) nor cortisol acetate had any significant restorative effects on milk secretion or synergistic effects when combined with sheep prolactin or HGH. The probable development of immune responses to sheep prolactin and HGH was observed. After hypophysectomy, changes in milk composition were found which were similar in trend to the more gradual normal changes observed in late lactation. Sheep prolactin and HGH restored the composition of the milk as well as the yields to normal levels, and both hormones caused rapid increases in lactose yields. The pigeon crop-stimulating potency of the HGH preparation was low (equivalent to 3·7 i.u. sheep prolactin/mg.), yet its lactogenic and galactopoietic potencies were high thus emphasizing the unreliability of assessing the mammotrophic potencies of HGH preparations in birds.

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