Insulin-like growth factor I (somatomedin C) in goats during normal lactation and in response to somatotropin treatment.
1. Two experiments were performed. In Experiment 1, IGF-I concentrations in serum were followed in four lactating dairy goats during normal lactation and before, during and after 14 days of daily administration of 10 IU recombinant bovine somatotropin, starting 10 weeks post-partum. In Experiment 2, IGF-I was measured in single blood samples obtained from 40 dairy goats in the first part of lactation. 2. Measured IGF-I concentrations ranged from 4.4-9.0 nM. Concentrations varied during the day with coefficients of variation from 8.9 to 18.4% in the four goats in Experiment 1. There were no systematic trends in the diurnal variations (P greater than 0.75). 3. Concentrations of IGF-I remained fairly constant in all goats in Experiment 1 during the lactational period, and were not related to the changes in milk yield (P greater than 0.65). Similarly, no relationship was found in Experiment 2 between level of milk production and IGF-I concentration in serum. 4. Somatotropin treatment stimulated milk yields by 14 +/- 2.9% (P less than 0.05) and IGF-I concentration by 27.9 +/- 6.7% (P less than 0.05). 5. IGF-I is the most likely factor which increases mammary gland synthetic capacity in response to somatotropin treatment, and thus is responsible for the galactopoietic effect of this hormone being exerted. 6. However, serum IGF-I may primarily be involved in regulation of nutrient partitioning during normal lactation, but a paracrine synthesis with local effect on the mammary gland cannot be ruled out.
Nielsen
M O
MO
Department of Animal Physiology and Biochemistry, Royal Veterinary and Agricultural University, Frederiksberg, Denmark.
Skakkebaek
N E
NE
Giwercman
A
A
D000818:Animals; D005260:Female; D006041:Goats / Q000097:blood*; D013006:Growth Hormone / Q000494:pharmacology*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000502:physiology*; D007774:Lactation / Q000097:blood / Q000187:drug effects / Q000502:physiology*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D011247:Pregnancy; D013002:Somatomedins / Q000502:physiology*
D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone