Individual variation in the milk yield response to bovine somatotropin in dairy cows.
The objective was to relate the short-term milk yield response (MYR) following use of exogenous bovine somatotropin (bST) to changes in plasma concentrations of metabolites and hormones. Twenty-four Holstein cows (52 +/- 4.1 d postpartum) received daily subcutaneous injections of saline for 1 wk followed by subcutaneous injections of 33 mg/d of bST for 2 wk (Trial 1). The difference in milk yield between wk 1 and 3 for each cow was used to determine the 5 cows with the highest (HR) and 5 with the lowest responses (LR) to bST. These 10 cows were then used in 3 further trials of the same design (Trials 2, 3, and 4, conducted at 122, 181, and 237 +/- 7.6 d postpartum, respectively). Blood samples were taken 2 h after the administration of bST on d 1, 3, 5, 15, 17, and 19 of each trial. The HR group had consistently greater MYR to bST than the LR group throughout their lactation. The LR group had a higher milk yield and lower plasma insulin like growth factor-I (IGF-I) concentrations during the saline treatment in all trials. The increase in plasma somatotropin concentrations following injections of bST was greater for the LR group, whereas the difference in plasma IGF-I level between wk 1 and 3 was greater for the HR group. The HR group had lower levels of 3-hydroxy-butyrate and nonesterified fatty acids before bST treatment. Low short-term response to bST was associated with plasma concentrations of hormones and metabolites that indicate negative energy balance, although other factors may be involved.
School of Agriculture, Food and Rural Development, University of Newcastle upon Tyne, NE1 7RU, United Kingdom. mir@aber.ac.uk
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D020155:3-Hydroxybutyric Acid / Q000097:blood; D000818:Animals; D001835:Body Weight / Q000187:drug effects; D002417:Cattle / Q000502:physiology*; D005230:Fatty Acids, Nonesterified / Q000097:blood; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage* / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis; D007700:Kinetics; D007774:Lactation / Q000187:drug effects*
D005230:Fatty Acids, Nonesterified; C073294:growth hormone, bovine; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D020155:3-Hydroxybutyric Acid