J.H. Burton

Somatotropin and insulin-like growth factor-I concentrations in plasma and milk after daily or sustained-release exogenous somatotropin administrations.

Effects of daily injectable or sustained-release bovine somatotropin (bST) administrations on plasma and milk bST and insulin-like growth factor-I (IGF-I) concentrations were monitored in 74 lactating cows through early, mid- and late lactation. Treatments beginning at wk 4 of lactation were excipient (CO, 24 cows) at 2 wk intervals, daily injections of 10.3 mg bST (DI, 25 cows) and 350 mg sustained-release bST at 2 wk intervals (SR, 25 cows). The duration of treatments was 40 wk. Data were first analyzed for the overall mean concentrations covering the 40 wk treatment period. Overall mean plasma bST, milk bST and plasma IGF-I concentrations were significantly increased by both bST treatments (p < 0.05). On the other hand, milk IGF-I concentrations were significantly increased (p < 0.05) only in the DI group. Next, data were analyzed according to stage of lactation. The bST treatments resulted in significant increases (p < 0.05) in plasma and milk bST concentrations for all early, mid- and late lactation periods. Even though plasma IGF-I concentrations were higher (p < 0.05) in all lactation periods for bST treatment groups, higher milk IGF-I concentrations (p < 0.05) occurred only in mid- and late lactation periods for the DI group. The patterns of bST and IGF-I concentrations in milk follows those of the plasma after bST treatments.

Function of bovine mammary macrophages as antigen-presenting cells

The ability of mammary macrophages treated with Staphylococcus aureus to induce antigen-specific T-cell proliferation was compared to that of the autologous blood monocytes. Induction of T-cell proliferation has been correlated with changes in major histocompatibility complex (MHC) class II antigen expression and interleukin 1 (IL-1) production by mammary macrophages and blood monocytes. The present study showed that both monocytes and mammary macrophages treated with S. aureus induced T-cell proliferation. However, there was a 3-fold decrease (P less than 0.05) in T-cell proliferation in macrophage cultures compared to those of blood monocytes, when these cells were treated with S. aureus. Mammary macrophages, the cells less effective in stimulating T-cell proliferation, expressed lower levels (2-fold) of MHC class II molecules and produced less IL-1 (3-fold) than blood monocytes. These data suggest that S. aureus may affect macrophage-T cell interaction by modulating the expression of MHC class II molecules and the synthesis of IL-1 by macrophages.

Effect of bovine somatotropin on the growth rate, hormone profiles and carcass composition of holstein bull calves

A study was conducted to determine the effects of BST on the growth rate, hormone profiles and carcass composition of preweaned Holstein bull calves. Injection of BST resulted in increased average daily gains and feed intakes (P less than .05) compared to that of control animals. This increased rate of gain coupled with increased intakes resulted in identical feed conversion efficiencies between treatments. Fractional weights (organ weight/body weight) of selected organs and tissues were unaffected by BST treatment. Carcass fat percentage was reduced in BST-treated calves (28.1 +/- 1.18% and 32.8 +/- 1.84% for BST and controls groups respectively, P less than .05) while no differences were seen for carcass DM, CP, ash or gross energy content. Plasma BST levels were higher (P less than .0001) in BST treated calves while plasma IGF-1 levels were not different between treatments. Plasma IGF-1 concentrations correlated (P less than .0001, R = .71) with average daily gains. The results of this trial suggest that growth responses are inducible with BST in young calves (7 days to 3 months).