The objective of this trial was to study the effects of recombinant bovine somatotropin on milk yield and composition, blood metabolites and hormonal profile in lactating goats. Twenty-four Toggenburg goats were assigned to one of two treatments as follows: T1 (n=12) received injection of 250 mg of r-bST, every 14 days (four injections), and T2 (n=12) received injections of saline solution (control). No significant differences on milk yield and composition (fat, protein, and dry extract) were observed comparing r-bST-treated goats with non-treated animals. However, milk lactose content was higher (P<0.05) on goats that received r-bST (4.47 ± 0.2) than on those treated with saline solution (4.34 ± 0.2 %) while somatic cells count was lower on T1 (681.1 ± 689.9) than on T2 [(1,001.84 ± 610.9 (x103 cells/mL)]. Injection r-bST increased the concentration of non-esterified fatty acid compared to the saline-treated animals (309.67 ± 169.62 vs. 247.34 ± 126.38 mEq/L) but the opposite was observed for urea concentration (86.84 ± 33.81 vs. 121.16 ± 42.57 mg/dL). The r-bST treatment reduced the total cholesterol and HDL levels (82.46 ± 19.25 vs. 89.29 ± 23.66 and 155.95 ± 19.67 x 177.67 ± 32.79 mg/dL for T1 and T2, respectively) in lactating goats. Concentrations of albumin, glucose, total proteins, beta-hidroxybutirate and thyroxin as well as body weight and body condition score all remained unchanged comparing both treatments. It can be concluded that r-bST increased milk lactose content, reduced somatic cells count, and changed the profile of blood metabolites of Toggenburg goats.
goat; lactation; metabolite; milk composition; thyroxin
