Effects of Treatment of Dairy Cows with Recombinant Bovine Somatotropin over Three or Four Lactations

¹ Research Institute for Animal Production ‘Schoonoord’ (IVO-DLO), PO Box 501, 3700 AM Zeist. The Netherlands
² Elanco Animal Health, Raadstede 15, 3431 HA Nieuwegein, The Netherlands
³ Lilly Industries Limited, Animal Health Registration Department, Dextra Court, Chapel Hill, Basingstoke, Hants RG 21 2SY, England

Jersey, Dutch Red and White, and Friesian cows were subcutaneously injected with 640 mg of recombinant bST at 28-d intervals from 87 to 115 d after calving through four successive lactations. A TMR (6.72 MJ of NE_L and 168 g of CP/kg of DM) was fed for ad libitum consumption. The bST effects per day were 3.3 kg for milk yield, 189 g for fat yield, 109 g for protein yield, 157 g for lactose yield, 4 MJ of NE_L for feed intake, and –4 kg for body weight. Responses in blood parameters measured 7 d after injection were –.007 ml for glucose, –1.3 mg of N/l00 ml for urea, 221 µmol/L for 3-hydroxybutyrate, 59 µmol/L for NEFA, 65 ng/L for insulin, 2.8 µg/L for thyroxine, and 26.7 µg/L for somatotropin. Somatic cell count in milk was 75,000 cells/ml higher in treated cows. Concentrations of NEFA, Ca, Mg, and phosphorus were unaffected. Repeatability of the maximum response in milk yield after bST treatment was low: .2 within and .5 between lactations. Cows treated in the previous lactation had slightly more retained placentas, and birth weight of their calves was 2 kg less. No differences were observed between treated and control cows in disease incidence. Six treated cows were culled in third and fourth lactations. No indications for tissue damage, inflammation, or stress after bST injections were detected.

Key Words: somatotropin • multiple lactation • metabolism

Submitted on May 14, 1992
Accepted on September 21, 1992

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