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1 Department of Animal Science, Michigan State University, East Lansing 48824
2 Animal Science Department, University of Maryland, College Park 20742
3 Department of Animal Science, Cornell University, Ithaca, NY 14853
4 Animal, Dairy, and Veterinary Science Department, Utah State University, Logan 84322
5 Department of Clinical and Population Sciences, University of Minnesota, St. Paul
6 Monsanto Agriculture Company, St. Louis, MO 63167
Cows (890) in 15 US herds were assigned randomly in equal numbers to control or bST injections (500 mg in a prolonged-release form every 14 d for 12 wk) within three stages of lactation (57 to 100, 101 to 140, and 141 to 189 d postpartum) and two parity groups (primiparous and multiparous). Yield and milk composition were monitored 1 d/wk for 16 wk including 2 wk pretreatment and 2 wk posttreatment. Increases in milk and FCM due to bST injections were less at 57 to 100 d than at 101 to 189 d postpartum (milk 3.6 vs. 5.5; FCM 3.9 vs. 6.1 kg/d per cow), and increases in milk and FCM were more for multiparous than for primiparous cows (milk 5.5 vs. 4.2; FCM 6.0 vs. 4.7 kg/d cow). Temporarily, concentration of milk fat increased and protein decreased; later, concentrations for control and injected cows were similar. Postinjection milk fat concentration decreased, but milk protein concentration increased temporarily. The net increase in milk (and FCM) varied significantly among herds from 2.9 to 7.6 kg/d per cow (mean, 4.9 kg). Responses in FCM were similar over a wide range of pretreatment yields. A great variety of feed ingredients were fed as total mixed rations, and nutrient concentrations varied greatly. The SCC were similar b6efore, during, and after treatment, but increase in FCM of injected cows exhibited a negative correlation with pretreatment SCC. Changes in body condition score of sometribove-injected cows varied among herds (25 to –.45) and averaged –.02 compared with .07 for controls. There was no pattern in incidence of mastitis during sometribove injections.
Key Words: somatotropin • lactating cows • commercial dairies
Submitted on April 19, 1990
Accepted on August 3, 1990
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