Use of recombinant bovine somatotropin for up to two consecutive lactations on dairy production traits.
Fifteen (control) cows were injected with saline; 28 cows were treated with rbST (15 with 10.3 and 13 with 20.6 mg/d). Fourteen of the 28 treated cows had between injected with rbST in the previous lactation. A total of 29 cows in the present trial had not received rbST in previous lactation. Treatment injections were started between wk 4 and 5 of lactation and continued for 266 consecutive days. Milk production, fee intake and efficiency, and BW data were recorded for 3 wk before and 3 wk after a 38-wk rbST treatment period. Administration of rbST increased average FCM yields in the current lactation by 19%, increased feed energy intake by 7%, and decreased feed conversion (energy intake per unit FCM output) by 17%. Previous treatment with rbST did not significantly affect current milk production but caused a nonsignificant increase in feed intake and a significant, unfavorable, increase in feed conversion of 12%. The results suggest that the advantages of rbST in terms of increased milk yield are maintained for a second consecutive lactation of rbST administration. However, the advantages of rbST in terms of improved feed conversion may be substantially reduced in a second consecutive lactation of administration.
McBride
B W
BW
Department of Animal and Poultry Science, University of Guelph, Ontario, Canada.
Burton
J L
JL
Gibson
J P
JP
Burton
J H
JH
Eggert
R G
RG
D000818:Animals; D002417:Cattle / Q000502:physiology*; D004435:Eating; D005260:Female; D013006:Growth Hormone / Q000008:administration & dosage*; D007774:Lactation; D011994:Recombinant Proteins / Q000008:administration & dosage
D011994:Recombinant Proteins; D013006:Growth Hormone