Comparison of different patterns of exogenous growth hormone administration on milk production in Holstein cows

Bovine growth hormone (bGH) was administered by three different methods to four Holstein cows in late lactation (13.4 kg/d). Treatments were 1) a placebo treatment, 2) single daily sc injection of bGH, 3) pulse iv injection of bGH at 4-h intervals and 4) continuous sc infusion of bGH. The three bGH treatment groups all received the same quantity of bGH (51.5 IU/d). Daily plasma profiles of bGH consisted of 1) a relatively constant concentration of 6 ng/ml for the placebo group, 2) a single peak (48 ng/ml) followed by a steady decline, for the single injection treatment, 3) six transient peaks (57 to 72 ng/ml) 4 h apart for the pulse injection treatment and 4) a relatively constant elevation of bGH (26 ng/ml) for the continuous sc infusion treatment. Total amount of immunoreactive bGH measured in the plasma of the cows over 24 h was equal for the three bGH treatments. Increases in milk yield for the three bGH treatments did not differ and averaged 31%. Growth hormone treatment did not affect the percentage of milk fat or lactose, but resulted in a 10% decline in protein percentage. Dry matter intake declined an average of 9% and, coupled with increased milk yield resulted in a large increase in feed efficiency (47%). The similarity of the lactational responses to the three methods of administering bGH indicates that there is considerable flexibility in the method by which GH can be administered to dairy cows.