No abstract

Bovine growth hormone (51.5 IU/day) and placebo injections were administered for 10 days to four Holstein cows in early lactation (wk 12) and again in late lactation (wk 35). Milk productions in the last 5 days of each period were compared. In early lactation, growth hormone increased milk yield by 15%, fat yield by 17%, protein yield by 14%, and lactose yield by 21%. In late lactation the respective increases were 31, 42, 18, and 35%. For responses of early and late lactation to growth hormone on a quantitative basis, increases for milk yield (4.3 versus 3.9 kg/day) and milk energy secretion (3.3 versus 3.4 Mcal/day) were similar. Concurrent with these increased milk yields, ad libitum intakes of a complete mixed diet declined during the period of growth hormone treatment by 3% in early lactation and 16% in late lactation. During the 6 h immediately following injections of growth hormone, blood plasma concentrations of growth hormone were elevated about 400% in early lactation and 700% in late lactation. Concentrations in plasma of free fatty acids were also higher during growth hormone treatment in late lactation but not in early lactation. Treatments did not affect plasma concentrations of glucose, insulin, glucagon, prolactin, tri-iodothyronine, thyroxine, or cortisol in either early or late lactation. Daily administration of growth hormone in early or late lactation resulted in similar and substantial increases of milk yield and efficiency of milk production.

Changes in blood metabolites and milk production were measured in eight cows with subclinical or clinical ketosis following treatment with daily doses of 12 g nicotinic acid fed with the concentrate mixture. Ketotic cows displayed a positive milk ketone test, reduced milk production and feed intake, hypoglycemia, hyperketonemia, and elevated free fatty acids in plasma. The milk ketone test was negative in all cows 5 to 9 days following initiation of treatment. After 7 days of treatment, milk production and glucose in plasma were increased while there were decreases in plasma beta-hydroxybutyrate and free fatty acids. No relapses occurred.

Milk production responses to 1) growth hormone injections (51.5 IU/day), 2) a mixture of glucose (274 g/day) and sodium caseinate (441 g/day) infused into the abomasum, 3) a combination treatment, and 4) a placebo treatment were determined in 4 cows in a 4 x 4 Latin square design. Treatment periods were 10 days, and production responses were based on the last 5 days of each treatment. Growth hormone administration increased milk yield 15.2% without changing milk composition or feed intake. Infusions of glucose-sodium caseinate into the abomasum increased milk yield 3.9% and milk protein yield 6.4% but when combined with growth hormone treatment did not stimulate a greater response than observed for growth hormone alone. Plasma concentrations of growth hormone were increased 4-fold with growth hormone injections but were not affected by the infusion of glucose-sodium caseinate into the abomasum. There were no significant changes in plasma concentrations of glucose, free fatty acids, insulin, glucagon, prolactin, triiodothyronine, thyroxine or cortisol with any of the treatments. Growth hormone increased milk synthesis and the efficiency of milk production, but its effect was not enhanced by the postruminal supply of additional nutrients.

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.