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An 8-hour hyperinsulinemic-euglycemic clamp is insufficient to alter milk production in lactating dairy cows.

S. I. Arriola Apelo



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An 8-hour hyperinsulinemic-euglycemic clamp is insufficient to alter milk production in lactating dairy cows.
V. L. Pszczolkowski1,2, H. Hu2, J. Zhang2,3, M. K. Connelly2, A. S. Munsterman4, S. I. Arriola Apelo*2,1. 1Endocrinology and Reproductive Physiology Graduate Training Program, University of Wisconsin-Madison Madison, WI, 2Department of Animal and Dairy Sciences, University of Wisconsin-Madison Madison, WI, 3Department of Animal Science, China Agricultural University Beijing, China, 4Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin-Madison Madison, WI.

The hyperinsulinemic-euglycemic clamp (IC) technique is an important tool to study energy metabolism in a variety of species. In dairy cattle, IC is usually performed continuously over several days, which can result in decreased intake. Since intake and insulin secretion are not naturally continuous in cows but rather follow a diurnal rhythm, our objective in this study was to test whether a single 8-h IC would be sufficient to observe milk production changes in response to IC and to insulin-responsive amino acids. Six second-lactation ruminally cannulated Holstein cows (155 � 9 DIM) were used in a 2 � 2 Latin square design (7-d periods). Cows were fed a 20% MP-restricted diet, and abomasally infused with water (8 L/d) or Met (26 g/d) plus Leu (70g/d, ML) dissolved in the same volume water. Abomasal infusions were administered for 8 h/d. On d 6, cows were fitted with jugular catheters. Feed intake and refusals were measured daily. On d 7, IC was performed as infusion of 1ug/kg/hr insulin, with euglycemia maintained by varying glucose (50%wt/vol in saline) infusion rate based on tail vein blood glucose concentration; saline (0.9% NaCl, SAL) was infused at same volume rate than insulin (110 mL/h). Milk samples were taken on d 7 p.m. Data were analyzed by 2-way ANOVA for main effects and interaction of AA and IV. Dry matter intake on d 7 was decreased by IC during the infusion period by 7 kg (P = 0.02), but this difference was recovered by post-IV intake (P = 0.45). Blood glucose was lower for IC by 8.2 mg/dL at 4 h, and the difference was maintained until the end of infusion (P = 0.03). Milk yield was numerically increased by IC (3 kg, P = 0.14), as was protein yield (60 g, P = 0.19), but fat was unaffected. Lactose yield was numerically higher for IC (P = 0.22), but percent was lower (P = 0.03). Amino acid infusion had no effect on any response except for increasing MUN (P = 0.07). Despite our preliminary data suggests that insulin mediates the effect of TOR-AA on milk production, 8 h IC seems insufficient to achieve that effect.

Keywords: insulin clamp, amino acids, milk production.