Effects of dry period energy intake on insulin resistance, metabolic adaptation, and production responses in transition dairy cows on grass silage-based diets.

High energy intake in the dry period has reportedly had adverse effects on mobilization of body reserves, dry matter intake, and productivity of dairy cows. We investigated whether grass silage (GS) fed ad libitum (high energy intake, HEI; 141% of daily metabolizable energy requirements) in an 8-wk dry period affects metabolic adaptation-specifically, peripheral insulin resistance-compared with a total mixed ration consisting of GS, wheat straw, and rapeseed meal (55/40/5%; controlled energy intake, CEI; 108% of metabolizable energy/d) fed ad libitum. Multiparous Ayrshire dairy cows (n = 16) were used in a randomized complete block design until 8 wk after parturition. Commercial concentrates were fed 1 and 2 kg/d during the last 10 to 6 and 5 to 0 d before the expected calving date, respectively. Postpartum, a similar lactation diet with ad libitum access to GS and increasing concentrate allowance (maximum of 16 kg/d) was offered to all. The HEI group gained more body weight and had higher plasma insulin, glucose, and β-hydroxybutyrate concentrations than the CEI group prepartum. Postpartal plasma glucose tended to be higher and milk yield was greater from wk 5 onward for HEI compared with CEI cows. An intravenous glucose tolerance test (IVGTT) was performed at -13 ± 5 d and 9 ± 1 d relative to calving. The HEI cows had greater insulin response to glucose load and smaller area under the response curve for glucose than CEI cows in prepartal IVGTT. Thus, compensatory insulin secretion adapted to changes in insulin sensitivity of the peripheral tissues, preserving glucose tolerance of HEI cows. Higher insulin levels were needed in HEI cows than in CEI cows to elicit a similar decrement of nonesterified fatty acid concentration in prepartal IVGTT, suggesting reduced inhibition of lipolysis by insulin in HEI cows before parturition. In conclusion, high energy intake of moderately digestible GS with low concentrate feeding in the close-up dry period did not have adverse effects on metabolic adaptation, insulin sensitivity, and body mobilization after parturition. Instead, this feeding regimen was more beneficial to early-lactation performance than GS-based total mixed ration diluted with wheat straw.