Energy status, measured by computer tomography (CT)-scanning, and milk quality of dairy goats fed rations with various energy concentrations

The milk produced by Norwegian goats varies in quality with regard to level of free fatty acids (FFA) and sensory quality. The aim of this study was to relate the milk quality to the changes in the energy status of dairy goats during early and mid lactation when fed rations with various energy concentrations. Twelve goats of the Norwegian Dairy Breed were from lactation weeks 3 to 18 fed grass silages prepared from the primary growth at a very early or normal stage of maturity (harvesting times (HT) 1 and 3, respectively), supplemented with a low (LC: 0.6 kg daily) or normal (NC; 1.2 kg daily) level of concentrate. Energy status was estimated by changes in body composition measured by computer tomography (CT), calculated energy balance and blood parameters. Calculated increase in adipose tissue mass of the goats was highest for HT 1. During the first 18 weeks of lactation only the goats fed the lowest energy diet (HT 3 with LC) mobilized from the adipose tissue (in average 3.26 kg). The other goats deposited body fat throughout this period, and had low (<0.3 mmol/l) blood concentration of non-esterified fatty acids (NEFA). Calculated energy balance was positive throughout the indoor experiment for goats fed HT 1. Both net energy lactation (NEL) intake and milk yield increased with earlier stage of grass maturity and was positively correlated to daily gain in adipose tissue mass. Milk FFA tended to be higher (P = 0.09) for goats offered HT 1 (1.48 mEq/l) than HT 3 (0.99 mEq/l), but was not significantly affected by concentrate level. A high milk FFA concentration was correlated to a high NEL intake. The level of milk HA increased when the goats were let out on mountain pasture in lactation weeks 26-30. This study documents that it is possible to avoid fat mobilization in early lactation by feeding the goats high energy diets, based on high quality grass silage. However, a high plane of nutrition during early and mid lactation seemed to increase milk lipolysis. A high-energy diet offered indoors during the first 18 weeks of lactation did neither improve milk quality during the same period nor in the following mountain pasture period. (C) 2011 Elsevier B.V. All rights reserved.