Changes in body reserves and milk quality throughout lactation in dairy goats

Abstract

Due to variations in the flavour of Norwegian goat milk, it has been difficult to develop new goat milk products with constant flavour characteristics. In particular, rancid and tart flavour is a challenge for the dairy industry. Milk produced during periods when goats experience a negative energy balance tends to have low dry matter content and a high frequency of rancid and tart flavour. In the present experiment the energy status of goats was examined throughout lactation by studying changes in body composition and blood parameters. The experiment included twelve goats of the Norwegian Dairy Breed, studied from kidding until 7 months of lactation. The goats grazed cultivated lowland pasture during spring and autumn, and mountain pasture for 9 weeks in summer. Milk and blood samples were collected on days 11, 60, 74,125,145 and 199 of lactation and connected to estimation of body composition by means of computer tomography. From day 11 until day 125 of lactation, energy supply from the pasture was insufficient, and adipose tissue mass decreased by 3.5 kg in average. Plasma concentrations of non-esterified fatty acids (NEFA) and acetoacetate were elevated. Likewise, the concentration of free fatty acids (FFA) in milk increased, as did the relative proportion of C18 acids. The goats started to produce milk of inferior quality (FFA > 2.0 mmol/l) around day 74 of lactation, when approximately 40% of their prepartum adipose tissue mass was mobilized. After three weeks with lowland grazing in the autumn, the goats deposited body fat again and the concentration of free fatty acids in milk was lowered. The situation improved further during the following 8 weeks on indoor feeding as fat accretion continued.