An evaluation of the use of blood metabolite concentrations as indicators of nutritional status in free-ranging indigenous goats

The aim of this study was to determine whether blood metabolite concentrati ons in free-ranging indigenous goats are sensitive to expected variations i n nutrient supply, and whether they could be used to evaluate different kid ding seasons at two locations subject to similar seasonal variations in ter ms of nutrient supply. Monthly blood samples were taken over a period of on e year. At Delftzyl farm, where a winter kidding season (June) was practise d, glucose concentrations decreased from Februrary onwards and reached thei r lowest levels just prior to the kidding season. Plasma glucose concentrat ions increased sharply after parturition and subsequently decreased until t he end of lactation. Glucose concentrations were lower in lactating does th an in non-lactating does during the first two months of lactation. In contr ast, glucose concentrations during lactation in does at Loskop farm, where kidding took place during spring (October), did not differ from those recor ded during the four months following weaning, and neither were there differ ences between lactating and non-lactating does. Glucose concentrations duri ng lactation at Loskop farm were also higher than at Delftzyl farm. The dif ferent responses can be attributed to the fact that lactation at Loskop far m coincided with peak nutrient availability during the summer period of veg etative growth, whereas lactation at Delftzyl farm coincided with low nutri ent availability and quality during the winter period of plant dormancy. Pl asma urea concentrations were also elevated during the last month of pregna ncy and the first two months of lactation at this location, and were higher during lactation than those recorded at the summer kidding site, indicatin g that body protein reserves may have been catabolized to support gluconeog enesis in these animals. Plasma cholesterol concentrations were higher in l actating goats than in non-lactating goats at Delftzyl farm but not at Losk op farm. Cholesterol concentrations during lactation were also higher at De lftzyl than at Loskop. This suggests that body adipose tissue reserves were catabolized during the winter lactation at Delftzyl farm. These results in dicate that lactating does at Delftzyl farm were unable to maintain glucose homeostasis during pregnancy and lactation without significant catabolism of body reserves, and suggests that the winter kidding practised there was inappropriate in relation to the available nutrient supply. It was conclude d that the plasma concentrations of all the blood metabolites studied were sensitive to seasonal changes in nutrient supply, and that they could be of use as a management tool in free-ranging farming systems in which conventi onal methods of nutritional assessment are difficult to apply.