Seasonal variations in chemical composition and dry matter degradability of the forage consumed by goats in a highly deteriorated rangeland of North Mexico

The aim of this study was to determine the seasonal variations in chemical composition and dry matter (DM) degradability of the diet of grazing goats on a thorn scrubland in a semi-arid region of Durango, Mexico. Extrusa samples from four oesophageal fistulated goats (33) kg liveweight) were used. The samples were obtained two consecutive days each month from October 1992 to September, 1993. Approximately five g of sample DM were incubated in the rumen of three sheep fed alfalfa hay ad libitum (120 g/kg CP; 400 g/kg NDF) for 0, 3, 6, 12, 24, 48, 72 and 96 h. Degradability data were fitted to the model: P = a+b (1 - e(-ct)). Then, the immediately soluble fraction a, the insoluble but rumen degradable fraction b, the potential degradation a + b, the degradation rate c and the effective degradability (ED) were determined. The data were analyzed according to a completely randomized experimental design. Annual means of crude protein (CP), CP intake (CPI) and metabolisable energy intake (MEI) (90.0 g/kg, 47.8 g/d and 2.8 MJ/d, respectively), were insufficient to meet the maintenance requirements of goats. Degradation parameters differed between the studied seasons. Mean values for a, b and c were 41.0%, 45.1% and 2.7%/h, respectively and are considered low, whereas mean value for ED (63.5%) is moderate. Results indicated that the low values of CPI and MEI as well as the c fraction may negatively influence body condition and reproductive activity of the animals.