Effect of physiological state of grazing goats on dietary intake and composition in an arid rangeland of Mendoza, Argentina

EGEA, V.; PAEZ LAMA, S.; FUCILI, M.; BAKKER, M.L.; GRILLI, D.; PASSERA, C.; ALLEGRETTI, L.

Gran Canaria

Conferencia; XI INTERNATIONAL CONFERENCE ON GOATS; 2012

International Goat Asociation

Total intake, botanical composition and nutritional quality of diet of grazing goats in different physiological states were assessed in the wet season (summer). In a desert rangeland in the northeast of Mendoza, twelve Criollo goats, six lactating and six dry, were gun-dosed a controlled-release capsule containing n-dotriacontane (C32) and n-hexatriacontane (C36) with a nominal release rate of 50 mg day-1 (CAPTEC Ltd, Auckland, NZ). Samples of faeces were collected from the rectum daily on days 5 to 10 after dosing. Forage diet components (grasses, shrubs and trees, n: 15), identified from previous studies, were sampled. Forage and faeces samples were analysed for n-alkanes by gas chromatography. Goat diet composition was estimated from the n-alkanes pattern in forage species and faeces. Total dry matter intake (DMI, g day-1) was computed from the estimated C32 dose and the n-alkanes contents in the diet and faeces. Plant samples were analysed for crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF) and total tannins (TT). One-way ANOVA and Tukey’s multiple comparison tests were used to detect differences in diet composition, total forage and nutrient intake between animal groups. All n-alkanes from C23 to C35 were measurable in the plant samples. Diet was composed mainly of shrubs and trees (80 %), followed by grasses (20%), in all goats. Lactating goats consumed lower (P < 0.05) proportion of shrubs and more grasses and trees (69:21:10) than dry goats (85:14:1). Panicum urvilleanum was the most abundant grass (2-39 %), and Tricomaria usillo, Mimosa ephedroides, Lycium spp., Capparis atamisquea and Prosopis flexuosa were the most important woody species. Total forage intake was 63 % higher (P < 0.05) in lactating (2439 ± 846 g DMI day-1) than dry goats (1491 ± 468). Considering only the primary forage species in the diet, CP intake were 217 and 83.4 g d -1 for lactating and dry goats respectively (P < 0.05), there were no differences between groups of goats for NDF, ADF and TT intake. These results show that lactating and dry goats grazing on desert rangeland selected similar species, but in different proportions and the forages selected by both groups of goats were appropriate to meet their CP requirement. These findings suggest that goats are able to modify their dietary intake and composition according to their physiological state.