Influence of forage: concentrate ratio and type of starch in the diet on feeding behaviour, dietary preferences, digestion, metabolism and performance of dairy goats in mid lactation

In a 12-week trial, 12 Alpine and 12 Saanen dairy goats in mid lactation we re housed in individual stalls for behavioural, digestive and metabolic stu dies. Eight of them were fitted with ruminal cannulae. They were offered ad libitum four complete diets CA, CS, FX and FS (450 g dry matter (DM) per k g) in a 4 X 4 Latin-square design. Forage: concentrate ratio was either low (C = 30:70) or high (F = 55:45) and starch source either rapidly (R, barle y) or slowly (S, maize) degraded in the rumen. Diet preferences were tested. DM intake, chewing activities and performance were determined. Ruminal pH and ammonia-nitrogen (NH3-N) concentrations we re measured. Goats were also challenged intravenously with glucose (0.2 g/k g live weight) to assess glucose homeostasis. CX was the most preferred diet. The level of intake differed according to t he type of starch (2.2 kg DM per day of CR and FR and 2.0 kg DM per day of CS and FS). FS lowered ruminal pH significantly less than the other diets a fter the meal. Ruminal NH3-N concentrations were lower in goats given CR an d CS than FR and FS. Goats' resistance to a glucose challenge was not diffe rent among diets. Milk yield was 2.00, 1.85, 2.01, 1.85 kg/day on CR, CS, F R and FS respectively. Milk fat content decreased significantly with diets rich in concentrate (24 v. 26 g/kg milk) but milk protein content varied on ly a little. In conclusion it appears that (1) higher forage: concentrate ratios were le ss preferred and decreased ruminal acidity but increased daily chewing, rum inal NH3-N and milk fat content; and (2) rapidly degraded starch increased intake, ruminal acidity and milk yield.