Effect of different molar proportions of isoenergetic volatile fatty acids on the nitrogen retention of lambs sustained by total intragastric infusions

Two experiments were carried out to study the effects of intraruminal infusions of acetic, propionic or butyric acid and mixtures of these acids with different molar proportions on nitrogen (N) retention in lambs. In Experiment I, 12 lambs (liveweight 21.7±0.4 kg), fitted with rumen and abomasum cannulas and nourished by total intragastric infusions, were allocated into three groups and intraruminally infused with isoenergetic amounts of acetic, propionic or butyric acid, as Treatments I, II and III, respectively. In Experiment II, twelve lambs (liveweight 24.9±0.4 kg), fitted with rumen and abomasum cannulas and also nourished by intragastric infusions, were allocated into four groups and intraruminally infused with isoenergetic mixtures of acetic, propionic and butyric acid with molar proportions of 10:78:12, 27:65:8, 49:47:4 and 60:38:2, as Treatments I, II, III and IV, respectively. Both energy and N supplied to the lambs in Experiments I and II were kept at the level of 1.2 times of maintenance requirement. The results indicated that no significant difference was found in the N digestibility, N retention or N retention rate of the lambs between different treatments either in Experiment I (P>0.05) or in Experiment II (P>0.05). It was concluded that the N retention of the 4 month old lambs was unchanged by different molar proportions of isoenergetic amount of acetic, propionic or butyric acid and the mixtures of these acids with different molar proportions when both energy and N supply were kept at the level of 1.2 times of maintenance requirement. Further research with higher levels of energy and protein supply, lambs with different age and more lambs for treatments is needed to verify these findings.