Abstract
As other ruminants, buffaloes utilize micro-organisms in the rumen to digest the feed. In buffaloes a higher rumen degradability of nitrogen and carbohydrates in concentrates promotes the growth and the synthesis of rumen bacteria, even when fed diets with low protein content. It appears that buffaloes use more efficiently nitrogen coming out from rumen fermentation and metabolism and by recycling it. This efficient accommodation to more limiting feeding condition is enhanced by a higher availability of purine derivatives (PD) of metabolic origin. Many measurements done on buffaloes of various breeds have shown a lower PD nitrogen excretion in urine. In buffaloes, urinary PD excretion is not linked to i) the availability of microbial cells in the rumen or ii) small intestine uptake of purines. Such PD excretion seems to be related more to tissue metabolism differences of which the mechanisms are not yet fully understood. Some explanation is emerging with new studies on swamp buffaloes, summarized in the following two: i) in the first study, weaning of swamp buffalo and cattle calves was accomplished by colostrum administration, and rearing followed by milk bottle feeding. To assess differences in the endogenous secretion of purines, urine samples from the two species were collected. Solid food was not made available in the course of the first month, but access to it was granted in the course of the intervening 2 successive months in order to stimulate rumen development. Then a mixed ration of purines and milk was given to the animals, together with an infusion of intravenous allantoin, so that the effect of the introduced purines in the plasma could be tested. From the results obtained in the course of the suckling period, no differences between the two species in purine excretion was reported. Following rumen development though, purine excretion from buffaloes was less than half when compared to cattle, and likewise, following allantoin infusion, purine recovery in buffaloes was half the amount when compared to cattle ; ii) in the second study in the course of fasting and bottle milk feeding, a determination of urinary PD, basal PD excretion and glomerular filtrate (GFR) rate was made. Following access of the animals to solid feed, an assessment of urinary PD, basal PF excretion and glomerular filtrate rate was also performed. No significant differences were observed between the two species in the course of the milk feeding period in terms of urinary PD excretion, although the same differences were highly significant between the two species at 3 months of age and following 2 months of access to solid feed. In buffaloes, both during the milk feeding and following solid food access, GFR was found lower in buffaloes when compared to cattle. To date it can be stated that some studies report a higher rumen fluid NH3 concentrate in swamp buffaloes in comparison to yellow cattle. Other studies have shown that only following rumen development, a difference in PD excretion can be seen, and the difference between buffaloes and cattle is due to differences in GFR, so that more urea and PD are recycled, highlighting the fact that buffaloes can tolerate less N in the feed to satisfy microbial needs.
Keywords: Buffaloes, Feeding, GFR, Microbial protein, Purine derivative, Rumen, Rumen NH3
