The influence of replacing slow with rapid starch in growing rams’ diets on the level of rumen microbial proteosynthesis

The objective of the study was to estimate the level of microbial proteosynthesis in sheep, following the replacement of a classical ingredient (corn) with a rapidly fermentable energy source (barley), when protein ingredient of the compound feed is highly degradable (rapeseed meal).The diets were tested on two groups of four Merinos rams each, weighing 50-55 kilos. Regular procedure for in vivo digestibility tests was used and urine was collected for determination of purine derivatives concentrations. The consumption of the two diets led to similar nutritional supplies: 1.26-1.29 MFU, 124-129 g IDPN, 112-118 g IDPE; the groups being distinguish only in terms of the dynamics of energy availability at the ruminal level. The amount of purine derivatives excreted in urine were 12.58 mmols/day in the corn group and 9.49 mmols/day in the barley group; consequently, the rumen microbial proteosynthesis was estimated at 43.11 g IDMP/day for the corn group and 31.3 g IDMP/day for the barley group (P=0,396). It is concluded that the effect of synchronizing the energy and protein dynamics in barley group was counteracted by the fact that energy and protein availability were limited to the first hours after administration of the compound feed, when the capacity of the ruminal microorganisms to grow was probably exceeded. In order to maximize their growth potential, it is necessary to extend the period of synchronized ruminal availability of energy and protein.