Efficiency of microbial protein production in cattle grazing tropical pastures

Abstract

Microbial protein (MCP) provides a significant proportion of the total protein supply to the ruminant. Some reports indicate low efficiencies of microbial protein production ( eMCP) in ruminants consuming tropical forages. Thus this research determined eMCP in cattle grazing a range of tropical pasture types over varying seasonal conditions and examined strategies to increase eMCP under these conditions.

A method was developed to estimate MCP production in grazing ruminants by using purine derivative (PD) concentration in urine and intravenously administered markers to estimate total urine output. In Experiment 4.1, five Friesian (Bos taurus) and five high-grade Brahman (> 75 % B. indicus) steers were fasted for 7 d in metabolism crates to determine the endogenous excretion of PD in the urine. The excretion of endogenous PD in urine of high-content B. indicus steers (190 µmol/kg w0·75) was ca. half that for B. taurus steers ( 414 µmol/kg w0·75) indicating the need to adjust the equation proposed by Chen & Gomes (1995) to estimate MCP production, when B. indicus cattle are used. In Experiments 5 .1 and 5 .2, when Cr EDT A was continually infused intravenously, Cr recovery in urine of steers was relatively constant over time and with varying diet quality (ca. 90 %) indicating its suitability as a urine output marker. In contrast, intravenously infused lithium sulphate was unsuitable, as urinary recovery of Li was variable and was influenced by feed quality and duration of infusion.