Abstract
Two experiments (Exp1 and Exp2) were conducted to investigate the effect of dietary inclusion of Zn and(or) monensin on performance and rumen fermentation in beef cattle fed a barley grain, alfalfa hay and sunflower meal. In Exp1, 20 calves were assigned to one of the following treatments: CON = control; Z = 430 mg Zn/kg of DM; M = 35 mg monensin/kg of DM; and ZM = both Zn and monensin. Dry matter intake (DMI), DM digestibility (DMD), average daily gain (ADG), and feed to gain (F/G) ratio were determined. Blood analyses included hematocrit, glucose, urea, total protein, alkaline phosphatase and creatinine. In Exp2, the rumen fluid of four cannulated steers, in identical treatments, was studied for Zn concentration, pH, NH3-N, VFA. Rumen dilution rate, turnover time, and volume; in situ DM disappearance of barley and alfalfa were also determined. In Exp1, no treatment response was observed for DMI, ADG or DMD (P > 0.10). Differences in F/G were not significant, despite a numeric F/G decrease in M (6.6 kg/kg). No differences were detected in blood variables. In Exp2, an interaction of treatment x time (P = 0.0174) for Zn concentration was detected, where ZM, followed by Z, had highest mean values at all time intervals. Ruminal parameters, kinetics or DM degradability were not modified by treatments; pH reached the lowest value (6.1; P < 0.05) 12 h after supplement feeding. Overall, supplying more than 20 times the Zn requirement has not substantially affected performance or digestion.
Highlights
Increased rumen fermentation efficiency leads to improved animal performance
For example, increases rumen propionate production while decreasing methane production and protein degradation, which results in improved energy metabolism and protein utilization (Callaway et al, 2003)
Previous research indicated that dietary addition of 250 to 400 mg Zn kg-1 DM to low-quality forage altered rumen fermentation by retarding ammonia accumulation and increasing molar proportions of propionate (Arelovich et al, 2000)
Summary
Increased rumen fermentation efficiency leads to improved animal performance. To promote this biological response, scientists have made numerous attempts to manipulate rumen fermentation by the dietary addition of a large variety of feed additives. For example, increases rumen propionate production while decreasing methane production and protein degradation, which results in improved energy metabolism and protein utilization (Callaway et al, 2003). Several other additives that could be used to manipulate fermentation of dietary substrates by rumen microbes are currently under study. Previous research indicated that dietary addition of 250 to 400 mg Zn kg-1 DM to low-quality forage altered rumen fermentation by retarding ammonia accumulation and increasing molar proportions of propionate (Arelovich et al, 2000). It was shown that when administered at over 20 times the daily NRC (2000) requirement, Zn could increase the concentration of rumen propionate (Arelovich et al, 2000) and decrease the acetate:propionate ratio (Bateman II et al, 2004)
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