Three experiments involving a total of 7 forages ranging in N content from 6.6 to 26.8 kg DM were conducted to examine comparative ad libitum digestible organic matter intake (DOMI) in goats and sheep. Digestibility trials were conducted for 7 to 10 d during each trail when water consumption and rumen NH3N concentration were also monitored. DOMI in goats was higher than in sheep with forages of less than 0.6 OM digestibility (OMD). The relationship between the DOMI (g/kgW0.75/d) of goats and sheep was described as DOMI (goats) = 0.74 DOMI (sheep) + 10.6. The ratio of DOMI (goats)/DOMI (sheep) was greater than 1.15 for forages of OMD less than 0.6 and close to 1 for forages of OMD greater than 0.6. Goats maintained higher rumen NH3N concentration (109 mg NH3N/l). Of the 5 forages with OMD<0.6, 2 resulted in rumen NH3N>50 mg NH3N/l, considered the critical level for microbial digestion. The other 3 forages resulted in rumen NH3N<50mg NH3N/l (15 to 41 mg NH3N/l) in sheep whilst goats were able to maintain higher concentrations (43 to 60 mg NH3N/l). The ability of goats to maintain higher rumen NH3N with low N diets was associated with their lower water intake. The mean water intake of goats and sheep was 1884 and 2795 ml/kg DMI, respectively. It is concluded that goats have a greater DOMI than do sheep particularly when offered forages with OMD<0.6 and of low N content partly because of their ability to maintain higher rumen NH3N concentrations.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 97-102, 1985
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