Interpretive Summary: Effects of concentrate input on nutrient utilization and methane emissions of two breeds of ewe lambs fed fresh ryegrass
By: Jackie Walling
Over 50% of nutritional requirements in sheep can be met by grass depending on variation and quality available. An article published in the January 2019 Issue of Translation Animal Science evaluates if high-quality ryegrass fed to two breeds of ewe lambs can sustain high feed efficiency comparable to diets with concentrate supplementation. Concentrate increases dry matter (DM) intake and nutrient digestibility, but decreases N losses ultimately optimizing rumen microbial activity.
16 three-month-old ewe lambs were designated to a 2x2 factorial study with four lambs per treatment. Two breeds, Highlanders and Texel, were fed two diets: only fresh perennial ryegrass and fresh perennial ryegrass with .5kg/d concentrate. All lambs were individually housed and adapted to diet for 19 days before moved to climate-controlled respiration chambers for five days. Nutrient digestibility and methane emissions were measured the last four days. Feed intake, forage samples (determined DM), and feces and urine samples (determined N, gross energy, and neutral dietary fiber (NDF) concentrations) were collected regularly.
For nutrition intake and digestibility by breed, Highlander ewes had higher intake capacity than Texel ewes. By diet, grass with concentrates was slightly higher in DM and organic matter intake than grass only though concentrates reduced grass intake. For energy utilization, grass with concentrates was only slightly higher in values than only grass. A significant difference in enteric methane emissions was only seen in Highlanders according to methane per body weight. Breed had no effects on N utilization, but grass with concentrates had higher N intake and excretion in feces and urine. N outputs expressed as proportion of N intake were not affected. A high concentrate substitution rate was calculated at .56kg/kg likely due to the high-quality forage used.
NDF was similar in diets and key to determining intake and digestibility resulting in no significant differences. Methane emissions were determined by feed intake and an increase in NDF increased emissions. The concentrate diets increased DM intake, but reduced NDF concentration (concentrates reduce grass intake) resulting in no effects on methane production, but total emission levels were still higher than grass only diets. Emissions as a proportion of DM or gross energy intake were unaffected because of the low .5kg/d concentrate level. N utilization efficiency can be manipulated by diet. N intake directly relates to manure excretion. Concentrates could improve N utilization helping microbial protein synthesis shift N excretion from urine to feces, but the concentrate level in this study was too low to make a difference.
Overall, few differences were seen between diets and breeds. Improving grass quality could be an efficient way to improve nutrient and N utilization.
For the full article, visit Translation Animal Science.