A trial was undertaken to determine the extent to which genetic makeup of cows can influence methane production. Ten non-lactating cows with permanent rumen fistulae (5 cloned and 5 unrelated cohorts) were fed ryegrass silage for six weeks, during which a range of physiological and microbiological measurements was undertaken. The trial comprised three phases; initially (Phase 1) the voluntary feed intake (VFI) was recorded, and the diet was fed at 95% of VFI thereafter (weeks 2-6). Baseline measurements (week 2) included dry matter intake (DMI), methane production, rumen pH, concentrations of ammonia and volatile fatty acids (VFA), liquid and solid digesta outflow and microbial growth. The same measurements were made in Phase 2 (weeks 3 and 4) to determine effects of switching rumen contents between clones and cohorts (day 15) on return to baseline values, and in Phase 3 (weeks 5 and 6), following ruminal administration of chloroform (1.3 mL/day) on days 29 and 30 to suppress methanogenesis. Average DMI (kg/day) was higher (P < 0.05) for the cloned cows than for the cohorts (10.2 v. 8.8), most likely related to larger mean body size (535 v. 440 kg). Expressed on the basis of DMI, however, mean values for methane production (g kg/DMI) were similar between clones (11.50) and cohorts (10.3). There were no differences between groups in rumen pH (6.76), total VFA concentration (74.5 mmol/L), molar proportions of acetate (A), propionate (P) or butyrate (0.72, 0.18, and 0.07, respectively), or passage rate of liquid (0.096/h) or solids (0.025/h) from the rumen. Exchanging rumen contents between clones and cohorts did not affect methane production in week 3 (13.0 g/kg DMI), but ammonia and VFA concentrations were lower than previously and A:P ratios increased (P < 0.05), which suggests a significant perturbation of fermentation. Chloroform reduced methane production in both groups by more than 100 g/day by the second day of treatment, after which production gradually returned to pre-treatment values. Chloroform also caused marked shifts in molar proportions of propionate (nearly doubled) and acetate (decreased) and reduced DM digestibility from about 71% to about 53%, but there were no differences between the clone and cohort groups. The two main observations from this trial included the very low levels of methane production, relative to typical values of 19-21g/kg DMI for cows fed forages, and some indications of a greater variance in methane production among cohorts than among clones. Relating methane (g/kg DMI; y) to liveweight (kg; x) yielded a negative relationship for the cohort cows (y = -64x + 40.7; R2 = 0.80), but a weak positive relationship for the clones (y = 0.72x - 24.1; R2 = 0.33). Average liveweight (LW) of cohort cows ranged from 391 to 495 kg, whereas the clones ranged from 517 to 561 kg. The variance in daily feed intake (kg DMI) was larger for cohorts (1.26) than for clones (0.06; P = 0.02), and when methane production was expressed on the basis of DMI as a proportion of metabolic liveweight (CH4/DMI/LW0.75; g/kg/kg0.75), there was a significantly lower (P = 0.07) variance among the clones (0.00030) than among the cohorts (0.00201). These data suggest a reduced variance in methane production amongst the cloned cows relative to the unrelated cohorts, implying that the genetic makeup of animals may influence methane production.
|Original language||English (US)|
|Journal||Australian Journal of Experimental Agriculture|
|State||Published - Jan 9 2008|
All Science Journal Classification (ASJC) codes
- Agricultural and Biological Sciences(all)