K RE UZ E R. 1999. Diets containing either coconut oil or rumen-protected fat (54 g kg −1 dry matter each) were supplied to Rumen Simulation Technique fermenters filled with faunated and defaunated rumen fluid in a 2 × 2 factorial design. Defaunation immediately reduced methane formation by about 40% with each diet. With coconut oil, methane gradually declined in faunated and defaunated rumen fluid. Finally, the extent of methane suppression was similar, both with coconut oil and with defaunation. Independently of the status of protozoa, the population of methanogens in rumen fluid was significantly reduced by coconut oil. The results suggest that defaunation and coconut oil independently and additively suppress rumen methanogenesis.

-In two experiments, system differences were determined between dairy cows (18-20 kg milk·d -1 ) and suckler beef (cows with calves; 1.1-1.2 kg weight gain·d -1 ) exclusively fed on grass. This included measurements of dry matter intake (DMI) and nitrogen (N) turnover on an alpine pasture (n by group = 5; 2000 m a.s.l.; experiment I), and of DMI, N and energy turnover in a lowland cowshed equipped with respiration chambers (n by group = 6; 400 m a.s.l.; experiment II). Within experiment II a high accuracy of slow-release alkane capsules for intake estimation was confirmed for grass-only diets because the difference between known intake and the prediction made using the C 31 :C 32 alkane ratio was only 0.19 kg·d -1 (1%). Estimates were best with early-morning faeces samples. In experiment I grass DMI and N intake were equal in dairy cows and suckler beef with 16 and 0.30 kg·d -1 , respectively. System N retention was higher in dairy cows with 25.7% of N intake vs. 9.2% in suckler beef. In experiment II, DMI of individual cows was equal in both systems (16 kg·d -1 ), whereas total system DMI (cows and calves) was higher in suckler beef (20 kg·d -1 ). Nitrogen intake was higher in the suckler beef system (0.54 vs. 0.44 kg·d -1 in dairy cows). Nitrogen retention relative to intake in dairy cows and suckler beef was 21.6% and 6.1%, respectively. Also system energy retention was higher in dairy cows (23.1% of intake) than in suckler beef (9.2%). This resulted particularly from a proportionately higher energy expenditure at a similar diet digestibility. The environmentally important excretion of total N, urine N (both experiments) and methane (experiment II) was higher in suckler beef than in dairy cows. The latter resulted from the difference in fermentable fibre intake. Overall this study suggests a greater efficiency of the dairy system on high-quality grass, although the potential difference in the effort necessary to maintain the respective system was not considered.

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The effects of calf age and dam breeds of different milk yield potential on turnover of energy and nutrients were followed in 16 Simmental and 16 Angus beef cows with Angus-sired calves. Calf ages investigated were 1, 4, 7, and 10 mo. The forage offered for ad libitum access consisted of hay for the calves and of a constant mixture of grass silage, meadow hay, and straw (1:0.7:0.3 on a DM basis) for the cows. Calves of 10 mo of age received an additional 2.6 kg DM/d of crushed barley. The animals were kept in groups of four cows and four calves except in the respiration chambers, where only one cow (tethered) and her calf (loose) were grouped together. Indicator techniques were applied to obtain individual data on feces and urine volumes during group housing. In the Simmental cows, heavier on average by 22 kg, voluntary DMI was higher than in the Angus cows (14.0 vs 12.3 kg/d). In calves, DMI from supplementary feeds was 1.6, 3.9, and 6.3 kg/d, on average, at 4, 7, and 10 mo of age, respectively. Dam breed had no significant effect on DMI and ADG of calves and on BW changes of cows. System retention of energy, N, and P showed a curvilinear development with calf age. System energy expenditure, which linearly increased with calf age, was higher with Simmental than with Angus dams (11%), even when adjusted for metabolic BW (8%). Energy loss through methane linearly increased with NDF intake and, consequently, with calf age from 18 to 30 MJ/d (446 to 751 L/d) for cows and calves together. Similarly, fecal and urinary N excretion and fecal P excretion steadily increased with calf age. In calves, the easily volatile N percentage of manure N rapidly decreased from very high levels in young calves. The resulting changes in inclination to gaseous N loss during manure storage for 8 wk were more than compensated by alterations in N intake of the calves, resulting in an increased total system N loss with progressing lactation. Overall, the present results indicate a difference between Angus and Simmental in efficiency of nutrient and energy utilization that might be explained by the difference in amount of delivery of nutrients to the calves via milk vs forage. Suggestions are made as to how the emissions of N, P, and methane, which were excessive in relation to productivity, could be reduced by nutritional means.

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