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1. Experiments were undertaken to examine the kinetics of large ciliate protozoa in the rumen of cattle on sugar-cane diets.2. Three Zebu bulls were fed once daily on a diet of sugar cane and wheat bran. The diurnal patterns of volatile fatty acids and amm0n.a concentrations, and the numbers of protozoa in rumen fluid were determined. The numbers of protozoa re.iched values of 5 x l(r/ml for holotrichs (large ciliates) mainly Isotrichu and Dasytrichu spp and 4 x 105 for smaller protozoa, mainly Entodiniu (small ciliates).3. A method was delieloped which allowed large ciliate protozoa in rumen fluid to be separated from plant material and bacteria ar.d concentrated in a relatively uncontaminated form. Analysis of these protozoa indicated that 1.8 x 10' large ciliates contained 1 mg nitrogen and approximately 32 mg dry matter.4. A labelled preparation consisting tnainly of large ciliates (principally Zsotrichn spp.) was obtained by incubating isolated protozoa in rumen fluid (free of plant materials) containing [14C-methyl]choline and then isolating them by sedimentation and differential centrifugation.5. A portion of the preparation containing labelled protozoa was incubated in vitro with rumen fluid to determine the turnover of "C-labelled metabolites. There was no apparent dilution of the label in the protozoa over a 22 h period.6. A major portion of the preparation containing labelled protozoa was returned to the rumen of each of the donor cattle as a single injection. The specific radioactivity in the large protozoa @Ci/mg N) was monitored frequently for over 30 h, and thereafter daily for a further 12 d. The kinetics of tracer dilution were analyzed to give estimates of the size of the pool of these large ciliates in the rumen (2446 g N), and of their apparent rate of turnover.7. In contrast to thi: slow turnover of the large ciliates, the rate of turnover of the rumen fluid pool (approximately 54 I), esimated from the rate of dilution of polyethylene glycol, was considerably faster. Large ciliates were therefore wlectively retained within the rumen.Involvement of protozoa in the nutrition of ruminants has been studied mainly in animals in which small ciliate protozoa (Entodinia spp.) rather than the large ciliate protozoa (Holotricha spp.) wcre predominant in the population. The smaller protozoa actively engulf bacteria (Coleman, 1975), and do not pass out of the rumen in proportion to their concentration in rumen fluid (Weller & Pilgrim, 1974;Harrison et al. 1979). It has been suggested that these characteristics may reduce nutrient availability to the host animal Bergeii & Yokoyama, 1977) particularly on low-protein diets. Elimination of protozoa from the :umen has increased the growth rates and efficiency of food utilization for live-weight gain (Bird'& Leng, 1978;Bird et al. 1979) indicating that under some circumstances the presence of protozoa in the rumen reduces animal productivity.In cattle given sugar cane diets (Valdez et al. 1977) or grazing some temperate pastures (Clarke, 1965), although th...

The objective of this study was to compare restricted suckling of tropical cows by their own or another cow's calf with artificial rearing of the calves and no suckling. In Exp. 1, cows were mechanically milked twice daily, after which for 15 min they were either suckled by their own calf (Treatment O) or multiple-suckled by other cows' calves (Treatment M) or unsuckled, with the calves reared artificially (Treatment A). Machine milk yield was similar for the three treatments, but in the two suckling treatments the additional milk consumed by the calf increased (P = 0.02) total production (2,682, 2,634, and 2,336 kg/lactation for Treatments O, M, and A, respectively). Machine milk fat concentration was reduced (P = 0.05) by suckling (2.90, 3.07, and 3.20% for Treatments 0, M, and A, respectively), but the milk sampled just before suckling (to represent that taken by the calves) had a high fat concentration (mean 7.9%). Machine milk somatic cell count was also reduced (P = 0.05) by suckling, from 106,000/mL (Treatment A) to 85,000/mL (Treatment M) and 95,000 (Treatment O). Cows suckling their own calf lost more weight and body condition than cows whose calves were reared artificially, with multiple-suckled calves intermediate. Cows suckling their own calf had postpartum interval to first estrus increased (P = 0.01) by 31 d and conception rates to first service of 44% compared to 77% for the other two treatments (P = 0.01). The growth of the suckled calves was compared with that of the artificially reared calves, which were given recommended milk allowances. The artificially reared calves consumed more milk and concentrates, which were available ad libitum to all calves, and gained (P = 0.03) 0.07 kg/d more weight than suckled calves. A second experiment determined that suckling once daily did not reduce reproductive performance compared to artificial rearing. We conclude that suckling cows twice daily increases total milk production but reduces body weight in early lactation. Cows suckling their own calves have reduced reproductive performance compared to those suckling other calves or reared artificially.

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