Resistance to the cattle tick Boophilus microplus was assessed in heifer herds of various breeds of beef and dairy cattle in spring and summer in Queensland. All cattle had had tick experience before assessment. Resistance levels were determined as the percentage of larval ticks that failed to survive to maturity following infestations with c. 20,000 larvae. Bos indicus Brahman beef cattle were the most resistant (99%), followed by B. indicus × B. taurus (95–97%) and B. taurus British cattle (85%). In the dairy breeds, B. taurus Jersey cattle (98%) were more resistant than Guernsey (93%), Australian Illawarra Shorthorn (89%), and Friesian (85%), but not significantly different from B. indicus × B. taurus Australian Milking Zebu (96%). Cattle were classified as having high (> 98%), moderate (95–98%), low (90–95%), or very low (< 90%) resistance. The frequency distributions of resistance in B. indicus × B. taurus cattle showed that 80% had moderate to high resistance and that culling of 20% of the cattle would about halve the mean tick population. Of B. taurus cattle, 80% had low to very low resistance. Supplementary information on sibling bull herds showed that their resistance levels and frequency distributions of resistance were similar to those of the heifer herds.

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S U M M A R YFour swamp buffaloes (Bubalus bubalis) and four crossbred Bos indicus x B. taurus cattle, fistulated at the rumen and abomasum or duodenum, were offered rice straw with mineral supplements in two experiments. In Expt 1, the straw was supplemented with 5% of leaf of Leucaena leucocephala, and in Expt 2 with either urea or urea with sunflower meal and rice grain. Intake of supplements of urea or urea/sunflower/rice respectively was 935 and 681 g/kg offered in buffaloes and 566 and 789 in cattle.Buffaloes ruminated longer than cattle (Expt 1, 635 v. 452 min/day; Expt 2, 626 v. 466 min/day, P < 001). In Expt 1, voluntary intake and frequency of ' A ' sequence forestomach contractions of both species was not affected by species, but buffaloes had a greater (P < 005) contraction force in the rumen and omasum, lower rate o f ' B ' sequence rumen contractions, and faster (P < 0001) rate of gastrointestinal passage than cattle. In Expt 2, voluntary intake of both species was similar, and addition of concentrates did not affect voluntary roughage consumption, nor in situ rate of digestion of rice straw. Rate and predicted extent of digestion of dietary materials did not differ between species in Expt 1, despite lower concentrations of ammonia in rumen fluid in cattle than buffaloes; however in Expt 2, the rate of digestion of rice straw was higher (/> < 005) and predicted extent of digestion was 14-20% (P < 005) lower in buffaloes. Digestibility of cell wall constituents was lower (P < 005) in buffaloes than in cattle in both experiments, but in Expt 2, provision of concentrates reduced (P < 001) the proportion of digestible cell wall constituents digested in the forestomach of buffaloes, but not of cattle. Plasma urea concentrations were higher (P < 0-05) and transfer of urea to the rumen tended to be higher (7-4 v. 3-7gN/day; P<0-l0) in buffaloes. Faster fractional outflow rates of microbes and of small digesta particles from the rumen were observed in buffaloes in Expt 1.In Expt 1, more microbial N left the abomasum (35 v. 30 g per kg organic matter apparently digested in the forestomach; P < 005) of buffaloes than cattle, and in Expt 2 more non-ammonia N (43 v. 31 g per kg organic matter apparently digested in the forestomach) flowed into the intestines of buffaloes. In Expt 1 microbial retention time was shorter (26 v. 47 h; P < 001) in the rumen of buffaloes.Patterns of appearance of plastic particles with time after dosing indicated faster escape from the rumen of buffaloes of non-chewed particles, and a greater proportion of particles subjected to ruminative chewing, than in cattle. Ruminative chewing of plastic particles in buffaloes was progressively more efficient than in cattle with increasing particle length and decreasing specific gravity. Analysis of faecal particle distribution indicated buffaloes tended to excrete smaller particles than cattle.The adaptive significance of faster digesta passage in the buffaloes appeared to derive from a more balanced supply of absorbed protein relative to dige...