Diurnal, daily, find seasonal flllci,uat�iollS in t.he concentrations of bnetcria wiiJtin tho rumon find in rumon pJI We1'O determined ill mature sheep.

Diets of wheat or oat grain with or without chaff, mixtures of all three, and a diet of chaff, oats, and bran with and without lucerne chaff were fed to sheep for the purpose of determining silica metabolism on diets approximating those in the field. These diets supplied from 0.08 to 16.6 g silica per day. Silica digestibilities and balances showed marked positive and negative values, which were considered to be due to variable retention in, or passage of particulate silica from, the rumen. The mean urinary silica excretion on wheat was 22 and 25 mg/day and oats 126 and 163 mg/day for two levels of feeding. Values for wheat plus chaff and oats plus chaff were respectively 190 and 224 mg/day and for mixed diets from 169 to 205 mg/day. No relationship between total urinary silica excretion and apparent absorption of silica was observed, but excretion seemed dependent on silica intake up to a level of about 8 g/day. Beyond this intake, urinary excretion plateaued at approximately 200 mg/day. Urine volumes on wheat grain diets were greater than on the corresponding oat grain diets, and these in turn were greater than on the mixed diets. The combined effects of urine volume and total excretion of silica resulted in urinary silica concentrations of 30 and 32 µg/ml on wheat grain diets, 255 and 336 µg/ml on oat grains, 266 µg/ml on wheat plus chaff, 419 µg/ml on oats plus chaff, and 421–728 µg/ml on mixed diets. A hyperbolic relationship between silica concentration and volume of urine, similar to one obtained in field studies, and also one between specific gravity and volume of urine were demonstrated. These findings are discussed in relation to the absorption and excretion of silica and the formation of siliceous urinary calculi.

Data are presented from a replicated feeding trial with sheep, designed to determine the influence of varying dietary intakes of starch and protein upon digestibility, protein utilization, and the numbers and types of "free" bacteria in the rumen.

In pen feeding trials with eight Merino wethers, digestion coefficients were estimated for rations of cereal chaff-wheat grain-oat grain mixture, and wheat grain and oat grain fed separately at two levels of intake. Digestion coefficients for wheat and oat grain fed at 675 g/day in a double crossover experiment were dry matter 89.4, 80.8 per cent, organic matter 90.1, 82.6 per cent, protein 82.3, 77.6 per cent, ether extract 84.1, 90.9 per cent, crude fibre 33.2, 59.9 per cent, nitrogen free extractives 93.2, 85.8 per cent, energy 88.1, 81.0 per cent, total digestible nutrients 91.6, 87.1 per cent, and starch equivalents 90.7, 85.7. When these grains were fed at 785 g/day there was about 10 per cent improvement in crude fibre digestibility for both grains and 1-2 per cent improvement for other estimations with oats but not with wheat. The gross energy content of the wheat and oat grains when fed at 675 g/day was 4407 and 4700 calories/g dry matter. The digestible energy of the wheat in calories/g dry matter and organic matter was 3869 � 30, 3933 � 30 and for oats 3791 � 59, 3910 � 61. When fed at 785 g/day these values for wheat were 3850 � 50,3911 � 51 and for oats 3796 � 34, 3913 � 51. A highly significant relationship was found between energy and dry matter digestibility which for wheat diets was Y = 1.074x 7.840. r = 0.993 (P<0.001), and for oats and the mixed diet of cereal chaff-oat grain-wheat grain, Y = 0.983x + 1.550. r = 0.996 (P<0.001) where Y = energy and X = dry matter digestibility and r = the coefficient of correlation. Because of the similar digestible energy content of, and the body weight gains of sheep on, these two grains it was concluded that under the present conditions these grains were equivalent weight for weight.

No abstract