Effect of intake on digestibility of plant cell walls and cell contents of complete diets for ruminants

Comparative digestion in cattle and sheep fed wheat silage diets at low and high intakes

Winter wheat (Triticum aestivum L.), harvested at late milk, early dough, and hard dough stages of maturity was ensiled for nutritive comparisons. Diets were adjusted to 13% CP with a soy protein concentrate and fed to six ruminally fistulated growing steers and nine adult wethers in a repeated 3 x 3 Latin square design to study the effects of maintenance and ad libitum intakes on digestibility of different feed fractions. At both intakes, digestion values for the steers were greater than or equal to those for the sheep for all feed fractions except CP. Wethers achieved greater intake per unit of BW than steers during ad libitum intake. Voluntary OM intakes of steers only differed between the milk stage diet and the dough stage diets. At low intake, the diets containing the more mature silage were more digestible. At high intake, the OM of diet containing the early dough stage silage ws most digestible. Increased intake caused a depression in digestibility of different feed fractions. The magnitude of the depression varied among diets and fractions. Data indicated that the nutritive value of diets based on whole crop wheat silage is affected by stage of maturity, animal species, and amount of intake. The assessment of the nutritive value of diets based on whole crop wheat silage should therefore be made with the animal species and at the amount of intake for which the diets are intended.

Comparative digestion in sheep and cattle fed different forage to concentrate ratios at high and low intakes

Effect of maintenance and ad libitum intakes on digestibility of different feed fractions was studied with six ruminally fistulated cows and six ruminally fistulated wethers to validate the use of sheep as a model for cattle. Complete diets were made up of ratios of alfalfa:cracked corn and soybean meal of 80:20, 55:45, and 30:70. The regression coefficient of the line relating organic matter digestibility with proportion of concentrate in the diet was smaller for the cows at ad libitum intake than for the other groups. Increasing the intake caused a decrease in digestibility of different fractions. The depression in digestibility was greater for the 30:70 forage:concentrate diet than for the others. At high intake, digestion values in the cows were less than those in the sheep for all diets. An increase in intake depressed the digestion of cell wall fractions and cell solubles including starch in cows, whereas in sheep, an increase in intake reduced cell wall digestion and to a lesser extent cell solubles, without affecting starch digestion. The digestive physiology of these species is sufficiently different to preclude the use of sheep data in formulating nutrient requirements for cows.

[The effect of pregnancy and lactation on digestive processes in sheep]

The average passage time, the rumen fluid volume and the digestibility of the organic matter were determined in addition to 3 individual feeding experiments with fertility oriented crossbreed ewes, which received pelleted straw-concentrate mixtures. The average passage time of the feed particles through the digestive tract is shorter in pregnant animals than in lactating ones. It is longest in non-pregnant sheep. High quotas of straw and coarse particles prolong the passage time, increasing feed intake and supplements of long straw shorten it. The volume of rumen fluid is lower in ewes fed ad libitum in the stage of late pregnancy and after lactation than during lactation. The rumen fluid volume is also lower in restrictively fed animals during the stage of late pregnancy than during lactation. In animals in the stage of late pregnancy it correlates negatively with the weight of the litter. On an average of all experiments at maintenance level the digestibility of the organic matter in ewes in the 4th month of pregnancy gravidity amounted to 56.6%, in the 2nd month of lactation to 59.8% and in wethers to 59.5% Due to an increase of energy intake from maintenance to 2. maintenance digestibility of the straw-concentrate mixture with 40% straw decreased by 5.5 units and of that with 60% straw by 17.8 units in the period before delivery. Pregnancy in the 4th month resulted in a digestion depression of between 3.0 and 5.8 units.