Effects of particle length and maturity stage of whole crop barley silage on feed intake, chewing activity and eating behaviour by growing dairy steers

Abstract: Whole crop cereal silage has proven to be a good and flexible feed alternative to growing cattle and can be fed alone or together with other forage sources. Whole crop silages constitute a less homogenous material compared to grass silage, with awns rich in starch and stalks with a high fiber concentration. A regular intake of fibrous materials, such as whole crop silage, is of importance to stimulate chewing and to ensure proper digestion and a healthy rumen environment of cattle and other ruminant animals. Stage of maturity at harvest and particle size of forage affects feed intake, chewing activity and production of animals. A later maturity of the crop is followed by a decrease in fiber digestibility and consequently a decreased feed intake. In barley silage, the feed intake is often unaffected by stage of maturity or even increased at higher maturity silages. This is probably due to a decreasing NDF content as the grain content increases. Chopping before feeding can increase feed intake because of a faster passage rate and a decreased need for chewing. The neutral detergent fiber (NDF) content of the feed is highly correlated with chewing time. Together with particle size of the roughage, the NDF content is a major determinant of chewing activity. The aim of this study was to investigate the effects of maturity stage and particle size of barley silage stored in round bales on feed intake, chewing activity and eating behaviour by growing dairy steers. Eight dairy steers, weighing around 350 kg at the beginning of the trial, were divided into a duplicated latin square with four periods and four steers in each square. Four diets, which were made up of silage at two different maturity stages and particle sizes of whole crop barley silage, were fed to two randomly selected steers per diet and period. At the end of the trial, all steers had been fed with four diets. Each period lasted for 21 days and the two squares were dislocated in time. During the collection period, data concerning feed intake, chewing activity and eating behaviour were collected. Chewing activity was measured using elastic halters with magnetic sensors fitted under the lower jaw of each steer. Feeding behaviour was mainly described as eating rate and sorting of feed. Sorting was determined by comparing the particle size distribution expressed as the percentage of particles from orts retained on three sieves with different pore sizes to the particle size distribution of the feed. The dry matter intake (DMI) of long silage harvested at heading was higher than for long silage harvested at dough stage and chopped silage harvested at heading. However, chopping the silage harvested at dough stage resulted in a higher DMI compared to long silage harvested at dough stage. The NDF intake of silage was higher at heading compared to dough stage, whereas no significant differences were found between chopped and long silage. Time spent ruminating was longer than time spent eating for all diets except for chopped silage at harvested at dough stage, where time spent eating was longer than time spent ruminating. Particle size and stage of maturity affected eating time only, whereas rumination time was constant among diets. The longest time spent eating was for chopped silage harvested at dough stage. Chopping increased the time spent eating for both stages of maturity. Time of harvest only affected time spent eating per kg of NDF intake with a longer eating time for silage harvested at dough stage compared to silage harvested at heading. The number of jaw movements increased when feeding chopped diets. Feeding silage harvested at dough stage also increased the number of jaw movements per kg of NDF intake. Chopping before feeding increased the eating rate for both harvest times. The number of chewing cycles per chewing period was higher for long silage harvested at heading compared to chopped silage harvested at heading and long silage harvested at dough stage. When feeding silage at dough stage, chopping the silage increased the number of chewing cycles per period compared to long silage. Chopping before feeding increased sorting behaviour compared to feeding long silage and resulted in sorting in favor of shorter particles. Interactions between effects of stage of maturity and particle size on intake and chewing activity by the steers might have been affected by differences in fermentation between silage at the two different maturity stages. Eating time and the number of jaw movements increased for silage harvested at dough stage, which was probably because of a decreased fibre digestibility. This indicates that rumen fill affects intake resulting in a decreased fibre intake of silage harvested at dough compared to silage harvested at heading. Also, rumen fill probably had an effect on DMI of the long silage. Chopping whole crop barley silage is more advantageous when harvested at dough stage. However, time of harvest should be adapted to the most suitable combination of harvest time and particle length at feeding in relation to existing production conditions.