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Technology has recently made it possible to count forage boli consumed daily in ruminants. This tec+ique can presently be used to measure grazing time and rates of nutrient intake. However, to determine total daily intake, the ifiuence of inherent variations in bolus weight and associated forage conditions must be known. An attempt was made to determine if degree of uniformity in forage boli weights were statistically nonsignificant to be counted and used as a measure of daily dry matter intake of an animal. Herbage allowances varying from 15.4 to 3.4 kg DM/lOO kg BW/day did not have a significant effect on bolus weights in mature cows grazbg bahiagrass pastures during mid-summer and early winter (PrO.05). Cow size and season of the year also had no significant effect on bolus weight. Bolus weight of the cows averaged 4.4fO.l g across seasons and cows. Much effort has been directed toward relating forage intake of livestock to sward characteristics by measurement of size and rate of biting by the grazing animal (Allden and Whittaker 1970, Stobbs 1975, Chacon et al. 1976, Chaconand Stobbs 1976). Allden and Whittaker (1970) noted that as tiller height increased, size or weight of bite increased and rate of biting decreased. Hence, intake remained static over nonlimiting range forage availabilities. It appears that an animal has a strong tendency to maintain a given level of daily intake by varying bite size and grazing time (Spedding et al. 1966). The end result of these prehensile measurements is the swallowed bolus. Since rate of intake (g/min) by the animal was static in the Allden and Whittaker (1970) study, it would appear that the animal can maintain a static intake by creating boli that have little variation in dry matter weight. Thus, rate of swallowing boli and time spent grazing would determine daily intake of an animal. This hypothesis would imply that the animal gathers forage in its mouth until a “critical” density or weight is attained to form the bolus. The shorter the vegetation the greater time spent forming the bolus. If grazing time does not exceed some inherent behavioral limitation of the animal, intake can be maintained at a stable level under nonlimiting forage conditions by adjusting grazing time. If the forage bolus is uniform across a wide array of forage conditions, then measurements of daily swallowing events of boli should provide a technique which measures daily intake and avoids the fluctuations in size and bite and rate of biting associated with variable forage availabilities. Information to date on swallowed boli is limited to confined animals fed known feed sources (Schalk and Amadon 1928, Bailey 196 I, Gill et al. 1966). Boli in these studies were collected by partial evacuation of the rumen and collection by hand of the swallowed bolus at the cardia in the rumen. Access for collection was provided by a rumen fistula. Bolus weight varied among studies, cows, and feed source. In general, as initial dry matter density of a feed source increased, bolus weight increased. The boli in these studies were reasonably uniform within each feed source and cow. Authors are assistant professor and research technician, Department of Range Science, Texas Agricultural Experiment Station, Texas A&M University System, College Station, respectively. Published with permission of the Director, Texas Agricultural Experiment Station as TA 16095. Received for publication May 5, 1980. JOURNAL OF RANGE MANAGEMENT 35(2), March 1982 Recently, Stoner et al. (1979, 1980) and Stuth et al. (1981) described systems capable of measuring the various swallowing events of cattle, goats, and whitetailed deer. They were able to identify and distinguish among swallowing events of green forage, hay, concentrate feed, water, and regurgitation. In light of these findings, it appears that more information is needed to characterize dynamics of bolus weight under actual grazing situations in order that this information could be used to develop a new technique for determination of intake of animals. It is the purpose of this paper to test the hypothesis that bolus weight is reasonably uniform throughout a nonrestrictive range of herbage allowance and that season has a negligible effect on weight of dry matter in the bolus.

Effect of Seasonal Herbage Allowance on Bolus Weights of Cattle