Relationship of Rumen Capacity of Mature Angus Cows to Body Measurements, Animal Performance and Forage Consumption on Pasture

Abstract

Rumen capacities of dry, mature Angus cows (total of 75 cows) were estimated during October of 2 years. Rumen capacity was defined as the rumen lithium sulfate space estimated after consumption to satiety of a cotton-seed hull-salt diet under defined conditions. Estimated rumen capacity was studied in relation to: (1) body weight, an estimate of fatness and a series of body measurements taken at the time rumen capacity was estimated, and (2) measures of cow performance during the previous grazing season, including forage intake and digestibility, milk production and weights of calves weaned. During lactation, these cows had grazed either high quality, tall fescuelegume pasture clipped regularly (average dry matter digestibility of 60%) or low quality, tall fescue pasture allowed to mature (average dry matter digestibility of 55%). Digestibility and intake were estimated continuously during the grazing season (152-day period from April 29 to September 28 each year) by the internal (acid detergent lignin)-external(Cr203) indicator ratio technique. Type of forage grazed previously was not related to rumen capacity estimates. Structurally large cows (taller at withers; longer, wider at hooks, and deeper at heart girth) had larger (P.10) to structural size. Fatter, heavier cows had smaller (P .10) between these two factors among cows that had grazed high quality pasture. On the basis of these results, it was hypothesized that forage intake was controlled by different factors for cows grazing high and low quality pastures and that this is probably an underlying cause of genotype x environment interactions.