Grazing or cutting frquency has been shown to nffect yield and quality of many grasses, but similar data are lacking for tall wbeatgrass [Agropyrou e~ugu&ur (Host) Beauv. 'Jose'). The objective of the reseucb was to determine the effect of frequency of clipping on tall wheatgrass. The study was conducted at the Texm Agricultural Experiment Station at Bushland, Texas, in 1979,1980,1981, and 1984 on a Pullman clay loam soil. Plots were irrigated as needed from February to the end of the growing season and fertilized with 112 kg N/ha every 2 months for mrximum yield and clipped either every week, 2 weeks, of 4 weeks at a S-cm stubble height. Herbage yield was highest from spring harvests and de&red over summer as is typical of cool-season grasses. The plots that were clipped every 4 weeks produced greater herbage yields than plots th8t were clipped 1 or 2 weeks, suggesting that rot8tional grazing would increase productivity. The nutrient content of the herbage was highest during summer when herbage yield was lowest. Plants clipped less frequently had the highest concentrations of phosphorus and potassium and the lowest concentrations of calcium and magneshun. The greatest differences in nutrient content occurred among years, which emphasizes the importance of continual herbrge analysis to optimize mineral supplementation of graxing c8ttle.

Two lamb digestion experiments were conducted to evaluate the effect of alfalfa [Medicago sativa (L.)] grown under varying levels of water deficiency (stress) on the rate of passage and digestibility of various fibrous components. Experiment 1 consisted of a randomized complete block design in which 12 Suffolk X Hampshire crossbred wethers averaging 40 kg were fed alfalfa hay grown at three (10, 15 or 20 cm water/ha) levels of water per harvest. Experiment 2 consisted of a switchback design in which four Hampshire wethers averaging 45 kg were fed alfalfa hay grown at two (5 or 20 cm/ha) levels of water per harvest. Forage yields ranged from 1,420 (10 cm/ha in Exp. 1) to 4,200 (20 cm/ha in Exp. 2) kg/ha. In both experiments, water stress reduced cell wall constituents (neutral detergent fiber), acid detergent fiber, lignin and cellulose content of the alfalfa hay. Organic matter digestibility was decreased when the percentage of leaves fell below 60% at the highest yield. Digestibility of N and the rate of NDF digestibility were not affected by water stress. The second experiment additionally included nutrient balance and rate of passage measurements. Greater (P less than .10) amounts of N and P were absorbed from water-stressed than nonstressed hay. Ruminal retention time of particulate markers tended (P less than .10) to increase with greater water stress. The results of this study are interpreted to indicate that while moderate water stress may have little effect on in vivo digestibility of alfalfa, severe stress may reduce digestibility of fibrous fractions and total organic matter.

A lamb digestion trial was conducted to compare the ability of internal markers to predict digestibility of alfalfa. Lambs were fed alfalfa hay grown with varying amounts of water stress where water per harvest ranged from 10 to 20 cm/ha and yield ranged 1400 to 4200 kg/ha. In vivo dry matter digestibility was most highly correlated with digestibility determined using acid detergent fiber insoluble ash (r = .80) followed by acid insoluble ash (r = .69). In vivo digestibility of the fibrous components was most highly correlated with digestibility determined by acid detergent insoluble ash and indigestible neutral detergent fiber followed by acid lignin and acid insoluble ash.