Forty spring-born calves grazing subirrigated meadow regrowth after haying in July were assigned to 2 weaning and 2 supplementation treatments in fall of 1995 and 1996. Weaning treatments were weaning on 1 September or nursing during the duration of the trial. Supplementation treatments were no supplement or supplemental undegraded intake protein (UIP). An 80:20 (dry matter basis) blend of sulfite liquor treated soybean meal and feather meal was the source of undegraded intake protein (undegraded intake protein = 45% of supplement dry matter). Supplemented nursing calves received 0.50 kg of supplement daily whereas supplemented weaned calves received 0.91 kg of supplement daily. Weaned and nursing calves grazed subirrigated meadow regrowth throughout the trial. The trials were conducted from 17 October to 18 November 1995 and 5 September to 4 November 1996. Milk intake was measured by the weigh-suckleweigh technique. Diet samples collected from ruminally cannulated calves after rumen evacuation averaged 12.5% crude protein and 54.8% in vitro organic matter digestibility. No supplementation x weaning management interactions were detected (P > 0.18). Nursing calves had greater weight gains (0.95 vs. 0.59 kg day -1 ; P = 0.001) and lower forage intakes (2.36 vs. 2.96 kg day -1 ; P = 0.009) than weaned calves. Supplementation with undegraded intake protein increased (P = 0.03) daily gains of calves compared to nonsupplemented calves 0.88 vs 0.66 kg day -1 , respectively. Forage intake as a percentage of body weight tended to be higher in non-supplemented calves (P = 0.09). However, total intake (forage plus supplement) as a percentage of body weight tended to be higher in supplemented calves (P = 0.14). Total intake (kg day -1 ) was greater (P = 0.01) for calves supplemented with undegraded intake protein. Milk intake did not differ between supplemented and unsupplemented calves (P > 0.52). We concluded that subirrigated meadow regrowth forage was limiting in metabolizable protein and that milk represents an important source of metabolizable protein for grazing calves. Resumen 40 becerros nacidos en primavera, que apacentaban el rebrote de praderas subirrigadas después de segadas para heno en julio, se asignaron a 2 tratamientos de destete y 2 tratamientos de suplementación en otoño de 1995 y 1996. Los tratamientos de destete fueron: destetarlos el 1 de septiembre o amamantarlos durante la duración del experimento. Los tratamientos de suplementación fueron: no suplementación y suplementación de proteína no-degradada (PND). La fuente de proteína no-degradada fue una mezcla (80:20% en base seca) de pasta de soya tratada con licor de sulfito y harina de pluma (Proteína no-degradada = 45% de la materia seca suplementada). Los becerros amamantados suplementados recibieron 0.50 kg diarios de suplemento mientras que los becerros destetados suplementados recibieron 0.91 kg de suplemento al día. Durante el período de conducción del experimento los becerros destetados y los amamantados apacentaron el rebrote de las pr...

ResumenRuminally fistulated steers were used in a 4 x 4 Latin square to test effects of immature (vegetative) and mature (post reproductive) leaf and stem fractions from subirrigated meadow hay on organic matter intake (OMI), organic matter digestibility (OMD), and digestive kinetics. Hay was harvested 1 June (immature) and 1 October (mature), chopped into 3-to 5-cm lengths, then separated into leaf and stem fractions using a modified Clipper Cleaner Model Super 69D. Steers were provided ad libitum access to fractions and supplemented with urea so that diets were iso-nitrogenous. Particulate passage was determined usingYb labeled large hay particles [1.7-mm screen] and Er labeled small particles [< 1.7-mm and 0.212-mm screen]. Samples were collected from the rumen, omasum, feces, and un-masticated diets for particle size determination. Particle size was determined using wet sievin techniques. Voluntary OMI of immature fractions (15.4 g kg BW) was greater (P < 0.05) than mature fractions (12.5 g kg'' BW). Within maturity OMI and OMD of leaves and stems were similar. Immature fractions had greater (P < 0.05) OMD (63.2%) than mature fractions (55.7%). Large and small particle passage rates were faster (P < 0.05) for immature fractions [3.2% hour'1 (large) and 4.3% hour'' (small)] than mature [(2.3% hour"' (large) and 2.9% hour'' (small)]. Critical particle size for ruminal escape was 1.18 mm for both leaves and stems regardless of maturity. Differences in OMI and OMD between immature and mature fractions were explained by changes in structural components of the cell wall that made particles more resistant to mechanical and microbial breakdown.Key Words: digestibility, retention, particle size, rumen, feces, omasum Forage maturity influences quality of forages (Streeter et al. 1968, Nichols 1989. A decline in forage quality can be attributed largely to changes in the leaf and stem ratios (Nelson and Moser 1994) and associated decline in stem quality. Forage intake is associated with the proportion of indigestible fiber and the length of time retained in the rumen (Ulyatt et al. 1986). Particle size and passage rate were inversely related (Ehle 1984). Poppi et al. (1985) and Hendricksen et al. (1981) particulas chicas marcadas con Er [malla < 1.7-mm y 0.212-mm). Para determinar el tamano de particula se colectaron muestras del rumen, omaso, heces fecales y dietas sin masticar. El tamano de particula se determino usando la tecnica de cribado humedo. El consumo voluntario de materia organica de fracciones inmaduras (15.4 g kg'' PV) fue mayor (P < 0.05) que el de las fracciones maduras (12.5 g kg'' PV). Dentro de madurez, el consumo de materia organica y la digestibilidad de la materia organica de hojas y tallos fueron similares. Las fracciones inmaduras tuvieron una mayor (P < 0.05) DMO (63.2%) que las fracciones maduras (55.7%). Las tasas de paso fueron mas rapidas (P < 0.05) para las fracciones inmaduras [3.2% hora 1(grandes) y 4.3% hora'' (pequenas)] que para las maduras [(2.3% hora'1 (grandes) y 2.9% h...

Independent digestion trials with 5 forages were conducted to compare n-alkane with indigestible acid-detergent fiber (IADF) as internal markers to predict in vivo dry matter digestibility (digestibility). Forages were mixed grasses from subirrigated meadow (meadow), meadow regrowth (regrowth), native range (range), mature mixed grass hay from meadow, and alfalfa (Medicago sativa L.) hay. Meadow, regrowth, and range diets were immature grasses harvested 0.5 hours before feeding. Feces from the meadow hay and alfalfa hay trials were divided to compare freeze drying and oven drying (60°C). All diets were subjected to in vitro fermentation for 0, 48, or 96 hours. N-alkane was separated from samples by 4.5-hour saponification with alcoholic KOH followed by extraction with n-hexane. Indigestible ADF was measured by 96-hour in vitro fermentation followed by ADF extraction. Digestibility estimated by markers was compared with in vivo digestibilities. N-alkane based digestibilities were lower (P < 0.01) than in vivo digestibility for all diets. Nalkanes provided higher estimates of digestibilities than IADF for meadow (P < 0.01), regrowth (P = 0.06), and alfalfa hay (P = 0.06), and lower digestibility for meadow hay (P = 0.02). Digestibilities calculated using n-alkanes for range tended to be higher (P = 0.14) than IADF values. Freeze drying increased (P<0.01) the amount of n-alkane extracted from alfalfa hay, but did not affect (P = 0.1) the amount extracted from meadow hay. N-alkane disappeared (P < 0.001) from residue collected after 48 hours of in vitro fermentation, but no additional disappearance (P = 0.78) was evident at 96 hours. Neither marker was completely recoverable, although recovery of n-alkane was higher than indigestible ADF for 4 of the 5 forages tested.