Forage impact on subsequent finishing performance of wethers
A. L. Goetsch1 and G. E. Aiken2
1E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK, and 2Dale Bumpers Small Farms Research Center, USDA, ARS, Booneville, AR
High-forage diets are often consumed ad libitum (ALI) in a growing phase, followed by ALI of concentrate-based diets (CBD) during finishing. Splanchnic tissue energy use relative to absorbed energy is greater for ALI of forage-based diets than for limited intake or ALI of CBD (Goetsch, 1998). Sainz et al. (1995) observed lower live weight gain and efficiency of feed utilization during finishing for beef steers that previously consumed forage ad libitum compared with steers given restricted access to CBD. The proportion of the finishing period during which energy use was influenced by greater liver and stomach protein mass observed at the end of the growing phase (Sainz and Bentley, 1997) is unknown. If appreciable, a short period of limit-feeding CBD after growing phase ALI of forage might avert or lessen high energy use by splanchnic tissues during finishing. Hence, objectives of this experiment were to determine effects of ALI of forage (long-stemmed alfalfa hay) or restricted intake of CBD (80% concentrate) on subsequent finishing performance with ALI of CBD. Forty-eight wethers (9 months of age; 28.6 ± .40 kg initial live weight; 16 St. Croix and 32 St. Croix × Romanov) were used in the 14-wk experiment. Treatments were ALI of CBD for 14 wk (AC); ALI of forage for 8 wk followed by 6 wk ALI of CBD (F-AC); restricted intake of CBD for 8 wk followed by 6 wk ALI of CBD (LC-AC); and 6 wk ALI of forage followed by 2 wk restricted intake of CBD then 6 wk ALI of CBD (F-LC-AC). Transitions from forage to CBD occurred in 1 wk or less. At the beginning of wk 9 and end of wk 14, shrunk body weight and body composition (via urea dilution) were determined. Factors responsible for improved performance in wk 9-14 for F-LC-AC compared with F-AC are unknown and deserved of study. Nonetheless, a more rapid decrease with time in energy use by splanchnic tissues relative to absorbed energy for F-LC-AC after forage and(or) limited CBD consumption than for F-AC after ALI intake of forage is possible, which encompasses potential influences of changes in the quantity of nutrients absorbed and physical characteristics of digesta. In conclusion, growing phase restricted intake of CBD may affect subsequent performance with ALI of CBD differently than ALI of forage. A period of restricted intake of CBD following growing phase ALI of forage could offer potential to improve later performance with ALI of CBD.
DMI = dry matter intake; LWG = live weight gain; MEI = metabolizable energy intake.
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