BEEF CATTLE NUTRITION AND PERFORMANCE ON SEEDED CLEARCUTS IN SOUTHERN INTERIOR BRITISH COLUMBIA

The nutrient content of diets consumed, using a bite count technique, and the performance of beef cows and their calves grazing spruce and pine clearcuts in the southern interior rangelands of British Columbia on continuously and rotationally grazed pasture systems were evaluated in a 3- to 5-yr study. Forage species and plant parts ingested by cows were collected by hand clipping to simulate the diet. Nutrient composition of each sample forage was determined chemically and the nutrient levels of cattle diets were estimated from the bite counts of forages consumed and the chemical composition of the clipped samples. Dietary deficiencies, based on estimates of dietary intake of cows and chemical composition of samples, were noted for protein and phosphorus during August and September (rotational grazing); sodium during September; iodine, copper and zinc throughout the grazing season with the exception of zinc in the September diet of rotationally grazed cows. Selenium was adequate to excessive in the diet. Cow diets consisted of from 50 to 72% grass, from 23 to 42% forbs and from 4 to 20% shrubs. The diversity of diet components maintained nutrient levels of the diet above those provided by grass alone. Weight gains of cows and calves were obtained at monthly intervals for 3 yr and seasonally for 5 yr. There were no significant differences in cow performance among years or between grazing treatments. Cows gained an average of 0.22 kg d −1 over a 90-d grazing period. Average daily gains of cows decreased from 0.55 kg in July to −0.21 kg in September. Calf gains were significantly different between treatments over 5 yr. Calf gains averaged 0.92 kg −1 d on the continuously grazed pastures vs. 0.83 kg d −1 on those rotationally grazed. Total beef production of saleable beef (calves) under the continuous and rotational grazing system was 72.7 kg ha −1 and 65.3 kg ha −1 , respectively. Key words: Beef cattle, production, nutrition, clearcuts, daily gains