Effect of variety, growing region and growing season on digestible energy content of wheats grown in Western Australia for weaner pigs

An experiment was conducted to examine the digestible energy (DE) content for weanling pigs in a cohort of wheats grown in Western Australia, and to establish relationships between DE content and their chemical composition. The 3 x 3 x 2 factorial experiment examined the wheat variety (Arrino, Stiletto and Westonia), growing location (high, medium and low rainfall zone) and harvest year (1999 and 2000). Pigs (no. = 5 per diet) aged about 28 days were given a diet at a level of 0.05 x live weight containing 900 g/kg of the wheat and an acid-insoluble ash marker for 10 days, with samples of faeces collected from each pig for the final 5 days. The average live weight of pigs was 6.6 (s.d. 0.77) kg. The DE content of wheats harvested in 1999 varied by up to 1.3 MJ/kg, while wheats harvested in 2000 varied by up to 1.8 MJ/kg. When the 2 years' data were combined, the DE content ranged from 12.5 to 14.4 MJ/kg. Both the variety and growing region significantly influenced (P < 0.05, P < 0.001, respectively in year 1999; P < 0.001, P < 0.01, respectively in year 2000) the DE content of wheat. Also, DE content of wheat differed significantly due to growing season (P < 0.001). Correlation studies between chemical composition and DE content of the wheats found significant inverse relationships between DE content and total xylose (r = -0.719, P < 0.05), insoluble xylose (r = -0.742, P < 0.05), neutral-detergent fibre (r = -0.839, P < 0.01), total-P (r = -0.833, P < 0.01), and phytate-P (r = -0.753, P < 0.05) contents with the wheats harvested in 1999. However, such relationships were not significant (P > 0.05) with the wheats harvested in 2000. In addition, the precipitation level (mm) during the growing season of wheats was strongly correlated (r = -0.821, P < 0.01) to the DE content of wheat in year 1999, but was not correlated in 2000. The results indicate that the genetic and environmental conditions during the growth of wheat have a significant impact on the utilization of plant energy in weaner pigs, and that greater attention needs to be paid to these influences in the assignment of energy values for wheats given to weaner pigs.