Effects of soybean hull inclusion on dietary energy value and nitrogen balance in growing gilts

The objective of this study was to determine the effect of increasing dietary soybean hull inclusion on diet digestibility, energy content, and nitrogen (N) balance in growing gilts. A 21-day study was conducted with two groups of 24 gilts with a starting body weight of 45.5 kg ±2.2 kg housed in individual metabolism stalls. Gilts were fed one of four dietary treatments containing either 0%, 10%, 20%, or 40% soybean hulls for a total of 12 gilts per treatment. The four diets were formulated to equal a standardized ileal digestibility (SID) lysine: metabolizable energy (Lys: ME) of 3.41. During the 21 days, gilts were evaluated over three collection periods. Each period consisted of four days of total fecal and urine collection. Gilts remained on their respective diets for the duration of the study. Urine, fecal, feed, and soybean hull samples were analyzed for N and gross energy concentration. Data were analyzed using SAS 9.4 using the GLIMMIX procedure, and gilt was the experimental unit. Results were considered significant if P ≤ 0.05. Feed intake was not different as soybean hull inclusion increased but increased across collection periods (P < 0.001). Apparent total tract digestibility (ATTD) of crude protein decreased linearly as soybean hull inclusion increased (P ≤ 0.001). Fecal N excretion increased as soybean hull inclusion increased (P ≤ 0.001) and over the three collection periods (P <0.001). Total urine N excretion increased over time and soybean hull inclusion caused a linear reduction in urinary N excretion (P ≤ 0.001). Nitrogen retention (g/d) was reduced by greater soybean hull inclusion (P = 0.028). Metabolizable energy (ME) decreased as soybean hulls inclusion increased in the diets (P ≤ 0.001). In conclusion, increasing soybean hulls up to 40% in the diet increased fecal N excretion and decreases urine N excretion and the ATTD of N. Additionally, the increase in soybean hulls in the diet decreased the ME value, while ME values increased as the time on the diet increased.