Associative effects of feeding varying levels of soyhulls to lambs consuming grass hay
Soyhulls are routinely utilized as a supplement to forage based diets in ruminants. Previous studies have focused on low and moderate supplementation rates where soyhulls have generally been effective and economical. Recent grain prices have increased pressure on livestock producers to potentially expand their use of soyhulls in situations where higher levels of performance are desired. The objective of this study was to compare the effect of various levels of soyhull supplementation on nutrient digestibility in lambs fed a basal diet of chopped grass hay. Eight St. Croix cross wether lambs (39±4 kg) were randomly assigned to four diets using a 4x4 replicated Latin square design. All lambs were offered a chopped grass hay free choice and supplemented at 0, 1, 2 or 3% of body weight in soyhulls (DM basis). Each period consisted of a 9d adjustment period followed by a 5d collection period. Lambs were housed individually and fitted with total fecal collection bags during the adjustment period of each diet. At the conclusion of each collection period and before proceeding to the next adjustment period, lambs were weighed to adjust supplementation levels. During collection periods, daily feed, refusals and feces weights were recorded and samples retained for analysis. Samples were dried, ground, and analyzed for dry matter (DM), crude protein (CP), ash, neutral detergent fiber (NDF) and acid detergent fiber (ADF). Data were analyzed in SAS using the PROC GLIMMIX procedure with a model including diet and period. Linear, quadratic and cubic treatment effects were evaluated using preplanned contrasts. Daily DM intake increased linearly (P<.01) with increasing soyhull supplementation. Dry matter digestibility increased quadratically (P<.01) as soyhull supplementation increased (56.6, 63.0, 65.4 and 66.4, respectively). Similarly, both NDF and ADF digestibility exhibited a quadratic response (P<.01) as dietary soyhull level increased. However, contrary to DM digestibility, NDF and ADF displayed peak digestibility at the 2% supplementation level. Results would suggest that supplementation of soyhulls above 2% of body weight would provide diminishing benefits as compared to lower levels of supplementation. Depression of NDF and ADF digestibilities at the 3% supplementation level contributed to the reduced DM digestibility improvement. Further research is needed to determine if reduced fiber digestibility was the result of increased rate of passage and reduced ruminal digestion.
Keywords: Soyhulls, Associative effects, Lambs