FEED INTAKE AND NUTRIENT DIGESTIBILITY OF GROWING LAMBS SUPPLEMENTED INTRAGASTRICALLY WITH FULL-FAT RAPESEED (CV. TOWER)

Abstract

Seventeen lambs were used to study the effects of ruminal and/or abomasal infusions of rapeseed on voluntary feed intake, nutrient digestibility and nitrogen retention. The basal diet (65% barley, 30% ground hay) contained 92% dry matter, 12% protein and 3.9 kcal/g of gross energy as fed. In experiment 1, full-fat rapeseed (FFRS, 25% protein, 50% fat) was either heated in boiling water or non-heated and infused into the abomasum of lambs as a 20% solids suspension to provide 25% of the daily energy requirement for maintenance. The intake, nutrient digestion and nitrogen retention of lambs were not affected by the heat treatment. In experiment 2, abomasal infusions of 0, 100, 200 and 400 ml of saline did not affect the "hunger drive" or daily feed intake of lambs. In experiment 3, FFRS (20% solids) was infused into the abomasum at levels of 12.5 and 25% of the energy requirements for maintenance with no infusion as control. Within 30 min post-infusion, voluntary energy intake decreased with increasing levels of FFRS infused (r = − 0.68, P < 0.01), but the total of the energy consumed during this time period plus that infused was not different. Nutrient digestibility, nitrogen retention and average daily gains were not affected by the infusion level. In experiment 4, 15% of maintenance energy requirements were infused as FFRS into the rumen or abomasum. Voluntary energy intake at 30 min post-infusion was lower following infusions into the rumen or abomasum as compared to no infusion (P < 0.01). Daily energy intake, weight gain and nutrient digestibility were not affected by the site of infusion. Nitrogen retention was lower when FFRS was infused into the rumen. In experiment 5, partially extracted rapeseed (31% protein, 15% fat) was infused into the abomasum to supply either 0.1 or 0.2 g of nitrogen per kg0.75 body weight and compared to non-infused controls. Voluntary intake at 30 min post-infusion was lower for lambs that received the infusions (P < 0.02). Daily energy intake and nitrogen retention were not affected by the level of infusion. Nutrient digestibility increased gradually with each level of infusion (P < 0.01). These experiments indicate that intra-abomasal supplementation with Tower FFRS does not improve the performance of growing lambs fed a pelleted diet containing about 12% crude protein. The FFRS protein had low solubility in rumen fluid, in vitro, and therefore may be only partially degraded in the rumen in vivo.