SOYA OIL IN THE DIET OF GROWING-FATTENING BULLS .2. EFFECTS ON METABOLISM IN THE RUMEN, APPARENT DIGESTIBILITY, PLASMA HORMONES AND METABOLITES

Two experiments were carried out with growing-fattening bulls offered a fattening diet based on concentrate and supplemented with soya oil a t an incorporation rate of 33 g/kg, so that the ether-extract content was 57 g/kg dry matter vs. 21 g/kg in the control diet. In the first. experiment, the inclusion of soya oil tended to reduce pH (6.3 vs. 6.4 ), glucose concentration (10.4 vs. 23.6 mg/l) and ammonia concentratio n (73.1 vs. 83.1 mg N/l), and to increase the concentration of volatil e fatty acids (131.9 vs. 127.8 mmol/l) in the rumen liquid. Nylon bags containing different feedstuffs were incubated in the rumen. The over all effect of soya oil supplementation were higher dry-matter disappea rance, some of the differences being significant (p < 0.10, 0.05 or 0. 01 according to the incubation time and the feedstuffs). In experiment 2, the incorporation of soya oil slightly improved the apparent diges tibility of dry matter, organic matter and fibre (77.8 vs. 76.7, 79.4 vs. 78.3, and 70.0 vs. 67.9 %). There was also a significant increase (p < 0.001) in ether-extract apparent digestibility (83.0 vs. 62.9 %). There were no effects of soya-oil inclusion on plasma glucose, alpha amino nitrogen or urea levels, but there was a trend towards higher co ncentrations in triglycerides (451.8 vs. 404.1 mu mol/l), non-esterifi ed fatty acids (237.2 vs. 191.6 mu mol/l), and cholesterol (2.80 vs. 2 .27 mmol/l). The composition of non-esterified fatty acids in plasma w as also affected, mainly with a higher C18 proportion. Soya oil did no t affect plasma hormones but there was a trend towards higher insulin secretion.