THE EFFECTS OF PHYSICAL FORM OF FEED, CARBOHYDRATE SOURCE, AND INCLUSION OF SODIUM-BICARBONATE ON THE DIET SELECTIONS OF SHEEP

We proposed an hypothesis that ruminants attempt to select a diet that promotes high levels of feed intake by maintaining optimal ruminal co nditions. Three tests of the hypothesis considered whether the diet se lection of sheep given either a choice of two high energy density (ED) feeds or a choice between a high and a low ED feed is affected by 1) sodium bicarbonate inclusion (NaHCO3; 1, 2, and 4% [wt/wt]) in the hig h [ED] feed); 2) dietary carbohydrate source (barley-based, B and suga r beet/barley, S) of the high ED feed; or 3) physical form (alfalfa: p elleted, ALFP and long chop, ALFL) of the low ED feed. To conduct thes e, 42 lambs were used in seven 6 x 6 Latin squares, which were either foods ALFL and ALFP offered alone and paired with feed B or S and thei r NaHCO3 derivatives as a choice, or foods B and S offered alone and p aired with their NaHCO3 derivatives as a choice. Each Latin square per iod lasted for 3 wk. For the choices between a NaHCO3-supplemented hig h ED feed and either a high or a low ED one, the inclusion of NaHCO3 i ncreased feed intake. Its level of inclusion had a marked effect on th e proportion of unsupplemented high ED feed selected (P < .05) but not on the proportion of low ED feed (alfalfa) selected. More alfalfa was selected when the high ED feed was based on barley(B) rather than sug ar beet/barley (S) (P < .05). The physical form of the alfalfa affecte d diet selection because its selection was greater (P < .001) when ALF P (pelleted) was offered in the feed choice rather than ALFL (long-cho p). The significant effects of NaHCO3 level, dietary carbohydrate, and physical form on the diet selection and feed intake of the sheep are consistent with the proposed experimental hypothesis.