The effect of feeding protected dietary lipid supplements on the fatty acids composition of the blood serum and the milk fats of lactating ewes

This work was undertaken to assess the potential of acetaldehyde and diacetyl as alternative protective agents to formaldehyde, a carcinogen, for the commercial production of products from ruminant animals (cattle, sheep, goat) with increased unsaturated fatty acid (18:1, 18:2 and 18:3) contents. In experiment 1, different gels were prepared with emulsions of (1) defatted soy flour-casein-sunflower oil, (2) ground full-fat soybean seeds-casein and (3) ground full-fat sunflower seeds-casein. Each gel protein—oil emulsion was treated with 5% (w/w emulsion) formaldehyde (FA) (37% solution), acetaldehyde (AC), diacetyl (DA) to form a gel or not treated (CO).

The microstructures of type 1 gels were determined by scanning electron microscopy. Protection of the unsaturated fatty acids in all gel types from ruminal biohydrogenation for all treatments (FA, AC and DA) was evaluated in vitro before and after incubation with strained rumen fluid at 39°C for 48 hrs. At digestion times, 0, 24 and 48 hrs, the fatty acid contents of digested gels were determined by gas chromatography.

The first experiment showed that the levels of linoleic acid (18:2) were significantly lower in ruminal digests containing the control supplement than in digests containing FA, AC, and DA-treated gel digests, regardless of the type of oilseed. Meanwhile, the levels of octadecenoic (18:lc+t) and stearic (18:0) acids were higher in the control digest than in the treated ones. Results showed that FA, AC and DA treatment could protect the unsaturated fatty acids than the CO, in all types of gel. Diacetyl, at the level (5%) applied, was less effective in preventing biohydrogenation of the unsaturated fatty acids in the sunflower supplement.

In experiment 2, dietary lipid supplements in gel form were prepared with ground full-fat soybeans, treated with 2.2% FA, AC and DA or nothing (CO). Lactating ewes in a 4x4 Latin square feeding trial design received a daily ration (2.5 to 3.0 Kg) grass hay plus .5 Kg (ground corn, soybean meal, oats and alfalfa pallets) supplemented with 1.0 Kg of one of the lipid supplement gels.

The levels of linoleic acid (18:2) in the ewes blood serum fat increased (p<0.05) by 42, 41. and 25% for FA, AC and DA treatments, respectively, in relation to the control diet. The levels of 18:2 in the ewes milk increased (p<0.05) by 114, 52 and 43% for FA, AC and DA treatments, respectively, in relation to the control diet. Neither storage period nor treatment affected (p>0.05) the fatty acid content of the dietary lipid supplements. Feeding the protected supplements enhanced growth in the lambs but did not affect the weights of the ewes.