Effects of toasting and decortication of oat on nutrient digestibility in the rumen and small intestine and on amino acid supply in dairy cows

Abstract

This study examined the potential for decorticating and toasting of oat (Avena sativa) to supply crude protein (CP) and amino acids (AA) in dairy cows. Four lactating Danish Holstein Friesian cows fitted with ruminal, duodenal, and ileal cannulas were assigned to a 4 × 4 Latin square design. Cows were fed experimental diets ad libitum based on grass-clover silage and toasted fava beans, with oat included in different forms arranged in a 2 × 2 factorial: whole oat, decorticated oat, toasted oat, and decorticated toasted oat. In situ rumen degradability of processed oat was also evaluated. Decortication increased starch intake by 0.38 kg/d and reduced NDF intake by 0.91 kg/d. Toasting reduced ruminal AA digestibility and increased duodenal flow of CP by 0.41 kg/d. In situ degradation rate and effective degradability of CP in the rumen were reduced by 0.46 h −1 and 310 g/kg CP due to toasting. Both decortication and toasting increased microbial synthesis of CP by 0.20 and 0.41 kg/d, respectively. Decortication and toasting did not affect small intestinal AA digestibility, but did increase the total digested amount of AA by 154 and 250 g/d, respectively. Milk production was not affected by treatments. Methane production (L/d) decreased with decortication and toasting. In conclusion, unless an interaction exists between decortication and toasting, the results indicate additive effects of toasting and decorticating oat for increasing the supply of digestible AA to the small intestine of dairy cows.

Effect of toasting and decortication of oat on rumen biohydrogenation and intestinal digestibility of fatty acids in dairy cows

“…Therefore, in the present study, it is difficult to attribute the reduced total FA, and especially C18: 2n -6, to either nonenzymatic oxidation of FA or inactivation of antioxidants or both during toasting. However, the decrease in FA concentration in this study was large enough to make toasting at temperatures required for protein protection irrelevant for oat, as the potential gain in protein value (Panah et al, 2020a) is overruled by the decrease in crude fat and FA, and thereby energy value, of oat.…”

“…The average BW of cows at the onset of the experiment was 618 ± 47.9 kg (mean ± standard deviation); the cows were at 61.3 ± 49.9 d in milk, and their BCS was 3 ± 0.20 (mean ± standard deviation). On d 17 through 22, the enteric methane emission was measured in respiration chambers, as already reported by Panah et al (2020a).…”

“…However, Panah et al (2020a) reported an increase in both microbial protein and AA synthesis due to decortication, possibly as a consequence of the increased starch intake concurrent with the increased fat content of oat by decortication. Toasting can protect protein against rumen degradation and then counteract the negative effect of increased fat supply on the metabolizable protein supply to the cow (Panah et al, 2020a). Gonthier et al (2005) reported that heat treatment of oilseeds can protect the protein matrix surrounding the fat droplets against rumen degradation, and thereby protect UFA against ruminal biohydrogenation (BH).…”

“…Increasing the fat content in the diet through decorticated oat might compromise the supply of AA because fat is not fermented in the rumen (Brask et al, 2015). However, Panah et al (2020a) reported an increase in both microbial protein and AA synthesis due to decortication, possibly as a consequence of the increased starch intake concurrent with the increased fat content of oat by decortication. Toasting can protect protein against rumen degradation and then counteract the negative effect of increased fat supply on the metabolizable protein supply to the cow (Panah et al, 2020a).…”

“…Gonthier et al (2005) reported that heat treatment of oilseeds can protect the protein matrix surrounding the fat droplets against rumen degradation, and thereby protect UFA against ruminal biohydrogenation (BH). Panah et al (2020a) showed that toasting oat reduced the ruminal digestibility of AA and in situ degradability of CP, causing the increased flow of both CP and AA at the duodenum.…”