The effect of stage of harvest on the processes of digestion in cattle fed winter oats indoors. I. Digestion of organic matter, neutral detergent fibre and water-soluble carbohydrates

Abstract

The objective of this trial was to study the digestion process of organic matter (OM), neutral detergent fibre (NDF) and water-soluble carbohydrates (WSC) of winter oats ( Avena sativa L.) of different stages of harvest fed indoors. Treatments and dates of harvest were: A (25 May, autumn), EW (25 June, early winter), W (9 August, winter), ES (22 September, early spring), LS (20 October, late spring). Two Holstein heifers weighing 567.6 ± 17.8 kg were used, each fitted with cannulas in the rumen, proximal duodenum and distal ileum. Chromic oxide and Co-EDTA were used as external markers. A completely randomized design was arranged considering dates of harvest as treatment effect. OM intakes (g kg −1 live weight (LW)) were higher ( P < 0.03) in A (16.5) than in the other treatments. Apparent OM digestibilities (g g −1) ranged ( P < 0.002) from 0.63 (A) to 0.76 (LS). The fractions of digestible OM intake (DOMI) apparently digested (OMADR) and truly digested (OMTDR) in the rumen were not influenced ( P > 0.05) by treatments (mean 0.66 g g −1 and 0.87 g g −1 DOMI for OMADR and OMTDR, respectively). A high correlation was found between DOMI and OMTDR (OMTDR (g) = − 287.2 + 0.925DOMI (g); r = 0.89, P < 0.001). DOMI digested in the small intestine was not different ( P > 0.05) between dates (mean 0.27 g g −1). DOMI digested in the large intestine (g g −1) was lower ( P < 0.04) in ES and LS (mean 0.06) than for other dates. The NDF intakes (g kg −1 LW) ranged between 6.6 and 9.5, being higher ( P < 0.002) in A. Apparent OM digestibility was lower ( P < 0.01) in LS (0.51 g g −1). The digestible NDF intake digested in the rumen and small and large intestines was not different between dates. The WSC intake (WSCI) and apparent digestibility were higher ( P < 1 × 10 −7) in ES (4.13 g kg −1 LW, 0.99 g g −1) than in A (0.86 and 0.87, respectively). Nearly 98% of the digestible WSCI was apparently digested in the rumen. A correlation between pH and digestible WSC intake (DWSCI) was found (pH = 6.51 − 2.16 × 10 −4DWSCI, r = 0.65, P < 0.04). The acetic: propionic ratio was lower ( P < 7 × 10 −4) in ES (3.2) and highest in A (4.42). In fresh winter oats, OMTDR was high and the differences between dates were important only for WSC content and these could have affected pH and the acetic:propionic ratio.