Composition of flaxseed recovered from the faeces of dairy cows fed different proportions of whole flaxseed in the diet

Three multiparous lactating Holstein cows averaging 699 kg of body weight (SE = 76.2) were allotted in a 3 × 3 Latin square design to determine the nutrient profile of flaxseed recovered from the faeces of dairy cows fed different amounts of whole flaxseed and to compare the chemical composition of dietary flaxseed to that of flaxseed recovered from faeces. The three dietary treatments consisted of three total mixed diets containing 50, 75 or 100 g/kg dry matter (DM) whole flaxseed. Milk production, milk composition and total tract apparent digestibility (TTAD) were also determined. Intake of DM, milk yield and composition, production of milk components and TTAD of acid detergent fibre (ADF) and ether extract (EE) were similar among treatments. Total tract apparent digestibility of DM and crude protein (CP) decreased linearly with higher concentration of whole flaxseed in the diet and TTAD of neutral detergent fibre (aNDF) was quadratically affected. Composition of flaxseed recovered from the faeces of cows fed the three diets was generally similar. Concentrations of CP and EE in flaxseed recovered from the faeces were lower and higher, respectively, compared to those of flaxseed consumed by cows and there was no difference in aNDF and ADF concentrations. Proportions of 14:0, 15:0, 16:0, 17:0, trans11-18:1, cis9,trans11-18:2, and 20:0 in flaxseed recovered from the faeces decreased linearly with greater proportions of dietary flaxseed and that of cis9,12,15-18:3 increased. Proportions of 16:0 and cis9-16:1 decreased linearly and those of trans9-18:1, trans13+14-18:1+cis6+8-18:1, 19:0, cis9,cis12,cis15-18:3 increased linearly in milk fat with higher amounts of whole flaxseed in the diet. The amount of flaxseed recovered in faeces increased in parallel with the amount consumed. However, the linear decrease in TTAD of DM and CP with increasing proportion of whole flaxseed in the diet and the trend for better TTAD of aNDF for cows fed 50 g/kg DM than for those fed greater amounts of whole flaxseed suggest that productivity of dairy cows could be negatively affected when feeding more than 50 g/kg DM whole flaxseed.