Intake and digestion of fatty acids by dairy cows fed whole flaxseed and Ca salts of flaxseed oil

Four ruminally lactating Holstein cows averaging 602 kg of body weight and 64 days in milk were randomly assigned to a 4 × 4 Latin square design to determine the effects of feeding whole flaxseed and calcium salts of flaxseed oil on intake and total tract apparent digestibility (TTAD) of fatty acids (FA) and apparent transfer of linolenic acid in milk fat. The treatments were for ad libitum intake: a control diet with no flaxseed products (CON) or a diet of 42 g/kg dry matter (DM) whole flaxseed (FLA), 19 g/kg DM calcium salts of flaxseed oil (SAL) or 23 g/kg DM whole flaxseed and 8 g/kg DM calcium salts of flaxseed oil (MIX). Experimental periods consisted of 21 d of diet adaptation and 7 d of data collection and sampling. Intake of α-linolenic acid (cis9,12,15-18:3) was similar for cows fed FLA, SAL, and MIX and higher than for those fed CON. Output of linolenic acid in faeces was higher for cows fed FLA, followed by those fed MIX, CON, and SAL. Output of α-linolenic acid in milk tended (P=0.07) to be lower for cows fed CON than for those fed the other diets and there was no difference between cows fed FLA, SAL, and MIX. Although intake of α-linolenic acid was lower for cows fed CON than for those fed the other diets, transfer efficiency (g per 100 g of α-linolenic acid consumed) was higher for cows fed the former diet. Feeding FLA, SAL, and MIX resulted in similar apparent transfer of α-linolenic acid in milk. Cows fed FLA had the lowest TTAD of linolenic acid. The high digestibility of Ca-salts of flaxseed oil accounts for the interest in using it in practical applications for feeding cows. However, as previous results have shown that the use of Ca-salts of flaxseed oil did not allow a large modification in milk fat composition, the cheapest flaxseed product will be recommended to incorporate in the dairy cow diet.