Search

This experiment studied the effect of 3 forms of presentation of linseed fatty acids (FA) on methane output using the sulfur hexafluoride tracer technique, total tract digestibility, and performance of dairy cows. Eight multiparous lactating Holstein cows (initial milk yield 23.4 [+ or -] 2.2 kg/d) were assigned to 4 dietary treatments in a replicated 4 x 4 Latin square design: a control diet (C) consisting of corn silage (59%), grass hay (6%), and concentrate (35%) and the same diet with crude linseed (CLS), extruded linseed (ELS), or linseed oil (LSO) at the same FA level (5.7% of dietary DM). Each experimental period lasted 4 wk. All the forms of linseed FA significantly decreased daily C[H.sub.4] emissions (P< 0.001) but to different extents (-12% with CLS, -38% with ELS, -64% with LSO) compared with C. The same ranking among diets was observed for C[H.sub.4] output expressed as a percentage of energy intake (P < 0.001) or in grams per kilogram of OM intake (P < 0.001). Methane production per unit of digested NDF was similar for C, CLS, and ELS but was less for LSO (138 vs. 68 g/kg of digested NDF, respectively; P < 0.001). Measured as grams per kilogram of milk or fat-corrected milk yield, methane emission was similar for C and CLS and was less for ELS and LSO (P < 0.001), LSO being less than ELS (P < 0.01). Total tract NDF digestibility was significantly less (P < 0.001) for the 3 supplemented diets than for C (-6.8% on average; P < 0.001). Starch digestibility was similar for all diets (mean 93.5%). Compared with C, DMI was not modifled with CLS (P > 0.05) but was decreased with ELS and LSO (-3.1 and -5.1 kg/d, respectively; P < 0.001). Milk yield and milk fat content were similar for LSO and ELS but less than for C and CLS (19.9 vs. 22.3 kg/d and 33.8 vs. 43.2 g/kg, on average, respectively; P < 0.01 and P < 0.001). Linseed FA offer a promising dietary means to depress ruminal methanogenesis. The form of presentation of linseed FA greatly influences methane output from dairy cows. The negative effects of linseed on milk production will need to be overcome if it is to be considered as a methane mitigation agent. Optimal conditions for the utilization of linseed FA in ruminant diets need to be determined before recommending its use for the dairy industry. Key words: dairy cow, digestion, fatty acid, linseed, linseed oil, methane

We assessed the effects of nutrient supply and dietary bulk, both increasing with hay intake, on [O.sub.2] uptake and nutrient net fluxes across the portal-(PDV) and mesenteric- (MDV) drained viscera, and the rumen in adult ewes. Four ewes, fitted with a ruminal cannula, with catheters in the mesenteric artery, the portal, mesenteric and right ruminal veins, and with a blood flow probe around the right ruminal artery, were used in a 4 x 4 Latin square design. Treatments consisted of 500 g DM/d hay (LL, low bulk and low nutrient supply), 500 g DM/d hay + infused nutrients (LH, low bulk and high nutrient supply), 750 g DM/d hay + infused nutrients (MH, medium bulk and high nutrient supply), and 1,000 g DM/d hay (HH, high bulk and high nutrient supply). Infused nutrients consisted of volatile fatty acids (VFA) and casein dissolved in salts and infused continuously in the rumen to provide the same amount of metabolizable energy (7.6 MJ/d) and digestible protein (63 g/d) for LH, MH, and HH. Both increases in bulk and nutrient supply increased [O.sub.2] uptake in the MDV and PDV. Dietary bulk stimulated mainly blood flow, whereas nutrient supply stimulated mainly [O.sub.2] extraction rate. The [O.sub.2] uptake by the rumen was not significantly affected by hay intake, although blood flow increased due to nutrient supply. Increase in hay intake had no effects on portal net release of lactate and net uptake of glucose but increased VFA, 3-D-hydroxybutyrate, ammonia, and amino acids (AA) net release and urea net uptake across PDV. The increase in portal nutrient net fluxes with hay intake was entirely related to the increase of nutrient supply for VFA, 3-D-hydroxybutyrate, ammonia, and urea, irrespective of the amount of casein infused for AA. Dietary bulk had no effect on total energy net re]ease in the portal vein. We conclude that despite the increase in portal [O.sub.2] uptake, increasing dietary bulk had no significant impact on portal recovery of energy. In ruminal tissues, which were the main site of energy absorption, [O.sub.2] uptake appeared low and was not sensitive to dietary manipulation. In contrast, in mesenteric tissues, which contribute poorly to energy absorption with forage diets, [O.sub.2] uptake appeared high and very sensitive to dietary manipulation. Key Words: Intake, Dietary Nutrients, Oxygen Consumption, Nutrient Absorption

The effects of supplemental calcium salts of rapeseed oil fatty acids (FA) and rapeseed oil on ruminal metabolism and apparent digestibility of lipids in the small intestine were studied using three multiparous Holstein X Friesian cows in a 3 X 3 Latin square design. Cows fitted with ruminal, duodenal, and ileal cannulas were fed restricted amounts of a control diet (C) containing 65% corn silage and 35% concentrate mix or diet C with supplemental calcium salts of rapeseed oil FA (S) or diet C supplemented with rapeseed oil (O). Fatty acid contents were 1.9, 8.4, and 7.6% for diets C, S, and O, respectively. The average flow of total FA to the duodenum was lower than the intake for supplemented treatments, suggesting catabolism of FA by ruminal microbes. Fatty acid flows at the duodenum were higher (P < .10) for diets supplemented with fat than for diet C, except for C18:3(n-3) and straight-chain and branched-chain C15 and C17. Fat treatment affected total and individual FA flow to the ileum, except C14:0 and C18:2(n-6) and excreted amount of individual FA, except C14:0, C16:0, and total C18:1. In our trial, the addition of fat, regardless of origin, affected small intestinal digestibilities of C14:0 and C18:2(n-6) and did not affect changes in the amount of FA in the hindgut.

The aim of this experiment was to study the effects on digestion of a supply of Ca salts of vegetable oil as a fat source for ruminants. Total tract digestibility and ruminal digestion were studied using three ruminally and duodenally fistulated dairy cows in a Latin square design. Diets compared were a control diet (C) based on corn silage and concentrate, and the C diet supplemented with calcium salts of rapeseed oil (S) or supplemented with rapeseed oil (O). Organic matter digestibility was lower (P < .05) for diet O than for diet C; diet S was intermediate and not different (P > .05) from diet C. Treatment did not affect (P > .05) the proportion of OM digested in the rumen, total N and microbial N flow at the duodenum, or efficiency of N microbial synthesis. In situ degradation of DM and NDF was higher for diet S than for diet C. The molar concentration of ruminal acetate was lower (P < .05) for O than for C and S. Under the conditions of this trial, supplemental calcium salts rich in polyunsaturated fatty acids did not decrease ruminal digestion.