EFFECT OF FEED PROCESSING ON VOLATILE FATTY ACID PRODUCTION RATES MEASURED WITH 13C-ACETATE IN GRAZING LACTATING DAIRY COWS

The effect of processed cereal grain supplementation on volatile fatty acid (VFA) production rates of grazing, lactating Holstein-Friesian cows were measured in a 5x5 Latin square experiment. The experimental treatments were as follows: control (only grazing, no supplement addition, NS), pelleted barley (PB), pelleted maize (PM), toasted and subsequently pelleted barley (TPB), and toasted and subsequently pelleted maize (TPM) as supplements. An isotope dilution technique using stable isotope of carbon (13C) as an internal marker was employed for the estimation of VFA production. At the beginning of a 3-hour long allowed grazing time, 100 mg of 99% enriched 13C2 Na-acetate were introduced in the rumen and repeated after grazing with 50 mg isotope, after which the cows were starved for 6 hours until evening milking. During grazing disappearance rate (kdis) and production rate (kprod) of acetate, propionate and butyrate were significantly higher (P≤0.05) in supplemented than in NS cows. Moreover the effect of barley grain and pelleting treatment was higher than the effect of maize grain and toasting. During starvation significantly higher (P≤0.05) kdis and kprod of VFAs were observed in PM and TPM treatments. Total VFA production for the experimental period (grazing + starvation) were 49.5, 78.7, 69.9, 88.5, 80.8 mol/day for NS, PB, TPB, PM and TPM, respectively. The higher VFA productions measured in supplemented animals emphasis the extensive digestion that occurs in the rumen after feeding processed grains. In methodological terms, 13C2 Na-acetate labelling appears to be a useful means for examining the VFA acetate production in ruminants

Effects of feeding rapeseed oil, soybean oil, or linseed oil on stearoyl-CoA desaturase expression in the mammary gland of dairy cows

Stearoyl-CoA desaturase (SCD) is an important enzyme in the bovine mammary gland, and it introduces a double bond at the ¿(9) location of primarily myristoyl-, palmitoyl-, and stearoyl-CoA. The main objective of this study was to compare the effects of various fatty acids (FA) typically present in dairy cow rations on the expression of SCD1 and SCD5 in the mammary gland of dairy cows. Twenty-eight Holstein-Friesian cows were randomly assigned to 1 of 4 dietary treatments. The dietary treatments were a basal diet supplemented (dry matter basis) with 2.7% rapeseed oil as a source of C18:1 cis-9; 2.7% soybean oil as a source of C18:2 cis-9,12; 2.7% linseed oil as a source of C18:3 cis-9,12,15; or 2.7% of a 1:1:1 mixture of the 3 oils. The oil supplements were included in the concentrate, which was fed together with corn silage and grass silage. In addition, cows were grazing on pasture, consisting mainly of perennial ryegrass, during the day. Biopsies from the mammary gland were taken and analyzed for mRNA expression of SCD1 and SCD5 by using quantitative real-time PCR. Milk yield as well as milk protein and fat contents did not differ among the 4 dietary treatments. Dietary supplementation with rapeseed oil and linseed oil increased proportions of C18:1 cis-9 and C18:3 cis-9,12,15 in blood plasma, respectively, compared with the other treatments. Supplementation with soybean oil and linseed oil increased milk FA proportions of C18:2 cis-9,12 and C18:3 cis-9,12,15, respectively, but supplementation with rapeseed oil did not increase C18:1 cis-9 in milk. Mammary SCD1 expression was reduced by supplementation of soybean oil compared with rapeseed oil and linseed oil. In contrast, SCD5 expression did not differ among the 4 treatments. The C16 and C18 desaturation indices, representing proxies for SCD activity, were lower for the soybean oil diet compared with the diet supplemented with a mixture of the 3 oils. In conclusion, our study shows that mammary SCD1 expression is significantly downregulated in dairy cows by feeding unprotected soybean oil compared with rapeseed oil or linseed oil, and this is partially reflected by the lower desaturase indices in the milk. Furthermore, mammary SCD5 expression appears to be differently regulated than expression of SCD

Effects of forage type, forage to concentrate ratio, and crushed linseed supplementation on milk fatty acid profile in lactating dairy cows

The effects of an increasing proportion of crushed linseed (CL) in combination with varying forage type (grass or corn silage) and forage to concentrate ratio (F:C), and their interactions on milk fatty acid (FA) profile of high-producing dairy cows was studied using a 3-factor Box-Behnken design. Sixteen Holstein and 20 Swedish Red cows were blocked according to breed, parity, and milk yield, and randomly assigned to 4 groups. Groups were fed different treatment diets formulated from combinations of the 3 main factors each containing 3 levels. Forage type (fraction of total forage dry matter, DM) included 20, 50, and 80% grass silage, with the remainder being corn silage. The F:C (DM basis) were 35:65, 50:50, and 65:35, and CL was supplied at 1, 3, and 5% of diet DM. Starch and neutral detergent fiber content (DM basis) of the treatment diets ranged from 117 to 209 g/kg and 311 to 388 g/kg, respectively. Thirteen treatment diets were formulated according to the Box-Behnken design. During 4 experimental periods of 21 d each, all treatment diets were fed, including a repetition of the center point treatment (50% grass silage, 50:50 F:C, 3% CL) during every period. Intake, production performance, and milk FA profile were measured, and response surface equations were derived for these variables. Shifting from 80% grass silage to 80% corn silage in the diet linearly increased dry matter intake (DMI), net energy for lactation (NEL) intake, cis-9,cis-12-C18:2 (C18:2n-6) intake, and milk yield, and linearly decreased cis-9,cis-12,cis-15-C18:3 (C18:3n-3) intake and milk fat content. Shifting from a high forage to a high concentrate diet linearly increased DMI, NEL intake, C18:2n-6 intake, and milk yield, and decreased milk fat content. Supplementation of CL linearly increased C18:3n-3 intake, but had no effect on DMI, NEL intake, milk yield, or milk fat content. Shifting from 80% grass silage to 80% corn silage linearly increased proportions of trans-10-C18:1 and C18:2n-6 in milk fat, whereas the proportions of trans-11,cis-15-C18:2 and C18:3n-3 linearly decreased. Significant interactions between CL supplementation and F:C were found for proportions of trans-10-C18:1, trans-15-C18:1, cis-15-C18:1, trans-11,cis-15-C18:2, and C18:3n-3 in milk fat, with the highest levels achieved when the diet contained 5% CL and a 35:65 F:C ratio. The effect of supplementing CL on several milk FA proportions, including C18:2n-6 and C18:3n-3, depends significantly on the F:C ratio and forage type in the basal diet

Effects of feeding rapeseed oil, soybean oil, or linseed oil on stearoyl-CoA desaturase expression in the mammary gland of dairy cows

Stearoyl-CoA desaturase (SCD) is an important enzyme in the bovine mammary gland, and it introduces a double bond at the ¿(9) location of primarily myristoyl-, palmitoyl-, and stearoyl-CoA. The main objective of this study was to compare the effects of various fatty acids (FA) typically present in dairy cow rations on the expression of SCD1 and SCD5 in the mammary gland of dairy cows. Twenty-eight Holstein-Friesian cows were randomly assigned to 1 of 4 dietary treatments. The dietary treatments were a basal diet supplemented (dry matter basis) with 2.7% rapeseed oil as a source of C18:1 cis-9; 2.7% soybean oil as a source of C18:2 cis-9,12; 2.7% linseed oil as a source of C18:3 cis-9,12,15; or 2.7% of a 1:1:1 mixture of the 3 oils. The oil supplements were included in the concentrate, which was fed together with corn silage and grass silage. In addition, cows were grazing on pasture, consisting mainly of perennial ryegrass, during the day. Biopsies from the mammary gland were taken and analyzed for mRNA expression of SCD1 and SCD5 by using quantitative real-time PCR. Milk yield as well as milk protein and fat contents did not differ among the 4 dietary treatments. Dietary supplementation with rapeseed oil and linseed oil increased proportions of C18:1 cis-9 and C18:3 cis-9,12,15 in blood plasma, respectively, compared with the other treatments. Supplementation with soybean oil and linseed oil increased milk FA proportions of C18:2 cis-9,12 and C18:3 cis-9,12,15, respectively, but supplementation with rapeseed oil did not increase C18:1 cis-9 in milk. Mammary SCD1 expression was reduced by supplementation of soybean oil compared with rapeseed oil and linseed oil. In contrast, SCD5 expression did not differ among the 4 treatments. The C16 and C18 desaturation indices, representing proxies for SCD activity, were lower for the soybean oil diet compared with the diet supplemented with a mixture of the 3 oils. In conclusion, our study shows that mammary SCD1 expression is significantly downregulated in dairy cows by feeding unprotected soybean oil compared with rapeseed oil or linseed oil, and this is partially reflected by the lower desaturase indices in the milk. Furthermore, mammary SCD5 expression appears to be differently regulated than expression of SCD