Responses to graded postruminal doses of histidine in dairy cows fed grass silage diets

Five Finnish Ayrshire cows were used in a 4 x 4 Latin square experiment designed to study the effects of graded doses of postruminal His infusion on milk production, arterial concentrations, and mammary uptakes of plasma amino acids (AA) as well as utilization of added His. Grass silage (16.9% CP) was given ad libitum with 8 kg of cereal-based concentrate per day (11.3% CP). Treatments were abomasal or duodenal infusions of 250 g of glucose/d in combination with 0, 2, 4, or 6 g of His/d. Infusions did not affect dry matter intake (mean 18 kg/d). Infusion of His increased milk yield linearly from 27.0 to 28.8 kg/d, protein yield from 861 to 919 g/d and lactose yield from 1345 to 1457 g/d. Milk fat yield and content changed in a cubic manner (1240, 1167, 1296, and 1177 g/d and 4.60, 4.16, 4.60, and 4.09). Infusion of His had no influence on milk protein or lactose concentrations. Arterial Lys and His concentrations increased linearly, but other AA concentrations were unaffected as well as calculated arteriovenous differences and mammary AA uptakes. The extraction of His decreased linearly with an increasing amount of His. The utilization of added His (28%) was not affected by the level of infusion, and mammary AA uptake seemed to be regulated by an inverse relationship between arteriovenous difference of essential AA and calculated mammary plasma flow. This experiment confirmed that His is the first-limiting AA on grass silage-cereal based diets.     

Effect of plant oils and camelina expeller on milk fatty acid composition in lactating cows fed diets based on red clover silage

Five multiparous Finnish Ayrshire cows fed red clover silage-based diets were used in a 5 × 5 Latin square with 21-d experimental periods to evaluate the effects of various plant oils or camelina expeller on animal performance and milk fatty acid composition. Treatments consisted of 5 concentrate supplements containing no additional lipid (control), or 29 g/kg of lipid from rapeseed oil (RO), sunflower-seed oil (SFO), camelina-seed oil (CO), or camelina expeller (CE). Cows were offered red clover silage ad libitum and 12 kg/d of experimental concentrates. Treatments had no effect on silage or total dry matter intake, whole-tract digestibility coefficients, milk yield, or milk composition. Plant oils in the diet decreased short- and medium-chain saturated fatty acid (6:0-16:0) concentrations, including odd- and branched-chain fatty acids and enhanced milk fat 18:0 and 18-carbon unsaturated fatty acid content. Increases in the relative proportions of cis 18:1, trans 18:1, nonconjugated 18:2, conjugated linoleic acid (CLA), and polyunsaturated fatty acids in milk fat were dependent on the fatty acid composition of oils in the diet. Rapeseed oil in the diet was associated with the enrichment of trans 18:1 (Δ4, 6, 7, 8, and 9), cis-9 18:1, and trans-7,cis-9 CLA, SFO resulted in the highest concentrations of trans-5, trans-10, and trans-11 18:1, Δ9,11 CLA, Δ10,12 CLA, and 18:2n-6, whereas CO enhanced trans-13-16 18:1, Δ11,15 18:2, Δ12,15 18:2, cis-9,trans-13 18:2, Δ11,13 CLA, Δ12,14 CLA, Δ13,15 CLA, Δ9,11,15 18:3, and 18:3n-3. Relative to CO, CE resulted in lower 18:0 and cis-9 18:1 concentrations and higher proportions of trans-10 18:1, trans-11 18:1, cis-9,trans-11 CLA, cis-9,trans-13 18:2, and trans-11,cis-15 18:2. Comparison of milk fat composition responses to CO and CE suggest that the biohydrogenation of unsaturated 18-carbon fatty acids to 18:0 in the rumen was less complete for camelina lipid supplied as an expeller than as free oil. In conclusion, moderate amounts of plant oils in diets based on red clover silage had no adverse effects on silage dry matter intake, nutrient digestion, or milk production, but altered milk fat composition, with changes characterized as a decrease in saturated fatty acids, an increase in trans fatty acids, and enrichment of specific unsaturated fatty acids depending on the fatty acid composition of lipid supplements.