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Nutrient composition and organoleptic properties of milk can be influenced by cow diets. The objective of this study was to evaluate the forage type effects on volatile organic compounds, fatty acid (FA) profile, and organoleptic properties of milk. Timothy grass was fed as hay, pasture, or silage during a period of 27 d to a group of 21 cows in a complete block design based on days in milk. Each cow also received 7.2 kg/d of a concentrate mix to meet their nutrient requirements. Forage dry matter intake averaged 13.9 kg/d and was not different among treatments. Milk yield was higher for cows fed pasture, intermediate for cows fed silage, and lowest for cows fed hay. However, milk fat content was higher for cows fed hay and silage, compared with cows fed pasture. As a result, fat-corrected milk and fat yield were not different among treatments. Increasing the supply of dietary cis-9,cis-12 18:2 (linoleic acid) and cis-9,cis-12,cis-15 18:3 (α-linolenic acid) when feeding pasture enhanced the concentration of these 2 essential FA in milk fat compared with feeding hay or silage. Moreover, the ratio of 16:0 (palmitic acid) to cis-9 18:1 (oleic acid), which is closely related to the melting properties of milk fat, was lower in milk from cows on pasture than in milk from cows fed hay or silage. Cows fed hay produced milk with higher levels of several free FA and γ-lactones, but less pentanal and 1-pentanol. More dimethyl sulfone and toluene were found in milk of cows on pasture. Cows fed silage produced milk with higher levels of acetone, 2-butanone, and α-pinene. Results from a sensory evaluation showed that panelists could not detect a difference in flavor between milk from cows fed hay compared with silage. However, a significant number of assessors perceived a difference between milk from cows fed hay compared with milk from cows fed pasture. In a sensory ranking test, the percentage of assessors ranking for the intensity of total (raw milk, fresh milk, and farm milk), sweet (empyreumatic, vanilla, caramel, and sugar), and grassy (grass, leafy vegetable, and plant) flavors was higher for milk from cows fed pasture compared with hay and silage. Using timothy hay, pasture, or silage harvested at a similar stage of development, the current study shows that the taste of milk is affected by the forage type fed to cows. More research is, however, needed to establish a link between the sensory attributes of milk and the observed changes in volatile organic compounds and FA profile. [ABSTRACT FROM AUTHOR]

Eight ruminally fistulated, multiparous Holstein cows were arranged in a double 4 x 4 Latin square with 14-d periods to investigate the effects of lipid supplementation on performance, rumen parameters, the milk odd- and branched-chain fatty acid (OBCFA) profile, and the relationships between milk OBCFA and rumen parameters. Lipid supplementation is known to inhibit microbial growth in the rumen, decrease de novo microbial fatty acid synthesis, and increase the uptake of circulating fatty acids by the mammary gland; treatments were selected to isolate these effects on the milk OBCFA profile. The 4 treatments were (1) a lipid-free emulsion medium infused in the rumen (CTL), (2) soybean oil as a source of polyunsaturated fatty acids infused in the rumen (RSO), (3) saturated fatty acids (38% 16:0, 40% 18:0) infused in the rumen (RSF), and (4) saturated fatty acids infused in the abomasum (ASF). Fat supplements were provided continuously as emulsions at a rate of 450 g/d. Preplanned contrasts compared CTL to RSO, RSO to RSF, and RSF to ASF. Infusing RSO slightly decreased ruminal pH, but did not affect volatile fatty acids profile and milk fat concentration as compared with CTL. The yields of energy-corrected milk, fat, and protein were greater with RSF compared with RSO. The concentration of odd-chain fatty acids was decreased by RSO, whereas even-chain iso fatty acids were not affected. Milk fat concentration of 17:0 + cis-9 17:1 was higher for RSF than for RSO, due to the saturated fatty acids supplement containing 2% 17:0 + cis-9 17:1. Limited differences were observed in the milk OBCFA profile between RSF and ASF. A multiple regression analysis yielded the following equation for predicting rumen pH based on milk fatty acids: pH = 6.24 - (0.56 x 4:0) + (1.67 x iso 14:0) + (4.22 x iso 15:0) + (9.41 x 22:0). Rumen propionate concentration was negatively correlated with milk fat concentration of iso 14:0 and positively correlated with milk 15:0, whereas the acetate-to-propionate ratio gave the opposite correlations with milk iso 14:0 and 15:0. Milk fat concentration of 17:0 + cis-9 17:1 was not related to rumen propionate or to acetate-to-propionate ratio, due to the presence of 17:0 and cis-9 17:1 in the saturated fatty acids supplement. The results suggest that although lipid supplementation can affect the profile of milk OBCFA, the promise remains of using these milk fatty acids to evaluate rumen function. [ABSTRACT FROM AUTHOR]

Given its elevated content of carotenoids, alfalfa protein concentrates (APC) have the potential to prevent oxidation of milk enriched in polyunsaturated fatty acids. The effects of feeding APC or supplemental vitamin E on production, composition, and oxidative stability of milk enriched in polyunsaturated fatty acids were evaluated using 6 lactating Holstein cows (224 ± 18 d in milk) in a replicated 3 × 3 Latin square (21-d periods, 14 d for adaptation). Treatment diets contained (dry matter basis) (1) 9% soybean meal (control, CTL); (2) 9% soybean meal + 300 IU of vitamin E/kg (VitE treatment); or (3) 9% APC (APC treatment). Cows received a continuous abomasal infusion of 450 g/d of linseed oil. As a result, milk fat content of cis-9,cis-12 18:2 increased from 1.08 ± 0.13 to 3.9 ± 0.40% (mean ± SD), whereas cis-9,cis-12,cis-15 18:3 increased from 0.40 ± 0.04 to 14.27 ± 1.81% during the experimental period compared with the pretrial period. Milk yield tended to be higher for APC (14.7 kg/d) compared with CTL (13.4 kg/d), and was greater than that for VitE (13.0 kg/d). Protein yield was higher in cows fed APC (518 g/d) compared with VitE (445 g/d) but was not different from that in cows fed CTL (483 g/d). These effects resulted in improved milk N efficiency in cows fed APC (26.1% of N intake secreted in milk) compared with CTL (23.0%) and VitE (22.9%). Feeding APC increased milk fat content of lutein (252 μg/g) compared with CTL (204 μg/g) and VitE (190 μg/g). Milk fat content of vitamin E was higher for APC (34.5 μg/g) compared with CTL (19.0 μg/g) and tended to be lower than that with VitE (44.9 μg/g). Redox potential of fresh milk from cows fed APC (152 mV) was similar to that of VitE (144 mV), but lower than that of CTL (189 mV). Treatments had no effect on fresh milk contents of dissolved oxygen (8.1 ± 1.5 mg/L), and conjugated diene hydroperoxides (2.7 ± 0.5 mmol/L). The concentrations of volatile lipid oxidation products (propanal, hexanal, hept-cis-4-enal, 1-octen-3-one) tended to be decreased by APC relative to CTL, whereas similar values were observed for VitE, except for hexanal, which was reduced by 40% in VitE. In conclusion, feeding APC to lactating dairy cows could serve as a source of dietary protein that improves dietary N utilization efficiency, and also as a preharvest technology to increase natural antioxidant levels in milk to limit oxidation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the effects of conjugated linoleic acid (CLA), Sterculia foetida oil (STO), and fish oil (FO) on milk yield and composition, milk FA profile, Δ9 -desaturation activity, and mammary expression of 2 isoforms of stearoyl-coenzyme A desaturase (SCD-1 and SCD-5) in lactating dairy cows. Eight multiparous Holstein cows (69 ± 13 d postpartum) were used in a double 4 x 4 Latin square design with 28-d periods. For the first 14 d of each period, cows received an abomasal infusion of (1) 406 g of a saturated fatty acid (SFA) supplement (112 g of 16:0 + 230 g of 18:0) used as a control (CTL), (2) 36 g of a CLA supplement (13.9 g of trans-10,cis-12 18:2) + 370 g of SFA, (3) 7 g of STO (3.1 g of 19:1 cyclo) + 399 g of SFA, or (4) 406 g of FO (55.2 g of cis-5,-8,-11,-14,-17 20:5 + 59.3 g of cis-4,-7,-10,-13,-16,-19 22:6). Infusions were followed by a 14-d washout interval. Compared with CTL, STO decreased milk yield from 38.0 to 33.0 kg/d, and increased milk fat concentration from 3.79 to 4.45%. Milk fat concentration was also decreased by CLA (2.23%) and FO (3.34%). Milk fat yield was not affected by STO (1,475 g/d) compared with CTL (1,431 g/d), but was decreased by CLA (774 g/d) and FO (1,186 g/d). Desaturase indices for 10:0, 12:0, and 20:0 were decreased, whereas the extent of desaturation of 14:0, 16:0, 17:0, and 18:0 was not affected by CLA treatment compared with CTL. Infusion of STO significantly decreased all calculated desaturase indices compared with CTL; the 14:0 index was reduced by 80.7%. Infusion of FO decreased the desaturase indices for 10:0, 14:0, 20:0, trans-11 18:1, and 18:0. The effect of FO on the 14:0 index indicates a decrease in apparent Δ9 -desaturase activity of 30.2%. Compared with CTL, mammary mRNA abundance of SCD-1 was increased by STO (+30%) and decreased by CLA (-24%), whereas FO had no effect. No effect was observed on mRNA abundance of SCD-5. In conclusion, abomasal infusion of CLA, STO, and FO were shown to exhibit varying and distinct effects on desaturase indices, an indicator of apparent SCD activity, and mammary mRNA abundance of SCD-1. [ABSTRACT FROM AUTHOR]