| The objective of this study was to investigate the effects of supplemental vegetable oil on rumen fermentation and concentration of conjugated linoleic acid (CLA) in milk fat.A two way factorial trial was designed in Trial 1 to investigate the effect of supplementation of vegetable oils on rumen fermentation in vitro. Five kinds of oil sources (cotton seed, soybean, rapeseed, corn and sunflower) were used to substitute for cornmeal as culture substance at levels of 0, 2 and 4%, respectively. Gas syringes were used as incubators in gas production (GP) test. The incubation was stopped at 24 h. After the GP was recorded, the contents were determined for the pH, ammonia nitrogen and carboxymethyl cellulase(CMC) activity.Compared to the control, supplementation with vegetable oils reduced the GP (P<0.01), with lower GP value at higher level of supplemental oils. No significant differences were observed in the GP among the five oils (p>0.05), except that it was much lower in 2% rapeseed oil-supplemented group than in others (P<0.05). Supplementation of vegetable oils decreased CMC activity significantly (p<0.05), which was 3.74-9.34 and 6.99-11.88IU lower at levels of 2 and 4%, compared to the unsupplemented. The CMCactivity did not differ (p>0.05) among the oils from soybean, com and sunflower, and showed little differences between cottonseed oil and rapeseed oil (p>0.05). Vegetable oils did not alter pH and ammonia-N greatly at both supplemented levels. These results indicated that supplemental vegetable oils can cause the inhibition of fermentation and cellulase activity in the rumen, with greater effect at higher supplemental level. Based on the magnitude of these effects and the composition of fatty acids in oils, it is considered that the 2 % of oils from cotton seed, corn and soybean may be suitable to use in the diets for lactating dairy cows.In Trial 2, twelve Holstein lactating cows at early stage of lactation (30-45 d postpartum) were used in a 4 x 4 Latin square design to examine the effect of supplemental vegetable oils on milk performance and CLA concentration in milk fat. All cows were offered corn silage (18.3%), alfalfa hay (25%) and ground corn (31%) based diet with protein supplements (8.0%), CaHCO3 (1.2%) and vitamin/mineral premix (1.4%). In each period, the animals in each group received one of the following supplements: (1) None (control). (2) 500g cottonseed oil, (3) 500g soybean oil and (4) 500g corn oil. Five hundred grams of oils was equivalent to about 2% of diets. Each experimental period lasted for three weeks, the first two weeks of which was the period of adaptation to the diet.Supplemental vegetable oils tended to increase milk yield (P>0.05), with the highest milk yield in cottonseed oil supplemented group (35.04 kg/d), compared to the control (34.37 kg/d). Milk fat percentage was decreased (p<0.05), but there was little effect on daily protein percentage and yield, and milk fat yield. The cows supplemented with soybean oil produced milk with highest concentration of trans 11 18:1 (23.8 mg/g fat), which doubled that in the control (12.6 mg/g fat). The concentration of trans 11 18:1 in milk fat for cottonseed oil and corn oil was 19.9 and 20.1 mg/g. The concentration of cis 9, trans 11-CLA in milk fat was increased to 6.0, 7.1 and 10.3 mg/g for the animals supplemented with cottonseed oil, corn oil and soybean oil, respectively from 3.5 mg/g for the control. A significant linear relationship existed between trans 11 C18:l and cis 9, trans11-CLA (R2=0.655, p<0.05). Supplementation with vegetable oils resulted in tripletotal fatty acid concentration in blood plasma (P<0.01), with little difference between different oil sources (P>0.05). The concentrations of octadecenoic acid (18:1) was significantly (P<0.05) higher in blood plasma of animals supplemented with oils from cottonseed and soybean than that with corn oil and control. The plasma trans 11-C18:1 concentration was 11.1, 12.5 and 14.2 mg/g in animals with oils from cottonseed, corn and soybean respectively, and signif... |
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