Research and Reviews: Dairy 2001

Special Circular 182-01

Factors Affecting the Production of Conjugated Linoleic Acid in Dairy Cows

Materials and Methods

Experiment 1

A dual-flow continuous culture system consisting of 4 glass fermentors was used in a 4 x 4 Latin square design. Compared to treatment 1 (Control), each of the other three treatments varied in one of the three factors: solid dilution rate (SDR), level of LA addition, and pH:

1. Control: pH = 6.5, LA addition = 1%, SDR = 4%/hour;
2. High SDR (HSDR): pH = 6.5, LA addition = 1%, SDR = 8%/hour;
3. High LA (HLA): pH = 6.5, LA addition = 3%, SDR = 4%/hour; and
4. Low pH (LPH): pH = 5.8, LA addition = 1%, SDR = 4%/hour.

Inoculum was collected 6 hours after feeding from a ruminally cannulated Holstein cow fed 40% alfalfa hay and 60% grain. The temperature of the fermentors was held at 39 + 0.1 °C, and liquid dilution rate was held at 12%/hour. Each period consisted of 10 days with the first 7 days for equilibration and the last 3 days for sample collection. The fermentors were continuously fed a diet (120 g/d DM) mainly containing alfalfa hay (38%), corn (27.5%), and soybean hulls (25.5%). All diets except HLA contained 2% tallow. The LA was dissolved in buffer and continuously infused into the fermentors at 3% of DM intake for HLA and 1% for the other three treatments.

On each morning of the last 3 days, contents from filtrate and overflow containers were mixed for each fermentor, and 1000 ml of the effluent mixture were evacuated into a plastic jug. Samples from the three consecutive sampling days were composited and frozen for later analysis. At 1500 hours of day 9, 20 ml of contents from each fermentor were collected as inoculum for the Most Probable Number (MPN) procedure (Dehority et al. 1989) to estimate the total and cellulolytic bacteria number. The fatty acid (FA) contents of feed and effluent samples were analyzed according to the procedure described by Sukhija and Palmquist (1988).