Research and Reviews: Dairy 2001

Special Circular 182-01

Factors Affecting the Production of Conjugated Linoleic Acid in Dairy Cows

Materials and Methods

Experiment 2

Four ruminally and duodenally cannulated primiparous cows averaging 106 + 17 days in milk were used in a 4 x 4 Latin square design. The treatments were as follows:

1. control = diet contained 2% fish oil and fed ad libitum;
2. buffer addition (BUFF) = same as control except that 0.8% sodium bicarbonate was added as a buffer;
3. low DM intake (LDMI) = fish oil and nutrient concentrations were increased from control and DM intake was restricted to 80% of the control; and
4. soybean oil (SBO) = same as control except that 2% soybean oil was fed instead of fish oil.

The diets consisted of 13.9% legume silage, 6.5% grass hay, 15.9% corn silage, and 63.7% concentrate. Diets were prepared once daily as TMR and fed twice daily at 0700 and 1800 hours.

The four cows were fed for 18 days per period, with the last 7 days devoted to data collection for DM intake and milk yield. The last 4 days of each period were devoted to collection of milk composition and digestibility data. During the first 4 days of each period, the cow on the LDMI treatment was fed the control diet while the other three cows were on their assigned diets. The DMI during the first 4 days were then used to determine the amount of feed to be offered from days 5 to 18 based on 80% of ad libitum intake for the cow fed the LDMI diet.

Feeds offered and refusals were sampled during days 15 through 18, composited, and frozen for later analysis. The duodenal flow of DM was determined by ruminal dosing of Cr₂O₃ (mixed with soybean hulls and pelleted, 5% Cr₂O₃) as an external marker. Milk samples were taken at both the am and pm milkings on two consecutive days for determination of milk fat and protein. Duodenal samples were taken every 6 hours during the 4-day collection period, with the starting time being alternated by 1.5 hour each day.

The FA contents of feed, digesta, and milk samples were analyzed. Milk fat and protein were determined using infrared spectroscopy, and milk urea nitrogen (MUN) was determined by using a Skalar SAN Plus segmented flow analyzer (Skalar, Inc., Norcross, GA) at the Dairy Herd Improvement Laboratory (DHI Cooperative, Inc., Powell, OH).

All statistical analyses of the data except those of ruminal pH and VFA in Experiment 2 were performed using the General Linear Model procedure of the SAS (1997). Effects of cow (fermentor), period, and treatment were tested. Data of ruminal pH and VFA from Experiment 2 were analyzed with Proc Mixed procedure of SAS (1997). Effects of time, period, treatment, and treatment x time were tested. Mean separation was performed using the Least Significant Difference procedure when the treatment effect was significant. Significance was declared at P < 0.05 unless otherwise noted.