One of the strategies to reduce feed costs and increase efficiency is to control dry matter intake. Diets typically used for limit-feeding are more nutrient dense, allowing an increase in energy and nutrient utilization efficiency while decreasing nutrient loss. The term “Precision-feeding” is a program that provides heifers with the correct amount of nutrients necessary for adequate growth without affecting future performance. The objective of this study was to evaluate the effects on fermentation and nutrient digestion of including different unsaturated fat sources when high concentrate diets with high fat inclusion are used when simulating precision feeding in continuous culture. We hypothesized that incorporating different unsaturated fat sources to the aforementioned program can improve nutrient utilization without affecting rumen fermentation. Four treatments were randomly assigned to 8 continuous culture fermenters for 2 periods of 10 d. Treatments included a high concentrate diet (HC; 65%) with high fat inclusion starting with a basal level of fat as control [3% fat (0% fat inclusion; CON); 9% fat (6% poultry fat inclusion; PF); 9% fat (6% coconut oil inclusion; CO); and 9% fat (6% soybean oil inclusion; SOY)]. Data were analyzed using the MIXED procedure of SAS with repeated measures. The PDIFF option adjusted by Tukey method was included in the LSMEANS statement to account for multiple comparisons. Dry matter, OM, NDF, and ADF apparent digestibility (AD) were higher in CO-and PF-fed fermenters vs SOY and CON (Table 1). Mean culture pH and NH₃-N were highest in CO-fed fermenters followed by PF, then SOY, and CON. These results suggest that simulated high concentrate high fat diets can improve nutrient digestibility while affecting rumen fermentation by altering rumen pH and NH₃N concentration in continuous culture fermenters. Table 1 (Abstr. 430). Apparent digestibility of fermenters fed 3 types of fat

Digestibility, %	Type of fat				SE
CON 3%	PF 9%	SOY 9%	CO 9%
DM	66.9c	80.1a	76.4b	80.9a	0.35
OM	75.2c	85.1a	81.9b	85.8a	0.28
NDF	41.7c	59.9a	53.9b	60.7a	0.65
ADF	33.9c	50.6a	46.6b	51.2a	0.81