Saturated Fat Supplementation Interacts with Dietary Forage NDF Concentration during the Postpartum Period in Holstein Cows: Energy Balance, Nutrient Digestibility, and Metabolism
Forty-eight multiparous cows were used in a randomized complete block design experiment with a 2x2 factorial arrangement of treatments. Treatment diets were offered from 1 to 29 d postpartum and contained 20% or 26% forage NDF (fNDF) and 0% or 2% saturated free fatty acid supplement (Energy Booster 100; FAT). The 2% FAT treatment increased total tract digestibility of OM and NDF in the low fNDF diet (67.6% vs. 65.9% and 44.0% vs. 40.1%, respectively), but not in the high fNDF diet (interactions P ≤ 0.08). Overall, low fNDF vs. high fNDF and 2% FAT vs. 0% FAT increased digestible energy intake (DEI) (67.5 vs. 62.2 Mcal/d and 68.1 vs. 61.6 Mcal/d, respectively; both P < 0.01). An interaction between fNDF and FAT with time was detected for net energy balance (NEB): the low fNDF diet with FAT had higher NEB than the other treatments early but treatment differences diminished over time (interaction P = 0.10). Overall, low fNDF vs. high fNDF diets and 2% FAT vs. 0% FAT improved NEB (-13.0 vs. -16.3 Mcal/d and -12.0 vs. -17.3, respectively; both P < 0.05) but decreased efficiency of utilization of DEI for milk (Milk NEL/DEI; 0.575 vs. 0.634 and 0.565 vs. 0.643, respectively; both P < 0.05). Low fNDF diets increased plasma insulin (0.308 vs. 0.137 µg/L) and glucose concentrations (50.5 vs. 45.7 mg/dL), and decreased concentrations of NEFA (606 vs. 917 µEq/L) and BHBA (9.29 vs. 16.5 mg/dL; all P ≤ 0.001). The 2% FAT treatment tended to decrease plasma NEFA concentration (695 vs. 827 µEq/L; P = 0.06) compared with 0% FAT, but treatment differences diminished over time (interaction P < 0.05). The 2% FAT treatment increased maximum plasma insulin concentration during a glucose tolerance test in the low fNDF diet (84.5 vs. 44.6 µIU/mL) compared with the high fNDF diets (40.4 vs. 38.0 µIU/mL; interaction P = 0.07). FAT tended to interact with dietary fNDF concentration for insulin area under the curve: 2% FAT increased insulin area under the curve by 64% when included in the low fNDF diet (2586 vs. 1575 min*µIU/mL), but only by 5.1% when included in the high fNDF diet (1307 vs. 1243 min*µIU/mL; interaction P = 0.12). Supplementation of FAT and low fNDF diets increased DEI and improved NEB, but decreased apparent efficiency of utilization of DEI for milk production in the postpartum period.
Keywords: energy balance, postpartum, prilled fat