Ruminant Nutrition: Dairy: Protein and Fat

Dietary coconut oil (CO), a source of saturated, predominantly mediumchain fatty acids (FA), reduced enteric methane emission, but also reduced DMI and milk yield in our earlier studies. Here, we examined lactational performance of early lactation cows fed 2 sources of saturated FA, differing in predominant chain lengths. Dietary treatments were: no added fat (CTRL); 2.7% of DM as saturated long-chain FA (Energy Booster 100; EB) or 2.7% CO; or, a 2.7% mixture of equal parts EB and CO (INT). Primiparous (PP; n = 31) and multiparous (MP; n = 36) Holstein cows 10 to 14 d postpartum were fed one of 4 treatments for 16 wk in a randomized complete block design. CTRL diet contained corn and alfalfa silages (53% of DM), dry ground corn, soybean meal, plus mineral and vitamin supplement; it was formulated to contain 26.5% NDF (83% from forages), 17.6% CP, 29.6% starch, and 3.6% fat. Milk yield and DMI were recorded daily, and blood was collected weekly. Main effects of diet, parity, time (repeated measures), and relevant interactions were tested by least-squares ANOVA. Reported values differed (P < 0.05). Overall, cows fed CTRL had the greatest DMI. Fat source with greater chain length increased DMI linearly for MP cows (CO: 22.7; INT: 24.7; EB: 27.0 kg/d), and quadratically for PP cows (18.5; 21.0; 20.3 kg/d). Similar interactions of treatment by parity were observed for yields of solids-corrected milk and milk components. CO reduced milk fat (3.1%) and lactose (4.73%) concentrations compared with EB (3.8% and 4.92%), pooled across time and parity. Plasma glucose concentration did not differ among fat treatments and CTRL across the 16 wk. Fat source interacted with parity; INT had the lowest glucose concentration for PP, but highest for MP. During wk 1 to 4 of study, MP had lower plasma glucose than PP (52 vs. 58 mg/dL), which coincided with greater plasma BHBA (7.0 vs. 4.8 mg/dL) and NEFA (710 vs. 380 μeq/L) concentrations in MP. Body condition loss through wk 4 was greater for CO and CTRL than for INT and EB. Overall, dietary CO reduced DMI compared with EB leading to a greater FA mobilization in early lactation.