Evaluation of a high forage total mixed ration on the lactational performance of late lactation dairy cows

Dairy producers continuously ask questions challenging the paradigm of how much forage can be included in the ration to meet the nutrient requirements of lactating dairy cows to support milk production. The production and feeding of forages having both high dry matter digestibility (DMD) and neutral detergent fiber digestibility (NDFd) are needed to increase nutrient supply. Mid- to late-lactation lactating Holstein dairy cows were blocked by parity (10 primiparous and 10 multiparous), milk production (range 33.9 to 56.6; μ = 41.5 kg/d), and days in milk (DIM) (range 140 to 287; μ = 225 d) and randomly assigned within blocks to 1 of 2 rations based on medium forage (MF) or high forage (HF) inclusion rates. A forage blend consisting of 60% second cutting (2012) alfalfa haylage and 40% (2012) corn silage blended on a DM basis and then fed at either 60% (MF) or 80% (HF) of the ration DM. The alfalfa haylage DM (DMD = 75.7%) and NDF (NDFd = 55.7%) digestibility was above average, but corn silage (DMD = 72.9, NDFd = 52.3%, and starch = 32.1%) was average. The experimental design was a randomized completed block design with 4 continuous weeks for data collection preceded by a 1 wk covariate data collection period in which all cows were fed the MF ration. Cows were milked 3 times/d and milk weights recorded at each milking and milk samples were collected at each milking once weekly for analysis of milk composition. Rations were similar in crude protein (CP; 16.4%), starch (20.1%), acid detergent fiber (ADF; 21.8%), and NDF (34.1%) concentrations. Covariately adjusted milk production (28.1 and 24.1 kg/d for MF and HF, respectively) and 4% fat-corrected milk (FCM; 27.6 and 24.1 kg/d) were significantly reduced by feeding the HF ration compared with cows fed the MF ration, while milk fat (3.98 and 4.0%), milk protein (3.11 and 3.17%), milk lactose (4.81 and 4.77%), and milk solids-not-fat (8.87 and 8.77%) percentages were similar for cows fed both rations. Cows on the HF ration demonstrated a significant reduction in DMI and a trend for decreased body weight (BW) when compared with cows fed the MF ration. The forage nutrient digestibility was not adequate to support the milk production of mid- to late-lactation dairy cows when fed at 80% of the DM. The forage nutrient digestibility when fed at very high inclusion rate (80%) could not meet the nutrient requirements of mid- to late-lactation dairy cows.