Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: February 26, 2011
Publication Date: July 12, 2011
Citation: Boyd, J.A., Mertens, D.R. 2011. Abrupt changes in forage dry matter of one to three days affect intake and milk yield in late lactation dairy cows. Journal of Dairy Science. 94(E-Supplement 1):378. Technical Abstract: Our objective was to determine if late lactation cows were susceptible to 1-, 2-, and 3-day changes in forage DM. Forty-four Holstein cows (22 primiparous and 22 multiparous), averaging 155 DIM, 42.5 kg/d of milk, and 597 kg body weight, were used in a study conducted from Jan to Mar 2010. Within each parity, cows were assigned to 1 of 11 blocks based on production and DIM, and one cow of each parity block was randomly assigned to 1 of 2 groups. Study design was replicated 2x2 Latin squares for each set of 1-, 2-, or 3-day treatments. Each period consisted of a 3-day pretreatment, 1- to 3-day treatment, and a 3-day post-treatment phase. Diets contained about 18% alfalfa and 36% corn silage (DM basis). The control (Ctrl) was with no water added; treatment (Trt) was with water added to mimic rainfall events on a bunker silo and feeding an imprecise ration based on as-fed ratios of ingredients. Ctrl ration was adjusted daily to maintain constant DM ratios of ingredients during the study. Milk yield was recorded daily, and component samples were taken twice daily. Forages, TMR, and refusals were sampled daily, and concentrates were sampled twice weekly. Chemical composition (DM, CP, NDF) of samples was determined by NIR. Alfalfa silage samples dried at 55C for 48 hours obtained 2 percentage units higher DM than predicted by NIR. Thus, water addition was underestimated, resulting in a 3 percentage unit change in forage DM instead of the target 8 percentage unit change that was planned. Data were analyzed using Proc MIXED of SAS with cow within parity block as a random variable. On day 1, DMI was reduced 1.22 (P< 0.0001), 0.67 (P=0.04), and 2.06 kg (P=0.0001), for the 1-, 2-, and 3-day treatments, respectively. The amount of feed offered was adjusted based on refusal level, and DMI recovered during the following 1 to 3 days even during Trt phases. Milk yield and components were not affected by treatment (P > 0.37). We concluded that abrupt changes in forage DM reduce daily feed intakes, but a change >3 percentage units in forage DM is necessary to affect milk yields and components for late lactation cows.