Feeding Strategy and Pasture Quality Relative to Nutrient Requirements of Grazing Dairy Cows in the Northeastern U.S

Abstract Text: Pasture samples (n = 229) collected during the grazing season from 14 organic dairy farms in 2012 (PA, ME, NY, NH, VT) and from 11 of the same farms in 2013 (PA, ME, NY, NH) were analyzed for nutritional composition. Frequency analysis was used to determine the proportions of pasture samples that met minimum NE_L, CP, and macro-mineral requirements according to the NRC (2001) model for a 680 kg Holstein, producing 25 kg milk/d with 3.5% milk fat and 3.0% milk protein. The Large Ruminant Nutrition System (LRNS, Version 1.0.24) was used to describe feeding strategies that accompanied grazing on 8 of the participating farms. Four farms had moderate conserved feed input (> 20% diet DM not from pasture; MF), and fed corn silage, grass/legume balegae or haylage, and/or a grain mix and dry hay, 2 farms supplemented pasture with a grain mix (GS), and 2 farms fed forage only (pasture and dry hay; FO). Management and production information used in the LRNS model were specific to environmental conditions, nutrient concentrations of feeds, cow type, and level of production for each farm. If pasture was the only diet component, energy was the most limiting nutrient, with 39% of pasture samples failing to meet the minimum NRC NE_L requirement. Only 7% of pasture samples did not meet the minimum CP requirements. Calcium, P, and S did not meet minimum NRC requirements in 35, 18, and 10% of pasture samples, respectively. Average concentrations of Mg and K were in excess of 156 and 1,113% of dietary requirements. Milk production was observed to be higher on MF farms (23 kg/d), but was comparable on GS and FO farms, averaging 15 kg/d for both. Proportion of DMI from pasture was related to feeding strategy and ranged from 51 to 79% on MF farms, 84 to 96% on GS farms, and 91 to 100% on FO farms. Metabolizable protein provided by the total diet (pasture and supplementation) exceeded the requirements at the specified level of production and environmental conditions except for 1 farm (the MF farm with the lowest amount of DMI coming from pasture). Rumen N balance was negative for both GS farms (-18 and -33 g/d). Overall, the forage quality of pastures evaluated was high. Additionally, varying feeding strategies allow farmers to use resources such as pasture, homegrown forages, and grains to meet individual goals of milk production.

Keywords: pasture, grazing, dairy