Feeding strategy and pasture quality relative to nutrient requirements of organic dairy cows

Authors: Soder, Kathy; HAFLA, AIMEE - Agri-King, Inc; BRITO, ANDRE - University Of New Hampshire; Rubano, Melissa

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 12/13/2015
Publication Date: 12/13/2015
Citation: Soder, K.J., Hafla, A., Brito, A., Rubano, M.D. 2015. Feeding strategy and pasture quality relative to nutrient requirements of organic dairy cows[Abstract]. Proceedings of the 2015 National Grazing Lands Coalition meeting, December 13-16, 2015, Grapevine, TX. p. 1.

Interpretive Summary: An interpretive summary is not required.

Technical Abstract: Pasture samples (n = 216) were collected during the grazing season from 14 certified northeastern organic dairy farms in 2012 and 2013 for nutritive composition (Dairy One). A Mixed model (SAS Inst., 1998) was used to test effect of year of sampling, month of sampling, and farm on crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), net energy for lactation (NEL), calcium (Ca), phosphorus (P), magnesium (Mg), potassium (K), and sulfur (S). Frequency analysis was used to determine the proportions of pasture samples that met minimum energy, CP and macro-mineral requirements, according to the Dairy NRC (Nutrient Requirements of Dairy Cows, 2001) for a 1496 lb Holstein, producing 55 lbs milk/day, with 3.5% milk fat and 3.0% milk protein. Finally, the Large Ruminant Nutrition System (LRNS, Version 1.0.24) was used to model feeding strategies that accompany grazing on 3 of the participating farms, early in the grazing season. Farm 1 practiced component feeding of grain, silage, and hay, Farm 2 supplemented with a homegrown grain mix, and Farm 3 fed an all-forage diet (pasture) with minimal dry hay. Year of sampling affected (P < 0.05) pasture CP, ADF, NEL, and Mg- pasture quality was slightly better in 2012 compared to 2013, as characterized by greater levels of CP (19.9 vs. 18.1%) and NEL (0.63 vs. 0.60 Mcal/lb) and lower ADF (30.7 vs. 33.0%) due to dry environmental conditions in 2012. Year had no effect on pasture NDF, Ca, P, K, and S. Month of sampling affected (P < 0.05) all pasture quality parameters except ADF (P = 0.19), revealing the expected patterns in seasonal variation of forage quality within each year. Farm affected (P < 0.05) forage quality parameters and macro-mineral concentrations except S. If pasture was the only diet component (Farm 3), energy was the most limiting nutrient, with 39% of pasture samples failing to meet the minimum NRC energy requirements. Only 7% of pasture samples did not meet minimum CP requirements. Calcium, P and S did not meet minimum NRC dietary requirements in 33, 17, and 10% of pasture samples, respectively. Average concentrations of Mg and K were in excess of 161 and 1,117% of dietary requirements. Cows on Farms 1, 2, and 3 obtained 79, 85 and 91% of daily DM intake from pasture, respectively. Metabolizable protein provided by the total diet (pasture and supplementation) exceeded requirements for all 3 farms evaluated. However, nitrogen available to rumen microbes was found to be slightly deficient for Farm 2 (balance of -0.04 lbs/day; pasture + 5 lbs DM grain), possibly due to the low soluble protein in the diet (28.8% of CP). Energy concentrations of the total diets were comparable for Farms 1, 2 and 3 (0.69, 0.70 and 0.71 Mcal/day NEL DM, respectively). Crude protein concentrations (as a % of DM) of the diets were 15.2, 14.9, and 18.5% for Farms 1, 2, and 3, respectively. Energy was found to be the first limiting nutrient for milk production while CP generally met or exceeded minimum NRC animal requirements. Regardless of supplementation strategy, cows were observed to consume a comparable amount of pasture daily (approximately 28 lbs DM). Varying feeding strategies allows producers to use feed resources such as pasture and homegrown forages and grains to meet individual goals of milk production for each farm.