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ARS Home » Northeast Area » University Park, Pennsylvania » Pasture Systems & Watershed Management Research » Research » Publications at this Location » Publication #302312
Title: Feeding strategy and pasture quality relative to nutrient requirements of organic dairy cows

Author
item Orr, Aimee
item Soder, Kathy
item BRITO, ANDRE - University Of New Hampshire
item KERSBERGEN, RICHARD - University Of Maine
item BENSON, FAY - Cornell University
item DARBY, HEATHER - University Of Vermont
item Rubano, Melissa

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2014
Publication Date: 4/1/2014
Citation: Orr, A.N., Soder, K.J., Brito, A., Kersbergen, R., Benson, F., Darby, H., Rubano, M.D. 2014. Feeding strategy and pasture quality relative to nutrient requirements of organic dairy cows[abstract]. Proceedings of the Northeast Pasture Consortium. p 1.

Interpretive Summary:

Technical Abstract: According to the recently revised National Organic Program “Pasture Rule”, certified organic dairy cows are required to obtain at least 30% of diet dry matter (DM) intake from pasture during the grazing season. Therefore, understanding the nutritive quality of pasture as a feed relative to requirements of dairy cows has become increasingly important for organic farmers. Pasture samples (n = 216) were collected during the grazing season from 14 certified organic dairy farms in 2012 (in PA, ME, NY, NH, VT) and on 12 farms in 2013 (in PA, ME, NY). Nutritive composition of the pasture was measured by an independent commercial laboratory (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). Least square means are presented and differences significant at P is less than 0.05. 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**-1, 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. During farm visits, current management and production information was collected for input to LRNS. Model inputs were specific to environmental conditions, nutrient concentrations of feeds, and cow type and level of production on each farm. Year of sampling affected (P is less than 0.05) pasture CP, ADF, NEL, and Mg, such that 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**-1) and lower ADF (30.7 vs. 33.0%). This may have been due to regional areas of drought at many of the sampling areas in 2012, resulting in drought stressed forages with greater concentrations of nutritive components. Year had no effect on pasture NDF, Ca, P, K, and S. Month of sampling affected (P is less than 0.05) all pasture quality parameters except ADF (P = 0.19), revealing the expected patterns in seasonal variation of forage quality within each year. Forage quality decreased during warm, dry months when forage growth slowed and began to increase again in late summer/early fall. Farm affected (P is less than 0.05) forage quality parameters and macro-mineral concentrations except S. If pasture was the only diet component (as in Farm 3), energy was the most limiting nutrient, with 39% of pasture samples failing to meet the minimum NRC energy requirement for a Holstein cow producing 55 lbs of milk day**-1. Only 7% of pasture samples did not meet the minimum CP requirements, at the same level of production. 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; however these values are typical for pastures in this region. It is important to note that all farms in this study did provide mineral supplementation of some form. Milk production was 45.6, 37.0 and 29.9 lbs day**-1 for Farms 1, 2 and 3, respectively. Percent of daily DM consumed from pasture was related to feeding strategy, even though total DM consumption of pasture was very similar between farms, ranging from 27.2 to 28.5 lbs day**-1. Cows on Farms 1, 2, and 3 ob