Surface Runoff Quality Evaluations from Two Systems for Over-wintering Beef Cows.

Over-wintering cattle out of doors can be detrimental to the areas that cattle occupy and cause increased runoff, sediment loss, and nutrient transport.  Two systems of over-wintering cattle were evaluated for their environmental impacts over a 12-yr period, November 1974 – October 1986.  In one system, beef cows were moved on 6-7 day intervals among four pastures during the summer growing season (May – October), rotated through hayed areas to eat fall regrowth, and rotated through these areas to feed on the hay made in those areas.  In another system, cows were rotated weekly during summer and then continuously fed hay in one winter area during the dormant season (November – April).  Vegetative cover in the continuous wintering area frequently decreased to less than 50% by late winter/early spring.  Monthly runoff averages were greater from the continuous wintering system than the rotational wintering system in 9 out of 12 months (annual runoff of 120.4 and 37.5 mm, respectively),  Sediment loss was greater from the continuous system (2.68 and 0.24 Mg ha^-1, respectively).  Surface runoff losses of N were greater during the dormant season (13.2 and 6.7 kg ha^-1 for the continuous and rotational wintering systems, respectively) than the growing season (4.6 and 1.3 kg ha^-1, respectively).  Runoff, sediment, and N losses were less with a rotational wintering system than with a continuous occupancy wintering system, but the animal occupancy rate was also much greater in the continuous system compared with the rotational system (1497 and 1860 cow days ha^-1 compared with 528 and 576 cow days ha^-1).  Although a direct comparison cannot be made between these two systems because of differences in several variables, this rotational wintering system was more sustainable than the continuous wintering system, but more land area per cow was necessary.