Pine needle consumption by cattle during winter in South Dakota.

Abstract

Pregnant cattle that consume ponderosa pine (Pinus ponderosa (Lawson) needles often abort. The objectives of these studies were to: 1) determine needle consumption by grazing cattle; 2) relate consumption in pen-fed and grazing cattle to weather variables; and 3) determine if needle temperature influenced consumption in pen-fed cattle. Trial 1 was conducted from 3 Dec. 1991 to 12 Feb. 1992 near Custer, S. Dak. Eight mature cows grazed a 9-ha pasture. Needle consumption was measured using bite counts H. and fecal analysis. The winter was mild, and cattle consumed few needles (< 2% of bites). Trial 2 was conducted in the same location from 5 January to 2 March 1993, using 6 pregnant cows kept in pens and 5 open cows grazing the pasture. The pen-fed cows were offered 1 kg of fresh pine needles daily; methods for grazing cattle were the same as in the previous trial. Further, the pen-fed cows were offered warm or cold green needles in 2 acceptability trials. Grazing cattle consumed an average of 20% of bites as pine needles. As snow depth increased, pine needle consumption increased, particularly from short (< 2 m tall) tree (P < 0.01). The percent of bites of green needles was related (r2 = 0.69) to minimum temperature and snow depth, with greater consumption at colder temperatures and at deeper snow depths. As snow depth increased, cattle reduced daily grazing time (P < 0.01); at colder temperatures, cattle also reduced grazing time (P < 0.05). Pen-fed cows ate 483 g pine needles/day (fresh weight), with no abortions occurring. Cattle preferred cold needles to warm needles (P < 0.05) in January, despite tree size; whereas, the opposite result was noted in February. We conclude that snow depth, reduced amounts of grazable forage, and cold ambient temperatures are crucial factors in consumption of ponderosa pine needles by grazing cattle.