Journal of Dairy Research

Table of Contents - November 2008 - Volume 75, Issue 04  

Research Article

Performance of lactating dairy cows fed varying levels of total mixed ration and pasture

Ronaldo E Vibarta1 p1, Vivek Fellnera1 c1, Joseph C Burnsa1a2, Gerald B Huntingtona1 and James T Green Jra2

a1 Department of Animal Science, North Carolina State University, Raleigh, NC 27695–7621 USA

a2 USDA–ARS and Department of Crop Science, North Carolina State University, Raleigh, NC 27695–7621 USA

Abstract

Two, 8-week experiments, each using 30 lactating Holstein cows, were conducted to examine performance of animals offered combinations of total mixed ration (TMR) and high-quality pasture. Experiment 1 was initiated in mid October 2004 and Experiment 2 was initiated in late March 2005. Cows were assigned to either a 100% TMR diet (100:00, no access to pasture) or one of the following three formulated partial mixed rations (PMR) targeted at (1) 85% TMR and 15% pasture, (2) 70% TMR and 30% pasture and (3) 55% TMR and 45% pasture. Based on actual TMR and pasture intake, the dietary TMR and pasture proportions of the three PMR in Experiment 1 were 79% TMR and 21% pasture (79:21), 68% TMR and 32% pasture (68:32), and 59% TMR and 41% pasture (59:41), respectively. Corresponding proportions in Experiment 2 were 89% TMR and 11% pasture (89:11), 79% TMR and 21% pasture (79:21) and 65% TMR and 35% pasture (65:35), respectively. Reducing the proportion of TMR in the diets increased pasture consumption of cows on all PMR, but reduced total dry matter intake compared with cows on 100:00. An increase in forage from pasture increased the concentration of conjugated linoleic acids and decreased the concentration of saturated fatty acids in milk. Although milk and milk protein yields from cows grazing spring pastures (Experiment 2) increased with increasing intakes of TMR, a partial mixed ration that was composed of 41% pasture grazed in the fall (Experiment 1) resulted in a similar overall lactation performance with increased feed efficiency compared to an all-TMR ration.

(Received October 29 2007)

(Accepted April 16 2008)

(Online publication August 14 2008)

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Correspondence:

c1 For correspondence; e-mail: Vivek_Fellner@ncsu.edu

p1 Present address: Grasslands Research Centre, Palmerston North 4442, New Zealand