Performance of Lactating Dairy Cows Fed Varying Levels of Total Mixed Rations and Pasture

 

R. E. Vibart, V. Fellner, J. C. Burns and M. Gumpertz

Abstract

An 8-week study beginning October 2004 was conducted to examine animal performance under different combinations of partially-restricted total mixed ration (TMR) feeding and high-quality pasture grazing. Thirty Holstein cows in early to mid lactation averaging 33.3 kg/d of milk at the initiation of the study were used. Cows were assigned to either an all-TMR diet (100T, no access to pasture, positive control) or one of the following three TMR-restricted dietary treatments: 1) 85% TMR-restricted diet (85T), 2) 70% TMR-restricted diet (70T), and 3) 55% TMR-restricted diet (55T). Cows on TMR-restricted diets were confined to pasture (annual ryegrass, average paddock size 0.17 ha/d) as a single group for 7 h/d between the a.m. and p.m. milking. Individual pasture intake was measured weekly on one cow selected randomly from each grazing group for 6 weeks. Body weight and body condition scores were recorded at the beginning and during weeks 5 to 8 and averaged 570 kg/cow and 3.0, respectively. Data from individual pasture intakes (n=18), total mixed ration intakes (n=30), and milk weights (n=30) were analyzed separately according to a randomized complete block design using PROC GLM with initial days in milk as a covariate. Individual pasture intakes averaged 6.9 kg/d and did not differ between grazing groups due primarily to a large variation among cows. Intakes of total mixed ration were different (P < 0.05) among all treatments and were 26.7, 17.9, 14.8, and 12.0 kg/d for 100T, 85T, 70T, and 55T, respectively. Milk yields were 36.1, 33.6, 30.5, and 30.8 kg/d for 100T, 85T, 70T, and 55T, respectively, and only tended (P = 0.06) to be different between treatments 100T and 70T. Total intakes (pasture + TMR) and milk yields were similar between cows fed 85T and 100T. As the proportion of pasture in the ration increased cows ate less TMR and maintained pasture intake. Cows fed 70T and 55T had similar milk yields to cows fed 85T and 100T but lower TMR intakes suggesting a higher feed to milk efficiency.

 

Key words: total mixed ration, grazing, milk yield.

 

The authors wish to acknowledge Weston McCorkle and Wayne McLamb for their hard work and collaboration.