ARS | Publication request: Assessment of heifer grazing experience on adaptation to pasture and performance as lactating cows

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 31, 2013
Publication Date: April 22, 2013
Citation: Lopes, F., Combs, D.K., Hoffman, P.C., Coblentz, W.K. 2013. Assessment of heifer grazing experience on adaptation to pasture and performance as lactating cows. Journal of Dairy Science. 96:3138-3152.

Interpretive Summary: Dairy research facilities have struggled for years with lingering questions about how to properly select cows for use in grazing experiments. Several theories exist among researchers, as well as stakeholders, about the most appropriate approaches for resolving this problem. One approach has been to use cows from the research herd that are typically managed in confinement, provided an acceptable adaptation period is allowed before starting the grazing trial. Others feel that a designated grazing herd is required for grazing experiments; however, this adds a significant financial burden to research facilities. Our objective was to determine how grazing experiences early in life affect behavior and milk production of first-lactation cows grazing high-quality pastures. Four groups of dairy heifers were assigned to different grazing experiences during the first and second years of their developmental life. Subsequent grazing behavior and performance as first-lactation cows was then compared. Prior grazing experience (as heifers) affected distance walked, time spent grazing, and milk production of these cows during the first week of exposure to pasture. After this time, production and grazing activities were similar for cows with and without previous grazing experience as heifers. Results from this study suggest that grazing studies utilizing cattle normally managed in confinement should allow at least one week of adaptation to the grazing environment. This should provide adequate time for inexperienced animals to adjust to the new environment and recover milk production. This study confirmed that the short period of adaptation (10 to 14 days) normally used in grazing studies with cows raised in confinement can provide valuable data for grazing-based dairy producers.

Technical Abstract: A 3-yr study evaluated the carryover effects of dairy heifer grazing experience on behavior and first lactation performance as dairy cows. Forty-one Holstein and 23 Holstein-Jersey crossbred calves born between January and April 2008 were randomly assigned to one of four treatments (PP, PC, CP and CC; n = 8 per group, 2 groups per treatment) in a completely randomized design. Treatments were combinations of managing dairy heifers in confinement (C) or on pasture (P): PP, grazed year 1(yr1) and year 2(yr2); PC, grazed yr1, but were confined in yr2; CP were, confined in yr1 and grazed in yr2; CC, confined in yr1 and yr2. After calving, all heifers on all treatments were grazed as cows in year 3 (yr3). In yr1, PP and PC heifers were grazed for 41 d on Italian ryegrass pastures, while CP and CC were housed in bedded pack pens and fed a TMR. In yr2, PP and CP grazed Italian ryegrass pasture for 65 d, while PC and CC remained in confinement. In yr2 a mid-trial assessment of heifer grazing behavior was made on PP vs. CP heifers. Grazing activities were assessed by visual observation and heifer movement measured by portable GPS units. Heifers from all treatment groups subsequently calved between January and April, in yr3. All primiparous cows were then allocated to pastures by treatment group, grazed for 61 d, (May through July) in yr3, with grazing behavior and milk production evaluated while grazing. In yr2 heifers that grazed (PP) yr1 spent more time grazing than heifers with no grazing (CP) experience (78 vs. 35 % of the time, P < 0.05) when first exposed to pasture (day 1). On d 1 to d 3, PP heifers walked a greater distance than CP heifers, however, PP and CP heifers had similar daily grazing times and walking patterns after 3 days of pasture exposure in yr2. As lactating cows (yr3), cows with no (CC) grazing experience grazed less (P < 0.05) on day 1 as compared to cows with PP, PC or CP grazing experience. Day 1 grazing time in yr3 were 62, 59, 76, and 13% of the time for cows with PP, PC, CP and CC grazing experience, respectively. In yr 3 on d 1 to d 3, cows with previous grazing experience as heifers (PP, CP and PC) walked a greater distance than cows without previous grazing experience (CC). Milk production was lowest (P < 0.05) on d 1 to d 3 for cows with no previous grazing experience (CC). However, average daily milk production during the yr3 grazing phase of the experiment was not (P > 0.05) different (30.5, 30.1, 31.5 and 29.6 kg for PP, PC, CP and CC, respectively). Results indicate that grazing experiences as a heifer can impact behavior and milk production during a cow’s first days on pasture. After a short acclimation period, dairy cows without grazing experience as heifers develop similar grazing behaviors and performance as cows with grazing experience as heifers.