Over the past several years, researchers conducted a study at the Central Maryland Research and Education Center-Clarksville dairy farm to investigate the effects of improved grazing management on pregnant dairy heifer performance. The objectives were to determine the effect of improved grazing management on heifer growth characteristics and its economic feasibility relative to a conventional system. Researchers also followed heifers through their first lactation to investigate potential carry-over effects.

From 2021 to 2023, 166 pregnant Holstein dairy heifers from the University of Maryland dairy were enrolled in the study on a rolling basis, with heifers added following pregnancy confirmation and removed approximately three weeks prior to calving. Upon enrollment, heifers were randomly assigned to one of two treatments groups: control (CON) or grazing (ROT). Heifer groups varied in size, ranging from 15 to 22 head per group, but were kept consistent between treatments.

Heifers in the CON group received a total mixed ration (TMR) once per day and had access to one continuously managed 6-acre perennial pasture consisting of mostly tall fescue. Heifers in the ROT group were rotationally grazed across 21 acres of both perennial and annual pastures subdivided into approximately 0.6-acre paddocks; heifers were rotated to a new paddock every one to three days, depending on forage availability. Perennial pastures within the rotational grazing system also consisted of mostly tall fescue.

Annual pastures within the rotational grazing system were established on a seasonal basis using a cool-season mix of triticale, oat, annual ryegrass, and crimson clover followed by a warm-season sudangrass-cowpea mix. Heifers in the ROT group also received a daily ground corn/mineral mix at a rate of 1 pound per head per day.

The study ran annually from the beginning of April through the end of December. Throughout the growing season, heifers in the ROT group alternated between annual and perennial pastures, depending on forage availability and growth. Actual dates spent grazing the different forage types varied from year to year. Throughout the study, both groups of heifers were measured every two weeks to determine body weight, body condition score, hip height, and average daily gains. Forage samples were collected every two weeks to determine forage yield and nutritive value. For each treatment group, samples were collected from the paddock immediately prior to grazing.

Slower growth on grass

A full analysis of the results for this study is in progress, but some preliminary findings are included here. On average, heifers were enrolled in the study for 144 days, and there was no difference between treatment groups. The average nutrient composition of the TMR fed to the CON heifers and the pastures grazed by both CON and ROT heifers is shown in Table 1.

Initial body weight, body condition score, and hip height were similar between treatment groups, with heifers averaging 1,161 pounds and 3.7 body condition score when they started grazing. Final body condition score and hip height were not statistically different between the two treatment groups (Figure 1). However, average daily gain and final body weight tended to be lower for the ROT heifers compared to the CON heifers (Figure 2). Final body weight and average daily gain for the ROT heifers were 1,359 pounds and 1.3 pounds of gain per day, respectively, whereas final body weight and average daily gain for the CON heifers were 1,499 pounds and 1.9 pounds of gain per day, respectively.

Although these results indicate a slightly slower growth rate for ROT heifers, heifer body condition was still good and was comparable to their CON counterparts. Final body weights for the ROT heifers were acceptable and they achieved or exceeded 85% of mature body weight at first calving. Performance of heifers from both treatment groups were tracked as heifers went through their first lactation; additional data analysis moving forward will explore possible carry-over effects of these management systems on first lactation milk production, health, and reproductive performance.

Interestingly, heifers in both groups initially lost weight following their enrollment in the study, suggesting that both groups required an adaptation period to adjust to their new environment. Prior to study enrollment, all heifers were group-housed in a barn and fed a TMR once daily. Following study enrollment, CON heifers required an average of 23 days to regain their starting body weight, while ROT heifers required an average of 35 days. The longer adaptation period for the ROT heifers is not surprising given that they experienced a more dramatic change in housing and diet compared to the CON heifers. This highlights the importance of adaptation when making housing or feeding changes for heifers.

Heifer average daily gains varied considerably across weigh periods. The variability was likely due to a number of factors, including heifer adaptation; heifers entering or leaving the study; changes in forage type and forage quality over time, especially for the ROT group; and varying weather conditions throughout the grazing season. The ROT heifers appeared to perform substantially better while grazing the warm-season annual mixture of sudangrass and cowpeas during the heat of the summer, which might be expected given the nutrient profile of this pasture shown in Table 1.

A detailed economic analysis comparing expenses between these systems is forthcoming. Overall, these results demonstrate that bred heifers managed in an improved grazing system can achieve satisfactory growth relative to TMR-fed counterparts. Because the replacement heifer program is typically the second- or third-greatest expense on the dairy, and feed often exceeds 50% of those costs, expanding pasture utilization may be an economical choice for some producers to reduce costs without compromising animal performance.

Producers looking to improve grazing systems on their farm should explore simple changes like implementing rotational grazing, ensuring proper soil fertility, and boosting forage diversity. The incorporation of annual forages into the grazing system will help improve animal performance by offsetting the summer slump in perennial pastures and mitigating palatability and forage intake issues associated with endophyte-infected tall fescue during the summer.

Future studies will continue to explore how improvements in pasture management affect heifer performance and the economic viability of the heifer program

This article appeared in the November 2025 issue of Hay & Forage Grower on page 28.

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