There has been considerable activity in breeding orchardgrass (Dactylis glomerata L.) cultivars in North America during the latter half of the 20th century, but little effort devoted to quantification of breeding progress. The objectives of this study were to quantify changes in mean cultivar performance for that time compared with the progress achieved from one cycle of half‐sib progeny selection within the USDA population of orchardgrass accessions. Forty‐two cultivars (32 North American cultivars and 10 European cultivars) were tested at three locations (Arlington, WI and Rock Springs, PA, and Ottawa, Ontario, Canada) in 1995 through 1997. Cultivars were grouped into three experiments by maturity class: early, medium, and late. North American cultivars averaged 3, 9, and 12% higher in forage yield than European cultivars for early, medium, and late maturity groups, respectively. Between 1955 and 1997, forage yield and ground cover of early‐maturity cultivars increased by 2.5 Mg ha−1 decade−1 and 4.0% decade−1, respectively. Forage nutritional value of medium‐maturity cultivars increased during that time, although this was probably not due to direct selection. Significant gains were made in forage yield and Drechslera spp. leafspot reaction of cultivars derived from two individual breeding programs, although the majority of orchardgrass cultivars lack improvements in forage traits.

Stocking rate is a key management variable in determining productivity and profitability of grazing systems, but it has not been adequately researched in the USA with high producing dairy cows. A replicated farmlet study was conducted to investigate the potential for improving dairy profitability through increasing stocking rates without influencing milk yield per cow. The study was conducted at the Pennsylvania State University Dairy Research and Education Center in University Park, on pasture dominated by orchardgrass (`Dactylis glomerata L.) and Kentucky bluegrass (Poa pratensis L.). Forty‐eight high‐producing Holstein cows (Bos taurus) were rotationally grazed at seasonal stocking rates of 1.0 (low, LSR), 1.3 (medium, MSR), and 1.6 (high, HSR) cows/acre, and were fed grain at the rate of approximately 1 lb grain DM to 4 lb milk production during a 2 yr study. Stocking rate had a positive effect on pasture nutritional quality, particularly when growth was more vigorous, and had a negative relationship with the percentage of the pasture rejected by cows. Seasonal milk yield per cow (approximately 10 000 lb) and milk composition were not affected by treatments in either year. Consequently, milk production per acre was directly related to stocking rate. An economic analysis of costs and returns indicated that profits per unit area of land increase with stocking rate—a $481/acre advantage was shown for the HSR over the LSR. In contrast, profits per cow decrease with stocking rate—the LSR showed a $36/cow advantage over the HSR. The optimal stocking rate for a given farm therefore will depend on individual farm resources (e.g., land, buildings, cows, etc.), and can be adjusted to meet the constraints of those resources without fear of significant adverse economic impact. Research Question Stocking rate, defined as the relationship between the number of animals and the grazing management unit used over a specified time (a grazing season, for example), is key to determining the potential for production and the profitability of a grazing system. The objective of this trial was to compare forage production and quality, milk production, and profitability on a per cow and per acre basis for three different stocking rates, using high‐producing Holstein cows grazing grass pasture. Literature Summary Where pastures are the primary source of feed for dairy cows, research consistently has shown that stocking rate is a major factor in determining the efficiency of the system. It determines the amount of the pasture that is available per cow, the proportion of the pasture that is consumed, and also influences the quality and long‐term productivity of the sward. Stocking rate is a crucial variable in New Zealand because pasture systems there are designed to maximize returns per acre. In contrast, dairy production in the USA traditionally focuses on returns per cow, and even where pastures are used, concentrates and supplemental forage are fed to maintain high levels of milk production per cow. Although grazing is increasing in t...

The objectives were to estimate intake of pasture and total DMI by high producing cows grazing grass pastures and to measure changes in nutrient composition of grass pasture during the grazing season. Sixteen multiparous Holstein cows averaging 31 kg of 4% FCM/d at the start of the trial grazed grass pastures at a stocking rate of 2.5 or 3.9 cows/ha from April until October 1990. Intake was estimated using Cr2O3 as an indigestible fecal marker. Pasture samples were analyzed for nutrient composition at six times during the grazing season corresponding to the times of intake estimation. Total daily DMI increased from 21.3 kg in early spring to 22.4 kg in late spring and then decreased as lactation progressed; however, DMI exceeded NRC recommendations during most of the grazing season. Daily pasture DMI varied with season, ranging from 11.6 to 15.6 kg and was lowest (11.6 kg) in the summer. Estimated NEL intakes were lower than NRC recommendations in early spring. During the grazing season, pasture ranged from 39 to 48% NDF and from 22 to 30% CP with 15 to 20% ruminally degradable protein on a DM basis. Grazing cows consumed adequate DM from pasture except in early spring. Although nutrient composition of pasture varied with season, quality remained high.

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