Stocking Rate Affects Production and Profitability in a Rotationally Grazed Pasture System

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 QuestionStocking 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 SummaryWhere 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 the Northeast and North Central dairy states, little attention has been paid to stocking rate as a management tool, and there is virtually no current information available concerning the econommic implications of varying stocking rate with high-producing dairy cows. Study DescriptionThe trial was a replicated farmlet experiment, conducted in 1990 and 1991 at the Pennsylvania State University Dairy Research and Education Center in University Park. Pasture Composition: Old pasture, consisting mainly of orchardgrass and Kentucky bluegrass. Soil: Hagerstown silt loam. Stocking rates: 1.0, 1.3, and 1.6 cows/acre for a 6-mo grazing season. Grazing management: Stocking rates were achieved by adjusting paddock size for 8 cows/treatment. A total of 38 acres were used. The area for each treatment was divided into 14 paddocks for rotational grazing. In the spring, seven paddocks for each treatment were not grazed, and were set aside for silage. When regrowth from the silage area was available, all 14 paddocks were grazed. Nitrogen fertilization: 250 lb/acre of N as ammonium nitrate in five split applications. Supplementary feeding: All cows were fed grain daily at the rate of 1 lb grain dry matter (DM)/4 lb milk. Supplemental grass silage (previously harvested from pastures in the spring) was individually fed when pasture growth was limiting. Data collected: Pasture production, quality, and use; milk production and composition. Applied QuestionsWhat was the effect of stocking rate on pasture production? When pasture growth was adequate, as it was during 1990, increasing stocking rates above 1.0 cowdacre resulted in higher pasture production due to the fact that more forage was removed at the higher stocking rates, encouraging new growth. When pasture growth was slow, as it was during 1991 (a drought year), there was no effect of stocking rate on pasture production. What was the effect of stocking rate on pasture quality? Increasing stocking rate tended to increase the nutritional value of the forage, particularly when pasture growth was vigorous. What was the effect of stocking rate on pasture use? There was less pasture wasted due to trampling, fouling, and rejection as stocking rate was increased. At the low stocking rate, up to 44% of the paddock area was classified as “rejected,” compared with 22% for the high stocking rate in 1990. In 1991, because pasture growth was slower, grazing pressure was higher. Therefore, more of what grew was removed, resulting in no significant treatment differences in paddock area rejected. What was the effect of stocking rate on milk production? No effect of stocking rate on milk production per cow occurred because grass silage (previously harvested from the pastures) was fed when pasture production was limiting for any treatment. Average production per cow for the 6 mo trial was approximately 10 000 lb of milk (3.5% fat-corrected). What was the effect of stocking rate on profitability? When calculated on a per acre basis, profitability increased directly with stocking rate because of the greater amount of milk produced per acre. Returns over the costs examined were approximately $481/acre greater for the high than the low stocking rate during the pasture season. When calculated on a per cow basis, however, profitability was greatest at the low stocking rate, which showed a $36/cow greater return than the high stocking rate. How should the optimal stocking rate be determined? The ideal stocking rate in any given grazing situation will vary with each farm and can change from one year to the next, because it depends on the relative prices of inputs and outputs, as well as on farm resources. if land is scarce compared with other resources (barn space, cows, etc.), then a higher stocking rate will be the most profitable. On the other hand, if land is relatively plentiful, rental rates are low, or the value of the land for other uses is low, then a low stocking rate will be the most profitable.