Journal of the NACAA
Volume 12, Issue 2 - December, 2019
Development of an Index to Rank Ryegrass Varieties for Milk Production or Beef Gains Potential
- Downing, T. W., Dairy Extension, Oregon State University, Tillamook County
Ates, S., Assitant Professor, Oregon State University
Cruickshank, J., Dairy Extension, Oregon State University
The objective of this study is to develop a ryegrass forage value index (FVI) in Oregon. Twenty perennial ryegrasses were planted in the fall of 2015 in replicated plots of three complete randomized mixed blocks. Plots were harvested six times annually for two years and sent to Dairy One (Ithaca, NY) for analysis. Varieties were ranked for estimated milk production using an index based on energy (NEl). Estimated milk production per acre ranged from 284 cwt. to 241 cwt. for the varieties tested. This 43 cwt. difference could be estimated to be potentially worth from $600-$800 dollars and acre difference in total milk produced.
The grass seed industry has had difficulty explaining the economic merit or value of an individual grass cultivar to the livestock industry. Often producers renovate pastures based on seed availability and perceived adaptability with no real appreciation for the genetic selection, testing and breeding efforts that went into developing that cultivar.
In both the beef and dairy industries, livestock breeders have become used to using bull proofs to identify individual bull proofs based off an index system (AIPL, 2012). A similar ryegrass index process has also been successful in New Zealand and in Ireland. However, interest in developing a process for creating a forage value index (FVI) for individual grass cultivars is beginning to gain interest around the world. At this time, there is not a FVI in place in the United States.
In Ireland, researchers developed a program to develop an economic ranking index for Irish perennial ryegrasses (McEvoy, 2011). The economically important traits selected in their system were spring, midseason and autumn grass DM yield, grass quality, and sward persistency. Like all indexes, each parameter in the index had a different weight based on economic importance.
In New Zealand, researchers have developed an economically based FVI that ranks cultivars according to their overall value to a dairy farm business. This FVI attempts to take into account all the major plant traits that drive the productivity of the dairy farms (Chapman et al., 2016). There are substantial regional differences in New Zealand. This project looked specifically at genotype x environment interactions and used to delineate performance differences in four major regions throughout the country.
According to a New Zealand National Forage Variety Trial data, since 1991, the trend for genetic gain in perennial ryegrass has been greatest for summer pasture production (+24lbs DM/acre/year), followed by autumn (+18 lbs. DM/acre/year), winter and late spring (both at +5 lbs. DM/acre/year). Genetic gains in total production of 50-55 lbs. DM/acre/year, or 1,000 lbs. DM/acre since 1990 (Chapman et al., 2011).
The objective of this study is to develop an FVI for grass cultivar ranking in Oregon. Quality measurements weighted for energy is the driver of this index as energy is the single most limiting factor for milk production or growth in high quality ryegrass pastures. Energy from pasture is the result the digestion of soluble and structural carbohydrates, proteins, starch and fats. Net energy for lactation (NEl) is the estimated feed energy available for maintenance and milk production after digestive and metabolic losses. Included in the objectives of this project is to estimate milk production and beef gain potential differences between the tested cultivars on a per acre basis.
MATERIALS AND METHODS
Twenty ryegrasses were planted in the fall of 2015 in a completely randomized block design with three replicate plots measuring 4 ft. by 10 ft. The seed was donated by participating grass seed companies. All plots were fertilized with 300 lbs of N as urea annually both years. All sixty plots were harvested six times annually for two years with a Swift Current forage harvester (Swift Current, Saskatchewan). All individual yield measurements were recorded for each plot and extrapolated into estimated DM per acre and sub-samples of each replicate were analyzed for forage quality at Dairy One lab in Ithaca, NY. Data were analyzed using an analysis of variance (ANOVA) procedure in Genstat. A FVI was developed to rank individual varieties and estimate milk production potential and beef gain potential per acre. Energy from pasture is the result the digestion of soluble and structural carbohydrates, proteins, starch and fats. Net energy for lactation (NEL) is the estimated feed energy available for maintenance and milk production after digestive and metabolic losses. The index used for this project combined the total pounds of DM per acre times the NEL or total calories per lb. By multiplying these two values, we created the FVI of total calories per acre produced annually. Calories per acre harvested were then used to determine the theoretical milk production and/or lbs of gain for a beef operation based off book values reported in the literature.
Forage ryegrass plots were grown, harvested and analyzed six times a year over a two-year period. Table 1 and Table 2 show a listing of all twenty varieties in the study and DM production for each cultivar for the first and second year of the project. The cumulative DM production for each cultivar over all six cuttings through the growing season is totalled in the far right column. In year 1, the variety Trojan had the highest DM yield all of twenty varieties tested at 15,085 lbs DM per acre (Table 1). In the same year, the lowest production variety was Oroverde at 12,503 lbs. DM per acre. No significant differences were observed in DM yield this first year. In year 2, the highest DM producer was Alto AR37 at 17,393 and the lowest in year two was Albion at 14,340 lbs. DM per acre (Table 2).
Energy animals derive from pasture is a combination of calories from soluble and structural carbohydrates, proteins, starch and fats. Net energy of lactation (NEL) accounts for all these and is the estimated feed energy available for maintenance and milk production after digestive and metabolic losses. A cow’s total energy requirement will be the sum of what she needs for each function: maintenance, growth and production. For example, a cow weighing 1300 lbs (590 kg) making 100 lbs (45.5 kg) of milk containing 3.5% milkfat will require 9.57 Mcal per day for maintenance and 31 Mcal per day for milk production. The cow’s total NEL requirement would be 40.57 Mcal per day or 0.78 Mcal per lb of DM if she consumed 52 lbs of DM per day (Ondarza, 2000). With these assumptions, we can estimate how many Mcals per acre we have grown by a variety and estimate the amount of milk potentially produced per acre (100 lbs of milk is also called a cwt). With a similar approach, we can estimate the energy needs for gains on a steer and figure out approximately how many pounds of beef could be gained if we had a known quantity of energy. Table 3 shows the FVI for both growing seasons combined, the relative value compared to the others in the study, an estimated number of cwts of milk per acre and estimated lbs beef gained for an intensive grazing beef operation. Projected milk production and potential beef gains are also shown in Table 3. These values demonstrate major differences in expected performance with both milking cows and/or beef animals grazing these varieties.
Table 1. Dry matter yields (lbs per acre) per cutting for six cuttings and total dry matter yield for year 1. No significant differences were observed this year.
Table 2. Dry matter yields (lbs per acre) per cutting for six cuttings and total dry matter yield for year 2. Varieties with different letters noted are statistically different (P<0.05).
Table 3. Perennial ryegrasses ranked for milk production index, relative value, cwt milk per acre, lbs gain potential per acre. Varieties with different letters noted are statistically different (P<0.05). Milk production estimates based off the assumption of a Holstein cow producing 100lbs a day (40mcal). Weight gain estimates based off a 750 lb steer gaining 3 lbs a day (11mcal).
Ryegrass variety trials specifically looking at expected animal performance are limited in the US. Chapman (2016) has clearly indicated in New Zealand the challenges with environment x genotype interactions that may change the way one cultivar performs in a specific environment compared to others. This ryegrass performance data has clearly shown many ryegrass cultivars from around the world perform well on the Oregon coast. However, differences in performance were identified.
Net energy is usually the limiting factor in determining milk production performance of ryegrass pastures. Accounting for energy derived from the digestion of fats, proteins, soluble carbohydrates, starches and structural fiber is the most reasonable way to estimate performance per acre of these cultivars. Estimated milk production per acre ranged from 284 cwt. to 241 cwt. for the varieties tested. This 43 cwt. difference or range could be estimated to be worth from $600-$800 dollars per acre difference in total milk produced potentially (for milk valued at $15-$20 per cwt.). The potential gains per acre for a 750 lb. steer gaining 3 lbs. a day was also estimated (Table 3). Our top three varieties were estimated to produce over 1000 lbs. of gain per acre per year and the range from the highest to the lowest was over 150 lbs.
The varieties included in this trial are all modern varieties being developed by our grass seed industry. Clearly, this makes us wonder how these improved varieties perform compared to older unimproved varieties. The livestock industry has needed a way to rank varieties for potential animal performance for years. This work clearly demonstrates the production potential for using modern cultivars in your grazing and silage systems. These genetic differences appear to have major performance implications for grazing beef or dairy operations.
The Oregon Beef Council financially supported this study.
Animal Improvement Programs Laboratory (AIPL), 2012. http://aipl.arsusda.gov/eval.htm
Chapman, D., Lee, J., Matthew, C., Thom, E., and Bryant, J. (2011). Perennial ryegrass is the King- breeding and evaluating the next generations of ryegrass royalty. Primary Industry Management, Vol. 15, No. 4, pgs. 12-14.
Chapman, D., Bryant, J., Olayemi, M.E., Edwards, G.R., Thorrold, B.S., McMillan, W.H., Kerr, G.A., Judson, G., Cookson, T., Moorhead, A., and Norriss, M. (2016). An economically based evaluation index for perennial and short-term ryegrasses in New Zealand dairy farm systems. Grass and Forage Science. Doi:10.1111/gfs.12213.
McEvoy, M., O’Donovan, M., and Shalloo, L. (2011). Development and application of an economic ranking index for perennial ryegrass cultivars. J Dairy Sci. 94:1627-1639.
Ondarza, M.B. (2000). Energy for milk production. http://www.milkproduction.com/Library/Scientific-articles/Nutrition/Energy/.