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Developing heifers on cool-season forage

Kim Mullenix and Landon Marks for Progressive Cattleman Published on 25 January 2018
heifers on cool-season pasture

Representing the future of the cow herd, replacement heifers must be managed with the end in mind – that is to maintain an efficient, productive cow-calf operation.

Nutritional management is a significant component in the development of heifers. Whether a producer is retaining or purchasing his or her heifers, meeting nutrient requirements will aid in the heifer’s success.

To maximize reproductive efficiency, heifers should reach a target weight of 65 percent of their estimate mature weight at the start of the breeding season. Mature weight can be determined from the frame score of the animal. From weaning to breeding is an important period when gains of 1.5 to 2 pounds per day should be achieved to move toward the target mature weight.

High-quality, cool-season forages can be used almost exclusively to achieve these types of gains, and may be an especially good fit for spring-born, fall-weaned calves.

The relatively mild climatic conditions and high rainfall in the Southeast provide excellent conditions for growing winter forages. Some of the most common species used include tall fescue, the predominant perennial cool-season grass option in the region, and annual grasses such as ryegrass, cereal rye, oats, wheat and triticale.

Annual grasses can be established alone or in multi-species mixtures with other grasses, legumes or brassicas to provide high-quality grazing during the winter months.

The estimated cost of establishing and using winter annuals is $100 to $125 per acre, depending on the seed, fertility, labor and fixed costs. A diet capable of producing the needed levels of gain mentioned above must contain on average 60 percent total digestible nutrients (TDN) and 10 percent crude protein (CP). Dry matter intake should be between 15 and 19 pounds per day. Cool-season forages generally range from 55 to 75 percent TDN and 10 to 16 percent CP, which meets or exceeds the nutrient needs of developing heifers.

The research

A recent demonstration project at the Sand Mountain Research and Extension Center in northeast Alabama highlighted recommended methods for spring-born replacement heifer development using cool-season forage systems. A key principle of the project was to reduce the need for hay and supplementation during the winter months, which represents a significant amount of annual carrying costs on a per head basis. Stockpiled, novel endophyte-infected tall fescue, cereal rye and annual ryegrass were used in 2016 to provide grazing from January through June when heifers were picked up by the consignors. The tall fescue stand has been established for 10 years, and annuals were planted into a prepared seedbed in October 2015. This system provided 154 days of grazing and supported an average daily gain of 1.8 pounds per day during the first year of the project. Heifers consumed between 12 and 19 pounds of forage dry matter per day. On average, heifers weighed 618 pounds on delivery to the research station and left weighing an average of 907 pounds. Based on frame scores, the predicted mature weight of these heifers was 1,260 pounds at 4.5 years old.

Heifers were synchronized using a Select Synch plus CIDR protocol and artificially inseminated seven days later in March 2016. At the time of breeding, heifers were estimated to weigh 63 percent of their mature bodyweight, with a range of 52 to 75 percent. Ten days after heifers were bred, a cleanup bull was turned out and remained with the heifers for 57 days. Conception rates were 51 percent by natural service, 37 percent artificial insemination and 12 percent open in 2016.

In year two, drought conditions limited fall-planting potential of cool-season annuals and delayed establishment until December 2016. Dry weather hindered fall stockpiling of tall fescue and reduced the number of grazing days in the second year of the evaluation. There were 70 days of grazing provided by annual ryegrass from March to June 2017. Overall average daily gain was 1.6 pounds per day during the second year. Heifers achieved 70 percent of their estimated mature weight at breeding in March. Conception rates in year two were 50 percent natural service, 32 percent artificial insemination and 18 percent open. Reduced forage availability and the need for longer periods of feeding hay and supplement may have reduced production potential of heifers in the second year.

Data from this demonstration project illustrate that stockpiled tall fescue and winter annuals may provide adequate nutrition for developing beef replacement heifers to target bodyweights. However, sufficient time should be given to heifers changing from hay and supplemental feed to fresh forage diets in order for rumen microbes to adjust and use these resources most efficiently. Cool-season weather conditions significantly influence forage production and demonstrate the need for multiple forage options in the system to better guarantee grazing availability during these months.  end mark

For additional information on replacement heifer nutrition and management, click here.

Kim Mullenix
  • Kim Mullenix

  • Assistant Professor/Extension Specialist
  • Auburn University
  • Email Kim Mullenix

Landon Marks is a graduate student and a regional extension agent for Auburn University. Email Landon Marks.

PHOTO: A group of heifers at the Sand Mountain Research and Extension Center in northeast Alabama. Photo by Landon Marks.

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