Key to retaining heifers depends on nutrition
Selecting replacement heifers can be difficult. Relying on records, visual appeal, size and much more, ranchers are taking a gamble they are picking the best their genetics has to offer.
But even a bigger gamble is research that shows only 60 percent of the heifers selected and developed as replacements will still be part of the herd four years from now. University of Nebraska Beef Cattle Nutritionist Travis Mulliniks shows producers how they can improve those odds by carefully managing heifer nutrition.
By focusing on nutritional management during two key periods, Mulliniks said producers can improve the chances of heifers cycling and becoming pregnant. One of those key periods is 60 days before calving when nutrients need to be available in the right amount because it impacts fetal growth. The second critical period is 50-100 days after calving, when the heifers are starting to approach the breeding season. “It is important to make sure the nutrition program is up to par because it influences the pregnancy rate of the heifers,” he said.
The forage base should be the first priority for the cow/calf producer. “Limiting intake during critical times can cause a decrease in production, especially if it is before the breeding season,” Mulliniks said. “Many times, there will be a drop in pregnancy rates that can be attributed to the quantity of forage fed, not the quality.” Limiting intake is not something Mulliniks recommends unless the cattle are in a dry lot, where their feed intake is carefully monitored.
Another important factor is determining the cow’s requirements based on its physiological stage (dry, pregnant, lactating), age, climatic stressors and activity. “Cows that are in large pastures and have to walk a long way will have different nutritional requirements,” he said. Cows prioritize their nutritional needs with body maintenance first, followed by reproduction, lactation and storage. “The first limiting factor is energy, followed by protein, vitamins and minerals,” Mulliniks said.
Producers are encouraged to provide supplement during critical times. “If there is a supplement that will change animal performance in the future, we want to feed it as long as marginal revenue outweighs marginal cost. However, if pregnancy rates are already 92-94 percent, ranchers may not get much benefit from feeding a supplement to get a 95 percent pregnancy rate, he noted.
With reproduction being the main factor limiting production efficiency in a beef cow herd, optimizing reproduction with nutritional management is five times more important than other traits, like milk production and calf growth.
A University of Nebraska study shows the oldest heifers cycle earlier, and of those heifers, 81 percent calved within the first 21 days of the calving season. Mulliniks said those heifers that calve earlier have a big advantage in improving their longevity in the herd, and may be more profitable.
Chances of earlier conception can be achieved by turning heifers and young cows into a fresh, ungrazed pasture right before breeding. If the pasture has been dormant, it will allow the cattle to graze selectively, which can increase their diet quality 200 percent, or the equivalent of 2 pounds per day of crude protein supplement. This “flushing” concept only improves digestibility to 75 percent for about two weeks. It will then drop down to 60-65 percent for the next few weeks, Mulliniks said.
Sub-irrigated meadow regrowth can also be utilized as a grazing strategy to flush heifers at a critical point in their reproduction. “Use it to increase their nutritional value,” he said.
Mulliniks shared a study where pregnancy rates were 10 percent higher in heifers developed on low-input range versus a feedlot. During this study, 68 percent of the heifers range-raised were still in the herd at 5-years-old, compared to 42 percent of the feedlot-raised heifers. “That is a lot of difference in retention, based on how we managed heifers for 100 days. It shows us that how we handle heifers sets them up to how they will perform as first and second calf heifers. Heifers developed in a low-input grazing setting may be advantageous in maintaining a positive energy balance or be adaptable to a negative energy balance through the breeding season in many range settings, he said.
GLUCOSE CAN HELP
The ruminal fermentation of native range microbial crude protein is inadequate for the nutritional requirements in growing cows. The imbalance of the acetate to propionate ratio limits the available glucose for the cow, and can make her a type two diabetic at certain times in her reproductive cycle, Mulliniks said. Cows don’t have the glucose spike after eating that humans do, because 90-95 percent of the glucose from fermentation will be utilized by the rumen microbes. For the cow to utilize acetate, it has to have glucose.
To combat the problem, Mulliniks recommends during times of high stress, feeding the cows supplements high in bypass protein and high in undegradable protein. “It has a massive benefit in helping the cow get through highly stressful times, and a big benefit in future responses. Pregnancy rates can increase by feeding rumen undegradable protein, or bypass protein, versus feeding a rumen degradable protein source,” he said.
With most cows gestating 280 days, they need to be ready to rebreed 80-85 days post-partum. “The majority of young cows will be hard pressed to recover and start cycling by day 80. We need to focus on how to get these cows to cycle early to maintain the calving interval,” he said.
Mulliniks suggested finding ways to get them to gain body weight as soon as possible after calving. “The pregnancy rates in young cows are lower due to the inability to consume enough forage or energy. They can’t meet maintenance, lactation and growth requirements,” he said.
By repatriating nutrients away from lactation toward growth and maintenance, young cows may cycle sooner. Adding a source of glucose to the diet can help, he said. Other options are ionophores like Bovatec or Rumensin. “They have the same influence of increasing rumenal propionate to produce glucose,” he added. ❖
— Clark is a freelance livestock journalist from western Nebraska. She can be reached by email at firstname.lastname@example.org