Heifer calves that eat low-quality forages, even briefly, will utilize them better as mature cows. That’s the conclusion of Utah State University scientists who studied the effects of forage quality on replacement heifers.
“The importance of the study in heifer replacement development is exposing heifers to the nutritional environment they will be exposed to as a cow,” says Utah State professor Randall Wiedmeier. “If you develop replacements on high-quality pasture forages or high-quality hay and then you have a sudden management change to a lower-quality forage, you can expect to have lower productivity for three years.” Having cows with good adaptability to low-quality forages is especially helpful in areas hit hard by drought.
With the average cow producing six to seven calves, three years represents roughly half of her reproductive life. “So, it is of major importance in productivity,” he says.
Dr. Wiedmeier oversaw a study involving 16 pregnant heifers that ate ammoniated wheat straw with their mothers for 60 to 90 days while nursing and 16 heifers that had not eaten the wheat straw before. They wintered on ammoniated wheat straw with alfalfa hay, along with a vitamin mineral supplement, from Dec. 1 to May 15. Both groups had similar bodyweights when the study began.
Heifers who had previously eaten ammoniated wheat straw gained 81.4 pounds of bodyweight from December through February. This was within the range needed for cows of this type to maintain body condition and develop a healthy fetus. But the control group lost 48.4 pounds of bodyweight, which translated into a much lower energy intake and a loss of body condition, Dr. Wiedmeier says.
Researchers anticipated that differences in bodyweight between the two groups would be reduced in the summer and fall since both grazed in irrigated flood plains. But those that ate ammoniated wheat straw as calves were 63.8 pounds heavier the first week of November.
After the second wintering period (December through May), cows that ate wheat straw as calves were 77 pounds heavier than the others. “That appeared to carry on fairly strong the second year, but the third year there was some adaptation (in the control group) going on,” he says.
Dr. Wiedmeier says it is important to note that the heifers briefly exposed to ammoniated wheat straw as suckling calves had not received additional low-quality forage until the study began almost four years later. Utah State’s study also examined rebreeding and milk production. After the first winter, heifers fed wheat straw as calves conceived within the window needed to maintain a 365-day calving interval. The control group took nine extra days to conceive and did not make the 365-day calving interval.
This research came about by “accident” after Dr. Wiedmeier noticed during another study that some experiment-station cows responded much better to low-quality forages. Herd records revealed they ate ammoniated wheat straw with their mothers.
He consulted with Frederick Provenza, a Utah State professor who has long done forage research on range animals. “(Better performance) just reinforced the observations of animal behavior — the diet they are exposed to during the early time of life has major impact on how they respond years later,” Dr. Wiedmeier says.