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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #107899
Title: ANIMAL AGE AND SEX EFFECTS ON DIETS OF GRAZING CATTLE

Author
item Grings, Elaine
item Heitschmidt, Rodney
item Short, Robert
item Haferkamp, Marshall

Submitted to: Journal of Range Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2000
Publication Date: 1/1/2001
Citation: GRINGS, E.E., HEITSCHMIDT, R.K., SHORT, R., HAFERKAMP, M.R. ANIMAL AGE AND SEX EFFECTS ON DIETS OF GRAZING CATTLE. JOURNAL OF RANGE MANAGEMENT. 2001. v. 54. p. 77-81.

Interpretive Summary: A number of researchers have observed differences in diet selection due to animal age, but not sex. The effects of animal class (age or sex) on diet selection may be dependent on the quality as well as quantity of available herbage. As diet selection for different animal classes may vary, the choice of animals to use in evaluating diet quality may be critical. The objective of this study was to evaluate the influence of animal age and sex on botanical and chemical composition of cattle grazing Northern Great Plains rangeland. A study was conducted utilizing esophageally cannulated suckling calves, yearling heifers, mature cows, and mature steers. Determinations were made of crude protein and in vitro organic matter digestibility and of dietary botanical composition. Yearling heifers diets were more diverse than those of other classes of cattle. This was associated with an average dietary crude protein that was similar to calves, but greater than cows or steers. Digestibility, on the other hand, was less for heifers than other animal classes. Numerous interactions between animal class, year and month of sampling occurred. Differences in botanical diversity of diets resulted in differences in chemical composition among age and sex classes of cattle grazing native rangeland during the growing season. Animals used to obtain diet samples should, therefore, be of similar gender and age as any animals whose performance is being measured.

Technical Abstract: The effects of age and sex class on botanical and chemical composition of diets of cattle grazing native rangelands were evaluated in a 2-year study utilizing esophageally cannulated suckling calves, yearling heifers, mature cows, and mature steers. Samples were collected each month from June through October. Determinations were made of crude protein and in vitro organic matter digestibility and of botanical composition by microhistological analysis. Dietary diversity was evaluated using Shannon's and Simpson's indices. Yearling heifers' diets were more diverse than those of other classes of cattle. This was associated with an average dietary crude protein that was similar to calves, but greater than cows or steers. Digestibility, on the other hand, was less for heifers than other animal classes. Animal class x month interactions occurred for Simpson's index, protein, and digestibility but the 2 indicators of forage quality did not vary consistently within animal class x month. Animal class x month x year interactions occurred for Shannon's index, protein, and digestibility. Differences in botanical diversity of diets resulted in differences in chemical composition among age and sex classes of cattle grazing native rangeland during the growing season. Animals used to obtain diet samples should, therefore, be of similar gender and age as any animals whose performance is being measured.