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Perennial Irrigated Pastures. III. Beef Calf Production from Irrigated Pasture and Winter Annual Range¹

Irrigated pastures in the Western arid and semi-arid regions provide support to the beef cattle industry through the maintenance of beef cow herds and the production of calves. Increasingly unfavorable production economics, including the rising cost and logistical difficulty of seasonally moving cattle from seasonal range to other pastures (e.g., high mountain Federal granng allotments), necessitate evaluation of management options which permit increased stocking rate and year-around home ranch operation.

The objective of this study was to compare simple (range-only, yearlong) and complex [improved range and irrigated pasture plus winter supplementation with alfalfa (Medicago sativa L.) cubes] systems for beef calf production using a fall calving (November-December), early summer weaning (May-June) reproduction cycle.

In the complex system, cleared and reseeded range was used (winter) an average (4 years) of 6 months per year at a stocking rate of 2.2 ha/cow (2.8 AUM/ha). Irrigated pasture was used (summer) an average of 6 months per year at a stocking rate of 0.5 ha/cow (10.3 AUM/ha). Alfalfa cube supplement was fed (about 1 kg/ha per day) during fall and winter. In the simple system, cleared range was used yearlong at an average stocking rate of 5 ha/cow (2.4 AUM/ha). No supplements were fed except during the last year when drought prevailed. An average of 70 kg calf/ha was produced in the complex system. Average birth weight was 34 kg and average Lily gain (ADG) to 205 days was 0.76 kg. In the simple system, comparable values were 37.5 kg calf/ha, 32 kg birth weight, and 0.75 ADG. Birth weights and ADGs were not significantly different between systems. Average cow weights reflected seasonal changes in forage availability and quality. Cows in the simple system tended to lose weight more consistently during the months July. October than did those in the complex system, which, instead, more consistently lost weight during the months November-March. Economic return was similar but low in both systems. While total land per cow/calf unit was less for the complex system and total investment higher for the simple system, operating costs, depreciation, and interest were higher for the complex system.

It appeared that second and third trimester cow stresses, as evidenced by negative bodyweight changes, did not adversely affect calf birth weights and ADG, at least at the levels found under these experimental conditions.

Key Words: Grazing management • Annual clovers • Economics of range beef cattle production • Cow/calf systems on annual range

² Professor in agronomy and range science, and specialist and staff research associate in animal science, respectively, Univ. of California, Davis, CA 95616.

Received for publication February 12, 1979.