The greatest nutrient demand of beef cows is during lactation. During lactation cows need to be fed high quality hay and, sometime, supplemented to meet the energy and protein requirements. In most Northern Plains locations, much like the sandhills of Nebraska, the primary grasses available for grazing are warm-season grasses that become available in late May to June. If cows calve in March, this means they are fed a lactation diet for about 90 days before summer grass. It has been documented that the highest quality in warm-season grasses in Nebraska occurs in late May to mid- June and gradually decreases. Sequencing calving closer to the time when the grazed resource will meet the nutrient demands of the lactating female reduces feed costs and increase profit potential. Basically, this means moving “early spring” calving to “early summer” calving. Key components to changing calving time using a “systems” approach include: 1. Cows have access to vegetative forage for a short period of time prior to calving; 2. Cows meet their energy and protein needs from the pasture resource; 3. Hay and supplement costs are reduced because peak lactation now occurs when vegetative, high quality forage is available; 4. Reduced calf losses and sickness because calving occurs when the weather is warmer; 5. Less labor is needed at calving because calves weigh less at birth for June calving cows compared to February/March born calves; 6. Labor is reduced because less harvested feeds are fed; and 5. Different market alternatives are available for the calves and cull cows and bulls.

In 1993, a summer calving herd was developed at the University of Nebraska, Gudmundsen Sandhills Laboratory to compare spring and summer calving herds. In the spring herd, cows began calving in March and the breeding season began in June, and calves were weaned in October. For the summer calving herd, calving began in June, breeding season began in September, and weaning occurred in November or January. Data were collected in 1994, 1995, and 1996. Summer calving cows were fed 327 lb of hay/cow/year compared to 3,947 lb of hay/cow/year. Similar amounts of protein supplement were fed; summer calving cows were fed 154 lb/cow/yr and for spring calving 96 lb/cow/yr. The length of the grazing season went from 233 days to 357 days by adjusting the calving time from March to June. Cow reproductive performance was not different between groups. When calves were weaned at similar days of age, summer born calves were about 35 lb lighter. However, January calf prices tend to be higher for the same weight of calf sold in October; therefore, summer-born calves generate similar gross income as spring-born calves. Due to costs savings in the summer calving system, primarily due to less labor and less hay fed, the summer calving system was a more profitable even at weaning time.

Some concerns with this summer calving system include breeding season occurring at a time when the temperatures are hot. In the sandhills of Nebraska, the temperature decreases at night and the humidity is low. In areas of the United States, because of high humidity and no night cooling, a breeding season that occurs during this time period could result in lower pregnancy rates.