Cows can adapt their energy metabolism during periods of moderate feed restriction, Agricultural Research Service and U.S. Meat Animal Research Center researchers conclude.

Researchers hypothesized that restricting feed intake during the second trimester of gestation and providing saved feed during the third trimester were less energetically efficient than providing the feed during the second trimester.

Twenty multiparous cows (four-breed composite: ¼ Hereford, ¼ Angus, ¼ Red Poll and ¼ Pinzgauer) were fed a diet that consisted of (DM basis) 67.3% chopped corn silage, 27% alfalfa hay, 5.5% corn and 0.2% NaCl (sodium chloride, salt).

When cows were 87 days pregnant, the first nutrient balance measurement was conducted. Six subsequent nutrient balance measurements were taken on days 122, 143, 171, 206, 241 and 262 of gestation. Each nutrient balance measurement consisted of a 96-hour total collection of feces and urine and a 24-hour indirect calorimetry measurement.

Ten cows were fed for moderate body weight gain during the entire pregnancy and 10 cows were feed-restricted in the second trimester and realimented during the third trimester (low-high, L-H).

Cows' body weight at parturition (1,232 lbs.) did not differ between treatments. There was a general trend for the proportion of metabolizable energy (ME) intake retained to decrease in moderate cows as pregnancy progressed. The proportion of ME intake retained in L-H cows decreased during the first 49 days of feed restriction, but the proportion of ME retained after 77 days of restriction was greater than that retained at 49 days of restriction.

During realimentation, there were no time effects for efficiency of ME conversion to retained energy, but efficiency was greater for L-H cows than for moderate cows.

Researchers conclude that the ability of the cow to adapt its energy metabolism during periods of moderate feed restriction and realimentation allows managers to alter the time interval of the production cycle during which supplemental feed is offered. Total feed savings in feed offered during the production year are minimal, but management strategies can be developed that shift which feed resources are being used.
Freetly et al, 2008, Journal of Animal Science, 86:370.

Forage allocations for stockpiled tall fescue in a strip-grazing system are optimized at 2.25% of cow-calf body weight/day, researchers from the University of Missouri-Columbia report.

In a two-year study, researchers evaluated the effect of different forage allocations on the performance of lactating beef cows and their calves grazing stockpiled tall fescue.

Allocations of stockpiled tall fescue at 2.25%, 3%, 3.75%, and 4.5% of cow-calf pair body weight/day were set as experimental treatments. Conventional hay feeding was also evaluated as a comparison to grazing stockpiled tall fescue. The experiment had a randomized complete block design with three replications and was divided into three phases each year.

From early December to late February (Phase 1) of each year, cows and calves grazed stockpiled tall fescue or were fed hay in the treatment groups described above. Immediately after Phase 1, cows and calves were commingled and managed as a single group until weaning in April (Phase 2) so that residual effects could be documented.

Residual effects on cows were measured after the calves were weaned in April until mid-July (Phase 3).

During Phase 1 of both years, apparent dry matter intake of cow-calf pairs allocated stockpiled tall fescue at 4.5% of body weight/day was 31% greater than those allocated 2.25%. As allocation of stockpiled tall fescue increased from 2.25% to 4.5% of cow-calf body weight/day, pasture utilization fell from 84 ± 7% to 59 ± 7%.

During Phase 1 of both years, cow body weight losses increased linearly as forage allocations decreased, although the losses in Year 1 were almost double those in Year 2. During Phases 2 and 3, few differences were noted across treatment groups, such that by the end of Phase 3, cow body weight in all treatments did not differ either year.

Calf average daily gain in Phase 1 increased linearly with forage allocation. However, calf gain per acre decreased linearly as stockpiled tall fescue allocations increased such that gain per acre for cow-calf pairs allocated stockpiled tall fescue at 4.5% body weight/day was nearly 40% less than for those allocated 2.25% of body weight/day.

Researchers conclude that cow-calf pairs allocated stockpiled tall fescue at 2.25% of cow-calf body weight/day optimizes its use because: 1) calf weaning weights are comparable to greater forage allocations; 2) cow body weight loss in winter is easily regained in spring and early summer, 3) land requirements are decreased, and 4) calf gain per acre can be increased by nearly 40%.
Curtis et al, 2008, Journal of Animal Science, 86:780.