Yearling heifer growth data were obtained during 4 yr for 524 heifers allotted to either humid bermuda grass pastures (Overton) or semiarid rangeland (Uvalde). Each year, heifers were allotted on April 15 to four forage availability levels (400 to 2,800 kg of DM per 100 kg of BW at Uvalde and 80 to 260 kg of DM per 100 kg of BW at Overton) maintained by varying the stocking rate monthly until mid-October of each year. Forage availability and yearling heifer characteristics (weight, condition score, and height at hooks, taken on April 15) were treated as continuous variables in regression analyses. Final heifer weight, height, and condition responses to increased forage allowance were related to yearling phenotypes differently for the two locations. Generally, at Overton, forage availability influenced final characteristics to a greater extent than did yearling variables, whereas the trend was the opposite at Uvalde. At Uvalde, the yearling characteristic that had the largest effect on performance was height at hooks. Yearlings with large frames benefited from increased forage allowance by accumulating body fat at a faster rate than those with small frames. In contrast, at Overton, the yearling characteristic that had the largest effect on performance was condition. Fat heifers responded to increased forage availability to gain even greater advantages in fatness at the expense of potential growth in height and, thus, achieved early maturation. Yearling phenotypes were more broadly adapted to arrays of forage availability for humid, improved pastures than for semiarid rangeland.
Growth data were collected over 4 yr from 349 Brahman-Hereford F1, first-calf, lactating females that had been allotted as weanlings to either semiarid extensive rangeland (Uvalde) or humid improved Bermudagrass pasture (Overton) and to one of four herbage allowance levels at each location as yearlings. Heifers were wintered according to systems in local practice and maintained on allotted forage levels both as yearlings and during their first lactation. Heifers were bred to Braford bulls to calve as 2-yr-olds in January to March. Herbage allowance (400 to 2,800 kg of DM/100 kg BW at Uvalde and 80 to 460 kg of DM/100 kg BW at Overton) was maintained by adjusting stocking density monthly from April to weaning (October). Herbage allowance and yearling heifer hook height, condition score, or weight (taken on April 15) were continuous independent variables in regression analyses. Final heifer weight, height, and condition responses to increased herbage allowances were related to yearling phenotypes differently (P < .01) for the two locations. At Uvalde, yearling condition score interactions were especially important in that heifers that had more condition (especially those > 5 for 1 to 10 with 10 = fattest) as yearlings retained more (P < .05) weight and condition and grew more (P < .05) in height than did those of lower yearling condition. These females also responded to increased herbage allowance by gaining advantage (P < .05) in these variables, whereas those of lower yearling condition made smaller advances. At Overton, yearling condition played little role in subsequent growth. The yearling variable that had the greatest interactive effect was height. Shorter yearling heifers (< 123 cm) responded (P < .07) to increased herbage allowance so that they had greater final condition and grew more rapidly in height than those taller as yearlings.
Postweaning growth patterns and preweaning milk and forage intake were observed over a 4-yr period for 137 Angus calves allowed either fescue-legume or fescue pastures preweaning. After weaning, calves grazed fescue pasture until spring for a slow growth phase and then fescue, orchard grass, bluegrass and ladino clover pastures for 4 mo. Following this period, the calves were confined and fed shelled corn and a 36% crude protein supplement until they reached 12 mm of fat over the 12th rib. The spring growing period and the finishing period were classified as a rapid growth phase. Calves that were fatter at weaning lost more fat, but gained more in wither height during the slow growth phase, than those that were thinner at weaning. Apparently, fatter calves were more capable of continuous skeletal growth on a low plane of nutrition because they could retrieve fat energy for this growth. In spring, calves that had been relatively fat at weaning held no advantage in fatness, but had larger frames. Therefore, during the rapid growth phase, they were able to fatten more rapidly than those that were thinner at weaning. Also, calves that were more efficient in preweaning growth had more capacity for rapid postweaning growth when restricted to relatively low quality pasture. Preweaning pasture type influenced pattern of postweaning growth. Part of this influence was associated with differences detected at weaning. An additional part was associated with efficiency of forage and milk utilization during the preweaning phase.
Postcalving cow weight and subcutaneous fatness change patterns were described for 80 mature spring-calving Angus cows. The cows grazed either high (regularly clipped fescue-legume) or low (fescue clipped once) quality pastures. Forage consumption was estimated continuously by an internal (acid detergent lignin)-external (Cr2O3) indicator technique. Milk production (calf-suckle technique) was estimated seven times during lactation. Wither height was measured during the fall after the period of intensive measurment. Angus cows grazing high quality pasture lost an average of 36 kg postcalving, whereas those grazing low quality pasture lost an average of 22 kilograms. Minimum weights were observed about April 1, prior to the season of large pasture quality differences in digestibility of consumed forage. Taller cows, when allowed increased nutrient density during midlactation (high versus low quality), responded by increasing (P < .05) fatness at a more rapid rate than less tall cows. For cows grazing high quality pasture, weight change was independent of level of milk production. Cows grazing low quality pasture and giving relatively large amounts of milk maintained less weight and fat during the middle and last part of lactation than did those giving smaller amounts of milk. Shapes of the curves depicting change in weight and fatness were closely related (P < .01) to digestible dry matter intake. Cows apparently consumed forage in such a manner that they became more alike in both weight and fatness as the grazing season progressed.
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