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The finding that the mast cell can play an important role in innate immunity to bacteria reopens the question of the true role of this controversial cell in the immune system.

Effects of breed of service sire and cow on birth weight and prepartum and postpartum endocrine function were studied in multiparous Brahman (n = 20) and Angus (n = 20) cows bred to Brahman or Angus bulls. Before calving, blood samples were collected on d 34 to 28, 27 to 21, 20 to 14, and 13 to 7, and after calving, samples were collected from d 0 to 7. Progesterone (P4), estrogen (E2), and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) were quantified with RIA. Calves born to Brahman were smaller (P < .05) than calves born to Angus cows. Prepartum concentrations of P4 were greater in Angus cows and decreased more rapidly near parturition than in Brahman cows (breed of dam x period; P < .03). Cows bearing bull calves had greater concentrations of P4 on d 20 to 14 before calving than cows bearing heifer calves (sex of calf x period; P < .04). Prepartum E2 was influenced (P < .05) by the breed of dam x breed of sire x period interaction. The ratio of P4:E2 tended to decrease more in Angus than in Brahman cows near parturition (breed of dam x period; P < .09). Postpartum PGFM tended to be influenced (P < .08) by breed of dam x breed of sire; from d 3 to 5, Brahman cows bred to Angus bulls tended (P < .08) to have greater PGFM than Brahman cows bred to Brahman bulls or than Angus cows bred to Brahman or Angus bulls.2+ f1p4

Preweaning growth data were obtained during 4 yr on 349 Braford-sired calves from Brahman-Hereford F1 first-calf females. These females were allotted to either semiarid rangeland (Uvalde) or humid improved pasture (Overton) as weanlings and to one of four herbage allowance levels at each location as yearlings. Females were wintered on systems in local industry practice and maintained on various allotted herbage levels both as yearlings and during first lactation. The desired range in herbage allowance (400 to 2,800 kg of DM per 100 kg of BW at Uvalde and 80 to 460 kg of DM per 100 kg of BW at Overton) was accomplished by adjusting stocking rate monthly from April to weaning (October). Herbage allowance and yearling heifer characteristics (hook height, condition score, or weight) were treated as continuous, independent variables in regression analyses. Preweaning daily gain responded to increased herbage allowance differently for the two locations. Generally, at Overton, herbage allowance influenced suckling calf growth to a greater extent than for the F1 yearling variables, but at Uvalde this trend was reversed. Heifers with larger yearling heights had first calves that grew faster to weaning for both locations and all herbage allowances, although the relationship was stronger for greater herbage allowances at Overton (herbage allowance x yearling weight interaction, P < .07). This interaction was not detected (P > .15) at Uvalde. Interactions between herbage allowance and yearling condition score were detected (P < .05) at both Overton and Uvalde, but these interactions were different (P < .15) at the two locations.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

The ability of bovine lymphocytes to initiate in vitro blastogenesis in response to mitogen stimulation or to initiate DNA excision repair after treatment with a mutagen was evaluated as a function of the differing environmental conditions under which donor animals were maintained. Crossbred Brahman-Hereford F1 females were held on either a humid, coastal bermudagrass, improved pasture at Overton, TX, or in low or high grazing pressure herds on a semi-arid rangeland (Acacia-dominated shrubland) at Uvalde, Tx. Peripheral blood lymphocytes (PBL) from these animals were examined to determine their in vitro ability to engage in phytohemagglutinin (PHA)-stimulated blastogenesis and to initiate excision repair of DNA damage after exposure of the cells to the model polynuclear hydrocarbon carcinogen 7,8-dihydrodiol-9, 10-epoxy-benzo(a) pyrene (BPDE). PBL from cattle at both locations were compared, with significantly decreased blastogenesis and DNA excision repair observed in PBL from Uvalde high grazing pressure cattle. Cattle in the Uvalde high grazing pressure herd also exhibited significantly decreased reproductive efficiency. The data indicate that ingestion of sufficient quantities of palatable, but toxic, forage species available at the Uvalde test site is sufficient to decrease DNA synthesis associated with either mitogen-stimulated blastogenesis or DNA excision repair in bovine PBL, and suggest that the reduction in PBL DNA synthesis may be correlated with the changed reproductive efficiency in animals ingesting an increased ratio of forage from Acacia species.