Genotype x environment interactions in Angus, Brahman, and reciprocal-cross cows and their calves grazing common bermudagrass, endophyte-infected tall fescue pastures, or both forages

Reproductive and preweaning data on 190 Angus (A x A), Brahman (B x B), and reciprocal-cross cows (A x B and B x A) and 434 two- and three-breed-cross calves managed on common bermudagrass (BG), endophyte-infected tall fescue (E+), or a combination of both forages (ROT) were used to evaluate the interaction of forage type with individual and maternal heterosis and maternal and grandmaternal breed effects. Cows were born from 1988 to 1991, and calves sired by 13 Polled Hereford bulls were born from 1995 to 1997. Heterosis for calving rate was larger on E+ than on BG or ROT (P < .05), whereas maternal effects were larger on BG than on ROT (P < .10). Maternal heterosis for birth weight was negative on BG (P < .11) but positive on E+ and ROT (P < .10). Grandmaternal effects were evident on BG (P < .10) and E+ (P < .01) but not on ROT. Forage effects were generally substantial for 205-d weight, calf weaning hip height, and calf weaning weight:height ratio; BG was highest, ROT was intermediate, and E+ was lowest. Maternal heterosis for these traits was generally greater on E+ than on BG (P < .10). Grandmaternal effects for 205-d weight, hip height, and weight:height ratio were not important on any forage. Heterosis for weaning weight per cow exposed was substantial on all forages (P < .01) and was significantly greater on E+ (P < .01) than on BG or ROT, but maternal effects were not significant. Thus, we observed more advantage to Brahman-cross cows over purebreds on E+ than on BG. We also observed that moving cows and calves from E+ to BG in the summer will alleviate some, but not all, of the deleterious effects of E+ on calf growth, although it may be more beneficial for reproductive traits in purebred cows.     

Postweaning performance of calves from Angus, Brahman, and reciprocal-cross cows grazing endophyte-infected tall fescue or common bermudagrass

Data from 403 Polled Hereford-sired calves from Angus, Brahman, and reciprocal-cross cows were used to evaluate the effects of preweaning forage environment on postweaning performance. Calves were spring-born in 1991 to 1994 and managed on either endophyte-infected tall fescue (E+) or common bermudagrass (BG) during the preweaning phase. After weaning, calves were shipped to the Grazinglands Research Laboratory, El Reno, OK and stratified to one of two winter stocker treatments by breed and preweaning forage; stocker treatments were winter wheat pasture (WW) or native range plus supplemental CP (NR). Each stocker treatment was terminated in March, calves grazed cool-season grasses, and calves were then moved to a feedlot phase in June. In the feedlot phase, calves were fed to approximately 10 mm fat over the 12th rib and averaged approximately 115 d on feed. When finished, calves were weighed and shipped to Amarillo, TX for slaughter. Averaged over calf breed group, calves from E+ gained faster during the stocker phase (P<.10), had lighter starting and finished weights on feed (P< .01), lighter carcass weights (P<.01), and smaller longissimus muscle areas (P<.05) than calves from BG. Calves from E+ were similar to calves from BG in feedlot ADG, percentage kidney, heart, and pelvic fat, fat thickness over 12th rib, yield grade, marbling score, and dressing percentage. Maternal heterosis was larger in calves from E+ for starting weight on feed (P<.01), finished weight (P<.10), and carcass weight (P<.16). These data suggest that few carryover effects from tall fescue preweaning environments exist, other than lighter, but acceptable, weights through slaughter. These data further suggest that the tolerance to E+ in calves from reciprocal-cross cows, expressed in weaning weights, moderated postweaning weight differences between E+ and BG compared to similar comparisons in calves from purebred cows.     

Genetic x environment interactions on blood constituents of Angus, Brahman, and reciprocal-cross cows and calves grazing common bermudagrass or endophyte-infected tall fescue

Over a 2-yr period, effects of genotype and forage on blood metabolites, enzymes, and minerals were determined in Angus, Brahman, Angus x Brahman (sire x dam), and Brahman x Angus cows, and 129 calves from these cows sired by Hereford bulls. Cows and calves continuously grazed either common bermudagrass or endophyte-infected 'Kentucky-31' tall fescue pastures throughout the year. Blood samples were collected via jugular venipuncture in April, August, October (weaning), and November (after 30 d in a feedlot) of each year. Plasma urea N concentrations of cows and calves were affected by forage (P < 0.01) and breed (P < 0.05). Plasma cholesterol and FFA concentrations of cows were affected by forage (P < 0.01) and breed (P < 0.05). In calves, antibody titers to infectious bovine rhinotracheitis virus were not affected by forage but were affected by breed. Serum inorganic P concentrations of calves and cows were affected by forage (P < 0.05). Serum P concentrations and alkaline phosphatase activity of calves were affected by breed (P < 0.05). Calves grazing bermudagrass had higher (P < 0.05) serum concentrations of Fe and total iron binding capacity (TIBC). There was evidence of maternal heterosis for concentrations of free fatty acids, cholesterol, aspartate aminotransferase, Ca, Mg, alkaline phosphatase, ceruloplasmin, Fe, and TIBC. There was evidence of grandmaternal effects for plasma concentrations of urea N, cholesterol, Ca, P, Mg, and alkaline phosphatase. These results suggest that calves and cows grazing tall fescue are generally on a lower plane of nutrition than those grazing bermudagrass and that Brahman x Angus and Angus x Brahman crossbred cows and their calves seen to be more tolerant of the negative effects of tall fescue than the average of their purebred contemporaries.     

Genotype x environment interactions in milk yield and quality in Angus, Brahman, and reciprocal-cross cows on different forage systems

Milk yield and quality were observed on 93 Angus, Brahman, and reciprocal-cross cows over 3 yr to evaluate the interactions of direct and maternal breed effects and heterosis with forage environment. Forage environments were common bermudagrass (BG), endophyte-infected tall fescue (E+), and a rotational system (ROT) of both forages, in which each forage (BG or E+) was grazed during its appropriate season, usually June through October for BG and November through May for E+. Milk yield was estimated each of 6 mo (April through September) via milking machine and converted to a 24-h basis. Milk fat, milk protein, and somatic cell count were analyzed by a commercial laboratory. Heterosis for milk yield was similar among forages, averaging 2.4 kg (P < 0.01). Expressed as percentages of purebred means, heterosis for milk yield was largest on E+ (52.8%), intermediate on ROT (39.3%), and smallest on BG (23.7%). Direct breed effects for milk yield favored Brahman, and they were similar among forages but tended to be larger for E+ (2.5 kg) and ROT (2.8 kg) than for BG (1.3 kg). Direct breed effects for milk fat favored Brahman and were similar among forages but tended to be larger for E+ (1.0%) and ROT (1.0%) than for BG (0.6%). Purebred cows exceeded crossbreds in milk protein by 0.1% on ROT (P < 0.10). Crossbred cows had lower somatic cell counts than purebreds on BG (P < 0.05), E+ (P < 0.01), or ROT (P > 0.30). Heterosis for somatic cell counts as percentages of purebred means was similar for BG (-68.3%) and E+ (-68.9%) and less favorable for ROT (-31.6%). Maternal breed effects for somatic cell count favored Angus on ROT (P < 0.10) with a similar nonsignificant trend on BG and E+. Direct breed effects for somatic cell count favored Brahman on ROT (P < 0.10) with similar nonsignificant trends on BG and E+. These results suggested that a rotation of cows from E+ to BG in the summer can partially alleviate negative effects of E+ on milk yield. Conclusions also indicated an advantage to crossbred cows in somatic cell count and provided evidence of both direct and maternal breed effects for this trait. The results also suggested that direct breed effects for milk yield, milk fat, and somatic cell count and heterosis for milk yield and somatic cell count (as percentages of purebred means) tended to vary with forage environment, indicating a potential for genotype x environment interaction for these traits.     

Maternal and reproductive performance of Brahman x Angus, Senepol x Angus, and Tuli x Angus cows in the subtropics

To determine the maternal and reproductive performance of F1 cows in the subtropics, 42 Brahman x Angus, 34 Senepol x Angus, and 50 Tuli x Angus cows were bred to Angus bulls to calve first and subsequently bred to Charolais bulls to calve as 3- to 8-yr-olds. Age at first calving did not differ among crossbred cows. Angus-sired calf birth weights were heavier (P < 0.01) from Senepol x Angus than either Brahman x Angus or Tuli x Angus cows. Weaning weights of Angus-sired calves were heavier (P < 0.01) from Brahman x Angus (213.5 kg) than either Senepol x Angus (194.9 kg) or Tuli x Angus (191.5 kg) cows. As 3- to 8-yr-old cows, calf birth weights were heavier (P < 0.05) from Senepol x Angus compared with Brahman x Angus but not Tuli x Angus cows. Weaning weights of Charolais-sired calves were heaviest (P < 0.05) from Brahman x Angus cows (268.9 kg), lightest from Tuli x Angus cows (233.4 kg), and intermediate from Senepol x Angus cows (245.0 kg). Calf crop born and calf crop weaned were lowest (P < 0.05) for Senepol x Angus cows (76.9 and 70.2%) and did not differ between Brahman x Angus (89.0 and 86.1%) and Tuli x Angus (94.7 and 86.5%) cows. Tuli x Angus cows tended (P < 0.10) to have a lower percentage of unassisted births and lower (P < 0.10) calf survival to weaning than Brahman x Angus cows but not Senepol x Angus cows. As 3- to 8-yr-olds, weaning weight per cow exposed was greatest (P < 0.05) for Brahman x Angus (234.2 kg), least (P < 0.05) for Senepol x Angus (173.0 kg), and intermediate (P < 0.05) for Tuli x Angus (209.1 kg) cows. Also as 3- to 8-yr-olds, efficiency (205-d calf weight per 100 kg of cow exposed) was similar for Brahman x Angus (42.2) and Tuli x Angus cows (40.7), and both were greater (P < 0.01) than for Senepol x Angus cows (33.8). These data indicate that, in the subtropics, maternal and reproductive performance of Tuli x Angus cows, but not Senepol x Angus cows, was comparable to Brahman x Angus cows, except for lower calf survivability and weaning weight.     

Performance, forage utilization, and ergovaline consumption by beef cows grazing endophyte fungus-infected tall fescue, endophyte fungus-free tall fescue, or orchardgrass pastures.

Two 120-d trials (May to September, 1988 and 1989) determined the effects of grazing tall fescue (two varieties) or orchardgrass on forage intake and performance by beef cows. Each summer, 48 cow-calf pairs grazed endophyte-infected Kentucky-31 tall fescue (KY-31), endophyte-free Mozark tall fescue (MOZARK), or Hallmark orchardgrass (OG) pastures (16 pairs/treatment). Forage OM intakes and digestibilities were determined during June and August each year. Cow and calf BW and milk production were determined every 28 d. During June of both years, OM intakes did not differ (P greater than .10) among treatments. During August of 1988, intakes were 18% lower (P less than .05) by KY-31 cows (1.6% of BW) than by MOZARK or OG cows (average 1.95% of BW); however, no differences (P greater than .10) were measured in August of 1989. Estimates of ergovaline consumption during June from KY-31 were between 4.2 (1988) and 6.0 mg/d (1989), whereas August estimates were between 1.1 (1988) and 2.8 mg/d (1989). Ergovaline in MOZARK estrusa was below detection limits, except in August of 1989. Cows that grazed KY-31 lost three times (P less than .01) more BW than cows that grazed MOZARK or OG (42 vs 9 and 13 kg, respectively). Milk production by KY-31 cows was 25% lower (P less than .01) than that by cows that grazed MOZARK or OG (6.0 vs average of 8.0 kg/d). Similarly, slower (P less than .01) calf gains were noted for KY-31 than for MOZARK or OG (.72 vs .89 and .88 kg/d, respectively). Cows grazing KY-31 experienced accelerated BW loss and reduced milk production and weaned lighter calves than did cows grazing MOZARK or OG. Decreased performance was not explained by consistently reduced forage intakes; hence, altered nutrient utilization was suspected.     

Metabolic characteristics of multiparous Angus and Brahman cows grazing in the Chihuahuan Desert

Understanding metabolic differences between breeds of cattle is important when selecting for production in semiarid environments. Spring-calving multiparous Angus and Brahman cows (n = 8/breed) grazing in the Chihuahuan Desert were used to evaluate metabolic hormone status in February (i.e., 3rd trimester of pregnancy), May (i.e., early lactation), and September (i.e., late lactation) 2000. Crude protein in ruminal digesta collected from grazing companion ruminally cannulated cows during these months was 5.6, 6.0, and 10.3%, respectively. Angus cows were heavier (P < 0.01) than Brahman cows across months. Body condition scores among breed groups were 4.4, 3.6, and 4.6 in February, May, and September with Brahman cows tending (P < 0.10) to have greater body condition than Angus cows in May. Brahman cows tended to have greater fecal output per 100 kg BW than Angus cows in February (0.9 > 0.7 +/- 0.1, P < 0.10). Brahman cows had greater serum concentrations of leptin than Angus cows in September (1.8 > 0.70 +/- 0.1 ng/mL; P < 0.05), and serum concentrations of insulin were greater (P < 0.01) in Brahman than Angus cows throughout the study. Brahman cows also had greater (P < 0.01) serum concentrations of glucose during February and May than Angus cows. Serum concentrations of triiodothyronine were greatest (P < 0.01) during September and lowest during February and May in both breed groups and were greater (P < 0.01) in Brahman than in Angus cows in February, May, and September. Pregnancy rate and 205-d adjusted weaning weights were similar (P > or = 0.46) among breed groups. Results suggest that Brahman and Angus cows are sensitive to the seasonal dynamics of forage quality in the Chihuahuan Desert. Brahman cattle appear to have greater concentrations of metabolic hormones and metabolites than Angus cows in this environment, but Angus cows experience greater fluctuations in BW.     

Productivity of cow-calf pairs grazing tall fescue pastures infected with either the wild-type endophyte or a nonergot alkaloid-producing endophyte strain, AR542

The nonergot alkaloid-producing endo-phyte, AR542, has been shown to improve the persistence and yield of tall fescue pastures without causing the animal disorders commonly associated with tall fescue toxicosis. A 3-yr grazing study was conducted to compare effects of AR542-infected tall fescue pastures with wild type endophyte-infected (E+) tall fescue pastures on cow-calf performance. Replicated 7.3-ha pastures of each treatment were grazed by cow-calf pairs (16 pairs per pasture replication) each year from March to weaning in September. The cows were exposed to breeding on their respective pasture treatments from April 1 through June 15. The treatment groups were compared for reproductive performance, ADG, BCS, calf growth rate, and weaning weight. Blood samples were also collected for serum prolactin (PRL) analysis. There were no significant differences in calving rate (P = 0.98) or calving interval (P = 0.62) between pasture treatments. Cows that grazed the AR542 pastures subsequently gave birth to calves that were heavier (P < 0.05) than calves from cows that had grazed the E+ pastures. Cows grazing the AR542 pastures had higher (P < 0.05) BCS at the end of the grazing period, and had higher ADG during the grazing period. Calves raised on the AR542 pasture had higher (P < 0.05) ADG and weaning weights than calves of the same sex raised on the E+ pastures. Serum PRL concentrations were decreased (P < 0.05) in both cows and calves on the E+ pastures compared with serum PRL concentrations in cows and calves grazing the AR542 pastures. The results indicate that grazing tall fescue pastures infected with the AR542 endophyte may give significant advantages in cow-calf growth rates and BCS over grazing E+ pastures. However, there did not seem to be any benefit in reproductive performance in this trial. There was a small, but significant increase in birth weight in cows grazing AR542 pasture.     

Relationship of milk yield and quality to preweaning gain of calves from Angus,Brahman and reciprocal-cross cows on different forage systems

Interactions of the regression of preweaning ADG on dam milk yield and quality with breed group and forage environment were evaluated in a two-phase study. Phase I consisted of milk yield and quality and calf gain records from 1989 to 1991 for purebred Angus (n = 64) and Brahman (n = 62) cows mated to sires of both breeds. Phase II consisted of milk yield and quality and calf gain records from 1991 to 1997 for Angus (n = 94), Brahman (n = 85), Angus x Brahman (n = 86) and Brahman x Angus (n = 93) mated to Polled Hereford sires. In Phase I, forage environments included common bermudagrass and endophyte-infected tall fescue. In Phase II, forage environments included common bermudagrass and endophyte-infected tall fescue (1991 to 1995) and a rotational system of both forages (1995 to 1997) in which each forage was grazed during its appropriate growing season, usually June through October for bermudagrass and November through May for tall fescue. Milk yield was estimated monthly six times during lactation from spring through fall and converted to a 24-h basis. Milk fat, milk protein, and somatic cell count were analyzed by a commercial laboratory. In Phase I, the relation of preweaning ADG to milk yield, milk fat yield, and protein yield was greater (P < 0.05) in Brahman cows on bermudagrass than Angus on bermudagrass. The regression of preweaning ADG on milk yield in Phase I was greater (P < 0.05) for cows on tall fescue than cows which grazed bermudagrass. In Phase II, the relation of preweaning ADG to milk yield, milk fat yield, and milk protein yield was greater or tended to be greater (P < 0.01, P < 0.11, P < 0.01, respectively) in purebred cows compared to reciprocal-cross cows. The regression of preweaning ADG on milk yield and milk protein yield was greater (P < 0.05) on tall fescue than bermudagrass in Phase II. These results suggest that the influence of milk yield and quality on calf growth may differ among breed types and production system, and the efficacy of genetic improvements in milk traits may depend on the breed type and forage environment.     

Comparison of bite size, biting rate and grazing time of beef heifers from herds distinguished by mature size and rate of maturity

Sixteen-month-old heifers from herds having known genetic growth patterns were compared for differences in grazing behavior in a 3-yr study. Treatments were heifers from four size-maturity groups defined by the mature size and maturing rate of cow herds in which they originated. Average growth curve parameters indicating mature BW and rate of maturing in these cow herds were 387 kg and .19%/d for treatment Group I; 413 kg and .18%/d for Group II; 468 kg and .15%/d for Group III; and 589 kg and .16%/d for treatment Group IV. Data were from three heifers per treatment group grazing Midland bermudagrass during June and July observation periods. With the exception of the Group II vs Group III comparison, bite size increased with current or mature BW. Biting rate values were similar for all treatment groups but lower than those previously reported on other grass swards. Grazing time increased (P less than .01) in treatment groups defined by larger mature BW. Differences in grazing time for Group IV vs the other treatments and Group I vs Group II and Group III were observed repeatedly; the Group II vs Group III comparison was significant in one period during each of the 3 yr. Diurnal variations in grazing patterns among the treatments were observed. Period of observation affected (P less than .001) bite size and grazing time. These effects were not associated with month but could best be explained by differences in forage height and total mass. Forage availability had a direct influence on bite size, and a compensating effect of longer grazing time with smaller bite size was demonstrated as a regulator of intake. Differences in ingestive behavior were associated with genetic growth patterns in cattle.     

Growth curves of crossbred cows sired by Hereford, Angus, Belgian Blue, Brahman, Boran, and Tuli bulls, and the fraction of mature body weight and height at puberty

The objective of this study was to evaluate the growth curves of females to determine if mature size and relative rates of maturation among breeds differed. Body weight and hip height data were fitted to the nonlinear function BW = f(age) = A - Be(k×age), where A is an estimate of mature BW and k determines the rate that BW or height moves from B to A. Cows represented progeny from 28 Hereford, 38 Angus, 25 Belgian Blue, 34 Brahman, 8 Boran, and 9 Tuli sires. Bulls from these breeds were mated by AI to Angus, Hereford, and MARC III composite (1/4 Angus, 1/4 Hereford, 1/4 Red Poll, and 1/4 Pinzgauer) cows to produce calves in 1992, 1993, and 1994. These matings resulted in 516 mature cows whose growth curves were subsequently evaluated. Hereford-sired cows tended to have heavier mature BW, as estimated by parameter A, than Angus- (P=0.09) and Brahman-sired cows (P=0.06), and were heavier than the other breeds (P < 0.001). Angus-sired cows were heavier than Boran- (P < 0.001) and Tuli-sired cows (P < 0.001), and tended to be heavier than Belgian Blue-sired cows (P=0.097). Angus-sired cows did not differ from Brahman-sired cows (P=0.94). Brahman-sired cows had a heavier mature BW than Boran- (P < 0.001), Tuli- (P < 0.001), and Belgian Blue-sired cows (P < 0.04). Angus-sired cows matured faster (k) than cows sired by Hereford (P=0.03), Brahman (P < 0.001), Boran (P=0.03), and Tuli (P < 0.001) sires, but did not differ from Belgian Blue-sired (P=0.13) cows. Brahman-sired cows took longer to mature than Boran- (P=0.03) or Belgian Blue-sired cows (P=0.003). Belgian Blue-sired cows were faster maturing than Tuli-sired cows (P=0.02). Brahman-sired cows had reached a greater proportion of their mature BW at puberty than had Hereford- (P < 0.001), Tuli- (P=0.003), and Belgian Blue-sired cows (P=0.001). Boran-sired cows tended to have reached a greater proportion of their mature BW at puberty than had Angus-sired cows (P=0.09), and had reached a greater proportion of their mature BW at puberty than had Hereford- (P < 0.001), Tuli- (P < 0.001), and Belgian Blue-sired cows (P < 0.001). Within species of cattle, the relative range in proportion of mature BW at puberty (Bos taurus 0.56 through 0.58, and Bos indicus 0.60) was highly conserved, suggesting that proportion of mature BW is a more robust predictor of age at puberty across breeds than is absolute weight or age.     

Effect of endophyte type on carcass traits, meat quality, and fatty acid composition of beef cattle grazing tall fescue

Fourteen Hereford steers were used to compare carcass traits, meat quality, and fatty acid composition of beef from cattle grazing tall fescue infected with either wild-type (E+; n = 6) or novel, nil ergot alkaloid (AR542; n = 8) endophyte for 209 d. Average daily gain, live weight, and HCW were greater (P < 0.05) for AR542 cattle than for E+. No differences in LM color or pH were observed between AR542 and E+. Steaks from E+ cattle tended (P = 0.10) to have higher L* and b* than those from AR542 cattle at 0 d of display. Ground beef from E+ cattle also had higher (P < 0.05) L* than AR542 cattle, with no differences in a* or b* at 0 d of display. Color changes during display did not differ for both steaks and ground beef from E+ and AR542. Lipid oxidation levels increased (P < 0.05) during simulated retail display, but they did not differ between endophyte treatments. Adipose tissues from E+ cattle had a higher (P < 0.05) percentage of SFA, and a lower (P < 0.05) percentage of MUFA than adipose from AR542 cattle. Ground beef and i.m. fat had higher (P < 0.05) concentrations of SFA, MUFA, and cis-9, trans-11 isomer of conjugated linoleic acid, and lower (P < 0.05) concentrations of PUFA and PUFA:SFA ratio than s.c. fat. The n-6:n-3 fatty acid ratio did not differ among fat depots. Ergot-alkaloids were detected in s.c. adipose tissues, and alkaloid concentration was greater (P < 0.05) for E+ than AR542. Warner-Bratzler shear force values did not differ between endophyte types, but it decreased (P < 0.01) across the postmortem aging period. Conversely, sensory panel evaluation detected greater (P < 0.01) chewiness and lower (P < 0.05) juiciness for AR542 than for E+ steaks aged for 14 d. Although grazing cattle on tall fescue pastures infected with nil ergot alkaloid endophyte improved cattle performance, these results suggest that endophyte type has minor effects on carcass traits and meat quality of pasture-fed beef. Moreover, finishing cattle on tall fescue pastures showed the potential to enhance the fatty acid profile of beef from a human health perspective. Alkaloid concentration was greater (P < 0.05) in s.c. fat from E+ than AR542 (2.81 vs. 0.92 ppb; fresh-tissue basis). This is the first published report demonstrating the presence of alkaloids in beef tissues.     

Comparison of crossbred cows containing various proportions of Brahman in spring- or fall-calving systems: IV. Effects of genotype x environment interaction on lifetime productivity of young cows.

Lifetime productivity of young (2 to 6-yr-old) crossbred cows containing various proportions (0, 1/4, or 1/2) of Braham breeding was evaluated using 188 spring-calving and 154 fall-calving cows. Cows were mated to Limousin sires to produce 1983 through 1986 calf crops. The 1987 calf crops were produced using Limousin and Salers sires. Significant (P less than .10) genotype (crossbred cow group) x environment (season of calving) interactions were found for age at first calf and lifetime calving percentage and mature cow weight. Within the spring calving group, no differences were found between crossbred groups for age at first calf or lifetime calving percentage. However, within the fall-calving group, 0 and 1/2 Braham cows from Angus dams calved earlier than did those from Hereford dams. Age at first calf also tended to increase as proportion of Brahman increased in the fall-calving group. Within the fall-calving group, lifetime calving percentage for 0 and 1/2 Brahman cows from Hereford dams was lower than for those from Angus dams. The opposite was true for the 1/4 Braham crosses. In general, as the proportion of Brahman breeding increased, productivity, measured as weight per calf or weight weaned per year, increased; however, age at first calving increased also as proportion of Brahman increased. All spring-calving groups calved earlier in life (P less than .05) than their respective fall-calving counterparts and with the exception of the 0 Brahman groups, which were similar, spring-calving groups produced a higher (P less than .05) percentage of calves than did the fall groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of endophyte consumption and heat stress on intravaginal temperatures, plasma lipid oxidation, blood selenium, and glutathione redox of mononuclear cells in heifers grazing tall fescue

A grazing experiment was conducted to assess the effects of wild-type endophyte-infected (E+) tall fescue consumption and elevated ambient temperatures on intravaginal temperatures, plasma lipid peroxidation, and glutathione redox of peripheral blood mononuclear cells. Angus heifers (n = 34) were allotted by BW to 4 blocks consisting of E+ and endophyte-free (E-) fescue pastures. Monthly, in June, July, and August, temperature loggers were fixed into blank controlled internal drug releasers and inserted into a subsample of heifers (n = 16) for 2 d. After 48 h, heifers were weighed, and blood (30 mL) was collected via jugular venipuncture. Peripheral blood mononuclear cells were isolated for analysis of glutathione peroxidase activity, glutathione reductase activity, and reduced:oxidized glutathione. Plasma malondialdehyde was evaluated as a marker of lipid peroxidation, and whole blood Se concentration was determined. Serum prolactin was assayed after the grazing period. Heifer ADG was greatest in August and least in July (P < 0.001). In August, heifers grazing E+ fescue exhibited greater (P < 0.05) afternoon intravaginal temperatures and temperature fluctuations than heifers grazing E- fescue. In July and August, all heifers had greater afternoon temperatures (P < 0.02) and less reduced:oxidized glutathione (P < 0.0001) than in June. Glutathione reductase activity of all heifers was greater in June (P = 0.03) than in July. Similarly, all heifers exhibited decreased glutathione peroxidase activity (P < 0.0008) in July, whereas whole blood Se was reduced (P < 0.0001) in July and August. No treatment or date effects were detected for malondialdehyde, but serum prolactin was reduced at the end of the grazing period (P = 0.008) in heifers stocked on E+ fescue. Using these markers, differences in oxidative stress were not detected between heifers consuming E+ fescue and those consuming E- fescue. Date effects indicating altered glutathione redox and enzyme activity may have been related to heat stress and nutritional limitations.     

Growth rate, diet digestibility, and serum proclactin of yearling horses fed non-infected and infected tall fescue hay

To determine to effect of feeding tall fescue hay infected with endophyte on growth rate, diet digestibility, and serum prolactin, 17 Quarter Horse yearlings were fed a diet of 60% concentrate and 40% tall fescue hay for 5 months. Diets were formulated to meet 1989 NRC recommendations for moderate growth. The dietary treatments included either non-infected (E-, n=9) or infected (E+, n=8) tall fescue hay. Field sampling determined a 52% infection rate of the E+ hay with the endophyte Acremonium coenophialum. Initially and at 29-day intervals, yearlings were weighed and measured for skeletal growth including: (1) height at the withers, (2) length of bone between knee and fetlock, (3) length of bone between hock and fetlock, and (4) the circumference of fore and rear cannon bones. Total fecal collection from the 10 geldings during the last month of the trial permitted the calculation of diet digestibility. Serum samples were taken throughout the trial to determine prolactin response to dietary treatments.The E+ fescue hay did not affect (P>.05) growth rate of yearling horses. Yearlings gained .40 and .38 kg/d when consuming the E− and E+ based diets, respectively. Geldings gained more (P<.05) than fillies. Changes in height at the wither and length and circumference of the fore and rear cannon were positive but did not differ between hay treatments or sexes.E+ fescue hay diets tended to be lower in dry matter, apparent energy, and crude protein digestibility, but values were not statistically different. Fiber digestibility was lower (P<.01) for the diet based on E+ hay. Neutral detergent fiber digestibility averaged 66.2 and 54.4% for E− and E+ diets, respectively.Acid detergent fiber digestibility averaged 78.9 and 64.5% for E− and E+ diets, respectively. Although fiber digestibility of E+ tall fescue hay was lower than E-hay, grain supplementation supportive of a moderate growth rate produced equal growth among yearling horses. Also, no differences in prolactin were apparent between the yearlings fed E− and E+ tall fescue hay.     

Genotype x environment interactions involving proportion of Brahman breeding and season of birth. II. Postweaning growth, sexual development and reproductive performance of heifers

Postweaning growth, sexual development and reproductive traits were evaluated over a 3-yr period on 201 spring-born and 180 fall-born crossbred heifers with 0, 1/4 or 1/2 Brahman breeding. The proportion of Brahman breeding X season of birth interaction was significant for five traits (average daily gain weaning to yearling, yearling condition score, percentage of heifers detected in estrus, prebreeding condition score and percentage of heifers that became pregnant) and was not significant for six traits (yearling weight, hip height and conformation score, age and weight at puberty and prebreeding weight. Among spring-born heifers, 1/4 and 1/2 Brahman heifers outgained (P less than .05) 0 Brahman heifers from weaning to yearling by 50 and 66 g/d, respectively; among fall-born heifers, 1/4 and 1/2 Brahman heifers outgained (P less than .05) 0 Brahman heifers by 41 and 104 g/d, respectively. Yearling weight of 1/2 Brahman heifers was 13 and 10 kg heavier (P less than .05), respectively, than 0 and 1/4 Brahman heifers. Yearling hip height of 1/4 and 1/2 Brahman heifers were 1.9 and 5.7 cm taller (P less than .05), respectively, than 0 Brahman heifers. Weight prior to the start of the breeding season were similar among crossbred heifer groups and spring-born heifers were 66 kg heavier (P less than .05) than fall-born heifers. The percentage of heifers that became pregnant was similar among spring-born crossbred heifer groups, whereas among fall-born heifer groups 1/4 and 1/2 Brahman heifers were 25.2 and 49.4 percentage points lower (P less than .05), respectively, than 0 Brahman heifers.     

Effect of level of endophyte infection, nitrogen fertilization rate, grazing period, and paddock exchange on some chemical properties of four bovine tissues.

Three grazing experiments were conducted to determine the effect of level of endophyte infection, rate of N fertilization of tall fescue grass, grazing period, and paddock exchange on selected chemical properties of four bovine carcass tissues. Samples of semitendinosus and longissimus muscle and of subcutaneous and perinephric adipose tissue were excised from the left side of each carcass. In Exp. 1, percentage of stearic acid was higher (P less than .05) and percentages of palmitoleic and oleic acid were lower (P less than .05) in all tissues from steers grazed on LELN Au-Triumph fescue than in tissues from steers grazed on LELN KY-31 fescue. Grazing periods of 175 or 245 d or paddock exchange (Exp. 2) had no significant effect on proximate composition of semitendinosus and longissimus muscles; however, moisture content was higher (P less than .05) in the semitendinosus muscle from steers grazed on 100% (100E) endophyte-infected KY-31 fescue. Forage treatment, grazing period, and paddock exchange (Exp. 2 and 3) had no significant effect on percentage of saturated fatty acids in the subcutaneous, semitendinosus, and longissimus tissue samples. In Exp. 2 and 3, percentages of saturated fatty acids were higher (P less than .05) in subcutaneous and perinephric adipose tissue samples from steers grazed on 100E than in samples from steers grazed on zero endophyte (OE) fescue.(ABSTRACT TRUNCATED AT 250 WORDS)     

Breed comparisons of Angus,Brahman, Hereford,Pinzgauer, Sahiwal,and Tarentaise for weight,weight adjusted for condition score,height, and body condition score

Data from topcross cows (n = 468) from six breeds of sire (Angus, Brahman, Hereford, Pinzgauer, Sahiwal, Tarentaise) and two breeds of dam (Angus and Hereford) of Cycle III of the Germplasm Evaluation (GPE) program at the U.S. Meat Animal Research Center (MARC) comprising cow weight (CW, n = 9,012), height (CH, n = 9,010), and condition score (CS, n = 8,991) recorded in four seasons per year from 2 to 6 yr of age were used to estimate breed-group differences. The mixed models included cow age, season of measurement and their interactions, year of birth, pregnancy-lactation code (PL), and breed group as fixed effects for CW and CS. Analyses of weight adjusted for condition score included CS as a linear covariate. Model for CH excluded PL. Random effects were additive genetic and permanent environmental effects. Differences among breed-groups were significant for all traits for different ages and were maintained across ages, with few interchanges in ranking through maturity. Cows with Sahiwal sires were lightest (392 to 479 kg), whereas Hereford-Angus (HA) reciprocal-cross cows were shortest (119 to 123 cm) at each age. Cows with Brahman sires were heaviest and tallest among breed groups at all ages, exceeding HA cows by 19 to 24 kg and 9 to 10 cm, respectively. Cows with Pinzgauer and Tarentaise sires were intermediate for weight and height and interchanged ranking across ages. Differences in weight due to differences in condition seemed to be of small magnitude because adjustment for condition score did not affect rankings of breed groups across ages. Important changes for mature size of cows can be achieved by breed substitution with the breeds of sires used in this study.     

Economic evaluation of heterosis and culling policies for lifetime productivity in Hereford, Angus, shorthorn, and crossbred cows.

Experimental lifetime performance data obtained from 156 straightbred Hereford, Angus, and Shorthorn and 172 first-cross heifers were used to estimate heterosis for economic efficiency in a 100-cow herd at age equilibrium under three culling policies and at terminal ages from 6 to 12 yr. All nonpregnant heifers and cows greater than 9 yr of age were culled. The culling policy for removal of nonpregnant cows from second parity through 9 yr of age were 1) no culling, 2) after two consecutive years (actual), and 3) all (imposed). Efficiency was calculated as input cost per unit of output value. A 10-yr average was used for costs of replacement heifers, cow units, and the ratio of calf:cull cow prices (PR), plus higher and lower PR. Input included costs for both cow units and purchased replacements. Output value included both weaned calves and cull cows. Optimum terminal age was mainly a function of PR: 9 yr for average and high PR, but 6 through 9 yr when PR was low, regardless of culling policy or breed groups. Efficiency differences among culling policies were small for high or average PR, but more culling for infertility was beneficial when PR was low. Estimated reductions in unit costs of output value under any culling policy or terminal age were approximately 6% from crossbred cows plus another 6% from crossbred calves, or a total of 12% from specific three-breed crossing of these British breeds. Cost reductions would be somewhat less for rotation crossbreeding but greater for mating smaller crossbred cows with sires of superior growth-carcass breeds.