SUMMARY

SUMMARY Data were analyzed on 200-day weight, average daily gain (ADG) from 200 to 312 days, 312-day weight, ADG from 312 to 424 days and 424-day weight on 584 steers produced in 1973 and 1974 in a four-breed diallel crossing design including Red Poll, Brown Swiss (European and domestic), Hereford and Angus breeds to estimate heterosis and breed maternal and transmitted effects on major economic traits of beef cattle. Effects of heterosis were important (P< .01) for weight at 200 ( 12.7 kg), 312 ( 15.6 kg) and 424 (15.2 kg) days. Effects of heterosis on ADG decreased with increasing age of calf; most of the heterosis ob- served was expressed on preweaning ADG. Breed mean heterosis (h~) was highest in the Brown Swiss and Red Poll breeds and lowest in the Hereford breed; differences in la~ were significant for weight at 200, 312 and 424 days. Reciprocal differences were important (P <.01) in four of the six crosses. The average reciprocal effect on weight in favor of steers with Red Poll and Brown Swiss dams from Hereford-Red Poll, Angus-Red Poll, Hereford-Brown Swiss and Angus-Brown Swiss crosses was 35.4, 37.3 and 38.4 kg at 200, 312 and 424 days, respectively

Growth, puberty and pregnancy were studied in 665 crossbred heifers produced by breeding Hereford and Angus cows to Hereford, Angus, Red Poll, Brown Swiss, Gelbvieh, Maine Anjou, and Chianina sires. Estrus was determined from an average of 240 to 476 days of age. Puberty age was defined as age at first observed, standing estrus followed by an estrus within 45 days, except during the last 45 days of estrus detection when it was defined as first standing estrus. Heifers were bred by artificial insemination for 42 days and naturally for 22 days from an average age of 412 to 476 days. Brown Swiss, Gelbvieh, Maine Anjou and Chianina crosses were 5 to 7% heavier (P<.01), while Red Poll crosses were not different (P>.05) from the Hereford-Angus crosses at the 200-day weight. Compared to Hereford-Angus crosses at 400 days of age, Maine Anjou, Chianina and Gelbvieh crosses were 5 to 8% heav ie r ( (P< .01 ) , Red Poll crosses were 4% lighter (P<.01), and Brown Swiss were 3% heavier (P>.05). Sire breed influenced (P<.01) puber ty age and percentage of heifers reaching puberty by 270 to 450 days of age. Sire breed groups divided into three groups for puberty age with Gelbvieh (343 + 5), Brown Swiss (349 +4), and Red Poll (354 -+ 5) crosses the youngest (P<.01), Chianina (401 + 5) crosses the oldest (P<.01), and Maine Anjou (374 -+ 5) and Hereford-Angus (374 _+ 5) crosses intermediate. Chianina crosses were heaviest at puberty (319

This study included data on 1,207 calves born and l, 151 calves weaned in 1973 and 1974 in a fourbreed diallel crossing design including Red Poll, Brown Swiss (European and domestic), Hereford and Angus breeds to estimate heterosis and breed maternal and transmitted effects on economic traits of beef cattle. Birth weight, gestation length, calving difficulty, perinatal mortality, calf crop weaned, preweaning average daily gain (ADG), preweaning relative growth rate (RGR) and 200day weight were analyzed. The effects of heterosis were significant for birth weight, calf crop weaned, preweaning ADG and 200-day weight. The four breeds did not differ significantly in most traits in breed mean heterosis (h~) in their crosses. Breed maternal effects (gMi) showed the Brown Swiss breed with the lowest level of calving difficulty. The four breeds did not differ (P>.05) from each other in g~ for calf crop weaned but differed significantly from each other in g~ for ADG and 200-day weight ranking in order (high to low) of Brown Swiss, Red Poll, Angus and Hereford. The difference between Brown Swiss

An experiment was conducted to assess the effect of clitoral stimulation on pregnancy rate to artificial insemination in 1,856 beef females. For unadjusted data, pregnancy rate to first service in nonstimulated females was 61% for cows and 59% for heifers, and that of females receiving clitoral stimulation was 69% for cows and 58% for heifers. After adjusting the data for the influences of age, breed, technician, and postpartum interval, clitoral stimulation increased first service pregnancy rate in cows (74 ± 3% vs 59 ± 3%, P<0.05), but not in heifers (53 ± 5% vs 57 ± 5%, P>0.10). Postpartum interval significantly influenced pregnancy rate, regardless of treatment, and clitoral stimulation was beneficial when applied to cows with relatively short postpartum intervals. Variation in the effect of clitoral stimulation on pregnancy rate was observed among technicians. Clitoral stimulation improved pregnancy rate more effectively in 3 to 4 year old cows than in cows 2 years old and cows 5 years of age or older. We concluded that clitoral stimulation at the time of artificial insemination was an effective means of increasing pregnancy rate in cows, but not in heifers.

Twelve mature Angus bulls possessing similar semen quality were used to study the effects of single and multiple services and single-sire and multiple-sire mating on pregnancy rate of beef heifers. Heifers were observed for natural estrus twice daily and mated within 6 hr of onset of estrus. Pregnancy rate was determined by rectal palpation at 60 days post-mating. Pregnancy rate of heifers receiving one service per estrus averaged 62.1% (n=124) and pregnancy rate of heifers receiving multiple services (single-sire) per estrus averaged 62.9% (n=105). Pregnancy rate per estrus of heifers mated to three sires (multiple-sire, one service per sire; 74.0%, n=123) was significantly higher than that of heifers mated to a single sire (62.9%). The range in pregnancy rate per bull for single-sire matings was large (0 to 95%), but this range was reduced among the same bulls used for multiple-sire matings (68 to 84%). These results indicate that pregnancy rate to one service did not differ (P>.10) from pregnancy rate to multiple services among single-sire matings, but multiple-sire matings increased (P<.05) pregnancy rate per estrus by 11% over that obtained with single-sire matings.

Angus, Hereford and Red Poll crossbred yearling heifers (n = 81) were mated to Brown Swiss bulls. Pregnant heifers were assigned on the bases of weight and breed cross to one of three diets and fed to achieve maternal weight gains of 0, .5 or 1.0 kg/d. Heifers from each treatment group were slaughtered at about 120, 150, 180, 210, 240, or 255 d postmating. Reproductive tracts were recovered at slaughter. Weights of the gravid uterus, fetus, fetal membranes, fetal fluids, uterus, cotyledons and placenta were obtained and have been reported previously. Fetuses were frozen and later ground, mixed and sampled. Dry matter was determined. Samples of each fetus were ashed, and concentrations of Ca, P, Na, K, Mg, Fe and Zn were determined. Relationships between total fetal content of each mineral and day postmating were obtained, and daily fetal accretion rates of each mineral were estimated for several stages of gestation. Daily requirements and allowances of each mineral for pregnancy in beef cows were estimated. Estimated allowances for Ca, P, Na, K, Fe and Zn were small during early gestation but increased rapidly and reached maxima of 8.4 g, 5.2 g, .76 g, .63 g, 65 mg and 21 mg, respectively, at about 250 d postmating.

Postweaning growth and feed efficiency (megacalories metabolizable energy [ME] /kilogram gain) were determined for 798 steers representing Hereford and Angus straightbred (H and A), Hereford-Angus reciprocal cross (HAx), Red Poll-Hereford and Red Poll-Angus reciprocal cross (Rx), Brown Swiss-Hereford and Brown Swiss-Angus reciprocal cross (Bx), Gelbvieh-Hereford and Gelbvieh-Angus cross (Gx), Maine Anjou-Hereford and Maine Anjou-Angus cross (Mx) and Chianina-Hereford and Chianina-Angus cross (Cix) breed groups. Regression of pen mean weight and cumulative megacalories ME on days fed was used to estimate gain, ME consumption and feed efficiency (megacalories ME/kilogram gain) over (1) time- (0 days to 248 days) and (2) weight-constant (250 kg to 470 kg) intervals and to (3) marbling (0 days to a small degree of marbling, USDA choice quality grade) and (4) fat trim (0 days to 18.9% fat trim) endpoints. Breed groups with the most rapid growth rates and heaviest weights at birth, 200 days and 424 days (Bx, Gx, Mx) required fewer (P<.05) megacalories ME/kilogram gain over time- and weight-constant intervals than slower-gaining, lighter breeds (HAx, Rx). Breed groups reaching the marbling or fat trim endpoint in the fewest days generally required fewer .05) megacalories ME/kilogram gain to marbling (HAx < Cix) and fat trim (HAx < Bx, Mx and Cix) endpoints than did faster-growing, heavier breed groups that reached the endpoints at older ages. Contrary to previous reports, HAx did not gain significantly faster than H and A straightbreds during the postweaning period (the HAx advantage was only 2.0% for postweaning average daily gain). HAx required more (P<.05) megacalories ME/kilogram gain than H and A straightbreds over time- and weight-constant intervals.

Data on growth traits, puberty and pregnancy were analyzed on 490 crossbred females produced by artificial insemination from Hereford and Angus dams by Hereford, Angus, Brahman, Sahiwal, Pinzgauer and Tarentaise sires. Brahman crosses were heaviest (P<.01) at 200 and at 550 days. Brahman and Sahiwal crosses gained at a slower rate than Angus-Hereford, Pinzgauer and Tarentaise crosses from 200 to 400 days, whereas from 400 to 550 days, Brahman crosses gained significantly faster than all other crosses and Sahiwal crosses gained significantly faster than Angus-Hereford, Pinzgauer and Tarentaise crosses. Differences in growth traits among the Angus-Hereford, Pinzgauer and Tarentaise crosses generally were small. Females with Angus dams were significantly heavier at 200 and at 400 days than females with Hereford dams, but females with Hereford dams gained significantly faster than females with Angus dams after 200 days and were significantly heavier at 550 days. Major differences were observed among breed of sire groups for age and weight at puberty. Brahman crosses were significantly older and heavier than all other breed of sire groups at puberty. Sahiwal crosses were older (P<.01) than all remaining breed of sire groups at puberty and were heavier (P<.01) at puberty than Pinzgauer, but not Tarentaise or Angus-Hereford crosses. Pinzgauer crosses reached puberty at a significantly younger age than all other crosses. Females with Angus dams did not differ from females with Hereford dams in weight at puberty, but were 22 days younger (P<.01) at puberty. A significantly higher percentage of Brahman (93%), Sahiwal (98%) and Pinzgauer (94%) crosses, but not Tarentaise crosses (91%), were pregnant at 550 days than Angus-Hereford crosses (82%).

Heifers were fed three dietary energy levels to provide for gains of 0 to .1 (Low), .5 to .6 (Medium), and 1.0 to 1.1 (High) kg/day from 35 to 42 days of gestation until slaughtered. Animals on each dietary treatment were slaughtered at 90, 120, 150, 180, 210, 240 and 255 days of gestation in a study to characterize bovine fetal growth as a basis for assessing the stage of gestation at which fetal development might be altered without suppressing neonatal growth. Level of maternal dietary energy did not influence (P>.10) fetal weight or composition. Initial instantaneous growth rate (weight) was 7.4%/day and this rate declined at a rate of .0125% for each day of gestation. The instantaneous rate of increase of fetal weight reached a maximum at 232 days of gestation and declined thereafter. The rate of DNA synthesis reached a .maximum at 218 days of gestation followed by RNA (227 days), protein (243 days) and ash (250 days). The rate of growth due to hyperplasia (DNA per fetus) decreased relatively more with increasing fetal age than did the rate of growth due to hypertrophy (protein to DNA and RNA to DNA ratios). Correlations among fetal weight, fetal fluid weight, cotyledon area, placental weight and uterine weight were high and positive, but there was no indication that fetal growth can be effectively mediated indirectly by restriction of uterine or placental development.

The effects of daily metabolizable energy intakes of 9.5 (low), 15.4 (medium) and 24.9 (high) Meal in pregnant yearling heifers on maternal serum metabolite concentrations and on fetal development as indicated by RNA, DNA and protein concentrations in liver and semitendinosus muscle were studied in 88 crossbred heifers. Pregnant heifers were slaughtered at 90, 120, 150, 180, 210, 240 and 255 days of gestation. Average daily gains (kg) were .14, .58 and .95 and fetus, fluids and membranes accounted for 100%, 27% and 16% of the total live weight gain of the heifers fed the low, medium and high energy diets. Maternal serum free fatty acids (FFA) were not altered (P>.05) by maternal energy level. Glucose concentrations were highest (P<.025) and urea-N concentrations lowest (P<.025) in heifers fed high energy compared to low energy levels. Maternal liver DNA concentrations (mg/g tissue) were higher (P<.025) and the protein/ DNA ratio lower (P<.025) in the low energy diet compared to the medium or high energy diets. Concentrations of liver RNA and protein were not influenced (P>.10) in maternal liver by level of energy intake. Fetal liver and muscle RNA and DNA concentrations decreased (P<.05) with increasing gestational age. Fetal muscle protein increased (P<.05) and liver protein did not change with increasing gestational age. The only indications of an effect of dietary energy intake on fetal development were in fetal liver RNA concentrations which were increased and in the protein/RNA ratio in muscle which was decreased in fetuses from heifers fed low energy compared to the high level of energy intake. It is concluded from these studies that restriction of energy intake in the bovine female to a level that maintains maternal body weight has little influence on the development of the fetus even though maternal metabolism may be altered considerably by level of energy intake.

Gestation length, calving difficulty, perinatal mortality, calf crop weaned, birth weight, preweaning average daily gain (ADG), relative growth rate (RGR) and 200-day weight were examined on 1,610 calves born and 1,536 calves weaned in 1975 and 1976 from 4- to 11-year-old Hereford and Angus dams and by Hereford, Angus, Brahman, Sahiwal, Pinzgauer and Tarentaise sires. Angus dams were superior (P<.01) to Hereford dams in preweaning ADG, RGR and 200-day weight. Hereford dams produced calves with significantly heavier birth weights and longer gestation length than Angus dams. Effects of breeding group and sex of calf were significant for all traits except perinatal mortality and percentage calf crop weaned. All breed of sire groups except Pinzgauer and Tarentaise differed significantly from each other in gestation length; Sahiwal crosses had the longest (294.2 days) and Hereford-Angus crosses had the shortest (284.2 days) gestation length. Brahman crosses exhibited a significantly higher level of calving difficulty than all other breed of sire groups which did not differ (P>.05) from each other. Differences in perinatal mortality were not significant among sire breed groups. Hereford-Angus reciprocal crosses had a significantly higher percentage calf crop weaned than Brahman and Sahiwal crosses. Differences in percentage calf crop weaned were not significant among all other breed of sire groups. Birth weight was heaviest in Brahman crosses (40.6 kg) and lightest in Hereford-Angus (35.4 kg) crosses. All sire breed groups except Sahiwal and Tarentaise crosses differend significantly from each other in birth weight. Brahman crosses had significandy heavier 200-day weight than all other sire breed groups and had significantly higher preweaning ADG than all other breed of sire groups except Tarentaise. Sahiwal and Hereford-Angus crosses were similar (P>.05) in 200-day weight as were Pinzgauer and Tarentaise crosses. All other sire breed groups except Sahiwal and Pinzgauer differed significantly from each other in 200-day weight. Sahiwal and Pinzgauer crosses did not differ significantly from each other or from Hereford-Angus reciprocal crosses in preweaning ADG.

Birth weight, gestation length, dystocia and mortality were studied in 653 2-year-old and 622 subsequent 3-year-old carvings. Dams were Hereford-Angus reciprocal crosses plus crosses of Charolais, Simmental, Limousin, Jersey and South Devon sires on Hereford and Angus cows. Calves from 2-year-olds were sired by Hereford, Angus, Brahman, Holstein and Devon sires. Calves from 3-year-olds were sired by Hereford, Angus, Maine-Anjou, Chianina and Gelbvieh sires. Progeny of Charolais, Simmental and South Devon cross cows were heaviest at birth, (36.5, 35.5 and 36.1 kg; averaged over ages), and had the most dystocia (36.5, 36.5 and 39.5%). Calves from Jersey cross cows were lightest at birth (31 kg), had the shortest gestations (282 days), the least dystocia (17.5%) and had the least mortality (6%). In 2-year-olds, Brahman-sired calves were heaviest at birth (35.3 kg) and had the longest gestations (289 days), the most dystocia (67%), and the highest total mortality (21%). Calves by Hereford, Angus and Devon sires were lightest at birth and had the least dystocia and mortality. In 3-year-olds, calves by Maine-Anjou and Chianina sires were heaviest at birth (38.9 and 39.7 kg) and had the most dystocia (37 and 36%) and the most mortality (11 and 13%). Gelbvieh-sired calves were intermediate and calves by Hereford and Angus sires had the lowest birth weights (34.7 kg), the shortest gestations (283 days) and the least dystocia (12%). Significant curvilinear relationships between birth weight and dystocia and between birth weight and mortality were found at both ages.

Gestation length, calving difficulty, perinatal mortality, calf crop weaned, birth weight, preweaning average daily gain (ADG), relative growth rate (RGR) and 200-day weight were studied on 1,591 calves born and 1,494 calves weaned in 1973 and 1974 from 4- to 9-year-old Hereford and Angus dams and by Hereford, Angus, Red Poll, Brown Swiss (domestic and European), Gelbvieh, Maine-Anjou and Chianina sires. Hereford and Angus dams differed (P<.01) for most traits; the Angus dams reflected a generally higher level of maternal performance. Breed of sire effects were important (P<.01) for all traits; the Hereford-Angus, Red Poll and Brown Swiss crosses were superior in perinatal mortality and calf crop weaned whereas the Gelbvieh, Maine-Anjou, Chianina and Brown Swiss crosses were superior in ADG and in 200-day weight. Thus, average weight weaned per cow calving was highest for the Brown Swiss crosses. Level of calving difficulty was greatest (P<.01) in the Maine-Anjou crosses. The Hereford-Angus reciprocal crosses had the lowest level of calving difficulty, but the value was not significantly less than the value for the Red Poll and Gelbvieh crosses. The Brown Swiss, Maine-Anjou and Chianina crosses had a significantly higher level of calving difficulty than that of the Hereford-Angus reciprocal crosses. Age of dam (4-year-olds vs 5-year-olds and older) was important (P<.01) for birth weight, ADG, RGR and 200-day weight. The effects of sex of calf were important (P<.01) on all traits studied except perinatal mortality and calf crop weaned. When the data wereanalyzed with birth weight as a covariate on calving difficulty (with abnormal presentations included as difficult births), perinatal mortality and calf crop weaned; breed of sire, breed of dam and sex of calf effects were still significant for these traits. This result reflects the importance of factors, associated with breed of sire, breed of dam and sex of calf, other than birth weight on these traits.

Postweaning growth, puberty and pregnancy data were analyzed on 267 heifers produced by breeding yearling heifers of 12 crossbred groups (Hereford-Angus reciprocal crosses plus crosses produced by breeding Jersey, South Devon, Simmental, Limousin and Charolais sires to Hereford and Angus cows) to Hereford, Angus, Brahman, Devon and Holstein bulls. Effects of sire breed of heifer were significant for all growth traits and for age and weight at puberty. Holstein-sired heifers had the highest (P<.05) feedlot average daily gain (ADG). Brahman-sired heifers, due to their large weaning weights, had the lowest (P<.05) feedlot relative growth rate (RGR). Other differences in feedlot ADG and RGR were relatively small. Brahman- and Holstein-sired heifers had higher pasture ADG (P<.05) and were heavier (P<.05) at 400 and 550 days of age than Hereford-Angus or Devon-sired heifers. Brahman-sired heifers were older and heavier (P<.05) at puberty than heifers from any other sire breed. Effects of sire breed of the heifers' dam (breed of maternal grandsire) were significant for weights at 200, 400 and 550 days, puberty age, puberty weight and percentage pregnant. Heifers from Jersey cross cows had lower (P<.05) feedlot ADG and RGR than heifers from any other crossbred cow group. Heifers from Hereford-Angus cross cows had the lowest (P<.05) pasture ADG and heifers from Charolais cross cows had the highest (P<.05). Heifers from Simmental and Charolais cross cows were heavier than heifers from any other crossbred group at 400 and 550 days of age, although all differences were not significant. Heifers from Hereford-Angus, Limousin and Charolais cross cows were older (P<.05) at puberty than heifers from Jersey, South Devon and Simmental cross cows. Charolais crosses had the highest average puberty weight. Jersey crosses had the lowest. Even though 99% of the heifers from Limousin cross cows reached puberty before the end of the breeding season , only 69% were classified as pregnant which was the lowest (P<.05) percentage pregnant among the cross bred cow groups.