Size and management effects on reproduction in first-, second- and third-parity beef cows

The effects of size, management and size x management interactions on reproduction in beef cattle were determined by using 3,126 breeding and calving records from 1980 to 1985. Cows were from three synthetic lines that differed in mature size (small, medium and large). The lines differed also in the percentages of Jersey, Angus and Simmental. Each line was replicated in two herds. One herd (Rhodes) followed a spring calving schedule and weaned calves at about 180 d of age. The other herd (McNay) calved cows in the fall and weaned calves early at about 45 d of age. Cycling rate, conception rate, abortion rate and calving rate were each evaluated for first-, second- and third-parity dams. An important interaction (P less than .05) was found between lines and management in heifers. Cycling rate and calving percentage were almost identical for all three lines in the Rhodes herd, but small heifers in the McNay herd had about 20% higher cycling (83.8 vs 63.1%) and calving rates (73.8 vs 53.0%) than large heifers. Line x management interactions were not significant in second- and third-parity dams, but line did remain a significant source of variation in calving rate. Calving rates in second-parity dams were 85.0, 78.1 and 70.7% for small, medium and large cows, respectively. In third-parity dams, small cows had a higher calving rate (P less than .05) than either medium or large cows (80.9 vs 66.1 or 68.7%, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Influence of body condition score on by-product yield and value from cull beef cows.

Mature beef cows (n = 122) representing British and Continental phenotypes were slaughtered to measure the influence of body condition score (BCS) on by-product yield and value. All cows were weighed and assigned BCS, based on a 9-point scale, 24 h before slaughter. By-product weights were obtained during the slaughter process and included blood, feet (with hooves attached), oxlips, tongue, gullet, trachea, cheek meat, head meat, skull, tripe, honeycomb tripe, large and small intestines, spleen, mesenteric fat, weasand meat, kidneys, heart, lungs, and oxtail. By-product yields were calculated as a percentage of the animal's live weight taken 24 h before slaughter. By-product values were computed by multiplying the weight of each piece removed during the slaughter process by the 1997 average price. Live weight increased linearly (P<.001) as BCS increased from 2 to 8, whereas Continental cows were approximately 86 kg heavier (P<.05) at slaughter than British cows. Cows assigned a BCS of 2 or 3 had greater (P<.05) skull, feet, tongue, tripe, honeycomb tripe, trachea, and lung yields than cows assigned a BCS of 4 or higher. On the other hand, BCS-7 and 8 cows had greater (P<.05) weights and yields of large intestines and mesenteric fat than cows given a BCS of 6 or lower. The feet, trachea, lungs, and bone meal from BCS-2 cows had the greatest (P<.05) value, whereas the value of the large intestine, oxtail, and mesenteric fat was highest (P<.05) for BCS-7 and 8 cows. Weight, yield, and value of the skull, head meat, and feet were greater (P<.05) for Continental cows than British cows. Total by-product value was quadratically (P<.001) related to BCS. Cows assigned a BCS of 5 had lower (P<.05) total by-product values than either BCS-2 or BCS-7 and 8 cows. Drop credit for BCS-2 cows was greater (P<.05) than BCS-3, 4, 5, and 6 cows, with cows assigned a BCS of 7 and 8 having intermediate drop credit values. Continental cows tended to have greater (P<.10) total by-product and drop credit values than British cows. Information from this study indicated that the BCS of cows at the time of slaughter had a profound influence on by-product yields and, more importantly, values of by-products that are credited back against the cost of production to the beef cattle producer.     

Plasma hormones and metabolites in Piedmontese cows during late pregnancy: relationships with calf birth weight

Relationships among plasma hormonal and metabolic variables in the last trimester of gestation in 59 Piedmontese dams (n = 15 heifers, n = 44 cows) and the calf birth weight (BWT) class of their offspring were investigated in seven herds. The BWT data were categorized as follows: > 50 kg (BWT-A), 46 to 50 kg (BWT-B), 41 to 45 kg (BWT-C), and < 41 kg (BWT-D). Blood samples were collected at 33, 36, and 39 wk of gestation. Packed cell volume (PCV) and plasma concentrations of insulin, estrone sulfate (E1SO4), NEFA, and creatinine were determined and correlated to BWT class. Creatinine: E1SO4 ratio also was calculated. Duration of gestation was greater for dams producing a BWT-A calf than for the other BWT classes, and calf BWT was heavier (P < 0.001) for calves in the BWT-A vs. BWT-D class. The heaviest calf in BWT-A was associated with the highest calving difficulty score. Insulin and PCV values were not affected by week of gestation, whereas plasma E1SO4, NEFA, and creatinine content increased (P < 0.001) and creatinine:E1SO4 decreased (P < 0.001) during late gestation. Calf BWT class did not affect PCV value. Plasma E1SO4 concentrations were lower (P < 0.01) in BWT-D dams than the other dams, showing the greatest difference at 39 wk of gestation. At 36 and 39 wk of gestation, dams bearing BWT-C and BWT-D calves had a higher (P < 0.01) plasma insulin concentration than those bearing BWT-A and BWT-B calves. Plasma NEFA concentrations at 39 wk of gestation were higher (P < 0.05) in dams of calf BWT-A than in the other dams. We conclude that plasma E1SO4 level is a variable that can be used to monitor problems related to a small size calf. Conversely, the forthcoming birth of a calf with a heavy BW seems to be preceded by a pronounced increase in plasma NEFA level in the dam just a few days before calving.     

Effects of growth curve parameters on cow efficiency.

Weight-age data from 50 Retinta beef cows from 8 to 97 mo of age located in southwestern Spain were fitted to von Bertalanffy, Brody, and Richards functions to determine the relationship between growth curve parameters and cow efficiency. Only cows having at least 31 weights were included in the analysis. Von Bertalanffy, Brody, and Richards functions were fitted to weights of each cow. Relevant parameters of the three functions are A and K, associated with the asymptotic mature weight and rate of maturing, respectively. Criteria for comparisons among the three functions were computing difficulty, goodness of fit, and lack of bias of A. Productivity indicators were number of calves weaned during the first five calving seasons (NC), average birth weight (BWT), average weaning weight (WW), and average weaning weight per cow per year (WWY). The von Bertalanffy function was selected as the most appropriate. Least squares means for A and K were 650 +/- 8.17 kg and .038 +/- .001 mo-1, respectively. The values of NC, BWT, WW, and WWY were 4.0 +/- .11 calves, 38.2 +/- .4 kg, 218 +/- 5 kg, and 172 +/- 5 kg, respectively. Regression analysis for A indicated a decrease in NC when mature weight increased (P less than .05). There was a nonsignificant trend for heavier cows (higher A) to have calves with heavier BWT or WW. The value of WWY increased (P less than .05) with increased maturing rate (K) of cows. No significant associations were found between K and BWT or WW.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of induced hypothyroidism on ovarian response to superovulation in Brahman (Bos indicus) cows.

To evaluate the effects of hypothyroidism on ovarian function, multiparous, nonlactating Brahman cows (n = 18) were assigned randomly to dietary treatments containing either 0 (C; n = 9) or 4 mg x kg BW(-1) x d(-1) 6-n-propyl-2-thiouracil (PTU; n = 9), to suppress thyroid function, in the feed concentrate. Weekly changes in BW and body condition score (BCS) were recorded. Dietary treatments began on d 10 of the estrous cycle. Ten days after the first treatment estrus, all cows received daily i.m. injections of 25 IU of porcine FSH over a 3-d period. Seven days after AI, embryos were collected nonsurgically, and the ovaries were removed via midflank laparotomy. Based on thyroxine (T4) concentrations after 49 d of treatment, five cows were hypothyroid (H-PTU) and four were partially suppressed (P-PTU). Cows in the PTU group had greater (P<.01) ADG, (P<.05) ovarian weights, and numbers of large (> or =8 mm) (P<.05) follicles. Cows in the PTU group had lower embryo recovery rate (P<.001), fertilization rate (P<.001), and percentage of blastocysts (P<.1) than C cows. The H-PTU cows had greater numbers of luteinized follicles (P<.06), greater concentrations of progesterone (P4) in the follicular fluid at all size categories (P<.1), and greater numbers of corpora lutea (P<.05) than C cows. The ratio of luteal to serum P4 on d 7 was greater (P<.05) in hypothyroid cows. Induced hypothyroidism improved weight gain and BCS, increased ovarian response to FSH, and affected ovulation, fertility, and P4 secretion in superovulated Brahman cows.     

Across-breed expected progeny differences: use of within-breed expected progeny differences to adjust breed evaluations for sire sampling and genetic trend.

Data on 2,034 F1 calves sired by Angus, Hereford, Polled Hereford, Charolais, Limousin, Simmental, Gelbvieh, and Tarentaise bulls with Hereford or Angus dams and data on 3,686 three-breed-cross calves with 700 F1 dams of the same breed crosses were used for this study. Traits analyzed were birth, weaning, yearling, and 420-d weights (BWT, WW, YW, and W420, respectively) of F1 calves and WW of three-breed-cross calves. Expected progeny differences from national cattle evaluation programs for sires of F1 calves and cows for BWT, WW, YW, and net maternal ability (milk) were used to assess their value in prediction of crossbred performance. Regressions of actual F1 calf performance on sire EPD were positive for BWT (1.09 +/- .12 kg/kg of BWT EPD), WW (.79 +/- .14 kg/kg of WW EPD), YW (1.44 +/- .16 kg/kg of YW EPD), and W420 (1.66 kg/kg of YW EPD). These regression coefficients were similar to the expected value of 1.0 for BWT and WW but were larger than expected for YW and W420. Regressions of actual three-breed-cross calf WW on milk and WW EPD of their maternal grandsires were .95 +/- .14 and .42 +/- .10 kg/kg, respectively, and differed little from their expectations of 1.0 and .5, respectively. Observed breed of sire means for each trait were adjusted for sire sampling by using EPD regressions to adjust them to the average EPD of all sires of each breed born in 1970.(ABSTRACT TRUNCATED AT 250 WORDS)     

Performance of beef cows receiving cull beans, sunflower meal, and canola meal as protein supplements while grazing native winter range in Eastern Colorado

A 2-yr grazing performance study was conducted in Eastern Colorado to evaluate the effects of feeding raw cull beans (Phaseolus vulgaris) or canola meal, compared to sunflower meal, to beef cows grazing dormant, native winter range on body weight and body condition score (BCS) change, reproductive performance, and calf performance. Ninety-five pregnant, spring-calving crossbred cows (541 +/- 51 kg) in 1995 to 1996 and 65 cows (602 +/- 60 kg) in 1996 to 1997 were randomly assigned to one of five treatments (19 and 13 cows per treatment in 1995 to 1996 and 1996 to 1997, respectively): 1) unprocessed Great Northern beans to supply 182 g/d of CP (GNB); 2) canola meal to supply 182 g/d of CP (CM); 3) a mixture of Great Northern beans and sunflower meal, each to supply 91 g/d of CP, for a total of 182 g/d of CP (MIX); 4) sunflower meal to supply 182 g/d of CP (SFM+); and 5) sunflower meal to supply 91 g/d of CP (SFM-). Cow weight and body condition performance were broken into a gestation and a lactation phase in 1995 to 1996; calves were weighed at birth, at the end of the lactation phase in April, and at weaning the following September. Only gestation performance was monitored in 1996 to 1997, and subsequent calf birth and weaning weight were recorded. The SFM- group lost more weight during the gestation phase than other treatments (P < .05), yet no differences were detected for gestation phase daily BCS change, calf birth weight, lactation phase daily weight change, lactation phase daily BCS change, first-service conception rate to AI, or overall pregnancy rate. Off-test calf weight was higher in April for calves from dams of the SFM+ and CM treatments than for calves from dams on the GNB or SFM- treatments (P < .05), and calves from cows on the CM treatment were heavier in April than calves from cows on the MIX treatment (P < .05). No differences in calf weight were present at weaning. Consumption of beans by cows on the GNB treatment was low because of palatability problems. Mixing the beans with sunflower meal in the MIX treatment eliminated this problem. Canola meal, Great Northern beans, or a combination of sunflower meal and Great Northern beans were comparable to sunflower meal as protein supplements for beef cows grazing native winter range, despite obvious palatability problems with the beans.     

Effects of age on body condition and production parameters of multiparous beef cows

Pregnancy rate, calving interval, birth weight, weaning weight, and quarterly BCS were collected for 5 consecutive years on 454 fall-calving multiparous British crossbred cattle (3 to 10 yr of age) to evaluate associations of age with BCS and production parameters. Body weight and BCS were collected pre-calving, prebreeding, at weaning, and midway through the second trimester of pregnancy (August). Body condition score was correlated with age during all seasons (P < 0.01). At calving, breeding, and in August, 3-yr-old cows had the lowest BW and BCS, whereas 8-yr-old cows had the greatest. At weaning, these values were maximal in 10-yr-old cows. Pregnancy rate was near 80% up to 9 yr of age but decreased to 57% in 10-yr-old cows. The relationship of pregnancy rate with age appears to be correlated with the BCS decrease at breeding in the older cows, supported by the fact that inclusion of BCS at breeding in the statistical model eliminated the effect of age on pregnancy rate (P = 0.42). Calving interval was longer in 3-yr-old cows compared with 4- to 9-yr-old cows (P = 0.02); however, among older cows, there was little change in the calving interval. Birth weight reached a maximum at 8 yr of age (35 +/- 0.9 kg) and a minimum in 3-yr-old cows (32 +/- 0.7 kg). Birth weights of calves born to both 3- and 4-yr-old cows were lower than for those born to 5-, 6-, 7-, or 8-yr-old cows (P < 0.05). Ten-year-old cows weaned lighter calves (205-d adjusted weaning weight) than younger dams. Furthermore, 3-yr-old cows weaned calves 9 +/- 2.1 and 14 +/- 2.4 kg lighter than 4- and 5-yr-old cows, respectively (P < 0.001). Interpretation of the age analyses of calving interval, birth weight, and weaning weight was independent of the inclusion of BCS in the model. This study documents the effects of age on calving interval, birth weight, and weaning weight that are independent of BCS.     

Influence of body condition score on live and carcass value of cull beef cows.

Mature beef cows (n = 88) were slaughtered to determine the influence of body condition score (BCS) on carcass and live animal value. Cows were weighed and assigned a BCS (9-point scale), 24 h before slaughter. Hide and by-products weights were recorded during harvest. After a 48-h chill period, the right side of each carcass was fabricated into boneless subprimal cuts, minor cuts, lean trim, fat, and bone. Weights were recorded at all stages of fabrication. Carcass values (U.S.$/100 kg of hot carcass weight) were calculated for U.S. Utility and U.S. Cutter grades, as well as for the Utility/Cutter mix for each BCS. Gross value included the carcass value and the value of the hide and byproducts, whereas net value was calculated after harvest and fabrication costs and by-product value were considered. Live value (U.S.$/100 kg of live weight) was computed by dividing the net value by the animal's live weight 24 h before harvest. The value of the hide and by-products for BCS-2 cows was greater (P<.05) than for cows assigned a BCS of 3 through 8. Even though U.S. Utility carcasses from BCS-8 cows produced the least (P<.05) valuable subprimal cuts from the chuck, loin, and round, the gross and net values of BCS-8 cows were greater (P<.05) than those of BCS-3, 4, 5, and 6. Within the grade of U.S. Cutter, carcasses from BCS-6 cows had the highest (P<.05), and BCS-2 cows had the lowest (P<.05), gross and net values. Across the U.S. Utility/Cutter mix, cows designated with a BCS of 7 and 8 had greater (P<.05) gross and net values than cows assigned a BCS of 6, or lower. Live value increased linearly (P = .0002) from a low of $76.10/100 kg for BCS-2 cows to a high of $90.84/100 kg for BCS-7 cows. Carcasses from BCS-6 cows were relatively lean (8.4 mm of fat opposite of the longissimus muscle), and approximately 73% of the carcasses achieved a quality grade of U.S. Utility. Moreover, carcasses from BCS-6 cows had the highest total carcass values and live values comparable (P>.05) to BCS-7 cows. Information from this study can be used by the non-fed beef industry to establish a value-based marketing system. Data from this study would indicate that marketing cull beef cows at a BCS of 6 could optimize economic returns to both cow-calf producers and non-fed beef packers.     

Production characters of first generation cows of a five-breed diallel: reproduction of mature cows and preweaning performance of calves by two third-breed sires

The fourth through sixth parity of 5- to 10-yr-old cows were used to evaluate trade-offs involved with sires of large mature size vs medium mature size in a terminal sire crossbreeding program and to characterize five breeds and their crosses for their potential as dam lines. Charolais and Red Poll bulls, representing large (L) and medium (M) mature size, respectively, were mated to cows representing Angus (An), Brahman (Br), Hereford (He), Holstein (Ho) and Jersey (Je) and their crosses (reciprocals pooled). Cows were randomly assigned for mating to either an L or M bull for each breeding. Size of calf sire did not influence (P greater than .10) the subsequent calving interval of cows. Calving intervals for the straightbred (SB) dairy breeds (Ho and Je) were longer than for SB An and He, but the difference did not exist among the respective crossbred (CB) cows. As a group, Br crosses had shorter intervals than the other CB groups. Crossbred cows exhibited intervals that were 16 d shorter (P less than .05) than SB. Calves sired by L bulls were larger (P less than .01) and faster gaining (P less than .01) for all measures of size and growth studied, but exhibited lower (P less than .01) survival rates to weaning than M-sired calves. Calves of CB dams were 1.5 kg heavier (P less than .01) at birth than calves of SB dams and slightly greater (nonsignificant) hip and shoulder measurements were observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Life-cycle evaluation of Bos taurus and Bos indicus X Bos taurus breed types in a dry, temperate climate: performance of mature dams

Mature dams representing Hereford, Red Poll, F1 Hereford x Red Poll, F1 Red Poll x Hereford, F1 Angus x Hereford, F1 Angus x Charolais, F1 Brahman x Hereford and F1 Brahman x Angus breed types were evaluated. All cows were bred to Limousin sires to produce two-way or three-way-cross progeny. Mature Brahman x Hereford dams produced a higher (P less than .05) percentage of live calves than Herefords, but dam breed differences in percentage of calves weaned relative to the number of cows exposed for mating were not statistically significant. Progeny of Angus x Charolais and Red Poll dams were outstanding in weaning weight, but Hereford and Brahman-cross calves were below average. Planned comparisons showed that Angus x Charolais calves were heavier (P less than .01) at weaning than Hereford (23.0 +/- 3.8 kg) or Angus x Hereford (9.6 +/- 3.2 kg) progeny. Mature Angus x Hereford mothers weaned heavier calves than did Brahman x Herefords (7.4 +/- 3.2 kg, P less than .05) or Brahman x Angus (10.9 +/- 3.0 kg, P less than .01). Analysis of the Hereford-Red Poll diallel showed evidence of maternal heterosis in calf weaning weight (4.0 +/- 2.6 kg, P less than .05), but there was no difference in the percentage of calves weaned by crossbred vs straightbred dams.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maternal birth weight breeding value as an additional factor to predict calf birth weight in beef cattle

A total of 1,028 birth weight (BWT) and gestation length (GL) records were collected for calves from 1994 to 1997 in five U.S. Angus herds. Parental BWT EPD and dam BWT maternal breeding values (MBV) computed from the entire U.S. Angus data base after each breeding season were also available. A full model was fit to BWT that contained contemporary group (CG), sire BWT EPD, dam BWT EPD, and dam BWT MBV. A reduced model that dropped dam BWT MBV was also fit. The full model had smaller (P < .01) sum of squares for error than the reduced model. Calf BWT records were then adjusted for CG. Two data sets were formed to include adjusted BWT progeny records from sires with BWT EPD > or = .75 or > or = 1.0 SD above the mean of sires in the data set. Adjusted birth weights were assigned to either > or = .75 or other < .75 SD and > or = 1.0 or < 1.0 SD categories based on the mean BWT of calves in the entire data set. Dams were assigned to either > or =2 .75 or < .75 SD and > or = 1.0 or < 1.0 SD categories based on dam BWT EPD, MBV, or total maternal genetic contribution (TMGC = EPD + MBV). Chi-square analyses showed that dam BWT EPD, MBV, or TMGC categories were not independent (P < .10) of BWT SD categories, indicating that both dam BWT EPD and BWT MBV provide useful information to attenuate calf BWT. Calf BWT records were then adjusted for the overall mean, CG, sire and dam BWT EPD, and dam BWT MBV. Dams were then assigned to five categories: high dam EPD and MBV (HH), high dam EPD and low MBV (HL), low dam EPD and high MBV (LH), low dam EPD and MBV (LL), and other (OTH). High was > or = .75 or > or = 1.0 SD and low was < .75 or < 1.0 SD based on the mean BWT EPD or MBV of dams in the data set. In all adjusted BWT analyses, HH, HL, and LH categories did not differ (P > .05) from each other; however, the LL category was less (P < .05) than all other categories, indicating that calves from LL dams were lighter at birth than expected. For GL, LL was significantly different (P < .05) from only HH. The large differences in birth weight for the LL dams compared to other groups did not seem to be primarily due to shorter GL. Results showed that MBV provided additional information to control BWT; however, when both dam MBV and EPD were low, birth weight of calves was less than expected. Future research should focus on explanations for this interaction.     

Influence of body condition score on carcass characteristics and subprimal yield from cull beef cows.

Mature beef cows (n = 83) were slaughtered to measure the influence of body condition score (BCS) on carcass characteristics and subprimal yields. All cows were weighed and assigned BCS, based on a 9-point scale, 24 h before slaughter. Cows were slaughtered, and, after a 48-h chilling period, quality and yield grade data were collected on the left side of each carcass. The right side was quartered, fabricated into primal cuts, and weighed. Each primal cut was further processed into boneless subprimal cuts, minor cuts, lean trim, fat, and bone. Cuts were progressively trimmed to 6.4 and 0 mm of external and visible seam fat. Weights were recorded at all stages of fabrication, and subprimal yields were calculated as a percentage of the chilled carcass weight. Live weight, carcass weight, dressing percentage, fat thickness, longissimus muscle area, muscle:bone ratio, and numerical yield grade increased linearly (P = .0001) and predicted cutability and actual muscle-to-fat ratio decreased linearly (P = .0001) as BCS increased from 2 to 8. Carcasses from BCS-8 cows had the most (P<.05) marbling. The percentage of carcasses grading U.S. Utility, or higher, was 16.7, 20.0, 63.6, 43.3, 73.3, 100.0, and 100.0% for cows assigned a BCS of 2, 3, 4, 5, 6, 7, and 8, respectively. At 6.4 mm of fat trim, carcasses from BCS-5 cows had higher (P<.05) shoulder clod yields than carcasses from cows having a BCS of 6, 7, and 8. Carcasses of BCS-2 cows had lower (P<.05) strip loin yields than carcasses from BCS-3, 4, 5, 6, and 7 cows. Top sirloin butt yields were higher (P<.05) for carcasses of BCS-2, 3, 4, and 5 cows than those of BCS-6, 7, or 8 cows. Carcasses from BCS-7 and 8 cows had lower (P<.05) tenderloin and inside round yields than carcasses of BCS-5, or less, cows. At both fat-trim levels, carcasses from BCS-5 cows had higher (P<.05) eye of round yields than cows assigned BCS of 2, 7, or 8. When subprimal cuts were trimmed to 6.4 mm of visible fat, carcasses from BCS-5 cows had higher (P<.05) total lean product yields than cows assigned a BCS of 2, 4, 7, and 8. Regardless of fat trim, total fat yields increased (P = .0001) and total bone yields decreased (P = .0001) linearly as BCS increased from 2 to 8. Although carcasses from BCS-5 and 6 cows had the highest yields of lean product, cattle producers and packers may benefit most by marketing and(or) purchasing BCS-6 cows because a higher percentage of their carcasses had quality characteristics deemed desirable for fabrication into boneless subprimal cuts.     

Postpartum supplemental fat, but not maternal body condition score at parturition, affects plasma and adipose tissue fatty acid profiles of suckling beef calves

Three-year-old Angus x Gelbvieh beef cows, which were nutritionally managed to achieve a BCS of 4 +/- 0.07 (479 +/- 36 kg of BW) or 6 +/- 0.07 (580 +/- 53 kg of BW) at parturition, were used in a 2-yr experiment (n = 36/yr) to determine the effects of maternal BCS at parturition and postpartum lipid supplementation on fatty acid profile of suckling calf plasma and adipose tissue. Beginning 3 d postpartum, cows within each BCS were assigned randomly to 1 of 3 treatments in which cows were all fed hay and either a low-fat (control) supplement or supplements with either high-linoleate cracked safflower seeds (linoleate) or high-oleate cracked safflower seeds (oleate) until d 61 of lactation. Diets were formulated to be isonitrogenous and isocaloric, and safflower seed supplements were provided to achieve 5% of DMI as fat. Total concentration of fatty acids in plasma did not differ (P = 0.48) due to maternal BCS at parturition. Percentage of 20:5n-3 in plasma tended (P = 0.06) to be greater for calves suckling cows with a BCS of 6 at parturition. No other differences (P = 0.12 to 0.99) were noted in calf plasma fatty acid profile due to maternal BCS at parturition. Likewise, no differences were detected for total fatty acid concentration (P = 0.88) in calf adipose tissue due to maternal BCS at parturition. Weight percentage of 14:1 (P = 0.001) was greatest in adipose tissue of calves suckling cows fed control and oleate; however, the percentages of 14:0, 15:0, 16:0, 16:1, 17:0, and 18:3n-3 were greater (P < 0.001) in adipose tissue from calves suckling cows fed control compared with calves suckling cows fed linoleate or oleate. Percentages of 18:0, 18:1trans-11, 18:2n-6, and cis-9, trans-11 CLA were greater (P < 0.001) in adipose tissue from calves suckling cows fed linoleate compared with calves suckling cows fed control and oleate. Calves suckling cows fed oleate had greater (P < 0.001) percentages of 18:1trans-9, 18:1trans-10, and 18:1cis-9 in adipose tissue than calves suckling cows fed control or linoleate. Calf plasma and adipose tissue fatty acid profiles were reflective of milk fatty acids. Because fatty acids play an important role in metabolic regulatory functions, changes in milk fatty acid profile should be considered when beef cows are fed lipid supplements.     

Effects of intermittent injections of LHRH on specific binding of 125I-labeled gonadotropins to granulosa and theca, and concentrations of steroids in serum and ovarian follicles during postpartum anovulation in suckled beef cows

To examine ovarian follicular response to low-dose injections of luteinizing hormone-releasing hormone (LHRH), 32 anovulatory, suckled beef cows were allotted to one of four treatment groups and injected with either saline or 500 ng LHRH every 2 h for 48 or 96 h, starting 21.4 +/- .4 d after parturition. Two hours after the last injection of LHRH, cows were ovariectomized and 10 to 15 ovarian follicles per pair of ovaries were removed and categorized by diameter as small (1.0 to 3.9 mm), medium (4.0 to 7.9 mm) or large (greater than or equal to 8.0 mm). Injections of LHRH did not affect (P greater than .10) steroid levels in small follicles or numbers of gonadotropin receptors in small and medium follicles. Concentrations of progesterone in fluid of medium follicles increased 1.5-fold (P less than .05) after 96 h of LHRH, whereas concentrations of estradiol and androstenedione were unchanged. In fluid of large follicles, concentrations of progesterone were fourfold greater (P less than .05) in LHRH-treated than in control cows at 48 h, but by 96 h progesterone was twofold greater (P less than .05) in control than LHRH-treated cows. In large follicles, concentrations of estradiol were unchanged (P greater than .10) after 48 h of LHRH injections but after 96 h estradiol was twofold greater (P less than .05) in LHRH-treated than control cows. Increased concentrations of estradiol in large follicles coincided with increased numbers of binding sites for human chorionic gonadotropin (hCG) but not follicle stimulating hormone (FSH) in granulosa and theca.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of an early and normal weaning management system on cow and calf performance while grazing endophyte-infected tall fescue pastures

A 3-yr study used 16 cows and their spring-born calves (yr 1) and 48 first-calf heifers (yr 2, n = 24; yr 3, n = 24) and their spring-born calves in a completely randomized design. All cows and heifers were Angus x Beefmaster, and calves were sired by Angus bulls. Cow-calf pairs were assigned randomly to one of two management systems: 1) an early-weaning system, in which steer and heifer calves were weaned at 108 d of age and fed a postweaning growing diet (EW), or 2) a normal weaning system, in which calves were weaned at 205 d without supplementation (NW). Before early weaning and within each management system, calves and their dams were maintained in two 1.4-ha, endophyte-infected tall fescue pastures for 35 d (yr 1) or 14 d (yr 2 and 3). Early-weaned calves and cow-calf pairs were then randomly allotted to 1.4-ha, endophyte-infected tall fescue pastures with two (yr 1) or three (yr 2 and 3) calves or cow-calf pairs per pasture (four pastures per management system). Cow weights and BCS changes and calf gains were measured from early to normal weaning. Dietary intakes and nutrient digestibilities by EW and NW calves were determined during two periods of yr 1 and three periods of yr 2 and 3. Total gains and BCS changes were greater (P < 0.01) for cows that produced EW calves in all years. Calf ADG from early to normal weaning did not differ (P = 0.32). Similar to ADG, BW of calves at normal weaning were not different (P = 0.11). Forage intake was greater (P < 0.01) by NW calves during Periods 2 and 3 of yr 1 and Periods 1 and 2 of yr 2 and 3; however, total DM and CP intakes were greater (P < 0.01) for EW calves in Periods 2 and 3 of each year. Intakes of NDF tended (P = 0.11) to be greater by EW calves across all years. Estimates of CP and NDF digestibilities were higher (P < 0.01) for EW calves during yr 1 and 2; however, all components of the diet consumed by NW calves in yr 3 were more digestible (P < 0.05) than those consumed by EW calves. These results show the condition of cows with EW calves was improved by early weaning and gains by calves weaned at 108 d to pasture plus a commercial grower diet were comparable to those by calves continuing to nurse dams until weaned at 205 d.     

Relationship between serum insulin-like growth factor-I and genotype during the postpartum interval in beef cows

The objective of this study was to determine the effect of genotype and week postpartum on serum concentrations of IGF-I, body condition score (BCS), BW, and ovarian function in beef cows. Cows from the following genotypes were utilized in two consecutive years: Angus (A x A; n = 9), Brahman (B x B; n = 10), Charolais (C x C; n = 12), Angus x Brahman (A x B; n = 22), Brahman x Charolais (B x C; n = 19) and Angus x Charolais (A x C; n = 24). Serum concentrations of IGF-I, BCS, and BW were determined between wk 2 and 9 postpartum. Rectal ultrasound was used to determine days postpartum to first medium (6 to 9 mm) and first large (> or = 10 mm) follicle. Averaged across genotype, BCS decreased (P < 0.05) from 5.0 +/- 0.1 on wk 3 to 4.8 +/- 0.1 on wk 6 postpartum, and BW decreased (P < 0.05) between wk 2 and 3 and again between wk 4 and 9 postpartum. Averaged over year and week postpartum, serum IGF-I concentrations were greatest (P < 0.05) in B x B cows (46 +/- 5 ng/mL) compared with all other genotypes; lowest in A x A (12 +/- 4 ng/mL), C x C (13 +/- 4 ng/mL), and A x C cows (18 +/- 3 ng/mL); and intermediate (P < 0.05) in A x B (28 +/- 3 ng/mL) and B x C (26 +/- 3 ng/mL) cows compared with all other genotypes. Serum IGF-I concentrations did not change (P > 0.10) with week postpartum in C x C, A x A, and A x C cows, but increased (P < 0.05) between wk 2 and 7 postpartum in B x C, A x B, and B x B cows. Average interval to first medium (16 +/- 2 d) and first large (35 +/- 2 d) follicle did not differ (P > 0.10) among genotypes. Serum IGF-I concentrations correlated with BCS (r = 0.53 to 0.72, P < 0.001) but not with days to first large follicle (r = -0.19 to -0.22, P > 0.10). Averaged across genotypes, cows that lost BCS postpartum had lower (P < 0.01) serum IGF-I concentrations. Cows that calved with adequate BCS (i.e., > or = 5) had greater (P < 0.01) serum IGF-I concentrations postpartum than cows that calved with inadequate BCS (i.e., < 5) but days to first large and medium follicle did not differ (P > 0.10). In conclusion, concentrations of IGF-I in serum differed among genotypes and were associated with BCS but not days to first large or medium follicle in postpartum beef cows.     

Ovarian follicular recruitment,granulosa cell steroidogenic potential and growth hormone/insulin-like growth factor-I relationships in suckled beef cows consuming high lipid diets: Effects of graded differences in body condition maintained during the puerperium

The effects of graded differences in body condition score (BCS) on ovarian follicular development, granulosa cell steroidogenic potential, and growth hormone (GH)-insulin-like growth factor-I (IGF-I) relationships were examined during the puerperium in beef cows fed high fat diets. Cows (n = 36) were allocated randomly about 90 d before expected calving to dietary treatments that resulted in BCS of 3 (very thin), 4 (thin), 6 (optimal) and 8 (obese) at parturition. Body weight and BCS were maintained after parturition by adjusting individual intakes of forage throughout the 17-d experiment, and all cows were fed a high lipid supplement (soybean oil; 0.44 kg/500 kg body weight) during this period. Follicular development in BCS 3 and 4 lagged behind that of BCS 6 and 8 throughout most of the study; however, cows in BCS 4 developed numbers of medium and large follicles by day 15 postpartum that were comparable to those of cows in greater BCS. Mean concentrations of total cholesterol (TCH) and total triglycerides (TG) in serum were greater (P < .05) for cows in BCS 8 vs. 3, 4 and 6 through days 12 (TCH) and 16 (TG) postcalving, respectively. High-density lipoprotein cholesterol (HDL-CH), progesterone and estradiol-17β concentrations in follicular fluid were not affected by BCS at ovariectomy (day 17 postpartum). Addition of insulin and low-density lipoprotein (LDL) to culture media maximized (P < .05) production of progesterone by granulosa cells, but in vivo BCS treatments had no effect. Serum GH concentrations were elevated (P < .05) in cows in BCS 3 and 4 compared to those in BCS 6 and 8 throughout the puerperium. Serum IGF-I tended (P < .10) to increase during the first few days after parturition, and both serum and follicular fluid IGF-I increased (P < .02 and P < .001, respectively) with increasing BCS. Data indicate that cows calving in BCS < 4, and fed such that weight and BCS do not increase, are unlikely to respond to short-term dietary fat supplementation.     

Conjugated linoleic acid content in adipose tissue of calves suckling beef cows on pasture and supplemented with raw or extruded soybeans

The concentration of CLA in adipose tissue can be increased in ruminants by feeding pasture and extruded soybeans. The objective of this study was to evaluate maternal supplementation of raw (RS) or extruded (ES) soybeans on the concentrations of CLA in milk fat of cows and s.c. adipose tissue of suckling calves. Thirty-two spring-calving cows (BW 624 +/- 76 kg; BCS 3.5 +/- 0.4; mean +/- SD) and calves (BW 127 +/- 15 kg) were separated into 2 groups. Cows were distributed to have 8 calves of each sex in both groups. When animals were turned out to pasture, dams received 2 kg/d of either RS or ES. Dietary treatments had no effect on average milk intake (P = 0.22) and pasture forage intake (P = 0.13) for calves over the course of the grazing season. As a result, no effect of treatments was observed on ADG (P = 0.26). At weaning, milk fat content of CLA reached 15.4 and 24.2 mg/g of total fatty acids for cows fed RS and ES, respectively (P = 0.02). The CLA concentrations in adipose tissue were 16.9 and 25.0 mg/g of total fatty acids for calves suckling dams fed RS and ES, respectively (P < 0.001). Overall, results demonstrated supplementing grazing cows with ES increased CLA content in milk and adipose tissue of suckling calves.     

Winter grazing system and supplementation during late gestation influence performance of beef cows and steer progeny

A 2 x 2 factorial study evaluated effects of cow wintering system and last trimester CP supplementation on performance of beef cows and steer progeny over a 3-yr period. Pregnant composite cows (Red Angus x Simmental) grazed winter range (WR; n = 4/yr) or corn residue (CR; n = 4/yr) during winter and within grazing treatment received 0.45 kg/d (DM) 28% CP cubes (PS; n = 4/yr) or no supplement (NS; n = 4/yr). Offspring steer calves entered the feedlot 14 d postweaning and were slaughtered 222 d later. Precalving BW was greater (P = 0.02) for PS than NS cows grazing WR, whereas precalving BCS was greater (P < 0.001) for cows grazing CR compared with WR. Calf birth BW was greater (P = 0.02) for CR than WR and tended to be greater (P = 0.11) for PS than NS cows. Prebreeding BW and BCS were greater (P 0.32) by PS. Calf weaning BW was less (P = 0.01) for calves from NS cows grazing WR compared with all other treatments. Pregnancy rate was unaffected by treatment (P > 0.39). Steer ADG, 12th-rib fat, yield grade, and LM area (P > 0.10) were similar among all treatments. However, final BW and HCW (P = 0.02) were greater for steers from PS-WR than NS-WR cows. Compared with steers from NS cows, steers from PS cows had greater marbling scores (P = 0.004) and a greater (P = 0.04) proportion graded USDA Choice or greater. Protein supplementation of dams increased the value of calves at weaning (P = 0.03) and of steers at slaughter regardless of winter grazing treatment (P = 0.005). Calf birth and weaning BW were increased by grazing CR during the winter. Calf weaning BW was increased by PS of the dam if the dam grazed WR. Compared with steers from NS cows, steer progeny from PS cows had a greater quality grade with no (P = 0.26) effect on yield grade. These data support a late gestation dam nutrition effect on calf production via fetal programming.