Feeding dried distillers grains with solubles to lactating beef cows: impact of excess protein and fat on post-weaning progeny growth, glucose tolerance and carcass traits

Feeding dried distillers grains with solubles (DDGS), a feed high in fat and protein, to lactating beef cows can alter milk production and composition, resulting in improved pre-weaning growth of progeny. This alteration in milk profile may consequently alter the growth and carcass composition of the offspring after weaning. Therefore, Angus×Simmental steers (n=48) whose dams were fed one of two diets supplemented with either DDGS or soybean meal (CON) from calving to mid-lactation were placed in a feedlot to determine the effects of maternal nutrition during lactation on progeny development and carcass composition. Cow-calf pairs were allotted to two treatments at birth based on cow and calf BW, breed and age. Maternal diets were isocaloric (3.97 MJ/kg NEg) and consisted of rye hay supplemented with DDGS at 1% of BW (19.4% CP; 8.76% fat) or rye hay and corn silage supplemented with CON (11.7% CP; 2.06% fat). After conclusion of the treatments at 129 days postpartum, cow-calf pairs were comingled and managed as one group until weaning at 219 days postpartum. Steers were then transitioned to a common diet composed of 60% DDGS, 34% corn silage and 6% vitamin/mineral supplement and were placed indoors in individual pens with slatted floors. An intravenous glucose tolerance test (IVGTT) was performed 134 days after feedlot entry on 16 steers (CON, n=7; DDGS, n=9) to determine the effect of maternal diet on glucose and insulin sensitivity. Steers were slaughtered at a target BW of 645 kg. Categorical and continuous data were analyzed using the GLIMMIX and MIXED procedures of SAS, respectively. Steers from DDGS dams tended to be heavier on day 85 of feedlot finishing (P=0.09) compared with steers from CON dams. However, there were no differences in final weight, average daily gain, dry matter intake or efficiency (gain:feed, P⩾0.18). Maternal treatments did not affect progeny days on feed (P=0.15), despite a mean difference of 9 days in favor of DDGS. Glucose and insulin concentrations and area under the curve of progeny as measured by IVGTT were not affected by maternal diet (P⩾0.16). Maternal DDGS supplementation decreased marbling score (P=0.04), but did not influence carcass grading percentage or any other carcass characteristic (P⩾0.17).

Effect of dried distiller's grains plus solubles in postpartum diets of beef cows on reproductive performance of dam and heifer progeny

Forty-eight primiparous and multiparous cows were fed a silage-based total mixed ration (TMR; CON), a TMR with 2.5 kg/d DM dried distiller's grains plus solubles (DDGS; MID), or a TMR with 4.7 kg/d DM DDGS (HIGH) from 8.5 ± 4 to 116 ± 4 d postpartum (DPP). All diets were formulated to be isocaloric for a postpartum ADG targeted at 0.22 kg, whereas CP exceeded requirements in both diets containing DDGS. Blood samples were collected from dams at 7- and 21-d intervals for progesterone concentration (resumption of cyclicity) and plasma urea nitrogen, respectively. A weigh-suckle-weigh procedure was used to measure milk production, and samples were collected for milk composition and fatty acid profile. A 5-d Co-Synch + controlled internal drug release (CIDR) protocol was used, and cows were bred (97 ± 4 DPP) by timed AI (TAI). Ultrasonography was used for measurement of the largest antral follicle at TAI and pregnancy diagnosis. Nineteen days after TAI, cow and calf pairs were managed as a single group until weaning and exposed to natural mating for a total of a 60-d breeding season. Starting at weaning, blood samples were collected from heifer offspring at 7-d intervals for progesterone concentration used as an indicator of puberty. A 5-d Co-Synch + CIDR protocol was used, and heifers were bred by TAI. Transrectal ultrasonography was used for measurement of the largest antral follicle at TAI and antral follicle count (AFC) at CIDR device insertion as well as pregnancy diagnosis. There were no differences in dam ADG ( = 0.364); however, DMI decreased with increasing DDGS ( < 0.0001), resulting in an increased feed efficiency ( = 0.042). Milk fat and lactose tended to increase with the addition of DDGS in the diet ( ≤ 0.055), and milk urea nitrogen increased ( < 0.001). There were no differences in resumption of cyclicity ( = 1.00) or diameter of the largest antral follicle ( ≥ 0.372). Timed AI pregnancy rates were not different with the addition of DDGS in the diet ( ≥ 0.174). Heifer ADG was reduced with DDGS during late lactation ( = 0.031). Heifer AFC had a tendency to increase with increasing DDGS ( = 0.081), with no impacts on dominant follicle diameter at TAI ( = 0.161). Heifer TAI pregnancy rate also was not different among treatments ( = 0.508). Overall, feeding 4.7 kg/d DM of DDGS to dams during early lactation increases feed efficiency of the dam, with minor statistically significant effects on dam or heifer offspring reproduction.

Using corn gluten feed in post-partum diets of young beef cows to optimize reproductive performance

Forty-eight primiparous and diparous Angus-Simmental cows were fed 1 of 3 diets; 1) total mixed ration (TMR) based of corn silage and corn stalks (CON), 2) TMR with 3.3 kg/d DM of corn gluten feed (CGF; MID), or 3) TMR with 6.7 kg/d DM of CGF (HIGH). From 11 ± 5 days post-partum (DPP) to 105 ± 5 DPP, all diets were formulated to be isocaloric for a post-partum ADG targeted at 0.22 kg, but CP exceeded requirements in both CGF diets. Blood samples were collected from cows starting at trial initiation until estrous synchronization for determination of plasma progesterone concentration (7 d intervals), as an indicator of resumption of cyclicity, as well as for plasma urea nitrogen (PUN; 21 d intervals). Milk production was assessed at 62 ± 5 DPP via a weigh-suckle-weigh procedure, and milk samples were collected at 64 ± 5 DPP for composition analysis. A 5 d Co-Synch + Control Internal Drug Release (CIDR) protocol was used and cows were bred by timed artificial insemination (TAI). Trans-rectal ultrasonography was used for the evaluation of the dominant follicle at TAI, as well as pregnancy diagnosis. Nineteen days post-TAI, cow and calf pairs were managed as a single group until weaning (205 ± 5 DPP) and exposed to natural mating for a total of a 60 d breeding season. Dam ADG was not significantly different among treatments (P = 0.849), but, DMI decreased with increasing CGF in the diet (P = 0.049). There were no differences in final BW (P = 0.779), however, final BCS was lower in the HIGH treatment when compared to the MID (P = 0.042). Milk production (P = 0.457), as well as, milk components (P ≥ 0.188) were not different, with the exception of milk fat, which tended to be greater in the HIGH treatment (P = 0.059) when compared to the MID. A treatment by week interaction (P < 0.0001) was found for PUN concentrations. Concentrations were greater in the HIGH treatment compared to the MID treatment at 63, 84, and 105 d, and greater than the CON treatment at all time points except d-42. There were no differences in resumption of cyclicity (P = 0.419), dominant follicle (P = 0.648), or TAI conception rates (P = 0.761). However, season long pregnancy rates were significantly greater in the CGF treatments when compared to the CON (P = 0.009). In summary, feeding high or intermediate amounts of CGF neither has a positive nor negative effect on TAI conception rates of beef cows, however, it positively affected season long pregnancy.

Evaluation of forage soybean, with and without pearl millet, as an alternative for beef replacement heifers

Apparent ruminal digestibility of forage soybean-based silages, with and without pearl millet, was determined along with evaluation of silages on heifer performance and reproductive function. Fermenters were utilized in a Latin square design and randomly assigned to 1 of the following treatments: 1) control diet of alfalfa haylage (CON), 2) soybean silage (SB) or 3) soybean and pearl millet silage (SB×PM). All diets were formulated to meet or exceed nutrient requirements of replacement beef heifers targeted to gain 0.79 kg/d. These same diets were fed to 90 Angus-Simmental beef replacement heifers [body weight (BW) = 366 kg; body condition score (BCS) = 5.53; age = 377 ± 11 d] 65 d prior to timed artificial insemination (TAI). Heifers were randomly allotted by breed, BCS and BW to 1 of the 3 treatments, with 3 reps/treatment. Diets were terminated 21 d post-TAI and heifers were commingled and placed on a common diet. Pubertal status was determined by progesterone concentrations of 2 blood samples taken 10 d apart prior to both trial initiation as well as initiation of estrous synchronization. Ovulatory follicle diameter was determined at time of breeding by ultrasonography. Pregnancy diagnosis was accomplished 35 and 66 d post-TAI, respectively, to calculate TAI and end of season pregnancy rates. Neither SB nor SB×PM had an effect (P > 0.37) on apparent ruminal digestion of nutrients compared to the CON. Final BW (414 kg; P ≥ 0.10) and BCS (5.28; P ≥ 0.26) for the heifers were similar among treatments. Likewise, there were no differences in TAI (48%; P > 0.43) or overall breeding season (93%; P > 0.99) pregnancy rates. Ovulatory follicle diameters (11.7 mm) was not different (P > 0.19) among treatments. In summary, forage soybean-based silages, with and without pearl millet, was an acceptable alternative forage for developing replacement beef heifers.

Feeding dried distillers grains with solubles to lactating beef cows: impact of excess protein and fat on cow performance, milk production and pre-weaning progeny growth

Multiparous Angus×Simmental cows (n=54, 5.22±2.51 years) with male progeny were fed one of two diets supplemented with either dried distillers grains with solubles (DDGS) or soybean meal (CON), from calving until day 129 postpartum (PP) to determine effects of excess protein and fat on cow performance, milk composition and calf growth. Diets were formulated to be isocaloric and consisted of rye hay and DDGS (19.4% CP; 8.76% fat), or corn silage, rye hay and soybean meal (11.7% CP; 2.06% fat). Cow-calf pairs were allotted by cow and calf age, BW and breed. Cow BW and body condition score (BCS; P⩾0.13) were similar throughout the experiment. A weigh-suckle-weigh was performed on day 64 and day 110±10 PP to determine milk production. Milk was collected on day 68 and day 116±10 PP for analysis of milk components. Milk production was unaffected (P⩾0.75) by dietary treatments. Milk urea nitrogen was increased at both time points in DDGS compared with CON cows (P<0.01). Protein was decreased (P=0.01) and fat was increased (P=0.01) in milk from DDGS compared with CON cows on day 68 PP. Compared to CON, DDGS decreased medium chain FA (P<0.01) and increased long chain FA (P<0.01) at both time points. Saturated FA content of milk was decreased (P<0.01) at both time-points in DDGS compared with CON cows, which resulted in an increase (P<0.01) in monounsaturated and polyunsaturated FA, including cis-9, trans-11 conjugated linoleic acid. Daily gain of the DDGS calves was increased (P=0.01) compared with CON calves, resulting in heavier BW on day 129 (P=0.01). Heavier BW of DDGS calves was maintained through weaning (P=0.01). Timed-artificial insemination (TAI) rates were greater for cows fed DDGS compared with cows fed CON (P<0.02), but dietary treatment had no effect on overall pregnancy rates (P=0.64). In summary, feeding DDGS to lactating beef cows did not change cow BW or BCS, but did improve TAI rates and altered milk composition compared with CON. As a result, male progeny from cows fed DDGS during lactation had greater average daily gain and were heavier at day 129 and at weaning compared with male progeny from cows fed a control diet.

Feeding distiller’s grains as an energy source to gestating and lactating beef heifers: Impact on female progeny growth, puberty attainment, and reproductive processes

This study compared postweaning growth, puberty attainment, and reproductive processes of female progeny (n = 33) born to Angus-Simmental beef heifers treated with either a control diet or a diet in which dried distiller’s grains with solubles (DDGS) were fed as an energy source during late gestation and early lactation. From 192 d of gestation through 118 ± 4 d in lactation, dams were fed either a corn silage–based control diet (CON) orcorn residue with DDGS, where DDGS were supplemented as an energy source (DG). Diets were formulated to provide similar daily NEg between diets, but CP requirements were drastically exceeded in the DG treatment. Heifer progeny (n = 33) were weaned, commingled at 191 ± 4 d of age, and similarly managed for the remainder of the project. Heifer BW and blood samples for progesterone assessment to determine onset of puberty were collected weekly beginning at weaning. At 255 ± 4 d of age, a single follicular wave was mapped via ultrasonography in 10 prepubertal heifers per treatment. Prepubertal antral follicle count and ovarian size were determined at 253 ± 4 d of age. Hip height was recorded at 213,297, and 437 ± 4 d of age. Estrous synchronization and AI was initiated at 447 ± 4 d of age. Binary data were analyzed with the GLIMMIX procedures of SAS and all other data were analyzed with the MIXED procedures of SAS. Progeny from DG-treated dams tended to be heavier (P = 0.08) than progeny from CON-treated dams from weaning until breeding. In addition, DG progeny had a greater (P < 0.01) frame score than CON throughout the developmental period. Ovarian size, antral follicle count, and follicular growth parameters did not differ between treatments. Age at puberty did not differ between CON (303 ± 10 d) and DG (320 ± 10 d) progeny; however, BW at puberty was greater (P = 0.01) for DG (326 ± 7 kg) than CON (298 ± 8 kg) progeny. Pregnancy rates to AI were greater (P = 0.05) in DG progeny (70.6%) than CON (33.3%), but overall breeding season pregnancy rate did not differ (P = 0.97). Moreover, rate of dystocia in female progeny at first parturition and grand-offspring birth BW did not differ due to treatment (P ≥ 0.74). In summary, feeding DDGS as an energy source during late gestation and early lactation to first-parity heifers resulted in female progeny with greater skeletal growth that were heavier at onset of puberty and had increased AI pregnancy rates.

Effect of calcium oxide inclusion in beef feedlot diets containing 60% dried distillers grains with solubles on ruminal fermentation, diet digestibility, performance, and carcass characteristics

Two experiments were conducted to determine the effect of increasing dietary CaO on ruminal fermentation, diet digestibility, performance, and carcass characteristics of feedlot steers fed 60% dried distillers grains with solubles ( DDGS: ). In Exp. 1, 120 steers were allotted by weight (355 ± 7.9 kg) to 1 of 4 treatments containing 60% DDGS, 20% corn silage, 13.5 to 14.4% ground corn, 4% supplement, and 0 to 2.5% limestone on DM basis to determine the effects of CaO on performance and carcass characteristics. Treatments consisted of 0, 0.8, 1.6, or 2.4% CaO inclusion in the diet (DM basis), with CaO replacing limestone. Steers were slaughtered at a target BW of approximately 641 kg. In Exp. 2, 4 steers (initial BW = 288 ± 3 kg) were randomly allotted to the same diets in a 4 × 4 Latin square design (14-d periods) to determine the effects of CaO on ruminal pH, VFA, and nutrient digestibility. Statistical analyses were conducted using the MIXED procedure of SAS. Inclusion of CaO at 0.8, 1.6, and 2.4% increased ADG by 5.0, 3.9, and 0%, respectively, compared to 0% CaO (quadratic; P = 0.03). Intake was linearly decreased (P = 0.04) and G:F was linearly increased (P = 0.02) by CaO inclusion. Dressing percentage increased as CaO increased from 0 to 1.6% and then decreased for 2.4% CaO (quadratic; P < 0.01). In Exp. 2, steers fed 0% CaO had the greatest prefeeding ruminal pH, steers fed 0 and 0.8% CaO exhibited the most rapid postfeeding decline in ruminal pH, and steers fed 2.4% CaO exhibited a relatively stable ruminal pH throughout the 24-h period (treatment × time; P ≤ 0.01). Acetate, butyrate, and total VFA concentrations increased linearly (P ≤ 0.05) at 0, 3, 6, and 12 h postfeeding with increasing CaO. Propionate at 3 h postfeeding increased from 0 to 1.6% CaO and decreased from 1.6 to 2.4% CaO (quadratic; P = 0.10). Urine pH increased linearly (P ≤ 0.01) while urine output and urine ammonia decreased linearly (P ≤ 0.05) as CaO inclusion increased. Apparent NDF digestibility tended to increase (P = 0.07) and ADF digestibility did (P = 0.01) increase linearly with increasing concentrations of CaO. In conclusion, CaO improved ruminal pH variation, increased fiber digestibility, and decreased metabolic acid load in cattle fed 60% DDGS-based diets. Inclusion of CaO up to 1.6% was effective in improving performance of feedlot cattle.

Effect of decreasing dietary cation anion difference on feedlot performance, carcass characteristics, and beef tenderness

The manipulation of acid-base balance has been extensively investigated as a means of manipulating Ca homeostasis and managing milk fever in dairy cows. A low dietary cation anion difference (DCAD) increases urinary Ca, blood-ionized Ca, and responsiveness to Ca-homeostatic hormones. Very little attention has been focused on the possibility of using a low dietary DCAD to increase muscle Ca availability, calpain activity, and meat tenderness of beef cattle. Thus, 90 Angus × Simmental crossbred steers were allotted by weight (590.1 ± 2.4 kg) and breed composition (% Simmental) to 3 treatments (6 pens/treatment, 5 steers/pen) to evaluate the effects of DCAD on beef tenderness. Treatments were initiated 2 wk before slaughter and consisted of 3 DCAD (mEq/100 g) treatments: -16, 0, and +16. Basal diets (DM basis) were 62 to 64% corn, 6 to 9% soybean meal, and 20% corn silage, and were formulated to contain similar concentrations of protein, energy (NEm; NEg), and minerals, with the exception of sodium and chlorine. A commercial chloride ion supplement (PASTURChlor, West Central, Ralston, IA) was added to diets to decrease DCAD and sodium bicarbonate was added to diets to increase DCAD. Performance before initiation of the study did not differ among treatments (P > 0.22). Urine pH did not differ at the initiation of the study (P > 0.57), but did increase at a decreasing rate on d 7 (6.37, 7.69, 8.13) and d 14 (5.68, 7.66, 8.03) of the study as DCAD increased from -16 to 0 to +16, respectively (quadratic, P < 0.02). Gain and gain:feed responded quadratically to DCAD (P < 0.01), increasing from -16 to 0 DCAD and decreasing from 0 to +16 DCAD. Hot carcass weight, dressing percent, fat thickness, LM area, yield grade, marbling score, quality grade distribution, 48 h muscle pH, and Ca content of muscle did not differ among treatments (P > 0.16). In addition, DCAD did not affect Warner-Bratzler shear force among treatments after 7 and 21 d of aging (P > 0.23). Although urine pH was decreased by feeding a -16 DCAD diet, Ca influx into the LM and beef tenderness were not affected by altering the DCAD in finishing beef cattle diets.

Effects of feeding corn modified wet distillers grain plus solubles co-ensiled with chopped whole plant corn on heifer growth performance and diet digestibility in beef cattle

Two experiments were conducted to evaluate the effect of feeding corn modified wet distillers grain plus solubles (MWDGS; 48% DM) co-ensiled with chopped whole plant corn (WC) on growth performance, dietary intake, and nutrient digestibility of beef cattle. In Exp. 1, 96 Angus-crossed heifers (2 yr old; 522 ± 49.1 kg BW; 5.3 ± 0.1 BCS) were stratified and blocked according to BW and stratified by BCS in each block in a randomized complete block design (24 pens; 4 heifers/pen; 6 treatment replications). Groups were assigned to 1 of 4 dietary treatments for a 62 d trial. Treatments were 1) corn silage (CS) and soybean meal (CON), 2) MWDGS co-ensiled with chopped whole plant corn (WC; CO-EN), 3) CS mixed with MWDGS at feeding (CS+WDG), and 4) CS mixed with dry distillers grain plus solubles (DDGS) at feeding (CS+DDG). In Exp. 2, 4 crossbred beef steers (initial BW = 278 ± 18 kg) fitted with permanent ruminal cannulas were used in a balanced 4 × 4 Latin square to test the effects of feeding MWDGS co-ensiled with WC on DM intake, ruminal fermentation characteristics, and total tract digestibility. There were four 14-d periods, with 10 d for diet adaptation and 4 d for samples collection. Orthogonal contrasts were used and compared CON vs. diets containing distillers grains (DGD), CO-EN vs. diets where distillers grains were mixed at feeding (MIX), and CS+WDG vs. CS+DDG. In Exp. 1, the CON fed heifers resulted in greater G:F (P = 0.04) compared with those fed DGD. However, ADG (P = 0.03), final BW (P = 0.04), and BW gain (P = 0.03) were greatest for DGD diets compared with CON and greatest (P = 0.04) for CO-EN when compared with MIX. Apart from a slightly greater acetate concentration (P = 0.05), which resulted in a greater acetate to propionate ratio (P = 0.03) for the CON diet compared with DGD, no important differences were observed on intake, diet digestibility, or fermentation characteristics when comparing the CON treatment with DGD or when comparing CS+WDG with CS+DDG. However, the CO-EN diet resulted in decreased DMI (P = 0.05) and consequently decreased OM (P = 0.05), N (P = 0.04), and NDF (P = 0.02) intakes compared with MIX. Data from these studies suggest that MWDGS co-ensiled with WC can successfully replace traditional corn-based diets supplemented with soybean meal and corn silage diets supplemented with distillers grains without compromising digestibility and growth performance in pregnant heifers.

Effects of maternal natural (RRR alpha-tocopherol acetate) or synthetic (all-rac alpha-tocopherol acetate) vitamin E supplementation on suckling calf performance, colostrum immunoglobulin G, and immune function

The objective of this study was to determine the effects of maternally supplemented natural- or synthetic-source vitamin E on suckling calf performance and immune response. In a 2-yr study, one hundred fifty-two 2- and 3-yr-old, spring-calving, Angus-cross beef cows were blocked by age, BW, and BCS into 1 of 3 isocaloric, corn-based dietary supplements containing 1) no additional vitamin E (CON), 2) 1,000 IU/d of synthetic-source vitamin E (SYN), or 3) 1,000 IU/d of natural-source vitamin E (NAT). Maternal supplementation began approximately 6 wk prepartum and continued until the breeding season. Colostrum from cows and blood from calves was collected 24 h postpartum for analysis of IgG concentration as an indicator of passive transfer and circulating alpha-tocopherol concentration. At 19 d of age, blood was collected from calves to determine the expression of CD14 and CD18 molecules on leukocytes. At 21 and 35 d of age, humoral immune response was measured by a subcutaneous injection, in the neck, with ovalbumin (20 mg; OVA) and blood samples collected weekly until d 63 of age to determine antibodies produced against OVA. At d 63 of age, calves were administered an intradermal injection of OVA (1 mg) in the neck to assess cell-mediated immunity, which was determined on d 65 of age by measuring nodule size with calipers. Circulating alpha-tocopherol concentrations were increased at both 24 h (P = 0.001) and at the day of initial OVA challenge (P < 0.001) in SYN and NAT compared with CON calves. No differences were detected (P > 0.05) for calf birth BW, ADG, or weaning BW. There were no differences (P > 0.05) in calf serum total IgG or cow colostrum total IgG at 24 h or presence of CD14 and CD18 receptors at d 19 of age. The NAT calves had a greater antigen response to OVA at d 63 than SYN calves (P = 0.01; treatment x day interaction). As an indicator of cell-mediated immunity to OVA, nodule size at 65 d of age was not affected (P = 0.92) by maternal dietary supplementation. In conclusion, calves suckling cows supplemented with natural- and synthetic-source vitamin E had increased circulating concentrations of alpha-tocopherol at 24 h, which appeared to continue throughout maternal supplementation; however, calf immune function and performance were not affected.

Effects of crude glycerin on performance and carcass characteristics of finishing wether lambs

The objective of this study was to evaluate the effects of crude glycerin on performance and carcass characteristics in finishing wether lambs. Thirty black-faced, Suffolk-cross wether lambs (44.1 +/- 5.6 kg initial BW) were stratified and blocked by BW to 1 of 5 individually fed, isocaloric, isonitrogenous dietary treatments containing 0, 5, 10, 15, or 20% crude glycerin (88% pure) on a DM basis. Diets were fed once daily for ad libitum consumption and contained 15% chopped hay, approximately 25% dried distillers grains with solubles, and the specified treatment combination of cracked corn replaced with increasing amounts of crude glycerin. Wethers were weighed on 14-d intervals and were selected for slaughter when they reached an approximate 12th-rib fat depth of 0.51 cm (28 to 84 d on trial). Carcass characteristics were collected after a 48-h chill. Dry matter intake (linear, P = 0.004) and ADG (quadratic, P = 0.05) increased with increasing concentrations of glycerin in the diet during the first 14 d of the feeding period. Similarly, G:F tended to increase quadratically (P = 0.06) with increasing concentrations of crude glycerin in the diet during the first 14 d. However, there were no differences among treatments for final BW, days on feed, or cumulative DMI, cumulative ADG, and cumulative G:F (P >or= 0.11). Body wall thickness, dressing percent, HCW, LM area, flank streaking, leg score, conformation score, quality grade, yield grade, and percent boneless, closely trimmed retail cuts did not differ (P >or= 0.21). Adding up to 15% crude glycerin to finishing wether diets improved feedlot performance, particularly during the first 14 d, without any concomitant effect on carcass characteristics.

Effects of dietary fat and crude protein on feedlot performance, carcass characteristics, and meat quality in finishing steers fed differing levels of dried distillers grains with solubles

The objective of this study was to evaluate the influence of dietary protein and fat from distillers dried grains with solubles (DDGS) on feedlot performance, carcass characteristics, and meat quality in finishing steers. Angus-cross steers (n = 105; 443 +/- 20 kg of BW) were blocked by BW and randomly assigned to 1 of 5 dietary treatments: 1) corn-based diet with DDGS included at 25% of DM (CON), 2) CON with DDGS included at twice the amount of CON (50% of DM; 50DDGS), 3) CON with added corn protein to equal the CP in the 50DDGS diet (CON+CP), 4) CON with added vegetable oil to equal the fat in the 50DDGS diet (CON+VO), and 5) CON with protein and fat added to equal the CP and fat in the 50DDGS diet (CON+CPVO). Steers were fed to a common 12th-rib fat depth endpoint (1.3 +/- 0.2 cm; 68 to 125 d on trial). Loins and rounds were collected from 44 carcasses for Warner-Bratzler shear force (WBSF), ether extract, and case-life analyses. Data were analyzed using the MIXED procedure of SAS. Contrasts between 1) CON vs. elevated CP diets (50DDGS, CON+CP, and CON+CPVO; EP), 2) CON vs. elevated fat diets (50DDGS, CON+VO, and CON+CPVO; EF) and 3) CON vs. diets with elevated CP and fat (50DDGS and CON+CPVO; EPF) were analyzed. There were no differences in days on feed or DMI among treatments. Steers fed CON had greater ADG (P <or= 0.03) than EP, EF, and EPF diets. Steers fed CON also had greater G:F (P <or= 0.04) than EP and EPF steers. Final BW was greater for CON than EP and EPF diets (P <or= 0.03). Likewise, CON steers had heavier HCW than EPF steers (P = 0.04). Dressing percent, 12th-rib fat depth, LM area, KPH, and yield grade were not affected by treatment (P >or= 0.06). Steers fed the CON diet had greater marbling scores (P <or= 0.03) and quality grades (P <or= 0.02) compared with those fed EP, EF, and EPF diets. There were no differences in WBSF, ether extract, or lipid oxidation due to treatment (P >or= 0.44). However, CON steers had greater (P = 0.02) L* values than EF-fed steers and greater b* values than EP, EF, and EPF steers (P <or= 0.02) during retail display of ground product. Data from this study illustrate that live animal performance, marbling and quality grade, and color stability of ground product during retail display are negatively affected when DDGS are increased from 25 to 50% of the diet DM. This response appears to be due to elevated dietary fat, elevated CP, and a combination of elevated fat and protein within in the diet.

Development of a progestin-based estrus synchronization program: II. Reproductive response of cows fed melengestrol acetate for 14 days with injections of progesterone and prostaglandin F2alpha

We tested the efficacy of an estrus control system designed to provide optimal control of follicular development. In Exp. 1, postpartum cows (n = 133) and yearling heifers (n = 57) were fed either .5 mg x female(-1) x d(-1) of melengestrol acetate (MGA) or the carrier for MGA from d -13 to d 0 (d 0 = last day of MGA feeding). All females received 25 mg of PGF2alpha (i.m.) on d -13 and 0. On d -6, cows and heifers fed MGA were administered an i.m. injection of progesterone (200 mg; MGA/P4), and those fed the corn carrier (2XPGF2alpha) received no progesterone. Beginning on d 1, females were bred by AI from d 1 to at least d 5. During the estrus synchronization period (d 1 to d 5), more (P < .05) postpartum cows were observed in estrus (70.1 vs 42.4%), the timing of estrus was more (P < .05) precise, conception rate was similar, and pregnancy rate was higher (P < .05) in the MGA/P4 than in the 2XPGF2alpha treatment. More (P < .05) cows that were anestrous at the beginning of the breeding season were in estrus during the synchronization period in the MGA/P4 (55.8%) than in the 2XPGF2alpha (28.6%) treatment. In heifers, estrus was synchronized in over 90% of females, and neither conception nor pregnancy rate during the synchronization period differed between treatments. In Exp. 2, postpartum cows (n = 122) and heifers (n = 84) received treatments (MGA/P4 or 2XPGF2alpha) as described for Exp. 1 with one exception. In the MGA/ P4 treatment, progesterone was administered on d -7 rather than d -6. Females were bred by AI from d 1 to 5. The estrus response and conception rate during the synchronization period did not differ between treatments for either cows or heifers. We conclude that the progestin-based estrous synchronization system used in this study effectively synchronized an estrus of normal fertility in cyclic cows and induced a majority of anestrous cows to reinitiate estrous cycles.

In-vivo analysis of serum-borne growth factors in developing co-twinned fetuses

Double-muscled fetuses develop more muscle fibers than normal-muscled fetuses. To examine whether serum growth factors modulate muscle development in cattle, twin pregnancies were induced in eight Holstein heifers using embryos from Belgian Blue and Holstein genetics representing heavy (HM) and light (LM) muscled cattle, respectively. Twin combinations were 1) two pairs of Belgian Blue fetuses that were designated as HM (HM), 2) two pairs of Holstein fetuses that were designated as LM (LM), and 3) four pairs of mixed fetuses; the four Holstein fetuses were designated as LM (HM) and the four Belgian Blue fetuses were designated as HM (LM). Pregnancies were terminated at 175 +/- 5 d after conception and fetuses, with evidence of vascular anastomosis, were dissected. Carcass weights were greatest (P < .05) for HM fetuses. Total bone and individual femur weights were greatest (P < .05) for LM (LM) fetuses. Total skeletal muscle mass and mass of semitendinosus, quadriceps femoris, infraspinatus, and longissimus muscles were in the order of HM (HM) > HM (LM) > LM (HM) = LM (LM) (P < .05). Estimated apparent muscle fiber number determined from a cross-section of semitendinosus muscle was in the order of HM (LM) > HM (HM) > LM (HM) = LM (LM) (P < .05). These data show that the presence of a co-twinned fetus with a lower genetic propensity for muscle development reduces the capacity of heavily muscled fetuses to develop muscle mass by 175 d after conception and strongly support the idea that blood-borne factors regulate muscle hypertrophy in fetal cattle.

Electromagnetic scanning of beef quarters to predict carcass and primal lean content

To study the use of electromagnetic scanning in prediction of lean content in beef carcasses and cuts, 100 beef cattle (60 steers and 40 heifers), representing a broad range in external fat thickness (.1 to 2.9 cm) and live weight (414 to 742 kg), were selected. Chilled right sides were divided into streamlined (foreshank, brisket, and ventral plate removed) forequarters (FQ) and full hindquarters (HQ) and scanned. Primal rounds, loins, ribs, and chucks were fabricated from the right side, scanned, and physically separated into lean, fat, and bone. Prediction equations for dissected lean content and percentage of lean included the peak of the electromagnetic scan response curve (obtained from scanning the HQ or FQ), length, temperature and weight of the scanned cut, and fat thickness at the 12th rib. Using the coefficient of determination, root mean square error, and Mallows' Cp statistic, the best model for each dependent variable (weight and percentage of lean) that included up to five independent variables was selected. Prediction equations for the HQ or FQ of steers accounted for 84 to 93% of the variation in lean weight of beef sides and quarters and 71 to 93% of primals. Sixty-one to 75% of the variation in percentage of lean in sides and quarters and 48 to 65% of primals was also explained. Similar results were obtained for heifer carcasses. Predicting percentage of lean in any scanned cut, rather than weight of lean, accounted for less of the variation. Weight and fat thickness contributed significantly when predicting percentage of lean.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of production and postmortem technologies on composition and palatability of USDA Select grade beef

Improvement of USDA Select grade beef is essential for consumer acceptance of leaner beef. Seventy-two large- and medium-framed steer calves of mixed breeding were used in two experiments to evaluate feedlot performance, carcass composition, and beef palatability. Interactions of dietary energy level (corn concentrate or corn silage), breed type (Angus or Simmental), carcass electrical stimulation (ES) voltage (low or high), and chilling rate (normal or delayed) were determined. Grain-fed cattle had similar initial and slaughter weights, heavier carcasses, more marbling, higher quality grades, and higher dressing percentages (Exp. 2) compared with silage-fed cattle, even though all cattle were visually selected for a constant grade end point. Simmental cattle had heavier initial slaughter and warm carcass weights, larger loin eye area, less fat depth, and lower yield grade than Angus cattle. Percentage of lean in the 9-10-11th rib was lower and percentage of fat was higher for grain-fed and Angus steers than for silage-fed and Simmental steers, respectively. Neither diet nor breed influenced chemical composition of the edible portion, except that separable lean in Angus steers was higher in ether extract. No differences in palatability existed between Angus and Simmental steaks. High ES voltage compared with low voltage improved some tenderness characteristics and reduced some juiciness scores. The USDA Select grade beef of accepted palatability can be produced on either corn-grain or corn-silage diets, and only minor differences in beef palatability in such cattle are caused by ES voltage.

Weight gain and reproductive performance of spring-born beef heifer calves intraruminally administered oxfendazole

The effect of oxfendazole (Synanthic) on weight gain and reproductive performance of spring-born heifer calves was evaluated at five locations (IL, IN, MI, MO, ND). Three hundred thirty-eight mixed-breed beef heifers (293.4 kg) blocked by weight and age were randomly allotted to one of two treatments. Treatment 1 heifers were dewormed via intraruminal injection of oxfendazole. Treatment 2 heifers served as a control. Heifers were comingled during the winter phase in semi-confinement during the period from late January to late May (winter phase). Heifers were sorted by treatment at the beginning of the grazing season (approximately May 24, 1991) and remained separate until the end of the study (approximately July 31, 1991; summer phase). Dewormed heifers received oxfendazole (4.5 mg/kg BW) in late January and again 28 and 56 d after the beginning of the grazing season. Fecal samples were taken every 21 d from January through September and assayed for gastrointestinal parasite eggs. Fecal egg counts were similar across treatments at the beginning of the trial (P = .34). Deworming decreased fecal egg counts throughout the trial. Twenty-eight days after initial deworming a significant treatment effect on fecal egg counts was observed (P < .01). Winter ADG was significantly higher (P < .01) for dewormed heifers than for controls (.60 vs .52 kg, respectively). Summer ADG was not different between treatments. Dewormed heifers were 7.4 kg heavier than controls (P < .05) at the end of the trial. Age of puberty was not affected by treatment (P = .64). First-service conception and final pregnancy rates were not different between treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Estimation of net energy requirements (NEm and NE delta) of lactating beef cows

Spring-calving Angus cows (n = 24) in moderate body condition were assigned to either a high (H), maintenance-high (MH) to support superior milk, maintenance-low (ML) to support average milk, or low (L) energy diet at 12 d (SD = 4) postpartum. Energy balance for individual cows was determined by body condition change, weight change, and weigh-suckle-weigh milk production estimates. High energy intake increased (P < .05) BW, body condition score (BCS), and megacalories of body energy (BE) by 94 d postpartum. Neither dietary nor BCS accounted for significant (P > .30) variation in days to first ovulation or conception. Fasting heat production was estimated to be 72.5 kcal/BW.75 from the regression of log daily heat production/BW.75 on daily ME intake/BW.75. Rate of daily BW change did not affect concentration of energy in the weight change. Body condition score change was highly correlated (r = .98) to BW change, with each unit of BCS (1 to 5 scale) change associated with 68 kg of BW change. Two methods were used to determine NE for weight change (NE delta) based on empty body weight (EBW) change. Method 1 used the equation: BCS change = -.404 + .0147 (BW change) and Method 2 used only the regression coefficient of this equation to predict daily BCS change. Methods 1 and 2 resulted in similar regression equations: NE delta (Mcal/kg EBW change) = 1.590 + 1.251 (BCS) and NE delta (Mcal/kg EBW change) = 1.317 + 1.251 (BCS). Ranges of estimated protein and lipid in the EBW change, respectively, were 10.0 to 13.7% and 17.1 to 77.2%.

Effect of dietary energy, body condition and calf removal on pituitary gonadotropins, gonadotropin-releasing hormone (GnRH) and hypothalamic opioids in beef cows

Beef cows (n = 64) were slaughtered to evaluate effects of dietary energy and calf removal (CR) on hypothalamic and adenohypophysial endocrine characteristics. From d 190 of gestation until parturition, cows received maintenance (ME; n = 32) or low (LE; n = 32) energy diets (ME = 100%, LE = 70% NRC recommendations). After parturition, half (n = 16) of each prepartum diet group received low (LE; n = 32) or high (HE = 130% NRC; n = 32) energy diets. At 30 d postpartum, cows were slaughtered 0 or 48 hr after CR. Hypothalami [preoptic area (POA), hypothalamus (HYP), stalk-median eminence (SME)] and pituitaries were collected. Basal and K(+)-induced release of GnRH from SME, and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not differ among groups (P greater than .05). Hypophyseal LH was correlated (P less than .01) with body condition score (BCS) at parturition and slaughter (r = .36 and .47, respectively). Prepartum LE diet increased (P less than .05) met-enkephalin in POA compared to prepartum ME (.59 +/- .05 vs. .44 +/- .04 pmol/mg) regardless of postpartum diet or suckling status. Concentrations of beta-endorphin in combined HYP + POA were decreased (P less than .05) by 48 hr CR (15.1 +/- 1.1 vs. 18.1 +/- 0.7 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of body composition, pre- and postpartum energy intake and stage of production of energy utilization by beef cows

Mature Charolais x Angus cows (n = 128) were adjusted to a body condition score (BCS) of 3 (1 = very thin, 3 = moderate, 5 = very fat) between 130 and 190 d of gestation. When cows averaged 190 d of gestation, they were assigned randomly to a maintenance energy diet (ME) or to a diet very low in energy (LE). Cows were allotted within these prepartum (PRP) diets to a high-energy (HE) or LE diet at parturition. At 30 d postpartum (PP), cows were allotted to four treatments: a) slaughter at 0 (n = 32) or b) 48 h after calf removal (n = 32), c) cows whose calves were early weaned at 30 d PP (n = 32) or d) normally weaned at 205 d PP (n = 32). Low energy PRP intake reduced (P less than .01) BCS, cow weight, total empty body lipid (TEBL), body energy (BE) and daily predicted maintenance energy (PME)/W.75 by parturition. Pre- and postpartum energy intake combined to affect (P less than .10) these same factors in a similar manner at 30 d PP. From 30 to 60 d PP, early weaning reduced (P less than .05) PME/W.75. Cow BCS at 190 d of gestation had little effect (P greater than .10) on PME/W.75 or PME/Mcal of BE. Body condition score at parturition, however, affected (P less than .05) delta BCS, delta BE and PME/Mcal of BE by 30 and 60 d PP, with thinner cows losing less condition and requiring more PME/Mcal of BE. Cow BCS had a similar effect from 30 to 60 d PP. Total daily PME was greater for the fat cows during both the PRP and PP periods. Body composition, PRP and PP energy intake and early weaning affect energy requirements and energetic efficiency of beef cows.

Effects of body composition, pre- and postpartum energy level and early weaning on reproductive performance of beef cows and preweaning calf gain

Mature Charolais x Angus rotational cross cows were adjusted to moderate body condition by d 190 of gestation then randomly blocked to a maintenance (ME) or low-energy (LE) diet. At parturition, the 128 cows were randomly allotted within prepartum (PRP) diet to a high-energy (HE) or LE diet. At d 30 postpartum (PP), cows were randomly blocked to two treatments in which calves were weaned early (EW) or normally (NW) at 7 mo of age. Cows receiving a LE PRP diet had lighter calves at birth (34.7 vs 39.0 kg) and 105 d (127.9 vs 144.6 kg). Prepartum and PP energy interacted to affect postpartum anestrous interval (PPI, d) and cycling activity (%), respectively (LE-LE = 72.6, 33.3; LE-HE = 54.3, 56.3; ME-LE = 65.7, 52.9; ME-HE = 68.4, 54.3). High PP energy averaged over PRP diet increased (P less than .10) pregnancy rate by 22.7% and 105-d calf weight by 15.1 kg. Early weaning reduced PPI by 24.3 d (P less than .01) and first service conception rate by 21.7% (P less than .10). Cycling activity within 60 d PP was affected (P less than .01) by PRP diet and suckling status (LE-EW = 62.5, LE-NW = 26.7, ME-EW = 88.9, ME-NW = 13.3%). Thin cows had a longer PPI but had a higher first service conception rate than moderate and fleshy cows. Higher pregnancy rates were observed in cows approaching or maintaining average body condition from parturition to conception than for cows moving away from moderate body condition. Results suggest that fleshy and thin cows at parturition should be managed to approach moderate body condition before the breeding season to optimize reproductive performance and preweaning calf gain.

Adipose tissue lipogenesis in growing steers adapted to different levels of feed intake

The association between feed intake and lipogenic activity in adipose tissue was investigated in growing cattle. Twenty-five 300-kg steers were allotted by BW to one of five levels of intake of a single high-energy corn-corn silage-based diet. Steers were adapted to diets over 4 wk and intakes were adjusted weekly to achieve steady but varying rates of growth. Daily intakes (% of BW) averaged .92, 1.15, 1.64, 2.28 and 2.69 and resulted in growth rates over the final 3 wk of -.28, .07, .71, 1.67 and 1.69 kg/d, respectively. Lipogenic activities in biopsied tissue and circulating concentrations of glucose and insulin were lowest at maintenance feeding and below but increased linearly (P less than .01 for lipogenesis; P less than .1 for glucose and insulin) as intake increased above maintenance. Mean minimal and maximal rates (mumoles.-min(-1).10(6) cells(-1)) or concentrations were fatty acids synthesis ([14C]acetate---fatty acid)), .065 and .723; fatty acid synthetase (NADPH oxidized), .266 and 2.97; lipoprotein lipase (fatty acid released), .048 and .359; glucose (mg/dl), 60.4 and 70.7 and insulin (ng/ml), .70 and 1.66. In a preliminary study with the same 25 steers fed ad libitum, nearly 25% of the variability in adipose tissue lipogenesis was accounted for by variation in feed intake. Results indicate that activities of lipogenic enzymes and lipogenic capacity in growing steers coordinately adapt to the level of feed consumed and that nutrient availability and(or) insulin concentrations may participate in this adaptation.

Effect of suppression of prolactin secretion on adipose lipogenesis in the postpartum beef cow

Effects of inhibiting prolactin secretion and of calf removal at 3 d postpartum on the lipogenic capacity of s.c. adipose tissue were investigated in postpartum beef cows. The rate of fatty acid synthesis (SYN) from [1-14C]acetate and the activity of fatty acid synthetase (FAS) were assessed on adipose tissue obtained by biopsy at 1, 2, 4, 8 and 10 wk postpartum. Administration of bromocriptine (BR; a drug that suppresses prolactin secretion in rats) between d 7 and 42 postpartum decreased average serum prolactin concentrations nearly 90%, but BR had no effect on lipogenic rates at any week compared to control (CO) cows. Rates of SYN (nmol acetate.min-1.g-1 tissue) increased linearly in CO and BR cows from a nadir of 3.1 at wk 1 to 19.3 by wk 8. Within CO and BR, cows with the greater energy intake relative to requirements for lactation (energy balance) had the faster rates of recovery of SYN. Cows whose calves were weaned early (3 d) showed rapid early increases in SYN, reaching an average maximum rate of 46.2 by wk 2. Activity of FAS generally followed a pattern similar to that of SYN for all groups. Results indicate that prolactin is not responsible for low rates of postpartum lipogenesis in s.c. adipose tissue and that energy intake influences the rate of recovery.

Concentrations of bioactive and immunoactive luteinizing hormone in bovine anterior pituitary tissue

Tissue concentrations of LH as determined by radioimmunoassay (RIA) may not accurately measure actual changes that could occur in biological activity of the hormone. To examine this possibility, pituitary homogenates from 135 beef cows in various physiological states were analyzed for content of LH by both RIA and an in vitro bioassay. The ratio of biological/immunological active concentrations of LH remained constant (.52 +/- .02) even though tissue concentrations of immunoactive LH differed among groups. Tissue concentrations of bioactive LH were linearly related to, and highly correlated with (P less than .001), tissue concentrations of immunoactive LH. These data indicate that only a fraction of the immunoactive LH in the bovine pituitary is biologically active. However, this fraction does not vary with the reproductive status or plane of nutrition.

Collagen stability, testosterone secretion and meat tenderness in growing bulls and steers

Interrelationships among concentrations and maturation of intramuscular collagen, serum concentration of hydroxyproline and testosterone and meat tenderness were determined in growing bulls and steers. Sixty-four Charolais X Angus bulls were assigned to sex treatment groups (intact or castrate) and slaughter groups (9, 12, 15 or 18 mo of age). Animals were bled at 30-min intervals via intrajugular catheters between 0600 and 1400 beginning 48 h before slaughter. Serum concentrations of testosterone were determined in each sample from bulls and from four samples from steers; serum hydroxyproline was determined in the last sample from both sexes. Testosterone mean values for the collection period were calculated. Samples of the longissimus, semitendinosus and infraspinatus muscles secured within 45 min postmortem were analyzed for intramuscular collagen concentration, percent soluble collagen and collagen thermal shrinkage temperature. Tenderness of loin steaks was determined by Warner-Bratzler shear test. Serum concentrations of hydroxyproline and testosterone were higher (P less than .01) in bulls than steers. Age effects were noted for both hydroxyproline (P less than .01) and testosterone (P less than .06). Total intramuscular collagen was greater (P less than .01) in bulls than steers and was different (P less than .01) among muscles, but the muscle differences were not uniform over all ages (P less than .05). Percent soluble collagen declined (P less than .01) with age and was different (P less than .01) among muscles. Interaction of age and muscle (P less than .01) and age and sex (P less than .05) also were noted for percent soluble collagen.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of bovine udder, plate and viscera using near infrared reflectance spectroscopy

The objective of this study was to evaluate near infrared reflectance spectroscopy (NIRS) as an accurate and inexpensive alternative to conventional chemical analyses of nonconsumer bovine tissue. Udder, plate and visceral samples were collected from mature, Charolais-Angus and Hereford-Angus crossbred beef cows at slaughter, ground and analyzed for concentrations of lipid, protein and dry matter using standard AOAC chemical procedures. Samples were analyzed using NIRS. The collection of samples was randomly split into separate calibration and validation sets. Nine calibration equations representing each constituent and tissue combination were developed, using first- or second-order derivative mathematical transformations, and those calibration equations were validated. Correlation coefficients of calibration (R) and validation (r) ranged from .95 to .98 and from .87 to .97, respectively, for all analyses except plate dry matter (r = .77). Standard errors of calibration and prediction ranged from 1.89 to 5.81%. Results from this study are interpreted to indicate that bovine udder, plate and visceral tissue composition can be accurately, quickly and efficiently predicted using NIRS technology.

Use of insecticide-impregnated ear tags for the control of face flies and horn-flies on pastured cattle

Three studies were conducted to evaluate the effectiveness of insecticide-impregnated ear tags in controlling face flies, Musca autumnalis DeGeer, and horn flies, Haematobia irritans (Linn.), on pastured beef cattle. In one 16-week trial, polyvinyl chloride (PVC) ear tags treated with stirofos (Rabon) insecticide reduced horn fly numbers by 79% (P less than .05) and face fly numbers by 30% (P less than .05). Coumaphos (Co-Ral) insecticide dust bags used in a separate herd produced an 86% (P less than .05) reduction in horn flies and an 18% (P less than .05) reduction in face flies. In the second study, 5 and 10% permethrin (Atroban), PVC-treated ear tags in a one-piece design were tested. In this 11 week trial, horn fly control averaged 95% (P less than .05) with the 10% tag and 77% (P less than .05) with the 5% tag. Face fly control averaged 49% (P less than .05) for 8 weeks with the 10% permethrin tag. No significant face fly control was achieved with the 5% permethrin tag. In a herd treated with coumaphos dust bags, horn fly control averaged 93% (P less than .05) and face fly control averaged 34% (P less than .05). The third study tested 5 and 10% permethrin, PVC-treated ear tags in a two-piece design and two-piece 5% permethrin-treated ear tags in a polyurethane matrix. Fourteen-week horn fly control averaged 88% (P less than .05) with the 10% PVC-treated tag, 83% (P less than .05) with the 5% PVC-treated tag, 71% (P less than .05) with the 5% polyurethane-treated tag and 74% (P less than .05) with coumaphos dust bags. Face fly control averaged less than 50% (P greater than .05) throughout the trial with all treatments.

Effects of winter and summer energy levels on heifer growth and reproductive performance

Three heifer development trials were conducted with 337 crossbred heifers (125, 105 and 107 heifers in trials 1, 2 and 3, respectively) over a 3-year period. Heifers were fed low quality fescue hay ad libitum plus 0, 1.22 or 2.45 kg of ground ear corn (GEC) daily during the winter feeding phase of all three trials. Winter gains and final winter and summer condition scores increased (P less than .05) in each trial as winter level of GEC increased. In each trial, summer gains followed the reverse order of winter gains (P less than .05). Conception rate, mean number of days pregnant (as determined by rectal palpation) and adjusted weaning weight of progeny increased linearly with winter level of GEC when pooled over trials. Differences between animals fed 0 and 2.45 kg of GEC were significant. Conception rate and adjusted weaning weight of progeny of the heifers retained in the breeding herd increased (P less than .05) as level of GEC increased when data were pooled over trials. Calving date and percentage live progeny were not significantly affected by winter treatment. Summer daily gains and condition scores were increased by additional summer energy (2.45 kg GEC/day) in trial 3. Conception rate and mean number of days pregnant (conception date) favored heifers given the summer supplementary feeding (2.45 kg GEC) treatment. Among heifers retained in the breeding herd, there were no significant differences between the 0- and 2.45-kg GEC summer treatment groups in conception rate, calving date, percentage live progeny or adjusted weaning weight of progeny.