Developmental and reproductive characteristics of beef heifers classified by pubertal status at time of first breeding.

Data collected for 10 or more years at the West Central Research and Extension Center, North Platte, NE ( = 1,104); the Gudmundsen Sandhills Laboratory, Whitman, NE ( = 1,333); and the USDA, ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT ( = 1,176) were retrospectively analyzed to evaluate growth and reproductive performance of beef heifers classified by pubertal status before first breeding. Concentrations of progesterone in serum from 2 blood samples collected 9 to 11 d apart before the breeding season classified heifers as pubertal (progesterone ≥ 1.0 ng/mL in 1 or both samples) or nonpubertal (progesterone < 1.0 ng/mL in both samples). Average date of birth was earlier ( < 0.06) and proportion born in the first 21 d of the calving season was 10 to 20 percentage points greater for heifers that were pubertal at the start of breeding compared with heifers not pubertal by the start of breeding. Heifers that were pubertal by the start of breeding were 7 to 10 kg heavier ( < 0.01) and 1 cm taller ( < 0.01) at weaning than heifers not pubertal by the start of breeding. Differences in BW persisted through the start of breeding to pregnancy diagnosis. Heifers that achieved puberty by the start of breeding had greater ( < 0.05) feed intake and G:F during postweaning development and had greater ( < 0.01) LM area and fat thickness over the LM at approximately 1 yr of age compared with heifers not pubertal by the start of breeding. Heifers that achieved puberty before the start of breeding had greater ( < 0.01) ADG from birth to weaning but slower ( < 0.10) rates of gain from the start of breeding through pregnancy diagnosis. Pregnancy rate was greater ( < 0.01) for heifers that were pubertal at the start of breeding. In heifers that became pregnant, those that were pubertal before the start of breeding calved earlier ( < 0.01), with a greater ( < 0.01) percentage calving in the first 21 d of calving than heifers not pubertal at the start of breeding. Calves from heifers that achieved puberty before the start of breeding were heavier at weaning ( < 0.01) than calves from heifers that had not achieved puberty by the start of breeding. In summary, heifers that failed to achieve puberty by the start of breeding were less desirable for several traits evaluated. Based on these results, implementing feeding strategies to increase the proportion of heifers that achieve puberty before first breeding could result in propagation of undesirable characteristics.

Comparing Visual and Digital Counting Methods to Estimate Horn Fly (Diptera: Muscidae) Populations on Cattle.

Horn fly, Haematobia irritans (L.), population estimates often serve as a diagnostic tool prior to implementing managerial control options available to researchers and producers. Digital photographs taken of cattle infested with horn flies have been suggested to provide similarly accurate population estimates as compared with traditional visual assessments. The objective of this study was to compare visual and digital techniques used to estimate horn fly populations. Sixteen Angus × Hereford yearling heifers artificially infested with four levels of horn flies (Low = 0 flies; Medium = 250 flies; High = 500 flies; Extreme = 1,000 flies) were evaluated. Population estimates were taken visually by experienced (VE1) and inexperienced (VE2) technicians, as well as digitally, with photographs taken on both lateral sides of the south-facing animal. Horn flies were counted in both photographs and combined (CDC) for full body estimates. In addition, the highest photographed side population times two (DDC) was used for comparison. Estimations were made at 0700, 1200, and 1900 h the day following infestation. A time of observation × infestation level interaction (P < 0.01) was detected. On average, VE1 population estimates were greater (P < 0.01) than any other counting method observed. Morning estimates were greater (P < 0.05) than those taken at noon or in the early evening regardless of counting method. Further research regarding the standardization of these techniques to ensure more accurate population estimates is needed before these methods can be incorporated into integrated pest management programs.

Impact of supplemental protein source offered to primiparous heifers during gestation on I. Average daily gain, feed intake, calf birth body weight, and rebreeding in pregnant beef heifers.

A 3-yr study was conducted to determine the effect of supplemental protein source on ADG, feed intake, calf birth BW, and subsequent pregnancy rate in pregnant beef heifers. Crossbred, Angus-based, AI-pregnant heifers (yr 1, n = 38; yr 2, n = 40; and yr 3, n = 36) were stratified by BW (450 ± 10 kg) and placed in a Calan Broadbent individual feeding system at approximately d 142 of gestation. Following a 25-d adaptation period, an 84-d feeding trial was conducted. Heifers were offered ad libitum grass hay (8 to 11% CP, DM basis) and no supplement (CON), 0.83 kg/d distillers-based supplement (HI), or 0.83 kg/d dried corn gluten-based supplement (LO). Supplements were formulated to be isocaloric, isonitrogenous (28% CP, DM basis), and equal in lipid content but differed in RUP, with HI (59% RUP) having greater levels of RUP than LO (34% RUP). Dry matter intake was also calculated based on feed NE values to account for different energy levels of the supplement compared with the control diet. Control heifers tended (P = 0.09) to consume less total DM than either supplement treatment. However, forage-only DMI was greater (P < 0.01) for CON heifers (9.94 ± 0.12 kg) compared with HI or LO heifers (8.50 and 8.34 ± 0.12 kg, respectively). Net energy DMI was less (P < 0.01) for CON heifers (4.98 ± 0.23 kg) compared with HI or LO heifers (5.43 and 5.35 ± 0.23 kg, respectively). Control heifers gained less (P < 0.01; 0.59 ± 0.14 kg/d) than either HI (0.82 ± 0.14 kg/d) or LO heifers (0.78 ± 0.14 kg/d), resulting in lower (501 ± 9 kg) BW (P < 0.01) than HI (519 ± 9 kg) heifers at the end of the feeding period. Calf birth BW was similar (P = 0.99) among treatments. At prebreeding, CON heifers weighed less (P < 0.03) than LO heifers. Cow BW was similar (P = 0.48) among treatments at pregnancy diagnosis, and final pregnancy rate was also similar (87%; P = 0.22). Protein supplementation increased ADG in pregnant heifers; however, calf birth BW and subsequent pregnancy rates were similar.

Impact of supplemental protein source offered to primiparous heifers during gestation on II. Progeny performance and carcass characteristics.

A 3-yr study using primiparous crossbred beef heifers (n = 114) was conducted to determine the effects of protein supplement during late gestation on progeny performance and carcass characteristics. Pregnant heifers were stratified by heifer development system, initial BW, and AI service sire and placed in an individual feeding system. Heifers were offered meadow hay (8 to 11% CP) from early November to mid-February and provided no supplement (CON; n = 37), 0.83 kg/d (DM basis) of a dried distillers grains with solubles-based supplement (HI; n = 39), or 0.83 kg/d (DM basis) of a dried corn gluten feed-based supplement (LO; n = 38). Supplements were designed to be isonitrogenous (28% CP) and isocaloric but to differ in RUP with HI (59% RUP) having greater levels of RUP than LO (34% RUP). After the individual feeding period, heifers were placed in a drylot for calving. All heifers were bred using a fixed-timed AI protocol and pairs were moved to a commercial ranch in the Nebraska Sandhills for summer grazing. Calf weaning BW did not differ (P = 0.14) based on maternal diet. However, feedlot entry BW was greater (P = 0.03) for HI compared with CON calves. Average daily gain during the initial feedlot phase tended (P = 0.10) to be greatest for calves born to CON dams and lowest for calves born to LO dams. However, overall ADG was similar (P = 0.50) for the entire feedlot period. Residual feed intake during the reimplant and total feeding period was improved in calves born to supplemented dams in yr 2 and 3 compared with calves born to CON dams. There was no difference in final BW among treatments (P = 0.71). Hot carcass weight was similar (P = 0.72) among treatments; however, steers had greater (P < 0.01) HCW than heifers. Furthermore, percent empty body fat and 12th rib fat thickness were lowest (P = 0.05 and P = 0.04) for calves born to LO dams. Tenderness measured by Warner-Bratzler shear force was increased (P = 0.03) in longissimus samples from calves from CON dams compared to calves from LO dams. Similarly, crude fat levels tended to be greater (P = 0.07) for calves from CON dams compared with calves from LO dams. Based on these data, providing RUP supplements, similar to those used in this study, to primiparous heifers in late gestation consuming ad libitum grass hay resulted in increased initial feedlot BW for HI compared to CON calves, improved feed efficiency, and altered carcass characteristics in calves born to supplemented compared with CON dams.

Effect of beef heifer development system on average daily gain, reproduction, and adaptation to corn residue during first pregnancy.

Postweaning heifer development systems were evaluated at 2 locations in a 4-yr study for their effect on performance and subsequent adaptation to grazing corn residue as a pregnant heifer. In Exp. 1, heifers were blocked by BW and randomly assigned to graze winter range (WR) or graze winter range and corn residue (CR). In Exp. 2, heifers were assigned to graze winter range and corn residue (CR) or graze winter range and placed in a drylot (DL). Artificial insemination and natural mating were used at breeding on the basis of location. In Exp. 1, heifers developed on corn residue tended (P = 0.11) to have reduced ADG compared with WR heifers. Subsequently, BW at the end of the 82-d corn residue grazing period tended (P = 0.09) to be lower for CR compared with WR heifers. However, the proportion of heifers attaining puberty before the breeding season and pregnancy rates were similar (P ≥ 0.29) for CR and WR heifers. Developing heifers on winter range tended (P = 0.09) to reduce heifer development costs $36/pregnant heifer compared with CR heifers. In Exp. 2, DL heifers had greater (P < 0.01) overall ADG during development compared with CR heifers, resulting in greater (P < 0.01) prebreeding BW for DL heifers compared with CR heifers (355 vs. 322 ± 9 kg). At pregnancy diagnosis BW remained greater (P = 0.02) for DL compared with CR heifers (423 vs. 406 ± 7 kg). Corn-residue-developed heifers had increased (P = 0.03) AI conception rates compared with DL heifers (78% vs. 67% ± 6%). However, there was no difference (P ≥ 0.21) in percent pubertal before the breeding season or final pregnancy rates for CR and DL heifers. Developing heifers on corn residue reduced (P = 0.02) heifer development costs $38/pregnant heifer compared with DL-developed heifers. A subset of pregnant heifers from both experiments grazed corn residue fields in late gestation. As pregnant heifers grazing corn residue, WR heifers (Exp. 1) tended to have reduced ADG compared with CR heifers (0.34 vs. 0.43 ± 0.08 kg/d, P = 0.07). Furthermore, in Exp. 2 CR heifers had greater (0.41 vs. 0.30 ± 0.22 kg/d) ADG grazing corn residue as pregnant heifers compared with DL-developed heifers. Calving date, dystocia score, and calf birth BW were similar (P ≥ 0.15) between development systems in both experiments. There appears to be a potential learned grazing behavior for heifers developed on corn residue allowing them to better adapt to grazing corn residue as pregnant heifers compared with WR and DL heifers.

Epigenetics: setting up lifetime production of beef cows by managing nutrition.

Longevity of cattle is correlated to reproductive success. Many studies in different species report the influence of maternal nutrition on progeny performance, health, and reproduction. Maternal nutrient status can cause epigenetic alterations to the genome of the developing fetus, which potentially can impact future generations. This review discusses fetal programming mechanisms as well as maternal nutrition's impact on placental development and progeny heifer performance and reproduction owing to nutrient restriction, age, or production status. Furthermore, we discuss how early neonatal nutrient intake and type can influence future productivity in the beef and dairy cow. Understanding how these factors influence progeny performance will enable cattlemen to produce replacement females better adapted to their environment through maternal nutrient regulation by stimulating fetal programming.

Alpharma Beef Cattle Nutrition Symposium: implications of nutritional management for beef cow-calf systems.

The beef cattle industry relies on the use of high-forage diets to develop replacement females, maintain the cow herd, and sustain stocker operations Forage quantity and quality fluctuate with season and environmental conditions Depending on class and physiological state of the animal, a forage diet may not always meet nutritional requirements, resulting in reduced ADG or BW loss if supplemental nutrients are not provided It is important to understand the consequences of such BW loss and the economics of providing supplementation to the beef production system Periods of limited or insufficient nutrient availability can be followed by periods of compensatory BW gain once dietary conditions improve This may have less impact on breeding animals, provided reproductive efficiency is not compromised, where actual BW is not as important as it is in animals destined for the feedlot A rapidly evolving body of literature is also demonstrating that nutritional status of cows during pregnancy can affect subsequent offspring development and production characteristics later in life The concept of fetal programming is that maternal stimuli during critical periods of fetal development have long-term implications for offspring Depending on timing, magnitude, and duration of nutrient limitation or supplementation, it is possible that early measures in life, such as calf birth BW, may be unaffected, whereas measures later in life, such as weaning BW, carcass characteristics, and reproductive traits, may be influenced This body of research provides compelling evidence of a fetal programming response to maternal nutrition in beef cattle Future competitiveness of the US beef industry will continue to be dependent on the use of high-forage diets to meet the majority of nutrient requirements Consequences of nutrient restriction or supplementation must be considered not only on individual animal performance but also the developing fetus and its subsequent performance throughout life.