R. N. Funston

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

A 2 × 2 factorial arrangement of treatments was used to evaluate effects of dam winter grazing system and supplementation in the last third of gestation on subsequent BW gain, feed efficiency, and reproduction in heifer progeny. Crossbred cows (yr 1, n = 109; yr 2, n = 114; yr 3, n = 116) grazed range (WR) or corn residue (CR) during winter and within grazing treatment received 0.40 kg/d of 31% CP (DM basis) cubes (PS) or no supplement (NS). Heifer calves (yr 1, n = 56; yr 2, n = 56; yr 3, n = 54) grazed dormant pasture for 114 d postweaning and were individually fed for 87 d before a 45-d natural service breeding. Dam PS reduced (P = 0.04) heifer birth date and CR tended to increase (P = 0.07) heifer birth BW. Both PS and CR increased (P ≤ 0.05) heifer weaning BW; however, adjusted 205-d weaning BW was only lighter (P = 0.03) if the dam grazed WR with NS. Heifers from PS dams tended to be younger (P = 0.09) at puberty than NS, and there was a trend (P = 0.11) for more heifers to be pubertal by breeding if the dam grazed WR with PS compared with other treatment groups. Heifers from WR-NS dams tended to weigh less (P ≤ 0.09) at breeding and at pregnancy diagnosis than WR PS. There was a trend (P = 0.13) for pregnancy rate to be greater for heifers born to PS dams. Individually fed heifer DMI was not affected (P = 0.25) by treatment; however, heifers from dams that grazed CR with PS gained the least BW (P = 0.04) during individual feeding and had the smallest (P = 0.03) G:F. In contrast, there were no differences (P > 0.15) in feed efficiency when expressed as residual feed intake. The first calf birth and weaning BW of the heifer was unaffected (P > 0.15) by dam treatment. Heifers from dams that grazed WR with NS tended to have lighter (P = 0.09) BW before the second breeding season but similar (P = 0.97) pregnancy rates. Cows grazing CR with NS produced the most valuable heifer calf at weaning; however, heifers from cows that grazed WR with NS cost the least to develop per pregnant heifer. Winter grazing system and late gestation supplementation affected heifer progeny BW, feed efficiency, and fertility.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Nutritional aspects of developing replacement heifers 1

Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.

Effect of calving distribution on beef cattle progeny performance

Records collected between 1997 and 2010 were used to determine the effect of calving period on heifer (n = 1,019) and steer (n = 771) progeny from the Gudmundsen Sandhills Laboratory, Whitman, NE. Progeny were classified as being born in the first, second, or third 21-d period of the spring calving season within year. Heifer birth BW was lightest (P < 0.01) for heifers born in the first period. Birth to weaning ADG tended (P = 0.10) to be least for heifers born in the first calving period; however, weaning BW decreased (P = 0.03) with advancing calving period. Weaning to prebreeding ADG tended (P = 0.07) to be least for heifers born in the first period; however, prebreeding BW was greatest (P < 0.01) for calves born in the first period. Heifer ADG from the beginning of the breeding season to pregnancy diagnosis was greater (P = 0.03) for heifers born in the third vs. first calving period. Heifers cycling at the beginning of the breeding season decreased (P < 0.01) with advancing calving date (70, 58, and 39%, respectively) and 45 d pregnancy rates were lowest (P = 0.02) for heifers born in the third calving period (90, 86, and 78%, respectively). Birth date of the first calf of the heifer and birth BW decreased (P < 0.01) if the heifer was born in the first calving period. First calf progeny had the greatest (P ≤ 0.10) weaning BW if born to a heifer born in the first calving period. As steer calving period advanced, weaning BW decreased (P < 0.01). Calving period did not affect (P = 0.81) feedlot ADG. As calving period advanced, HCW, marbling score, and yield grade decreased (P < 0.01). The percentage of steers grading USDA small marbling was not affected (P = 0.13) by calving period; however, the percentage of steers grading USDA modest marbling or greater and the total carcass value declined (P ≤ 0.01) as calving period advanced. Heifer calves born during the first 21 d of the spring calving season had greater weaning, prebreeding, and precalving BW; greater percent cycling before breeding; and greater pregnancy rates compared with heifers born in the third period. First calf progeny also had an earlier birth date and greater weaning BW. Steer calves born during the first 21 d of the calving season had greater weaning, final, and carcass weights; greater marbling scores; a greater percentage grading USDA modest or greater; and greater carcass value. Calving period of progeny significantly impacts performance.

JOINT ALPHARMA-BEEF SPECIES SYMPOSIUM: Implications of beef heifer development systems and lifetime productivity1

Research emphasis has been placed on heifer development strategies in recent years, comparing traditional, more intensive systems to more extensive systems using less feed and relying on compensatory gain to reach a target BW. Recent research has indicated that developing heifers to a lighter target BW at breeding (i.e., 50 to 57% of mature BW compared with 60 to 65% BW) reduced development costs and did not impair reproductive performance. Research published through the late 1980s demonstrated greater negative effects of limited postweaning growth on age at puberty and pregnancy rates whereas more recent studies demonstrate less of a negative impact of delayed puberty on pregnancy rate. A limitation of most research concerning influences of nutrition on heifer development and cow reproductive performance is little or limited consideration of long-term implications. Longevity has relatively low heritability; therefore, heifer development and other management strategies have a greater potential to impact cow retention. Establishing the impact of heifer development protocols on longevity is complex, requiring consideration of nutritional factors after the start of breeding and through subsequent calvings. Lower-input heifer development, where all heifers are managed together after the postweaning period, did not impair rebreeding, but continued subsequent restriction in the form of marginal winter supplementation resulted in decreased retention in the breeding herd. Therefore, the compensatory BW gain period for restricted-growth heifers may be important to longevity and lifetime productivity. Adequate growth and development to ensure minimal calving difficulty can be of critical importance for longevity; however, providing additional supplemental feed during postweaning development to accomplish this may be less efficient than later in development. Restricting gain during postweaning development by limiting DMI or developing heifers on dormant winter forage resulted in increased economic advantages compared with developing heifers at greater rates of ADG to achieve a greater target BW. Implications of heifer development system on cow longevity must be considered when evaluating economics of a heifer enterprise; however, studies evaluating the effects of heifer development systems on cow longevity are extremely limited.

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.

Effect of beef heifer development system on average daily gain, reproduction, and adaptation to corn residue during first pregnancy1

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

Multi-state Beef Reproduction Task Force provides science-based recommendations for the application of reproductive technologies.

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

TRIENNIAL REPRODUCTION SYMPOSIUM: Beef heifer development and lifetime productivity in rangeland-based production systems

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.

Calving date and wintering system effects on cow and calf performance I: A systems approach to beef production in the Nebraska Sandhills 1

Since its formation, the Beef Reproduction Task Force (BRTF) has worked to enhance productivity and profitability of US beef herds by integrating research and extension efforts with the intent of more effectively transferring the use of reproductive technologies to the field. A key early step was to coordinate efforts in identifying effective breeding management protocols for beef cattle and to clarify their associated acronyms. A short list of recommended protocols and their acronyms for synchronization of estrus and ovulation in beef cattle was developed based on results from peer-reviewed, published research and a comprehensive review of data collected from the field. The list of recommended protocols was developed by the BRTF in cooperation with veterinarians and cattle AI industries. These protocols and their acronyms are presented uniformly in all of the major AI sire directories and are available online at http://www.beefrepro.info. Protocol updates are made annually to incorporate the most recent research findings related to estrous cycle control in beef cattle. The Estrus Synchronization Planner, a software program developed in cooperation with the Iowa Beef Center, now reflects these same recommendations. Beginning in 2002, the BRTF hosted and presented 11 educational workshops to more than 1,900 attendees in key cow-calf states. These Applied Reproductive Strategies in Beef Cattle workshops targeted beef producers, AI industry personnel, veterinarians, allied industry representatives, and academicians. A national media sponsor provided online coverage of the last 3 workshops at http://www.appliedreprostrategies.com. A postmeeting evaluation, developed to assess application of information from 2 recent workshops, was returned by 55% of those contacted (n = 150). Attendees averaged 16 (± 13.4 SD) yr of AI experience, and 80% of respondents represented more than 100 cows. Respondents were asked to estimate the value of AI-sired calves compared with natural-service-sired calves to their operation on a per-animal-marketed basis, and 17 and 31% responded

BEEF SPECIES SYMPOSIUM: Can we build the cowherd by increasing longevity of females?

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