Developmental and reproductive characteristics of beef heifers classified by number of estrous cycles experienced by start of first breeding.

A retrospective analysis was conducted to evaluate the effect of number of estrous cycles exhibited before breeding on growth and reproductive performance of replacement beef heifers fed ad-libitum or restricted by 20% less than ad-libitum during postweaning development over a 9-yr period. Progesterone concentration in blood samples collected at 9- to 11-d intervals were used to assign heifers into groups by number of estrous cycles exhibited before the start of breeding: 0 (nonpubertal; n = 395), 1 (n = 205), 2 (n = 211), 3 (n = 116), or >3 (n = 249). Heifers (P < 0.01) in the 0 cycle group were born 6 d later than the 1, 2, or 3 cycle groups, which were born 4 d later (P < 0.01) than the >3 cycle group. Weight of heifers at birth decreased (P < 0.05) as the number of cycles increased. Weaning weight and ultrasound measures of loin area and fat thickness over the loin at 1 yr age increased as the number of cycles increased (P < 0.01). Postwean weight gain, hip height at 1 yr age, and weights from the start of breeding through precalving increased with cycle numbers in a quadratic fashion (P < 0.02) and were greater (P < 0.05) in ad-libitum than restricted-fed heifers. Pregnancy rate in the 0 cycle group was lower (84%; P < 0.05) than the 1 (90%) or >3 (94%) estrous cycles groups and tended to differ (P < 0.1) from the 2 (88%) and 3 (89%) estrous cycle groups. Interval from the start of breeding to calving was 3 to 5 d longer (P < 0.05) for the 0 cycle group (300 ± 1 d) than other groups. Proportion of heifers calving in the first 21 d was less (P < 0.05) in the 0 or 1 cycle groups than other groups. Pregnancy rates of 2-yr-old cows (n = 898) were lowest (P < 0.05) for the 0 (73%) and 2 (79%) estrous cycle groups than the 1 (85%), 3 (90%), or >3 (92%) estrous cycle groups. Restricted level of feeding during postweaning development resulted in greater (P < 0.05) proportion of heifers in 0 cycle group and lower (P < 0.05) proportion in >3 cycle group, but reproductive performance was not influenced (P > 0.1) by level of feeding or interaction of feeding and estrous cycle grouping. In summary, date of birth and rate of physical maturation (weight, height, and fat deposition) were associated with timing of puberty. Pregnancy rate was greater in heifers that exhibited estrus before the start of breeding, but did not improve from having more than one estrous cycle. Proportion conceiving early was greater for heifers having two or more cycles before breeding.

Influence of weaning date and late gestation supplementation on beef system productivity II: economic analysis.

Cow-calf production systems were analyzed using experimental data and historical economic information to model four separate production year using the 10-yr price period from 2005 to 2014. Treatments included two weaning dates, October (OCT) and December (DEC), and four winter nutritional treatments, grazing winter range with no supplement (WR0), low supplement (WR1), high supplement (WR2); or grazing corn residue with no supplement (CR) applied in a 2 × 4 factorial arrangement. Net returns at the December weaning date were greatest (P < 0.05) for DEC systems where cows were fed the WR2 level ($151.14/cow) or CR ($140.17/cow), intermediate for cows fed the WR1 ($110.44/cow), and least for cows fed WR0 ($62.23/cow). Average net returns across winter nutrition treatments at the December weaning date were greater (P < 0.01) for DEC systems ($115.99/cow) compared with OCT systems ($110.28/cow). Marketing October weaned calves in December increased net returns on average by $47.24/cow compared with October marketing. Retained and owned (RO) slaughter steer net returns sold on a hot carcass weight (HCW) basis were greatest (P < 0.05) for CR systems ($190.62/cow) or WR2 ($188.13/cow), intermediate for WR1 ($132.67/cow) and least for the WR0 ($68.08/cow) treatment. In general, purchasing weaned calves (PC) and marketing them as finished steers either on a HCW basis or on a marketing grid were not profitable. The WR2 and the CR grazing regimes were more profitable than WR0 and WR1 regardless of market end point, primarily due to reduction in replacement and production loss costs.

Influence of weaning date and late gestation supplementation on beef system productivity I: animal performance.

A 4-yr experiment examined how weaning date and prepartum nutrition affected productivity in a spring (March and April) calving system. Crossbred beef cows (479 ± 59 kg, n = 144) were used in a completely randomized design with a 2 × 4 factorial treatment arrangement: 1) cows were weaned in early October or early December; and 2) during late gestation cows were fed on a dry matter basis a 32% crude protein supplement at 0, 0.41, or 0.82 kg/cow/d on dormant upland range or grazed corn residue without supplement. Cow body condition score (BCS) was affected (P ≤ 0.01) by treatment prior to parturition and breeding but was similar (P > 0.27) among all treatments in October. Dams on a higher nutritional plane during winter treatment had greater (P < 0.01) BCS and body weight (BW) prior to parturition and breeding. Subsequent pregnancy rates (88% to 97%) were not influenced (P > 0.76) by weaning date, but tended (P = 0.10) to be lower for cows grazing winter range without supplement. Calves born to dams grazing winter range without supplement had lower (P < 0.01) BW in October and adjusted weaning BW. Pre-breeding BW of heifers weaned in December born to cows grazing winter range without supplement was lower (P < 0.01) than contemporaries born to cows in all other treatment combinations. However, postweaning (0.48 kg/d) and postbreeding (0.42 kg/d) average daily gain, percentage cycling before breeding (33%), and pregnancy rate (81%) was similar (P > 0.12). Within weaning date, steers born to cows grazing winter range without supplement had lower (P < 0.05) hot carcass weight (HCW) than contemporaries born to cows grazing corn residue. Cows weaned in December had decreased BW and BCS but similar pregnancy rates as cows weaned in October. Weaning date and dam maternal nutrition had minimal impact on heifer progeny pregnancy rate. Steer progeny born to dams on a higher nutritional plane had similar HCW at slaughter when adjusted to equal fat thickness.

Effect of prenatal programming on heifer development.

In beef cattle, the main factors influencing nutrient partitioning between the dam and fetus include age of the dam, number of fetuses, production demand, and environmental stress. These factors play a critical role in programming the fetus for its future environment and available resources. Fetal programming reportedly affects neonatal mortality and morbidity, postnatal growth rate, body composition, health, and reproduction. Two main mechanisms responsible for fetal programming include DNA methylation and histone modifications. Alterations in the genome can be passed through multiple generations. Maternal environment (nutrition, age, physiologic status) can program progeny heifer growth and reproductive performance.

Postbreeding heifer management.

Rebreeding performance of the first-calf heifer has major economic consequences for cow-calf producers. Management systems that allow heifers to cost-effectively achieve a body condition score of 5 to 6 at calving and maintain this through rebreeding have a higher probability of pregnancy success.