Early weaning in Northern Great Plains beef cattle production systems: I. Performance and reproductive response in range beef cows

A study was conducted to determine if early weaning spring born calves can be an alternative management strategy during drought and if early weaning facilitates rebreeding of young cows. Our objectives were to determine effects of early weaning at the start of breeding on cow body weight, body condition score, and reproductive performance with or without estrous synchronization and AI in two herds in the Northern Great Plains, USA. In Exp.1and 2, crossbred cows were stratified within cow age by postpartum interval, and calf sex, and were assigned within strata to one of two weaning treatments at the start of breeding when calves averaged 80-d of age: (1) early weaned (permanent calf removal); or (2) no weaning (calves suckled cows until normal weaning approximately 210-d of age). Cows in Exp.1 were exposed to natural service whereas cows in Exp.2 were exposed to estrous synchronization for AI using a CIDR for 7 d with GnRH at CIDR insertion and PGF2α at CIDR removal followed by natural service. In Exp.3, cows were stratified within breed by age, postpartum interval, calf sex, and AI sire and were assigned within strata to one of two weaning treatments at the start of breeding, as described for Exp.1and 2. Estrous cycles of all cows were synchronized for AI using one of two protocols including 14 d CIDR + PGF2α 16 d following CIDR removal (primiparous cows) or a CIDR insert for 7 d with GnRH at CIDR insertion and PGF2α at CIDR removal (multiparous cows). Cows in Exp.2 and 3 were bred by AI approximately 12 h after observation of estrus or by timed AI at 80 h after PGF2α concurrent administration of GnRH. Artificial insemination (Exp.2), breeding season pregnancy rate, and day of conception was not influenced (P\u3e0.10) by weaning treatment for Exp.1and 2. However, early weaned cows in Exp.3 had 12.0% greater (P=0.03) AI pregnancy rates and conception occurred 3.78 d earlier (P=0.03) than normal weaned cows. At the time of normal weaning, cows that had their calves removed at early weaning were heavier and had greater body condition (P\u3c0.01)than normal weaned cows in each experiment. We conclude that early-weaning beef cows at the start of the breeding season improved BW gain and BCS allowing those females to enter winter in greater BCS then NW cows, but improvements in reproductive performance were inconsistent

Early weaning in Northern Great Plains beef cattle production systems: II. Development of replacement heifers weaned at 80 or 215 d of age

Studies were conducted to evaluate effects of weaning and subsequent heifer development treatments within two herds located in the Northern Great Plains, USA. Heifer calves from predominantly Angus x Hereford dams were stratified within damage and calving date (Fort Keogh Livestock and Range Research Laboratory (LARRL), Miles City, MT, USA; n=328) and randomly assigned within study and strata to one of three weaning treatments. Heifer calves from Angus and Angus x Simmental dams (n=167; Judith Gap (JG),MT,USA) were stratified within breed group by age, calving date, and AI sire. Heifer calves either remained with their dams until time of normal weaning (NW; approximately 213 d of age) or were early weaned (approximately 80 d of age) on to one of two early weaning (EW) diets. Heifer calves assigned to EW treatments received one of the following diets: (1)17.5% CP (69% RDP and 7.53 MJ/kg NEm or (2) 17.5% CP (57% RDP and 7.69MJ/kg NEm). At the time of normal weaning, heifers from LARRL (2005 and 2006) were further divided into two heifer development (HD) diet treatments that differed only in proportion of RDP: (1) 12.5% CP (83% RDP and 6.28MJ/kg NEm); or (2) 12.5% CP (72% RDP and 6.28MJ/kg NEm). Heifers from JG were fed a common heifer development diet. Heifer BW at time of normal weaning revealed that EW heifers were heavier, regardless of type of protein delivered by EW treatments (P\u3c0.10). Heifer BW at the end of the development period was greater for EW heifers at LARRL (P\u3c0.01) and similar for JG heifers (P=0.35) regardless of weaning treatment. Heifers at LARRL that received EW treatments had a greater percentage pubertal (P\u3c0.06) from 39 to 2 d before breeding compared to NW heifers. Pregnancy rates were not influenced by early weaning or heifer development treatments at LARRL (P\u3e0.05); however, a greater percentage of EW heifers became pregnant throughout the breeding season at JG (P=0.03). These experiments demonstrate early weaning is a viable option to develop and breed heifers in extensive beef production systems in the Northern Great Plains, USA. When production may be jeopardized by environmental conditions (e.g., drought), early weaning calves will not impair a heifers opportunity to be retained as replacement females as early weaned heifers have similar or greater reproductive success than heifers that are normal weaned

Estrus synchronization of suckled beef cows by using GnRH, prostaglandin F2α (PGF), and progesterone (CIDR): a multi-location study

Our objectives were to determine whether a fixed-time artificial insemination (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus and whether inclusion of a CIDR (a vaginal insert containing progesterone) in protocols using gonadotropin-releasing hormone (GnRH) and prostaglandin F2α (PGF) would enhance fertility. Postpartum suckled beef cows (n = 2,630) from 14 locations were assigned randomly to each of five estrus-synchronization protocols using PGF with GnRH and(or) a CIDR. Protocols were Control, CO-Synch, COSynch+ CIDR, Hybrid-Synch, and Hybrid-Synch+CIDR. The percentage of cows cycling at the initiation of estrus synchronization was 66.8%, the percentage of cycling cows ranging from 38 to 90% among locations. Overall pregnancy among locations ranged from 39% to 67%. Pregnancy rates were greatest for the Hybrid-Synch+CIDR (57.9%) treatment, although not significantly different from the CO-Synch+CIDR (53.6%) and Hybrid-Synch (53.0%) treatments, but greater than the Control (52.3%) and CO-Synch (43.4%), which yielded the poorest pregnancy rates. Overall, the Hybrid-Synch+CIDR protocol (AI after detected estrus for 3 days, and then a clean-up TAI) achieved the greatest pregnancy rates, but CO-Synch+CIDR is a reliable, fixed-time AI protocol that gives producers the option to eliminat

Early weaning in Northern Great Plains beef cattle production systems: III. Steer weaning, finishing and carcass characteristics

Studies were conducted to evaluate the effect of early weaning steer calves on BW gain, feedlot performance, and carcass characteristics in two herds located in the Northern Great Plains, USA. Steer calves from predominantly Angus x Hereford dams were stratified within damage and calving date (Fort Keogh Livestock and Range Research Laboratory (LARRL), Miles City, MT, USA; n=354)and randomly assigned to one of three weaning treatments. In addition, steer calves from Angus and Angus x Simmental dams (n=200; Judith Gap (JG), MT, USA) were stratified within breed group by age, calving date, and AI sire. Steer calves either remained with their dams until normal weaning (NW) at approximately 213-d of age or were early weaned at approximately 80-d of age on to one of two early weaning (EW) diets. Steer calves assigned to EW treatments received one of the following diets: (1)17.5% CP (69% RDP and 7.53 MJ/kg NEm); or (2)17.5% CP (57% RDP and 7.69MJ/kg NEm). At time of normal weaning all LARRL steers were gathered and brought into pens at LARRL and held for 22 (2005) or 28-d (2006) before being sold to a commercial feedlot. Sire-identified steers from JG were sent to the University of Illinois for a finishing trial following a 28-d holding period. Steers that were EW were heavier (PPP=0.79) regardless of weaning treatment whereas sire-identified JG steers that received EW treatment were harvested at a younger age (PP=0.05; upper 2/3 choice or better) than NW treated steers (

Estrus synchronization of replacement beef heifers by using GnRH, prostaglandin F2α (PGF), and progesterone (CIDR): a multi-location study

Our objectives were to determine whether a fixed-timed artificial insemination (TAI) protocol could yield similar fertility rates to a protocol requiring detection of estrus and whether an injection of gonadotropin hormone-releasing hormone (GnRH) at CIDR (vaginal insert containing progesterone) insertion enhances pregnancy rates. Replacement beef heifers (n=2,077) from 12 locations were assigned randomly to each of four estrussynchronization protocols. All heifers received a CIDR for 7 days, and an injection of prostaglandin F2α (PGF) on the day of CIDR removal. For treatment EAI, heifers were observed for estrus for 84 hours after PGF administration and were inseminated 6 to 12 hours after observed estrus. Any heifer not detected in estrus was injected with GnRH, followed by TAI. For treatment GnRH+EAI, heifers were treated as those for EAI, but also received GnRH at the time of CIDR insertion. For treatment TAI, heifers received a single TAI at 60 hours after PGF administration. For treatment GnRH+TAI, heifers were treated as those for TAI, but also received GnRH at CIDR insertion. The percentage of heifers cycling at the initiation of estrus-synchronization was 91%; the percentage of cycling heifers among locations ranged from 78 to 100%. Overall pregnancy rates among locations ranged from 38 to 74%. Pregnancy rates were 57.3, 54.5, 53.1, and 49.1% for GnRH+EAI, EAI, GnRH+TAI, and TAI, respectively. Although no statistically significant differences in pregnancy rates among treatments were observed, the GnRH+EAI treatment achieved the numerically greatest pregnancy rates. In addition, the GnRH+TAI protocol provides an alternative that allows producers to synchronize heifers without detection of estrus