Calving Distribution Research Articles

134 A 12-year summary of effects of body weight at breeding and synchronization protocols on reproductive success of Bos indicus-influenced beef heifers grazing warm-season grasses

Abstract A retrospective analysis of 5 studies (2011 to 2022) evaluated the effects of body weight and synchronization protocols before the start of breeding season on reproduction of Bos indicus-influenced beef heifers. Data were collected from 594 Brangus crossbred heifers weaned on average at 280 ± 26 d of age, allocated to bahiagrass pastures (4 to 5 heifers and 0.8 to 1.0 ha/pasture), and supplemented with soybean hulls-based concentrate (0.5 to 1.8% of body weight, (BW); dry matter basis] from 2 weeks post-weaning until the end of the breeding season (189 ± 24 days of supplementation). Heifers were initially sorted into those that were supplement (S) and were not supplemented (NS) assigned to an estrous synchronization protocol before the start of the breeding season. Then, within each synchronization group, heifers were sorted into those that were below (BE) or above (AB) the average BW of all heifers (300 kg) at the start of the breeding season (n = 130, 126, 146, and 192 for BE+NS, BE+S, AB+NS, and AB+S heifers, respectively). Data were analyzed using GLIMMIX procedure of SAS using synchronization, BW at breeding, and resulting interaction as fixed effects, and heifer (synchronization × BW), study, and pasture(study) as random effects. Effects of synchronization × BW at breeding and synchronization were not detected for heifer BW and overall average daily gain (ADG). However, AB heifers were always (P < 0.0001) heavier from post-weaning until the end of the breeding season and had (P < 0.0001) greater overall ADG than BE heifers. Effects of synchronization × BW at breeding tended (P = 0.07) to detected for puberty attainment at the start of the breeding season, which was least (P < 0.01) for BE+NS, did not differ between BE+S vs. AB+NS (P = 0.37), and was greatest for AB+S heifers (31, 66, 60, and 81 ± 7.4%, respectively). However, final pregnancy and calving percentages differed (P < 0.01) only for BE vs. AB heifers (68 vs. 81 ± 4.4% and 63 vs. 75 ± 5.2%, respectively). Effects of synchronization × BW at breeding tended (P = 0.10) to detected for percent of heifers calving within the first 30 days of the calving season, which was least (P < 0.03) for BE+NS and did not differ (P = 0.20) among BE+S, AB+NS, and AB+S heifers (48, 69, 61, and 64 ± 5.9%, respectively). Hence, in Bos indicus-influenced beef heifers, BW above 300 kg at the start of the breeding season led to improved overall reproductive performance compared to BW < 300 kg, whereas estrous synchronization protocols had positive effects to puberty attainment (regardless of heifer BW) and improved early calving distribution only when heifers were below 300 kg at the start of the breeding season.

Several aspects of the cows viability in the Amur region

The influence of intensive breeding of Australian Holstein heifers on their future viability and productivity in the dairy farm OAO "Zarya" (Khabarovsk region) is showed as an example. The researches determined, that the overweights of twenty-four-hours up to 400 g is the main cause of late coupling of heifers. From 3416 individuals 40,2 % had calvings in the age after 30 months. And what is more, the researches exposed the pronounced seasonal prevalence of calvings and the hightened meetings of cows with longevity (27) in the group of animals of born seasons and first calving "autumn-autumn", while there were no individuals elder than 4 calvings from 69 cows in the seasons "summer-summer". In practice, more attention should be paid to an even distribution of calvings throughout the year. It is advisable for owners of small dairy cattle farms to postpone summer calving to the autumn-winter season, which will significantly increase the economic efficiency of the farm.

The female to male calf sex ratio is associated with the number of services to achieve a calf and parity of lactating dairy cows.

Commercial dairy producers may get frustrated by the lower ratio of female to male calves born because female calves are more valuable than bull calves. Our objective was to determine if parity or stage of lactation at the time of breeding, using conventional semen, influenced the sex of the calf. Data from the University of Illinois and the University of New Hampshire dairy herds were collected and summarized for calf sex, the number of services to achieve a calf and the lactation number when conception of that calf occurred. Logistical regression procedures were used to analyze the dataset via version 9.4 of SAS. The final dataset contained 2,987 calvings, which consisted of 1,406 females and 1,581 males (47.1% and 52.9% for females and males, respectively). The frequency distribution of the number of services to achieve a calf was highest for the first service and progressively declined with increasing services (52.06%, 21.66%, 10.75%, 6.66%, 4.22%, and 4.65% for 1 to 6 services, respectively). The frequency distribution of calvings by lactation number was greatest for first lactation cows becoming pregnant with their second calf and declined with increasing parity (35.49%, 28.22%, 17.01%, 9.61%, 5.02%, 2.51%, 1.14%, 0.70%, and 0.30% for lactation numbers 1 to 9, respectively). Logistic stepwise regression indicated that the number of services to achieve a calf was significant in predicting the ratio of female to male calves. Calculation of odds ratios indicated that as the lactation number increased the likelihood of getting a bull calf decreased. Parity, services, and parity by services interaction were significant for cows having a greater number of parities and cows with a greater number of services yielding more heifer calves. However, an interaction occurred where cows with greater number of services along with greater parities more likely to have a bull calf. These data provide evidence that increasing the number of services to achieve a calf and increasing age of the cow increased the probability of a heifer calf being born. These data indicate that cows with greater parties (lesser cull rate) are more likely to produce heifer calves.

8 Efficacy of Sequential Estrus Synchronization and Timed Artificial Insemination Protocols in Beef Cattle

Abstract The objective of this study was to assess the efficacy of sequential estrous synchronization and timed artificial insemination (TAI) in beef cattle using transrectal ultrasonography (US) for pregnancy diagnosis 26d after the initial TAI (TAI-1;d0) to determine pregnancy status and eligibility for the second TAI (TAI-2) on d 29. Angus and angus cross primiparous and multiparous cows were randomly assigned to one of two treatment regimens; either single TAI (CON; n = 468) or two sequential TAI (RS; n = 473). Estrus was synchronized for both treatment groups using the 7-day CO-synch + CIDR protocol forTAI-1 at 60h - 66h post- Prostaglandin injection (PGf2α). A second 7-day CO-synch + CIDR protocol was initiated for RS groups on d 19 and pregnancy status determined by US coincident with CIDR removal on d 26 post TAI-1. Non-pregnant RS cows received an injection of PGf2α and Estrotect® estrous detection aid was applied. All non-pregnant cows received a second TAI (TAI-2) and GnRH injection 60-66h after PGf2α (day 29). The probability of pregnancy at 30d post TAI-2 was higher (P < 0.01) for RS (82%) than CON cows (56%). Overall pregnancy rate on d 120 post TAI-1 did not differ between treatments (92%; P < 0.823). The probability of pregnancy to AI on d 120 was higher (P < 0.0001) for RS (78%) than CON cows (50%). Conversely, the probability of pregnancy sired by natural service was higher (P < 0.03) for CON (41%) than RS (15%) by design. Mean fetal age at 120d pregnancy diagnosis did not differ (P < 0.5547) between treatments (RS, 94 days; CON ,96 days). In conclusion, re-synchronization for a second TAI beginning 19 d after the initial TAI increased total AI-sired pregnancies and has the potential to reduce the required number of natural service sires without negatively influencing calving distribution.

Analysis of the USDA’s 2017 Cow-Calf Management Practices Results: Part 1—Calf Crop and Calving Distribution

This publication analyzes the calf-crop and calving distribution data reported on NAHMS Beef 1997 and provides insights and practical recommendations. Written by Angela Gonella, Oscar Alejandro Ojeda-Rojas, João Bittar, and Mario Binelli, and published by the UF/IFAS Department of Animal Sciences, November 2021.

Pathogenic Leptospira spp. Seroprevalence and Herd-Level Risk Factors Associated with Chilean Dairy Cattle.

Simple SummaryLeptospirosis is a ubiquitous distributed infectious disease present in wild and domestic animals that can be transmitted to humans. This study aimed to estimate the burden of the bacteria in dairy cows from southern Chile and identify the factors associated with the herd-level status. We studied 147 herds and 4876 lactating cows from the area, and an infected herd was defined when at least one serologically positive reactor to MAT was detected. An epidemiological survey was applied to the herd’s owner. The estimated overall individual prevalence was 5.3% (95% CI 2.9–7.7), the overall herd-level prevalence was 42.2% (95% CI 34.2–50.2), and there was variation in both between different herd sizes. L. borgpetersenii serovars Hardjo and Tarassovi and L. interrogans serovar Pomona were the more frequent serovars in Leptospira non-vaccinated herds. Attenuated Leptospira vaccine usage was assessed as a factor that decreases the risk of a farm being infected (OR = 0.04; 95% CI = 0.02–0.11), and variables that increase that risk were using bulls for mating (OR = 3.43; (95% CI = 1.1–10.1) and continuous calving distribution (OR = 3.4; 95% CI = 1.3–8.8). The results from this study will contribute to unravelling the infection burden in the main dairy area of the country and designing control strategies.Leptospirosis is a ubiquitous distributed zoonotic infectious disease present in wild and domestic animals. This study aimed to estimate within-herd and herd-level seroprevalence against pathogenic Leptospira spp. in dairy cows from southern Chile and identify risk factors associated with the herd-level status. We used a multi-stage strategy combined with a stratified sample strategy for randomly sampling 147 herds and 4876 lactating cows. We considered as infected a herd with at least one positive reactor to MAT. In addition, an epidemiological survey was applied to the herd’s owners and a logistic regression (LR) model was constructed to analyze it. The overall within-herd prevalence was 5.9% (95% CI 4.9–6.8), the overall herd-level prevalence was 42.2% (95% CI 9.2–47.9), and there was variation in both between different herd sizes. L. borgpetersenii serovars Hardjo and Tarassovi and L. interrogans serovar Pomona were the more frequent serovars in non-vaccinated herds. A factor that decreases the risk of a farm being infected was Leptospira vaccine usage (OR = 0.04; 95% CI = 0.02–0.11), and variables that increase risk were using bulls for mating (OR = 3.43; 95% CI = 1.1–10.1) and continuous calving distribution (OR = 3.4; 95% CI = 1.3–8.8). The study’s results will contribute to unravelling the infection burden in the main dairy area of the country and designing control strategies.

BEEF SPECIES-RUMINANT NUTRITION CACTUS BEEF SYMPOSIUM: Maternal immune modulation prior to embryo arrival in the uterus is important for establishment of pregnancy in cattle1.

In 1953, Sir Peter Medawar first recognized the allogeneic properties of a developing conceptus and rationalized that an "immune-tolerant" physiological state must exist during pregnancy. Early theories speculated that the conceptus evaded the maternal immune system completely, but 40 yr after Medawar's observations, Wegmann proposed that the maternal immune system shifts the cytokine profile away from inflammatory cytokine production when an embryo is present. The economic consequences and production losses of subfertile animals have been well documented in studies evaluating calving distribution. Despite advances in understanding infertility or subfertility, few technologies exist to identify subfertile animals or improve fertility beyond hormonal intervention associated with synchronization protocols. Work in rodents and some livestock species indicates that the uterine immune cell population shifts dramatically after copulation and these early immune-modulated events establish a receptive uterine environment. Clearly, as evident in embryo transfer, the presence of a conceptus is sufficient to establish communication for pregnancy establishment but does not rule out the importance of other physiological events to prime the maternal immune system prior to blastocyst arrival in the uterus. In support of this concept, work in our laboratory and by others has demonstrated that autologous intrauterine transfer of peripheral immune cells prior to embryo transfer can increase pregnancy rates and accelerate conceptus development in women and cattle. Understanding aberrant immune regulation in subfertile animals may provide markers for subfertility or targets for clinical intervention to enhance fertility, particularly when using reproductive technologies.

Contribuição de fatores não-genéticos para o desempenho reprodutivo de vacas Mirandesa

Conhecer as características reprodutivas da raça bovina Mirandesa é fundamental para o melhoramento e conservação desta raça de carne, sobretudo pela sua baixa diversidade genética. A depressão por consanguinidade acompanha-se frequentemente de desempenhos individuais e maternais mais fracos, que podem agravar os efeitos ambientais. Neste trabalho utilizaram-se 7386 registos do Livro Genealógico para caracterizar alguns indicadores reprodutivos: a idade ao primeiro parto (AFC), a duração da gestação (PL), o intervalo entre partos (CI), a distribuição partos no ano (CD) e a longevidade produtiva (PLf). Testaram-se ainda efeitos não genéticos na sua expressão, através de métodos não-paramétricos, por não estarem cumpridos os pressupostos de normalidade. A mediana para a AFC aproximou-se dos 32 meses, variando com o sistema de produção, a exploração, e o ano e estação de nascimento. A média de PL (287±8.9 dias) foi afetada pela paridade e sexo da cria. A mediana do CI foi de 378 dias, e variou apenas com o programa de reprodução, paridade, ano e estação. Os partos, irregularmente distribuídos ao longo do ano, mostraram padrões distintos segundo o sistema de produção. A longevidade produtiva desta raça foi de 6,45 anos, e 20% da população apresentou uma PLf superior a dez anos. Este trabalho sugere serem a estratégia do agricultor e a nutrição os principais efeitos não genéticos limitando o desempenho reprodutivo nesta raça, a considerar para aumentar o número de vitelos produzidos anualmente em paralelo com uma cuidada seleção de reprodutores para reduzir o inbreeding da raça.

Estrus synchronization and fixed-time artificial insemination alter calving distribution in Bos indicus influenced beef heifers

To determine the effects of estrus synchronization (ES) and fixed-time artificial insemination (TAI) on calving distribution in Bos indicus influenced heifers, 751 Bos taurus × Bos indicus beef heifers were enrolled in a completely randomized design at 2 locations from January to May of 2016. Within location, all heifers were randomly assigned to one of two treatments: 1) SYNCH (n = 371); heifers were exposed to the 5-day CO-Synch + CIDR protocol where they were treated with 100 μg of GnRH, 25 mg of PGF2α, and a controlled internal drug releasing insert (CIDR) on d 0; heifers received 50 mg of PGF2α at CIDR removal on d 5, and were treated with 100 μg of GnRH and TAI 66 ± 2 h later on d 8; or 2) CONTROL (n = 380); heifers were exposed to natural service without ES or TAI. On d 9, all heifers were exposed to bulls for the remainder of the breeding season at each location. Blood samples were collected on d −9 and on d 0 to determine pretreatment estrous cyclicity (progesterone ≥ 1.0 ng/mL). Pregnancy was diagnosed via transrectal ultrasonography 54 d after TAI by determining the presence of a viable fetus. Fetal age was estimated based on fetal size and structural features at the time of pregnancy diagnosis. Pregnancy rates on d 54 differed (P < 0.001) between locations, but did not differ (P = 0.777) between CONTROL and SYNCH treatments. Pregnancy rates on d 54 were greater (P < 0.001) in cycling compared with non-cycling heifers (63.9 vs 42.4%). A greater (P < 0.05) proportion of SYNCH heifers became pregnant in the first 19 d of the breeding season compared with CONTROL heifers (52.2 vs 46.4%). Overall breeding season pregnancy rates did not differ (P = 0.982) between treatments. In summary, ES and TAI increased the percentage of heifers that conceived in the first 19 d of the breeding season, and therefore, potentially altered the calving distribution by ensuring that more heifers calve early during the subsequent calving season.

510 Impact of estrus synchronization and fixed-time artificial insemination on calving distribution in Bos indicus influenced beef heifers

To determine the effects of estrus synchronization (ES) and fixed-time artificial insemination (TAI) on calving distribution in Bos indicus influenced heifers, 751 Bos taurus × Bos indicus beef heifers were enrolled in a complete randomized design at 2 locations from January to May of 2016. Within location, all heifers were randomly assigned to one of two treatments: 1) SYNCH (n = 371); heifers were exposed to the 5-day CO-Synch + CIDR protocol where they received a 100-µg injection of GnRH (Factrel; gonadorelin hydrochloride; Zoetis Animal Health), 25 mg of PGF2α (Lutalyse; dinoprost tromethamine; Zoetis Animal Health), and a controlled internal drug releasing (EAZI-BREED CIDR; 1.38 g of progesterone; Zoetis Animal Health) insert on d 0, heifers received 50 mg of PGF2α (Lutalyse; dinoprost tromethamine; Zoetis Animal Health) at CIDR removal on d 5, followed by a 100-µg injection of GnRH and TAI 66 ± 2 h later on d 8; or 2) CONTROL (n = 380); heifers were exposed to natural service without any ES or TAI. On d 9, all heifers were exposed to bulls for the remainder of the breeding season at each location. Blood samples were collected on d -9 and on d 0 to determine pretreatment estrous cyclicity (progesterone ≥ 1.0 ng/mL). Pregnancy was diagnosed via transrectal ultrasonography 54 d after TAI by determining the presence of a viable fetus. Fetal age was estimated based on fetal size and structural features at the time of pregnancy diagnosis. Pregnancy rates on d 54 differed (P < 0.001) between locations, but did not differ (P = 0.777) between CONTROL and SYNCH treatments (64.5 vs 65.7%, respectively). Pregnancy rates were greater (P < 0.001) in cycling compared with non-cycling heifers (63.9 vs 42.4%). A greater (P < 0.01) proportion of SYNCH heifers became pregnant in the first 21 d of the breeding season compared with CONTROL heifers (52.2 vs 46.4%). Overall breeding season pregnancy rates did not differ (P = 0.982) between treatments. In summary, ES and TAI increased the percentage of heifers that conceived in the first 21 d of the breeding season, and therefore, potentially altered the calving distribution by ensuring that more heifers calve early during the subsequent calving season.

An economic evaluation of estrous synchronization and timed artificial insemination in suckled beef cows1

Partial budget analysis was used to determine the economic outcome of estrus synchronization (ES) and timed artificial insemination (TAI) in commercial cow-calf production. Suckled beef cows (n = 1,197) from 8 locations were assigned randomly within each location to 1 of 2 treatment groups: 1) cows were inseminated artificially after synchronization of ovulation using the CO-Synch + CIDR protocol, which includes a 100-μg injection of GnRH (OvaCyst; TevaAnimal Health, St. Joseph, MO) when a controlled internal drug-releasing device (CIDR; Pfizer Animal Health, New York, NY) containing 1.38 g of progesterone was inserted. The CIDR was removed 7 d later, and cows received a 25-mg injection of PGF(2α) (PGF; Lutalyse; Pfizer Animal Health), followed in 66 h with TAI and a second 100-μg injection of GnRH (TAI; n = 582), and 2) cows were exposed to natural service (NS) without estrous synchronization (Control; n = 615). Within each herd, cows from both treatments were maintained together in similar pastures and were exposed to bulls 12 h after the last cow in the TAI treatment was inseminated. Overall, the percentage of cows exposed to treatments that subsequently weaned a calf was greater (P < 0.05) for TAI (84%) than Control (78%) cows. In addition, survival analysis demonstrated that cumulative calving distribution differed (P < 0.05) between the TAI and Control treatments. Weaning weights per cow exposed to treatments were greater (P < 0.01) for cows in the TAI treatment (193.4 ± 4.3 kg) than those cows in the Control treatment (175.9 ± 4.3 kg). Overall, increased returns plus decreased costs ($82.32) minus decreased returns plus increased costs ($33.18) resulted in a $49.14 advantage per exposed cow in the TAI treatment compared with the Control treatment. Location greatly influenced weaned calf weights, which may have been a result of differing management, nutrition, genetic selection, production goals, and environments. We concluded that ES and TAI had a positive economic impact on subsequent weaning weights of exposed cows.

Effects of prepartum and postpartum bolus injections of trace minerals on performance of beef cows and calves grazing native range12

ABSTRACT Our objective was to evaluate the effects of pre- and postpartum bolus injections of a trace mineral solution on reproductive performance, BW change, and BCS change of beef cows and on growth of suckling calves. Mature beef cows (n = 460; initial BW = 497 ± 89 kg, initial BCS = 5.4 ± 0.74) managed in 2 locations were stratified by BCS, age, parity, and predicted calving date and assigned randomly to 1 of 2 treatments: 1) supplemental s.c. trace-mineral (TM) injection containing 15 mg/mL Cu, 5 mg/mL Se, 10 mg/mL Mn, and 60 mg/mL Zn or 2) s.c. injection of physiological saline (SA). Injections were administered to cows (1 mL/90 kg of BW) 105 d before the first projected calving date and again 30 d before fixed-time AI. Calves received the same treatment as their dams and were injected (1 mL/45 kg of BW) at birth and again at 71 ± 21 d of age. Cows grazed native pastures for the duration of the study; trace-mineral supplements and white salt were available to all cattle ad libitum before and during the study. Ovulation was synchronized using a 5-d CO-Synch + CIDR protocol, and cows were inseminated 72 h after CIDR removal. Cows were exposed to fertile bulls for natural-service breeding 10 d after AI for 50 d. Conception to AI and final pregnancy rate were assessed 36 d after AI via ultrasound and 120 d after AI via rectal palpation, respectively. Change in BW and BCS from initiation of the study to calving and from AI to weaning did not differ (P ≥ 0.15) between TM and SA cows. Conversely, TM cows had greater (P = 0.04) BCS increase than did SA cows between calving and AI. Calf BW at birth, ADG, and age-adjusted weaning BW did not differ (P ≥ 0.36) between treatments. Proportion of cows with estrous cycles 17 and 8 d before fixed-time AI was similar (P ≥ 0.51) between treatments. In contrast, conception to fixed-time AI was greater (P = 0.05) for cows receiving TM (60.2%) than for cows receiving SA (51.2%). Final pregnancy rate did not differ (P = 0.24) between treatments and averaged 92%; however, calving distribution by TM-treated cows was more favorable (P = 0.01; i.e., calving was generally earlier) than calving distribution of SA-treated cows. Under the conditions of this study, pre- and postpartum trace-mineral injections improved conception to fixed-time AI and subsequent calving distribution of beef cows.

Evaluation of human chorionic gonadotropin as a replacement for gonadotropin-releasing hormone in ovulation-synchronization protocols before fixed timed artificial insemination in beef cattle1

Two experiments were conducted during 2 yr to evaluate differences in ovulation potential and fertility in response to GnRH or hCG. In Exp. 1, 46 beef cows were given 100 microg of GnRH or 500, 1,000, 2,000, or 3,000 IU of hCG. Ovulation incidence was not different between GnRH and any of the hCG doses, indicating that ovulatory capacity of at least 500 IU of hCG was equivalent to GnRH. In Exp. 2, beef cows (n = 676) at 6 locations were assigned randomly to a 2 x 3 factorial arrangement of treatments. Main effects were: 1) pre-timed AI (TAI) treatment (GnRH or hCG) and 2) post-TAI treatment (saline, GnRH, or hCG) to initiate resynchronization of ovulation in previously inseminated cattle. Blood samples were collected (d -21 and -10) to determine progesterone concentrations and assess cyclicity. Cattle were treated with a progesterone insert on d -10 and with 100 microg of GnRH or 1,000 IU of hCG. A PGF(2alpha) injection was given at insert removal on d -3. Cows were inseminated 62 h (d 0) after insert removal. On d 26 after first TAI, cows of unknown pregnancy status were treated with saline, GnRH, or hCG to initiate a CO-Synch protocol. Pregnancy was diagnosed 33 d after first TAI to determine pregnancies per AI (P/AI). Nonpregnant cows at 6 locations in yr 1 and 1 location in yr 2 were given PGF(2alpha) and inseminated 56 h later, concurrent with a GnRH injection. Five weeks later, pregnancy diagnosis was conducted to determine pregnancy loss after first TAI and pregnancy outcome of the second TAI. Injection of pre-TAI hCG reduced (P < 0.001) P/AI compared with GnRH, with a greater reduction in cycling cows. Post-TAI treatments had no negative effect on P/AI resulting from the first TAI. Serum progesterone was greater (P = 0.06) 7 d after pre-TAI hCG than after GnRH and greater (P < 0.05) after post-TAI hCG on d 26 compared with saline 7 d after treatment in association with greater frequency of multiple corpora lutea. Compared with saline, injections of post-TAI GnRH and hCG did not increase second insemination P/AI, and inconsistent results were detected among locations. Use of hCG in lieu of GnRH is contraindicated in a CO-Synch + progesterone insert protocol. Compared with a breeding season having only 1 TAI and longer exposure to cleanup bulls, total breeding season pregnancy rate was reduced by one-third, subsequent calving distribution was altered, and 50% more AI-sired calves were obtained by applying 2 TAI during the breeding season.

Modelling the reproductive efficiency in a beef cow herd: effect of calving date, bull exposure and body condition at calving on the calving–conception interval and calving distribution

SUMMARYA model of reproductive performance was developed to study the influences of breeding management decisions and animal characteristics on the reproductive performance and the calving distribution in a beef herd. In the model, reproductive performance is formalized as a sequence of events (parturition, ovulation, conception), each of which modifies the reproductive status of the simulated cow. With respect to reproduction, a cow can be in one of three possible states: open-not-cycling, open-cycling or pregnant. The length of the different intervals that are included between two successive reproductive events (calving to first cycle interval, length of oestrous cycles, calving–conception and calving intervals) is formalized using stochastic or empirical laws that may be influenced by numerous animal or environmental factors or by management decisions (feeding strategy, breeding season and length of the breeding period). Within the herd, cows are considered to differ from each other by their parity, calving date, body condition at calving and their bull exposure.Calving to first oestrous interval (postpartum anoestrous interval (PPAI)) is expressed as the sum of three equations which formalize the respective effects of calving date, body condition score at calving (BCScalving) and the response to early bull exposure in interaction with BCScalving. The influences of these variables on reproductive performance were quantified by analysing data sets (three bibliographical and two experimental) or by expertise. Special attention was paid to the influence of calving date on PPAI and a biological interpretation of this effect is proposed. Probabilities of natural insemination success were estimated according to the number of oestrus and the number of matings.The model was fitted to data from primiparous Charolais cows (n=139) bred at the experimental station Laqueuille (French National Institute for Agricultural Research (INRA)). Its ability to simulate PPAI was tested using an independent data set of primiparous Charolais cows (n=188) from the experimental farm Le Pin. The model only accounts for 39% of the observed inter-individual variability. However, the analysis of the mean square deviation components led to validation of the structure of the model. In particular, the assumption that the influence of calving date on PPAI can be attributed to a sensitivity of the reproductive function to the variation of the photoperiod during the month preceding parturition was confirmed. Simulations also revealed that fat cows could have similar anoestrus to thin cows when they are exposed early to a bull. Such a result emphasized the necessity to investigate further and better calibrate the combined effects of BCS at calving and bull exposure on PPAI.

Influence of a CIDR prior to bull breeding on pregnancy rates and subsequent calving distribution

We determined whether insertion of a CIDR for 7 days prior to the breeding season enhanced pregnancy rates and altered the date of conception in suckled beef cows mated naturally. Suckled beef cows ( n = 2033) from 15 locations were randomly assigned to one of two treatments: (1) cows received a CIDR 7 days prior to the breeding season for 7 days (CIDR; n = 999); (2) cows received no treatment (Control; n = 1034). On the first day of the breeding season bulls were introduced to herds at a rate of 15–25 cows per yearling bull or 20–30 cows per mature bull. Pregnancy status and the date of conception were determined via transrectal ultrasonography at 56 and 120 days after initiation of the breeding season. Overall pregnancy rates ranged from 59.3 to 98.9% among the 15 locations. The percentage of cows becoming pregnant during the first 30 days of the breeding season was similar between CIDR (68.2%) and Control (66.7%) cows, and overall pregnancy rates were similar between CIDR (88.9%) and Control (88.6%) cows. The average day of conception after initiation of the breeding season was shorter ( P < 0.01) for CIDR (20.1 ± 0.8 days) compared to Control cows (23.2 ± 0.8 days). Of cows conceiving during the breeding season, more ( P < 0.05) CIDR cows (35.9%) conceived during the first 10 days of the breeding season than Control cows (30.8%). Neither body condition score and nor parity affected pregnancy rates or days to conception, whereas pregnancy rates and days to conception were affected ( P < 0.01) by location and days postpartum. Days to conception were greater for cows that calved within 40 days (31.6 ± 1.2 days) of initiation of the breeding season compared to cows calving between 40 and 50 days (25.3 ± 1.2 days) prior to initiation of the breeding season, which were greater than those cows calving between 50–60 days (20.0 ± 0.8 days) and 60–70 days (21.3 ± 1.0 days) prior to initiation of the breeding season. Cows calving greater than 70 days (17.3 ± 1.5 days) from initiation of the breeding season had the shortest interval to conception. We concluded that insertion of a CIDR prior to the breeding season failed to increase overall pregnancy rates, but did influence the average day of conception.

Non-genetic factors affecting calving interval and weaning weight in a buffalo herd located in flooded savannas,Cojedes state, Venezuela

The objective of the research work was to characterize a buffalo herd in flooded conditions in Cojedes state, Venezuela, being evaluated the calving distribution (CD), calving interval (CI) and weaning weight (WW). Birth and productive records from Hato La Soledad were used to determine monthly frequencies of calving (n=2106), calving interval (n=936) and weaning weight (n=1683). The statistical analysis included year (CY) and calving season (CS), sex of calf (SC), age of cow (AC) and interactions for CI, including additionally age to weaning for WW. Results showed significant differences (P≤0.05) in CD between years associated with year-on-year changes in climatic factors and progressive stabilization of the herd. CI averaged 473.9±3.0 days ( X – ± S.E.), with a significant effect of calving month (P≤0.05). CI in the herd showed an elevated percentage (75.6%) of buffalo cows with CI lower than 400 days. The effect of age at calving was not significant doubt to the fact that the herd was young. WW averaged 130.4±1.9 kg with age to weaning of 238.7±3.2 days, with significant effect of year and calving month, and age to weaning, with a daily gain of 128 g. The results showed the productive and reproductive potential of the buffalo in tropical conditions.

An evaluation of the use of synchrony technology in beef breeding herds

AbstractA model which was originally developed to derive the probability density of a calving distribution for beef cows under natural breeding has been modified to incorporate the effects of using oestrous synchronization at the beginning of the breeding period.The model has been used to investigate five oestrous synchronization strategies over four herds, each with differing calving patterns: no synchronization; every cow in the herd is synchronized; every anoestrous cow is synchronized; every cow calving more than 20 days after the date of the planned start of calving is synchronized; every cow calving 30 days after the date of the planned start of calving is synchronized. Two of the herds previously had long calving periods and two previously had short, compact calving periods.Model results showed that synchronization improved average herd calf live weight by 21 kg in the two herds with long prior calving periods but showed little effect in the two herds with compact prior calving periods. Synchronizing cows which calved more than 20 days after the start of calving in the herd showed similar results to synchronizing every cow in the herd and thus would be more cost effective. Synchronizing cows which calved more than 30 days after the start of calving in the herd showed a smaller advantage but only in the herds with long prior calving periods. The optimal strategy for oestrous synchronization in a herd will depend on the prior calving distribution and the average duration ofanoestrus in that herd as well as the relative costs of the treatment.

Use of a stochastic model of a calving distribution for beef cows for formulating optimal natural mating strategies

AbstractA model of a birthdate distribution for a herd of beef cows is constructed using the probability distributions of the variables that affect reproduction in the cow — anoestrous interval, oestrous cycle length, conception to each oestrus, gestation length, period of mating and the prior calving frequency distribution. The model is general and can be reparamaterized to deal with issues such as intervention to synchronize oestrous cycles among cows in the herd by changing the form of the relevant probability distributions.The model is applied to the question of what time to begin mating in a herd of beef cows. The average calf live weight at day 200, herd conception rate and proportion of cows calving before the planned start of calving were calculated from the model output. The model parameters given by the anoestrous period, conception rate to each oestrus and the regression between prior calving date and anoestrous period, were varied in a factorial design to investigate a range of circumstances found on a farm. Prior calving distributions were generated by random sampling from eight actual calving frequency distributions.Generally starling mating earlier produced an advantage in terms of extra calf live weight and herd conception rate. However, the proportion of the herd calving earlier than expected increased with early mating. Thus, the feasibility of early mating depends on the cost to the farmer of dealing with early calving cows as well as the advantage of heavier older calves.Altering the fixed parameters in the model (variances and covariances, prior calving distributions, mating period) to accommodate the circumstances of herds run under different conditions may produce different results. Model structure allows easy alteration of these parameters and also the introduction of different probability distributions for some variables. This might be necessary to model oestrous synchronization and artificial insemination, issues not considered in this paper.

Economic values for reproduction traits in beef suckler herds based on a calving distribution model

Economic values for the genetic improvement of gestation length, post partum anoestrus interval, conception rates at first or later post partum oestrus and calving day (relative to the first day of the calving season) in seasonal calving beef suckler herds were estimated. The approach used combines partial budgeting of the economic cost of a barren cow with a model of the herd calving distribution which is driven by assumed levels of reproductive parameters. Economic values for all traits were shown to be highly variable across farms and are also likely to vary across years. For an increase in gestation length and equivalently in post partum anoestrus interval, estimates of economic values ranged between −0.2 and −2.77 £/day with higher values apparent in herds with a wide calving spread. Economic values for conception rates were higher at later (0.25 to 1.28 £ per % increase) than at first (0.1 to 0.7 £ per % increase) post partum oestruses. For calving day, economic values were approximately half of those derived using an alternative method from the literature which assumes calving day to be normally distributed. Implications for establishing selection criteria to choose terminal beef sires and suckler beef cows are discussed.

Aspects of heifer management which limit productivity on dairy farms in Western Australia: a survey

In 1989, a survey of 53 producers from the major dairy areas of the south-west of Western Australia was conducted to determine current management practices for dairy heifers and to identify of areas of heifer management which could be improved to increase overall farm productivity. Total farm size averaged 220 ha, with an average market milk quota of 699 L/day (50% of total milk produced). One-third of producers described their farm activity as dairying only. Some 116 calves were born per farm, with a year-round calving distribution. Calves were fed 5.4 L whole milk/day, with an average age at weaning of 13 weeks (range 5-26 weeks). Mortality recorded to 3 months of age was 4% and the most important health problem associated with calf rearing was scours. Of those properties with a health problem, 25% used antibiotics on a regular basis. All producers provided supplementary feed pre-weaning. In the period between weaning and mating, more than half the producers ran heifers on paddocks 3-80 km distant from the main farm, with hay the most common form of supplementary feed. Most dairy heifers were naturally mated to Hereford, Friesian, or Angus sires; hence, few heifers from first calvers were kept as dairy replacements. Average age at first calving was reported to be 30 months, with 1 in 9 heifers culled post-calving, generally for low milk production. The survey highlighted several aspects of heifer management with the potential to improve overall productivity of dairy farms in Western Australia. They include earlier weaning, strategic use of antibiotics to prevent the development of antibiotic resistance, greater use of artificial insemination, and a reduction in age at first calving.