A Stochastic Model to Compare Breeding System Costs for Synchronization of Estrus and Artificial Insemination to Natural Service
The understanding of the importance of follicular fol·lic·u·lar
1. Relating to, having, or resembling a follicle or follicles.
2. Affecting or growing out of a follicle or follicles. growth for synchronizing synchronizing,
n a technique that a therapist uses to coordinate his or her breath with that of the client; builds trust and establishes relationship. ovulation ovulation /ovu·la·tion/ (ov?u-la´shun) the discharge of a secondary oocyte from a graafian follicle.ov´ulatory
The discharge of an ovum from the ovary. with subsequent high fertility has increased the number of options available to producers for fixed-time AI and synchronization (1) See synchronous and synchronous transmission.
(2) Ensuring that two sets of data are always the same. See data synchronization.
(3) Keeping time-of-day clocks in two devices set to the same time. See NTP. of estrus estrus
Period in the sexual cycle of female mammals, except the higher primates, during which they are in heat (ready to accept a male for mating). Some animals (e.g., dogs) have only one heat during a breeding season; others (e.g. . Low-cost production, the ability to produce a higher valued product, or both are essential for economic success in the cow-calf industry. Previous research has examined the costs of various AI breeding systems and some have compared those costs to natural-service options (Loseke, 1989; Miller et al., 2004; Johnson and Jones, 2005). If only the cost per pregnancy is considered, few AI systems consistently compete well with natural service. This may explain why only a small percentage of producers in the United States United States, officially United States of America, republic (2005 est. pop. 295,734,000), 3,539,227 sq mi (9,166,598 sq km), North America. The United States is the world's third largest country in population and the fourth largest country in area. reported using AI (National Animal Health Monitoring System, 1998). An assessment of the economic feasibility of estrus synchronization and AI should incorporate potential returns and account for the random nature of various inputs and economic risk in the decision making process. A stochastic By guesswork; by chance; using or containing random values.
stochastic - probabilistic model was developed to compare costs of several synchronization of estrus and AI systems with natural service and to identify the important factors in determining the differences between costs of breeding systems.
MATERIALS AND METHODS
An abbreviated cow-calf enterprise budget focused on breeding costs was the basis of the model (Johnson and Jones, 2005). Stochastic stimulations were performed using @Risk for Excel (Palisade Corp., Newfield, NY), which is a risk analysis spreadsheet add-in tool that allows the user to model various outcomes based on predefined distributions of input variables.
Breeding herds of 35, 116, and 348 head were examined to allow for culling culling
removal of inferior animals from a group of breeding stock. The removal is premature, i.e. before completion of its life span, disposal of an animal from a herd or other group. of nonpregnant and physically impaired See assistive technology. cows to yield calving calving
act of parturition in a bovine female, and presumably in any animal that bears a calf as its newborn. See also block calving, ease of calving.
calving-to-conception interval herds of 30, 100, and 300 head. The breeding season Breeding season is the most suitable season usually with favorable conditions and abundant food and water when wild animals and birds (wildlife) have naturally evolved to breed to achieve the best reproductive success. consisted of one synchronization and AI period, followed by a natural-service period. The number of cleanup natural-service sires was based on 50% of the breeding herd, and 3 cow-to-bull ratios of 20, 30, and 40 were examined. The number of bulls for natural service after AI reflected an AI pregnancy rate that most studies have met or exceeded (Miller et. al., 2004; for a review see Patterson et. al., 2003, and Johnson, 2005).
The following systems for synchronization of estrus and ovulation were used in the model to represent relatively lower and higher cost protocols: 1) heat detection only systems: a) Select Synch [gonadotropin-releasing hormone gonadotropin-releasing hormone
Abbr. GnRH A hormone produced by the hypothalamus that stimulates the anterior pituitary gland to begin secreting luteinizing hormone and follicle-stimulating hormone. (GnRH) and prostaglandin prostaglandin (prŏs'təglăn`dən), any of a group of about a dozen compounds synthesized from fatty acids in mammals as well as in lower animals. F^sub 2q^ (PG)], b) Select Synch + controlled intervaginal drug release (CIDR (Classless Inter-Domain Routing) An expansion of the IP addressing system that allows for a more efficient and appropriate allocation of addresses. The original class-based method used fixed fields for network IDs, which was wasteful. ; intravaginal progesterone progesterone (prōjĕs`tərōn'), female sex hormone that induces secretory changes in the lining of the uterus essential for successful implantation of a fertilized egg. insert, Pfizer Animal Health, New York New York, state, United States
New York, Middle Atlantic state of the United States. It is bordered by Vermont, Massachusetts, Connecticut, and the Atlantic Ocean (E), New Jersey and Pennsylvania (S), Lakes Erie and Ontario and the Canadian province of , NY), c) melengesterol acetate acetate (ăs`ĭtāt'), one of the most important forms of artificial cellulose-based fibers; the ester of acetic acid. The first patents for the production of fibers from cellulose acetate appeared at the beginning of the 20th cent. (MGA (1) (Monochrome Graphics Adapter) A display adapter that employs Hercules Graphics, combining graphics and text on a monochrome monitor.
(2) (Matrox Graphics Accelerator) A trade name used by Matrox Graphics Inc. ; Pfizer Animal Health) fed for 14 d and PG (MGA-PG); 2) a combination heat detection and cleanup timed AI: a) Select Synch, b) Select Synch + CIDR; and 3) fixed-timed AI: a) CoSynch (GnRH and PG) + CIDR, b) MGA-PG. In combination heat detection and cleanup fixed-time AI systems, insemination insemination /in·sem·i·na·tion/ (-sem?i-na´shun) the deposit of seminal fluid within the vagina or cervix.
artificial insemination (AI) that done by artificial means. was based on observed estrus up to 72 h after PG, and all animals not observed in estrus by that time were fixed-time AI. Fixed-time AI included GnRH at insemination. Each simulation model estimated costs associated with one synchronization and AI breeding system and compared it with the natural-service option.
In all models, calves born as a result of a synchronized syn·chro·nize
v. syn·chro·nized, syn·chro·niz·ing, syn·chro·niz·es
1. To occur at the same time; be simultaneous.
2. To operate in unison.
1. AI program were assumed to be, on average, older and heavier at weaning weaning,
n the period of transition from breast feeding to eating solid foods.
the act of separating the young from the dam that it has been sucking, or receiving a milk diet provided by the dam or from artificial sources. because of synchronization alone, and allowance was made for the possibility that Al-sired calves may be worth more at weaning based on either genetic merit for carcass carcass, carcase
1. the body of an animal killed for meat. The head, the legs below the knees and hocks, the tail, the skin and most of the viscera are removed. The kidneys are left in and in most instances the body is split down the middle through the sternum and the vertebral or maternal traits or preweaning gain. The magnitude of these premiums was allowed to vary with each iteration One repetition of a sequence of instructions or events. For example, in a program loop, one iteration is once through the instructions in the loop. See iterative development.
(programming) iteration - Repetition of a sequence of instructions. of the simulation.
The simulations were driven by the distributions of the random input variables shown in Table 1 and fixed input assumptions in Table 2. With the exception of genetic value, all distributions were assumed to be normal or truncated truncated adjective Shortened normal. Genetic value ($ per head) used a triangle distribution with 3 points: minimum (0), most likely ($5), and maximum ($50).
Simulations were performed for each of the 7 AI systems, 3 herd sizes, and 3 cow-to-bull ratios, for a total of 63 simulations. Each simulation consisted of 100 iterations. Each simulation summarizes the response (the average value and the dispersion around that average) when the input factors were allowed to vary.
The following correlations were imposed on the model to account for the failure of input variables to behave independently: cull cull
the act of culling. Called also cast. value and calf price, 0.70 (calculated from long-term price summaries); semen semen
or seminal fluid
Whitish viscous fluid emitted from the male reproductive tract that contains sperm and liquids (seminal plasma) that help keep them viable. cost and genetic value, 0.25 (calculated from semen prices and birth weight, milk, weaning, and yearling yearling
an animal in its second year of age, e.g. yearling cattle, yearling filly, yearling colt.
rinderpest in wildebeeste in the Serengheti. expected progeny PROGENY - 1961. Report generator for UNIVAX SS90. differences); and season pregnancy rate and percent calf crop, 0.90.
Three output variables were generated in each simulation. The output variable of breeding cost per pregnant female included the costs of synchronization of estrus and one AI and a natural-service cleanup period. The adjusted breeding cost was the breeding system costs per exposed female reduced for any increased revenue (age, weight, or genetic value) from ??-sired calves and expressed as a 227-kg equivalent, weaned-calf, breeding cost per 45.4 kg. The adjusted breeding cost per 45.4 kg for each synchronization system was subtracted from a comparable standardized value Standardized value
Also called the normal deviate, the distance of one data point from the mean, divided by the standard deviation of the distribution. for natural service alone to produce the output variable referred to as Aladvantage. A positive Aladvantage value indicated the AI breeding system had a net economic advantage over a natural-service breeding system. Simulation model results provide the average expected value Expected value
The weighted average of a probability distribution. Also known as the mean value. of the Aladvantage and the percentage of time the value was expected to be positive given the random events considered in the model.
RESULTS AND DISCUSSION
Simulation model output for each breeding system, herd size, and cowto-bull ratio combination are in Table 3 (heat detection only) and Table 4 (combination heat detection and cleanup timed AI and fixed-timed AI). Breeding cost per pregnancy ranged from $46 to $95 and largely reflected the difference in synchronization product inputs. This was expected because the modeled mean pregnancy rate was the same within synchronization system type. The values were significantly higher than those reported by Miller et al. (2004) because they incorporated the costs of the natural-service cleanup sires in addition to the cost of the synchronization protocol. The breeding cost per pregnancy and the adjusted breeding cost are the same for a calving herd size of 30 (35 females exposed for breeding) regardless of the cow-to-bull ratio because they all use one bull for cleanup natural service. The natural service only option used 2 bulls for cow-to-bull ratios of 20 and 30 and 1 for a cow-to-bull ratio of 40, which was reflected in the values for Aladvantage, and the percentage of simulations AI cost less than natural service (same values for cow-to-bull ratios of 20 and 30).
Few simulations incorporating a progesterone insert, regardless of the amount of heat detection, had lower adjusted breeding costs than natural service. The exception was for Select Synch + CIDR, heat detection only for 300 head, and a cow-to-bull ratio of 20, which was projected to have lower costs than natural service 70% of the time. Cost should be an important consideration in the selection of a synchronization protocol; however, factors not included in the model, such as ease of implementation and the proportion of noncycling animals, are important as well.
Synchronization and AI systems that combined both heat detection and cleanup fixed-time AI were least likely to be economically advantageous when compared with natural service (Table 5). Compared with fixed-time AI, synchronization systems based on heat detection alone were more likely to have lower costs than natural service. This difference was less for smaller herd sizes.
As herd size increased, AI was more likely to have lower costs than natural service. Simulations for herd sizes of 300, a cow-to-bull ratio of 20, and synchronization systems not using a progesterone insert had lower costs than natural service more than 83% of the time. The proportion of times AI was lower cost than natural service was less than 5% for herd sizes of 30 and cow-to-bull ratios of 40 regardless of the synchronization system.
Averaged over all simulations, the frequency of lower breeding costs for AI than natural service for cow-to-bull ratios of 20, 30, and 40 was 63, 46, and 14%, respectively. At a cow-to-bull ratio of 40, the average Aladvantage was -$3.66/45.4 kg across all systems and herd sizes, indicating natural service tended to be a lower cost breeding system at higher cow-to-bull ratios. When more bulls were used (lower cow-to-bull ratio) the Aladvantage value became more positive, indicating AI systems were more economically attractive. Averaged across all synchronization systems, AI produced pregnancies for $1.19/45.4 kg less than natural service for a cow-to-bull ratio of 20. Ac- cording to the 1997 National Animal Health Monitoring System survey, the average cow-to-mature bull ratio for herds less than 49 head, 100 to 299 head, and greater than 300 head was 23, 27, and 26, respectively (National Animal Health Monitoring System, 1998). This implies that if producers are not comfortable identifying bulls to service higher cow-to-bull ratios or have other management limitations such as pasture size, they should evaluate synchronization and AI more seriously.
Results for each simulation included regression coefficients Regression coefficient
Term yielded by regression analysis that indicates the sensitivity of the dependent variable to a particular independent variable. See: Parameter.
regression coefficient (standardized ß coefficients) from a step-wise analysis of the input variables. The standardized ß coefficients represent a 1 SD move in each individual variable. The regression coefficients for the AIadvantage output variable resulting from one simulation (MGA-PG, heat detection only, 100 head, cow-to-bull ratio of 30) are presented in Figure 1. The variation in the genetic value input variable was the most important determinant of the magnitude of the Aladvantage output variable. Whether this particular AI system will provide an economic advantage in a particular management setting, and how much, was largely determined by the ability to garner a genetic value premium associated with the AI-sired calves. The regression coefficient for genetic value was positive, indicating that higher genetic value premiums were associated with a positive move in the Aladvantage variable. For each SD in genetic value and semen cost above the mean, the Aladvantage increased by 0.58 and decreased by -0.55 SD, respectively, from its mean.
Semen cost variability was nearly as important as genetic value in influencing the difference in breeding cost output variable. Higher cost semen would be expected to result in a smaller (or negative) economic advantage for the AI system relative to natural service. Bull purchase price was third in terms of relative importance for this particular system comparison. Higher bull purchase prices resulted in the AI system becoming more economically competitive. This was expected because higher bull purchase prices increased the cost of the natural service alternative relative to the AI choice.
For this specific system comparison, the synchronized calving weight advantage variable (0.41) and the conception percentage variable (0.20) were marginally important contributors to the economic advantage or disadvantage of the AI system. Calf price variability (0.12), cull weight variability (-0.04), and percent calf crop variability (-0.03) were relatively unimportant.
Table 6 summarizes the ranking of input variables in the step-wise regression across the 63 simulation models for the Aladvantage output variable. Genetic value premiums and semen cost variability were among the top 3 in terms of relative importance across all systems, herd sizes, and cow-to-bull ratios. For models with low cow- to-bull ratios, bull purchase price was the most important variable. The increased value of the AI-sired calves based on genetic strengths of AI sires and semen costs were the most important variables at higher cow-to-bull ratios and larger herd sizes.
Variability in bull purchase price was always the most important factor when the assumed cow-to-bull ratio was low (i.e., 20). From an economic perspective, bull purchase price becomes a driving factor in the decision to use AI when a management system dictates a low cow-to-bull ratio (small pastures, etc.). Bull purchase price consistently dropped in the ranking of important factors that influence the Aladvantage output variable as the cow-to-bull ratio was increased. When a constant cow-to-bull ratio of 30 was used, Miller et al. (2004) found bull purchase price, semen price, and percent genetic change were the most prominent variables in determining net return through harvest when comparing synchronized AI and naturalservice breeding systems.
The model used a conservative estimate of genetic value for Al-sired calves. Reducing the genetic value distribution to a minimum of zero, most likely value of $2/head, and maximum value of $25/head reduced the proportion of times a Co-Synch + CIDR fixed-time AI system showed a net economic advantage over natural service by 0 to 10% for a herd size of 100. Averaged across all fixed-time AI systems, the average proportion of times AI had an economic advantage compared with natural service was 38%. If the genetic value distribution is changed to a minimum of zero, most likely value of 10, and a maximum of 100, the proportion of simulations in which AI is economically preferred to natural service increases to 64%. This further emphasizes the importance of capturing value from AI-sired calves in a commercial herd.
The current model assesses the costs of breeding systems with the end point considered to be a weaned wean
tr.v. weaned, wean·ing, weans
1. To accustom (the young of a mammal) to take nourishment other than by suckling.
2. calf. Any postweaning increase in value, such as carcass premiums or replacement heifer value from an AIsired calf, that might be attributed to the AI program was lumped into one genetic value input. Conversely, Miller et al. (2004) considered various retained ownership opportunities when comparing AI and natural-service breeding systems. In that study, retaining ownership to harvest and marketing either on a cash or grid market was advantageous to AI in all the synchronization protocols evaluated when compared with natural service.
The decision to incorporate AI should consider more than the cash costs associated with artificial breeding. When relatively minimal value increases from the age and genetics of AI-sired calves were considered for typical cow-to-bull ratios, AI became economically beneficial. Genetic value premiums and semen cost were consistently in the top 3 factors that determined expected economic differences between natural-service and AI systems across herd sizes and cow-to-bull ratios. Variability in bull purchase price was the most important factor when the cow-to-bull ratio was low. Estrous es·trous
Relating to or being in estrus.
pertaining to or emanating from estrus.
estrous cycle synchronization and AI were economically advantageous compared with natural service when a sufficient genetic value premium could be obtained from ??-sired calves at the time of weaning. In today's market, an increasing number of opportunities exist to receive a premium for known genetics, and the use of AI could assist in capitalizing returns in those markets.
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|Author:||S K Johnson and R D Jones|
|Publication:||Professional Animal Scientist|
|Date:||Dec 1, 2008|
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