Change In Herd Size Research Articles

Relationship Between Type Traits and Longevity in Canadian Jerseys and Ayrshires Using a Weibull Proportional Hazards Model

The aim of this study was to use a Weibull proportional hazards model to explore the impact of type traits on the functional survival of Canadian Jersey and Ayrshire cows. The data set consisted of 49,791 registered Jersey cows from 900 herds calving from 1985 to 2003. The corresponding figures for Ayrshire were 77,109 cows and 921 herds. Functional survival was defined as the number of days from first calving to culling, death, or censoring. Type information consisted of phenotypic type scores for 8 composite traits and 19 linear descriptive traits. The statistical model included the effects of stage of lactation; season of production; annual change in herd size; type of milk recording supervision; age at first calving; effects of milk, fat, and protein yields calculated as within herd-year-parity deviations; herd-year-season of calving; each type trait; and the animal's sire. Analysis was done one trait at a time for each of 27 type traits in each breed. The relative culling risk was calculated for animals in each class after accounting for the previously mentioned effects. Among the composite type traits with the greatest contribution to the likelihood function was final score followed by mammary system for Jersey breed, while in Ayrshire breed feet and legs was the second most important trait next to final score. Cows classified as Poor for final score in both breeds were >5 times more likely to be culled compared with the cows classified as Good Plus. In both breeds, cows classified as Poor for feet and legs were 5 times more likely to be culled than were cows classified as Excellent, and cows classified as Excellent for mammary system were >9 times more likely to survive than were cows classified as Poor.

Genetic Analysis of Herd Life in Canadian Dairy Cattle on a Lactation Basis Using a Weibull Proportional Hazards Model

The objectives of this study were to identify the most important factors that influence functional survival and to estimate the genetic parameters of functional survival for Canadian dairy cattle. Data were obtained from lactation records extracted for the May 2002 genetic evaluation of Holstein, Jersey, and Ayrshire breeds that calved between July 1, 1985 and April 5, 2002. Analysis was performed using a Weibull proportional hazard model, and the baseline hazard function was defined on a lactation basis instead of the traditional analysis of the whole length of life. The statistical model included the effects of stage of lactation; season of production; the annual change in herd size; type of milk recording supervision; age at first calving; effects of milk, fat, and protein yields calculated within herd-year-parity deviations; and the random effects of herd-year-season of calving and sire. All effects fitted in the model had a significant effect on functional survival of cows in all breeds. Milk yield was by far the most important factor influencing survival, and the hazard increased as the milk production of the cows decreased. The hazard also increased as the fat content increased compared with the average group. Heifers that were older at calving were at higher risk of being culled, and expanding herds were at lower risk of being culled compared with stable herds. More culling was found in unsupervised herds than in supervised herds. The heritability values obtained were 0.14, 0.10, and 0.09 for Holstein, Jersey, and Ayrshire, respectively. Rank correlation between estimated breeding values (EBV) obtained from the current national genetic evaluation of direct herd life and the survival kit used in this study ranged from 0.65 to 0.87, depending on the number of daughters per sire. Estimated genetic trend obtained using the survival kit was overestimated.

Analysis of the Relationship Between Type Traits and Functional Survival in Canadian Holsteins Using a Weibull Proportional Hazards Model

The aim of this study was to explore the impact of type traits on the functional survival of Canadian Holstein cows using a Weibull proportional hazards model. The data set consisted of 1,130,616 registered cows from 13,606 herds calving from 1985 to 2003. Functional survival was defined as the number of days from first calving to culling, death, or censoring. Type information consisted of phenotypic type scores for 8 composite traits (with 18 classes of each) and 23 linear descriptive traits (with 9 classes of each). The statistical model included the effects of stage of lactation, season of production, the annual change in herd size, type of milk recording supervision, age at first calving, effects of milk, fat and protein yields calculated within herd-year-parity deviations, herd-year-season of calving, each type trait, and the sire. Analysis was done one at a time for each of 31 type traits. The relative culling risk was calculated for animals in each class after accounting for the previously mentioned effects. Among the composite type traits with the greatest contribution to the likelihood function were final score, mammary system, and feet and legs, all having a strong relationship with functional survival. Cows with low scores for these traits had higher risk of culling compared with higher scores. For instance, cows classified as poor plus 1 vs. excellent plus 1 have a relative risk of culling 3.66 and 0.28, respectively. The corresponding figures for mammary system are 4.19 and 0.46 and for feet and legs are 2.34 and 0.50. Linear type traits with the greatest contribution to the likelihood function were fore udder attachment, udder texture, udder depth, rear udder attachment height, and rear udder attachment width. Stature and size had no strong relationship with functional survival.

Impact of type traits on functional herd life of Quebec Holsteins assessed by survival analysis.

Survival analysis was used to study the effects of composite and descriptive linear type traits on functional herd life of Quebec Holsteins. Functional herd life was defined as the length of life from first calving to death, culling, or censoring, and was adjusted for 305-d milk production. The dataset contained information from 331,105 cows from Quebec province calving for the first time between 1981 and 1995; 58% of the records had type information. Weibull models were fitted to analyze the data. The hazard function was described as the product of a baseline hazard function and the time-independent effects of age at first calving and type, and the time-dependent effects of year of calving, stage of lactation x lactation number, annual change in herd size, 305-d milk production, and herd-year (random). Analyses were done one at a time for each type trait. The strongest relationships between survival and composite type traits were found for final score, mammary system, and feet and legs. Among the linear type traits, the highest impact on functional herd life was found for traits related to the udder.

Patterns of change in beef production and consumption in Africa.

This paper analyses the patterns of change in the production and consumption of beef in Africa over the last two decades. A 'decomposition' method of analysis is used to examine the change in total beef production during this period, attributable to changes in herd size, in the proportion of cattle slaughtered and in productivity per head of cattle. Sub-regional aggregations are complemented with similar analyses for individual countries to demonstrate the diverse patterns of change in beef production and consumption. The results reveal an overall increase in total beef production (due mainly to an increase in cattle numbers and in the percentage of slaughtered cattle, rather than to productivity gains), a stagnation in per capita production, and an overall increase in the total consumption of beef and a decline in per capita consumption (due mainly to faster population growth and urbanisation, and a decline in per capita income, respectively).

An Analysis on Mortality Among Calves in Danish Dairy Herds

This study analysed the mortality among young calves born alive up to 180 days after birth, born in Danish dairy herds in 1998 and 1999. The objective of the study was to estimate the overall mortality and to analyse possible risk factors having an influence on the mortality. The data material comprised 914,000 recorded births of dairy race cows in 9,333 dairy herds including the following animal level information: Dates of birth and possible death, sex, breed, change of herd, size at birth, calving eas (dystocier), calving number of mother and the following herd level information: Herd size, milk production level, indicator of organic farming status, indicator of major change in herd size, and county. The effects of the animal and herd level factors on mortality in four periods after birth was investigated by a random effects model. The response being indicator of the calf dying during the period conditional on being alive at the beginning of the period. The four periods were defined as 1: 1?14 days, 2: 15?28 days, 3: 29?56 days, and 4: 57?180 days after birth. The three main breeds (Danish Holstein, Red Danish, and Jersey) were analysed separately. The observed overall mortality among heifers and bulls from day 1 to 180 after birth was 6.4%, respectively 7.8%. Among the animals not surviving 180 days a percentage of 45 died during the first 14 days. Although there is some variation between breeds, with Jersey having a higher level of mortality. The mortality of heifers is smaller than that of bulls. A small size of the calf at birth combined with a difficult delivery is increasing mortality, as well as the movement of an animal between herds increases its probability of not surviving. The management on the farm is assumed to be confounded by the yield level, as farms with higher yield level has a reduced mortality. There is some variation in mortality between counties, which may be related to differences in production and housing systems, which are not registered yet. As a conclusion, a number of production factors are documented to have an effect on calf mortality as well as some animal specific factors, which can help to focus on specific animals having an increased risk of dying prematurely. Abstracts – Oral presentations at 11th ICPD 225

Genetic Analysis of Herd Life in Quebec Holsteins Using Weibull Models

Survival analysis methodologies were used to study herd life in Canadian Holstein cows. Herd life was defined as true herd life or the length of time between first calving and censoring. True herd life adjusted for 305-d milk production was defined as functional herd life. Lifetime records (censored or completed) were from 331,147 Holstein cows registered in the Programme d’Analyse des Troupeaux Laitiers du Québec (PATLQ) that calved for the first time between March 1, 1981 and March 31, 1995. The Weibull (proportional hazards) model used to analyze true herd life and functional herd life contained a Weibull baseline hazard function and the time-dependent effects of year of first calving, lactation number by stage of lactation, annual change in herd size and herd-year (random), and the time-independent effects of the milk recording option (supervised or not) and age at first calving. The model for functional herd life included also the time-dependent effect of herd-year-parity class of 305-d milk production. Genetic differences between sires with regard to the hazard function of their daughters was clearly demonstrated. The hazard rate followed a different pattern in later lactations, particularly in the first 240 d in milk. Older age at first calving was found to be associated with higher risks of culling. Changes in herd size had a small impact on the hazard function of animals. The hazard decreased as production of the cow increased. Heritability in the log scale was 0.09 for true herd life and 0.08 for functional herd life, but when heritability was expressed on the original scale, the estimates for the two traits were 0.19 and 0.15, respectively. The difference in the median survival between a bull with an estimated transmitting ability of 0.6 and another bull with an estimated transmitting ability of 1.3 was 690 d or 1.7 lactations. Rank correlations between the official estimated transmitting abilities for true herd life and functional herd life and those obtained in this study were 0.62 and 0.66, respectively.

Dairy Cow Culling Strategies: Making Economical Culling Decisions

The purpose of this report was to examine important economic elements of culling decisions, to review progress in development of culling decision support systems, and to discern some of the potentially rewarding areas for future research on culling models. Culling decisions have an important influence on the economic performance of the dairy but are often made in a nonprogrammed fashion and based partly on the intuition of the decision maker. The computer technology that is available for dairy herd management has made feasible the use of economic models to support culling decisions. Financial components—including profit, cash flow, and risk—are major economic factors affecting culling decisions. Culling strategies are further influenced by short-term fluctuations in cow numbers as well as by planned herd expansion. Changes in herd size affect the opportunity cost for postponed replacement and may alter the relevance of optimization strategies that assume a fixed herd size. Improvements in model components related to biological factors affecting future cow performance, including milk production, reproductive status, and mastitis, appear to offer the greatest economic potential for enhancing culling decision support systems. The ultimate value of any culling decision support system for developing economic culling strategies will be determined by its results under field conditions.

Effects of Interactions Between Type and Milk Production on Survival Traits of Canadian Holsteins

Effects of the interaction between type and production on two measures of functional herd life were examined for Canadian Holsteins. Data were records of survival through first lactation for 1,153,706 cows and number of lactations initiated (maximum of five lactations) for 705,930 cows. Survival data were regressed on ETA for type traits of the sire of each cow after the cows were assigned to groups with low, medium, or high production. Survival through first lactation was analyzed with a threshold model. Factors in the model included herd-year-season; age at calving; month of calving; interaction of registry status, change in herd size, and season; fat and protein production; and linear regressions of sire ETA for type within each production class. Numbers of lactations were analyzed with a linear model that also included month of last calving. Overall conformation and udder traits had the largest effects on survival through first lactation. Effects on number of lactations for feet and leg traits were about the same as for udder traits. Interactions were significant. Type traits were relatively unimportant for herd life of low producing cows. Few differences were observed in the relationships between herd life and type for medium versus high producing cows, indicating no need to increase the emphasis on type in response to current trends for greater production.

Economic evaluation of risks to producers who use milk residue testing programs

Objective— To evaluate the decision to test for milk antimicrobial residues in milk from dairy cows treated with procaine penicillin G (PPG). Design— Economic-decision analysis after stochastic simulation. Sample Population— 1,000 computer-simulated cows/model. Procedure— Meta-analysis of the Food Animal Residue Avoidance Databank was used to generate PPG disappearance curves for cows given single PPG treatments, IM, of 6,600 U/kg (3,000 U/Ib) of body weight or 26,400 U/kg (12,000 U/lb), and multiple treatments at 26,400 U/kg (12,000 U/lb), IM. These curves were entered into 1,000-replication stochastic pharmacokinetic models, generating population-level milk PPG profiles for each treatment group for each day after treatment, which were subjected to economic-decision analyses of feasibility of residue testing. The model was evaluated for changes in herd size, proportion of herd available for testing, milk production, test price, test sensitivity/specificity, and withdrawal periods. Results— For both single-treatment groups, a 2-day withdrawal period avoided violative residues. However, nearly two thirds of the cows risked false identification for violative residues. For the multiple-treated group, nearly 40% had violative residues after a 5-day withdrawal period, and an additional 10 to 15% risked false identification for violative residues. Economic analysis yielded a decision against testing; mean cost was $2 (ie, 5% more than the mean cost of not testing). Clinical Implications— Complex dynamics of current milk residue tests discourage practitioners from recommending procedures to clients. In general, increases in herd size, milk production, proportion of a herd available for testing, or milk price will increase the value of testing. Increasing test sensitivity decreases its desirability to producers. (J Am Vet Med Assoc 1997;211:419–427)

Livestock productivity assessment and modelling

Individual production traits, such as reproduction and mortality rates, are partial, but readily estimated, measures of performance, which may be utilized in ‘herd growth models’ to predict potential offtake and changes in herd size and structure. Such models are readily constructed using a spreadsheet package or simple purpose-built computer programmes, such as LPEC. Livestock productivity assessment requires the use of a steady-state (stationary) herd model. The output thus derived is then presented on a per livestock unit basis to measure productivity. These are not optimizing models but they do provide a useful method for estimating average productive performance, even for small household herds of cattle or flocks of sheep and goats.

Simulation of host—parasite interactions within a resource management framework: impact of brucellosis on bison population dynamics

We describe development of a simulation model representing bison (host)—bbrucellosis (parasite) interactions within a natural resource management framework. We document three phases in model development which focus on the simulation of bison population dynamics in (1) a brucellosis-free herd, (2) a brucellosis-infected herd, (3) and infected herd subjected to different vaccination schemes. The first phase represents bison populations dynamics based on age-specific rates of natural mortality and natality and rates at which animals are harvested. The second phase represents the influence of brucellosis-induced abortions, brucellosis transmission, and naturally acquired immunity. The third phase represents acquired immunity to brucellosis (or lack thereof) due to immunization, which is a function of vaccine efficacy and the percentage of bison to which the vaccine can be delivered. The model accurately simulated historical changes in herd size, annual recruitment, population age structure, and survivorship of individual cohorts over a 17-year period in a brucellosis-free bison herd on the National Bison Range, U.S.A. (Phase I). The model also accurately simulated historical changes in herd size, and predicted the most likely year of infection, in a bison herd in Grand Teton National Park, U.S.A., that contracted the disease during a 20-year period (Phase II). Finally, the model was used to evaluate a proposed bison brucellosis management plan for the Grand Teton National Park herd which involves annual vaccination of female calves (Phase III). Simulations suggested that, after 20 years, the proportion of the herd infected with brucellosis might be reduced from 69% (current level) to between 50% and 20%, depending on the (currently unresolved) vaccine efficacy.

Trends in Herd Age Structure and the Relationships with Management Characteristics in Wisconsin Holstein Herds

Relationships between characteristics of dairy herds and age structure of cows were examined between 1969 and 1984 in member herds of Wisconsin Dairy Herd Improvement Cooperative. Herd totals were summarized yearly from individual lactation records of cows in 376 herds with DHI and DHIR records and 747 owner-sampler herds. Variables studied were average age, percent culled in first lactation, and turnover rate. Herd and year were associated with most of the variation in herd age structure, although, including trend in herd size, herd size, calving intervals, age at first calving, percent nonregistered cattle, average production, production trend, and production of those culled relative to herdmates explained significant variation in some variables after herd and year effects were removed. Average expected herdlife was estimated from turnover rate adjusted for changes in herd size and was 2.8 and 3.4 yr in official and owner-sampler herds. Herd age structures indicated a higher percentage of young cows than has been suggested as economically optimal. Trends for average herdlife were increasing within herd as were trends for average age and percent culled in first lactation.

A White-Tailed Deer Harvesting Strategy

We describe a harvest strategy that integrates a population dynamics model, a rationale for choosing a harvest rate, a means of implementing harvesting, and a change-in-ratio (CIR) population estimation technique. The size of the harvest is determined by selecting a proportion of the postharvest (residual) population (#) chosen between about zero and the intrinsic rate of increase in a given environment (rm), with a maximum sustained yield (MSY) at about 0 = r,/2 based on logistic growth, or about i = 0.5 based on McCullough's (1979:118, 1984) studies of the George Reserve white-tailed deer (Odocoileus virginianus) herd. The advantages of proportional harvesting are that the population stabilizes for all proportions, the location of the population along the sustained yield (SY) curve is unambiguous, and proportions are naturally self-correcting because harvests are tied to population size. Taking 2 separate single-type (sex) harvests provides a means for achieving the harvest quota and also yields a CIR population estimate based on observations of the proportion of antlered deer in the population at 3 times. The 2-stage CIR technique is robust to unequal observability, a major weakness of the traditional CIR methods. Our harvest strategy is most applicable where harvests can be controlled closely, and hunting seasons are relatively short. Field experiments are required to establish the efficacy of our harvest paradigm. J. WILDL. MANAGE. 52(4):589-595 Several components are needed to provide a framework for managing harvests of white-tailed deer to attain harvest and population goals. Among these are an underlying model of population dynamics that incorporates removals due to hunting, a rationale for choosing a harvest level, a means of implementing and controlling the removals, and a procedure to evaluate the success of the harvest strategy. Our objective is to integrate these requirements into a management paradigm based on a stock-recruitment model of population responses to harvesting (McCullough 1979:123-127, 1984), on 2 separate single-type (sex) removals during the hunting season, and on a 2-stage CIR population estimation technique (Pollock et al. 1985). We present a management paradigm, based on logic and theory that incorporates the concept of proportional harvesting. The 2-stage CIR is used to estimate population size, but any suitable estimation technique could be applied. We caution that our paradigm requires testing under field conditions. Our analysis begins with a deterministic model and then expands to consider briefly stochastic variability. Our strategy is most appropriate for herds closely controlled by managers. To support our rationale, we draw upon published literature and our experiences studying the deer herd on Remington Farms, Chestertown, Maryland. O r paradigm differs from the strategy developed by Hayne and Gwynn (1977), which uses the proportion of females in the harvest as a management objective. They reasoned that if th adult male harvest is inherently limited because hunter effort declines as males become scarce, then the female harvest could also be limited at a lower level by relating it to the male harvest. Their approach does not estimate population size or incorporate a measure of productivity, yet it has apparently been misinterpreted by some deer managers to reflect recruitment or changes in herd size (Downing 1981). Furthermore, Downing (1981) showed tha , alone, the proportion of females in the kill reveals little about the status of the herd. Our paradigm differs from Hayne and Gwynn's (1977) in that ours incorporates an estimate of the population and a measure of productivity. We thank Remington Farms and especially E. C. Soutiere and E. H. Galbreath for their encouragement and support. D. A. Adams, G. Caughley, P. D. Doerr, E. C. Franklin, and D. R. McCullough reviewed earlier drafts and provided helpful comments. This is paper 11498 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. IPresent address: Florida Game and Fresh Water Fish Commission, Route 7, P.O. Box 440, Lake City, FL 32055.

Relationship of Use of Dairy Herd Improvement Records to Herd Performance Measures1,2

Questionnaires and DHI herd summaries from 543 Ohio dairy farmers with Holstein cows were analyzed in relation to changes in herd performance measures, milk production, and herd size from 1976 to 1983. Milk production per cow increased 77.3 kg/yr and herd size increased by 11.8 cows during the period. Percent cows culled increased, but age at first and last calvings decreased significantly. Calving interval, days to first service, age at first calving, and age at last calving were significant contributors to change in milk production from 1976 to 1983. Respondents who agreed strongly that DHI records were worth the price increased production per cow by 816kg from 1976 to 1983 compared with 254 and 63kg for respondents who where neutral or strongly disagreed with the question. Percent changes in herd size and production were highest for younger farmers. Respondents with more productive herds thought they had adequate time to analyze their records.

Immediate Effects of Changing Herd Size Upon Milk Production and Other Dairy Herd Improvement Measures of Management

Consecutive yearly herd averages were compared to determine the effects of changing herd size on production and management variables for 13,614 Dairy Herd Improvement Holstein herd average records completed between 1965 and 1970. Herd average milk production increased by 56kg per year. Changes in herd size had a marked effect on average milk production the following year. This effect was dependent on herd size prior to change with larger herds showing serious losses in production as herd size increased. Conversely, smaller herds were less affected as herd size fluctuated. Income over feed cost and other management variables showed trends similar to those for milk production.