Change In Herd Size Research Articles

Impact of reproductive traits on productive life in Iranian Holstein dairy cows.

Enhancing reproductive performance is a key strategy to mitigate involuntary culling rates, thereby extending productive life (PL) and ultimately improving profitability in dairy cattle herds. A piecewise Weibull proportional hazards model was used to investigate the effect of several important reproductive traits on PL in Holstein dairy cows. Data comprised 200,747 lactation records from 82,505 cows sired by 1952 bulls across 36 dairy herds. PL was defined as the number of days from the first calving to the last milk record or censoring. The statistical model accounted for the time-dependent fixed effects of changes in herd size, year-season, milk production, fat and protein contents, and the time-independent fixed effect of age at first calving. Herd-year and sire effects were also included as random effects. Reproductive traits include calving traits such as calving ease (CE), calf size (CZ), and calf survival (CS), as well as female fertility traits such as number of inseminations per conception (NI), days from calving to first service (CFS), days from first service to conception (FSC), and days open (DO). All reproductive traits had a significant effect on PL (p < 0.001). Each reproductive trait was analysed separately. The relative risk (RR) of being culled increased as the severity of calving difficulties increased in both primiparous and multiparous cows. Cows that calved small or large calves showed a higher risk of being culled compared with those that calved medium size calves. The increased RR of culling was observed only for primiparous cows that gave birth to dead calves. In addition, cows that required more NI, a longer CFS, FSC, and DO had shorter longevity. These insights can deepen our comprehension of the factors affecting PL and provide information for refining management and breeding strategies, which could lead to increased profitability and sustainability in Iranian dairy farming.

Stabilizing effects of group formation by Serengeti herbivores on predator-prey dynamics

Predator-prey theory often assumes that potential prey individuals are solitary and evenly distributed in space. This assumption is violated in social, mobile prey, such as many ungulates. Here we use data from 80 monthly field censuses to estimate the parameters for a power relationship between herd density and population density for eight species of large herbivores commonly found in the diet of Serengeti lions, confirming a power relationship proposed from a preliminary Serengeti dataset. Here we extend our analysis of that model to demonstrate how parameters of the power function relate to average herd size and density-dependent changes in herd size and evaluate how interspecific variation in these parameters shapes the group-dependent functional response by Serengeti lions for eight prey species. We apply the different prey-specific functional response models in a Rosenzweig-MacArthur framework to compare their impact on the stability of predator–prey dynamics. Model outcomes suggest that group formation plays a strong role in stabilizing lion–herbivore interactions in Serengeti by forcing lions to search over a larger area before each prey encounter. As a consequence of grouping by their prey, our model also suggests that Serengeti lions are forced to broaden their diets to include multiple species of prey in order to persist, potentially explaining the generalist foraging by lions routinely recorded across multiple ecosystems.

U.S. Dairy Farm Transition and Exits, 1987–2017

AbstractThis analysis examines aggregate structural changes in the United States dairy industry, 1987–2017. We estimate the likelihood of operation changes in herd size, entry, or exits for each of the lower 48 states using a semiparametric Markov process model. Small- and medium-sized dairy longevity correlates with higher dairy margins and productivity improvements. An increase in consumer expenditures on dairy products is associated with smaller operation exits. Industry dynamics exhibit a persistent trend toward consolidation in most states. The exit probability for each state and all size classes has increased significantly for most states since 2002.

Effect of Calving Difficulties and Calf Mortality on Functional Longevity in Polish Holstein-Friesian Cows.

Simple SummaryLongevity, or the length of a cow’s productive life, is important in terms of profitability, animal welfare and environmental sustainability. In genetic evaluations, interest focuses on functional longevity, defined as a cow’s ability to avoid forced culling, an ability that increases the possibility of voluntary disposal based on economic criteria. Longevity is affected by several non-productive functional traits, among them those related to calving performance: calving ease (dystocia) and perinatal calf mortality (stillbirth). Parturition is a critical event in a cow’s life that has a number of different short- and long-term consequences. In the Polish Holstein-Friesian population, the incidence of dystocia and stillbirth is within the lower range of frequencies found in other dairy cattle populations. Our research showed that both traits affect functional longevity. Difficult calvings occur more frequently in heifers and increase the risk of involuntary culling more than in later parturitions. Additionally, a higher risk of culling is related to birth of a male calf. Moreover, the negative impact of calf mortality on longevity is also more pronounced in primiparous cows and in the case of delivery of male calves. Reducing the incidence of calving problems and perinatal mortality may improve the longevity of dairy cows.Longevity is one of the functional traits that considerably affect dairy herd profitability. A Weibull proportional hazards model was used to evaluate the impact of difficult calvings and calf stillbirths on cow functional longevity, defined as length of productive life corrected for milk production. The data for analysis comprised calving ease and calf mortality scores of 2,163,426 calvings, 34.4% of which came from primiparous cows. The percentage of male calves was 53.4%. Calving ease was scored as “without assistance” (34.44%), “with assistance” (62.03%), “difficult—hard pull” (3.39%), and “very difficult, including caesarean section” (0.14%). Calf mortality scores were “live born” (94.21%) and “stillborn or died within 24 h” (5.79%). The Weibull proportional hazards model included classes of calving ease or calf mortality scores × parity (1, ≥2) × sex of calf as time-dependent fixed effect. The model also included time-dependent fixed effects of year × season, parity × stage of lactation, annual change in herd size, fat yield and protein yield, time-independent fixed effect of age at first calving, and time dependent random herd × year × season. In first-parity cows, very difficult birth of a bull or heifer increased the relative risk of culling, respectively, 2.18 or 1.26 times as compared with calving without assistance. In later parities, the relative risk of culling related to very difficult calving was 2.0 times (for male calves) and 1.33 times (for female calves) higher than the relative risk of culling associated with calving without assistance. Calf mortality showed a negative impact on longevity in both heifers and cows. First-parity stillbirth increased the relative risk of culling depending on sex of calf by 18% in females and by 15% in males; in later parities the increase of the relative risk of culling was lower (by 7% for females, 9% for males). Difficult calvings and their consequences, especially in primiparous cows, may negatively influence dairy herd profitability by reducing the length of cows’ productive life.

Short and medium-term impact of dairy barn investment on profitability and herd size in Switzerland

Investing in larger barns and increasing herd size are crucial milestones in dairy production. Based on the Swiss Farm Accountancy Data Network and data on government-supported investments, we investigate the development of two key variables over the first eight years after investment: change in herd size and calculated profit, that is, farm income minus opportunity costs for family labour and capital. We apply a fixed-effects panel regression and test for autocorrelation present in the time series. Compared to the year before the investment, calculated profit decreases in the first three years, while in the remaining years no significant difference compared to the year before investment can be seen. Herd size increases slowly, predominantly in the second and third years after investment, to some extent explaining the less favourable development of profitability in these years. We conclude that investment in a dairy barn does not lead to improved profitability in the short and medium term, pointing to the question of whether this picture changes in the long term.&lt;br /&gt;

Genetic evaluation for functional longevity in Polish Simmental cattle

The Weibull proportional hazards model was applied for genetic evaluation of functional longevity in Polish Simmentals. Data consisted of production and disposal records for 12 527 Simmental cows, daughters of 294 sires, calving for the first time from 1995 to 2014 in 286 herds. Length of productive life of cows was calculated as number of days from the first calving to culling or censoring. Average length of productive life of 4462 cows with complete (uncensored) survival records was 1198 days (39.3 months); mean censoring time for the remaining 8065 cows was 1093 days (35.8 months). Functional longevity was defined as length of productive life corrected for production. The model included time-independent fixed effect of age at first calving, time-dependent fixed effects of year-season, parity-stage of lactation, annual change in herd size, relative fat yield and protein yield, and random herd-year-season and sire effects. Likelihood ratio tests showed a highly significant impact of all fixed effects on longevity, except for relative fat yield. Estimated sire variance was 0.069, resulting in the equivalent (accounting for censoring level) heritability of 0.09. Standardized relative breeding values (RBV) ranged from 71 to 139 (mean 101.4, SD 9.12). Average reliability of RBVs was 0.47. Moderate heritability supports the possibility of effective selection for functional longevity, which will be included in the total selection index for Polish Simmentals.

Comparison of intervention methods for reducing human exposure to Mycobacterium bovis through milk in pastoralist households of Tanzania

Bovine tuberculosis (bTB), caused by Mycobacterium bovis, is a disease of zoonotic concern, especially in countries with no control programs in livestock and where routine pasteurization of milk is not practiced. In Tanzania, bTB is widespread in livestock and has been diagnosed in humans; however, herd bTB testing is primarily carried out for bTB-free certification in commercial dairy herds at the expense of the dairy cattle owner. For rural livestock holders, such an expense is prohibitive, and consequently there is no control of bTB in most areas. Although effective long-term solutions to control bTB in livestock are desirable, there is a need to assess the effect of preventive measures on reducing human exposure to bTB in such settings. We utilized locally relevant cattle herd characteristics and management data from the Health for Animals and Livelihood Improvement (HALI) project in south-central Tanzania to build a Reed-Frost model that compared the efficacy of alternative methods aimed at reducing the exposure of humans to infectious milk from a typical pastoralist cattle herd. During a 10-year simulation period, the model showed that boiling milk 80% of the time is necessary to obtain a reduction in liters of infectious milk approximately equivalent to what would be obtained with a standard 2-year testing and removal regimen, and that boiling milk was more effective than animal test and removal early in the time period.In addition, even with testing and removing infected cattle, a residual risk of exposure to infectious milk remained due to imperfect sensitivity of the skin test and a continuous risk of introduction of infectious animals from other herds. The model was sensitive to changes in initial bTB prevalence but not to changes in herd size. In conclusion, continuous complimentary treatment of milk may be an effective strategy to reduce human exposure to M. bovis-infected milk in settings where bTB is endemic and a comprehensive bTB control program is yet to be implemented.

Relationship between conformation traits and longevity in Polish Holstein Friesian cattle

A Weibull proportional hazard model was applied to examine the impact of conformation on true and functional longevity of Polish HF cattle. Lifetime records of 592,639 cows from 2369 herds calving from 1995 to 2008 were used. Conformation data available for 236,137 cows consisted of phenotypic scores for 14 linear traits. True longevity (LPL) was defined as the number of days from first calving to culling or censoring, and functional longevity (FLPL) as LPL adjusted for production. Linear type traits were added into the reference model, which included random effect of herd–year–season, and fixed effects of age at first calving, year–season, parity-stage of lactation, annual change in herd size, and (for FLPL) fat and protein yield. The strongest and positive influence on true longevity was found for udder traits. Capacity traits, rump traits, teat length and rear leg set displayed intermediate optima with respect to LPL. The highest impacts on functional longevity were from udder depth, body depth, chest width, and dairy character. Those traits can be considered early predictors. In respect to FLPL, udder depth had a positive impact, body depth showed an intermediate optimum, and the influences of chest width and dairy character were negative.

The impact of system changes to a dairy farm in south-west Victoria: risk and increasing profitability

A case study modelling approach was used to examine changes to a dairy farm in south-west Victoria to maintain or increase profit in the future 5–10 years in the face of some ‘cost-price squeeze’, emphasising impacts on both returns and risk. Five changes to the status quo system were analysed. Each involved increasing pasture consumption on the milking area and non-milking leased area (where appropriate). The five changes were: (1) reducing leased non-milking area by 100 ha; (2) converting 60 ha of non-milking leased area to milking area, reducing leased non-milking area by 100 ha and reducing stocking rate on the milking area; (3) converting 187 ha of leased non-milking area to milking area, increasing herd size to 800 cows and reducing stocking rate on the milking area; (4) discarding all leased area, reducing herd size to 370 cows and reducing stocking rate; and (5) converting 127 ha of non-milking leased area to milking area, discarding all other lease arrangements and reducing stocking rate. Mean ± standard deviation of nominal owner’s equity at the end of Year 10 was $2.59M ± $1.33M, $5.42M ± $1.26M, $5.76M ± $1.21M, $7.47M ± $1.64M, $6.01M ± $0.78M and $6.10M ± $1.19M for the status quo and development options 1–5, respectively. For most but not all of the development options, the risk associated with the profit, cash and equity as measured by a range of indicators improved markedly over the performance of the farm system under the status quo. Both substantial increases and decreases in herd size were attractive. Irrespective of the direction of change in herd size, the most profitable options involved reducing stocking rate per ha and reducing purchased supplementary feed compared with the status quo. Significantly, changing to increase productivity greatly reduced the risk of having less equity at the end of Year 10 than the starting equity. Optimising the amount of home-grown grazed feed, and using purchased supplements efficiently are important, particularly if the milk being sold is subject to export market prices and variation. The most appropriate changes to dairy farm businesses in response to changes in the operating environment will vary from farm to farm – but maintaining the status quo in the face of change is not an option that meets farm family goals.

Ecological determinants of herd size in the Thornicroft’s giraffe of Zambia

AbstractEcological factors have a pervasive impact on animal population sizes and the structure of their social systems. In a number of ungulate species, predator pressure exerts a major influence on group size. Given that giraffe (Giraffa camelopardalis) live in an extremely flexible social system, and that breeding is nonseasonal, they are an ideal species for examining how ecological variables contribute to fluctuations in herd size. We present an analysis of 34 years of data on a population of Thornicroft’s giraffe (G. c. thornicrofti Lydekker 1911) that reveal how herd size changes with season and habitat. Sex differences in herd size were apparent, with bulls often travelling as singletons, whereas cows were generally observed with conspecifics. Herds were larger during the wet than dry season, but herd size changed in a parallel fashion across habitats. Giraffe herds were smaller in woodland and thicket areas than in open habitats, regardless of season. We suggest that the regular fluctuations in herd size among giraffe indicate a fission/fusion social system embedded within a larger social community. We conclude that changes in herd size among giraffe reflect a dynamic process regulated by individuals adjusting the number of associates based upon an interaction of foraging, reproductive, social and antipredator strategies.

Analysis of the relationship between workability traits and functional longevity in Canadian dairy breeds

The aim of this study was to assess the effect of workability traits like milking speed and temperament on functional longevity of Canadian dairy cattle using a Weibull proportional hazards model. First-lactation data consisted of the following: 1,728,289 and 2,426,123 Holstein cows for milking temperament and milking speed, respectively, from 18,401 herds and sired by 8,248 sires; 39,618 and 60,121 Jersey cows for milking temperament and milking speed, respectively, from 1,845 herds and sired by 2,413 sires; and 54,391 and 94,847 Ayrshire cows for milking temperament and milking speed, respectively, from 1,316 herds and sired by 2,779 sires. Functional longevity was defined as the number of days from the first calving to culling, death, or censoring adjusted for production. Milking temperament and milking speed were recorded on a 1- to 5-point scale from very nervous to very calm and from very slow to very fast, respectively. 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 as within herd-year-parity deviations; herd-year-season of calving; sire; and milking temperament or milking speed class. The relative culling rate was calculated for animals in each milking temperament or milking speed class after accounting for the above-mentioned effects. The study showed that there was a statistically significant association between workability traits and functional longevity. Very nervous cows were 26, 23, and 46% more likely to be culled than very calm cows in Holstein, Ayrshire, and Jersey breeds, respectively. Similarly, very slow milkers were 36, 33, and 28% more likely to be culled than average milkers in Holstein, Ayrshire, and Jersey breeds, respectively. Additionally, very fast milkers were 11, 13, and 15% more likely to be culled than average milkers in Holstein, Ayrshire, and Jersey breeds, respectively. Producers might want to avoid consequences associated with the fast milkers such as udder health problems.

Study on functional longevity of Tunisian Holstein dairy cattle using a Weibull proportional hazard model

Records of functional longevity (FL), from first calving to last recording (or culling), of 36,888 Tunisian Holstein cows in 169 herds were studied using survival analysis. Using a Weibull proportional hazard model, the influences of age at first calving, herd–year–season, lactation number–stage of lactation, milk production within the herd and year, annual change in herd size and random genetic effect of sire on FL were studied. Besides a random time-dependent effect of herd–year–season, the model included fixed effects of parity and stage of lactation, within herd and parity production level (all time-dependent), and age at first calving (time-independent). All factors had a significant effect on FL at a level of P < 0.001. Milk yield was by far the most important factor influencing FL and the hazard increased as the milk production decreased. Within the first three lactations, the relative culling risk increased stepwise with lactation stage. The highest risk of culling was found for cows at the beginning and at the end of the first lactation and at the end of any other lactation. The risk of culling decreased with parity.

Central Arctic Caribou and Petroleum Development: Distributional, Nutritional, and Reproductive Implications

We synthesize findings from cooperative research on effects of petroleum development on caribou (Rangifer tarandus granti) of the Central Arctic Herd (CAH). The CAH increased from about 6000 animals in 1978 to 23000 in 1992, declined to 18 000 by 1995, and again increased to 27 000 by 2000. Net calf production was consistent with changes in herd size. In the Kuparuk Development Area (KDA), west of Prudhoe Bay, abundance of calving caribou was less than expected within 4 km of roads and declined exponentially with road density. With increasing infrastructure, high-density calving shifted from the KDA to inland areas with lower forage biomass. During July and early August, caribou were relatively unsuccessful in crossing road/pipeline corridors in the KDA, particularly when in large, insect-harassed aggregations; and both abundance and movements of females were lower in the oil field complex at Prudhoe Bay than in other areas along the Arctic coast. Female caribou exposed to petroleum development west of the Sagavanirktok River may have consumed less forage during the calving period and experienced lower energy balance during the midsummer insect season than those under disturbance-free conditions east of the river. The probable consequences were poorer body condition at breeding and lower parturition rates for western females than for eastern females (e.g., 1988–94: 64% vs. 83% parturient, respectively; p = 0.003), which depressed the productivity of the herd. Assessments of cumulative effects of petroleum development on caribou must incorporate the complex interactions with a variable natural environment.

Herd size and bovine tuberculosis persistence in cattle farms in Great Britain

Bovine tuberculosis (bTB) infection in cattle is one of the most complex and persistent problems faced by the cattle industry in Great Britain today. While a number of factors have been identified as increasing the risk of infection, there has been little analysis on the causes of persistent infection within farms. In this article, we use the Cattle Tracing System to examine changes in herd size and VetNet data to correlate herd size with clearance of bTB. We find that the number of active farms fell by 16.3% between 2002 and 2007. The average farm size increased by 17.9% between 2002 and 2005. Using a measure similar to the Critical Community Size, the VetNet data reveal that herd size is positively correlated with disease persistence. Since economic policy and subsidies have been shown to influence farm size, we used a simple financial model for ideal farm size which includes disease burden to conclude that increasing herd size for efficiency gains may contribute to increased disease incidence.

Relationship Between Reproduction Traits and Functional Longevity in Canadian Dairy Cattle

The aim of this study was to use survival analysis to assess the relationship between reproduction traits and functional longevity of Canadian dairy cattle. Data consisted of 1,702,857; 67,470; and 33,190 Holstein, Ayrshire, and Jersey cows, respectively. Functional longevity was defined as the number of days from first calving to culling, death, or censoring; adjusted for the effect of milk yield. The reproduction traits included calving traits (calving ease, calf size, and calf survival) and female fertility traits (number of services, days from calving to first service, days from first service to conception, and days open). The statistical model was a Weibull proportional hazards model and included the fixed effects of stage of lactation, season of production, the annual change in herd size, and type of milk recording supervision, age at first calving, effects of milk, fat, and protein yields calculated as within herd-year-parity deviations for each reproduction trait. Herd-year-season of calving and sire were included as random effects. Analysis was performed separately for each reproductive trait. Significant associations between reproduction traits and longevity were observed in all breeds. Increased risk of culling was observed for cows that required hard pull, calved small calves, or dead calves. Moreover, cows that require more services per conception, a longer interval between first service to conception, an interval between calving to first service greater than 90 d, and increased days open were at greater risk of being culled.

Analysis of Milk Urea Nitrogen and Lactose and Their Effect on Longevity in Canadian Dairy Cattle

The aim of this study was to assess the phenotypic level of lactose and milk urea nitrogen concentration (MUN) and the association of these traits with functional survival of Canadian dairy cattle using a Weibull proportional hazards model. A total of 1,568,952 test-day records from 283,958 multiparous Holstein cows from 4,758 herds, and 79,036 test-day records from 26,784 multiparous Ayrshire cows from 384 herds, calving from 2001 to 2004, were used for the phenotypic analysis. The overall average lactose percentage and MUN for Ayrshires were 4.49% and 12.20 mg/dL, respectively. The corresponding figures for Holsteins were 4.58% and 11.11 mg/dL. Concentration of MUN increased with parity number, whereas lactose percentage decreased in later parities. Data for survival analysis consisted of 39,536 first-lactation cows from 1,619 herds from 2,755 sires for Holsteins and 2,093 cows in 228 herds from 157 sires for Ayrshires. Test-day lactose percentage and MUN were averaged within first lactation. Average lactose percentage and MUN were grouped into 5 classes (low, medium-low, medium, medium-high, and high) based on mean and standard deviation values. 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 as within herd-year-parity deviations, herd-year-season of calving, lactose percentage and MUN classes, and sire. The relative culling rate was calculated for animals in each class after accounting for the remaining effects included in the model. Results showed that there was a statistically significant association between lactose percentage and MUN in first lactation with functional survival in both breeds. Ayrshire cows with high and low concentration of MUN tended to be culled at a higher than average rate. Instead, Holstein cows had a linear association, with decreasing relative risk of culling with increasing levels of MUN concentration. The relationship between lactose percentage and survival was similar across breeds, with higher risk of culling at low level of lactose, and lower risk of culling at high level of lactose percentage.

Analysis of the Relationship Between Somatic Cell Score and Functional Longevity in Canadian Dairy Cattle

The aim of this study was to assess the level of somatic cell count (SCC) and to explore the impact of somatic cell score (SCS) on the functional longevity of Canadian dairy cattle by using a Weibull proportional hazards model. Data consisted of 1,911,428 cows from 15,970 herds sired by 7,826 sires for Holsteins, 80,977 cows in 2,036 herds from 1,153 sires for Ayrshires, and 53,114 cows in 1,372 herds from 1,758 sires for Jerseys. Functional longevity was defined as the number of days from the first calving to culling, death, or censoring. The test-day SCC was transformed to a linear score, and the resulting SCS were averaged within each lactation. The average SCS were grouped into 10 classes. 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; SCS class; and sire. The relative culling rate was calculated for animals in each SCS class after accounting for the aforementioned effects. The overall average SCC for Holsteins was 167,000cells/mL, for Ayrshires was 155,000cells/mL, and for the Jerseys was 212,000cells/mL. In all breeds there were no appreciable differences in the relative risk of culling among classes of SCS breed averages (i.e., up to a SCS of 5). However, as the SCS increased beyond the breed average, the relative risk of cows being culled increased considerably. For instance, Holstein, Ayrshire, and Jersey cows with the highest classes of SCS had, respectively, a 4.95, 6.73, and 6.62 times greater risk of being culled than cows with average SCS.

Genetic evaluation of length of productive life in the Spanish Holstein-Friesian population. Model validation and genetic parameters estimation

Functional longevity (FL), measured as length of productive life (LPL) adjusted by production level, has been regarded as an important trait to measure the global functional aptitude of a cow, particularly when direct measures of the functional traits (health and reproductive performance) are not available. The objective of this study was to analyze the trait FL making use of survival analysis techniques in order to propose a model for the genetic evaluation of this trait in the Spanish Holstein Friesian population. The data set consisted of 133,629 registered cows of three regions; Andalusia, Basque Country and Catalonia. The hazard function was described as the product of a baseline hazard function and the time-independent effects of age at first calving, lactation number-stage of lactation, annual change in herd size, milk, fat and protein yield. Sire and maternal grandsire and herd-year-season of calving were considered as random effects. Percentage of right-censored data ranged from 41.9% to 52.7% for the analysed data sets. All the effects analyzed were significant (P < 0.0001) and had a great influence on the risk of culling of a cow, except for the age at first calving which showed a relatively small effect. Higher risk for factors such as age at first calving, change in herd size and relative level of milk production was associated with the more extreme classes. The consistency of the results among regional samples which represent diverse production systems in the population indicated that the proposed model could be applied at the national level. The relatively low heritability (0.048 to 0.074) suggests that genetic improvement of LPL could be effective if the direct evaluation is combined with indirect measures of LPL.

Analysis of Inbreeding and Its Relationship with Functional Longevity in Canadian Dairy Cattle

The aim of this study was to assess the level of inbreeding and its relationship to the functional survival of Canadian dairy breeds by using a Weibull proportional hazard model. Data consisted of records from 72,385 cows in 1,505 herds from 2,499 sires for Jerseys, 112,723 cows in 1,482 herds from 2,926 sires for Ayrshires, and 1,977,311 cows in 17,182 herds from 8,261 sires for Holsteins. Longevity was defined as the number of days from first calving to culling, death, or censoring. Inbreeding coefficients (F) were grouped into 7 classes (F=0, 0<F<3.125, 3.125≤F<6.25, 6.25≤F <12.5, 12.5≤F<18.25, 18.25≤F<25.0, and F≥25.0%). 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 as within herd-year-parity deviations, herd-year-season of calving, inbreeding, and sire. The relative culling rate was calculated for animals in each class after accounting for the above-mentioned effects. A trend toward increased risk of culling among more inbred animals was observed for all breeds. Little difference in survival was observed for cows with 0<F <12.5%. The relative risk ratios (relative to F=0) for cows with inbreeding coefficients up to 12.5% were 1.19, 1.16, and 1.14 for Jersey, Ayrshire, and Holstein cows, respectively. Greater effects of inbreeding were seen, however, when F increased beyond 12.5%.

8000 years of caribou and human seasonal migration in the Canadian Barrenlands

Caribou (Rangifer tarandus) are the common thread running through thousands of years of cultural evolution in northern mainland Canada. From the earliest Indian traditions, through the Pre-Dorset and Dene cultural evolution, up to historic times, the vast herds of migratory Barrenland caribou provided food, clothing and shelter. They determined the human cycle -- seasonal migrations, seasonal levels of fitness, and season of procreation. Caribou even permeated Dene mythology and supernatural beliefs. Within the Beverly caribou (R. t. groenlandicus) range in the Canadian Barrenlands, investigation of 1002 archaeological sites points to long-term stability of human band and caribou herd interaction. Caribou bone and hunting tools occur in multiple levels, the earliest to 8000 years, based on 131 radiocarbon dates. Through time, specific hunting bands aligned with specific migratory barren-ground caribou herds. This relationship helps to explain observed archaeological and ethnological differences within different caribou ranges for these hunting bands. In general, biological evidence concurs with ethnographic and archaeological evidence. But short-term variations in migration routes between northern boreal forest, taiga and tundra may have followed changes in herd size and environment, e.g., unfavorable snow and ice conditions or forest fires. However, such influences were not discernible archaeologically.