Mean Herd Size Research Articles

Implications of the re-invasion of Southeast Uganda by Glossina pallidipes on the epidemiology of bovine trypanosomosis

A study to assess the influence of re-invasion of Glossina pallidipes on the epidemiology of bovine trypanosomosis was conducted in Southeast Uganda. A total of 1,992 cattle were screened in villages, with (949) and without G. pallidipes (1043) for trypanosomosis using a combination of the BCT and HCT methods. The prevalence of trypanosomosis (15.5%), Trypanosoma brucei infection (1.4%), T. congolense infection (7.2%), T. vivax infection (5.3%) and mixed infection (1.6%) in cattle in villages with was significantly higher than in those without G. pallidipes: trypanosomosis (7.1%), T. brucei infection (0.6%), T. congolense infection (2.0%), T. vivax infection (3.3%) and mixed infection (1.2%) (overall trypanosome infection, χ 2 = 35.5, d.f. = 1, P < 0.05; T. brucei infection, χ 2 = 8.06, d.f. = 1, P < 0.05; T. congolense infection, χ 2 = 22.8, d.f. = 1, P < 0.05 and T. vivax infection, χ 2 = 6.4, d.f. = 1, P < 0.05). Infections of Trypanosoma congolense were predominant in cattle in villages with G. pallidipes, while T. vivax infections were predominant in cattle in villages without. In all villages, T. brucei infections were fewer than either T. congolense or T. vivax infections. The risk of transmission of T. brucei, T. congolense and T. vivax infections was 3, 2.7 and 1.6 times, respectively, higher in villages with G. pallidipes than in those without, despite the presence of G. f. fuscipes in either set of villages. The mean PCV (28.27 ± 0.41, 95% CI) and mean herd size (3 ± 0.46) of cattle in villages with G. pallidipes were significantly ( P < 0.05) lower than in those in villages without (mean PCV, 29.48 ± 0.34; mean herd size, 4 ± 0.72). It is evident that presence of G. pallidipes brings about an increase in the prevalence of T. congolense, which causes a more severe disease in cattle than other species of trypanosomes. This is a rare case of a re-invasion of a tsetse species whose disease transmission capability calls for refocusing of the traditional national tsetse and trypanosomosis control strategies to contain it.

Area use by white-lipped and collared peccaries ( Tayassu pecari and Tayassu tajacu) in a tropical forest fragment

We present the first long-term radio telemetry study of area use by white-lipped and collared peccaries in a tropical forest fragment. Population densities of both species in a 2178-ha fragment of semideciduous Atlantic forest in southeastern Brazil were similar to estimates from another regional fragment with 16 times the area. The population of 150 (±52) white-lipped peccaries was divided among 3–4 subherds. We observed a high frequency of switching of individuals among subherds and documented periodic subherd fusion. Seven to 22 collared peccary herds (mean herd size, 9) persisted in the main forest fragment. Average home range size for the white-lipped peccaries was 1871 ha (90% HM). This was similar to the few reliable estimates available from continuous tropical forests. Despite supposed area restrictions, white-lipped peccaries maintained distinct seasonal ranges with a minimum of overlap. Within seasons, subherds overlapped spatially, but were separated temporally. Average home range sizes of two radio-tracked collared peccary herds were 305 and 123 ha. Home range boundaries and seasonal ranges of collared peccary herds shifted minimally, and herd subgrouping was short-lived. Spatial overlap between the two peccary species varied seasonally with white-lipped herd movements. We discuss future research needs and management actions for conservation of these species in fragmented landscapes.

Towards a Baseline Assessment of Organic Pig Welfare

AbstractOrganic farming is based on the premise that animal welfare is safeguarded primarily through good management; only when this fails are veterinary medicines used to intervene. As this premise is frequently quoted in marketing strategies, there is a need to assess the efficacy of this approach to reassure consumers. To move towards this assessment, a survey was conducted between August 1999 and April 2002 on nine organic pig farms located predominantly in the South West of England. This combined direct measurements of animals and facilities with structured questions to staff. The mean herd size (± standard error of mean) was 212 ± 74 sows, with all progeny being reared outdoors from farrowing to finish. The herds had been in existence for an average of 37 ± 7.0 months. Mange and lice were the highest-ranking current health concerns, and post-mortem report of endoparasitism was the highest-ranking historical health concern chosen by producers from a list pre-written by the experimenters. The main welfare issues reported by the primary stockperson were related to keeping stock clean and dry during periods of high rainfall, managing porcine dermatitis and nephropathy syndrome (PDNS) and postweaning multisystemic wasting syndrome (PMWS) within their herd, and recruiting and retaining good quality personnel. Facility assessment indicated good living conditions, with the exception of some wet paddocks during winter. Sow condition scores were not significantly different from accepted target values during pregnancy, at farrowing, or at weaning. Levels of lameness, skin damage and cleanliness did not cause concern in any class of stock.

Herd size in large herbivores: encoded in the individual or emergent?

In large mammalian herbivores, the increase of group size with habitat openness was first assumed to be an adaptive response, encoded in the individual. However, it could, alternatively, be an emergent property: if groups were nonpermanent units, often fusing and splitting up, then any increase of the distance at which animals perceive one another could increase the rate of group fusion and thus mean group size. Dynamical models and empirical data support this second hypothesis. This is not to say that adaptive modifications of mean herd size cannot occur. However, this changes the way in which we can envisage the history of gregariousness in large herbivores during the Tertiary.

Characteristics of Minnesota Dairy Farms that Significantly Increased Milk Production from 1989-19931,2

This study evaluated factors that affected decision making and changes within the Minnesota dairy industry. The 50 herds selected for this study had at least 75 cows registered with the Dairy Herd Improvement Association in 1993 and were selected based on the total percentage increase in milk production on the farm from 1989 to 1993. These 50 herds had a mean herd size of 131 cows and a mean milk production of 8807kg per cow in 1993. On average, from 1989 to 1993, the surveyed herds increased their total milk output by 90%, increased their herd size by 51 cows, and increased mean herd milk production by 926kg. Of the farms, 50% were partnerships or family corporations, and 50% were owned by a single family. The surveyed producers were 39 yr of age on average. During the period studied, the use of free-stall housing increased from 36 to 48%, use of the milking parlor increased from 32 to 54%, and use of tie stalls decreased from 42 to 28%. The daily hauling of manure decreased from 34 to 20% on these farms. The use of hired labor increased by a mean of 0.61 full-time workers and 0.34 part-time workers. Strategies for herd growth included internal growth (no purchased animals), 24%; the purchase of cows, 24%; and the purchase of springers, 52%. Over 90% of the producers were very satisfied or somewhat satisfied with dairy farming operations, but only 33% of the spouses were very or somewhat satisfied. Satisfaction levels were positively associated with overall production levels on the farms. Although there is no single established pattern for the expansion of herds, practices utilized by those producers surveyed can be scrutinized by others who are contemplating expansions to determine what might be efficient for their operations.

Segregation or use of separate milking units for cows infected with Staphylococcus aureus reduced prevalence of infection and bulk tank somatic cell counts

Dairy herds (n = 76) with initial prevalence of Staphylococcus aureus IMI&gt; 10% were included in this study, from among approximately 2800 herds visited between January 1992 and July 1994 by the Quality Milk Promotion Services at Cornell University. The farms were located in New York and Pennsylvania. Other inclusion criteria were that herds did not change teat dipping or dry cow treatment practices, were not segregating cows that were positive for S. aureus at the initial visit, and did not cull &gt; 50% of those found positive on the initial visit. Paired t tests and Wilcoxon rank sum tests were methods of statistical analysis. Mean herd size was 59 lactating cows, and herd size ranged from 28 to 436 cows. Percentage of herds teat dipping, using dry cow treatment, and mean herd size were not different among segregation groups. Mean number of visits (3.5 per herd) did not differ among groups. During a follow-up period (6-to-24 mo), segregation or separate milking of cows (n=21 herds) that were positive for S. aureus resulted in reduction of prevalence from 29.5 to 16.3%, and bulk tank SCC from 600,000 to 345,000/ml. Prevalence of S. aureus mastitis was unchanged for herds (n=55 herds) not segregating S. aureus cows, 22.5 to 20.2%, and the change in SCC from 698,000 to 484,000 for nonsegregated herds was less of a reduction than for the segregating herds. Segregation or use of separate units for cows known to be positive for S. aureus is an effective mastitis control practice.

Alberta Dairy Farm Survey Response

All dairy producers in the Canadian province of Alberta were mailed a questionnaire to determine current management practices and production. This survey was undertaken to develop and to plan extension programs based on current dairy producer needs. Of the producers contacted, 802 (57%) responded to the survey questionnaire. The results indicated that the mean herd size was 67 cows, and mean daily milk production was 21.9 kg/d per cow. More than 60% of the producers reported that the majority of their calf losses occurred at birth, and another 15.6% stated that losses occurred within the 1st wk. Less than one-third of the cooperators individually penned calves to prevent contact among calves prior to weaning. Approximately 31% of the cows in the herds surveyed required two or more breedings, partially because of inadequate estrus detection; only 50.3% of the respondents had daily scheduled detection times. The most frequent health concerns perceived by the producers were mastitis, foot problems, and silent estrus. Educational and extension programs should focus on specific areas, such as newborn calf management and reproductive management, to improve the efficiency and profitability of dairy production in Alberta.

Prevalence and severity of lameness in lactating dairy cows in a sample of Minnesota and Wisconsin herds

Summary: An epidemiologic study investigating the prevalence of lameness in lactating dairy cows was performed in 17 dairy herds in Minnesota and Wisconsin. The mean herd size was 50 cows. Cows from 14 herds were housed in stanchions or tie stalls, and cows from 3 herds in free stalls or dry lot. During visits to each farm in the summer and subsequent spring, 2 investigators simultaneously but independently evaluated the ambulation of lactating cows by use of a standardized scoring system. The lameness scoring system was reliable at the 2 visits, with 92.7 and 91.3% agreement between the 2 observers and κ coefficients of 0.60. The prevalence of lameness detected by the investigators (“clinical” lameness) was 13.7% (117/853) in summer and 16.7% (134/801) in spring in lactating dairy cows. These prevalences were 2.5 times higher than those estimated by the herd managers. Parity was significantly (P ≤ 0.03) associated with lameness, with higher prevalence of clinical lameness found in cows of higher parity.

The national animal health monitoring system in Colorado beef herds: Disease rates and their associated costs

Forty cow-calf operations were selected randomly from Colorado herds during Round 2 (October 1986–September 1987) of the National Animal Health Monitoring System (NAHMS). The monthly NAHMS data on disease prevention, incidence, and associated costs were collected from 39 of the 40 herds. A subset of 14 herds was included in a subsampling study to validate the accuracy of the disease events reported by the livestock producers. There were 12 673 cows in these herds on 31 May 1987. The size of the herds ranged from 15 to 3259 cows with a mean herd size of 325±529 cows. Diseases were categorized into five classes: (1) reproductive; (2) respiratory; (3) enteric; (4) sudden death/clostridial diseases; (5) miscellaneous. The annual cost of the disease preventive measures in these cow-calf herds was $6.39 per cow, which included the cost of vaccines and drugs ($5.11 per cow) and the cost of veterinary service ($1.28 per cow). Additionally, 0.32 h of labor was spent, on a per-cow basis, on activities related to disease prevention. A total of 4180 disease incidents were reported in the 39 beef cow-calf herds. The annual cumulative disease incidence rates were highest for the miscellaneous (10.3%) and enteric (9.7%) disease classes and lowest for the sudden death/clostridial diseases class (1.6%). The total annual number of disease cases in these herds was 33 per 100 cows at risk. The total annual mean cost associated with the occurrence of diseases in these herds was $20.56 per cow. The serologic results indicated that nearly all herds had been exposed to bluetongue and/or epizootic hemorrhagic disease. However, there were no confirmed clinical cases of bluetongue during the observation period. There were no herds that had animals with positive titers to any serotype of leptospirosis. Biological samples were submitted from 31 cases for diagnostic testing. Confirmed diagnostic results were obtained on only three of the 31 cases.

The incidence, cost and factors associated with foot lameness in dairy cattle in south-western Victoria.

A survey of 73 dairy farms in south-western Victoria was conducted to assess the cost and mean herd incidence of foot lameness for the period from calving to the end of November, 1985, and to identify the herd, management and environmental factors associated with foot lameness. The mean herd size was 125 cows (range 82 to 220). Lameness occurred in 64 (88%) herds, and the mean herd incidence was 7.0% (range 0.0 to 30.9%). The main clinical signs associated with lameness were the presence of overworn and/or bruised soles, or stones lodged in the interdigital cleft. Factors associated with lameness were: property and herd size, age of cow, bail feeding, voluntary entry into the bails, and features of the farm track including its length, the presence of steep slopes, the type of surface material, presence and treatment of broken sections and maintenance including rolling history. The association of these factors with specific clinical signs was examined. The mean cost was estimated to be $42.90 per lame cow due to loss of production, treatment, the culling or death of lame cows, and extra man hours spent managing lame cows. It was concluded that the site, construction, maintenance and use of the farm track were of major importance to the incidence of lameness in herds in this area and recommendations for reducing lameness are made.

The Production Structure of Pennsylvania Dairy Farms

The production structure of a selected cross-section sample of family owner-operated dairy farms is investigated using a translog variable cost function. Elasticities of scale, input substitution, and input own- and cross-price elasticities are estimated. At the sample mean herd size of 67 cows producing at 15,173 pounds of milk per cow, the elasticity of scale parameter was 1.00, implying constant returns to scale. The elasticities of substitution between feeds and hired labor and the own- and cross-price elasticities were inelastic.

Case study of estimation of prevalence of bovine brucellosis in El Salvador

In many developing countries quite a large proportion of the resources available for animal health improvement are diverted to the control of bovine brucellosis. It is imperative therefore that these control measures are decreasing the incidence of the disease. In El Salvador it has been found extremely difficult to evaluate the efficacy of the brucellosis control campaign due to a lack of epidemiological data. Retrospective evaluation of results from brucella herd tests indicated that the prevalence was 3.7% for 190,044 animals tested between 1971–1976. This data related to only 254 herd tests per year in herds of more than 100 cows. The national herd, however, has 93,985 herds and a mean herd size of only 6 cows. For this reason a properly designed serological survey of brucellosis was carried out in 1978. A total of 786 herds was studied and blood samples were collected from 21,624 females and 891 males. These were submitted to the Rose Bengal and Serum Agglutination Tests for brucellosis. The herds studied were selected on the basis of geographical location and herds size. In each region the selected herds were sampled by the government veterinarian, who also completed a detailed questionaire on each farm. Very low animal (0.93%) and herd prevalence (1.46%) rates were detected.

Winter Behavior of Pronghorns in Relation to Habitat

The winter behavior of pronghorn antelopes (Antilocapra americana) was studied from 6 January to 12 April 1969 in southeastern Alberta and northern Montana. January, climatically an exceptionally severe month in the study area, saw a pronounced movement of pronghorns southward. The mean herd size was 39.8 11.5 head. Herds did not mix, nor move more than a few km from local sites during February and March; a distinct disbanding process was noted after 25 March. Fences and roads limited day to day movements. Herd composition counts for 6 herds (221 head) indicated a low fawn proportion (41 fawns to 100 does). The male to female fawn ratio of 42 to 100 indicated poor production or survival of male fawns. Pronghorns were adept at pawing away snow cover to reach their food. They spent 6.2 to 11.5 percent of their feeding time pawing. Interactions at feeding craters and bedding sites indicated a social heirarchy with male adults at the top, followed by female adults, and fawns. Pronghorns selected microhabitats with more favorable conditions than the average for the area as a whole, these being: 63 percent lower wind velocities, 24 percent less snow, and 87 percent softer snow. The daytime activity pattern began with a feeding period shortly after sunrise. Resting animals oriented the longitudinal axis of the body so that their anterior portions were downwind when chill factors were extreme; they also curled their heads alongside the body more often at lower chill factors. J. WILDL. MANAGE. 41(3):560-571 Few efforts have been made to determine how wild ungulates have adapted their behavior to winter conditions. Pruitt (1959) has shown that snow influences much of the behavior of caribou (Rangifer arcticus). Henshaw (1968) confirmed much of this with supporting data for Alaskan caribou. In Quebec, DesMeules (1964, paper presented at N.E. Wildl. Conf., Hartford, Conn.) learned that moose (Alces alces) capitalize on the insulating properties of loose fluffy snow when selecting bedding sites. They also travel under large conifers where the snow is less deep. Verme (1968) was able to demonstrate that temperature and wind were the major climatic factors causing heat loss in white-tailed deer (Odocoileus virginianus) in normal habitat. Moen (1968) concluded that behavior of animals may easily turn a negative heat exchange into a positive one. The objective of this research was to determine the winter behavioral adaptations of pronghorn antelopes. I am indebted to V. Geist for his support, valuable suggestions, and criticisms. Gratitude is also expressed to my wife, E. Scheinberg and D. R. Flook for their assistance.

The numbers and distribution of buffalo in the Ruwenzori National Park*, Uganda

SummaryThe buffalo (Syncerus coffer (Sparrman)) in the Ruwenzori National Park, Uganda were censused by means of aerial survey. Details of earlier censuses of buffalo from the air are given. Herds were located by flying along flight lines 1–6 km apart at a height of 300 m above ground. Buffalo in small herds and in bachelor groups containing less than thirty animals were counted individually but most herds were photographed and the number of buffalo counted from the prints. Two full photographic counts were made in November 1968 and December 1969 and subsequently, counts of herds only were made four times a year during each wet and dry season. The total numbers of buffalo were estimated from the herd counts on the basis of the mean herd size and percentage of bachelors recorded earlier. A total of 17 835 buffalo, comprising 16 749 in 165 herds and 1086 bachelor bulls, was recorded in 1968 and 18 040 buffalo made up of 17 141 in 162 herds and 899 bachelors were counted in 1969. The mean herd size was 101‐5 in 1968 and 105‐8 in 1969 with bachelors representing 6‐1% and 5‐0% of the totals in 1968 and 1969 respectively. The mean size of the bachelor groups was 4–7 and 3‐3 in 1968 and 1969 respectively. The density of the buffalo was the same each year at twelve animals per sq. km. If only the preferred habitat is considered, the density becomes thirty‐eight buffalo per sq. km. The mean areas occupied by a single herd were 9‐4 and 9‐6 sq. km in 1968 and 1969 respectively. The mean area of preferred habitat used by one herd was 2–9 sq. km each year. It is concluded that herd counts are not a satisfactory method for assessing the total buffalo population although they have value as indices, provided the same observer is used. However, they do suggest in the present work that there is a slight but definite seasonal movement of buffalo into forested areas or towards permanent water during the dry season.