Dairy-heifer management in the Netherlands

The objective of this study was to describe the Dutch rearing performance of dairy heifers by the evaluation of performance indices at weaning, breeding and calving. The second objective was to determine the extent to which dairy farmers use pre-set rearing targets and data monitoring for the evaluation of their rearing results. A questionnaire was sent to 3000 randomly chosen dairy cattle farmers to survey their heifer-rearing practices. Almost a third of the farmers (n=959) completed and returned the questionnaire. Of the farms responding, 29% realised an age at first calving of < or =24 months, 51% from 25 to 27 months, and 20% of > or =27 months. The farmers indicated that the average body weight after calving was within the range 525-550 kg. Average wither height class was 141-145 cm. Most farmers estimated the body-condition score of their heifers at calving to be 3-3.5. In 29% of the cases, weaning occurred at an age of < or =8 weeks, 35% at 9-10 weeks of age and 36% at > or =11 weeks of age. Most farmers (81%) commenced breeding at an age of > or =15 months.Intermediate evaluation of the rearing policy by means of performance goals and measurements was limited, and many of the reported performance indices on age and body weight were outside the range of the recommended target values. These results indicated that the common Dutch heifer-rearing management system could be improved considerably.     

Comparison of target breeding weight and breeding date for replacement beef heifers and effects on subsequent reproduction and calf performance

A 3-yr study was conducted with spring-born heifers (n = 240) to determine the effects of developing heifers to either 55 or 60% of mature BW at breeding on reproduction and calf production responses. A concurrent study was also conducted with summer-born heifers (n = 146) to examine effects of breeding heifers with the mature cow herd or 1 mo earlier on reproduction and calf production variables. Spring-born crossbred heifer calves were weaned and developed on two different levels of nutrition to achieve the desired prebreeding BW. Summer-born heifers were developed to similar target breeding BW (60% of mature BW) to begin calving either 1 mo before (May) or at the same time as the mature cowherd (June). Blood samples were taken before breeding to determine differences in estrous cyclicity. Pregnancy rates through the fourth pregnancy were determined. Cow and calf production variables were evaluated through the third gestation. Spring-born heifers reached 53 or 58% of mature BW at breeding and had similar reproduction and first calf production traits between the two, groups. Calving difficulty with the second calf was greater (P < 0.05) for heifers developed to 58% of mature BW at breeding. Subsequent second calf weaning weight and ADG were decreased (P < 0.05) for heifers developed to 58% of mature BW at breeding. Feed costs were $22/heifer less for heifers developed to 53% of mature BW. Summer-born first-calf heifers calving in June had less (P < 0.01) calving difficulty than did heifers calving in May; however, calf birth weights were similar. Breeding summer-born heifers 1 mo before the cowherd did not influence pregnancy rates over three calf crops; however, first calf adjusted weaning weights and ADG were greater for calves born earlier. Development costs were $11/heifer more for heifers developed to calve in May vs. June. Developing spring-born heifers to 53% of mature BW did not adversely affect reproduction or calf production traits compared with developing heifers to 58% of mature BW, and it decreased development costs. Breeding summer-born heifers before the cowherd increased heifer development costs, increased calving difficulty, and improved calf performance, but had no effect on pregnancy rates.     

Rearing conditions, morbidity and breeding performance in dairy heifers in southwest Sweden

We carried out a longitudinal study of 122 dairy herds in southwest Sweden to investigate relationships of rearing conditions and health with heifer breeding performance and to estimate the incidence of clinical diseases and survival until 1st calving. A total of 3081 animals born in 1998 (47% Swedish Red; 50% Swedish Holstein breed) were followed from birth until calving, culling or death. Information about housing, management, breeds and dates of birth, breeding and calving was obtained from farmers. Diseases were recorded by farmers and veterinarians; antibiotic treatment was used in <25% of all cases.Median time to breeding was 17.5 months, 64% of all heifers bred by AI conceived at 1st breeding, and median time to calving was 27.6 months. Age at 1st breeding (log-transformed), conception at 1st breeding (binary), and age at 1st calving (log-transformed) were analysed with three mixed models, accounting for clustering by considering random-intercept and random-slope effects at the herd level. Around 40 potential predictors or confounders were recorded and considered for modelling. Time to breeding and calving increase greatly with the time heifers spend grazing, although up to 5 months of grazing before 1st calving appears to be more favourable than no grazing at all. The effect of grazing differs depending on the season of birth. Zero-grazed heifers calve 20% later if exposed to indoor ammonia concentrations >10 ppm after start of breeding. There is considerable variation between herds in breeding performance, except for conception at 1st breeding—limiting the potential for improving conception by herd measures.Observed total disease incidence rate was 14 per 100 animal-years from 7 months of age to estimated conception and 4.7 per 100 animal-years from conception to calving, with great variation between herds. Infectious diseases were predominant, and diarrhoea, respiratory disease and ringworm were the most common diagnoses. Eight hundred and fifty-three heifers left the study before calving, due to herd exits (incidence risk 0.073%), selling off live (0.061%), spontaneous deaths (0.050%) or slaughter (0.092%).     

Nutrition and the development of replacement heifers

Does the system work? After having been on a controlled heifer replacement program for 3 to 5 years, the entire herd will develop a short calving season resulting in more weaned calf weight per cow exposed to breeding. Wiltbank has reported on the advantage of feeding heifers for a selected target weight at breeding. Two groups of Brahman-cross heifers were fed to weigh 600 or 700 lbs at the beginning of the breeding season. They were pastured and fed similarly from breeding through weaning their first calves. The heifers that weighted 700 lb at breeding weaned 86 lb more calf per heifer exposed. They bred earlier and more became pregnant. The return above feed costs after 2 years breeding was $52 greater for the heavier heifers. Obviously, the benefits continue through subsequent calvings, emphasizing the importance of managing the replacement heifers for 3 years, through their second breeding and calving.     

An economic model to calculate farm-specific losses due to bovine respiratory disease in dairy heifers

This paper describes a personal-computer-based model estimating the economic losses associated with clinical bovine respiratory disease in replacement heifers raised on individual dairy farms. The model is based on the partial-budgeting technique, and calculates the losses for two types of the disease separately: calf pneumonia and a seasonal outbreak. Model input includes farm-specific data such as the incidence of bovine respiratory disease, prices, and effects of the disease on the heifers' productivity. The input database was linked directly with the economic model. For all input parameters, default values used are available to the user and can be modified easily.Losses considered by the model include treatment expenditures and costs associated with increased mortality, increased premature culling, reduced growth, reduced fertility and reduced milk production in first lactation. Uncertainty is taken into account for parameters related to disease incidence, mortality and culling.Basic calculations for a typical Dutch dairy farm with 60% of the heifers (<3 months) affected, indicated total annual losses due to pneumonia average 31.2 per heifer present on the farm (range 18.4-57.1). The estimated losses for one seasonal outbreak with heifers up to 15-months old affected were 27.0 per heifer present (range 17.2-43.1). For both BRD types, the model's outcome was most sensitive to the number of heifers affected. Most of the parameters that had a major impact on the total losses were related to treatment or to the effects on the heifers' productivity.The model is user-friendly and flexible, and can be used as an interactive tool by farmers and veterinarians in the (economic) decision-making process regarding on-farm prevention and control of bovine respiratory disease.     

Relative calving date of first-calf heifers as related to production efficiency and subsequent reproductive performance

Relative date of first calving of beef heifers was studied in relation to production efficiency and subsequent reproductive performance. Crossbred heifers were managed in a drylot environment for 1 yr with feed intake measured through weaning of the first calf. Mean heifer age at entry into drylot was 572 d. Production traits were evaluated by calving group (CG), where CG1 included records of heifers calving (and calves born) in the first 21 d of the calving season for a particular year, CG2 included those calving from 22 through 42 d and CG3 included those calving after 42 d. Calving groups did not differ significantly for preweaning calf ADG, but weaning age differences resulted in heavier weaning weights for CG1 compared with CG2 and CG3. An earlier relative calving date was associated with increased cumulative feed energy intake of heifers and their calves during the 1-yr test period. In terms of production efficiency, the weaning weight advantage of earlier calving was offset only partly by the increased feed energy intake of the dam-calf unit, resulting in 6.3 Mcal (12.4%) less ME per kg calf weaning weight for CG1 vs CG3 for the 1-yr period. Within a limited calving season, earlier calving dams tended to be biologically and economically more efficient because a greater proportion of their annual production cycle was in a productive (lactating) mode, diluting maintenance costs as a fraction of all costs. Heifers in CG1 also tended to calve earlier than CG3 heifers for the second calf. Calving interval was a biased measure under the management conditions of a limited breeding season and culling of open cows.     

Prevalence and risk factors for dystocia in dairy cattle: a review

This review focuses on the case definition of dystocia, its current prevalence and recent temporal trends, the different types of dystocia and their associated risk factors in dairy cattle. The reported dystocia rates in dairy cattle internationally are generally <5%, apart from those in the United States, where they are higher. Given the skewed distribution of herd dystocia rates, average figures mask high prevalence herds. Phenotypic dystocia trends are generally increasing internationally and this trend has been partially attributed to the introduction of Holstein genes. The principal types of dystocia differ between primiparae and pluriparae, with feto-pelvic disproportion (FPD) predominating in the former and fetal malposition in the latter. In order of importance, the two major determinants of FPD are calf birthweight and maternal pelvic size. Abnormal fetal position is most influenced by the number of fetuses, parity and calf sire breed. Adequate weighting of dystocia in selection indices, achievement of heifer rearing targets prior to both service and calving, and appropriate periparturient management decisions are prerequisites for controlling dystocia in dairy cattle.     

Influence of herd structure and type of virus introduction on the spread of bovine viral diarrhoea virus (BVDV) within a dairy herd

A herd is a population structured into groups not all equally in contact, which may influence within-herd spread of pathogens. Herd structure varies among cattle herds. However, published models of the spread of bovine viral diarrhoea virus (BVDV) assume no herd structure or a unique structure chosen as a representative. Our objective was to identify--for different index cases introduced into an initially BVDV--free dairy herd - risky (favourable) herd structures, which increased (decreased) BVDV spread and persistence compared to a reference structure. Classically, dairy herds are divided into calves, young heifers, bred heifers, lactating cows and dry cows. In the reference scenario, groups are all equally in contact. We evaluated the effect of isolating or merging groups. Three index cases were tested: an open persistently-infected (PI) heifer, an open transiently-infected heifer, an immune heifer carrying a PI foetus. Merging all groups and merging calves and lactating cows were risky scenarios. Isolating each group, isolating lactating cows from other groups, and merging calves and young heifers were favourable scenarios. In most structures, the most risky index cases were the following: first, the entry of a PI heifer; second, the birth of a PI calf; last, the entry of a transiently-infected heifer. Recommendations for dairy herds are to raise young animals together before breeding and to isolate lactating cows from others as much as possible. These recommendations will be less efficient if a PI adult enters into the herd.     

Dam-related effects on heart girth at birth,morbidity and growth rate from birth to 90 days of age in Swedish dairy calves

We investigated the effects of dam-related factors (such as calving performance, milk leakage, diseases, milk production, and somatic-cell count (SCC)) on heart girth at birth and the incidence risk of diarrhoea and respiratory disease during the first 90 days in Swedish dairy calves. The effects of these dam-related factors and environmental and management-related (but not dietary) factors on the calves' growth rate during the first 90 days of life also were analysed. The study used nearly 3,000 heifer calves born in 1998 on 122 farms in the south-west of Sweden. Individual health records were kept by the farmers and visiting project veterinarians. The calf's heart girth was measured at birth and weaning. We used generalised linear mixed models for the size of the calf at birth and growth rate. Variables associated with the heart girth at birth were breed, calving performance, mastitis in the dam in the last 49 days before calving, milk production and parity. Variables associated with the growth rate were breed, calving performance, disease in the calf during its first 90 days of life, heart girth at birth, and housing of calves. The effect of the dam on the relative risk of diarrhoea and/or respiratory disease in the calf was evaluated by a generalised linear mixed model with a logit link. Morbidity in the dam during late pregnancy, retained placenta and SCC were associated with the relative risk of respiratory disease in the calf. None of the explanatory variables (other then breed) was associated with the relative risk of diarrhoea.     

Physiology and Endocrinology Symposium: Nutritional aspects of developing replacement heifers

Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.     

Pathogen group specific risk factors at herd, heifer and quarter levels for intramammary infections in early lactating dairy heifers

Risk factors for intramammary infections caused by coagulase-negative staphylococci, contagious major pathogens and environmental major pathogens in early lactating heifers were evaluated at the herd, heifer and quarter levels. In total, 764 quarters of 191 dairy heifers in 20 randomly selected farms in Flanders (Belgium) were sampled. Quarter milk samples were collected between 1 and 4 days in milk and between 5 and 8 days in milk for bacteriological culture. Data were analyzed using multivariable, multilevel logistic regression analysis. Higher average herd milk somatic cell count (>200,000 cells/mL), not having an effective fly control strategy, contact with lactating cows prior to calving and moderate to severe udder edema prior to calving increased the odds of intramammary infections caused by contagious major pathogens. Poor heifer hygiene and lack of mineral/vitamin supplementation prior to calving were risk factors for intramammary infection caused by environmental major pathogens. Teat apex colonization with coagulase-negative staphylococci prior to calving seemed to protect quarters against intramammary infections caused by major pathogens. Poor heifer hygiene before calving, a non-clipped udder and not practicing of teat dipping prior to calving increased the odds of intramammary infection with coagulase-negative staphylococci. Although management is important in the prevention and control of intramammary infections in early lactating heifers, most variation in the prevalence of intramammary infections resided at the heifer and quarter levels, indicating that the susceptibility for intramammary infections around calving is mainly determined by heifer and quarter characteristics.     

Feeding Strategies for Rearing Replacement Heifers in Small-scale Dairy Production Systems in the Highlands of Central Mexico

The growth of Holstein heifers in the campesino dairy systems in the highlands of Mexico was evaluated in three feeding strategies. Thirty-three heifers from 11 farmers, grouped according to strategy, were weighed every 14 days for 28 weeks. The live weight change over each 14-day period was estimated by individually regressing live weight over period, taking the regression coefficient as an unbiased estimate of live weight change. Regression coefficients were analysed as a randomized design with feeding strategies as treatments. Strategies were as follows: S1: grazed or cut pasture all year, maize silage and maize straw in the dry season, and 1.0–1.5 kg concentrate/heifer per day. S2: maize straw in the dry season, cut pasture forage, grazing of native grass, weeds from maize fields, and 1.0–1.5 kg concentrate/heifer per day. S3: maize straw in the dry season, grazed native grasses and weeds in the rainy season. Live weight gains were: S1, 0.511 kg/heifer per day; S2, 0.271 kg/heifer per day; and S3, 0.252 kg/heifer per day. Despite the better gains in S1, they are 24% below recommendations, arriving to service at 20 months of age. Not rearing their replacements may be a better alternative for campesino farmers under current economic conditions.     

Dairy calf rearing unit and infectious diseases: diarrhea outbreak by bovine coronavirus as a model for the dispersion of pathogenic microorganisms

Dairy calf rearing unit is a management system that is only recently being implemented by some milk producer’s cooperatives in southern Brazil. However, aspects related to the health profile of the heifer calves that arrive in the rearing unit as well as about biosecurity practices and microbiological challenges have not yet been evaluated in this rearing system in a tropical country. Diarrhea is the main and most frequent consequence of enteric infections in newborn calves. This study, through some etiological and epidemiological characteristics of an outbreak of neonatal diarrhea, has the aim to alert to the possibility of pathogenic microorganism spread in a dairy heifer calf rearing unit. The diarrhea outbreak presented some non-regular characteristics observed in bovine coronavirus (BCoV) enteric infections in dairy calves. The spread of infection was extremely rapid (1 week); the attack rate (>?50%) was much higher than that observed in calves subjected to conventional rearing; and the age range (5 to 90 days) of the affected heifer calves was much broader than that often observed in the BCoV diarrhea worldwide. These unusual epidemiological characteristics observed in this BCoV diarrhea outbreak raise awareness of the health threat present in calf rearing units as well as of the easy and rapid viral spread in a population of young animals from different dairy herds and, therefore, with very distinct immunological status.

     

Production performance of beef cows raised on three different nutritionally controlled heifer development programs

The objective of this study was to determine primiparous heifer performance following three different heifer development strategies that were the result of timed nutrient limitation. Two hundred eighty-two spring-born MARC III heifers were weaned at 203+/-1 d of age and 205+/-1 kg BW. The experiment was conducted on two calf crops with 120 heifers born in 1996 and 162 heifers born in 1997. Treatments consisted of different quantities of the same diet being offered for a 205-d period. Heifers in the HIGH treatment were offered 263 kcal ME/(BWkg)0.75 daily. Heifers in the MEDIUM treatment were offered 238 kcal ME/(BWkg)0.75 daily. Heifers in the LOW-HIGH treatment were offered 157 kcal ME/(BWkg)0.75 daily the first 83 d and 277 kcal ME/(BWkg)0.75 daily for the remainder of the 205 d. Treatments differed in total ME intake (P < 0.001); heifers on the HIGH treatment consumed 3,072+/-59 Mcal/heifer, those on the MEDIUM treatment consumed 2,854+/-21 Mcal/heifer, and those on the LOW-HIGH treatment consumed 2,652+/-19 Mcal/ heifer. At the beginning of breeding, heifers on the HIGH treatment were taller at the hips (P = 0.01) and weighed more (P < 0.001) than heifers in the other two treatments. The percentage of heifers that calved expressed as a fraction of the cows exposed did not differ among treatments (89.7%; P = 0.83). The age of heifer at parturition (P = 0.74) and the time from first bull exposure to calving (P = 0.38) did not differ among treatments. Birth weight of calves (P = 0.80) and the calves' weaning weight (P = 0.60) did not differ among the treatments. Calf survival rate on the LOW-HIGH treatment (73%) was lower than that on the moderate treatment (89%; P = 0.007) but did not differ from that on the HIGH treatment (81%; P = 0.26). The second-calf pregnancy rate (92.8%) for cows with a nursing calf at the start of breeding did not differ between treatments (P = 0.83). These findings suggest that as long as heifers are growing and meet a minimal BW before mating, patterns of growth may be altered in the post-weaning period without a decrease in the ability of the heifer to conceive or a decrease in calf growth potential. However, limit-feeding heifers may decrease first-calf survival. These alterations in postweaning gain through monitoring the amount of feed offered can be used to optimize feed resources.     

Endocrine measurements and calving performance of Swedish red and white and Swedish Holstein dairy cattle with special respect to stillbirth

During 3 consecutive calving seasons, calving performance, placental characteristics and endocrine profiles of total 98 pregnancies of late pregnant Swedish Red and White (SRB) and Swedish Holstein (SLB) dairy heifers and cows, were investigated. Ninety-four singleton pregnancies and 4 sets of twins were recorded. In animals with singleton pregnancy, 8 stillbirths, 7 weak calves, 3 premature parturitions and 1 abortion were registered. In the SLB heifers, 19% of stillbirth (5/26) were observed, while 5% (2/42) were noted for the SRB heifers. One stillborn calf derived from the SRB cows and none was found from the SLB cows. In the heifers and cows delivering a normal living calf with unassisted parturition, the placentome thickness monitored by ultrasonography was constant towards the end of pregnancy. The numbers of foetal cotyledons varied individually between animals but in total, fewer cotyledons were found in the foetal membranes of the SRB animals than in the SLB animals (69 +/- 19) vs. (88 +/- 29) (p < 0.05). No morphological and numerical differences of the placentome thickness in animals delivering a stillborn or weak calf, compared to animals delivering a normal living calf, could be observed. In animals with unassisted parturition and without birth complications, the levels of progesterone (P4), PGF2alpha metabolite (PG-metabolite), cortisol, oestrone sulphate (E1SO4) and pregnancy associated glycoproteins (PAGs) were not different by breeds and parities. In animals carrying stillbirth, higher levels of E1SO4 were found in 3 SRB animals and 1 SLB heifer, whereas lower levels of E1SO4 were recorded in 3 SLB heifers during the last week of pregnancy, compared to the profiles found in animals with unassisted parturition. Additionally, the levels of PAGs remained low and constant in 1 SRB cow (delivering a stillborn calf), 1 SRB heifer (giving birth prematurely), 4 animals (carrying twins) and 1 aborting SRB cow. Our results show a very high rate of stillbirth in especially SLB heifers and deviating profiles of E1SO4 and PAGs in animals with impaired parturition were recorded.     

Cubicle refusal and rearing accommodation as possible mastitis risk factors in cubicle-housed dairy heifers.

Fifty-nine of the 65 dairy farms with cubicle sheds in the Norwegian county of Oppland in 1990 were included in a study of rearing accommodation, cubicle refusal and mastitis incidence. The farmers recorded the favoured resting location of the individual cows and heifers throughout the final week of pregnancy as well as during calving. The observations were matched with individual records of mastitis cases during the first 30 days after calving. Mastitis incidence in the heifers was analysed by logistic regression using rearing accommodation and cubicle refusal as independent variables, controlling for herd as a clustering factor. Cubicle refusal was found in 29% of the heifers, but in only 3% of older cows. The results of the analysis indicated a tendency for cubicle refusal to be associated with an increased mastitis incidence among the heifers (OR = 2.2, c.i.95%OR = 0.9-5.4, P = 0.08). Cubicle refusal accounted for 21% (0-32%) of the mastitis cases in the study population (PAF = 0.21).     

Evaluation of the California Mastitis Test as a precalving treatment selection tool for Holstein heifers

The objective of this study was to evaluate the California Mastitis Test (CMT) and a portable electrical conductivity meter for diagnosing precalving intramammary infection (IMI) in Holstein heifers. A total of 428 dairy heifers from 23 dairy herds were enrolled between 6 and 12 days before the expected calving date from June 2002 to June 2003. Mammary secretions were tested by both diagnostic methods and by bacterial culture for evidence of IMI. California Mastitis Test was considered negative if the score was negative, trace or 1 and was considered positive otherwise. Two cut-off points were evaluated for milk electrical conductivity (>5 and >6.5 mS/cm). From this study, an overall proportion of 69% of heifers had precalving IMI and the overall heifer prevalence of major pathogen IMI was 16.8%. At the quarter level, sensitivity and specificity of CMT (68.9% and 68.4%, respectively) and milk conductivity >5 mS/cm (41.0% and 65.2%, respectively) or >6.5 mS/cm (25.2% and 83.3%, respectively) to identify all IMI were low. However, the heifer level sensitivity and specificity of CMT for major pathogens were 91.0% (81.5-96.6) and 27.5% (22.8-32.6), respectively. Using a cut-off point of 5 mS/cm, the heifer level sensitivity and specificity for major pathogens was 68.7% (56.2-79.4) and 44.1% (38.7-49.6), respectively. A conductivity cut-off value of 6.5 mS/cm decreased the sensitivity and increased the specificity to 53.7% (41.1-66.0) and 59.5% (54.0-64.8), respectively. California Mastitis Test and milk electrical conductivity are not good predictors of major pathogen IMI in heifers during the last 2 weeks before calving. However, the negative predictive values at quarter or heifer level were high and the heifer false negative rate was 6-14% using CMT or conductivity, respectively. Therefore, these measures could be useful for screening out heifers or quarters that are unlikely to have a major pathogen IMI.     

Time of zeranol implantation on growth, reproduction and calving of beef heifers

Zeranol implants were administered to 250 crossbred heifer calves at 1, 6 or 9 mo of age to evaluate growth, reproduction and calving performance. Heifers were assigned to eight treatment groups with 25 animals per group. Two additional groups of 25 heifers each were used to study the effects of multiple implants at two levels of nutrition on heifer performance. Implants at 1 mo of age (branding) increased heifer weights at 6 mo of age (weaning) by 5 kg (P = .08). Heifers receiving a combination of two implants gained faster (P less than .05) from weaning to breeding (6 to 13 mo) than controls or heifers implanted three times. Implants at either 6 or 9 mo increased (P less than .05) precalving pelvic areas (247 vs 241 cm2 and 248 vs 240 cm2 over controls, respectively). Implants did not affect the percent of heifers reaching puberty prior to breeding season. Conception rates in 62 d of breeding were comparable for implanted and control heifers (93 vs 96%), with the exception of heifers receiving implants at both 1 and 6 mo of age (56%). Calf birth weight, dystocia score, cow rebreeding rate and calf weaning weight were not affected by implant treatments. Heifers that received three implants and were fed at a high nutritional level (gained .62 vs .49 kg/d for regular level after weaning) tended (P greater than .10) to reach puberty at a higher rate prior to breeding and to have a higher total conception rate than implanted heifers on the regular nutrition level.     

A simulation of Johne's disease control

A dynamic and stochastic simulation model (the "JohneSSim model") was developed to evaluate the economic and epidemiological effects of different strategies for control of paratuberculosis in dairy herds. Animals occupy one of the six defined infection states; the spread of Johne's disease is modeled with five infection routes. Many different dairy farm situations can be simulated. Control strategies that can be simulated are: (1) test-and-cull; (2) calf hygiene management; (3) vaccination and (4) grouping of animals. Losses are caused by: (1) reduced milk production; (2) diagnosis and treatment costs; (3) lower slaughter value of cows and (4) sub-optimal culling. The benefits were calculated as reduction in the losses caused by Johne's disease; the costs of each strategy were calculated on the basis of actual costs of each item; and net present value (NPV) was calculated as benefits minus costs. Herd and prevalence data from The Netherlands and Pennsylvania, USA were used. In both situations, a low true mean prevalence within 20 years could be reached only when all calf management tools were applied. The Dutch control program (PPN) was on average economically attractive (with or without labor costs, the average NPV was Euro 1183 and 12,397, respectively). In Pennsylvania, contract heifer rearing and improved calf hygiene reduced the prevalence effectively and had large economic benefits (US$ 43,917 for 20-year period) if the calves were sent to the heifer facility while very young. Validation with data from 21 infected Dutch dairy farms (as well as face-validation: comparison of the results of the JohneSSim model with experiences of Johne's experts) supported the basic assumptions in the model.