P.A. Oltenacu

Selection for increased production and the welfare of dairy cows: are new breeding goals needed?

Abstract In many European countries, milk production per cow has more than doubled in the last 40 years. The increase in production has been accompanied by declining ability to reproduce, increasing incidence of health problems, and declining longevity in modern dairy cows. Genetic selection for increased milk yield increasingly is viewed as increasing profit at the expense of reducing animal welfare. The economic future of the dairy industry is related directly to public acceptance of its breeding and production practices. It is important to the dairy industry that welfare problems should be addressed before there is widespread condemnation of breeding and management practices. A new breeding goal aimed at improving fitness and tolerance of metabolic stress is necessary to prevent the decrease in the quality of life of dairy cows and instead, perhaps, enhance it.

Epidemiological study of several clinical diseases, reproductive performance and culling in primiparous Swedish cattle

Abstract An epidemiological study of stillbirth, dystocia, retained placenta, metritis, cystic ovaries and silent heat and their effect on the risk of culling and reproductive performance is presented. Data consisted of 69 832 Swedish Red and White (SRB) and 39 178 Swedish Friesian (SLB) first lactation records. Logistic regression and path analysis were used to estimate the effects of age, season and herd production level on the risk of diseases, interrelationships between diseases and the effect of diseases on the risk of culling. The least squares procedure was used to estimate the effects of diseases on reproductive performance. The general pattern of interrelationships between diseases was similar for the two breeds but a stronger link between dystocia, stillbirth, retained placenta and metritis was found for the SRB breed than for the SLB breed (odds ratios connecting diseases were about two times larger in SRB breed). The dominant disease with respect to culling was cystic ovaries which increased the risk of culling about three times. All other diseases (except ketosis) increased the risk of culling about 1.5 times. Most diseases had a negative effect on reproductive performance. The largest effects were associated with retained placenta, metritis, cystic ovaries and silent heat which increased days open by approximately 7, 20, 40 and 40 days respectively.

Modelling reproduction in a herd of dairy cattle.

Abstract A dynamic stochastic model to simulate the reproductive process in a herd of dairy cattle has been constructed. The next event scheduling approach was utilized with four events being specified: perturition, ovulation, embryonic loss and replacement. The control variables included in the model are first breeding policy ( 1BDG ), reproductive culling policy ( RCLG ), heat detection program ( HDPM ), breeding program ( BDPM ) and service sires selection program ( SSPM ). In addition, the model uses numerous endogenous variables such as parturition type (PRTY), oestrus behaviour (EBHV), cows fertility (CFTY), embryonic mortality (EBLS), non-reproductive culling rate (NRCL) and others. The model was evaluated against independent experimental results. The simulated result closely approximates the average reproductive performance and variability of reproductive performance in a dairy herd.

Genetic and phenotypic relationships among milk production and composition traits in primiparous Holstein cows in two different herd environments

Abstract Genotype by environment interactions for mature equivalent milk yield (MEM), mature equivalent protein yield (MEP), mature equivalent fat yield (MEF), protein percentage (P%), fat percentage (F%), and lactation mean somatic cell score (LMSCS) were studied using 248 230 first parity records of Holstein cows calving from 1987 to 1994, daughters of 588 sires in 3042 herds. Herds were classified into low and high yield environment classes. Genetic parameters were estimated with bivariate linear mixed models using the multiple trait derivative free software ( mtdfreml ). For low yield environment herds, heritabilities for MEM, MEP, MEF, P%, F% and LMSCS were 0.22, 0.20, 0.23, 0.51, 0.58 and 0.11, while for high yield environment herds they were 0.30, 0.27, 0.27, 0.56, 0.56 and 0.09. All genetic correlations, except between MEM and P% and F%, were different in low and high yield environment herd classes. These results indicate that differences in management between the two herd environment classes modify the genetic expression of the traits studied and their genetic association. This suggests that, when these traits are considered in a selection index, appropriate weights for these traits depend on the herd environment class. These results also indicate that different correlated responses for MEP, MEF and LMSCS are expected in high relative to low yield environment herds when selection is based on MEM only.

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%).

Prion protein gene frequencies in three Sicilian dairy sheep populations

Abstract The objective of this paper was to investigate the prion protein (PrP) genotype and haplotype frequencies in three Sicilian dairy sheep populations. The three populations were: (1) 1096 Valle del Belice animals, (2) 1143 Comisana animals, and (3) 1771 individuals from 5 flocks with scrapie outbreaks, in which the animals were crossbreds derived from indigenous Sicilian dairy breeds. PrP genotypes are described for the three codons 136 (Alanine or Valine; A, V), 154 (Histidine or Arginine; H, R), and 171 (Glutamine, Arginine or Histidine; Q, R, H) which represent polymorphisms known to be linked with scrapie susceptibility. The Valle del Belice haplotype frequencies were 32.3% ARR, 6.5% AHQ, 1.0% ARH, 58.8% ARQ, and 1.4% VRQ. The Comisana frequencies were 39.4% ARR, 2.9% AHQ, 2.9% ARH, 50.9% ARQ, and 3.9% VRQ. In the flocks with scrapie outbreaks the frequencies were 32.8% ARR, 2.4% AHQ, 1.7% ARH, 59.1% ARQ, and 3.9% VRQ. In all three populations ARQ and ARR were the most frequent haplotypes. Multiple generations of strong selection will be needed to fixate the most resistant ARR haplotype.

Selecting linear-score distributions for modelling milk-culture results☆

The data for this cross-sectional retrospective study are from surveys of 65 dairy-cattle herds in central New York, USA sampled between February, 1993 and March, 1995. The objective was to identify probability distributions of logarithmically transformed somatic-cell counts (linear score) for use in a simulation model of mastitis and milk quality. Probability density functions were estimated using maximum-likelihood estimators for the linear score of individual-cow composite-milk samples culture negative and culture positive for the pathogens Streptococcus agalactiae, Streptococcus non-agalactiae, Staphylococcus aureus, and coagulase-negative staphylococci for the complete dataset and by bulk-tank somatic-cell count group (< 500,000, > or = 500,000 SCC/ml). Based on the rankings of three goodness-of-fit tests (Anderson-Darling, Kolmogorov-Smirnov and chi 2), the Weibull distribution (among the three top-ranking distributions for 14 out of 15 cases) may be used to model the individual-cow linear-score response by culture-result-specific bulk-tank somatic-cell count group. A beta distribution was among the three top-ranking distributions for nine out of 15 culture-result-specific bulk-tank somatic-cell count groups and has a logical relationship to linear score because it is defined on a fixed interval. On the other hand, the normal distribution had a poorer fit than the Weibull and at least two other distributions for all culture negative and coagulase-negative staphylococci samples. We do not assume that the underlying biological processes are fully explained by either Weibull or beta distribution--but modelling the linear score for the above culture results with these distributions provided an adequate fit to the survey data, reduced the need for two-sided truncation that open intervals needed, and had errors that did not appear to be systematically positive or negative.

An integrated computer instructional approach to improve dairy cattle estrus detection

Creative teaching methods aimed to train learners to improve farm management decisions need to be explored. In that context a microcomputer software package (ESTRUS-DETECTION) was developed to address a major economic problem in dairy herd management - estrus detection - by integrating tutorial and simulation instruction. ESTRUS-DETECTION was developed in the cT programming language. A pretest/posttest experimental design measured changes in learning for 45 students in an undergraduate dairy management course. Total learning was significantly increased among students. Comparable learning increases were shown for students working in pairs and individually. Student feedback and a subjective evaluation of knowledge retention affirmed the importance of integrated simulation and tutorial computer instruction as an agricultural teaching tool.