A case-control study to identify farm factors affecting fertility of dairy herds: multivariate description of factors.

OBJECTIVES: To determine whether a multivariate model could be developed to describe farm factors affecting fertility of dairy herd and to examine the factors that determined better reproductive performance on dairy farms in New South Wales. PROCEDURE: We examined the results of a survey of breeding practices, mating policies, recording systems, timing of mating, heat detection, treatment of metritis and manager demographics of dairy farms using Principal components analysis, logistic regression and the sign test. RESULTS: Eight principal components for heat detection computed using Principal component analyses were included in the multivariate model to reflect primary and secondary heat detection signs used in the breeding decisions of managers. A final model identified three variables: optimum number of days to first service, number of people detecting heats, and age of manager which significantly influenced the risk of being in the high or low reproductive performance groups. A failure to breed at an appropriate time after calving and having more people responsible for heat detection was associated with herds with a prolonged intercalving interval. While the model provided a good fit for the data, it was not highly discriminatory. Examination of 83 management practices affecting fertility using the sign test (P = 0.01) indicated that managers of herds with good reproductive performance employed better management and breeding practices more often than managers of herds with poor reproductive performance. CONCLUSIONS: Mating cows sooner after calving and using fewer people to detect oestrus should reduce calving to conception intervals. Veterinarians investigating herd reproductive performance should consider the potential for a number of subtle failures of management to significantly impair fertility rather than limit investigations to a few factors.

A case-control study to identify farm factors affecting fertility of dairy herds: univariate description of factors.

OBJECTIVE: To identify farm factors which were associated with reproductive performance in dairy herds in New South Wales. PROCEDURE: A survey was administered by face to face interview to examine the responses of producers drawn from 757 herds, which used the New South Wales Agriculture Department Dairy Herd Improvement scheme. A case-control approach was used to select a total of 126 herds from the first (top group-cases) and fourth quartiles (low group-controls) for intercalving interval. RESULTS: We found that the estimated interval from calving to first mating was significantly different between group (P = 0.03) and that the groups significantly differed in both their target for interval to first mating (P = 0.02) and their perceived optimum time for first mating (P = 0.04). Other factors associated with a longer intercalving interval included, use of embryo transfer programs (P = 0.08), younger managers (P = 0.02), fewer breedings per day (P = 0.01), a greater number of people detecting heats (P = 0.07), but less hours spent detecting heats while handling the cows (P = 0.11), and a failure to vaccinate bulls for campylobacteriosis (P = 0.14). CONCLUSIONS: Managers of herds with poorer reproductive performance did not intend to mate cattle as soon after calving as managers with better reproductive performance, were not as active in seeking veterinary advice on reproduction, and were attempting to treat reproductive diseases and disorders themselves.

Evaluation of somaclonal variation during somatic embryogenesis of interior spruce (Picea glauca engelmannii complex) using culture morphology and isozyme analysis.

Somaclonal variation during interior spruce (Picea glauca engelmannii complex) somatic embryogenesis was evaluated using culture morphology and isozyme analysis. Genotype-specific abscisic acid-dependent developmental profiles and isozyme patterns were similar for subclone and parent line embryogenic cultures and cotyledonary somatic embryos. Extensive analysis of fifteen hundred subclone embryos of one genotype revealed no isozyme pattern variation. Initiation of embryogenic cultures was dependent on the developmental stage of the explant although cultures derived from different stages were morphologically similar. The embryogenic cultures initiated from interior spruce embryos show a high degree of genetic stability in that the morphological behavior and isozyme phenotype were always consistent with that of the explant genotype. These results support the conclusion that this culture system is appropriate for clonal propagation of interior spruce.

Characterization of immature embryos of interior spruce by SDS-PAGE and microscopy in relation to their competence for somatic embryogenesis.

SDS-PAGE analysis of total proteins from cotyledonary embryo explants reveals that their competence to form somatic embryos is limited to a specific stage of development prior to the accumulation of storage proteins. When protein profiles of embryo explants of different open pollinated families from the same collection date are compared, there is a close relationship between the absence of storage proteins and their ability to produce embryogenic callus. In addition, the appearance of storage proteins in embryos from subsequent collections is associated with their loss of competence. Light microscopy combined with staining for total protein demonstrates that competent immature embryos have cotyledons but do not contain protein bodies.