The objective of this prospective field study was to evaluate the effects of extending the lactation period on various reproductive measurements of highyielding Holstein cows. On 40 d in milk (DIM), cows were gynecologically examined (transrectal palpation, sonography, vaginoscopy). Cows without signs of clinical endometritis were blocked by parity and were randomly allocated to 1 of 3 experimental groups with a voluntary waiting period (VWP) of 40, 120, and 180 d, respectively (G40, n = 135; G120, n = 141; G180, n = 139). Cows of G120 and G180 were reexamined at the end of the VWP. If natural estrus was detected within 46 d after the end of the VWP, an artificial insemination was performed. If no estrus was detected, the respective cows were synchronized by applying the classical Ovsynch protocol. We found no difference in the proportion of cows in which estrus was detected between 40 to 86 DIM or in the days to first estrus between the 3 groups. Estrus detection in this period was lower in cows with body condition score <3 on 90 DIM compared with body condition score ≥3 (61.5 vs. 76.0%) and in cows with high energy-corrected milk production (ECM) on 92 DIM [58.6 vs. 70.1%, for cows with higher and lower than the median (39.9 kg) ECM, respectively]. The proportion of cows that estrus was detected within 46 d after the VWP was greater in G120 (88.9%) and G180 (90.8%) compared with G40 (70.4%). These effects were more apparent in cows with high ECM. The rate of estrus detection and of becoming pregnant in this period was greater for G120 (hazard ratio = 2.2 and 1.6, respectively) and for G180 (hazard ratio = 2.4 and 1.8) compared with G40. Cows in both groups with extended lactation had greater overall first service conception rates (G120 = 48.9%; G180 = 49.6%) and a lower number of services per pregnant cow (G120 = 1.56 ± 0.1; G180 = 1.51 ± 0.1) compared with G40 (36.6%; 1.77 ± 0.1). We observed no difference in pregnancy loss or in the proportion of cows culled up to 305 d of lactation between the 3 groups. The number of Ovsynch protocols per 1,000,000 kg of ECM was reduced by 75% in G180 and by 74% in G120 compared with G40 (5.9 vs. 7.1 vs. 25.1). In conclusion, extending the lactation of dairy cows can improve main reproductive measurements in high-yielding cows.

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Aim of the present study was to examine the relationship between the herd status for claw health and herd parameters. Herd parameters were derived from an assessment of the housing conditions and were based on a welfare index and critical checkpoints. Data has been collected on four conventional large dairy farms in northeast Germany. All farms have free-stall systems with cubicles offering a lying area. During the period from 2005 to 2008 on each farm claw disorders were recorded at time of regular hoof trimming, i.e. two or three times a year. Data was augmented by data on veterinary treatments of feet and legs. The Data comprises 18 119 observations of 3 690 cows. Housing conditions were assessed in the year 2008. The results show that a consequent and determined management of herd health is necessary to substantially improve the status of claw health. Housing and management confirming the rules of animal welfare will contribute to the well-being of dairy cows. Keywords

the objective of the present study was to investigate possible long-term effects of calf and heifer feeding intensity on first-lactation milk yield and lifetime efficiency (milk per day of life). Detailed records from a total number of 2,252 female german holstein calves from one commercial farm were obtained from birth to culling. Data regarding all information about calf's birth, rearing time until first insemination, first calving, first-lactation yield and lifetime performance were collected over a 12-year period. This large data volume was merged, handled, checked for plausibility, classified and evaluated. Analyses revealed that body weight at an age of six months was significantly influenced by the average daily gain in the first two weeks of life (P<0.0001) and by the duration of treatment for respiratory diseases (P=0.0080). Moreover, first-lactation yield was affected by average daily gain in the whole first year of life (P=0.0013) and particularly in the period of month nine to twelve (P=0.00187). Lifetime efficiency was significantly influenced by body weight at first insemination (P=0.0051), average milk yield (P<0.0001) and reason for culling (P<0.0001). The results of this long-term study confirm that growth is important in general, but as shown by the negative correlation between average daily gain from month nine to twelve and the first lactation milk yield, nutrient intake (energy and protein) should be adapted to enable a controlled growth especially at certain periods of life. After six months of age, daily gain has to be controlled to avoid fat accumulation for a healthy and effective start of lactation. In addition, this analysis revealed that after passing first lactation, particularly health and fertility are the keys for a long efficient lifetime of dairy cows.Producing and rearing well developed calves and heifers is the key issue of an economical milk production with healthy, productive and long living cows. Several *This study was funded by Sloten B.V.

Ammonia and greenhouse gases have a negative impact on the environment. The most important agricultural sources of ammonia are dairy cattle housing systems, which are mainly naturally ventilated. Estimating emissions for naturally ventilated barns (NVB) is challenging due to the large number of influencing factors. Most notably, the direct coupling of the inside flow regime with ambient and turbulent weather conditions causes difficulties in measuring ventilation rates, gas concentrations and emissions; thus, different methods are available. In this study, we compared the outputs of total volume flow obtained by two indirect methods (CO2 mass balance) to the direct method. The latter we assume in this study as the reference method since it is a fundamental approach that estimates airflow on the inlet. In the context of mass balancing, we compared wind related (sampling method 1) and non-wind related (sampling method 2) approaches for measuring CO2 concentrations. The total volume flow calculations were based on hourly measurements of CO2 concentrations obtained by Fourier transform infrared (FTIR) spectrometer. Data were collected over a period of six months. The values of the total volume flow were filtered for prevailing southern winds (90∘ angle). The wind related method (sampling method 1) in stable cross-inflow conditions produces more accurate and realistic values in terms of the general representation of the values in comparison with direct method and can be considered further for measurements of volume flow in the NVBs.