H. Valk

Effect of reducing nitrogen fertilizer on grassland on grass intake, digestibility and milk production of dairy cows

To quantify the effect of a reduction in nitrogen fertilizer on grass intake and animal performance, four zero-grazing experiments were carried out, two in spring/early summer and two in late summer. Grass was fertilized at three levels of N fertilizer, 450, 300 and 150 kg/ha per year and harvested daily at dry matter yields between 1500 and 2000 kg/ha. Grass was fed ad libitum to three groups of 12 dairy cows in mid lactation. Reducing fertilizer N decreased crude protein content and in-vitro digestibility, but increased sugar content in grass. Overall, in the spring experiments, a reduction in N fertilization from 450 to 150 kg/ha per year did not affect grass intake. In one of the experiments carried out in spring, net energy intake of cows offered 150N grass was lower, resulting in lower milk yields. In late summer, cows consumed less 150N grass and produced less yields of milk, fat and protein compared to the other treatments. Except for milk production differences in S92, a reduction of N fertilizer from 450 to 300 kg/ha per year did not affect intake or milk production.

Immunohistochemical Evaluation of a Panel of Tumor Cell Markers During Malignant Progression in Barrett Esophagus

Histopathologic grading of dysplasia in Barrett esophagus (BE) shows substantial interobserver and intraobserver variation. We used immunohistochemical analysis with a set of tumor cell markers, ie, epidermal growth factor receptor (EGFR), ERBB2 (HER2/neu), MYC, CDKN2A (p16), SMAD4, MET, CCND1 (cyclin D1), CTNNB1 (beta-catenin), and TP53 (p53), in histologic sections of endoscopic biopsies of 86 patients with BE in various stages of neoplastic progression. The markers, except SMAD4, were scored as 0 (<1% of cells stained), 1 (1%-25%), 2 (26%-50%), or 3 (>50%). All markers, except EGFR, showed a significant trend for immunohistochemical protein overexpression during malignant progression in BE (P <.01). When the successive stages along the metaplasia-low-grade dysplasia (LGD)-high-grade dysplasia (HGD)-adenocarcinoma axis were compared, protein overexpression of beta-catenin separated LGD from metaplasia, whereas protein overexpression of cyclin D1 and p53 discriminated HGD from LGD (all P <.001). beta-Catenin can be helpful for a diagnosis of LGD in BE, although it stains positively in a subset only, whereas p53 remains an appropriate marker to define HGD. In case of doubt, cyclin D1 can be added to separate LGD from HGD in BE.

Energy metabolism of dairy cows fed on grass

Production performance of grass-fed dairy cows is often lower than expected from the estimated energy supply. To explain the overestimation of the energy content of grass for dairy cows, data from energy balance trials from three different laboratories (Wageningen, Lelystad and Hillsborough) were collected. The trials in Wageningen and Lelystad were carried out in the 1970s and those in Hillsborough in the 1990s. Regression analyses were carried out with the complete data set as well as per laboratory to identify differences per laboratory. Average net maintenance requirements per kg3/4 (NEm) were 0.573 MJ, whereas the efficiency of metabolizable energy utilization for lactation (k1) was 0.777. When NEm was fixed at the presently used value of 0.293 MJ/kg3/4, k1 was 0.60. Between-laboratory NEm varied between 0.294 (Lelystad) and 0.786 MJ/kg3/4 (Hillsborough), whereas k1 varied between 0.57 (Lelystad) and 0.84 (Hillsborough). For Wageningen and Hillsborough, NEm was high, whilst k1 was also high. With the intercept fixed at 0.293 MJ/kg3/4, efficiency varied between 0.53 (Hillsborough) and 0.62 (Wageningen). The k1 and NEm are interrelated. Based on these data we surmise that the maintenance requirements for grass-fed dairy cows are 10% higher than presently assumed, with no change in k1.

Voluntary intake and in vivo digestibility of forages from semi-natural grasslands in dairy cows

To study in vivo digestibility of forages from semi-natural grasslands two experiments were carried out. In the first experiment lactating dairy cows were offered three different silage-based diets. Silage originated from intensively managed grassland (IM), extensively managed species-poor grassland (SPP), or extensively managed species-rich grassland (SPR). In the second experiment lactating dairy cows were offered IM or a diet in which part of the IM had been replaced by 20% SPP (20SPP), 60% SPP (60SPP) or 60% SPR (60SPR). Intake was significantly lowest on diets with SPP, but intake on diets with SPR was not significantly lower than intake on IM. In both experiments gross energy and in vivo digestibility of organic matter, crude protein and neutral detergent fibre were highest for IM. In the first experiment SPP had a significantly higher digestibility than SPR, but in the second experiment differences in digestibility between 60SPP and 60SPR were not statistically significant. In both experiments in vivo digestibility was almost similar to in vitro digestibility, but no suitable equation could be found to estimate in vitro or in vivo digestibility from the chemical composition. Although digestibility and crude protein content were significantly lower for SPR than for SPP, intake of digestible organic matter appeared to be higher. It was concluded that there appears to be more scope for silage from extensively managed species-rich than for silage from extensively managed species-poor grassland.

Dairy cow performance on silage from semi-natural grassland

The effects of including forage from semi-natural grassland in the diet of dairy cows were studied in a feeding trial with cows in mid-lactation. Diets were compared in which part of the silage from intensively managed grassland was replaced with 0% (100IM), 20% (20SPP), 40% (40SPP) or 60% (60SPP) silage from species-poor semi-natural grassland or with 60% silage from species-rich semi-natural grassland (60SPR). On a dry matter basis, the total mixed ration (TMR) contained 63% grass silage, 18% maize silage and 19% concentrates. Concentrates were either low or high in protein to prevent protein surpluses or shortages. High producing cows were offered additional concentrates in concentrate boxes. The additional concentrates had the same composition as the concentrates in the TMR. With the 60SPP diet voluntary daily intake decreased by 1.4 kg DM cow−¹ day−¹. Uncorrected milk production was the same for all diets, but milk fat yield was lower with the 60SPP diet and milk protein yield lower with the 60SPR diet than with the other diets. No statistically significant differences in fat and protein corrected milk production were observed between the 100IM and the 20SPP diet. The fat and protein corrected milk production with the other diets was significantly lower than with 100IM. All cows gained body weight, but there were no statistically significant differences between diets. In conclusion, if used in low quantities (< 40%), silage from semi-natural grassland can be included in the diet of lactating dairy cows without reducing production. This conclusion is based on the presented results and cannot be generalized.

Improved diagnostic stratification of digitised Barrett's oesophagus biopsies by p53 immunohistochemical staining

Interobserver agreement for dysplasia in Barretts oesophagus (BO) is low, and guidelines advise expert review of dysplastic cases. The aim of this study was to assess the added value of p53 immunohistochemistry (IHC) for the homogeneity within a group of dedicated gastrointestinal (GI) pathologists.