Meta-analysis-based estimates of efficiency of calcium utilisation by ruminants.

The most abundant mineral in the body of animals is Ca, which has crucial importance for the regulation of various processes. The maintenance of Ca balance has become more challenging, especially in lactating ruminants, owing to the increased milk yields and thus Ca requirement. To determine the Ca requirement, factors such as Ca secretion via milk or Ca deposition in body tissues and conception products are summed up to the net Ca requirement. Nevertheless, dietary Ca cannot be completely utilised by the animal to cover the net Ca requirement, therefore a value for the efficiency of Ca utilisation is applied, which is the maximum proportion of Ca from the feed that the animal can use for covering the net requirement. However, current estimates for the efficiency of Ca utilisation are inconsistent. Therefore, the objective of the present meta-analysis was to estimate the efficiency of Ca utilisation for ruminants, considering the Ca supply of the animal. A data set of 223 observations was compiled from 37 studies, including data on cattle and small ruminants. Standardised Ca digestibility was calculated from data on Ca intake and faecal Ca excretion, corrected for faecal endogenous losses. Furthermore, a data subset on only lactating ruminants was created. For this subset, Ca excretion via faeces and urine and standardised Ca digestibility were related to the Ca supply of the animal. An exponential function was fitted to standardised digestibility data in response to Ca concentration in the diet and Ca supply, revealing that standardised Ca digestibility decreased with increasing dietary Ca concentration and Ca supply. The median for standardised Ca digestibility was 40%, with a remarkable variation between 9% and 88%. In response to Ca supply, faecal Ca excretion increased in a strong linear manner (slope = 0.76, R2 = 0.96). Excretion of Ca via urine was very low even when Ca supply was very high. To conclude, Ca digestibility is a suitable indicator for the efficiency of Ca utilisation, since excessive Ca is almost completely excreted in faeces; however, Ca digestibility has to be determined at a Ca supply level below the requirement of the animal. To date, only very limited number of data have been reported for such supply conditions. Comparative studies using various Ca sources are suggested for future studies but should be conducted using a marginal Ca supply level.

Effect of glycine supplementation in low protein diets with amino acids from soy protein isolate or free amino acids on broiler growth and nitrogen utilisation.

Here, it was investigated whether substitution of amino acids (AA) from soy protein isolate with free AA in low crude protein diets influences the growth performance and N utilisation in broilers, and whether interactions with dietary glycine equivalent (Glyequi) concentration exist. Birds were distributed in two 2 × 2 factorial arrangements of 48 floor pens containing 10 birds each, plus 48 metabolism cages containing two birds each. Experimental feed was provided for ad libitum consumption from d 7 to 22. Diets contained either a soy protein isolate at 79 g/kg or a mix of free AA, which supplied the same amount of 18 proteinogenic AA. A mix of free glycine and l-serine was used to obtain low and high (12.0 and 20.5 g/kg dry matter) levels of dietary Glyequi. Substitution of soy protein isolate with free AA reduced the average daily gain and feed efficiency, mainly due to reduced feed intake. Efficiency of N accretion was not influenced by the AA source or Glyequi concentration on d 21, possibly due to the lower AA digestibility of soy protein isolate and higher urinary excretion of nitrogenous substances in the treatments with the AA mix. The average daily weight gain of the treatments with high Glyequi concentration was higher for both AA sources. This increase was due to higher average daily feed intake by broilers in the treatments with soy protein isolate and due to the increased feed efficiency in the treatments with the AA mix. Broilers exhibited different growth responses to dietary Glyequi between the AA sources; however, these responses could not be attributed to the different utilisation of Glyequi for uric acid synthesis.

A cytogenetic study on the teaching staff of a polluted school with a questionable increased incidence of malignancies.

Exposure to pollutants, in particular polychlorinated biphenyls (PCB), was established at a school built in 1966. Because of a statistically conspicuous increased frequency of breast cancer observed in the teachers of the school this study was performed to ascertain whether the teachers in the polluted school have an increased level of micronucleated cells (MN) or sister chromatid exchanges (SCE) as an expression of a raised cytogenetic risk. Teachers in a directly adjacent school served as one control group and those from a school about 30 km away as a second one. Each teacher had to answer a questionnaire and after venous blood samples had been taken, the number of MN and SCE in peripheral lymphocytes were determined. For the teachers in the polluted school, in addition, the length of stay in the building during the last month and year was recorded. Thereby no correlation with the number of MN and SCE was proven. In comparison with the two control groups, neither the number of MN nor SCE was increased in the teachers of the polluted school. Even if their predictive value for cancer risk assessment is disputed, MN and SCE have a high rating as standard procedures in the proof of an exposure to genotoxic agents. This study thus does not provide any evidence that, for the teachers in the polluted school, a relevant exposure to genotoxic agents exists.