A series of twenty-four swards containing different proportions of white clover (OOO-O55) and perennial ryegrass were created by using different seed mixtures, herbicide applications and previous cutting frequencies. These swards were used to study the diet of oesophagcally-fistulated wether sheep which grazed the various swards for a 30-min period after 1. 2 and 3 weeks of regrowth.The proporiion of white clover In the diet was generally greater than that in the sward. Fiftyseven percent ofthe variation in the proportion of white clover in the diet could be attributed to the proportion ofwhite clover in the sward. White clover and perennial ryegrass leaf and stem were grazed to the same height and the proportion of white clover in the grazed horizon of the sward explained 83% ofthe variation in the proportion of white clover in the diet. The proportion of white clover in the diet was greater than the proportion in the grazed horizon of the sward in week 3 of regrowth, but not in weeks 1 and 2. and greater when the proportion of white clover in the grazed horizon was lower than 0-40. Both these observations were interpreted as indicating selec-tion for white clover by the sheep within the grazed horizon.There was a positive and linear relationship between ,the depth of the grazed horizon and sward height which, together with the relationship between the proportion of white clover in the grazed horizon and in the diet, would allow the prediction ofthe proportion of white clover of the diet from the height and the white clover content of the grazed horizon of the sward.

Aim Magnesium (Mg) deficiency (known as grass tetany) is a serious metabolic disorder that affects grazing ruminants. We tested whether Mg-fertiliser can increase Mg concentration of Italian ryegrasses (Lolium multiflorum L.) including a cultivar (cv. Bb2067; 'Magnet'), bred to accumulate larger concentrations of Mg. Methods Under controlled environment (CE) conditions, three cultivars (cv. Bb2067, cv. Bb2068, cv. RvP) were grown in low-nutrient compost at six fertiliser rates (0-1500 μM MgCl 2 .6H 2 O). Under field conditions, the three cultivars in the CE condition and cv. Alamo were grown at two sites, and four rates of MgSO 4 fertiliser application rates (0-200 kg ha −1 MgO). Multiple grass cuts were taken over two-years. Results Grass Mg concentration increased with increasing Mg-fertiliser application rates in all cultivars and conditions. Under field conditions, cv. Bb2067 had 11-73% greater grass Mg concentration and smaller forage tetany index (FTI) than other cultivars across the Mg-fertiliser application rates, sites and cuts. Grass dry matter (DM) yield of cv. Bb2067 was significantly (p < 0.05) smaller than cv. Alamo. The effect of Mgfertiliser rate on DM yield was not significant (p ≥ 0.05). Conclusions Biofortification of grass with Mg through breeding and agronomy can improve the forage Mg concentration for grazing ruminants, even in highgrowth spring grass conditions when hypomagnesaemia is most prevalent. Response to agronomic biofortification varied with cultivar, Mg-fertiliser rate,

Precise, unbiased estimates of genetic parameters, such as heritability and genetic covariance, are necessary to optimise breeding programs and to predict rates of change for various selection schemes. A classical method of estimation is to use high and low selection experiments. We consider two generation selection experiments when observations in the parental generation are only taken on one sex, resulting in half-sib family information. We consider cases of two standardised traits, with zero mean and unit variance, and assume that the traits are normally distributed. The genetic and phenotypic variance-covariance matrices for the traits are denoted by G and P respectively. The genetic variances and covariances of the standardised traits are then heritabilities and co-heritabilities.The construction of other designs is examined, assuming the phenotypic correlation of rp between traits is known. For simplicity, comparisons of designs are developed by considering the variance of the genetic variances when the traits are uncorrelated both phenotypically and genetically.

In order that genetic progress in British beef breeds could be improved, performance traits have been recorded by the Meat and Livestock Commission for many years. A large number of pedigree beef herds have recorded with the Meat and Livestock Commission during this period. Until recently, these records were only made use of via within herd contemporary comparisons such that the results for animals could not be compared across herds or time.Through the use of Individual Animal Model Best Linear Unbiased Prediction (BLUP), differences between herds and contemporary groups within herds can be accounted for provided there are genetic links between herds and contemporary groups. As a result of the small pedigree herd size in Great Britain, typically less than 20, sires are often chosen from outside the herd in order to reduce inbreeding. This practise has resulted in there being a relatively high level of connectedness between contemporary groups and this enables the BLUP procedure to disentangle management and genetic effects.