The treatments in this summer-grazing experiment were designed as a 3 x 3 factorial; 3 levels of nitrogenous fertilizer, supplying 0, 336 and 672 kg N/ha per annum, and 3 stocking rates. The fertilizer was applied in 6 to 8 dressings at intervals of 3 to 4 weeks. The animals used were fattening Hereford x Friesian steers. The stocking rates were calculated on the basis of data available on herbage production under N and irrigation treatments and varied according to the level of N input. The experiment was laid out in 6 randomized blocks, which were grazed in rotation. Blocks were removed from the grazing cycle in spring and early summer of each of the 3 years (1962-4) over which the experiment was conducted and cut for conservation; yields were recorded. Details are given of: grazing management; results of studies of soil-N levels; the quantities of herbage removed for conservation; the quantity, chemical and botanical composition of the herbage available for grazing; and herbage consumption.

Recent improvements in dairy cow fertility and female reproductive technologies offer an opportunity to apply greater selection pressure to females. This means there may be greater incentive to obtain genomic breeding values for females. We modeled the impact of changes to key parameters on the net benefit from genomic testing of heifer calves with and without usage of sexed semen. This paper builds on earlier cost-benefit studies but uses parameters relevant to pasture-based systems. A deterministic model was used to evaluate the effect on net benefit due to changes in (1) reproduction rate, (2) genomic test costs, (3) availability of parent-derived breeding values (EBV), and (4) replacement rate. When the use of sexed semen was included, we also considered (1) the proportion of heifers and cows mated to sexed semen, (2) decreases in conception rate in inseminations with sexed semen, and (3) the marginal return for surplus heifers. Scenarios with lower replacement rates and no availability of EBV had the largest net benefits. Under current Australian parameters, the net benefit of genomic testing realized over the lifetime of genotyped heifers is expected to range from A$204 to A$1,124 per 100 cows for a herd with median reproductive performance. The cost of a genomic test, a perceived barrier to many farmers, had only a small effect on net benefit. Genomic testing alone was always more profitable than using sexed semen and genomic testing together if the only benefit considered was increased genetic gain in heifer replacements. When other benefits (i.e., the higher sale price of a surplus heifer compared with a male calf) were considered, there were combinations of parameters where net benefit from using sexed semen and genomic testing was higher than the equivalent scenario with genomic testing only. Using sexed semen alongside genomic testing is most likely to be profitable when (1) used in heifers, (2) the marginal return for selling surplus heifers (sale price minus rearing costs) is greater than A$400, and (3) conception rates of no more than 10 percentage points lower than those achieved using conventional semen can be realized. Net benefit was highly dependent on the marginal return. Demonstrating that the initial investment in genomic testing can be recouped within the lifetime of the heifers tested may assist in the development of extension messages to explain the value of genomic testing females at the herd level.

In a 3 X 3 factorial experiment, the effects of three levels of nitrogenous fertilizer (0, 336 and 672 kg/N per ha) and three grazing intensities on live-weight gains and carcass attributes were measured. The live-weight gains of the animals (per head) over the season were greater at the low and moderate grazing intensities than at the high; this effect occurred mainly from July to October each year. Gains were low on the no-nitrogen swards from July 1962 to the end of the grazing season and throughout 1963: this was related to the very high clover content of the swards. In all years, as grazing intensities increased, the carcass weights per animal became lower. Carcass balance, carcass length, depth of longissimus dorsi muscle, fat thickness over the longissimus dorsi, weight of kidney suet and channel fat, and weight of the alimentary tract also reflected the effect of treatment on weight gains. The results are discussed in relation to the botanical composition and consumption of the herbage, presented in Part I.

SummaryDuring 3 years, three groups of 20 Scottish half-bred ewes were grazed on perennial ryegrass, white clover or red clover. During this period the two legumes were oestrogenic, in terms of teat-length extension of wethers, but the perennial ryegrass was not. The white clover was only markedly oestrogenic when there was a high proportion of diseased leaves. The mean litter size and lambing percentage of the ewes grazed on red clover was significantly reduced. White clover, although it was oestrogenic, had no effect on mean litter size or lambing percentage. The mean litter size of the ewes on the perennial ryegrass was 2·35, 2·30 and 2·24, on the white clover was 2·20, 2·33 and 2·23 and on the red clover was 1middot;60, 1·67 and 1·78 for the three lambings. Lambing percentage of the ewes on the perennial ryegrass was 175, 225 and 218, on the white clover was 210, 222 and 189, and on the red clover was 160, 128 and 118 for the three lambings. The lambing date of the ewes grazing on the red clover was significantly later at the third lambing.