A double isotope derivative assay and a simple competitive protein-binding assay were used to measure peripheral plasma progesterone levels during the pig oestrous cycle. In view of the similarity between the results, the more convenient protein-binding method was employed to determine progesterone levels during prepuberty, the oestrous cycle, early and late pregnancy, parturition and lactation. Peripheral plasma oestradiol-17\g=b\ levels were measured during the oestrous cycle, early pregnancy and around the time of parturition.

Twenty-eight weaning pigs were used in a feeding experiment to detennine the effect of different levels of lactose in the diet on growth perfonnance and carcass characteristics. Seven pigs weighing initially 50 lb and penned individually were allocated to each of four treatment diets in which lactose was substituted for wheat starch at levels of 0%, 15%, 30%, or 45% of the diet. The meal mixtures were fed as a gruel using three parts water: one part meal (w/w).Over a period of 56 days pigs receiving diets containing 30% or 45% lactose grew 10% and 39% slower respectively than the controls (P < 0.01). The pigs on the 45% lactose diet also grew significantly slower (P < 0.05) than those fed diets containing either 15% or 30% of lactose. Reduced food consumption was a major factor contributing to the poor and very variable performance of the group fed the 45% lactose diet. Similar treatment differences were evident for food conversion efficiency but there was little treatment effect on carcass fatness. The incidence and duration of diarrhoea increased with increasing levels of dietary lactose. Diets containing up to 30% lactose caused a transient diarrhoea, but some of the animals on 45% lactose continued to scour until the termination of the experiment.

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Puberty was induced, using boars as a stimulus, in 83 grade Large White gilts starting on average at 162 days of age and 82.9 kg live weight. Gilts were allocated to three mating groups and mating was done over a 21-day period starting 19, 40, or 60 days from the start of induction. Matings corresponded to first, second, and third post-pubertal heats. Each mating group was randomised to 3 Ca and P levels in gestation corresponding to daily intakes of 7.8 and 6.2 (L), 12.3 and 8.4 (M), and 16.5 and 10.4 g (H) respectively. Of the 73 gilts mated 27 returned to service a second time, were culled, and their ovaries examined. Forty-six gilts farrowed to a single and first service and were kept for up to 3 parities when 31 remained. Average ages and weights respectively of the 46 gilts at first mating for the 3 groups were 189.7 days, 97.8 kg; 207.5, 103.3 kg; and 233.0, 115.9 kg. Apart from a depression in litter weight at weaning in Parity 1 for the earliest mated group no other differences were associated with initial mating groups. The higher intakes of calcium and phosphorus resulted in a lowering of the litter weight born and, less frequently, weaned. Although several mating groups X Ca and P level interactions were found for litter trials, these generally occurred within parities and were not consistent between parities. Despite early mating of gilts and their low live weights, daily intakes of 7.8 g of calcium and 6.2 g of phosphorus in gestation were apparently adequate for good sow and litter performance in the presence of high intakes in lactation. 249

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