1. From a review of the literature it has been shown that there are two opposing views regarding the best method of interpreting growth data, which arise from conflicting opinions as to the role of fat deposition in the growth of the animal.2. Data of McMeekan and Palsson and Verges have been re-analysed and their own results are compared with results obtained when the effects of variation in fat content are eliminated.3. No evidence has been found of any effect of plane of nutrition on the total weights of bone and muscle relative to the weight of bone plus muscle together.4. The weight of bone plus muscle in the head and neck was increased relative to the total weight of bone plus muscle during periods of restricted nutrition. Apart from this there was no clear evidence of a relationship between the order of maturity of the joints and their relative retardation of development.5. Huxley's allometry equation was found appropriate for standardising the measurements, and the exponent was taken as a numerical expression of the relative maturity of each tissue or part.

1. Twelve gilts, six pregnant and six non-pregnant, were each given a daily ration of 2.2 kg. for a 110-day period.2. Live-weight gain during this period was 53 kg. for the pregnant animals compared with 23 kg. for the non-pregnant animals.3. Apparent digestibility of nitrogen and dry matter and the energy of digested feed did not differ significantly between the pregnant and non-pregnant animals.4. Daily nitrogen retention was on average 9·2% higher for the pregnant animals, the difference between the two groups becoming progressively greater during the trial.5. Highly significant differences were found in pre-slaughter live-weight, weight of reproductive tract and weight of mammary region. The difference in the weight of free draining blood was also significant. No difference was found in the weight of alimentary tract, visceral organs, head or decapitated carcass.6. The carcasses of the pregnant animals contained less subcutaneous fat plus skin and more intermuscular fat plus muscle than those of the non-pregnant animals. The weights of bone did not differ.

1. Twelve sets of 3 litter-sister Large White gilts were mated at first oestrus after reaching 250 lb. live-weight and given daily during 3 successive pregnancies either 6 lb. (A), 3 lb. (B) or 3 lb. for 76 days then 6 lb. until parturition (C) of the same meal mixture. During an 8-week lactation all were given 4 lb. meal plus 0·8 lb. per piglet suckled.2. There was a significant linear increase in numbers born with successive parities (P<0·05) but no significant differences between treatment or sister groups. There was a highly significant difference between treatment groups in mean piglet birth weight (P< 0·001) but no parity effect; mean birth weights were 2·76, 2·40 and 2·58 Ib. for Groups A, B and C respectively. Differences between sister groups in mean piglet birth weight were also significant (P<0·05).3. Post-natal litter performance was poor for all groups, probably because of the presence of E. coli, but there was no evidence of treatment effects other than on 3-week weight of third litters, which was significantly greater in Group C than in A or B (P<0·05). There were no significant effects on either number or weight of piglets at 8 weeks.

SUMMARYTwenty-four gilts were used at each of two centres in an experiment designed to examine the effects of dietary energy intake during lactation on yield and composition of sows' milk and the growth of their litters. Gestation feed intake was standardized at 2 kg per day supplying 6·28 Meal digestible energy (DE) and 280 g crude protein. The energy levels fed during lactation ranged from 12·2 to 18·25 Meal DE per day for gilts, 12·9 to 19·6 Meal DE per day for second parity and from 13·2 to 20·25 Meal DE per day for third parity sows. Daily crude protein intake and amino acid balance ofthe protein were kept constant.In the first lactation milk yield and composition and growth of litters were not influenced by dietary energy intake. In the second lactation milk yield was depressed by lower energy intakes and this was reflected in litter weights at 21 though not at 42 days. In the third lactation lower energy intakes seriously depressed milk yield and daily output of milk nutrients. On the lowest level of energy, milk yield was 32% lower at day 24 and 20% lower at day 41 of lactation than on the highest energy level. The corresponding depressions in litter weights were 17·2 and 13·5% at 21 and 42 days respectively.

SUMMARYEight research and teaching centres have co-operated in an experiment involving 132 sows. Six treatments were used, combining three levels of feeding in pregnancy with two in lactation. Pregnancy treatments were High 3−2 kg meal/day, Medium 2·4 kg/day and Low 1·6 kg/day; in lactation either a high level, 4·1 kg plus 0·2 kg/pig (h) or a medium level, 2·3 kg plus 0·2 kg/pig (m) were given. The sows were maintained on the same nutritional regime for three parities although inevitably some sows were lost before the completion of the trial. Sow live-weight gains in pregnancy were directly related to feed intake; in lactation, losses in sow live weight were dependent on gains made in the previous pregnancy and on the level fed while suckling. After the first parity, in which animals fed the low level in pregnancy tended to produce larger litters (though the difference was not significant), there were no differences in numbers born attributable to treatments.Increases in the feed intake of sows in pregnancy resulted in consistent and significant increases in the weight of the pigs at birth. This increase in birth weight also resulted in an increase in weight at weaning in the second and third parities. Level of feeding in lactation, which had a highly significant effect on sow live weight, had much less influence on weaning weights of pigs. There were no consistent pregnancy × lactation interactions, the effects of treatments in the two phases being additive.An assessment is made of the relative efficiency of the six treatments and the value of the experiment is discussed in relation to other studies concerned with sow nutrition.

The live-weight changes of 48 sows were recorded over three reproductive cycles. All sows were given standard amounts of feed in gestation and one of four energy allowances during lactation. The daily intakes of digestible energy during lactation ranged from 12-2 to 18-2 Meal in the first, 12-9 to 19-6 Meal in the second and 13-2 to 20-2 Meal in the third lactation. Weight change in lactation responded to energy intake; sows on the lowest energy intake lost weight whilst those on the highest intake gained. At weaning of their third litters, sows on the highest energy allowance weighed 44 kg more than those on the lowest level and this was equivalent to a carcass difference of 37-3 kg at slaughter. All the sows were slaughtered after the third litters had been weaned and the carcasses were dissected into lean, subcutaneous fat+skin, and bone. Sows from all treatments had less subcutaneous fat+ skin and more muscle and bone than non-pregnant gilts killed at a mean weight of 129 kg, a weight equivalent to that of the experimental animals at their first mating. The reduction in fat reserves was linearly correlated with dietary energy intake of the sows. Sows receiving the lowest energy intake in lactation possessed fat reserves which were estimated to be only 25% as great as in gilts comparable to those used to initiate the experiment. This reduction in body reserves has implications with regard to the long-term effects of feeding lactating sows low intakes of energy during 6-week lactations.

Fifty-two Large White gilts, arranged in thirteen groups of four litter sisters, were allocated at mating to one of four treatment groups. These treatments, arranged as a 2x2 factorial, allowed daily energy intakes in pregnancy of 8-3 Meal (H(e)) or 5-2 Meal (L(e)) and of average daily intake during lactation of 20 Meal (h(e)) or 13-8 Meal (m(e)). Daily intakes of protein, minerals and vitamins were similar for all treatments. There were no consistent differences in health or breeding regularity between the treatments.The H(e) sows had a net gain in pregnancy 22 kg greater than the L(e) sows. Feeding the higher level in lactation (h(e) resulted in a reduced sow weight loss during lactation of 20, 12 and 10 kg in the first, second and third parities respectively, as compared with the m(e) sows. There were no consistent effects on the numbers of pigs born apart from the first litter in which L(e) sows produced significantly larger litters at birth. The higher energy intakes in pregnancy and lactation led to very similar increases in the weights of the piglets, of the order of 0-1 kg at birth, 0-4 kg at 3 weeks of age, and 1-1 kg at 8 weeks of age. Sows given the same overall energy intake throughout their reproductive life (H(e) m(e), L(e) h(e)) at the end of the third litter had similar live weights and had produced a similar total weight of weaned pigs. The practical implications of these results are discussed.

Plasma volume and haematocrit were measured at approximately 20 days intervals in 3 gilts (sows in their first pregnancy and lactation) throughout pregnancy and in 2 of these gilts during lactation. Measurements were made at the beginning and end of pregnancy in a further 9 sows and also at mid-pregnancy in 4 of these latter sows.In the gilts PV declined during the first 40 days and then increased until parturition. In lactation the PV continued to rise during the first 14 days and then decreased steadily until weaning. Calculated RCV increased linearly during pregnancy and fell inmediately after parturition.The results obtained from the sows again showed only a slght rise in PV and RCY until day 70 and then a sharp rise until parturition. There was no relationship between the increase in PV and the weight of the litter born.