R. M. MacPherson

Performance of sows first mated at puberty or second or third oestrus, and carcass assessment of once-bred gilts

1. Of 80 gilts reared on a restricted plane of nutrition, 75 were allocated to one of four groups. Group 1; 17 gilts mated at puberty were slaughtered after farrowing their first litter. Group 2; 20 gilts mated at puberty were observed for three parities. Group 3; 18 gilts mated at second oestrus were observed for three parties. Group 4; 18 gilts mated at third oestrus were observed for three parities. Group 5; nine additional gilts reared on feed ad libitum and mated at first oestrus were observed for three parities. All animals received the same ration after the first mating. 2. The mean age (±SD) of the restricted gilts at puberty was 186 ± 17 days at a weight of 89 ± 9 kg. The gilts fed ad libitum were significantly (P 3. Conception rates were 83, 86, 94 and 82% for Groups 1 and 2 combined, 3, 4 and 5 respectively. 4. Gilts mated at first, second and third oestrus produced, respectively, 7·8, 9·8 and 10·4 ± 2·2 piglets in the first parity. Group 5 gilts had 11·0 ± 2·2 piglets. All significant differences were confined to the first parity. 5. By the end of the third parity there were no differences between the restricted gilts mated at first, second or third oestrus in total number of piglets born or reared. 6. The gilts slaughtered (at 135 kg) after producing one litter yielded carcasses which were heavier but leaner than those from contemporary maiden gilts grown to 120 kg on a semi-restricted feeding scale.

The effects of level of feeding of sows during pregnancy. I. Reproductive performance

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 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

Thin sows: 2. Observations on the energy and nitrogen exchanges of thin and normal sows in environmental temperatures of 20 and 5 °C

The experimental animals were sows which had been made thin by underfeeding for several parities (thin sows), and siblings which had received adequate energy (standard sows). The energy metabolism of three thin anoestrous and three non-pregnant standard sows were measured at 20 and 5 °C. There were no differences between the two groups of sows. The fall in temperature increased the average maintenance requirement by 60% from 476 to 753 kJ/kg 0·75 /day (1192–1922 kJ/kg 0·56 /day). The tissue insulation of the thin sows was 28% lower than that of the standard sows, although this difference was not statistically significant. The thin sows compensated by having a better external insulation. The average total body conductance was 306 kJ/m 2 /°C/day. The standard sows were in positive nitrogen balance (+ 4·2 g/day, 95% confidence limits 1·5 to 7·0 gN) and the thin sows in negative nitrogen balance (– 4·4 g/day, 95% confidence limits – 2·1 to – 6·8 g N) at energy equilibrium. It is suggested that this difference might be explained if the total nitrogen requirement of the two groups of sows was similar, but that their requirement for energy was related to their body surface area. There were no differences between the two groups of sows in their digestive efficiency, but the digestibilities of both energy and nitrogen were reduced at 5 °C. It is concluded that the primary cause of the ‘thin sow syndrome’ is underfeeding, particularly in cold environments. Other features of the syndrome are probably a consequence of undernutrition and depletion of the body energy reserves.

Weight changes in sows during pregnancy and lactation

Results are presented on weight changes in sows which indicate (1) that checks to increases in weight at specific stages appear to be a normal function of pregnancy in sows, (2) that most of the weight gained during pregnancy in excess of that accounted for by the litter and placenta is lost before the next pregnancy, either during lactation or, if this is prevented, immediately after weaning, (3) that considerable weight loss occurs between weaning and re-mating on a level of feeding which is sufficient to allow a mean gain of 1 lb. per day during pregnancy, and (4) that sows given a relatively low level of total feed during lactation appear to lose considerably less weight between weaning and re-mating, and to gain weight more rapidly during the first few weeks of pregnancy, than those fed to a relatively high level during lactation. Practical implications of these results are considered.

The effect of pregnancy, energy intake and mating weight on protein deposition and energy retention of female pigs

1. In a comparative slaughter experiment, 12 female pigs (six at 80 kg and six at 100 kg) were allocated at first oestrus to each of five treatments: Treatment 1 initial slaughter, or Treatments 2, 3 and 4 mated and given 19·5, 25·8 or 32·1 MJ ME/day for the last 100 days of pregnancy, or Treatment 5 not mated (virgin) and given 25·8 MJ ME/day over a similar period. Pigs on Treatments 2, 3, 4 and 5 were given the same amount of protein and were killed about 123 days after first oestrus. Piglets were removed at birth. 2. Total protein deposition (carcass+viscera+piglets) was increased from a total (±SE) of 5·50 to 8·47 (±0·43) kg as ME intake was increased from 19·5 to 32·1 MJ ME/day. About 75% of the increase in protein deposition was in the carcass component. The average response to ME was 2·2 ± 0·58 g total protein deposition per MJ increment in ME. 3. The once-mated pigs deposited similar amounts of total protein to the virgin pigs but significantly less (P 4. Increasing energy intake from 19·5 to 32·1 MJ ME/day increased total fat deposition from 2·8 to 16·0 kg. The average response to ME was 13·5 ± 1·53 g fat deposited per MJ increment in ME. 5. There were no significant differences between the once-mated and virgin pigs in their calculated maintenance requirement, nor in the efficiency with which ME surplus to requirement for maintenance was utilized for energy retention. The average maintenance requirement for all pigs was 530 (95% limits 303·882) kJ/kg 0·85 . day. The average efficiency of utilization of ME for energy retention was 58·5 ± 6·2%. 6. There was no evidence of any pregnancy anabolism other than that involving the conceptus, the needs of the dam specific to pregnancy and preparation for lactation.

The effect of pattern of food intake in pregnancy upon sow productivity.

Seven research and teaching centres have co-operated in an experiment involving 154 sows. The experiment compared the effect of feeding four different patterns of feed intake during pregnancy upon reproductive performance of sows. In each case approximately 220 kg of feed were given during each gestation according to four patterns of intake designated Constant (C), Low-High (L-H), High-Low (H-L) and High-Low-High (H-L-H). During lactation all animals were given a daily ration of 3·7 kg of feed for litters of five pigs or less, and 0·4 kg for each additional piglet. Wherever possible the sows remained on the same nutritional regimes for three parities. Although the pattern of feed intake slightly affected the live-weight changes of the sows during the course of pregnancy, the treatments had no significant effects on overall change in weight of the sows in pregnancy or in lactation in any of the three parities. The live weights of the sows at the end of the third parity were very similar for all treatment groups. The patterns of feed intake had no appreciable or significant effect on the numbers of pigs born, their average weight at birth or upon the numbers of pigs which survived to weaning at 6 weeks or their live weight. The health and breeding regularity of the sows were also unaffected by the treatments. There were differences between the centres in many of the variables which were compared, but there was no evidence of any important centre × treatment interactions. It is concluded that, at the levels of intake given in pregnancy and lactation in this experiment, there are no beneficial or detrimental effects of changing the pattern of intake during pregnancy.

The influence of dietary protein intake during lactation on the reproductive performance of sows

1. Forty-five Large White gilts were given 2·20 kg daily of a diet containing 14·0% crude protein during three successive pregnancies. During a 6-week lactation they received 5·30 kg daily of one of three diets containing 19·0% (HP), 16·5% (MP) or 14·0% (LP) crude protein. 2. Daily milk yield was estimated on the 10th, 20th, 30th and 40th day of lactation. Milk samples were obtained from the same sows for the determination of protein, fat, lactose and total solids on the 11th, 21st, 31st and 41st day. 3. One sow and litter from each treatment in each lactation was placed in metabolism cages during lactation and estimates of nitrogen and dry matter excretion obtained. 4. As the concentration of protein in the diet decreased the average 42-day gain in litter weight from birth increased significantly in the first lactation. This trend continued in the second lactation although it was not significant but did not appear in the third. 5. There was no marked difference in daily milk yield between treatment groups. 6. There was a significantly greater loss of live weight by the sows on the lower levels of protein in the first lactation. These differences were not significant in the second and third lactations.

Thin sows: 1. Observations on the fecundity of sows when underfed for several parities

Six pairs of gilts were taken at first mating. One of each pair was given about half the A.R.C. recommended amounts of protein and energy during pregnancy and lactation until she became anoestrus (thin group). The other gilt of each pair was given the same amount of protein, but double the amount of energy (standard group). All the thin sows lost condition and became infertile. Their appearance conformed to that of sows with the ‘thin sow syndrome’. This took up to three reproductive cycles. There was no clear effect on the number of piglets born, but the litters of the thin sows contained an increasing proportion of small piglets. One of the thin sows died in her second pregnancy. The standard sows performed well producing an average of 10·3 piglets weighing 1·4 kg over three parities. There were no differences between the two groups in their digestive efficiency. The thin sows retained less nitrogen in the later stages (days 80–100) of their first pregnancy than did the standard sows. There were no differences between the groups in milk production during the first lactation when litters were standardized at eight piglets. There was some evidence that in the second lactation the thin sows secreted less fat and lactose. The five remaining thin sows were repleted at the end of the experiment when their average weight was 96 kg. They were mated as quickly, produced litters which were as large, and piglets which were as heavy as those produced by the standard sows whose mating weight was 182 kg.

Further observations on the relative influence of birth weight and creep-feed consumption on the 3- and 8-week weights of sucking pigs

1. Data from the first 3 litters of each of 21 Wessex Saddleback sows were analysed on within-Utter, between-litter/within-sow and between-litter/ between-sow bases. 2. There were highly significant differences between sows in the mean weight of their pigs at birth, 3 and 8 weeks of age; between litters of the same sow there were no significant differences at birth or 8 weeks but pigs in third litters were significantly lighter than those of the first and second Utters at 3 weeks of age. There was a significant increase in number born but not in number weaned from first to third litters. 3. Within litters, the variation in 3-week weight accounted for by variation in birth weight was 30% in first litters, 48% in second litters and 45% in third; respective relationships between birth weight and 8-week weight were 14, 27 and 26%. Between litters of the same sow, differences in mean birth weight accounted for 50 % of the difference which occurred in 3-week weight and for 26 % of the difference in 8-week weight. Differences in mean creep-feed consumption accounted for 18% and differences in mean 3-week weight for 44% of the differences which occurred in weight at weaning. Between litters of different sows, the variation in birth weight accounted for 48% of the variation in 3-week weight, and 8% of the variation in 8-week weight. Differences in creep-feed consumption accounted for 36% and differences in 3-week weight accounted for 26 % of the difference in weight at weaning. 4. Season of birth had some effect on weaning weight due in part to an effect on creep-feed consumption. There was a negative correlation between birth weight and mortality and a positive correlation between mortality and Utter size.