RESUMEThe mortality rate in 6890 Yorkshire piglets Le

Records of piglet mortality were taken on 775 first and 657 second litters farrowed at four locations and representing 28 combinations of two-breed crosses involving eight breeds. All the sows were mated to Poland China boars. Overall mortality was 18% of which 4·2% occurred at birth, 13·2% between birth and 21 days and 1·2% from 21 to 42 days. Landrace x Yorkshire dams had the lowest mortality rate (10·4%) followed by Duroc x Lacombe (12·3%) whereas the highest rate was found in the Hampshire x Lacombe sows (21·6%). Piglets with Tamworth and Yorkshire ancestry had the lowest mortality (16·2 and 16·7%) while those with Berkshire ancestry had the highest (20·0%). Mortality rate was slightly (2%) higher in first than in second parity litters, and highest in summer and similar in the three other seasons. Mortality rate was highest in very small and very large litters and among the lightest and the heaviest piglets. The results showed a linear relationship between mortality rate and homogeneity of piglet weights at birth within litter, mortality rising with the increase in intra-litter variation. The effect of sires on piglet mortality was significant in one, and non-significant in the three other locations.

Failure to recycle after weaning and the interval from weaning to oestrus were studied using sows representing 28 crosses from eight breeds at three stations. Of the sows farrowing their first litter, 12-9 % failed to recycle within 50 days. The least squares mean for weaning to oestrus interval for all crosses was 13-5 days. Hampshire x Landrace, followed by Hampshire x Yorkshire sows had the shortest intervals (8-0 and 8-7 days respectively) whereas Large Black x Lacombe sows had the longest interval (22-1 days). Crosses involving the Yorkshire, Hampshire, Berkshire and Tamworth breeds had shorter intervals than those involving Landrace, Duroc, Large Black and Lacombe. Season of farrowing had significant effect (P < 0-05), with the shortest interval (11-4 days) occurring in autumn and the longest (15-1 days) in spring and summer. Weaning to oestrus interval increased with the increase in litter size. The interval was longer (15-7 days) at Lennoxville but similar at the other stations. There was a steady increase in size in the following litter with the increase in the weaning-oestrus interval. The heritability estimate (full-sib analysis) for the weaning-oestrus interval was 0-25 + 0-10. Repeatability based on limited data was calculated at 0-28.

1976). Effects of post-weaning stress and feeding management on return to oestrus and reproductive traits during early pregnancy in swine. SUMMARYA total of 177 sows representing five two-breed crosses were used in a 2 x 2 factorial experiment to study the effects of post-weaning stress (changing environment and group housing) and feeding regime (flushing by feeding ad libitum until mating) on the weaning-oestrus interval and other reproductive traits up to 30 days of pregnancy. The group which was stressed had about 10% (P<0-05) fewer reproductive failures than those not stressed, while little difference was found between the two feeding regimes. About 61 % of the flushed sows returned to oestrus within 7 days after weaning, 9% higher than for those not flushed. The stress treatment had little effect on the weaning-oestrus interval. Neither treatment affected ovarian and follicular-fluid weights, percentage of follicles of different sizes, ovulation rate nor number of viable embryos. The flushed group, however, had 9 % lower embryo survival than the group not flushed. A positive relation was found between the number of days on ad libitum feeding and ovulation rate and embryonic mortality. Differences among breeds were significant for all the traits, except weaning-oestrus interval, weight of follicular fluids, percentage of large follicles, ovulation and survival rates. The weaning-oestrus interval was not significantly correlated with any of the reproductive traits studied.

Concentrations of folates in serum and milk were determined during the first two parities in 7 Suffolk, 12 Finnsheep, and 15 Romanov ewes at 0 (mating), 60, 110, and 140 d of gestation and 1, 7, 14, 21, and 50 d of lactation. The number of lambs born at first and second parturitions was 1.38 +/- .13 and 1.71 +/- .13 for Suffolk, 2.00 +/- .32 and 2.33 +/- .57 for Finnsheep, and 2.67 +/- .24 and 3.20 +/- .22 for Romanov, respectively, and the concentration of folates at d 0 was 1.17 +/- .21, 1.87 +/- .19, and 2.14 +/- .17 ng/mL, respectively. During gestation, serum concentrations of folates declined in the three breeds, more quickly in Romanov and Finnsheep (from d 0 to 60) than in Suffolk (from d 0 to 110). This decline was followed by an increase in serum concentrations of folates from d 110 to 140 of gestation in the three breeds; the largest increase was observed in Romanov (breed x quadratic effect of time, P = .001). During lactation, Romanov had higher serum concentrations of folates than Finnsheep, which in turn had a higher concentration than Suffolk (P = .001). Colostrum of Romanov had the highest concentration of folates (164.9 +/- 11.9 ng/mL), followed by that of Finnsheep (125.0 +/- 9.5 ng/mL) and Suffolk (98.2 +/- 13.3 ng/mL). On d 7 of lactation, concentration of folates was similar in milk of Romanov (97.1 +/- 5.6 ng/mL) and Finnsheep (94.9 +/- 4.0 ng/mL) and was higher than in Suffolk (72.4 +/- 3.7 ng/mL). From d 14, the concentration of milk folates was similar among breeds and decreased slowly to approximately 40 ng/mL at d 50 (breed x quadratic effect of time, P = .005). The changes in serum concentration of folates during gestation of ewes were similar to those observed in sows, suggesting that exogenous supply of folates may not be optimal in ewes during gestation and lactation.