Françoise Martinat-Botte

Effect of some parameters on the drying-off - 1st oestrus interval. Results from 1975-1982

The effect of some parameters on the onset of oestrus after the end of lactation was studied on the basis of data from the National computerized programme for management of sow herds. The data analysis was performed on two samples (I, n : 5 867 ; II, n : 36 926) and over two periods at 7-year interval (1975-1982). Synchronization of oestruses between Day 3 and 9 after drying-off represented 85.5 p. 100 as compared to the 1975 value (80 p. 100). Whatever the year, the maximum frequency of oestrus onset was observed on Day 5. The frequency was about 6 p. 100 higher in 1982. Primiparous sows returned to oestrus later than multiparous sows (p. 100 oestrus Day 3 to 9 primiparous, 1975 : 69.9 p. 100 ; 1982 : 75.9 p. 100 multiparous, 1975 : 83.5 p. 100 ; 1982 : 88.8 p. 100). The optimum synchronization of heats after drying-off (Day 3-9) corresponded to weanings between Day 26 and 35 in primiparous as well as in multiparous sows whatever the year. There was an influence of the season on the return to oestrus. However, in 1982, the « season effect was more marked in primiparous sows ; the variation range between the most favourable months (November to February) and the less favourable ones (July and August) reached 8 p. 100. It was only 3 p. 100 in multiparous sows. The data analysis per herd (n = 292) showed that in 84.2 p. 100 of the cases the return to oestrus of the primiparous sows was less synchronized than that of the multiparous ones and this disturbed the batch management.

Seasonal variation in the litter size in relation with variations in the ovulation rate and the embryo mortality in the sow

The mean number of piglets born was maximum for litters conceived in August, September, November and minimum for those conceived in December and January. On an average a difference of one piglet was noticed between the two extreme months, i.e., November, January. Piglets were all issued from dams in fourth gestation (N = 10 981), where prolificacy reaches a plateau and varies little. Variation in the ovulation rate during the year in sows slaughtered at 30 days post coitum in third and fourth gestation (N = 415) was parallel to that of the number of embryos and that of the litter size. The maximum corresponded to fertilization in August, September, October, November and the minimum to fertilization in December, January and February. On an average, a difference of two ovulations was noticed between FebruaryOctober.

Better control of post lactation oestrus by means of a progestagen (RU 2267)

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