M. Terqui

Control of Oestrus in Gilts II. Synchronization of Oestrus with a Progestagen, Altrenogest (Regumate): Effect on Fertility and Litter Size

Abstract After control of puberty, 525 crossbred gilts were randomly distributed between two groups: a control group (281), and a treated group (244) receiving 20 mg of Regumate daily for 18 days in the food. Ninety-six percent of Regumate-treated gilts were in oestrus between days 4 and 7 after the end of the treatment. After double A.I. with 6 billion spermatozoa, the farrowing rates and the litter sizes were 88.4% and 9.6, respectively, for the Regumate group, and 80.8% and 9.1 for the controls. This progestagen treatment not only allowed a good synchronization of ovulations, but improved the fertility and the litter size simultaneously.

Control of oestrus in gilts I. Management-induced puberty

Abstract The occurrence of the first ovulation was observed in 559 crossbred gilts from one breeding stock by oestrus detection using a boar, and by a circulating progesterone assay. Five hundred gilts (89.4%) presented oestrus at an average age of 173 days, whereas 40 (7.2%) presented ovulation without overt oestrous behaviour. Transport stress, associated with a change in environment and presentation to the male, induced oestrus in 363 (72.6%) gilts within 7 days. Neither the age at transport nor the season influenced the induction of puberty. However, significant differences appeared between sires (from 51 to 73.5% of oestrus within 7 days).

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.