Abstract
The weaning to estrus interval (WEI) and litter size are points that influences sow reproductive parameters and consequently the swine production. This study evaluated the effect of equine chorionic gonadotrophin (eCG), applied 5 hours after weaning, in sows of 1st to 5th parturition order (PO1-5) and sows with parturition order equal to or greater than 6 (PO6+) on reproductive parameters. PO1-5 sows (n = 240) were allocated into three groups: control group (n = 80), received 4 ml of saline solution; eCG800 group (n = 80), received 800 UI of eCG; and eCG1000 group (n = 80), received 1000 UI of eCG. PO6+ sows (n = 160) were allocated in control group (n = 80), receiving 5 ml of saline solution, and eCG1000 group (n = 80), that received 1000 IU of eCG. The estrous duration and litter parameters (mean weight, number of piglets per litter, number of live piglets, stillborn and mummified), insemination number and parturition order were evaluated. Chi-square test and analysis of variance with Tukey test were used in MIXED procedure of statistical package SAS (p < 0.05). An increased estrus duration and a mean increase of 1.5 piglets per litter was observed in eCG1000 group of PO1-5 sows, without affecting their mean weight. For PO6+ sows, the eCG1000 group was increased by one piglet per litter without interfering in the mean weight at birth. The economic analysis revealed a revenue of 400% of eCG investment in the PO1-5 sows, and 268% in the PO6+ group. It was concluded that the use of 1000 UI of eCG improves the reproductive parameters of sows of both (PO1-5 and PO6+) parturition orders.
Highlights
Luteinizing hormone (LH) suppression at the start of lactation is related to an effect of lactation itself, and not to a hormonal block due to pregnancy or parturition, since LH secretion is not suppressed in late gestation of sows (Ziecik et al, 1982)
parturition order 1 to 5 (PO1-5) females showed a reduction in the weaning to estrus interval (WEI) when treated with equine chorionic gonadotrophin (eCG) in comparison to the control group
In parallel, increased duration of estrus in the females treated with 1000 UI of eCG was observed in comparison with control group (Table 1)
Summary
Luteinizing hormone (LH) suppression at the start of lactation is related to an effect of lactation itself, and not to a hormonal block due to pregnancy or parturition, since LH secretion is not suppressed in late gestation of sows (Ziecik et al, 1982). Sows show episodic LH secretion, which is suppressed 66 to 78 hours afterwards (De Rensis et al, 1993). The piglets suckling causes LH inhibition, which blocks follicular development and leads to a lactational anestrous in sows (De Rensis et al, 1993). The follicle-stimulating hormone (FSH) concentration in lactating and weaned sows is not different soon after farrowing, suggesting that FSH is not a limiting factor for follicular development in the early postpartum period (De Rensis et al, 1993). To evaluate lactational anestrus, Varley and Foxcroft (1990) removed the piglets just after birth and observed that some sows return to normal estrus in two weeks, a high incidence of cysts and an increased birth to conception interval were verified
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