Livestock Research for Rural Development 15 (2) 2003

Citation of this paper

Financial and reproductive performance of lactating-pregnant Creole sows 


D Mota-Rojas, M Alonso-Spilsbury, O M E Trujillo*, N L Mayagoitia**, R Ramírez-Necoechea, I I Escobar and M J Valencia

Universidad Autónoma Metropolitana-Xochimilco. DPAA.
Área de Investigación: Ecodesarrollo de la Producción Animal
Calz. del Hueso 1100. Col. Villa Quietud, México, D. F. 04960
Universidad Nacional Autónoma de México. FMVZ. CU, México, D. F. 04510
Instituto Nacional de Psiquiatría. Lab. de Etología
Camino a Xochimilco 101. Col. San Lorenzo Huipulco. México, D. F. 14370.


Generally sows are in anoestrus during lactation, however there are situations that may alter their state by manifesting signs of oestrus and ovulation. A practical advantage of this finding is the reduction of the reproductive cycle. The objective of this study was to evaluate the productivity of the lactating Mexican Hairless sows, which were induced to get pregnant by using natural stimuli, eight days after farrowing. To analyze the effects of the removal of the litter and the presence of a boar on the reproductive performance, one, two and three way ANOVA analyses were run; also, post hoc comparisons were done using Tukey and Kruskal-Wallis tests. Twenty sows were distributed in 4 experimental groups.

One hundred per cent of the sows treated with both stimuli (presence of a boar and partial removal of the litter), presented oestrus and 80% of them became pregnant, obtaining 2.8 farrowings per sow per year. The removal of the litter significantly (p<0.01) increased the number of piglets born alive. Profit percentage for each extra weaned piglet for sows receiving both stimuli was 29.5%. Non-productive days were reduced, so was the interval between farrowings; moreover, 2.3 extra piglets per sow per year were obtained in comparison with the other groups.

We conclude that inducing gestation during lactation with the boar and litter withdrawn is an alternative that allows an improvement in the sow productivity; the productive cycle was reduced without diminishing the period of lactation.  

Key words: Lactational oestrus, Mexican hairless pigs. productive performance,  


Mexican native swine are known by the generic names of Mexican Hairless and Cuino. These pigs are not commercially used, the sale price is very low due to an excess of fat, situating them between a rate of 30% and 40% less than the price paid for pigs of improved breeds (Cenobio 1993; Méndez 1997). 

Mexican Hairless indigenous pigs, descendants of the Iberian pig, are considered a rustic breed in danger of extinction due to the constant introduction of improved breeds (FAO 1997; Lemus 1999; Sierra-Vásquez 2000). Traditionally in Mexico, these pigs are raised in what is called backyard conditions without technical nor sanitary supervision, resulting in not very flattering productivity indicators (Salinas 1996). Their importance in the communities where they are raised is double; on the one hand they represent an improvement in the quality of the peasant’s diet, and on the other, the fattened pigs are sold to help the family economy (Conejo 1993). At the same time its fatty characteristic is advantageous in the production of high quality cold cuts like the ham or “jabugo”, or sausage and blood sausage, which confer an added value (Pérez et al 1999). 

A common practice in porcine production consists of increasing the number of piglets/female/year, reducing the interval between farrowings, by weaning the animals early (Koketsu and Dial 1997; Koketsu et al 1998). However, the productive cycle in the sow can also be reduced during the lactation period (Mota et al 1999) by establishing pregnancy during nursing, without affecting the prolificacy of the dam or her litter performance (Mota et al 2002). This means piglets will continue to suckle while the mother is pregnant, thus reducing the reproductive cycle, achieving a higher number of farrowings per female per year (Kirkwood and Thacker 1998), and improving the company profit (Becerril et al 2000; Mota et al 2000). 

The techniques needed to induce lactational oestrus in the sow vary: natural management of the animal by changing its patterns of nursing (Alonso-Spilsbury et al 1998a, b) or by interrupting lactation (Loseth and Crabo 1994), or the use of exogenous hormones (Varley and Foxcroft 1990). Even though a physiological check-up has been practiced on the female, these techniques still have not been applied for commercial use. 

Generally, sows are in anoestrus during lactation; nonetheless, there are situations that may alter their state, manifesting not only signs of oestrus but of ovulation as well (Newton et al 1987). Some practical advantages in these findings are: the reduction of the sow’s reproductive cycle, by diminishing the weaning-oestrus interval and the non-productive days of the herd (Mota et al 1999, 2002). 

The objective of this study was to evaluate the reproductive and financial efficiency in Mexican indigenous pigs, which were induced to get pregnant while still lactating. 

Materials and methods 

Experimental design

Twenty Mexican hairless sows and 5 boars were used. Different authors have described the morphological characteristics of these animals. The Mexican native pig, and within this, the biotype Mexican Hairless, descends from the Iberian pig, representing an endemic swine population, which is located on the Pacific and Atlantic Mexican south east coasts. The name “hairless” derives from its main characteristic, which is the absence of hair on the skin´s surface. The morphological characteristics of the Mexican Hairless pig (MHP) are: small size, grey-black colour, long-winded head with a sub-concave side view; long face, narrow snout, medium size ears that point down and to the front, slightly covering the eye zone; and short neck. They also show slightly straight back, not very arched ribs and strong and long feet; their hind legs are higher than the front ones (Flores and Agráz 1983). 

After farrowing the herd was divided into 4 experimental groups of 5 lactating females each, which were classified under experimental conditions 1 and 2. Two replicates were performed during 2 consecutive parities. The stimuli applied on the 8th post-partum day to induce lactational oestrus were the presence of the boar and the partial removal of the litter, as shown in Table 1.

Table 1. Experimental design

Experimental condition 1

Experimental condition 2


Litter remains with sow until weaning



Temporary removal of the litter



Absence of boar



Abscence of boar



Presence of boar



Presence of boar


Lactating sows were housed in individual pens of 6 square meters with a cement floor and straw bedding, here they remained for a lactation period of 28 days. Daily diet during lactation consisted of 3 kg. of balanced feed (12.5 MJ ME/Kg and 15% of CP). After weaning sows were grouped in communal pens were they remained for 18 hours a day, the rest of the time they were put out to pasture in an acorn forest. Boars were maintained in complete confinement and were housed in individual corrals of 5 square meters with cement flooring, far from the sows. 

Experimental manipulations 

In order to induce lactational oestrus in the sows, stimuli were given on the 8th day of post partum. These consisted in the presence of a boar and temporary weaning, as shown in Table 1. 

The evaluation and follow-up of the reproductive variables were done during the second and third parities. Sows that did not present oestrus or were not pregnant during lactation were bred again once they had weaned their litter, and follow-up was performed to compare reproductive indicators in relation to the lactating pregnant females. 

The method used to determine the cost of production of a litter at birth was that from Becerril et al (2000), and the interpretation of the reproductive parameters was based on the methodology of Ramírez et al (1999). To analyze the effects of the removal of the litter and the presence of the boar in terms of the reproductive parameters, one, two and three way analysis of variance was run, using the general lineal model (SAS 1987). Post hoc comparisons were done using Tukey and Kruskall Wallis test. 

The evaluated parameters are presented in Tables 2, 3 and 4. 

Results and discussion

The stimulus used in the experimental design of this study were similar to those used by other researchers; days of lactation and sample period changed, though. The results of the present study were compared with those of white breed commercial sows in crating systems with a wide spectrum of possible stimulus to induce oestrus during lactation. Even with this circumstance, we compared our results with experimental designs related to the induction of fertile lactational oestrus only in those variables in common, previously reported by other authors. 

Oestrus display 

None of the females from treatments C, BS and TW presented oestrus, while all the sows from BS-TW (where both stimuli were applied) showed oestrus and 80% (8) of them became pregnant. 

Photo 1: Lactational-oestrus creole sow, 11 days post-partum.


In this experiment oestrus was not observed when the stimulus were applied in an isolated manner, but when combined (B+LW), this stimulus induced the presence of oestrus in 100% of the females, coinciding with Rowlinson and Bryant’s work (1982). These authors found that when sows and their litters are grouped on the 10th day of lactation and the boar is introduced 24 hours later, 100% of the females showed oestrus up until the 34th day of post-partum. On the other hand, Petchey and Jolly (1979), found that only 49% of the sows grouped with their litters presented lactational oestrus, whereas in another experiment, Loseth and Crabo (1994) determined that if the experimental group was removed from the litter 8 hours a day, and during this time the sows had contact with a boar --to evaluate the presence of oestrus signs-- 66.6% of the females were bred 5 to 6 days after separation. 

Born alive piglets 

The removal of the litter significantly affected (p<0.015) the number of born alive piglets (BAP). This parameter was higher in third parity sows, as shown in Figure 1. Also, there were more BAP in those groups were the litter was removed (TW and BS-TW), as compared with Groups C and BS (Table 2). The variable age of the sow (number of parity), was equally important (p<0.006) in determining BAP. This coincides with previous work from Trujillo (1998).  

Table 2. Mean and standard error of the productive performance per group


(mean±standard error)

n = 10

n = 10

n = 10

n = 10

Stillborn piglets





Born alive piglets





Litter birth weight (kg)





Weaned piglets/sow/farrowing





Litter weight at weaning (kg)





*Significant difference (p<0.05).

The litter size in BS-TW increased in 2.1 live piglets at birth in comparison to groups C and BS. This finding has not been reported at the moment by any of the researchers that have used the lactational oestrus model. One of the possible explanations to try to interpret the increase of the number of live born piglets may be that the uterus of the sows that were pregnant hadn’t finished shrinking which could have resulted in an increase of length and weight. Studies performed by Perry and Rowlands (1962) showed that 50% of the uterine growth during gestation appeared between days 2 and 6 after mating, and because of the lack of uterine space, the embryo death is higher (Bazer et al 1969; Wu et al 1989). In this sense, experiments had been performed to try to increase the size of the litter by augmenting the size of the uterus, using temporary gestation and subsequent abortions in pubescent females (Wu et al 1987; Conejo 1992), but the issue is still controversial.

Figure 1. Effect of the sow parity number on the mean number of born alive piglets according to the treatment group

Litter weight at birth 

Litter weight at birth was not significantly affected by any of the treatments, this coincides with Rowlinson and Bryant (1982), who found that when sows and their litters are grouped on day 10 of lactation, and the boar is introduced 24 hours later, the subsequent litter size does not decrease. 

Weaned piglets 

According to the analysis of variance (p=0.484) the experimental manipulation did not significantly influence the number of weaned piglets. Neither did the presence of the boar; there was also no effect by the removal of the litter (p=0.081), nor the interaction with the boar X removal of the litter (p=0.572). 

The profit percentage obtained from each extra weaned piglet from group BS-TW was 29.5%. The cost of production per piglet and litter at birth is shown in table 3. 

Table 3. Production costs and profits per group

Variables, in USD

n = 10

n = 10

n = 10

n = 10

Production cost of a litter at birth

$ 64.50

$ 64.50

$ 64.50

$ 64.50

Production cost of a piglet at birth

$ 11.51

$ 11.51

$ 9.62

$ 8.37

Total production cost of a weaned litter

$ 94.60

$ 94.60

$ 94.60

$ 83.47

Average total cost of a weaned litter

$ 16.89

$ 16.89

$ 15.76

$ 11.92

Weaned piglet profit

$ 13.10

$ 13.10

$ 14.23

$ 18.07

Cost of sale/weaned piglet = $30.00 USD

Litter weight at weaning 

The treatment did not have any effect on the weight of the litter at weaning. According to the multivariable analysis for repeated samples analysis (p=0.637), boar presence did not significantly have effects on this variable. Also, there was no effect of the removal of the litter (p=0.535), nor the interaction with the boar X removal of the litter (p=0.722). It is important to stress that at birth, some piglets had to be donated due to the large litter size surpassing the number of the female’s functional teats. 

Interval between stimuli and conception (IBSC) 

The IBSC for 8 of the 10 sows of group BS-TE was of 3 days because sows did not repeat heat and were pregnant at first natural breeding. This parameter increased for 29 to 46 days for the other 2 repeating animals, respectively. 

The effect of the parity number of the sow on the stimuli-conception interval is given in Figure 2.

Figure 2. Effect of the parity number on the stimulus-conception interval 

Weaning-oestrus interval (WOI) 

The ANOVA showed a significant interaction (p<0.001) between the two stimuli.  

The duration of WOI was significantly lower in animals treated with the two stimuli (Group BS-TW) in relation to the rest of the groups (Table 4). Only 2 of the 10 females from group BS-TW did not achieve pregnancy, showing a WOI of 8 and 9 days, each one. 

Table 4. Reproductive performance

Variable,  arithmetic mean±estándar error

n = 10

n = 10

n = 10

N = 10

Weaning-oestrus interval (days)





Weaning-conception interval (days)





Productive cycle (days)





Number of farrowings/sow/year





*Significant difference (p<0.05).

In this variable, the parity number was not a source of important variation (p=0.575). 

Currently, the techniques used to reduce the weaning-oestrus interval include a reduction of litter size several days before weaning the dam (Stevenson and Britt 1980; Stevenson and Davis 1984), or split weaning, when weaning the heavier half of the litter 2 to 3 days before weaning the remainder (e.g. Cox et al 1983; Henderson and Hughes 1984; Kunavongkrit et al 1985; Riley et al 1985). 

Weaning-conception interval (WCON) 

The analysis of variance revealed a significant interaction (p<0.003) between the two stimuli, plus the interaction removal of litter X number of parity (p<0.034). The number of parity was not a source of important variation (p=0.115) in the WCON. The removal of the litter had a significant effect on this interval; only on the females that had gone through a second parity (p,0.001), a factor that did not occur in sows who underwent a third pregnancy (p=0.607). The duration of WCON was significantly lower in the sows from group BS-TW in relation to the other groups (Table 4). 

The WCON was lower in an average of 10 days for group BS-TW compared with the other three groups; however, no non-productive days were seen for the 8 sows that became pregnant on the 11th day of lactation. It could also be said that this indicator was negative in 25 days for each of these sows in respect to the sows that were pregnant 8 days after weaning. The cost of one non-productive day for this herd was estimated in $1.10 USD, and the financial savings for each lactating pregnant sow was $25.70 USD. 

Interval between farrowings (IBF) 

Analysis of variance showed a significant interaction (p<0.013) between the effect of the boar presence and the removal of the litter, as well as for the interaction of the removal of the litter x the number of parity (p<0.04) 

The interval between farrowings was significantly lower for group BS-TW regarding the rest of the groups (Figure 3). In this variable the parity number did not represent an important variation factor (p=0.179). 

Figure 3.
Experimental treatment effects on the farrowing interval 


The ever more frequent practice of shorter lactation periods in animals subjected to intensive pressure obliges us to propose alternative systems of production. The induction of conception during lactation through the use of temporary weaning and the use of the boar conjunctively, was deemed a useful procedure in reducing the non-productive days and shorten the productive cycle of the Mexican hairless sow. It also allowed the decrease of production costs per piglet or litter at birth. 


The present study was financed by CONACYT (Consejo Nacional de Ciencia y Tecnología, Mexico; project No. 4213P-B9607). We greatly acknowledge the farm authorities at the CEIEPASP, FMVZ, UNAM (Mexico). 


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Received 23 November 2002; Accepted 12 February 2003

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