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Influence of parity on productive performance of Pelibuey ewes under intensive management in the Mexican dry tropics

R Macedo and J D Hummel

Facultad de Medicina Veterinaria y Zootecnia. Universidad de Colima. Km. 40 autopista Colima - Manzanillo.
Tecomán, Colima, México. C.P. 28100


Data on 113 births and 233 lambs of a purebred Pelibuey flock under an intensive management were studied in Colima, Mexico, to determine the influence of parity on lambing rate, weaning rate, lamb mortality, lamb birth and weaning weight, lamb growth rate and litter birth and weaning weight.

The effects of number of births on lambing rate and weaning rate were not significant, averaging 2.26 and 2.08. Preweaning lamb mortality was positively associated with parity (c2 > Pr ), with starvation as the main cause of death in multiple births in 2 to 4 parity ewes. Number of births did not influence (P>0.05) lamb birth and weaning weight, lamb growth rate and litter birth and weaning weight. Lambs averaged 2.80 kg at birth, 16.7 kg at weaning and had 174 g/d of growth rate. Average litter birth and weaning weights were 6.27 and 36.1 kg respectively.

It is concluded that parity did not affect the productive performance of Pelibuey ewes under an intensive tropical management.

Keywords: birth weight, growth rate, hair sheep, parity, prolificacy, weaning weight

Efecto del número de parto sobre el comportamiento productivo de ovejas Pelibuey bajo manejo intensivo en el trópico seco Mexicano


Con el objetivo de determinar la influencia del número de parto sobre la prolificidad, la tasa de destete, la mortalidad, el peso al nacimiento y al destete de los corderos, la tasa de crecimiento y el peso al nacimiento y a destete de la camada, se analizó información de 113 partos y 233 corderos de un rebaño de ovejas Pelibuey puras manejados intensivamente en Colima, México.

El número de parto no afectó significativamente (P>0.05) la prolificidad, la tasa de destete la cual se ubicó en 2.26 y 2.08. El número de parto se asoció positivamente con la mortalidad predestete (c2 > Pr ) siendo la inanición en camadas mayores a tres corderos la principal causa de muerte en ovejas de 2 a 4 parto . Asimismo, el número de parto no influenció (P>0.05) el peso al nacimiento y al destete de los corderos, la tasa de crecimiento así como el peso al nacimiento y al destete de la camada. Los corderos promediaron 2.80 kg al nacimiento, 16.69 kg al destete con una ganancia diaria de peso de 174 g. El peso promedio de la camada al nacimiento y al destete fue de 6.27 y 36.08 kg respectivamente.

Se concluye que el número de parto no afecta el comportamiento productivo de ovejas Pelibuey manejadas intensivamente en condiciones tropicales.

Palabras clave: número de parto, oveja de pelo, peso al destete, peso al nacimiento, prolificidad, tasa de crecimiento


In recent years, there has been an increasing interest in the understanding of the influence of some factors such as parity on sheep productivity. Studies carried out on different breeds in temperate countries demonstrated that parity had influence on litter size, lamb mortality, lamb birth weight, lamb weaning weight, lamb postnatal growth rate, lambing interval, milk yield and milk quality (Mavrogenis 1996;de la Fuente et al 1997; Franci et al 1999; María and Ascaso 1999; Ploumi and Emmanouilidis 1999; Sevi et al 2000).

Other studies have shown that the incidence of negative maternal behavior, such as rejection (butting and abandoning the lamb) and fear-like behavior (withdrawing from the lamb, moving as the lamb attempts to suck), were related to the number of birth experiences of the ewes (Dwyer and Lawrence 1999). Also, the difficulty in serving yearling ewes, because of their reluctant standing attitude, was due to a lack of reproductive experience (Rosciszewska 1985).

Under tropical conditions, the relationships between these previous mentioned factors are poorly understood, although a few studies carried out under extensive conditions showed that hair sheep have a similar productive performance as temperate breeds (Rajab et al 1992; Galina et al 1996; Segura et al 1996; Dickson et al 2004; Pérez et al 2005a; Pérez et al 2005b). The present investigation was undertaken to evaluate the influence of parity on productive performance of Pelibuey ewes under an intensive tropical management in Colima, Mexico.

Materials and methods

Area description

The study was carried out in the Agriculture and Forestry Training Center (CECAF) located in Tecomán, Colima, México, at 18°58'43'' north latitude, 103°52'18'' west longitude and 73 m above sea level. Koppen´s climate classification is BS1(h')w(w)(i') described as semiarid with a rainy season during summer providing 750 mm a year. Dry season extends eight to nine months with an average temperature of 26 °C (García 1988).

Animals, feed and management

The study analized data from 113 births and 233 lambs, corresponding to a flock of Pelibuey purebred ewes. Parity distribution was: 1-parity (42), 2-parity (16), 3-parity (11), 4-parity (14), 5-parity (10) and 6-parity (20).

Ewes grazed tropical pastures containing Star grass (Cynodon plectostachyus), Guinea grass (Panicum maximum) and native grasses (Paspalum sp., Axonopus sp.) and were supplemented with a concentrate mixture containing 2.80 Mcal ME/kg DM and 18.80% CP, 1500 g/ewe/d at mating (flushing) and early gestation (35 days after mating), 150 g/ewe/d at intermediate gestation (75 days after mating), 250 g/ewe/d at late gestation (40 days before calving) 2000 g/ewe/d at early lactation (30 days after calving) and 550 g/ewe/d at late lactation (60 days after calving).

The mating was achieved in a controlled system with one male serving 20 ewes every 35 days. Ewe lambs were mated at the moment that they reached 70 percent of their mature body weight whereas for multiparous ewes it was at the time of weaning (80 days after lambing) and with an average body condition of 2.4 and 3.0 (using the 5-point scale described by Russel et al 1969) at the beginning and at the completion of mating, respectively. Seven days before mating, ewes were dewormed with albendazole (10 mg/kg LW), and twenty days before lambing were vaccinated against haemorrhagic septicaemia and pneumonia with a live tissue culture vaccine. Body condition at lambing was 3.5.

Lambs were creep fed from the first week of age up to weaning, with a pelleted feed containing 17% CP, 3% fat and 2.5% CF. The average amount of creep feed consumed by lambs was estimated as 100 g/d. Average age of lambs at weaning was 83 days.

Variables and statistical analysis

Lambing rate, weaning rate and lamb mortality were calculated as:

Lambing rate = lambs born alive / mated ewes
Weaning rate = lambs weaned / ewes lambing
Lamb mortality = 100*[1- (lambs weaned / lambs born alive)]

Lamb birth and weaning weight, litter birth and weaning weight were estimated by weighing the lambs at these times. Growth rates were derived by taking the difference within the period from birth to weaning and dividing it by the time interval in days. Lamb and litter weights at weaning were adjusted to 80 days.

Data were statistically analyzed by ANOVA as a Completely Randomized Design using the GLM Procedure (SAS 1985) fitted with the following model:

ŷi = μ + Pi + ei

ŷi = dependent variable (lambing rate, weaning rate, lamb mortality, lamb birth weight, lamb weaning weight, lamb growth rate, litter birth weight, litter weaning weight),
μ = overall mean,
Pi = random effect of parity,
ei = residual error term.

The difference between means was compared using the Tukey test. Statistical significance was accepted at the 5% level and tendency toward significance at the 10% level. Mortality data were analyzed by Chi-square (Snedecor and Cochran 1990).

Results and discussion

Parity was not as significant a source of variation (P>0.05) for lambing rate and weaning rate as it was in association with lamb mortality (Table 1). Performance of primiparous ewes in this study was not similar to those described in hair sheep such as Pelibuey, Blackbelly, West African, Morada Nova, Brazilian Somali and Santa Ines in which prolificacy was increased with advances in parity, showing the lowest values by young and primiparous ewes (Rajab et al 1992; Galina et al 1996; Pérez et al 2005a).

Table 1.  Effect of parity on lambing rate, weaning rate and lamb mortality of Pelibuey ewes under an intensive tropical management


Lambing rate(lambs/ewe)

Weaning rate (lambs/ewe)

Lamb mortality,


2.21 ± 0.72

2.10 ± 0.76



2.31 ± 0.79

1.94 ± 1.06



2.09 ± 0.70

1.82 ± 0.60



2.14 ± 0.77

1.86 ± 0.86



2.10 ± 0.74

2.10 ± 0.74



2.55 ± 0.76

2.45 ± 0.69


Pr > F




c2 > Pr



7.86 > 0.16

According to Pérez et al (2005a), average litter size increased from 1.27 to 1.53 from the first to the fifth lambing in Blackbelly, Mexican Pelibuey and Cuban Pelibuey ewes. Average litter size was 1.82 for Blackbelly, 1.43 for Cuban Pelibuey and 1.22 for Mexican Pelibuey. Lambs born per ewe lambing and increased curvilinearly with age and hence with parity of ewe from 126% at 2 year to 177% at 7 year and decreased to 143% at 8 year (Rajab et al 1992). Prolificacy of primiparous ewes in this study was also significantly higher than those reported by authors on hair ewes handled under extensive production systems. This result could be explained by the difference between the mating weight of the ewes utilized in both studies. In most of the tropical extensive sheep production systems, breeding is achieved under a non-controlled continuous system, settling the female lambs in a range between 20 to 26 kg, described as the minimum weight necessary for mating (Ramón and Sangines 2002). Brown et al (1990) and the Meat and Livestock Commission (1983) indicated that a ewe lamb should weigh 60 to 70 percent of her mature body weight before the breeding season to achieve a satisfactory reproductive performance in her first pregnancy. In this study, this criteria was fulfilled, reaching 70 percent of their mature weight, equivalent to 35 kg. This management, along with the highly nutritional plane established, suggests that in spite of growth, a greater amount of nutrients were available to enhance reproductive performance. Previous studies reported a positive relationship between ewe weight and ovulation rate (Michels et al 2000) and a high correlation (0.992) between ewe body weight and prolificacy (Foote and Mathews 1983).

With respect to multiparous ewes performance, which showed litter size above 2 lambs/ewe lambing, the central role that body condition at mating plays in determining ovulation rate is evident, and is also apparent in the results of this work. Body condition score of the ewes targets closely for optimum reproductive performance (Robinson et al 2002). A previous study carried out in this region showed that litter size of Pelibuey ewes under intensive management with a similar average body condition was 2.30. Ewes under extensive management mated with a body condition of 1.9 produced 1.55 lambs (Macedo y Alvarado 2005). Pelibuey ewes, which grazed on native vegetation, with lower weights than the flock means, had fewer multiple births (13.7%) than heavy ewes (27.2%). Blackbelly ewes with weights lower or higher than the flock mean had 46.1% and 65.5% multiple births, respectively (Segura et al 1996). Bradford (1985) explained this behavior in terms of the scarcity and low quality of the forage in the tropical rangelands, which are subject to uncertain seasonal rainfall patterns, and where supplemental feed is also scarce and economically unfeasible (Bradford 1985).

Lamb growth rate, birth weight and weaning weight were not affected by parity (P>0.05), whereas litters of 6-parity ewes tended to be heavier at birth and at weaning than the rest of the litters (Table 2).

Table 2.  Effect of parity on lamb growth rate and on lamb and litter weight at birth and at weaning of Pelibuey ewes under an intensive tropical management


Lamb birth
Weight, kg

Lamb weaning weight*, kg

Lamb growth rate, g/d

Litter birth weight, kg

Litter weaning weight*, kg


2.72 ± 0.59

16.28 ± 3.89

170 ± 44.24

6.05 ± 1.36

34.96 ± 9.74


2.77 ± 0.64

16.50 ± 4.05

172± 45.76

6.30 ± 1.52

36.54 ± 9.73


2.98 ± 0.64

18.73 ± 4.92

197 ± 56.28

5.84 ± 1.85

33.12 ± 10.56


2.85 ± 0.64

16.53 ± 4.00

171 ± 45.05

6.31 ± 1.39

35.86 ± 9.39


2.88 ± 0.78

16.08 ± 3.93

165 ± 42.44

5.71 ± 1.22

32.05 ± 9.96


2.83 ± 0.66

17.06 ± 4.39

178 ± 51.25

7.19 ± 1.63

41.86 ± 8.72

Pr > F






* Values adjusted to 80 days.

Lamb performance was different than those described by other authors working with hair sheep in America handled under extensive systems based on grazing native or introduced forages. Dickson et al (2004) found that West African lambs out of 1-parity ewes, were characterized by a significantly lower birth weight compared with lambs out of 2-parity to 9-parity ewes. No effect of parity on weaning weight was found. Rajab et al (1992) indicated lambs out of 2 years old ewes were lighter at birth and at older ages than were lambs out of older ewes. Lambs out of 6 year old ewes were heavier at birth and at older ages than were lambs from older and younger ewes. Pérez et al (2005b) indicated that the lambs born from the third to the seventh parity were heavier and  later had higher weaning weight than those born from ewe lambs.

These results suggest that, given the suitable body weight and nutrition of primiparous ewes at mating and hence at lambing, a greater amount of nutrients were directed to foetal demand and milk production despite maternal growth, as with prolificacy. Rajab et al (1992) indicated that young dams that had not reached adult size continued to grow during pregnancy and thus competed with the fetus for available nutrients. Dickson et al (2004) found that when body weight increased from 30.1 kg in 1-parity to 35.5 kg in 7-parity ewes, lamb birth weight increased from 2.25 to 2.75 kg respectively, whereas Zambrano et al (1999) indicated that West African lamb birth weight increased 56.5 g for each kg of body weight of ewe at lambing. Segura et al (1996) indicated that ewes with lower weights than the mean of the flock had lower productivity at lambing (3.39 kg) and weaning (11.1 kg) than ewes with higher weights (4.16 and 14.5 kg, respectively).

In this study, ewe parity did not influence lamb growth rate. Similar results were reported by Dickson et al (2004) in West African ewes. Contrary to this, Thieme et al (1999) found that ewes lambing the first time produced lambs with the lowest growth rate. With increasing age of ewe, growth rate of lamb improved until the age of 4 years, but decreased again with higher ewe ages. In general, early lamb growth fitted a culvilinear model with maximum weight of progeny from intermediate ages of ewes and lower performance from very young and aged ewes (Rajab et al 1992).

Ploumi and Emmanouilidis (1999) have concluded that the ewe weight at lambing had a significant effect on weight of lambs at birth and weaning. Brown et al (1990) indicated than ewe size is correlated with milk production as well as Foote and Mathews (1983), who reported that correlations between ewe bodyweight and weight of lambs born per ewe lambing and weight of lambs weaned were 0.998 and 0.672 respectively. Contrary to some authors (Warren and Mysterud 1995; María and Ascaso 1999) who showed a negative association between lamb mortality and age of dam, (being higher among lambs of yearlings), in this study lamb mortality was higher in progeny from 2 to 4 parity ewes.  In general, starvation was the main cause of lamb mortality, while according to Hinch et al (1986) for single lambs from primiparous ewes, dystocia was the dominant cause of death. Starvation was of increasing importance with decreased birth weight of lambs, especially in triplets. Creep-fed lambs from the first week of age to weaning maintained a low mortality rate.

On the other hand, negative maternal behavior related to the number of birth experiences, was not observed in the primiparous group of ewes. This rich maternal behavior may be induced by genetic (breed) and management factors such as nutrition. With respect to this, Dwyer and Lawrence (1999) suggested that there is some evidence that nutritional status during pregnancy had an effect on the maternal behavior immediately after birth. Ewes that lost the most condition or back-fat in their pregnancy were slightly more likely to become separated from their lambs, spent less time grooming the lamb and were apparently less bonded to their lambs than ewes with higher body condition.

Due to high prolificacy and low lamb mortality along with high productivity expressed in litter weight (32.1 to 41.9 kg at 80 days), productivity performance of Pelibuey sheep was superior than those reported about specialized breeds. Nevertheless, Dorper sheep achieved 264 g/d of average pre-weaning daily weight gain, and lamb output at 100 days was 31.4 kg (Schoeman and Burger 1992). These results indicate that purebred Pelibuey ewes have an excellent potential as a maternal line, for improving mutton yield in terminal crossbreeding schemes with less prolific terminal meat sire breeds. At the same time, this breed allows the development of production systems with a high replacement rate without decreasing in productivity.



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Received 12 January 2005; Accepted 26 April 2006; Published 14 June 2006

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