EFFECTS OF NON-GENETIC FACTORS ON PRE-WEANING GROWTH TRAITS IN DORPER SHEEP MANAGED INTENSIVELY IN CENTRAL MEXICO
Efectos no genéticos sobre características del crecimiento predestete de corderos Dorper manejados intensivamente en el centro de México
Jesús Mellado1, Víctor Marín2, Jose L. Reyes-Carrillo3, Miguel Mellado1, Leticia Gaytán3, Ma. de los Ángeles De Santiago3*
1 Universidad Autónoma Agraria Antonio Narro, Departamento de Nutrición Animal Calzada Antonio Narro No. 1923, Buenavista, Saltillo, Coahuila, CP. 25315. México.
2 Instituto Tecnológico de Torreón, Departamento de Ingeniería. Antigua Carretera a San Pedro, s/n, Torreón, Coahuila, CP.27170. México.
3 Universidad Autónoma Agraria Antonio Narro, Departamento de Producción Animal, Periférico Raúl López Sánchez y Carretera a Santa Fe S/N, Torreón, Coahuila, CP. 27054. México. *Corresponding author: email@example.com
Scientific note received july 10, 2015
Accepted September 2, 2015
The objective of this study was to determine the non-genetic factors which affect growth traits in Dorper lambs under intensive conditions. Nine hundred and ninety birth weight records and 851 weaning weight data from acommercial sheep farm were used. A model containing the effects of year of birth, season of birth, litter size, dams’age and gender was used for identification of factors affecting growth traits. Birth weight was highest (p < 0.05) insummer and lowest in winter and spring. Male lambs excelled females in birth weight, weaning weight, and averagedaily gain. Young dams produced offspring with a lower (p < 0.05) birth weight and weaning weight than older ewes As a conclusión, important influences of environmental factors on growth traits were identified for Dorper lambs.
Key words: Birth weight, weaning weight, pre-weaning, weight gain, growth traits, Dorper lambs
Para determinar los factores no genéticos que influyen en las características de crecimiento de corderos Dorper en condiciones intensivas se registraron 990 pesos al nacimiento (PN) y 851 pesos al destete de una unidadde producción de ovejas entre 2006 y 2010. Se analizó el efecto del año, estación de nacimiento, tamaño de camada, edad de la madre y sexo de los corderos. El año de nacimiento afectó (p < 0.05) el peso al nacer pues fue más elevadoen verano y más reducido en invierno y primavera. Los machos fueron más pesados (p < 0.05) al nacimiento y al destete y las tasas de crecimiento pre-destete fueron mayores que en las hembras (p < 0.05). Las ovejas primíparas produjeron crías más livianas (p < 0.05) al nacimiento y destete que las ovejas pluríparas. Se concluyó que diversos factores ambientales tuvieron un importante efecto en las características de crecimiento de corderos Dorper.
Palabras clave: Peso al nacimiento, peso al destete, pre-destete, ganancia de peso, características de crecimiento, corderos Dorper.
The importance of sheep production as a source of meat in México has been increasing duringrecent years, particularly in tropical areas and the central températe zone of the country (Montaldo et al. 2011, Osorio-Avalos et al. 2012). This production of mutton has experienced changes regardingthe use of introduced meat breeds, in order to increase the growth rate of lambs (Pérez-Hernández et al. 2011, Ríos-Utrera et al. 2014). During the last decade, the production of crossbred lambs has increased, using native Pelibuey and Criollo as maternal breeds and the Dorper and Katahdin as sires (Hinojosa-Cuéllar and Oliva-Hernández 2009, Hinojosa-Cuéllar et al. 2013). Dorper rams have proved to work well as terminal meat sires because they produce lambs which pre-weaning growth rate, post-weaning average daily gain (ADG), feeding efficiency, and carcass characteristics are similarto those of Suffolk crossbred lambs and purebred Columbia lambs but with a slight improvement in tenderness (Snowder and Duckett 2003).
Thus, there is a great demand for Dorper sheep to improve the growth performance of lambs, which is an important trait that determines the overall productivity of the flock. Also, Dorper sheeps as purebred have increased in the past few years due to its superior conformation, high survival of lambs to weaning, high mother ability (Kosgey et al. 2008), the ability to breed out of season (Burke 2005), and superior rates of gain and carcass characteristics relative to some wool (Schoeman 2000) and mhair (Wildeus 1997). Under intensive conditions, Dorper breeders focus on conformation, fertility, masculinity, and femininity to ensure that Dorper mcan be the basis for a productive and economical lamb industry. Studies on non-genetic factors neinfluencing growth traits of Dorper sheep are scarce for sheep reared under intensive conditions and bred in all seasons of the year in México (Hinojosa-Cuéllar et al. 2009). Birth weight as an early measurable trait is of great interest because of its positive genetic correlation with further live weights. On the other hand, weaning weight is the most important economic trait determining economic returns from commercial sheep flocks (Mousa et al. 2013, Shiotsuki et al. 2014). A number of non-genetic factorsaffect growth of lambs and interfere with the objective evaluation of the growth genetic potential of lambs. Due to the increasing interest in fast growing, excellent meat yields and fat distribution, easy to handle and fertile sheep breeds in México, such as Dorper, a clearer understanding of the influence of diverse non-genetic factor affecting weight traits of this breed of sheep is required, particularly for intensive production Systems. Therefore, the objective of this study was to evalúate non-genetic factors affecting the growth traits of purebred Dorper sheep under intensive conditions in central México.
MATERIAL AND METHODS
Data were obtained on purebred Dorper sheep raised on a large commercial farm in central México (19° 32’ N, 1240 m of altitude, mean annual temperature 21.5 °C and mean annual precipitation623 mm). Birth (n= 990) and weaning (n= 851) weights were registered in Dorper lambs born from2006 to 2010, inclusive. Mating and parturition occurred throughout the year.
All lambs were raised as either singles or múltiples and had a pelleted, commercial, creep feed available ad libitum. Diets for the lambs consisted of a pelleted feed (2.99 Mcal ME Kg-1 DM with 20 % CP, Lamb Tech, Purina® Salamanca, Mexico.
Young lambs were allowed to suckle freely through the day and they remained with their mothers for24 hours up to weaning. Lambs were weaned at anaverage of 88 ± 2.6 days of age and weights wererecorded. The individual weaning lamb weight wascorrected to 90 days of age by using the following equation:
Ewes were maintained as one group in an or-chard grass (Dactylis glomerata) pasture throughout gestation. Ewes were supplemented with 300 g d-1 concentrate (Ovina 14, Purina®) and al falfa hay ad libitum from the third month of gestation until the end of lactation. Traits studied were birth weight, weaning, and average preweaning weight (ADG). Fixed environmental factors investigated were year and season of birth, litter size, dams’ age, and gender.
Birth and weaning weights as well as ADG were analyzed by univariate general linear model (GLM procedure of SAS) with explanatory variablesas fixed effects. The model for traits measured on lambs fit effects of year of birth (four years), season of birth (four seasons), dams’ age (three categories) gender, litter size (three categories; litters with three and four lambs were combined into a single category) and two-way interactions between variables; the non-significant interactions were removed from the final model. Birth weight was fitted as a covariate for ADG analysis. Means of variables íse analyzed were compared using the probability of a statistical difference (PDIFF option of SAS). Statistical differences were considered significant at p < 0.05.
RESULTS AND DISCUSSION
The birth weight of Dorper lambs in the present study (3.8 ± 0.8 kg) is cióse to that found by other researchers (3.3 - 3.9 kg) under pasture conditions (Neser et al. 2001, Hinojosa-Cuéllar et al. 2013). Year of birth had a significant effect on birth weight, producing shifts in this trait of up to 0.5 kg (Table 1). These effects occurred despite no obvious difference in flock management, nutrition, and health practices. The mean birth weight of lambs was lower in 2010 (3.4 ± 0.8 kg) than in the other years, whereas the higher mean birth ± 0.7 kg). It is well established that year of birth causes variationson weight and performance of lambs due to climatic 208 variations (rate of rainfall, humidity, and temperature). It is presumed that the environment during pregnancy may have influenced overall birth weight. Likewise, occurrence of diseases in different years (Gardner et al. 2007) as well as sample size may explain the influence of year of parturition on lambbirth weight. The significant influence of year onbirth weight of lambs obtained matches the results from previous studies in other countries in different breeds of sheep (Dixit et al. 2001, Gardner et al. 2007). There was also a significant interaction between the year and season of birth (p < 0.01), between year of birth and gender of lambs (p < 0.01), between year of birth and dams’ age and between year of birth and litter size (p < 0.01). Means for year-season interactions ranged from 3.1 ± 0.7 kg in summer of 2007 to 4.1 ± 0.6 kg in summer of 2006.
Mean birth weight was highest (p < 0.05) in summer and lowest in winter and spring. The seasonal differences in birth weight in the present studymay have been partly due to alterations in ambient temperature and maternal pre-natal effects during gestation. The lower body weights of winter and spring-born lambs emphasizes the need of providing supplementary food and adequate management forewes at the end of fall in order to increase the growthrate of fetuses. Múltiple studies have shown thestrong influence of season on birth weight of lambsof all breeds (Dixit et al. 2001, Yilmaz et al. 2007, Rosov and Gootwine 2013).
As expected, males were, on average, 200 g heavier at birth than female lambs (p < 0.01). Agreat number of authors have documented this re-sult in sheeps (Afolayan et al. 2006), which is dueto the fact that males grow faster than respectivefemales in-utero (Loos et al. 2001), because ofthe testosterone secretion. Acute prenatal androgen treatment increases birth weight of lambs (Gilíand Hosking 1995). Means for the interaction (p < 0.01) between year of birth and gender of lambs ranged from 3.4 ± 0.7 kg (females born in 2010) to 4.2 ± 0.6 kg (males born in 2006). Other significant interactions detected were gender x litter size and gender x age of dams. The proportional decrease inbirth weight relative to litter size was greater in females. On the other hand, to illustrate gender x ageof dam interactions on birth weight, the percentage increase in birth weight relative to maternal age wasgreater in males than in females.
Litter size was the most important factor affecting birth weight of lambs. Lambs born as singles were 0.6 kg heavier (p < 0.05) than twins, 1.6 kg heavier than triplets and 1.9 kg heavier than quadruplets. The maternal uterine space has a finite capacity to géstate offspring, and as litter size increases, individual birth weights decline (Gluck-man and Hanson 2004). The standard deviation forbirth weight decreased with increasing litter size, indicating that the compact uterine space limits variance in birth weight. Means for the interaction(p < 0.01) between season of birth and litter size ranged from 2.3 ± 0.6 kg (quadruplets born in fall) to 4.4 ± 0.7 kg (singles born in summer).
Young ewes (< 20 months of age) produce lambs that were 300 g lighter (p < 0.05; Table1) at birth than ewes > 20 months of age. primiparous ewes are growing during gestation and complement their growth in addition to fetus growth, which increases metabolic strain, and that affects lamb weight. Additionally, as ewes grow older, their uterus gets larger which allows allocating more nutrients to the nourishment of lambs in the uterus than immature ewes. Other researchers (Gardner et al. 2007, Petrovic et al. 2011) have widely documented the same results. Additionally, Córner et al. (2013) have previously shown that ewe lambs have the potential to partition available resources towards themselves rather than the growing fetus.
Weaning weight adjusted to 90 d
Year of birth affected greatly (p < 0.01) the weaning weight of lambs (Table 1). In addition, significant interactions existed between year and season of birth (p < 0.01), between year of birth and sex (p < 0.01), and between year of birth and age of dam at birth (p < 0.05). The significant influence of year of birth in the present studyagrees with results of previous studies at various locations in different breeds of sheep (Assan and Makuza 2005, Bermejo et al. 2010). Differences in lamb performance between years reflect environmental variations (variation of quantity and qualityof herbage available), which cannot be controlled.
Season of the year affected (p < 0.01) weaning weight with the lowest weights being forlambs born in winter. Thus, external environmentor climate during early growth may have influence doverall pre-weaning growth rate, as it has been observed in a variety of sheep breeds (Yilmaz et al. 2007). Gender of lambs was an important (p <0.01) factor affecting weaning weight, with males being 2.1 kg heavier than females. Significant effects of lamb sex on weaning weight traits have been reported in various sheep breeds (Fogarty et al. 2005, Hopkins et al. 2005).
It is well documented that single lambs are heavier at weaning than twins (Yilmaz et al. 2007, Mohammadi et al. 2010). In the present study single born lambs weighed 6.9 kg more than triplets. This result shows that heavier weight of single overmúltiple lambs is partly due to the birth weight advantage of single born lambs. Average weaning weight increased linearly with increased age of dams, which is in line with other researchers’ findings (Momany-Shaker et al. 2002). It is well known that mothering ability (milk yield) increases with parity, and older ewes are usually larger in body size and produce more milk, which explains the greater weaning weights of lambs from older dams.
Pre-weaning daily weight gain
The average pre-weaning ADG of 319 ± 62 g for Dorper lambs in this study is higher than the 240-280 g published valúes by Schoeman (2000) and Neser et al (2001) for Dorper flocks from widely different production Systems. This indicates that sheep in the present study had very favorable conditions in nutrition and management compared to other studies where suboptimal conditions prevailed. Both year and sea son of birth had marked effects on preweaning ADG (Table 1). Lambs born in spring grow faster than those born in winter. Numerous studies have documented the important influence of year and season for pre-weaning daily weight gain in lambs (Hassen et al. 2004).
The only significant interaction observed for this trait was year x season of birth, which may indícate variation in quantity and quality of feed across seasons and years, which can be directly connected to the amount of precipitation and its dis- tribution. Moreover, changes in the occurrence of disease and management have a marked influence on lambs’ growth performance. Birth type represented the greatest barrier on pre-weaning growth of any of the environmental factors studied. The comparative growth rates of lambs born as singles and as múltiples are presented in Table 1. The differences between singles and twins, twins and triplets, and triplets and quadruplets were significant, which matches a number of studies in differentbreeds and management Systems (Rios-Utrera et al.2014, Teklebrhan et al. 2014). This is explained inpart by competition for suckling between múltiplebirth lambs from birth to weaning period.
Lambs out of young ewes (< 20 months) grew slower (p < 0.001) than ewes > 20 months of age.This is explained by the fact that young ewes thathad not reached adult size continué to grow andthus muscle synthesis compete with milk synthesisfor available nutrients, and thus less milk is availablefor suckling lambs. It is well known that motheringability (milk yield) increases with parity, and olderewes are usually larger in body size and producemore milk. This response has been amply documented with other sheep breeds in different environments (Momany-Shaker et al. 2002, Mohammadi etal. 2010, Rashidi et al. 2008).
Several researchers (Bermejo etal. 2010, Mohammadi et al. 2010) have shown that male lambs grow faster than female lambs before weaning. Thepresent study confirms these findings and indicatesthat part of the advantage of male lambs in pre-weaning weight gains results from the larger birthweights of males. Thus, heavier lambs at birthindícate rapid growth rates which are expressed pre-natally and which result in faster growth rates. Thepresent paper shows that the single greatest effecton birth and weaning weight as well as pre-weaningweight gain of Dorper lambs was litter size. Fur-ther, significa nt effects on birth weight were foundto be year of birth, age of dam, and sex of the lamb.These results have practical implications not onlyfor the husbandry of the sheep as an economical commodity, but also for the increased knowledgeof factors that significantly influence variation ingrowth traits in Dorper sheep in central México.
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