The effect of some factors on growth performance of Lori Bakhtiari lambs

M Mirderikvandi, A Masoudi, M Khaldari, M Bojarpour¹ and P Nazari²

Department of Animal Science, Faculty of Agriculture, Lorestan University, Khorramabad, Iran.
Abbas.Masoudi@yahoo.com
¹ Department of Animal Science, Ramin (Khuzestan) Agricultural and Natural Resources University, Mollassani, Khuzestan, Iran.
² Department of Biology, Lorestan University, Khorramabad, Iran

Abstract

The present study was conducted to analyze the effect of sex and type of birth on growth curve of Lori Bakhtiari lambs. The data were collected from 3081 male and female lambs from the birth to one-year old. In order to estimate the growth parameters, body weight of lambs was fitted to Gompertz model.

Male lambs were heavier than females over the growth period (P<0.05). Moreover, single-born lambs were heavier than twin ones (P<0.05). Growth parameters were significantly affected by sex (P<0.05). There was a significant difference among the growth parameters for type of birth, except the weight at maturity (A) and weight at inflection point (y) (P<0.05). In addition, single-born lambs had higher K (rate of maturity) than twin ones (P<0.05). Male lambs had a higher growth rate than the female ones (P<0.05). The results showed male lambs had a faster growth and reached larger mature weight than female also, sex and type of birth are the main factor affecting on the growth of Lori Bakhtiari lambs.

Key words: birth type, Gompertz model, growth curve

Introduction

In Iran, sheep breeds are generally multipurpose and they have been reared for meat, milk, and wool production. Twenty-seven different breeds of sheep are accounted for about half of the livestock production in Iran (Kamalzadeh and Shabani 2007). All of these breeds are fat-tailed sheep (except Zel), which are well adapted to the prevalent extensive, migratory, or semi-pastoral production systems (Farid et al 1977; Kianzad et al 2003). The fat-tailed Lori Bakhtiari breed sheep is one of the most common native breeds that farmer rear in southwest and parts in west of Iran (the Zagros Mountains), with a population of more than 1.7 million heads. This breed is mostly kept in village under semi-intensive systems and is well known for its favorable meat quality and positive economic return for producers (Shadnoush et al 2004). In order to increase economic return on these animals, there is a need to improvement in the weight and growth rate of lambs (Bathaei and Leroy 1998).

Growth is trait of interest in domestic animals and it has been described as the change in live weight per unit of time or as plotting body weight against age (Bathaei and Leroy 1998). Rapid growth during the early period can minimize the cost of rearing and thus provide more profit to the farmer. The birth weight and early growth rate of animals are determined not only by genetic potential but also by maternal and environmental factors (Mandal et al 2006; Zhang et al 2009). So, these traits are affected by various non-genetic factors like sex, season, year, and type of birth (Bharathidhasan et al 2009). It seems that non-linear models have become very popular in the analysis of grow curves (Topal et al 2004). The weight difference between males and females can influence the shape of the growth curve as has been noted by several authors (Yildiz et al 2009; Daskiran et al 2010; Csizmar et al 2013). Changes in the live weight or dimension in a period of time are explained by growth curves. The shape of the growth curves has been reported to vary according to the species of animal, environment, and kind of trait (Akbas et al 1999). The main aims of non-linear models are to describe and predict the growth and make inferences based on an interpretation of growth parameters. Therefore, the objective of this study was to evaluate of the effect of sex and type of birth on growth parameter in Lori Bakhtiari lambs by Gompertz non-linear growth model.

Materials and methods

A total of 3083 records of birth weight and body weight at five age times (one, three, six, nine and twelve-month) were used to analyze from 2001 through 2011, in Lori Bakhtiari research flock at the Shooli station, Shahrekord, Iran. The herd was managed in a semi-migratory or village system, as it was kept in-door from December to May and was fed using hand feeding. The pasture and the range were used in the rest of year. Ewes were mated from the late August to the late October. Consequently, lambing started in the late January. Lambs were reared with their dams, and they had free access to a creep feeding from day 15 of age. The lambs were weaned about 90 days of age. After weaning, the male and female lambs were separated. Ewe lambs were kept on a pasture of cultivated alfalfa, while the ram lambs were kept in-door and up to twelve months of the age received a maintenance and growth diet ad libitum.

A total of 10694 weight-age data were obtained from 2001 through 2011. This dataset has all information regarding lamb weights at different ages of position–birth, early weaning, late weaning and slaughter – and information about the origin of each lamb (livestock, date of birth, parentage, type birth, sex birth and etc.). Real weighing dates were used to estimate the growth parameter. Data were grouped as birth weight (W0); weighed lambs between 25 and 35 days of age (W₁); weighed lambs between 85 and 95 days of age (W₂); weighed lambs between 175 and 185 days of age (W₃); weighed lambs between 265 and 275 days of age (W₄); and weighed lambs between 360 and 375 days of age (W5).

To estimate the growth parameters, body weights of lambs were fitted to Gompertz model (Lupi et al 2015):

Where W_t is the expected body weight (kg) at the t time (day); A indicates an estimation of the asymptotic weight explicating as the weight at maturity time; b indicates an integration constant, related to the initial animal weight, but lacking an apparent biological explanation; k represents the rate of maturity and indicates the growth rate of animal in reaching to the asymptotic weight and t is the age of lamb (day). The parameters of the models were estimated using non-linear (NLIN) procedure of SAS Institute (2003) with iterative least squares regression (Gauss-Newton method). The derived parameters were then used to estimate the inflection point t_i; body weight at the inflection point (kg; y_i) and growth rate (GR; kg/day) as follows (Lupi et al 2015):

The goodness of fit was assessed by using R², MSE and AIC values (Lupi et al 2015). The Akaike information criterion was calculated as:

Where p is the number of parameters +1, SSE is the residuals sum of squares and n is the number of observations. The pseudo R2 was calculated as:

Data including body weight, growth parameters, ti, ­yi and GR were analyzed using the general linear models (GLM) procedure of SAS (SAS Institute 2003) and the corresponding means were compared by Tukey Kramer test for all statistical analyses.

The fixed model used was:

Where Yij is the adjusted weight of the nth lamb, is the overall mean, is the fixed effect of the ith sex (i= male, female), is the effect fixed of jth birth type (j= single, twin), is s the interaction between sex i and birth type j, is the random error attributed to the nth lamb.

Results and discussion

Descriptive statistic of weight gain over different age periods was presented at Table 1. Body weight increased with age. Maximum and minimum body weight gain at 12 months of age were 89.0 and 34.5 kg, respectively.

Overall means for body weight by sex and type of birth considering age are represented in Table 2. Over the growth period of lambs, males were heavier than females (P<0.05). Moreover, single-born lambs were heavier than twin-born ones (P<0.05). At the age of one month, the average weight of male and female of Lori Bakhtiari lambs were 11.8 and 11.1, respectively and single-born lambs were heavier (12.5) than twin-born ones (10.4 kg) (P<0.05). Moreover, at the age of 3, 6, 9 and 12 months of age the average weight of male and female Lori Bakhtiari lambs were 27.3, 41.6, 54.9, 61.9 and 24.8, 34.7, 45.8, 50.7, respectively. In total period (1 to 12-month) males were heavier than females (P<0.05). The differences between the reported birth weights in single lambs could be due to the different nutrition that pregnant ewes received during gestation and also the uterine capacity for numerous embryos. Weaning weight is a great interest for breeders as it determines the economic returns from the sheep (Csizmar et al 2013). The birth weight of lambs differed significantly due to year and season of the birth, age of the dam, birth type and sex of lamb born and it has been documented by many studies. Hussain et al (2013) reported that single-born lambs were slightly heavier at weaning (18. 9±0.23 kg) than twins (18.8±0.25 kg) and triplets (17.8±1.26 kg). Wojtowskt et al (1990) found that effect of the year and month of birth, type of birth (single, twin or triplet), sex, and age of dam were significant on the birth weight. Birth weight was affected by sex and male lambs weighed heavier than those female lambs at birth (Petrovic et al 2011). Type of birth was also significant (P<0.0001) for birth weight. Single-born lambs were heavier than their multiple-born contemporaries (3.20±0.04 kg vs. 2.55±0.11 kg). Other authors also obtained similar results for Gumuz (Abegaz 2007) and Washera sheep (Taye et al 2009). Baneh and Hafezian (2009) reported that, interactions between lamb’s sex, age and birth type significantly affected the weight of birth. Other researchers (Notter et al 1991) have also reported that birth weight of lambs was influenced by lamb sex and ewe x season interaction. Dixit et al (2001) found that the effect of sex, birth type and lamb’s age was statistically significant on the weight of lambs. Lakew et al (2014) reported that the growth performance of the crossbred lambs is better than the local sheep lambs and the pre-weaning and post-weaning growth rates of the crossbred lambs are also higher than the local sheep ones.

According to Table 2 interaction between sex and type of birth to 3 months of age was not significant, but from 6 through 12 months of age was significant (P<00). Birth weight was significantly affected by sex and type of birth; single-born lambs were significantly heavier than twin-born ones with an average 5.01 kg and 4.20, respectively. These results agree with ones established by study of Bazzi (2013), who reported that the average daily weight gain of twin kids was lower than single kids. Differences in sexual chromosomes, probably in the position of genes related to growth, physiological characteristics, difference in endocrinal system (type and measure of hormone secretion especially sexual hormones) lead to difference in animal growth. In relation to endocrinal system, estrogen hormone has a limited effect on the growth of long bones in females. It could be one of the reason in which females have smaller body and lighter weight than males (Rashidi et al 2008; Roshanfekr et al 2011).

The effect of sex and type of birth on growth parameters in Lori Bakhtiari lambs are shown in Table 3. High values of the parameter K indicates that the animals reach maturity earlier (Brown et al 1976; McManus et al 2003). Lori-Bakhtiari sheep is the heaviest in Iran and late maturity weight is expectable. The sex of lambs significantly effects on growth parameters (P<0.05), and male lambs were heavier than female ones. There were significant differences between growth parameters for type of birth, except for the A parameter (weight at maturity) and weight at inflection point (yi). Moreover, single-born lambs had higher K (rate of maturity) than twin-born ones (P<0.05). It can be expected that animals with lower K parameter would reach Ti later than others with higher K parameter. In the present study, twin-born lambs reached Ti later (P<0.05).

According to table 3, an inflection point (Ti) occurs around 87 and 76 days for males and females, respectively (P<0.05). Body weight at the inflection point was 22.9 kg for male and 19.8 kg for female lamb (P<0.05). Therefore, it follows that the optimal age of slaughter for females should be around 11 days earlier than males. Logically, the recommended slaughter weight for females must be lower, because animals tend to reserve fat and not muscle growth after inflection point. In agreement with the current study, Daskiran et al (2010) reported Male lambs grew faster and attained larger mature weight relative to female ones showing that sex is the main factor affecting the growth of Norduz lambs. Type of birth had no effects on the growth of the Lori Bakhtiari lambs (P>0.05). Daskiran et al (2010) reported that average daily gain of twin kids was significantly lower than that of single kids.

Interaction among type of birth and sex for growth parameters are shown in Table 3. This effect was not significant on growth parameters (P>0.05). It is well known that mammalian female maturity and puberty are related to their body conditions. Females have to reach a critical physiologic weight to start their reproductive life (Alexandre et al 1997). Male lambs grow faster and attained larger mature weight than female ones showing that sex is the main factor affecting the growth of Norduz lambs (Daskiran et al 2010). Bathaei and Leroy (1998) reported that type of birth affected on early weight changes but had a minor effect on mature weight. The differences between successive weights, with an interval of one month, didn’t become significant after 36 months of age. Influences of year, sire and sex on mature weight were also reported by Pitchford (1993), Bathaei and Leroy (1998) and Savar-Sofla et al (2011).

The effect of sex and type of birth on growth rate in Lori Bakhtiari lambs are shown in Table 4. Male lambs had higher growth rate than female lambs in total period of growth (P<0.05). Single-born lambs had higher growth rate than twin-born lambs (P<0.05. Interaction between sex and type of birth was not significant in growth period except for 3 months of age. Herein, at the 3 months of age male single-born lambs had a higher growth rate (0.24) and female twin-born had a lowest growth rate (0.18). These results are in agreement with Gavojdinan et al (2012) that compared the growth rate of Romanian indigenous Turcana to Turcana×Dorper crossbred lambs and reported that Single-born Turcana×Dorper lambs were heavier than multiple lambs. Non-significant effect of birth type on weaning weight has been reported in Sabi sheep by Matika et al (2003). Vatankhah and Talebi (2008) also reported the significant effects of lamb’s sex, birth type, birth year and age of dam on BW and 6MW in Lori-Bakhtiari. Also, Rashidi et al (2008) reported that both birth weight and weaning weight were significantly affected by lamb’s sex, birth type, birth year and age of dam at lambing in Kermani sheep.

The birth weight advantage of single-born lambs over the multiple-born lambs may be due to competition for nutrient and uterine space. The multiple-born lambs may have demonstrated compensatory growth after weaning. On pre and post-weaning growth rates, single-born lambs exhibited superiority of growth over the multiple-born lambs for the same reason above-mentioned. Male and female single-born lambs had higher weight than male and female twin-born ones, but final weight for male single and twin-born lambs were higher than female single and twin-born ones. In agreement with our results, Vatankhah and Talebi (2008) reported that single-born and male lambs of Lori Bakhtiari were heavier than multiple-born and female ones. Type of birth was a significant source of variation for lambs pre-weaning growth rate. Single-born lambs grew faster than their multiple contemporaries between birth to 30 days of age and to weaning (Hassen et al 2002; Babar et al 2004; Saghi et al 2007; Taye et al 2009). Benyi et al (2006) also reported that the superiority of single-born lambs in weight and growth rate increased only up to weaning and declined thereafter and thus multiple-born ones had comparable growth rate as single ones after weaning. Part of this difference can be explained by the carry-over effect of the heavier weight single-born lambs at birth and the fact that single-born lambs are the sole users of their dam milk. Baneh et al (2013), found that all traits of growth performance are influenced by birth year, lamb sex, type of birth and dam age. These results showed that final weight in lambs is more affected by sex, but type of birth doesn’t effect on final weight.

Conclusion

• Our results showed that final weight in lambs was affected by sex, but type of birth doesn’t effect on final weight.
  
  
• The male lambs grew faster and attained larger mature weight than female ones showing that sex is the main factor affecting the growth of Lori Bakhtiari lambs.
  
  
• It was found that the Ti (inflection age) for male and female occurs around the 3 months of age, and after 3 months of age, growth rate decreased with age.
  
  
• It can be recommended that the 3-month age may be used as a slaughter age for Lori Bakhtiari lambs.

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Received 10 September 2016; Accepted 7 October 2016; Published 1 December 2016

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