In India, the livestock sector is a cornerstone of the rural economy and supporting the livelihoods of almost two-thirds of rural population, especially small, marginal and landless farmers. The Union Territory of Jammu and Kashmir, with its diverse agro-climatic conditions from subtropical Jammu to temperate Kashmir offers significant potential for sustainable sheep production. Corriedale sheep was introduced in Kashmir from New Zealand in the 1970s and propagated through state breeding farms (Khan et al., 2020). These are dual-purpose sheep known for early maturity, robust build and adaptability to local conditions. They have good maternal qualities, twinning rates (5-25%). Lambs weigh 3-4.5 kg at birth with adult body weight around 79-125 kg (Rams) and 59-82 kg (Ewes).
       
Growth traits viz. pre-weaning and post-weaning weight are key indicators for productivity and profitability in sheep production. These traits are affected by both genetic and non-genetic factors such as season and year of birth, parity of dam, birth type and sex of the lamb (Ahmad et al., 2020). The effects of non-genetic factors are specific to a particular environment (Momoh et al., 2013). Adjusting data for important non-genetic factors is essential for improving performance through management interventions. Thus, the current study was aimed to analyze the impact of period and season of birth, sex of lamb and dam parity on growth traits in Corriedale sheep.

The research was conducted on 5492 records spanning from 1988 to 2024 of Corriedale sheep maintained at Mountain Sheep and Goat Research Station (MRCS and G), SKUAST-Kashmir, under organized conditions. The farm is situated in the Ganderbal District of J and K, India, with longitude and latitude coordinates of 74.47°E and 34.14°N, respectively and an elevation of 5300 ft above the mean sea level. The climate at the farm is temperate, characterized by cool winters (average daytime temperature of 2.5°C with night temperatures below freezing point) and warm summers (average temperature of 24°C). The spring season is marked with regular rainfall, while the autumn season tends to be predominantly dry. The animals are reared under a semi-migratory and semi-intensive production system. During the day, they are allowed to graze and are kept in enclosed paddocks at night. The animals from mid-June to mid-September, migrate to highland pastures (Laderwas, Sonamarg, at an altitude of 11,800-14,000 ft above mean sea level) for summer grazing. The breeding season begins in September and lasts until November, with flushing conducted prior to mating season. Ewes are included in breeding plan after reaching 18 months of age. Rams are kept separate from ewes during grazing and tupping is allowed inside paddocks during night only. Following mating, rams are marked with different wool colors on their briskets and ewes receive rump stamps every morning. Close inbreeding is avoided by planned and controlled mating, via housing ewes with specific only and separately rearing male and female flocks during the day.
       
The growth data was classified into 9 periods (According to the generation interval in sheep), two seasons of lambing (Nov-Feb and Mar-June), sex of lamb (male and female) and dam parity (1 to 9). The traits under study were i.e. Birth Weight (BW), Weaning Weight (WW), Six Month Weight (6M), Nine Month Weight (9M) Yearling Weight (12M). The analysis was carried out by emmeans package in R software for non-orthogonal data (R Core Team, 2020). The difference of means between subclasses of periods, seasons, sex, parity and birth type were tested for significance using Duncan’s Multiple Range Test using agricolae package in R software (R Core Team, 2020).

Average of the traits
 
Table 1 and Table 3 describe the descriptive statistics, Analysis of variance (MS values) and coefficient of variation of growth traits in Corriedale sheep. Coefficient of variation (CV%) was moderate to low for all the ages with highest and lowest variability at 6 and 12 months of age (22.47% and 17.98%). Rather et al., (2020) reported a CV of 20.05% for BW in Corriedale sheep. Ahmad et al. (2022) reported maximum CV (18.59%) at 6 months, whereas Khan et al., (2022) observed highest CV (43.80%) at weaning weight in Corriedale sheep.
 
Least square means
 
The least square means and standard errors (LSM’s ± SE) of body weight traits viz; BW, WW, 6M, 9M and 12M are presented in Table 2. The overall least-squares means were estimated as 3.55±0.04 for birth weight, 11.31±0.27 for weaning weight, 17.76±0.30 for 6M weight, 18.88±0.17 for 9M weight and 22.97±0.34 for 12M weight, respectively. Baba et al., (2020) reported lower estimates, whereas Khan et al., (2020) and Hamadani et al. (2021) reported higher overall least-square means for body weight traits in Corriedale sheep.






 
Effect of period
 
Period had significant (P<0.01) effect on BW, WW, 6M, 9M and 12M weights in Corriedale sheep. Over the years, BW and WW have decreased slightly, while post-weaning traits have improved significantly, indicating improved breeding, nutrition and management practices at the farm. Birth weight has slightly increased in the last period (2020-24) reflecting overall good management practices and decision making at the farm. Similar findings were reported by Rather et al., (2020); Khan et al. (2020); Hamadani et al. (2021) and Baba et al. (2020) in corriedale sheep.
 
Effect of sex
 
Sex had a significant (P<0.001) effect on all growth traits. The pattern suggested that males had a higher growth potential, especially after weaning, likely due to hormonal and physiological differences favouring muscle growth and weight gain. The difference was most pronounced at 6 months (18.19 kg vs. 17.33 kg) and 9 months (19.51 kg vs. 18.25 kg), suggesting that males had a superior advantage in growth after weaning. Mullaney (1969) and Rather et al., (2020) found significant (P<0.01) effects on BW only. Hamadani et al., (2021); Khan et al., (2020) and Baba et al., (2020) reported that sex had a significant effect on body weight traits in Corriedale sheep. These results highlight the importance of considering sex as a factor in evaluating growth performance and breeding decisions.
 
Effect of season
 
The study revealed significant season effect on the body weight traits. Hamadani et al., (2021) found season significantly affecting weaning and 12M weight in Corriedale sheep. Lambs born in winter season exhibited superior growth performance compared to those born in spring. This might be due to better nutrition for mothers during the later stages of pregnancy and more favourable conditions for lambs in their early development. Seasonal differences narrowed by yearling weight, the winter season consistently showed a better growth rate.
 
Effect of parity
 
The effect of parity had significant effect (P<0.01) on all growth traits. Parities 3-5 produced lambs with a higher body weights at all growth stages, due to increased maternal ability and body reserves. Extreme parities other than 3-5^th produced lighter lambs, indicating that both very young and very old ewes are less productive. Hamadani et al., (2021) reported significant effect of parity on birthweight in pleuriparous ewes producing lambs with a higher birthweight than primiparous ewes.

The overall least-squares means for birth weight was estimated as 3.55±0.04, for weaning weight 11.31±0.27, for 6M weight 17.76±0.30, for 9M weight 18.88±0.17 and for 12M weight 22.97±0.34 respectively. Period, sex, season and parity had significant effect on all growth traits in Corriedale sheep. Moderate to low variability across the traits with highest CV (22.47%) at 6 months of age. Post weaning body weight exhibited notable improvement over the years suggesting better farm management practices. Male lambs consistently outperformed females, particularly after weaning. Winter-born lambs had better growth than their spring-born counterparts, probably because of better mothering and environmental conditions. Growth rates improved up to 5^th parity and then decreased, underlining the impact of ewe maturity on the lambs growth. The study highlights the importance of accounting for these determinants to optimize selection accuracy and on-farm decision-making.

The authors are indebted to the Hon’ble Vice Chancellor SKUAST-Kashmir for providing the infrastructure facilities that enabled the successful completion of the project.

The authors declare that no actual or potential conflict of interest could inappropriately influence the work.