Effects of lambing season, birth type and sex on early performance of lambs

Abstract

The effects of lambing season, birth type and sex on growth performance were studied using 249 Balouchi lambs (94 winter-born and 155 spring-born lambs) under farm conditions. The lambs were weighed within 12 h of birth, at 60 (weaning) and 120 days of age. Body measurements (heart girth [HG], height at withers [HW] and body length [BL]) were determined at weaning and at 120 days of age. Lambs born in the winter were heavier than those born in the spring at 60 (P < 0.01) and 120 (P < 0.05) days of age by 1.53 and 1.76 kg, respectively. Ram lambs were heavier (P < 0.01) than ewe lambs at 60 and 120 days of age by 1.7 and 3.43 kg, respectively. Single-born lambs were heavier than those born as twins at birth (P < 0.01), 60 and 120 (P < 0.05) days of age by 0.50, 1.18 and 1.99 kg, respectively. Winter-born lambs had a higher average daily gain (ADG) than spring-born lambs (P < 0.05). Ram lambs had a higher pre-weaning and overall ADG (P < 0.01) compared with ewe lambs. Single lambs had a higher ADG (P < 0.05) at pre-weaning than twin lambs.

Keywords:

• birth type
• early performance
• lambing season
• sex

Introduction

The sheep industry is the largest enterprise of animal agriculture in Iran. The total number of sheep in Iran is estimated to be about 52 million, which accounts for nearly 42% of the available total animal units. The fat-tailed Balouchi is the largest and most productive breed of sheep in Iran. It comprises about 12% of the national sheep production. These sheep, found in the eastern provinces of the country, are characterized by their adaptation to harsh environments and feeding conditions (Valizadeh et al. 2009).

The mating season of sheep in eastern Iran is 2–3 months during the autumn, with mating activity at its highest level in September and October. Lambing occurs once a year during February and March (spring lambing) and lambs are slaughtered throughout the summer and autumn.

Out-of-season breeding is not generally used in Iran and this has been identified as a major limitation to lamb meat production.

Out-of-season lambs would be an ideal source of stock to meet the objectives of a year-round kill. In recent years there has been increasing interest in the development of out-of-season lambing systems (winter lambing systems) in Iran. The lambing season has been shown to have a significant influence on lamb productivity (Stritzke & Whiteman 1982; Cristian & Suvela 1999; Dixit et al. 2001). Stritzke & Whiteman (1982) reported that winter-born lambs were heavier at birth and weaning than autumn- or summer-born lambs. In contrast, some studies reported that spring-lambs were heavier at birth than autumn-born (Gould & Whiteman 1971) or winter-born lambs (Cruickshank & Smith 1989; Morris et al. 1993).

Lambing season has also been shown to affect the body weight of lambs at weaning. Stritzke & Whiteman (1982) reported that the body weights of lambs at 70 days of age were highest in winter-born lambs, followed by autumn- and summer-born lambs. Consistent with this finding, winter-born lambs were reported to be heavier than spring-born lambs at 6 weeks of age (Cristian & Suvela 1999) and at weaning (Zapasnikiene 2002). However, Gould & Whiteman (1971) observed that spring-born lambs were heavier at 70 days of age than autumn-born lambs.

Previous studies on lambing season have focused mainly on tailed breeds, therefore the aim of this study was to evaluate the effects of lambing season, as well as birth type and sex, on early growth performance in fat-tailed Balouchi lambs.

Materials and methods

The current study was conducted at a sheep farm that raises approximately 300 lambs a year outside the city of Mashhad, in the derived wilderness zone of east Iran (latitude 36°20′, longitude 54°11′, altitude 1830 m). The climate is semi-arid, with a mean annual precipitation of 236 mm and a mean annual temperature of 33.9 °C.

A total of 249 Balouchi lambs (94 winter-born and 155 spring-born) were used in this study. At birth, lamb identification number, sex and birth type were recorded for each lamb. In addition to the ewe’s milk, the lambs were offered alfalfa hay ad libitum and a concentrate mixture including 40% corn, 20% soybean meal, 20% beet pulp and 20% wheat bran (300 g per lamb per day to weaning). The feeding management for winter- and spring-born lambs was similar until weaning at 60 days of age. After weaning, the winter-born lambs were housed indoors and fed alfalfa hay ad libitum supplemented with concentrates (250 g/d), whereas the spring-born lambs used grass pasture for 6 h per day after weaning.

Lambs were weighed at birth, weaning (60 days of age) and 120 days of age for calculation of the average daily gain (ADG). Live weight (kg) of individual lambs was determined prior to morning feeding to avoid error due to gut fill. Body measurements were obtained using a measuring tape calibrated in centimetres (cm) while restraining the animals in an enforced position. Reference points for the body measurements were determined according to the procedure outlined by Searle et al. (1989). Height at withers (HW) was determined as the highest point over the scapulae vertical to the ground. Heart girth (HG) was determined as the smallest circumference just behind the foreleg, and body length (BL) was determined as the distance from the head of the humerii to the distal end of the pubic bone.

The effect of independent factors (lambing season, birth type and sex) on performance traits was analysed using the GLM procedure of SAS, and least squares means were compared using the t-test (Harvey 1987).

Results and discussion

Least squares means and standard errors of body weight at different stages are given in Table 1. Single lambs were 0.5 kg heavier (P < 0.01) at birth than those born as twins. Lambing season or sex did not, however, affect birth weight.

Table 1 Least squares means (±SEM) of body weight at different stages.

		Body weight (kg)
Factors	No. of lambs	Birth (0 days)	Weaning (60 days)	120 days
Lambing season		ns	**	*
Winter	94	3.84 ± 0.13	12.66 ± 0.45	19.79 ± 0.80
Spring	155	3.84 ± 0.07	11.13 ± 0.33	18.03 ± 0.71
Sex of lamb		ns	**	**
Male	123	3.88 ± 0.07	12.81 ± 0.48	22.27 ± 0.88
Female	126	3.80 ± 0.14	11.11 ± 0.30	18.84 ± 0.60
Birth type		**	*	*
Single	215	4.02 ± 0.07	12.28 ± 0.36	19.57 ± 0.55
Twins	34	3.52 ± 0.12	11.10 ± 0.46	17.58 ± 0.65

ns, not significant.

*P < 0.05, **P < 0.01.

Consistent with the current study, Cruickshank & Smith (1989) and Morris et al. (1993) did not observe any effect of lambing season on birth weight. In contrast, Cristian & Suvela (1999) and Yilmaz et al. (2007) found that lambs born in the winter were heavier than spring-born lambs. Yilmaz et al. (2007) suggested that seasonal differences in birth weight may have been due to differences in ambient temperature and maternal pre-natal effects during gestation.

Also consistent with this study, Notter & Copenhaver (1980), Arslan et al. (2003) and Yilmaz et al. (2007) did not observe any effect of birth type on lamb birth weight. In contrast, Yilmaz et al. (2007) demonstrated that ram lambs were 0.5 kg heavier at birth than ewe lambs.

Winter-born lambs (12.66 ± 0.45 kg) were 1.53 kg heavier (P < 0.01) at 60 days of age (weaning time) than those born in the spring (11.13 ± 0.33 kg). This is in agreement with the findings of Zapasnikiene (2002) and Yilmaz et al. (2007) and could be in part be due to differences in post-natal effects such as the dam’s milk production and dry matter intake. Winter-born lambs (19.79 ± 0.80 kg) were also heavier (+1.76 kg; P < 0.05) at 120 days of age than those born in the spring (18.03 ± 0.71 kg), which could be due to extra supplements provided in the barn.

Ram lambs were heavier (P < 0.01) at 60 and 120 days of age compared with ewe lambs. Similarly, single lambs were heavier (P < 0.05) than twin lambs at weaning and 120 days of age. The lower body weights of twin lambs at weaning could be due to lower birth weight as well as the competition between twins for the limited milk available from the dam (Yilmaz et al. 2007).

Body measurements at weaning (60 days of age) and 120 days of age are presented in Table 2. Heart girth has been suggested to be the most satisfactory single variable in estimating live bodyweight (Ibiwoye et al. 1993). In the current study, male and single lambs had a higher HG (P < 0.01) at pre- and post-weaning compared with female and twin lambs, respectively. This is consistent with Sowande & Sobola (2008) who demonstrated that differences in body weight and body measurements are sex dependent.

Table 2 Least squares means (±SEM) of body measurements (cm) at weaning time (60 days of age) and 120 days of age.

		60 days of age			120 days of age
Factors	No. of lambs	HG	HW	BL	HG	HW	BL
Lambing season		ns	**	*	**	ns	*
Winter	94	43.61 ± 0.72	41.04 ± 0.55	38.16 ± 0.54	66.61 ± 0.69	50.48 ± 0.77	50.16 ± 0.69
Spring	155	42.78 ± 0.47	39.45 ± 0.37	36.66 ± 0.47	64.84 ± 1.46	51.42 ± 0.79	48.48 ± 0.80
Sex of lamb		**	**	*	**	**	**
Male	123	45.85 ± 0.48	41.81 ± 0.42	37.99 ± 0.45	68.42 ± 0.83	52.28 ± 0.62	50.80 ± 0.55
Female	126	41.71 ± 0.42	39.95 ± 0.55	36.26 ± 0.55	60.97 ± 1.26	48.59 ± 0.90	46.76 ± 0.87
Birth type		*	*	*	**	*	ns
Single	215	45.29 ± 0.79	41.98 ± 0.64	38.25 ± 0.60	66.34 ± 0.11	51.72 ± 0.27	49.87 ± 0.63
Twins	34	43.67 ± 0.42	40.50 ± 0.34	36.68 ± 0.43	65.04 ± 0.28	50.78 ± 0.59	48.71 ± 0.91

BL, body length; HG, heart girth; HW, height at withers; ns, not significant.

*P < 0.05, **P < 0.01.

Least squares means (±SEM) for ADG are presented in Table 3. Winter lambing resulted in greater ADG at the weaning period (25.53 g/day; P < 0.01) and greater overall ADG (14.65 g/day; P < 0.05) compared with spring lambing. However, lambing season did not affect ADG at the post-weaning period. Consistent with our findings, Yilmaz et al. (2007) reported that winter-born lambs were heavier than spring-born lambs at the pre-weaning period, while lambing season did not affect ADG at the post-weaning period (90–180 days of age) in that study.

Table 3 Least squares means (±SEM) of ADG (g/day) at different stages.

Factors	No. of lambs	Pre-weaning (0–60 days)	Post-weaning (60–120 days)	Overall (0–120 days)
Lambing season		**	ns	*
Winter	94	211.09 ± 7.54	118.73 ± 12.26	164.91 ± 6.68
Spring	155	185.56 ± 5.52	114.95 ± 10.32	150.26 ± 5.94
Sex of lamb		**	ns	**
Male	123	213.55 ± 7.97	127.49 ± 13.57	170.52 ± 7.30
Female	126	185.17 ± 5.06	108.28 ± 9.12	149.72 ± 5.04
Birth type		*	ns	ns
Single	215	204.65 ± 5.94	121.55 ± 8.80	163.10 ± 4.54
Twins	34	185.0.5 ± 7.74	108.06 ± 14.54	146.55 ± 9.38

ns, not significant.

*P < 0.05, **P < 0.01.

Male lambs had a higher pre-weaning and overall ADG (P < 0.01) than female lambs. However, the effect of sex was not significant at post-weaning.

Single lambs showed a higher ADG (P < 0.05) at pre-weaning than twin lambs, which is in agreement with the findings of Dimsoski et al. (1999) and Zapasnikiene (2002).

The overall growth of lambs born in winter tended to be greater than those born in the spring which is in agreement with Cristian & Suvela (1999) and Yilmaz et al. (2007) and could be related to the intensive indoor feeding of winter-born lambs. Faster growth rate results in lambs that reach a target weight earlier, while a lower growth rate means that lambs must be fed or kept on pastures for a longer period before marketing. This could directly affect profitability of sheep production.

The overall data suggest that the winter lambing system resulted in heavier lambs at weaning and post-weaning and can be used as an alternative lambing system for sheep farmers. However, these practices can incur greater costs, associated with extra supplements provided in the barn.